NeuLAND - FAIR

FAIR/NUSTAR/R 3 B/TDR NeuLAND
Technical Report for the Design,
Construction and Commissioning of
NeuLAND:
The High-Resolution Neutron
Time-of-Flight Spectrometer for R 3 B
November 1, 2011
R 3 B Name E-Mail
Project Leader/Spokesperson Thomas Aumann t.aumann@gsi.de
Deputy Bjoern Jonson bjoern.jonson@chalmers.se
Technical Coordinator Roy Lemmon roy.lemmon@stfc.ac.uk
Deputy Olof Tengblad olof@iem.cfmac.csic.es
Project Coordinator Heiko Scheit hscheit@ikp.tu-darmstadt.de
GSI Contact Haik Simon h.simon@gsi.de
NeuLAND WG Convener Konstanze Boretzky k.boretzky@gsi.de
Deputy Ushasi Datta Pramanik ushasi.dattapramanik@saha.ac.in

The R 3 B Collaboration
Brazil
University of Sao Paulo: Alinka Lepine-Szily
Canada
Saint Mary’s University Halifax: Rituparna Kanungo
TRIUMF Vancouver: Reiner Krücken
China
Institute of Modern Physics Lanzhou: Ruofu Chen, Songlin Li, Hushan Xu, Yu-Hu
Zhang
Denmark
Arhus University: Dmitri Fedorov, Hans Fynbo, Aksel Jensen, Karsten Riisager
VTT: Simo Eränen, Juha Kalliopuska
Finland
France
CEA/DAM Bruyères-le-Châtel: Farouk Aksouh, Audrey Chatillon, Julien Taieb
CEA/DSM/IRFU Saclay: Alain Boudard, Diane Dore, Bernard Gastineau, Wolfram
Korten, Philippe Legou, Sylvie Leray, Stefano Panebianco
GANIL: David Boilley, Wolfgang Mittig, Fanny Rejmund, Patricia Roussel-Chomaz,
Herve Savajols, Christelle Schmitt
IPN Orsay: Bernard Genolini
2

Germany
EMMI and FIAS: Enrico Fiori, Bastian Löher, Deniz Savran
GSI Darmstadt: Yuliya Aksyutina, Denis Bertini, Konstanze Boretzky, Peter Egelhof,
Hans Emling, Hans Feldmeier, Hans Geissel, Jürgen Gerl, Kathrin Goebel, Magdalena
Górska, Jörg Hehner, Michael Heil, Jan Hoffmann, Günter Ickert, Aleksandra Kelic-Heil,
Ivan Kojouharov, Nikolaus Kurz, Karl-Heinz Langanke, Yvonne Leifels, Thomas Neff,
Chiara Nociforo, Maria Valentina Ricciardi, Dominic Rossi, Thomas Roth, Takehiko
Saito, Karl-Heinz Schmidt, Haik Simon, Klaus Sümmerer, Wolfgang Trautmann, Helmut
Weick, Martin Winkler
Helmholtz-Zentrum Dresden-Rossendorf: Daniel Bemmerer, Zoltan Elekes, Arnd Junghans,
Mathias Kempe, Manfred Sobiella, Daniel Stach, Andreas Wagner, Jörn Wüstenfeld,
Dmitry Yakorev
TU Darmstadt: Leyla Atar, Thomas Aumann, Timo Bloch, Christoph Caesar, Joachim
Enders, Diego Gonzalez-Diaz, Marcel Heine, Matthias Holl, Alexander Ignatov, Oleg
Kiselev, Dmytro Kresan, Thorsten Kröll, Alina Movsesyan, Manfred Mutterer, Valerii
Panin, Stefanos Paschalis, Marina Petri, Norbert Pietralla, Achim Richter, Heiko Scheit,
Mirko von Schmid, Linda Schnorrenberger, Philipp Schrock, Stefan Typel, Vasily Volkov,
Felix Wamers
TU Dresden: Thomas Cowan, Marko Röder, Kai Zuber
TU Munich: Michael Bendel, Michael Böhmer, Thomas Faestermann, Roman Gernhäuser,
Walter Henning, Reiner Krücken, Tudi Le Bleis, Olga Lepyoshkina, Max Winkel, Sonja
Winkler
University of Cologne: Jannis Endres, Andreas Hennig, Vassili Maroussov, Lars Netterdon,
Peter Reiter, Andreas Zilges
University of Frankfurt: Sebastian Altstadt, Olga Ershova, Christoph Langer, Christian
Müntz, Ralf Plag, René Reifarth, Kerstin Sonnabend, Meiko Volknandt, Christine
Wimmer
University of Gießen: Horst Lenske
Unversity of Mainz: Jens Volker Kratz
Hungary
ATOMKI: Margit Csatlós, Zoltán Elekes, Zsolt Fülöp, János Gulyás, Attila Krasznahorkay,
László Stuhl, János Timár, Tamás Tornyi
University of Budapest:
Ákos Horváth
3

India
AM University Aligarh: Rajeshwari Prasad, Manoj Kumar Sharma , Pushpendra Pal
Singh
BARC Mumbai: S. Kailas, Kripamay Mahata, Aradhana Shrivastava
SINP Kolkata: Bijay Agrawal, Padmanava Basu, Pratap Bhattacharya, Sudeb Bhattacharya,
Santosh Chakraborty, Sujib Chatterjee, Ushasi Datta Pramanik, Pradipta
Kumar Das, Janaki Panja, Anisur Rahaman, Jayati Ra, Tinku Sinha
Tata Institute: Rudrajyoti Palit
RCNP Osaka: Isao Tanihata
Japan
Tokyo Institute of Technology: Takashi Nakamura
University of Bergen: Jan Vaagen
Norway
Poland
IFJ PAN Cracow: Bronislaw Czech, Stanislaw Kliczewski, Maria Kmiecik, Jerzy Lukasik,
Adam Maj, Piotr Pawlowski, Miroslaw Zieblinski
University of Cracow: Reinhard Kulessa, Wladyslaw Walus
Portugal
LIP Coimbra: Alberto Blanco, Paulo Fonte, Luis Lopes, Rui F. Marques
University of Lisbon: Daniel Galaviz Redondo, Ana Henriques, Jorge Machado, Pamela
Teubig, Paulo Velho
UTL Lisbon: Raquel Crespo
Romania
Horia Hulubei National Institute of Physics: Mihai Stanoiu
Institute of Space Sciences Bucharest: Madalin Cherciu, Maria Haiduc, Dumitru Hasegan,
Mihai Potlog, Emil Stan
4

INR Moscow: Alexander Botvina
Russia
Ioffe PTI St. Petersburg: Yuri Tuboltsev, Elena Verbitskaya
IPPE Obninsk: Anatoly V. Ignatyuk
JINR Dubna: Irina Egorova, Sergey N. Ershov, Andrey Fomichev, Mikhail Golovkov,
Alexander V. Gorshkov, Leonid Grigorenko, Sergey Krupko, Yulia Parfenova, Sergey
Sidorchuk
PNPI Gatchina: Georgy Alkhazov, Vladimir Andreev, Andrey Fetisov, Victor Golovtsov,
Anatolii Krivshich, Lev Uvarov, Vladimir Vikhrov, Sergey Volkov, Andrey Zhdanov
RRC Kurchatov Institute Moscow: Boris Danilin, Leonid Chulkov, Alexei Korsheninnikov,
Eugenii Kuzmin, Aleksey Ogloblin
Saudi Arabia
National Center for Mathematics and Physics: Hamoud AlHarbi, Nasser AlKhomashi,
Abdulrahman AlGhamdi, Abdulrahman Maghrabi
King Saud University: Khalid Kezzar, Safar AlGhamdi, Mohamed AlGarawi, Farouk
Aksouh
Slovakia
Slovak Academy of Sciences: Martin Veselsky
Spain
IEM-CSIC Madrid: Maria José Garcia Borge, Eduardo Garrido, Enrique Nacher, Angel
Perea, Guillermo Ribeiro, José Sanchez del Rio, Jorge Sanchez Rosado, Olof Tengblad
IFIC Valencia: Alejandro Algora, Berta Rubio, José L. Tain
Universidad Complutense of Madrid: Samuel España, Luis M. Fraile, Jose Udias-Moinelo
University of Santiago de Compostela: Héctor Alvarez-Pol, Francesc Ayyad, José Benlliure,
Manuel Caamaño, Dolores Cortina-Gil, Paloma Díaz, Ignacio Durán, Beatriz
Fernández-Domínguez, Martín Gascón, David González-Caamaño, Carlos Paradela, Noelia
Montes, Juan Ramón Pereira, Benjamin Pietras
University of Vigo: Enrique Casarejos
UPC Barcelona: Francisco Calvino
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Sweden
Chalmers University: Christian Forssén, Johan Gill, Julius Hagdahl, Andreas Heinz,
H˚akan Johansson, Björn Jonson, Thomas Nilsson, Goran Nyman, Natalia Shulgina,
Ronja Thies, Staffan Wranne, Mikhail Zhukov
KTH Stockholm: Bo Cederwall, Stanislav Tashenov
Lund University: Vladimir Avdeichikov, Joakim Cederkall, Pavel Golubev, Lennart
Isaksson, Bo Jakobsson
CERN: Vladimir Eremin
Switzerland
The Netherlands
KVI: Nasser Kalantar, Ali Najafi, Catherine Rigollet, Branislav Streicher
University of Groningen: Jarno Van de Walle
United Kingdom
CCLRC Daresbury Laboratory: Patrick Coleman-Smith, Marc Labiche, Ian Lazarus,
Roy Lemmon, Simon Letts, Vic Pucknell, John Simpson
University of Birmingham: Nick Ashwood, Matthew Barr, Martin Freer
University of Edinburgh: Tom Davinson, Phil Woods
University of Liverpool: Marielle Chartier, J. Cresswell, Simon Gannon, Paul Nolan,
M. Norman, J. Sampson, Janet Sampson, D. Seddon, T. Stanios, Jonathan Taylor, J.
Thornhill, D. Wells
University of Manchester: David Cullen, Sean Freeman
University of Surrey: Jim Al-Khalili, Carlo Barbieri, Wilton Catford, William Gelletly,
Ron Johnson, Zsolt Podolyak, Patrick Regan, Arnau Rios, Edward Simpson, Paul
Stevenson, Jeffrey Tostevin
University of York: Charles Barton
Argonne National Laboratory: Jerry Nolen
EMMI/JINA: Justyna Marganiec
USA
Michigan State University: Bradley Sherrill, Remco Zegers
Texas A&M University Commerce: Carlos Bertulani
6

Contents
Executive Summary 11
1. Introduction and Overview 13
1.1. NeuLAND – A Key Instrument of R 3 B for High-Resolution Multi-Neutron
Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2. NeuLAND Design Goals – General Remarks . . . . . . . . . . . . . . . . . 16
2. Physics Scenarios: Requirements for NeuLAND 19
2.1. Evolution of the Collective Response of Exotic Nuclei . . . . . . . . . . . 19
2.2. Dipole Strength at the Particle Threshold . . . . . . . . . . . . . . . . . . 21
2.3. Light Exotic Systems - Unbound States and Multi-Neutron Configurations 22
2.4. Quasi-Free Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.5. Fission and Multifragmentation . . . . . . . . . . . . . . . . . . . . . . . . 26
2.6. Flow and Equation of State . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3. Summary of NeuLAND Prototype Results 29
3.1. Scintillator Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2. Studies with Fast Protons . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3. Studies with 31 MeV Electrons . . . . . . . . . . . . . . . . . . . . . . . . 31
3.4. Other Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4. Monte Carlo Simulations 35
4.1. Overview and Comparison of the Various Simulation Codes . . . . . . . . 35
4.1.1. Simulation Frameworks . . . . . . . . . . . . . . . . . . . . . . . . 35
4.1.2. Neutron Data Validation . . . . . . . . . . . . . . . . . . . . . . . 37
4.2. From a Passive Converter to a Fully-Active Scintillator Concept . . . . . 43
4.3. Effect of Granularity and Timing Properties for a Fully-Active Detector . 45
4.4. Light-Transport Simulations . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.5. Scintillator Studies of Full-Size NeuLAND . . . . . . . . . . . . . . . . . 51
4.5.1. One-Neutron Response . . . . . . . . . . . . . . . . . . . . . . . . 52
4.5.2. Multi-Neutron Response . . . . . . . . . . . . . . . . . . . . . . . . 52
4.5.3. Neutron Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.5.4. Physics Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5. Technical Specifications and Design Details of NeuLAND 65
5.1. Final Detector Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
7

5.2. Structure of the NeuLAND Submodule . . . . . . . . . . . . . . . . . . . . 65
5.2.1. Material, Sizes and Wrapping . . . . . . . . . . . . . . . . . . . . 65
5.2.2. Light Guides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.2.3. Light Readout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5.3. Full Detector Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.3.1. Grouping of Submodules — Double Planes . . . . . . . . . . . . . 67
5.3.2. Full Detector Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.4. Peripheral Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.4.1. Read-Out Electronics - TacQuila . . . . . . . . . . . . . . . . . . . 73
5.4.2. High-Voltage Distribution System . . . . . . . . . . . . . . . . . . 74
5.4.3. Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
6. Radiation Environment and Safety Issues 77
7. Production, Quality Assurance and Acceptance Tests 79
8. Calibration 81
8.1. Calibration with Fast Neutrons . . . . . . . . . . . . . . . . . . . . . . . . 81
8.1.1. Calibration of a Subset of NeuLAND Modules . . . . . . . . . . . 81
8.1.2. Characterization of Neutron Interactions with the Full-Size Detector 84
8.2. Cosmic Ray Tracking in NeuLAND for Adjustment and Calibration . . . 84
9. Infrastructure 87
10.Installation procedure, its Time Sequence, Necessary Logistics from A to Z
including Transportation 89
11.Cost and Funding 91
11.1. Cost Estimate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
11.2. Funding Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
12.Time Schedule Table and Milestones 93
13.Organization and Distribution of Responsibilities 95
A. NeuLAND Working Group Members 97
B. Neutron MRPC Results in Details 99
B.1. Principle of Operation of an MRPC-Based Neutron Detector with a Thick
Iron Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
B.2. 40 MeV Single Electron Test Facility at ELBE . . . . . . . . . . . . . . . . 101
B.3. Design Issues Addressed with 40 cm × 20 cm Prototypes . . . . . . . . . . 104
B.4. Construction and Test of a Full-Size 200 cm × 50 cm Prototype . . . . . . 105
B.5. Monte Carlo Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
B.6. Further MRPC Prototype and Offline Tests . . . . . . . . . . . . . . . . . 110
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B.7. MRPC Solution using Glass as Converter . . . . . . . . . . . . . . . . . . 112
B.8. Summary and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Bibliography 115
9

Executive Summary
The R 3 B (Reactions with Relativistic Radioactive Beams) experiment at FAIR will be
the only facility worldwide providing the capability for kinematically complete measurements
of reactions with relativistic heavy-ion beams of short-lived nuclei up to about
1 AGeV. These measurements require a high resolution to allow for a comprehensive experimental
investigation of fundamental science questions related to nuclear structure,
astrophysics, and reactions with neutron-proton asymmetric nuclei. The experimental
setup has been designed and will be built by the R 3 B collaboration on the basis of more
than 20 years of experience with the reaction setup LAND at GSI. The newly designed
instrumentation thereby overcomes major limitations of the present setup. The main
design goals emerging from the physics cases are the applicability of the experimental
approach to energetic beams maintaining the high resolution, as well as the extension
of the physics program, i.e., the capability to measure a large variety of reaction types.
The beams provided by Super-FRS at FAIR will be more neutron-rich than presently
available, up to uranium. Consequently, high beam energies are needed in order to ensure
fully-stripped ions for heavy beams. At the same time, the capability to detect
multi-neutron events is required due to the low thresholds of neutron-rich nuclei.
NeuLAND (new Large-Area Neutron Detector) is the next-generation neutron detector
designed for R 3 B which meets all requirements defined by the ambitious physics program
proposed for the R 3 B facility. NeuLAND features a high detection efficiency, a high
resolution, and a large multi-neutron-hit resolving power. This is achieved by a highly
granular design of plastic scintillators, avoiding insensitive converter material. The detector
will consist of 3000 individual submodules with a size of 5×5×250 cm 3 , arranged
in 30 double planes with 100 submodules providing an active face size of 250×250 cm 2
and a total depth of 3 m. NeuLAND can be divided into two detectors for special applications
and will be placed at different distances from the target, in order to meet specific
experimental demands.
The neutron detector NeuLAND is an integral part of the R 3 B experiment, and is
the key instrument for a major part of the physics program. The main design goals
comprise a one-neutron detection efficiency above 95% in a wide energy range and a full
acceptance corresponding to an angular coverage of ±80 mrad. The desired resolutions
for momenta and thus the excitation energies, as described in detail in chapter 2, lead to
the required spatial resolutions of σx,y,z ≤ 1.5 cm and to a time resolution of σt ≤ 150 ps
for the standard distance between detector and target of 15.5 m. When placed at a
distance of 35 m, an excitation-energy resolution of less than 20 keV(!) will be reached
for an excitation energy of 100 keV above threshold for a beam energy of 600 AMeV.
11

Apart from the excellent energy resolution of NeuLAND, the enhanced multi-neutron
recognition capability with an efficiency of up to 60% for a reconstructed four-neutron
event will constitute a major step forward.
The presented design is the result of several years of R&D studies. Summaries of prototype
tests and simulations are presented in chapters 3 and 4, respectively. Different
design concepts have been followed, including converter-based solutions, e.g., a detector
based on steel converter plus charged-particle detection with resistive-plate chambers
(RPC). The RPC concept has been ruled out mainly because of its insufficient multineutron
detection capability. A fully active detector with calorimetric properties has
turned out to be the best solution. Submodules have been tested with proton and electron
beams resulting in time resolutions of better than the required σt ≤ 150 ps, even
with inexpensive photomultipliers. In accordance with simulations, improved timing
properties have been obtained with optimized light guides.
Extensive simulation studies have been performed leading to the final design. Different
frameworks have been applied such as GEANT and FLUKA, leading to a remarkable
agreement. The good accordance of simulations with available data leads to a consistent
prediction of the neutron response for the detector. A fully-active detector design is
required to provide the unambiguous identification of primary neutron interactions, the
large efficiency at lower neutron energies and the high multi-neutron resolving power,
the latter being due to its calorimetric properties. The effect of the granularity and
the time resolution of the detector has been investigated in detail (section 4.3), leading
to the most cost-effective solution presented here, which still meets the required design
criteria. The final performance is demonstrated in section 4.5 for several physics cases.
The details of the technical realization including mechanics, readout electronics, tests,
calibrations, as well as the construction procedure are summarized in chapters 5 to 10.
A detailed estimate of the investment cost for the construction is given in chapter 11.
Several groups of the R 3 B collaboration will contribute to the construction of the Neu-
LAND detector. The final assembly will take place at the GSI/FAIR site. We expect the
beginning of construction in 2012, as soon as funding will be available. The construction
of the full detector will take about 3.5 years, allowing for first experiments with the
complete detector in 2016. An important milestone will be met by using a 20% detector
for physics experiments in the end of 2014 in Cave C at GSI, which will already profit
from an improved resolution for neutron detection.
We consider the risk for technical difficulties in the production or for an insufficient
performance of the detector to be negligible. The design based on fully-active scintillators
with photomultiplier readout is rather robust and the simulations, on which our
design decisions are based upon, have been verified against each other and experimental
data. The fully-equipped detector – after full commissioning and first production runs
in Cave C – will move to its final location in the R 3 B hall at the FAIR site in 2017,
being fully operational for physics experiments in 2018 when Super-FRS will deliver first
beams at FAIR.
12

1. Introduction and Overview
1.1. NeuLAND – A Key Instrument of R 3 B for
High-Resolution Multi-Neutron Detection
The acronym R 3 B stands for Reactions with Relativistic Radioactive Beams. The
R 3 B experiment will be installed at the high-energy branch focal-plane of the Super-
FRagment-Separator Super-FRS at the FAIR Facility for Antiproton and Ion Research.
The R 3 B activity is embedded into the NUSTAR (NUclear STructure, Astrophysics and
Reactions) pillar of the FAIR experimental program. The design and construction of the
R 3 B facility is being pursued within a large international collaboration, the R 3 B collaboration,
which is a consortium of more than 200 scientists from more than 20 countries.
The physics cases and the conceptual layout of the experiment including its instrumental
parts have been laid out in the Conceptual Design Report for FAIR [CDR-01] in 2001
and in more technical detail in the R 3 B Technical Proposal [R3B-05] in 2005. Since
then, an extensive R&D program has been pursued which led to the final design of the
different detection components. In this report, we describe in detail the technical design
of the neutron detector NeuLAND (New Large Area Neutron Detector). This detector
serves as a high-resolution time-of-flight spectrometer for neutrons in the energy range
from 100 to 1000 MeV. The superior time and position resolution of this detector in
conjunction with an excellent resolving power for multi-neutron events is the key for the
realization of the ambitious physics program of R 3 B and will enable the investigation of
nuclear reactions with unprecedented precision.
The R 3 B experiment will enable kinematically complete measurements of reactions with
relativistic beams up to energies of approximately 1 AGeV. (The upper limit in energy is
defined by the maximum magnetic rigidity of 20 Tm of the Super-FRS). The flexibility of
the setup with its detection systems allows us to accommodate experiments investigating
different types of reactions and physics cases. An overview on the physics subjects to
be investigated has been given in the Conceptual Design Report [CDR-01]. In the
next chapter we discuss a selection of physics cases for which the neutron detector
NeuLAND and its performance play an important role, which could be summarized in
the question: How do nuclear properties evolve as a function of isospin? This includes
nuclear-structure properties of short-lived nuclei with extreme neutron-to-proton ratios
as well as properties of asymmetric nuclear matter. Both, the experimental answers
to this question as well as a fundamental understanding from a theoretical point of
view, form the basis to the understanding and description of astrophysical objects and
13

processes in the universe, such as the properties of neutron stars and the synthesis of the
heavy elements. R 3 B will constitute a unique setup to investigate these topics utilizing
relativistic beams. The advantages of utilizing high-energy beams are many-fold. First,
the production, separation, and identification of radioactive beams at high energies is
very efficient due to the kinematical forward focussing and the possibility to use thick
targets. Second, it also enables a clean separation of even heavy beams with masses
A ≥ 200 due to the fact that ions are fully stripped, a pre-requisite for the magnetic
analysis and separation of heavy ions. Similar arguments hold for the measurement
of secondary reactions with these beams. R 3 B will be the first experiment which will
allow a kinematically complete measurement of peripheral reactions with such heavy ion
beams including the coincident detection and identification of the heavy residues as well
as neutrons and photons. Other advantages of the high beam energy are related to the
reaction mechanisms, which become simpler, permitting reliable model description, at
higher beam energies. At high velocity, reactions can be accurately described by theory,
nuclear-structure observables are less entangled with the reaction mechanism, and can
thus be deduced more precisely.
In this report we do not describe the complete R 3 B experimental setup with its instrumentation
but we would like to refer the reader to the R 3 B Technical Proposal [R3B-05].
However, to understand the context, we briefly mention the development and construction
status of the main components of the R 3 B setup, as shown in figure 1.1.
Key instruments besides NeuLAND, are the photon and particle calorimeter CALIFA,
the silicon tracker R 3 B-Si-TRACKER, and the super-conducting large-acceptance dipole
R 3 B-GLAD. In addition, several charged-particle detectors are used for beam tracking,
∆E and time-of-flight measurements. The CALIFA detector consists of two parts, the
forward end-cap and the barrel part. A Technical Design Report for the barrel part of
CALIFA is being submitted in parallel to this report. Construction is foreseen to start
in 2012. The Technical Design of the end-cap is still ongoing and will be finalized in
2013. The target recoil detector is being designed by a consortium of institutes from the
UK under the leadership of Daresbury laboratory. The funds for the R&D and the final
construction are secured by the UK funding agencies and the complete detector will be
available for experiments in 2016. The construction of the superconducting dipole magnet
has already started at CEA Saclay and the cold mass including the superconducting
coils have been already assembled. The completion and delivery of the device is foreseen
for the end of 2012. The magnet will then be installed in Cave C at the present GSI
facility.
The challenges of performing nuclear-structure and reaction experiments at relativistic
beam velocities are related to the high magnetic rigidity of the ions and the demands
on the overall resolution of the detection system. The experiment has to resolve excitation
energies in the 100 keV domain populated in a reaction with, e.g., a 132 Sn beam
(1 AGeV) with a momentum of 220 GeV/c. The precursor experiment of R 3 B, the
ALADIN-LAND setup at GSI, on which the concept of R 3 B is based, does not have these
capabilities. Although very successful during the past 20 years, the main limitations of
14

RIB from
Super-FRS
R 3 B-Si-TRACKER
CALIFA
R3B Start version 2016
Heavy
fragments
Protons
R 3 B-GLAD
NeuLAND
Figure 1.1.: The R 3 B setup in its startup phase 2016 with its main components: the silicon
tracker R 3 B-Si-TRACKER, the calorimeter CALIFA, the dipole magnet
R 3 B-GLAD and the neutron time-of-flight spectrometer NeuLAND.
the present setup are the limited magnetic rigidity, the limited resolution in momentum
for fragments and neutrons, the lack of good resolution for γ-ray detection (mainly due
to the Doppler broadening) and the limited capability to detect multi-neutron events.
Here, NeuLAND will have a key role. A substantial improvement in resolution of about
a factor of three compared to LAND will result in improved invariant-mass resolution,
even with the higher beam energies up to approximately 1 AGeV. Complementary, lower
beam energies and a large time-of-flight path for neutrons will enable high-resolution experiments
for special cases. An excitation energy resolution down to below σ=20 keV (!)
around the particle threshold will allow the investigation of narrow resonances as well as
a precise determination of differential cross sections at low excitation energies relevant
for the synthesis processes of elements in the universe. The unprecedented multi-neutron
hit capability of the new design will be the basis for studying very neutron-rich nuclei,
whose emission thresholds become low. Another highlight related to the multi-neutron
detection capability is the study of the most neutron-rich systems – the unbound continuum
states beyond the neutron dripline like, for instance, the bench mark cases 28 O
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decaying into 24 O plus 4 neutrons and the tetra-neutron system. In the next section we
summarize the capabilities and design goals of NeuLAND. In chapter 2 we provide a more
detailed view of the various physics cases of R 3 B with emphasis on those cases where
the performance of the newly designed NeuLAND is key to crossing borders into new
frontiers, i.e., entering ”Neuland” (terra incognita) in physics with radioactive beams.
1.2. NeuLAND Design Goals – General Remarks
The detection of fast neutrons plays a crucial role for the exploration of light and heavy
exotic nuclei towards the neutron dripline. Since the neutron separation thresholds decrease
with increasing neutron-proton asymmetry, the emission of several neutrons after
excitation is the dominant decay process. Neutrons emitted from projectiles with high
velocities in the laboratory frame are kinematically strongly forward focussed, although
isotropically emitted in the projectile rest frame. This allows for a very efficient coverage
of the full solid angle with moderate detector sizes. The excitation energy of the
projectile can be determined, using the invariant-mass technique, from measurements of
the momenta of all emitted particles. The neutron momenta are determined from the
measured position of the interaction in the neutron detector and the time-of-flight from
the target to the neutron detector. The desired resolutions for momenta and thus the
excitation energies, see details in chapter 2, lead to the required spatial resolutions of
σx,y,z ≤ 1.5 cm and a time resolution of σt ≤ 150 ps. The main design goals comprise,
besides the improved resolution, a detection efficiency above 95% for single neutrons
for a wide energy range, a large geometrical acceptance and an excellent multi-neutron
hit reconstruction efficiency. The major achievements in performance, compared to the
present LAND detector, are an improved resolution by a factor of three, the extension of
the very high efficiency for neutrons down to lower energies, and the substantial improvement
of the multi-neutron reconstruction efficiency from a few percent up to 60 percent.
The latter will be a major and necessary advantage for future studies with more neutronrich
systems including nuclear states beyond the neutron dripline. The performance of
the detector is described in great detail in this report on the basis of extensive simulations
and prototype tests. Here, we give a brief overview on the main features with some
examples including large acceptance, high resolution, a large multi-neutron-hit resolving
power, and high efficiency in a very wide energy window.
The active area of the detector of 250 × 250 cm 2 allows to cover the full acceptance
of ±80 mrad determined by the gap of the dipole magnet if the detector is placed
15.5 m downstream of the target. This solid-angle coverage corresponds to a 100%
acceptance (4π) measurement of neutrons with kinetic energies up to around 5 MeV in
the center-of-mass (CM) frame if emitted from a projectile fragment with a kinetic energy
of 600 AMeV. This has to be compared with a typical neutron energy distribution, e.g.,
a Maxwellian distribution of a statistical decay, which peaks at kinetic energies of 1 to
2 MeV and contains more than 90% of the events within the 5 MeV coverage. At higher
beam energies, either a larger acceptance can be chosen (up to about 10 MeV neutron
16

energy at 1 AGeV), or the detector can be placed further downstream to increase the
resolution by keeping the nominal acceptance of up to 5 MeV neutrons. At 1 AGeV,
a 5 MeV neutron emitted perpendicular to the beam axis will appear at 57 mrad in
the laboratory frame, which is fully covered by NeuLAND at a distance of 22 m to the
target.
In the full-acceptance mode (15.5 m distance), the position resolution of 1.5 cm corresponds
to a resolution in transverse momentum of 10 −3 relative to the total momentum
of the neutron. The resulting invariant-mass resolution depends on the beam energy and
the excitation energy. For the 600 AMeV case, this corresponds to around 60 keV energy
resolution at an excitation energy of 1 MeV above the neutron emission threshold. The
longitudinal component of the resolution is more complicated depending not only on
beam energy and excitation energy, but also on the emission angle. Simulations have
shown that the excellent excitation-energy resolution stemming from the position measurement
can be maintained if the time resolution is better than 150 ps. The ultimate
resolution can be reached by placing the detector at the longest possible distance to the
target, which is 35 m in the R3B/FAIR experimental hall. Then a resolution of better
than 20 keV can be reached at 600 AMeV for an excitation energy 100 keV above the
neutron threshold. This means that it will be possible to measure the differential (γ, n)
cross section in an energy range corresponding to the stellar temperature window. The
measurement of narrow resonances close to the threshold of unbound nuclei beyond the
dripline is another example where the ultimate resolution is required.
Apart from the excellent energy resolution of NeuLAND, a major step forward is the
multi-neutron recognition capability of the new design. A reliable reconstruction of the
momentum vectors for several neutrons hitting the detector will be achieved even if the
neutrons impinging on the detector are spatially not well separated. An efficiency, for
instance, of up to 60% can be reached for a reconstructed four-neutron event. This is an
important achievement for many physics cases including the study of neutron droplets
and nuclear systems beyond the dripline in general. Also for giant resonance studies,
or excitations in general, the multi-hit recognition becomes essential for neutron-rich
systems. Even for medium-heavy and heavy nuclei, Super-FRS at FAIR will deliver
neutron-rich beams with low neutron separation thresholds causing the multi-neutron
decay channel being the dominant one. Other examples for reaction studies involving
the detection of several neutrons are fission and multifragmentation.
Last but not least we mention the large neutron energy range which is covered by Neu-
LAND with high efficiency. Here, the goal is to improve the detection efficiency and
response compared to LAND for lower energies down to approximately 50 to 200 MeV.
Similar as for the multi-neutron capability, this goal can be achieved due to the fullyactive
scintillator concept omitting passive converter material. The efficiency of >95%
at high energies drops only to 90% for 200 MeV neutrons. This is particularly important
for the quasi-free scattering program. NeuLAND will allow the energy-resolved detection
of knocked out neutrons in (p,pn) reactions at angles around 45 degrees.
17

2. Physics Scenarios: Requirements for
NeuLAND
In the following sections we detail the demands for the detection of fast neutrons derived
from the main types of experiments within the broad R 3 B physics program. For a more
detailed description of the overall R 3 B physics programme we refer to the Conceptual
Design Report for FAIR [CDR-01] and the R 3 B Technical Proposal [R3B-05] and references
therein. NeuLAND will be located downstream from the target. In the full
acceptance mode, the distance from the target is chosen such, that the face-size of the
detector covers the same angular range as the yoke of the dipole magnet R 3 B-GLAD,
namely 80 mrad. For a detector of 2.5×2.5 m 2 face-size the full-acceptance distance is
15.5 m downstream from the target. For some applications, see e.g. section 2.2, the
highest possible resolution is demanded. Here we profit from the length of the R 3 B cave
allowing to position the detector up to 35 m downstream. As a third option NeuLAND,
or parts of NeuLAND, can be placed closer to the target for the detection of neutrons
stemming from quasi-free scattering interactions, see section 2.4.
2.1. Evolution of the Collective Response of Exotic Nuclei
Electromagnetic excitation of exotic nuclei is a very powerful tool for exploring the evolution
of collective phenomena like giant resonances, especially the giant dipole resonance
(GDR) as a function of neutron-proton asymmetry [Har-01]. At beam energies of up to
1000 AMeV, cross sections for dipole excitations are large, on the order of barn, and the
excitation energies transferred reach up to approximately 20 MeV [Ber-85]. The LAND
collaboration has played a pioneering role in this field discovering the double giant dipole
resonance in stable nuclei [Bor-03], and more recently the pygmy mode in neutron-rich
Sn isotopes [Adr-05]. The appearance of low-lying strength in exotic nuclei [Kli-07],
[Wie-09], is particularly interesting from a nuclear structure point of view since its occurrence
is interpreted as a consequence of neutron-proton asymmetry and the evolution
of skin effects. Similar to the collective giant resonances, this so-called pygmy strength
is related to bulk properties of nuclei and nuclear matter. Various, and partly contradictory,
microscopic theoretical models describe this resonance as discussed in an overview
by N. Paar et al. in Ref. [Paa-07] and references therein. It has been suggested, that the
density dependence of the symmetry energy close to saturation density is correlated with
the low-lying dipole strength in neutron-rich nuclei [Pie-06], very similar to the earlier
reported correlation of the symmetry energy parameters to the neutron-skin thickness in
19

heavy neutron-rich nuclei [Bro-00], [Hor-01]. A first attempt to extract the parameters
describing the neutron-proton asymmetry part of the equation of state for nuclear matter
from the measured low-lying dipole strength has been made by Kliemkiewicz et al.
[Kli-07] and by Carbone et al. [Car-10]. Experimental data concerning the collective response
of exotic nuclei including the giant resonances and the pygmy dipole strength are
still rather scarce. The existing dipole strength measurements suffer from an insufficient
response of the detector system.
From the experimental point of view, there are several challenges to deal with. The
heavy-ion induced electromagnetic excitation process requires high beam energies which
in turn put high demands on the detection systems. The combination of a largeacceptance
superconducting dipole with large field integral, a highly granular calorimeterlike
photon detector together with a high-efficiency and high-resolution detection of
neutrons make the R 3 B setup an ideal facility to study the collective response of exotic
nuclei.
The neutron detector has to be optimized for high detection efficiency and acceptance in
the beam-energy region from 200 to 1000 AMeV. A variation of beam energy is necessary
to disentangle dipole and quadrupole contributions to the excitation cross section. The
lower energy of 200 AMeV will be used to study giant monopole resonances in neutronrich
nuclei which are related to the incompressibility of asymmetric nuclear matter. We
will use alpha scattering in inverse kinematics in an active He gas target which will be
developed for these measurements. For heavy nuclei, like Pb, the beam energies around
1 AGeV are necessary to allow for fully stripped ion beams. It is mandatory to apply
a magnetic analysis for an identification of the fragments using a tracking system. So
far, this has not been possible due to the limitations of the present detection devices.
The improved resolution of NeuLAND will make a high-resolution detection of neutrons
possible even at a laboratory energy of 1 AGeV.
The kinetic energy of neutrons evaporated from collective states in the continuum follows
usually a Maxwellian distribution with a maximum at approximately 1 to 2 MeV.
An angular acceptance which allows detection of up to about 5 MeV kinetic energy is
required to cover the full distribution. This requirement is met by the ±80 mrad acceptance
defined by the gap of the dipole magnet and will be covered by the neutron
detector. The envisaged position and time resolution of 1.5 cm and 150 ps for NeuLAND
will result in an excitation energy resolution of about 100 keV at an excitation energy
of 1 MeV above the threshold (or 1 MeV kinetic energy of the neutron) for a 600 AMeV
beam at a distance fulfilling the full-acceptance criterium. At 1 AGeV, the detector can
be placed further away while providing the same acceptance and about the same energy
resolution.
The high intensities of radioactive beams provided by the Super-FRS at FAIR will
push the frontier towards more neutron-rich systems. In such nuclei, the effects of
asymmetry are magnified and the electromagnetic response of the nucleus reflects these
isospin-related changes. The Pygmy resonance is one example, but also the dipole and
quadrupole response as a whole change. The neutron-rich medium-mass nuclei which can
20

e studied at R 3 B at FAIR include nuclei which are produced in explosive astrophysical
scenarios where the heavy elements are synthesized in the r-process. While ground-state
properties like masses and half-lives are the most important properties necessary for
modeling the rapid neutron capture process in an equilibrium stage, it has been shown
that for an accurate theoretical description of the r-process the dipole response of these
nuclei plays an essential role in determining the final abundance of nuclei as observed
in the solar system. A systematic change of the response of nuclei alters the result of
the elemental synthesis significantly [Gor-98], [Rau-08]. An experimental and theoretical
effort has to be undertaken in order to understand the response of these neutron-rich
nuclei. Since the neutron separation energies for these nuclei are typically approximately
one to two MeV only, the decay of excited projectiles involves many neutrons. In order
to enable an invariant-mass analysis, the momentum vectors of the different neutrons
have to be resolved. Typically around four neutrons from the decay of the GDR will
have to be detected. NeuLAND will be the first detector which will be capable to satisfy
such a demand. An efficiency for a correct detection of a four-neutron event of about
60% is envisaged.
2.2. Dipole Strength at the Particle Threshold
Electromagnetic excitation of exotic nuclei is of importance as well from an astrophysical
point of view as mentioned already in the previous section. While the paths of the nucleosynthesis
processes like the r-, and rp-processes are essentially determined by nuclear
masses and lifetimes, the final abundance patterns depend also on the (p,γ) and (n,γ)
reaction rates. For the modeling of astrophysical processes with network calculations,
the reaction rates are usually calculated using a standard dipole response of nuclei as an
input to a Hauser-Feshbach calculation. It has been shown by Litvinova et al. [Lit-09]
that for a microscopically calculated dipole response (which predicts a significant shift
of strength towards lower excitation energies for neutron-rich nuclei) used as input, the
capture cross sections in the astrophysical temperature range change significantly, and
the final abundances as a consequence as well. Beside a fundamental understanding of
the dipole response and its decay patterns, a direct measurement of critical capture cross
sections is needed [Sur-09]. The heavy-ion induced electromagnetic excitation process
enables a measurement of the inverse process, i.e., the Coulomb breakup into fragment
and proton or neutron. The capture cross section or astrophysical S-factor can then
be deduced by using the detailed balance theorem. Prominent examples from previous
studies are the S-factor for the 7 Be proton capture [Sch-03], [Sch-06], the 14 C neutron
capture studied in 15 C Coulomb breakup [Dat-03], or the breakup of 7 Li [Ham-10].
The energy region where the cross section is needed is determined by the relevant temperatures
in the astrophysical processes. Usually, this corresponds to an energy window
around or even below 100 keV. For the measurement of the inverse process, this translates
into low relative kinetic energies between fragment and neutron in the CM system
after excitation. The excitation and detection process takes advantage of the high beam
21

velocities (large number of virtual photons, thick target, etc.). The challenge is to
measure the fragment-neutron relative kinetic energy precise enough to allow for the
extraction of an energy-differential cross section below 100 keV. This defines the requirements
on the neutron detection, since the relative-energy resolution is dominated
by the neutron detection. The design goals comprise an envisaged resolution of about
20 keV at an excitation energy of 100 keV above the threshold. For these type of measurements
the longest time-of-flight path for the neutrons of about 35 m will be used.
Since the neutrons are emitted with small relative energies, the limited acceptance of
the neutron detector at the far distance (for a detector with a face size of 250×250 cm 2
about 35 mrad coverage corresponding to 100% acceptance of up to 800 keV relative
energy at 500 AMeV beam energy) does not imply a cut into the neutron distributions.
The aimed for resolution allows for the measurement of the differential cross section in
20 keV bins in the astrophysical relevant energy window from 0 to 500 keV.
2.3. Light Exotic Systems - Unbound States and
Multi-Neutron Configurations
Experiments with neutron-dripline nuclei have been possible so far only for the lightest
nuclei up to Oxygen. After the first experiments at the Bevalac by Tanihata et al.
[Tan-85] 20 years ago which lead to the discovery of the neutron halo in 11 Li [Han-87],
tremendous experimental and theoretical progress has been made. The light dripline nuclei
played a key role in the progressing understanding of nuclei with large neutron excess
and weak binding. Meanwhile exclusive multi-coincidence experiments of reactions with
dripline nuclei have been realized. Precise experiments with light neutron-rich nuclei are
still a major frontier due to the fact that predictions from ab-initio theory are possible for
these light nuclei which can be contrasted to experimental findings. In the past years, the
experimental investigation of continuum states, in particular for nuclear systems beyond
the neutron dripline has become possible with good precision and statistics. A recent
example from experiments with the LAND neutron detector are the unbound heavy Li
[Aks-08] and He isotopes. The kinematically complete measurement of the two-neutron
decay of, e.g., 10 He [Aks-09], [Joh-10a] allowed for a detailed study of correlations in the
decay of the continuum states of 10 He [Joh-10b]. It has been demonstrated, that the
correlations allow for disentangling contributions from overlapping resonances and for
assigning their quantum numbers. The study of such systems constitutes the frontier
in neutron-to-proton ratio. The extreme case will be the study of neutron droplets, of
course. We briefly mention here three cases which we consider as benchmarks for future
studies in this direction, these are the 28 O, 7 H, and 4-neutron systems, which will only
be accessible after NeuLAND has been completed.
There is copious of experimental evidence that the oxygen dripline is reached at 24 O.
Production of heavier oxygen isotopes failed, and the ground state of 25 O has been
measured to be unbound by observing the resonance in the continuum. Until recently,
22

all theoretical calculations predicted 28 O to be doubly magic and bound. Experimentally,
we know meanwhile that 24 O is doubly magic. A theoretical explanation came recently
from Otsuka and Schwenk et al [Ots-10], [Hol-11]. They explain a change in the singleparticle
energies as a function of neutron number if 3-body forces are included in the
theory which become more important for the neutron-rich systems. Both the dripline
is correctly reproduced as well as the magicity of 22,24 O. However, continuum effects
become important and have to be addressed as well. How the energy of the states
evolves beyond the dripline towards 28 O remains a key question. 28 O could be produced
in a (p,2p) reaction from a 29 F beam which will be produced with sufficient intensities
at the FAIR facility. The next challenge is to detect the four-neutron decay into 24 O+4n
and reconstruct the relative energy of the system. An observation of a resonance state
would locate the 28 O ground state, i.e., measure its mass. Since we can guess that 28 O is
almost bound, the four neutrons will fly in a narrow cone hitting the neutron detector in
a confined spatial area. The neutron detector has to be capable to correctly disentangle
the four momentum vectors without large contamination from misidentification. In
addition, a high resolution is required in order to measure the width of the resonance.
The requirement for multi-neutron detection is induced by the appearance of neutron
clusters in breakup reactions of extremely neutron rich systems. The heaviest known hydrogen
system forming a resonance is 7 H [Evs-81], [Kor-03], [Ter-07], [Gur-07], [Cam-07],
[Nik-10] consisting of a proton with 6 neutrons and forming the system with the largest
known A/Z ratio. The main decay channel is 7 H → t+4n where the coincident detection
of four neutrons will facilitate the precise and detailed study of the 7 H=t+4n system.
This is achieved by utilizing the information of the observed correlations in order to
separate the initial phase space populated by the reaction from final state interaction
effects in the 7 H system. A similar demand comes from the tetra-neutron case. There
were speculations induced by an experiment performed at GANIL that the 4-neutron
system might be bound [Mar-02]. The data could also be explained if the 4-neutron
system would be slightly unbound forming a narrow resonance which would explain the
high signal in one detector if all neutrons hit the same detector. However, the data are
not conclusive. A measurement of the decay including an individual measurement of the
4 neutrons and their momenta would potentially be able to reconstruct a resonance in
the continuum. One may populate the 4n system via breakup of 14 Be like in the GANIL
experiment or via alpha knockout from 8 He.
Due to the overdetermined kinematics, including the information from CALIFA and the
silicon target detector system, one expects very clean production conditions for both
cases.
Again, a precise reconstruction of the four-neutron event is necessary with good resolution.
The envisaged performance of the NeuLAND detector would make such a
measurement possible for the first time.
23

2.4. Quasi-Free Scattering
The measurement of quasi-free nucleon-knockout reactions constitutes a quantitative
tool to provide information on the single-particle structure of nuclei. From electroninduced
proton-knockout reactions, spectral functions and momentum distributions of
nucleons inside the nucleus have been deduced. Such measurements revealed the role
of correlations which govern the distribution of the single-particle strength at the Fermi
surface. Beyond the shell-model-like correlations among valence nucleons and their coupling
to collective states, nucleon-nucleon correlations have been identified, which lead
to the highest components of the nucleon momentum distribution and to a depletion of
occupancy of single-particle states. From such measurements, it has been concluded that
about 20% reduction of spectroscopic factors should be attributed to such short-range
correlations. In total, a typical occupancy of single-particle states in the order of 60%
has been established. Recent (e,e’p) experiments performed at the JLAB have measured
proton knockout reactions at high momentum transfer and detected a second correlated
nucleon in coincidence [Sub-08]. The authors concluded from such measurements, that
the nucleon-nucleon correlations inside a nucleus causing the high-momentum components
of nucleons are related mainly to neutron-proton pairs, and to a lower degree to
p-p or n-n pairs. This conclusion is, however, not yet established. It would of course be
extremely interesting to probe such correlations for neutron-proton asymmetric nuclei,
where a change of the importance of the different types of correlations is expected, as it
is for asymmetric nuclear matter. The amount of correlations in neutron-rich matter, for
instance, has significant influence on the properties of neutron stars. Radioactive beams,
potentially, provide the possibility to probe the role of nucleon-nucleon correlations in
nuclei as a function of neutron-proton asymmetry.
Nucleon-knockout reactions from high-energy radioactive beams using light targets (usually
Be or C) have been extensively used in the past decade to probe the shell-structure of
exotic nuclei. It has been demonstrated that this reaction is well understood by Eikonal
reaction theory and that spectroscopic factors for valence nucleons can be deduced with
rather good accuracy and less ambiguities as it is the case, for instance, for transfer reactions
at lower beam energies. The method has recently also been applied to knockout
of more deeply bound nucleons, and a strongly reduced spectroscopic factor has been
found compared to shell model calculations. Gade et al. have published a systematic
investigation [Gad-08], where they plot the ratio of experimental-to-theoretical singleparticle
cross sections as a function of the difference of separation energies of neutrons
and protons, i.e., the difference in the Fermi energies. The surprising result is, that proton
knockout from a neutron-rich nucleus yields to a much larger reduction of this ratio,
i.e., a ratio of only 0.3. The same holds for neutron knockout from a neutron-deficient
nucleus, while the factor approaches unity for weakly-bound nucleons, and about 0.6 for
symmetric cases, as established from (e,e’p) experiments. This has raised the question
of isospin effects on the correlations, but also a debate on the experimental method, observable,
and their interpretation. In contrast to an electron-induced knockout reaction,
the reaction with a beryllium or carbon target leads to a localization of the reaction
24

at the surface of the nucleus. The reaction solely probes the tail of the wave function.
The fraction of the density to which the reaction is sensitive, depends strongly on the
separation energy. In the extreme case of a weekly bound neutron, i.e., knockout of
a halo neutron, this fraction is rather large, e.g., in the order of 50% for knockout of
the 2s neutron from 11 Be. The higher the separation energy and the larger the angular
momentum, the smaller the fraction, which approaches values of only a few percent for
cases where the largest reduction has been found.
Since electron-induced knockout reactions cannot be realized at present with short-lived
nuclei, proton-induced knockout reactions are an alternative. High beam energies have
the advantage that the nucleon-nucleon cross section is small, causing some transparency
of the nucleus which makes the reaction more sensitive to the inner part of the nucleus.
Quasi-free (p,2p) reactions have been used with stable nuclei. Spectroscopic factors
consistent with (e,e’p) have been extracted for sufficiently high proton beam energy. The
(p,2p) and (p,pn) reactions in inverse kinematics thus provide an ideal tool to explore
isospin effects on the single-particle character of nuclei and of correlations beyond the
mean field in asymmetric nuclei. The beam energies available at FAIR are ideally suited
for quasi-free scattering and can be chosen that the ’incoming’ proton as well as the
outgoing nucleons have sufficiently high energy (i.e. always above 200 MeV) in a range
where the nucleon-nucleon cross section is minimal. This maximizes the transparency
of the nucleus and minimizes final state interaction. A typical beam energy will be
approximately 600 AMeV leading to nucleon energies depending on angle between 150
and 450 MeV. The R 3 B collaboration has carried out pilot experiments in this direction,
demonstrating the feasibility of the method for quasi-free knockout reactions in inverse
kinematics [Pan-11], [Tay-11]. Quasi-free scattering events were clearly identified and
the spectral function for proton knockout from 12 C has been reconstructed, showing
the three states in 11 B populated after knockout from the p-shell, as well as a broad
maximum around 20 MeV resulting from knockout reactions of the deeply bound 0s
proton. The excitation energy after knockout has been determined from a measurement
of the photon and particle decay of 11 B using the invariant-mass method.
The quasi-free scattering in inverse kinematics has an advantage compared to the previously
used reaction in direct kinematics. This is due to the fact, that the heavy residue
after knockout can be observed, its recoil momentum and excitation energy can be determined,
independently from the measurement of the nucleons. The same quantities
might be extracted from the kinematics of the nucleons as well. With this method, the
single-particle structure of nuclei and the role of correlations can be explored systematically
as a function of (N-Z) in (p,pn) and (p,2p) reactions. We also plan studying the
cluster structure of exotic nuclei, e.g., the alpha clustering by (p,pα) knockout reactions.
In the previous paragraph we pointed out that the (p,2p) reaction is also ideally suited
to populate continuum states, in particular states beyond the driplines. Pilot experiments
have been performed with a preliminary setup. A dedicated recoil detector, to be
placed inside the future calorimeter CALIFA, is presently being developed within the
R 3 B collaboration and will be ready for experiments in 2016.
25

The role of the NeuLAND for this kind of reactions is two-fold. Neutrons stemming
from the quasi-free scattering process like (p,pn) are emitted with an energy around
half the beam energy at 45 ◦ down to about 150 MeV for large emission angles. The
neutrons could be detected in the CALIFA calorimeter. This would provide a rough
angle measurement but no energy information. For cases, where the energy of the
knocked out neutron and its emission angle has to be measured precisely, part of the
NeuLAND neutron detector will be placed near the target at an angle of around 45 ◦
with respect to the beam direction. With a very good time resolution of 150 ps, neutron
energies in the range of 200 MeV can be determined with 1 to 3 % resolution depending
on the solid angle to be covered. The second half of the detector would be placed at zero
degree as usual to detect the neutrons from the decay of continuum states populated
after nucleon knockout. The excitation energy of the residue can then be reconstructed
from the measured momentum vectors. In this case, the full-acceptance mode will be
used yielding a kinetic-energy resolution of about 100 keV for a 1 MeV neutron assuming
a position resolution of NeuLAND of 1.5 cm. Multi-neutron capability will be important
for experiments with neutron-rich nuclei. Knockout of a deeply bound proton from a
neutron-rich nucleus yields rather high excitation energies, and the open decay channel
in such a case is mainly multi-neutron evaporation.
2.5. Fission and Multifragmentation
This section details two different physics scenarios whose demands on neutron detection
are, however, similar. Fission and multifragmentation are violent processes associated
with the emission of prompt neutrons as well as of neutrons from the decay of the highly
excited fragments. The coincident measurement of neutrons is essential for determining
the energy transfers and for identifying isotopic effects appearing in the neutron channels.
Thus, both fission and multifragmentation require a precise recognition of a large number
of neutrons.
Nuclear fission probes the large-scale collective motion of cold and hot nuclear matter.
The former is strongly influenced by microscopic nuclear properties while the latter is
governed by dissipation and friction-like processes in nuclear matter. Radioactive beams
provide access to a wide range of nuclei because they are not restricted by the lack
of stable or long-lived targets. This means that the fissioning system can be explored
as function of its proton and neutron number, while the initial conditions, especially
angular momentum and excitation energy, are tightly restricted. Fission at excitation
energies close to the fission barrier can be studied via electromagnetic excitation in
inverse kinematics [Sch-00] or via beta-delayed fission (see e.g. Ref. [And-10] for recent
results). The R 3 B set-up is optimal for inverse-kinematic experiments and allows to
measure the nuclear mass and charge yields of both fission fragments simultaneously.
This information, which is not accessible with conventional techniques, together with
the measured total kinetic energy release is of great interest to extract information on
26

the evolution of fission channels (see e.g. Ref [Bro-90]) or, in more general terms, to
probe the potential-energy surface and the scission configuration.
NeuLAND adds an important observable for this type of experiments, as it provides
the unique information on the neutron multiplicity as function of the mass and charge
split. Furthermore, the pre-scission neutron multiplicity is an important observable
for the investigation of highly-excited compound nuclei after fragmentation-fission reactions
(e.g.[Hil-92]), which can be studied simultaneously [Sch-10]. For NeuLAND, such
experiments require a high detection efficiency for multi-neutron events as well as reliable
information on the neutron multiplicity. For low-energy fission neutron multiplicities are
expected to be below 4, while this number, for high-energy fission, is comparable to the
multiplicities expected for multifragmentation [Hil-92] (see below).
Multifragmentation reactions can be used to explore possible modifications of fragment
properties in the hot environment of the freeze-out state. This is of interest because
the temperatures and lower-than-normal densities at freeze out are similar to conditions
encountered in supernova scenarios [Ish-03, Bot-04]. As shown very recently for
the case of multifragmentation of relativistic projectiles [Ogu-11], the observed neutron
richness of the produced intermediate-mass fragments requires a significant reduction of
the symmetry term in the liquid-drop description used for the emerging fragments in the
Statistical Multifragmentation Model. These findings will have to be complemented by
measurements of free neutrons whose multiplicities should respond accordingly. It will
offer a new and additional possibility for exploring fragment properties in neutron-rich
matter under extreme conditions.
The requirements for neutron detection will be more demanding than in the experiments
performed so far. Mean neutron numbers of up to about 6 with a wide distribution have
been simultaneously detected with LAND which covered only part of the populated
phase space [Ogu-11]. The presence of a more powerful magnet will permit positioning
NeuLAND more symmetrically with respect to the beam in order to achieve full coverage
of the spectator neutron source. The improved capabilities of the new detector will be
essential for individually identifying the emitted neutrons and for determining their
momenta as well as multiplicity and momentum correlations.
2.6. Flow and Equation of State
Heavy-ion reactions at relativistic energies represent the only means for compressing
nuclear matter in laboratory experiments and for studying the nuclear equation of state
(EoS) at supra-saturation densities [Dan-02]. Several observables have been identified
to be sensitive to the strength of the symmetry term in the EoS: Isotopic yield ratios of
nucleons, pions, or kaons, or the directed and elliptic flows of neutrons with respect to
protons or light complex particles in collisions of neutron-rich systems [Li-08].
27

Neutron with respect to proton/hydrogen flow at supra-saturation densities has been
already studied in 197 Au + 197 Au collisions with a combination of LAND and the FOPI
set-up for event characterization. In a re-analysis of the existing data-set and comparison
to predictions of the UrQMD [Li-05] and other transport models [Coz-11] it was
confirmed that in particular the elliptic flow observable is a sensitive measure of the
strength of the symmetry term in the nuclear matter EOS. These findings have initiated
a dedicated measurement of collective flows in collisions of 197 Au + 197 Au as well as 96 Zr
+ 96 Zr and 96 Ru + 96 Ru which has been carried out with the LAND detector coupled
to part of the CHIMERA detector array [Lem-09].
Because of the quadratically rising importance of the symmetry energy, the continuation
of this program with systems of larger asymmetry is very promising and important. The
reduced luminosities to be expected from the use of secondary beams and isotopically
enriched targets will require highly efficient detector setups.
A pre-requisite of such studies is to measure neutrons and protons within the same
phase space region. Hence, a neutron detector is needed with excellent calorimetric
characteristics augmented by a veto detector for charged particle identification. The
limited calorimetric capabilities of LAND allowed only for the separation of protons
from heavier hydrogen isotopes but has proven to be essential for such type of analyses.
Better calorimetric properties are highly desirable.
The neutron detector, typically placed near 45 ◦ for detecting mid-rapidity emissions for
the main part of the transverse-momentum spectra, should cover a maximum range of
polar angles in order to extend the measurements at given transverse-momentum to
forward and backward rapidities to measure directed and elliptic flow simultaneously.
This can be achieved by dividing the detector into two or more parts, placed at different
polar angles and used as separate detector units [Lei-93]. The distance to the target,
and with it the solid-angle coverage, will be determined by the capability of resolving
individual neutrons in high-multiplicity events. The improved efficiency of NeuLAND for
detecting neutrons in the 100 to 400 MeV energy range will be essential for extending
the program to reactions at lower energies for which significant mean-field effects are
predicted for directed and elliptic flows [Guo-11].
28

3. Summary of NeuLAND Prototype
Results
3.1. Scintillator Concept
We propose to build the neutron detector fully from organic scintillator material. The
volume should be arranged in bar-shaped modules, with the scintillation light read out
at the far ends. In our studies we focussed on various bar sizes and read-out devices.
As scintillation material we chose RP408, similar to BC408, a well known and well
understood material for time-sensitive applications with an affordable price.
3.2. Studies with Fast Protons
In a very first test we explored two bars of RP408 with 500 MeV protons during a physics
experiment on 60 Fe.
The protons were produced as a byproduct of dissociation reactions of the 60 Fe beam
on a Pb target. The 2 m long plastic bars were mounted behind the proton ToF wall
at the height of the beam axis. The first bar, hereafter called S1, with dimensions of
200 × 5 × 5 cm 3 was read out with two two-inch Hamamatsu photomultipliers (R9779-
20) and the second scintillator S2 with dimensions 200 × 3 × 3 cm 3 was read out with
two one-inch photomultipliers (R9800-20). Time and charge signals were recorded with
TacQuila digitizing cards [Koc-05]. To obtain the time resolution the time signals of
both ends of scintillator S1 were averaged tS1 = tA S1 +tB S1
2
and subtracted from the average
of scintillator S2 times tS2. The position along a scintillator bar was obtained by the
time difference of the two time signals of one bar xS1 ∼ tA S1 − tB S1 . An average charge
was calculated by taking the square root of the product of the two charge signals of each
paddle.
A Gaussian fit of the time difference spectrum (figure 3.1, upper panel) yields a width
of 176 ps. This results in a time resolution of σt=125 ps for each scintillator bar,
assuming equal time resolution for both paddles. In the lower part of figure 3.1, a
position dependence of the time difference spectrum is observed due to a remaining
correlation of time and signal height. Especially hits close to the ends of the bars lead
to small amplitudes at the opposite end and therefore to walk effects. A walk correction
can be performed to remove this dependency at least partially.
29

counts
Time difference S2-S1 with cut on protons
time (ns)
350
300
250
200
150
100
50
0
12 13 14 15 16 17 18 19 20
time (ns)
T2-T1 vs. position S2
20
19
18
17
16
15
14
13
12
-150 -100 -50 0 50 100 150
position (cm)
Figure 3.1.: The measured time difference tS1 − tS2 of the two scintillator bars S1 and
S2 is shown in the upper panel. The Gaussian fit corresponds to a width of
σt = 176 ps. The two-dimensional plot in the lower panel shows this time
difference tS1 − tS2 as function of the position along the scintillator bar,
derived from xS2.
Here, in figure 3.2 we display the time difference spectrum with a condition on central
hits, thus neglecting the position dependence. In this case a Gaussian fit yields a width
of 125 ps which results in a time resolution of σt=88 ps for one single module.
In the following two parameters were varied. We used a different photomultiplier type
and varied the length of the bars. As read-out device we chose a similar, but more
economical 1 inch photomultiplier, i.e. R8619 from Hamamatsu. At the same time we
explored the effect of the length of the scintillator bars. We extended the 2 m long bars
each by attaching a 1 m long piece of the same cross section with optical grease. A
measurement, again with fast protons from a nuclear reaction, results in a width of the
30
9
8
7
6
5
4
3
2
1
0

counts
70
60
50
40
30
20
10
0
15 15.5 16 16.5 17
time (ns)
Figure 3.2.: The measured time difference as shown in the left part of figure 3.1, but
with a condition on central hits in order to exclude position dependencies.
time difference spectrum of bar S1 and S2 of 186 ps, thus a time resolution of σt=132 ps
for each bar, with a condition on central hits. We interpret this increase of about 50%
for the time resolution to be similar shared in between the two modifications, i.e. the
increase in length, causing a loss of light, and the read-out with the more economical
photomultiplier. The effect of the bar length was studied independently in experiments
with single-electron beams, see section 3.3. We observe about 25% degradation, when
going from 2 to 3 m length.
3.3. Studies with 31 MeV Electrons
Detailed studies of the detector response of the scintillator bars were performed using the
single-electron per bunch mode of the superconducting electron linac ELBE at HZDR
Dresden-Rossendorf. The electrons had an energy of 31 MeV. For the time reference
determination a similar technique as for the tests of resistive-plate chambers at ELBE
was applied, see appendix B for details. The energy loss of these minimum ionizing
particles (MIPs) is slightly less compared to the 500 MeV proton beams (see section 3.2).
In this experiment the two bars of sizes 200×3×3 cm 3 and 200×5×5 cm 3 were exposed
to the beam individually. As light readout we selected again the 1 inch photomultiplier
R8619, as in the second part of the proton tests. The time resolution was measured
versus the radio-frequency signal from the accelerator, which delivers a very precise
timing information. Together with the resolution of our readout electronics TacQuila,
the time resolution of this reference signal amounted to σref =30 ps, see figure 3.3.
From the measurement with the 2 m long bars we derive a time resolution of σ200×3×3 =154 ps
31

counts
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
χ 2 / ndf
2014 / 83
Constant 8683 ± 42.0
Mean 406.2 ± 0.0
Sigma 0.02941 ± 0.00008
406 406.1 406.2 406.3 406.4 406.5 406.6
time (ns)
Figure 3.3.: Time spectrum representing the resolution of the TacQuila read-out
channels.
and σ200×5×5 =157 ps for the bar with small and larger cross section , respectively, at
central positions.
For the bigger bar with the 5 × 5 cm 2 cross section a measurement was performed in
addition using the 1 m elongation bar, thus reaching a bar length of 3 m. The time
resolution achieved here amounts to σ300×5×5 =192 ps. Compared to the result with the
2 m long bar, we observe an increase of the time resolution by a factor 1.23. With respect
to the proton results for the 3 m long bars using the same read-out devices, we see a
degradation by a factor of 1.45. We note, however, that the results might be influenced
by an imperfect light coupling from the 2 m main bar to the 1 m elongation bar. A
sudden increase of the measured time resolution close to the position of bar coupling
supports this assumption.
In a second experiment we exposed the final shape NeuLAND submodules to the electron
beam. The bars have a length of 270 cm, of which 250 cm are rectangular shaped with
a cross section of 5 × 5 cm 2 . The outer 10 cm on each side form the light guide, see
section 5 for technical details. Again, we used photomultipliers of type R8619 for the
readout. The time resolution observed has a slight position dependence. In order to
minimize the walk effect for the determination of the time resolution a condition on
small intervals in the measured energies was set during the analysis. A gaussian fit
was used to derive the resolution. The values obtained for the first measurement, using
optical grease to couple the photomultipliers to the light guide, vary in the range of
σt = 125–135 ps, see figure 3.4. For comparison, we performed a measurement without
optical coupling, seeing an immediately decrease of signal height at the photomultiplier
readout, translating directly into a worse time resolution of about σt = 143–155 ps.
32

Figure 3.4.: Shown is the time resolution obtained with single-electron beams as a function
of position along the NeuLAND submodule bar. Circles (blue) indicate
the results when optical coupling was applied for the connection of photomultiplier
window to the light-guide exit. Squares (red) display the time
resolution obtained when omitting the optical coupling. The dotted line
indicates the center of the scintillator bar.
The results obtained from the prototype tests lead to the following conclusions:
• The derived time resolutions using electron beams, fully satisfy the the NeuLAND
design goals, as detailed in chapter 4. However, due to the typically higher energy
loss from neutron interactions in NeuLAND, the time resolution observed in
neutron events might improve.
• The use of light-guides improves significantly the timing properties of the scintillator
bar, as predicted from simulations, laid out in section 4.4. Comparing the
results for the 200 cm long rectangular bar without light-guides, and the 270 cm
bar including light-guides, we find an improvement of about 20%, even overcompensating
the decrease of resolution with the length of the bar.
33

• Using a readout with a cost-effective photomultiplier, as R8619, the design goals
with respect to time resolution are achieved.
3.4. Other Approaches
Following the R 3 B Technical Proposal [R3B-05], besides scintillator based detector concepts,
the development of NeuLAND using multigap resistive plate chambers (MRPCs)
was also studied. Although very successful with respect to the construction of large
detector chambers, and excellent response to minimum ionizing particles, finally, the response
to fast neutrons cannot compete to the one of a fully-active scintillator solution.
The design goals for the multi-neutron recognition can not be reached with this approach.
A summary over the achievements and final conclusions is given in appendix B.
Moreover, other concepts based on scintillators have been proposed and studied in the
development of the detector design for NeuLAND. PbWO4 as a very dense scintillation
material was investigated, which would allow a rather compact detector design. The high
price of PbWO4 crystals and its limitations in size were striking counter-arguments.
Also, a design close to the existing LAND detector [Bla-92], improved basically in terms
of higher granularity was investigated. The detection principle of the current LAND
detector is based on the conversion of neutrons to charged particles (mostly protons) in
a passive iron converter with 5 mm thickness. Consequently, for the registration of a
signal the protons have to pass the iron and deposit energy in the successive scintillator.
However, with respect to the design goal of NeuLAND, detailed simulations show (see
section 4.2) the limitations of a scintillator detector based on interactions in passive
converter zones.
34

4. Monte Carlo Simulations
Within this chapter we summarize the simulation work, which led to the final design of
NeuLAND. First, we define and test various frameworks against each other and against
data for neutron reference cases, as laid out in section 4.1. This is followed by an investigation
of the effect of passive converters on the detection performance, detailed in
section 4.2. Following the decision on a fully active scintillator structure, the role of
granularity was studied in detail, summarized in section 4.3. From this, we conclude
on the final bar sizes of NeuLAND submodules. Optical photon tracking simulation
were performed investigating the effect of light-guides for the readout of the NeuLAND
submodules, as detailed in section 4.4. The chapter closes with extensive detector response
simulations with respect to efficiency, multi-neutron recognition capability and
with respect to several physics cases, discussed in section 4.5.
4.1. Overview and Comparison of the Various Simulation
Codes
4.1.1. Simulation Frameworks
In order to study the neutron response, comparative studies in various frameworks were
undertaken. Two independent FLUKA simulations were performed [FLU-05] [FLU-07].
In addition GEANT3 [GEA-93] and GEANT4 [Ago-03] were used, partly as standalone
versions and partly via R 3 BRoot [Ber-08], a framework for simulation and analysis
of R 3 B experiments, based on ROOT [Bru-97] and the Virtual Monte Carlo concept
[VMC-03]. Table 4.1.1 gives more details about the recently used versions for
the various frameworks. One key quantity addressed was the deposited energy of neu-
framework version or date packages
GEANT4 4.9.4.p01 QGSP BIC HP
FLUKA 2008.3d precision mode
FLUKA 2011.2 default physics model
FLUKA 2011.2 calorimetry physics model
R 3 BRoot/GEANT3 July 2011 GCalor
Table 4.1.: Overview over the recently used simulation packages for the results presented
within this chapter.
35

trons hitting the neutron detector. In the following, we compare the deposited energy
for neutrons of 200, 600, and 1000 MeV, respectively, and a detector volume of
250 × 250 × 300 cm 3 . Figure 4.1 displays the deposited energy distribution divided by
the neutron bombarding energy before and after applying the quenching correction for
the secondary protons, also known as Birk’s law [Bir-64]. The simulations, performed for
normalized counts
3
2.5
2
1.5
1
0.5
200 AMeV, 1n, without quenching
Geant4
FLUKA
R3BRoot/Geant3
0
0 0.2 0.4 0.6 0.8 1
E /E
dep
beam
normalized counts
3
2.5
2
1.5
1
0.5
200 AMeV, 1n, with quenching
Geant4
FLUKA
R3BRoot/Geant3
0
0 0.2 0.4 0.6 0.8 1
E /E
Figure 4.1.: Presented is the distribution of deposited energy Edep divided by neutron
impinging energy Ebeam = 200 MeV neutrons hitting centrally a plastic detector
volume of 250×250×300 cm 3 . The graphics displays on the left hand
side the distribution before light quenching correction, on the right hand side
the distribution after light quenching correction. We compare simulations
using GEANT4 (red curve), FLUKA (blue curve), and GEANT3/R 3 BRoot
(green curve).
GEANT4, FLUKA, and GEANT3/R 3 BRoot, result in similar distributions for 200 MeV
neutrons. Also, for higher neutron energies a remarkably good agreement is obtained,
(figure 4.2). From this comparison and similar tests we conclude, that the three frameworks
make nearly identical predictions for the response of the NeuLAND detector.
Fluka is used here as a reference since it integrates in one common code the most advanced
physics models relevant for NeuLAND simulation. Besides an excellent MORSElike
neutron transport capability, FLUKA incorporates EGS4-like electromagnetic interactions
and an Intra-Nuclear Cascade hadronic interaction model with pre-equilibrium
stage extensions. The treatment of neutrons in GEANT3 is complementary to the
FLUKA approach. GEANT3 with the GCALOR interface [Zei-94] uses the MICAP(Monte
Carlo Ionization Analysis Package) [Joh-87], which is a point-like cross-section neutron
code. However, the simulated data are in remarkable accordance with each other.
36
dep
beam

normalized counts
normalized counts
3
2.5
2
1.5
1
0.5
600 AMeV, 1n, without quenching
Geant4
FLUKA
R3BRoot/Geant3
0
0 0.2 0.4 0.6 0.8 1
E /E
3
2.5
2
1.5
1
0.5
1000 AMeV, 1n, without quenching
Geant4
FLUKA
R3BRoot/Geant3
dep beam
0
0 0.2 0.4 0.6 0.8 1
E /E
dep
beam
normalized counts
normalized counts
3
2.5
2
1.5
1
0.5
600 AMeV, 1n, with quenching
Geant4
FLUKA
R3BRoot/Geant3
0
0 0.2 0.4 0.6 0.8 1
E /E
3
2.5
2
1.5
1
0.5
1000 AMeV, 1n, with quenching
Geant4
FLUKA
R3BRoot/Geant3
dep
0
0 0.2 0.4 0.6 0.8 1
E /E
Figure 4.2.: Same as figure 4.1, but for neutrons with beam energies of 600 and
1000 MeV.
4.1.2. Neutron Data Validation
The simulation packages were compared to relevant neutron response data in order to
prove their predictive power for NeuLAND.
First, we selected neutron data on two plastic scintillator materials with close similarities
to the proposed BC408/RP408 scintillator for NeuLAND. Neutron efficiency as a function
of energy thresholds has been measured for neutron energies up to 120 MeV using
the scintillation material NE-110 [Bet-76] and up to 200 MeV using Pilot-U [Ede-72].
These data have served already in the past as benchmarks for Monte-Carlo neutron
codes [Cec-79]. We present here the comparison of the published data to the GEANT4
dep
beam
beam
37

findings, see figure 4.3. Overall, a very good agreement is found for the two scintillator
materials, the large range of neutron energies and the various energy threshold
settings.
efficiency [%]
40
35
30
25
20
15
10
5
0
20 40 60 80 100 120
neutron energy [MeV]
2.8 MeV exp
5.58 MeV exp
7.89 MeV exp
11.15 MeV exp
15.75 MeV exp
2.8 MeV sim
5.58 MeV sim
7.89 MeV sim
11.15 MeV sim
15.75 MeV sim
efficiency [%]
70
60
50
40
30
20
10
0
1 10
PILOT-Y
0.2 MeV exp
1.0 MeV exp
4.0 MeV exp
0.2 MeV sim
1.0 MeV sim
4.0 MeV sim
10
neutron energy [MeV]
Figure 4.3.: Neutron efficiency as a function of the energy of impinging neutron for the
two plastic scintillator materials. The data (symbols) for the scintillator
NE-110 are displayed on the left hand side [Bet-76] and the data for the
scintillator Pilot-U on the right hand side [Ede-72]. The GEANT4 simulated
neutron efficiencies are presented as solid curves. The legends detail
the different threshold settings in equivalent-electron energies for the experimental
and simulated data.
Second, we compare the simulation to the neutron response of the existing LAND detector
[Bla-92], which has been used since almost 20 years for the detection of fast neutrons.
LAND is used for detection of fast neutrons stemming from the projectile nuclei reacting
in the target. The detector measures the time-of-flight (ToF) of neutrons with respect to
the target with good position and time resolution. With this information the momentum
of neutrons can be determined. The detector covers an area of 2 × 2 m 2 with a depth
of 1 m. It consists of 10 planes. Every plane contains 20 modules, each covering an
area of 200 cm×10 cm and 10 cm depth. The detection principle is based on conversion
of neutrons to protons via reactions in iron. Secondary protons are then detected in
plastic scintillators layers. In order to avoid the stopping of protons in the Fe converter
a sandwich structure with thin layers of iron and scintillators is used. One module of the
detector contains 11 sheets of iron, each 5 mm thick, besides the two outer ones which
have a thickness of 2.5 mm, and 10 sheets of scintillators with a thickness of 5 mm, each.
The scintillation light is read out at both ends of the scintillator with photomultipliers
(for more information see Th. Blaich et al.,[Bla-92]).
This geometry was modeled in detail in the simulation package R 3 BRoot using the
38
2

GEANT3 interface. Here, we compare data from a deuteron breakup experiment, performed
in the year 1992, with simulation results. Various deuteron beam energies of 170,
270, 470, 600, 800, and 1050 AMeV were used, thus the characteristics of the detector
can be determined for a wide range of neutron energies.
During the interaction of the primary neutrons secondary particles are produced. For
the energy deposited in the scintillator, secondary protons and neutrons dominate but
also gamma-rays and electrons contribute, especially at small energies. The response of
the detector strongly depends on the choice of the threshold for the light detection of
the photomultipliers.
Light quenching for protons was taken into account using Birk’s relation [Bir-64]
L(∆E) = ∆E/(1. + 0.013 ∗ dE/dx + 9.6E − 6 ∗ (dE/dx) 2 ), (4.1)
where L is the light output, ∆E the energy deposit in the scintillator in MeV, and dE/dx
the energy loss in MeV/g/cm 2 .
A typical interaction of a high energy neutron with an iron nucleus produces several
protons, neutrons and gamma-rays. If the protons have sufficient energy to leave the
iron sheet, they deposit energy in a scintillator, giving rise to scintillation light. The
neutrons travel through the detector and produce further secondary particles. This
happens either again in iron sheets or directly in the scintillator material by elastic
scattering on protons. The gamma-rays produce electrons which again deposit energy in
the scintillators. Therefore, in a typical LAND event several modules fire. The detected
multiplicity strongly depends on the photomultiplier threshold applied. Figure 4.4 shows
tracks of typical events for 470 MeV neutrons.
Sometimes, no light is produced during the first interaction of the primary neutron.
This leads to an incorrect determination of the position and consequently to an incorrect
neutron momentum via the ToF method. Figure 4.5 shows the distance between the first
interaction points of 470 MeV neutrons and the position of the first light generation. In
this example 40 % of the events are outside of the geometrical dimension (10 cm) of a
module.
A large detection efficiency is a key feature of LAND. The simulated efficiencies in
table 4.2 were determined with the GEANT3 and GEANT4 simulation packages and
are compared with the measured values.
The most important quantities for the comparison between data and simulation are the
multiplicity of modules, the total deposited energy, the energy deposit during the first
interaction and the energy deposit in a single paddle. Figure 4.6 presents simulation
results for GEANT3 in comparison with the measured data. Thresholds were adapted
within reasonable range to match the multiplicity spectra. An all-over factor of 0.4
necessary to adapt the GEANT3 total energy findings to the measured energy deposits
points to some mismatch in the absolute calibration of the experimental data. With
39

Figure 4.4.: Display of simulated neutron events at 470 MeV hitting the existing LAND
detector. Tracks of neutrons (blue), gamma-rays (green), and protons (red)
are visible. The upper left figure details the modularity of LAND. The upper
right display shows an inelastic scattering event leading to one fast proton.
The lower left plot displays an inelastic scattering event as well, but here
low energy protons are produced. The lower right figure shows a typical
case of emission of slow neutrons after excitation of an iron nucleus.
40

Counts
1000
900
800
700
600
500
400
300
200
100
0
-40 -20 0 20 40
x position (cm)
Counts
1000
900
800
700
600
500
400
300
200
100
0
-100 -80 -60 -40 -20
z position (cm)
0 20
Figure 4.5.: Simulation of the error in determination of the first interaction point in x
(left) and z position (right) for 470 MeV neutrons in LAND.
neutron energy simulated eff. GEANT3 simulated eff.GEANT4 measured
(MeV) (%) (%) (%)
270 80 88 85(7)
470 92 93 93(2)
600 96 95 94(1)
800 97 96 96(1)
1050 98 98 96(1)
Table 4.2.: Efficiencies for the neutron detection with LAND simulated with GEANT3
and GEANT4 are compared to the measured values from a calibration experiment
[Bor-03].
one set of parameters the variation of spectra with the neutron beam energy are well
described by the GEANT3 simulations. The largest deviations can be seen for the lowest
neutron energy of 170 MeV.
For the detailed response and resolution studies laid out in section 4.5, we decided to use
primarily the R 3 BRoot framework, since it can be used in a later stage for an identical
treatment of simulated and real data. The GEANT3 interface was selected for practical
reasons.
41

Counts
Counts
Counts
Counts
Counts
Counts
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.6
0.5
0.4
0.3
0.2
0.1
0
Experiment
Simulation
0 2 4 6 8 10 12 14
Multiplicity
Experiment
Simulation
0 2 4 6 8 10 12 14
Multiplicity
0.5
0.45
Experiment
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
Simulation
0
0 2 4 6 8 10 12 14
Multiplicity
0.5
0.45
Experiment
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
Simulation
0
0 2 4 6 8 10 12 14
Multiplicity
0.5
0.45
Experiment
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
Simulation
0
0 2 4 6 8 10 12 14
Multiplicity
0.5
0.45
Experiment
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
Simulation
0
0 2 4 6 8 10 12 14
Multiplicity
Counts
Counts
Counts
Counts
Counts
Counts
0.05
0.045
Experiment
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
Total Energy (MeV)
0.05
0.045
Experiment
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
Total Energy (MeV)
0.02
0.018
Experiment
0.016
Simulation
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
0 10 20 30 40 50 60 70 80 90 100
Total Energy (MeV)
0.02
0.018
Experiment
0.016
Simulation
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
0 10 20 30 40 50 60 70 80 90 100
Total Energy (MeV)
0.02
0.018
Experiment
0.016
Simulation
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
0 10 20 30 40 50 60 70 80 90 100
Total Energy (MeV)
0.02
0.018
Experiment
0.016
Simulation
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
0 10 20 30 40 50 60 70 80 90 100
Total Energy (MeV)
Counts
Counts
Counts
Counts
Counts
Counts
0.1
0.09
Experiment
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
First Energy (MeV)
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Experiment
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
First Energy (MeV)
0.05
0.045
Experiment
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
First Energy (MeV)
0.05
0.045
Experiment
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
First Energy (MeV)
0.05
0.045
Experiment
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
First Energy (MeV)
0.05
0.045
Experiment
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
First Energy (MeV)
Counts
Counts
Counts
Counts
Counts
Counts
0.1
0.09
Experiment
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
Energy in one paddle (MeV)
0.1
0.09
Experiment
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
Energy in one paddle (MeV)
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Experiment
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
Energy in one paddle (MeV)
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Experiment
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
Energy in one paddle (MeV)
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Experiment
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
Energy in one paddle (MeV)
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Experiment
Simulation
0
0 5 10 15 20 25 30 35 40 45 50
Energy in one paddle (MeV)
Figure 4.6.: Comparison of LAND response to neutrons from 170 to 1050 MeV from experiment
(black lines) and from GEANT3 simulations (red lines). Displayed
is in each row from left to right the paddle multiplicity, the total energy deposit,
the energy deposit in the first interaction, and the energy deposit in
one paddle. The rows display the neutron energies, starting with 170 MeV
neutrons in the first row, followed by 270 MeV, 470 MeV, 600 MeV, 800
MeV, and 1050 MeV neutron energy in the last row.
42

counts
5
10
4
10
3
10
2
10
10
LAND standard
LAND - zero time res.
10 cm plastic bars - zero time res.
1
-2 -1.5 -1 -0.5 0 0.5 1
∆t
(ns)
Figure 4.7.: Effect of passive detector material on the time resolution from a GEANT3
simulation of 470 MeV neutrons for three different detector configurations.
For ∆t the time of first detected light was subtracted from the time of the
first interaction.
4.2. From a Passive Converter to a Fully-Active Scintillator
Concept
The reason for the use of dense, passive converters, as technically realized for LAND
[Bla-92] by iron layers, has been, to improve the neutron efficiency via the detection
of particles created in the converter material. The passive material has an enhanced
interaction probability due to its higher density in comparison to scintillators. The active
scintillator layers combined with the passive converters serve to detect the interaction
products, mostly protons and γ-rays. In the following, we detail the difference in response
for a fully active detector and for a converter-based detector (LAND, 5 mm iron converter
layers) with respect to the achievable time resolution and to the efficiency. For a more
detailed description of LAND we refer to section 4.1.2 and [Bla-92].
A typical interaction of a high energy neutron with the iron converter leads to the production
of several protons, secondary neutrons and gammas. Since the protons mainly
come from evaporation of excited iron nuclei the angular distribution is isotropic and
typical proton energies are a few MeV with a high-energy tail. Therefore, the time resolution
is limited by the time jitter introduced by the protons traveling through the iron
until reaching the active part of the detector. The secondary neutrons from the primary
interaction have to pass part of the detector until they transfer energy to protons via
elastic scattering in the scintillator material. Again a time delay is introduced.
43

We investigate this timing effect in a GEANT3 simulation for the LAND detector. In
figure 4.7, the time difference between the first interaction of the primary neutron and the
detection of the first light is displayed. The response of LAND (black line) is compared
to an ideal LAND assuming a time resolution of σt=0 ps for the scintillator (red line).
The time resolution of the scintillator was set to zero for the latter case in order to study
the effect of the passive material solely. Overlayed is the time difference for a detector
which has the same module size as LAND but no passive converter material (blue line)
in the following denoted with LAND’.
The width of the timing peak expanding to negative ∆t values stems from the timedelayed
protons which have to escape from the passive converter material. Events in the
far tails originate from neutrons where no light was created by the particles stemming
from the first neutron interaction. e.g. protons which are absorbed in the iron sheets.
This leads to a background caused by a wrong determination of the position and time.
The entries in the region of positive ∆t stem from events, where more than one secondary
particle contributes to the production of the light within one module at the same time.
The reconstruction algorithm which calculates the time of an event from the mean-time
of the two photomultiplier signals thus delivers smaller times than actually possible.
In order to fulfill the design criteria for NeuLAND with respect to time resolution, the
use of passive converters is problematic, as seen in figure 4.7. With inserted converter,
even with ideal time resolution, the timing peak is broadened, and moreover, the fraction
of events in the tails is increased drastically.
In order to study the efficiency for low energy neutrons (≈ 200 MeV), again GEANT3
simulations for the same hypothetical detector as above (LAND’) were performed. Modules
of the same dimensions were used but without iron converter. Instead, the depth
of the detector was doubled, resulting in 20 layers of scintillator. In table 4.3 the comparison
shows, that the efficiency without passive material is almost independent of the
incident neutron energy, while for the LAND detector the efficiency decreases towards
lower neutron energies. The efficiency at lower neutron energies will be important for
the use of NeuLAND e.g. in quasi-free scattering experiments (see section 2.4), which
need to use NeuLAND modules at large scattering angles from the target.
Even for energies below the design limit of 200 MeV, a high efficiency is observed,
which may be beneficial in quasi-free scattering experiments at large scattering angles,
see section 2.4. In conclusion the use of passive converters has negative implications
with respect to both resolution and efficiency. On a later stage of the simulation, we
observe, that with respect to multi-neutron recognition, calorimetry plays a crucial role,
see section 4.5. In consequence, the MRPC concept for NeuLAND (see appendix B),
using inserted passive converters and a detection mechanism, which is rather insensitive
to the deposited energy, is not competitive to the fully-active scintillator concept.
In further design considerations for NeuLAND passive converters are omitted.
44

incident neutron fully active detector LAND converter-based detector
energy [MeV] simulated efficiency [%] measured efficiency [%]
100 97 -
170 97 78(10)
270 94 85(7)
470 95 93(2)
600 96 94(1)
800 97 96(1)
1050 97 96(1)
Table 4.3.: Comparison of efficiencies for neutron detection for LAND and a hypothetical
LAND’ without passive material. The efficiency values for LAND stem from
a calibration experiment using fast neutrons from deuteron-breakup [Bor-03].
The values for the fully-active detector were simulated using GEANT3.
4.3. Effect of Granularity and Timing Properties for a
Fully-Active Detector
In the present section, the required detector parameters regarding time and spatial
resolution are determined in a physics-driven approach from the experimental cases listed
in chapter 2. Amongst the design goals for NeuLAND is a relative energy resolution of
σ ≤ 20 keV at small relative energies of neutrons and fragment; we refer to section 2.2.
Simulations, assuming uniform phase-space distributions, have been performed with the
aim to match the position and time resolution for given distances to the target. The two
distances taken into account represent for the final detector design with a face-size of
250×250 cm 2 the distance of full-acceptance mode (15.5 m), and the highest-resolution
mode (35 m), respectively.
For the simulations, the breakup of 132 Sn at 600 AMeV into 131 Sn and one neutron
was considered. Table 4.4 gives an overview of the resolution σ(Erel) achieved for
Erel=100 keV.
15.5 m 35 m
σt=0 ps σt=100 ps σt=150 ps σt=0 ps σt=100 ps σt=150 ps
3x3 cm 2 13 keV 25 keV 32 keV 7 keV 12 keV 16 keV
5x5 cm 2 19 keV 29 keV 35 keV 10 keV 14 keV 17 keV
10x10 cm 2 38 keV 44 keV 49 keV 18 keV 21 keV 23 keV
Table 4.4.: Effect of target-detector distance, time resolution, and scintillator size on the
relative energy resolution σ(Erel) at Erel=100 keV for 132 Sn decaying into
131 Sn and one neutron at beam energies of 600 AMeV.
At first, for all simulations the time resolution of the scintillator was set to σt = 0 ps.
We varied the cross section of the scintillator bars: 3 × 3, 5 × 5, and 10 × 10 cm 2 cross
45

section were used. From a Gaussian fit to the relative energy distributions obtained from
phase-space simulations we derived a resolution of σ(Erel)=13, 19, and 38 keV for the
three bar sizes at 15.5 m. As a consequence, at this distance to the target only the bars
with a cross section of 3 × 3 cm 2 and 5 × 5 cm 2 fulfill the design criterion of σ ≤ 20 keV.
At a distance of 35 m we obtained a relative energy resolution of σ(Erel)=7, 10, and
18 keV for the three bar cross sections. For the longer flight path the bars with a cross
section of 10 × 10 cm 2 match the requirements as well. However, here we assumed an
ideal time resolution. The relative energy distribution is shown in figure 4.8 derived from
a similar R 3 BRoot simulation for a distance of 35 m between the target and NeuLAND
to the target for the three bar sizes. The resulting resolutions are in very good agreement
to the ones derived from phase-space simulations. Exemplarily, for the bar with a cross
section of 5 × 5 cm 2 , a value of σ(Erel)=10 keV was obtained, identical to the findings
using the phase-space simulations.
events
400
200
3x3cm , σ
0
0 0.1 0.2 0.3
(MeV)
2
Erel
=0
t
2
5x5cm , σ =0
t
2
10x10cm , σ
Figure 4.8.: Study of the effect of granularity of NeuLAND on the resolution of relative
energy distributions, simulated using R 3 BRoot. Relative energy spectra are
shown for scintillator bar cross sections of 3×3 (dashed blue line), 5×5 (solid
red line), and 10×10 cm 2 (solid blue line). One-neutron events were emitted
from 132 Sn with Erel = 100 keV at 600 AMeV. NeuLAND was located at a
distance of 35 m to the target, the time resolution was set to zero, in order
to investigate only the effect of granularity.
As the next step, the influence of the time resolution on the energy resolution was
46
=0
t

investigated. Three values for the time resolution were simulated: σt=0 ps, 100 ps,
and 150 ps. For distances of 15.5 m, the ultimate relative energy resolution has the
highest demands on time and position resolution. For none of the investigated bar cross
sections the relative energy resolution of ≤20 keV is obtained with a time resolution of
σt=100 ps. Only a detector with a scintillator bar cross section of 3 × 3 cm 2 and a time
resolution of σt=50 ps fulfills the demanded relative energy resolution of ≤20 keV. For a
target-detector distance of 35 m, the maximum achievable distance between the target
and NeuLAND in the R 3 B experimental hall, scintillator bars with a cross section of
5×5 cm 2 and a time resolution of σt=150 ps are sufficient to meet the design criterion.
Again, we compare the results from the phase-space simulations for one example to the
result of R 3 BRoot simulations. The influence of time resolution is shown in figure 4.9
for a distance of 35 m and a cross section of the scintillator bars of 5 × 5 cm 2 . The
values of the two simulations are in good agreement. A relative energy resolution of
σ(Erel)=15 keV for σt=150 ps from R 3 BRoot, similar to the result of σ(Erel)=17 keV
derived within the phase-space approach.
However, to cover the acceptance of 80 mrad defined by the magnet yoke in this highresolution
mode at 35 m would require an unreasonable large face-size of NeuLAND of
more than 5.6 m. For the detector design we finally select scintillator bars with a cross
section of 5 × 5 cm 2 , an active length of 250 cm, and a corresponding 250 × 250 cm 2
face-size. Thus, at a distance of 35 m the NeuLAND acceptance amounts to about
35 mrad. We note, that in physics cases, where the high-resolution mode is demanded,
this angular coverage is fully satisfactory, since small relative energies are investigated,
which are characterized by a small relative emission angle between neutron and projectile
fragment. The full-acceptance for the final detector face-size is given at a distance of
15.5 m to the target.
The use of larger bar cross sections together with larger face-sizes and volumes, assuming
a fixed number of modules, has several advantages. First, the demands for time resolution
can obviously be relaxed, since the full-acceptance is covered at a larger distance. For a
detector with a time resolution of σt=100 ps at 12.5 m from the target (full-acceptance
for 200×200 m 2 ) we derive, for example, a similar relative energy resolution as for a
detector with σt=150 ps at a distance of 15.5 m. Second, and this turns out only on
a later stage of simulations, see section 4.5, the larger detector volume is of advantage
for the association of hits from the secondary particles in the detector to the primary
neutrons, and thus for the multi-neutron recognition. The overlap of shower volumes
of individual neutrons at larger distances is smaller. Also, since calorimetric properties
play an important role in the multi-neutron recognition, the larger detector volume is
advantageous, because of a better collection of energy deposited by secondary particles.
From the considerations presented in this chapter and from the prototype results, see
chapter 3, we select scintillator bars with active sizes of 250 × 5 × 5 cm 3 as NeuLAND
submodules. The submodules in the standard configuration will be arranged in planes
with face-sizes of 250 × 250 cm 2 .
47

events
300
200
100
σt=0
σt=100ps
σ
=150ps
t
0
0 0.1 0.2 0.3
Erel
(MeV)
Figure 4.9.: Study of the effect of timing properties of NeuLAND on the resolution of
relative energy distributions, simulated using R 3 BRoot. Relative energy
spectra are shown for an ideal time resolution (dashed blue line), σt = 100 ps
(solid blue line), and σt = 150 ps (solid red line). One-neutron events were
emitted from 132 Sn with Erel = 100 keV at 600 AMeV. NeuLAND was
located at a distance of 35 m to the target, the scintillator cross section of
5×5 cm 2 was adopted.
The detector depth plays am important role for the efficiency of one- and more-neutron
events. The neutron recognition and its consequences with respect to the final detector
depth were investigated carefully in simulations, which are presented in section 4.5.
4.4. Light-Transport Simulations
In fast scintillator materials the time resolution is given by the number of photons and
their arrival time distribution at the photomultiplier. In this section we investigate the
effect of light guides which serve for the coupling between the quadratic cross section
of the scintillator of 5 × 5 cm to the circular entrance window of the photomultiplier.
Diameters of 1 and 1.5 inch were considered for the photomultiplier entrance window.
For the simulations the optical photon process of GEANT4 was used which allows the
definition of scintillation materials, including their properties like scintillation photon
48

spectrum, absorption length, refraction index, decay times, scintillation yield etc.. In
order to determine reflection properties, we made use of the possibility of defining optical
borders in GEANT4. In this simulation a polished dielectric-metal border between the
scintillator and a surrounding aluminum foil was chosen. Figure 4.10 shows the used
geometries for the light guides and some snapshots of photon tracking. The first row
shows the standard case with the PM directly coupled to the scintillator without a
light guide. The other rows show light guides with pyramidal, spherical, and parabolic
shapes. In the figure only the coupling to the 1 inch photomultiplier is shown but similar
simulations were performed for the 1.5 inch photomultiplier. For the scintillator module,
consisting of RP408 material, we chose the dimensions 5 × 5 × 200 cm. The light-output
was simulated based on a 50 MeV proton crossing the center of the scintillator bar. On
average 315000 optical photons were produced and in the table we list the numbers of
detected photons for the corresponding geometry for the photomultiplier with 1 and
1.5 inch, accordingly. The second far end of the scintillator was covered with a fictitious
photomultiplier covering the full area. On average 53000 photons were detected on this
”ideal read out” at this side.
We do not observe a substantial increase in read-out photons when applying light guides.
The photon tracking pictures displayed in the right column of figure 4.10 can serve to
interpret this effect as detailed in the following. Photons which are often reflected and
have large angles relative to the scintillator surface are often reflected back into the
scintillator bar by the light guide, while, in absence of a light guide, they had hit the
photomultiplier window. On the other hand, photons which travel almost parallel to
the scintillator but do not hit the photomultiplier directly have a high probability to
be reflected by the light guide into the direction of the photomultiplier. In total, the
number of photons hitting the photomultiplier stays almost constant. However, the
arrival time distribution of the photons is affected. This can be seen in Figure 4.11
where the simulated arrival time for the different light guide geometries is presented.
Relative to the case without light guide the amount of photons with short travel times
(”early” photons) are enhanced in cases with introduced light guides. Thus, the implementation
of light guides could lead to an improved time resolution since the fastest
photons determine the timing properties. For the 1 inch case, the light guides formed
like a truncated pyramid and the parabolic one, show very good performance. Following
closely these findings, we propose for the NeuLAND submodules light-guides of conical
shape for practical reasons, see section 5.2.2.
In order to obtain information on the number of photons expected close to the detection
threshold, electrons with an energy of 1 MeV were also simulated. In this case about
300 photons were detected with a 1 inch and 600 with a 1.5 inch photomultiplier.
49

Number of detected photons (1”): 9835 Direct coupling of the PM to the scintillator.
Number of detected photons (1.5”): 21728
Number of detected photons (1”): 10227 Pyramidal light guide.
Number of detected photons (1.5”): 24146
Number of detected photons (1”): 10525 Spherical light guide.
Number of detected photons (1.5”): 21052
Number of detected photons (1”): 10229 Parabolic light guide.
Number of detected photons (1.5”): 23067
50
Figure 4.10.: Shapes of light guides and photon tracks.

Counts
600
500
400
300
200
100
without light guide
light guide: pyramidal
light guide: spherical
light guide: parabolic
0
5 6 7 8 9 10 20
Time (ns)
Counts
900
800
700
600
500
400
300
200
100
without light guide
light guide: pyramidal
light guide: spherical
light guide: parabolic
0
5 6 7 8 9 10 20
Time (ns)
Figure 4.11.: Arrival time photons from simulations with different light guide shapes, displayed
on the left-hand side for an entrance window of the photomultiplier
of 1 inch, and of 1.5 inch in the figure at the right-hand side.
4.5. Scintillator Studies of Full-Size NeuLAND
The detailed simulations shown in the following subsections were performed using the
R 3 BRoot framework. As reference the most important parameters are again summarized
here. Within R 3 BRoot the TGEANT3 interface was selected, including the interaction
option GCalor for low-energy neutrons. The dimensions of the NeuLAND detector in
these simulations are defined very similar to the proposed final detector design, see section
5. Only the light guides are omitted within this study due to the high computational
effort of optical photon tracking, see section 4.4. The detector submodules are 250 cm
long and have a cross section of 5 × 5 cm 2 . Twenty submodules are grouped in planes
of 250 × 250 cm 2 and the detector depth of 3 m is built up from 60 planes, which are
stacked alternating with horizontal and vertical paddles. Light quenching for protons
was taken into account using Birk’s relation [Bir-64]. The transport of the resulting
light from the position of production to the readout positions of the scintillator bars
takes into account the scintillator time response and the light attenuation length of the
bar. Energy thresholds were set to approximately 160 keV for both read-out sides, including
a small variation to simulate typical behaviour of jitter in read-out electronics.
An integration time of approximately 200 ns is applied for the collection of the light
output. The time of each hit is derived from the mean time of the both readout times
of the bar. Unless specified differently a time resolution of 150 ps was assumed. The
adaption factor for the total energy deposit, obtained from the R 3 BRoot comparison to
the neutron calibration data of LAND, see section 4.1.2, was applied for the description
of energy loss in NeuLAND accordingly. 1 Figure 4.12 shows exemplarily a typical event,
displayed in a NeuLAND side view.
1 Although the mismatch in the total energy deposit spectra is most likely originating from a malfunctioning
absolute energy calibration in the experiment, we take the reduction of total energy loss for
further simulations as a safety margin into account.
51

Figure 4.12.: Displayed is a side view of NeuLAND together with the interaction of one
incoming neutron at 1000 MeV. In blue we see the track of the incoming
neutron from the left hand side. After interaction in one of the first layers,
one fast proton is traversing part of the detector (red), while the neutron is
scattered. Several other neutrons with short tracks and gammas (in green)
are visible. The display was created using GEANT4.
4.5.1. One-Neutron Response
Regarding first the key quantity, the detection efficiency, the advantage of a fully-active
detector over a converter-based one, manifests itself predominantly at lower neutron
energies, see section 4.2 and table 4.3 as well. For the final detector design, simulated
here, we find a value of 90% efficiency of 200 MeV neutrons, 94% at 600 and 96% at
1000 MeV, respectively 2 . The submodule multiplicity for 200 MeV neutrons amounts to
about 4, for 600 MeV neutrons on average about 14 paddles have a valid entry, and for
1000 MeV per neutron, 25 paddles are involved.
4.5.2. Multi-Neutron Response
The following criteria are used in order to identify and resolve multi-neutron events:
1. The number of incident neutrons. It has to be determined as unambiguous as
possible.
2. The momentum of each identified neutron. It has to be resolved with good resolution.
2 These values comprise the loss of neutrons due to interactions in air for the distance of 15.5 m between
52
target and detector, an effect of 1 to 2%

Since, as discussed above, several hits in the detector occur per neutron, it is essential
to find not only the correct number of neutrons but also to reconstruct their momentum
from the first interaction point.
In the following we describe the methods developed for the NeuLAND neutron reconstruction,
as of today. It turns out that a generalized tracking mechanism alone does
not lead to satisfactory results with respect to the multi-neutron identification. Instead,
we use a method which combines tracking with calorimetric information in order to
resolve multi-neutron events. We first introduce the definition of a valid cluster in Neu-
LAND, then detail the calorimetric resolving power and finally, by a combination of
both, determine the number of neutrons and their momentum.
Clusters
Within one event a hit in NeuLAND is defined as a coincident observation of a signal,
above threshold, at both ends of a NeuLAND submodule. The hits are sorted time-wise,
and then, in a first step, neighbouring hits are identified, starting from the first hit in
time. Hits belonging to a cluster are thus defined by certain distance in space (≤ 7.5 cm
in x, y and z each) and a certain time difference (≤ 1 ns) to at least one other member
of the cluster. After all hits have been assigned to clusters, for each cluster only the first
and last hit in time are stored. 3 Again, the clusters are sorted according to their time of
the first hit. The first cluster is treated as occurring from a first interaction of an incident
neutron. For all following clusters a procedure with kinematical conditions is applied
in order to check whether these clusters could stem from elastically scattered neutrons
from a prior incident point with an earlier cluster. That takes into account the scattering
angle of the particle of the earlier cluster (most likely a proton), which we define from
the first and last hits of the cluster. If one of the later clusters fulfills the criteria of
an elastic scattering process of the incident neutron, this cluster is eliminated from the
further analysis. This procedure is iterated for all clusters until no more correlated
secondary clusters can be found.
The number of remaining clusters still is substantially higher than the number of incident
neutrons and depends on the energy of impinging neutrons. Exemplarily, for 200 MeV
neutrons, a mean value of about 2.7 clusters is observed for one-neutron events, at
600 MeV the value increases to about 6.3 and for 1000 MeV we observe on average
10.5 clusters per neutron. In figure 4.13 the number of clusters is displayed for one- to
six-neutron events at 600 MeV. The overlap of the number of clusters for the different
neutron channels is large. Therefore, in the following we detail the use of the calorimetric
properties of NeuLAND for the assignment of proper neutron multiplicities.
3 As special case hits without any neighbour are defined as clusters by themselves.
53

events
2000
1000
0
0 20 40 60 80
Nclusters
Figure 4.13.: Number of clusters in NeuLAND from 600 AMeV neutrons for multiplicities
of 1 (black), 2 (green), 3 (red), 4 (blue), 5 (yellow) and 6 (magenta).
Calorimetric Properties
Several quantities are regarded here in order to investigate their information content
with respect to the number of incident neutrons. The left part of figure 4.14 shows
the total energy deposited Edep in NeuLAND as a function of incident neutron number.
We see a clear and linear increase of the mean value of Edep, however the distributions
overlap for consecutive neutron numbers. When studying the multiplicity, the number
of hits with valid entries in NeuLAND, a similar behaviour is observed, see right part
of figure 4.14. As in the case of number of clusters, see figure 4.13, no clear separation
is possible for each of the regarded parameters. However, we can gain a more clear
separation by correlating two of the above mentioned quantities. The best separation
of neutrons is obtained when combining the number of clusters and the total energy
deposited. We observe an anti-correlation, as displayed for neutron multiplicities of 1 to
6 in figure 4.15 for 600 AMeV neutrons.
The cuts indicated in the individual spectra allow for a very satisfactory neutron separation,
as presented in the combined presentation in figure 4.16. The determination of
neutron multiplicities is derived from the conditions in the two-dimensional plane. In
the case displayed here cuts were chosen in a manner, that strongly suppresses a shift
towards higher neutron multiplicities. Additionally, we chose the upper cut for a neutron
multiplicity of four generously, a reasonable assumption for cases where the cross section
for higher neutron multiplicities either drastically drops or vanishes (see the discussion
of GDR studies for 136 Sn with a separation energy for 5 neutrons of S5n=19.6 MeV and
the case of 4 correlated neutrons in section 4.5.4). Depending on the cross sections for
different neutron multiplicities and the investigated physics case, cuts can be optimized
to suppress either too high or too low neutron multiplicities.
54

events
800
600
400
200
0
0 200 400 600 800 1000
total light (a.u.)
events
600
400
200
0
0 50 100 150
multiplicity
Figure 4.14.: Left hand side: Total energy deposited in NeuLAND from 600 MeV neutrons
for multiplicities of 1 (black), 2 (green), 3 (red), 4 (blue), 5 (yellow)
and 6 (magenta). Right hand side: Multiplicity from number of submodules
with valid signals, again for 1 to 6 neutrons impinging with 600 MeV.
4.5.3. Neutron Tracking
For the final assignment of neutrons we now utilize the calorimetric information for
the neutron multiplicity. Typically, the number of clusters in the event is much larger
than the derived neutron multiplicity, as detailed before. We, therefore, have to select
from the list of clusters the ones that are most reliable, thus ensuring that also the
correct momenta of neutrons are reconstructed. The time-wise first cluster is taken as
the first neutron track. For the remaining clusters, a resorting procedure is performed.
An excellent criterion appears to be a combined requirement on the smallest difference
of velocity of the neutron βcluster (associated with the cluster), the beam velocity βbeam
and the largest energy deposit of the cluster Ecluster dep . The clusters are sorted according
to their values of
Rcluster = |βcluster − βbeam|
E cluster
dep
(4.2)
starting with the smallest value of Rcluster. Finally, clusters from this sorting are defined
as neutron tracks up to the maximum number of neutrons from the calorimetry
argument. The remaining clusters are eliminated from the further analysis.
The quality of the neutron detection and its separation into the various multiplicities can
be understood from the so-called neutron separation matrices, displayed in tables 4.5 for
200, 600 and 1000 MeV neutrons impinging on NeuLAND, at a distance of 15.5 m to
the origin of the neutrons. For multiplicities of up to 5 neutrons simulated (columns),
the percentage of detection in the various neutron channels derived from the tracking
algorithms is indicated, respectively (rows).
55

clusters
N
clusters
N
clusters
N
100
50
100
0
0 500 1000 1500
total light (a.u.)
50
100
0
0 500 1000 1500
total light (a.u.)
50
0
0 500 1000 1500
total light (a.u.)
clusters
N
clusters
N
clusters
N
100
50
100
0
0 500 1000 1500
total light (a.u.)
50
100
0
0 500 1000 1500
total light (a.u.)
50
0
0 500 1000 1500
total light (a.u.)
Figure 4.15.: Displayed is the number of clusters versus the total energy deposited for
600 MeV neutrons. The upper left part shows the 1 neutron case, upper
56
right the 2 neutron case. In the middle left part multiplicity 3 events
are plotted, and 4 neutron events in the middle right part of the figure.
Accordingly the multiplicity 5 and 6 events are found in the lower left and
right panels, respectively. For all neutron multiplicities the same number
of events was calculated.

clusters
N
100
50
0
0 500 1000 1500
total light (a.u.)
Figure 4.16.: Same as in figure 4.15, but now for the data combined for all neutron
multiplicities. The lines present the conditions which are applied in the
further analysis to distinguish the different multiplicities.
detected
200 MeV
generated
% 1n 2n 3n 4n 5n
1n 88 31 6 1 0
2n 2 62 37 10 2
3n 0 5 49 38 14
4n 0 0 8 48 54
5n 0 0 0 3 26
6n 0 0 0 0 3
detected
600 MeV
generated
% 1n 2n 3n 4n 5n
1n 92 22 2 0 0
2n 2 71 32 7 1
3n 0 6 55 32 9
4n 0 0 10 57 50
5n 0 1 1 4 35
6n 0 0 0 0 5
detected
1000 MeV
generated
% 1n 2n 3n 4n 5n
1n 89 12 1 0 0
2n 7 78 23 3 0
3n 0 8 63 26 5
4n 0 0 12 63 40
5n 0 0 0 7 46
6n 0 0 0 0 8
Table 4.5.: Neutron separation matrices for multiplicities of 1 to 5 neutrons. Columns
display the neutron multiplicity simulated, rows the neutron multiplicity derived
from the neutron tracking algorithm. Values are given in percent. Neutrons
were simulated with 200 (left), 600 (middle) and 1000 MeV (right matrix).
NeuLAND was located at a distance of 15.5 m to the target. Neutrons
were generated with a relative energy of 500 keV with respect to a medium
heavy projectile fragment. The distance between target and NeuLAND was
filled with air.
57

We observe a very high percentage of proper neutron recognition, i.e. the neutron
number is correctly derived from the algorithm, indicated in bold in the tables. Even
for the lowest neutron energies the 4-neutron recognition still stays close to 50%, for
the highest beam energies values of more than 60% are obtained. In this example the
calorimetric cuts were set in manner favouring too low neutron multiplicities over too
high ones. So, more events are erroneously assigned to a lower neutron multiplicity than
to a higher neutron multiplicity. The separation matrices derived in this simulation,
explore a combined efficiency, taking both the neutron tracking capabilities and the
geometrical acceptance into account. NeuLAND is located in the full-acceptance distance
for the relative energy example of Erel = 500 keV discussed here. However, a certain
fraction of neutrons does not reach the detector volume, due to scattering in the air along
their flight path from the target to the detector at a distance of 15.5 m. Exemplarily,
for 600 MeV neutrons approximately 1.5% of the neutrons undergo such an interaction.
For events with a neutron multiplicity of four, in approximately 6% of the events at least
one neutron will not arrive at the detector volume. These losses are contributing to the
values derived in the separation matrices.
The high values for correct multiplicities for 3 and 4 neutron cases are of extreme importance
for the envisaged physics programme with NeuLAND, since the investigation
of more and more neutron-rich nuclei is accompanied by higher neutron multiplicities.
The detector depth of 3 m plays a major role for the multi-neutron recognition, since
the calorimetric properties depend significantly on the detector volume. Exemplarily, we
study the one- to five-neutron recognition of a detector, same as NeuLAND, but with
a reduced depth of 2 m only. The neutron separation matrix for 600 MeV neutrons is
shown in table 4.6.
detected
600 MeV, 2m depth
generated
% 1n 2n 3n 4n 5n
1n 83 30 7 1 0
2n 7 63 45 17 5
3n 0 5 39 36 18
4n 0 0 8 42 54
5n 0 0 0 3 22
6n 0 0 0 0 2
Table 4.6.: Neutron separation matrix for 600 MeV neutrons, as in the middle panel of
table 4.5, but for a reduced depth of NeuLAND, i.e. 2 m instead of 3 m.
While the one-neutron recognition is affected mildly, decreasing from 92% (3 m) to 83%
(2 m), the impact on the multi-neutron recognition is more drastic. For the detector
depth of 2 m, four-neutron events are detected with the correct multiplicity in 42%
of all cases, which is a decrease by 26% compared to the 57% detected with the 3 m
depth of NeuLAND. Correspondingly the fraction of misidentified neutron multiplicities
is enlarged.
58

In the following section we discuss the NeuLAND performance along some of the physics
examples, as laid out in chapter 2. However, to summarize the overall relative energy
resolution σ(Erel), we display in figure 4.17 σ(Erel) as a function of Erel, exemplarily for
132 Sn decaying into 131 Sn and one neutron at beam energies of 600 AMeV, derived from
phase-space simulations.
Figure 4.17.: The relative energy resolution σ(Erel) for Erel values from 100 to 3000 keV
is shown for 132 Sn decaying into 131 Sn and one neutron at beam energies of
600 AMeV. The values, derived from phase-space simulations, are displayed
for distances between the detector and the target of 15.5 m (squares) and
35 m (circles). The resolution is proportional to the square-root of Erel,
the curves present fit functions with a proportionality to √ Erel.
4.5.4. Physics Cases
Evolution of the Collective Response of Exotic Nuclei
For the investigation of heavy exotic nuclei with respect to their collective response, we
discuss, exemplarily, the case of 136 Sn, excited in inverse kinematics via the Coulomb
interaction. The input distribution of dipole strength takes into account a giant dipole
resonance (GDR) and additional strength at lower energy, resembling the pygmy dipole
resonance (PDR). For the GDR, a peak energy of Em = 15.5 MeV and a resonance
width of Γ = 4 MeV were adopted as resonance parameters from systematics. The
GDR exhausts 100% Thomas-Reiche-Kuhn (TRK) sum rule strength. For the PDR,
59

exemplarily, the strength of 5% TRK sum rule is represented by a Gaussian distribution
with Em = 8 MeV and a width of σ = 1 MeV. The Coulomb cross section distribution is
calculated for 136 Sn projectiles impinging on a Pb-target with 1000 AMeV. According to
the energy-differential Coulomb cross section distribution, events were simulated within
a statistical-model approach, detailing the decay channels (1 to 4 neutrons), the neutron
and fragment momenta and the γ-transitions below the particle thresholds on an eventby-event
basis. Figure 4.18 presents the total excitation-energy-distribution input to the
NeuLAND simulation, together with its one- to four-neutron contributions.
events
15000
10000
5000
1 n
2 n
3 n
4 n
0
0 10 20 30
E* (MeV)
Figure 4.18.: The input excitation-energy distribution is shown for a combination of PDR
and GDR in 136 Sn (Coulomb excitation on a Pb target at 1000 AMeV). The
overall distribution is displayed (black line), together with the composition
into the 1 neutron (red), 2 neutron (cyan), 3 neutron (blue), and 4 neutron
channels (magenta). The distribution is calculated for excitation energies
from the one-neutron threshold up to 20 MeV.
Approximately 7×10 5 events were collected into the input for the R 3 BRoot simulation of
the NeuLAND response. NeuLAND is located at a distance of 23.5 m to the target in this
simulation. Neutrons were reconstructed from the NeuLAND tracking algorithm output.
Together with the momentum of the fragment and the γ-transitions, the excitation
energy was reconstructed using the invariant-mass method. Since our aim is to study
the performance of the response of NeuLAND, γ-transitions and the heavy fragment
were treated as ideal.
Figure 4.19 displays the comparison of the excitation-energy-distribution input to the
response of NeuLAND from the R 3 BRoot simulation. For the reconstruction, neutron
multiplicities of 1 to 4 were taken into account. The mass of the projectile fragment
is used as a cross check for the detection of the each neutron channel. Thus, only
channels with the correctly identified neutron multiplicities (diagonal elements of the
60

events
15000
10000
5000
input
output
0
0 10 20 30
E* (MeV)
Figure 4.19.: The excitation-energy distribution from figure 4.18 (dashed black line) is
displayed together with its reconstruction from the R 3 BRoot simulation
response of NeuLAND (solid red line).
separation matrices displayed in table 4.5) are taken into account and corrected according
to their respective tracking efficiency. The shape of the low-energy part (PDR) and the
mean energy of the GDR are in very good agreement with the input distribution. The
distribution in between the two maxima is only marginally affected. For larger excitation
energies the resolution turns slightly worse. Above approximately 13 MeV, we observe a
redistribution of strength towards higher excitation energies. For a more detailed analysis
of the response, we investigate the various neutron channels, as shown in figure 4.20.
The shift towards higher excitation energies originates mostly from the 3 and 4 neutron
channels. The reconstruction of a too large energy in case of multi-neutron events
stems from a false identification of the first interaction of at least one of the impinging
neutrons. However, a further development of the neutron tracking algorithm is in process
and will improve the 4-neutron-recognition with respect to the identification of the first
interactions.
Dipole Strength at the Particle Threshold
As detailed in section 2.2, we aim for a resolution of about 20 keV at an excitation
energy of 100 keV above the threshold. Here, we present the relative energy spectrum,
obtained for the one-neutron evaporation from a medium-heavy nucleus at 600 AMeV
with a relative energy of 100 keV. In order to optimize the energy resolution, NeuLAND
was placed at the maximum distance of 35 m. In figure 4.21 we present the resulting
relative-energy spectrum for this one-neutron-detection scenario. An excellent resolution
of σE = 15 keV is observed at an excitation energy of 100 keV above the threshold.
61

events
events
3000
2000
1000
8000
6000
4000
2000
1 n
2 n
3 n
4 n
0
0 10 20 30
E* (MeV)
0
0 10 20 30
E* (MeV)
events
events
8000
6000
4000
2000
4000
2000
0
0 10 20 30
E* (MeV)
0
0 10 20 30
E* (MeV)
Figure 4.20.: The input excitation energy distribution (dashed lines) and its reconstruction
from the R 3 BRoot simulation (solid lines) is displayed, similar as in
figure 4.19, but for the individual neutron decay channels. The upper left
panel shows the one neutron case (red), the upper right panel the two
neutron decay channel (cyan), the lower left panel the three neutron case
(blue) and the lower right panel the four neutron decay channel (magenta).
In contrast to the display in the previous figure, here the efficiency correction
of the individual neutron channels is not applied for the reconstructed
data.
62

events
2000
1500
1000
500
σ = 15 keV
0
0 0.2 0.4
Erel
(MeV)
Figure 4.21.: Relative energy spectrum for one neutron events at 600 MeV, simulated
with a relative energy of 100 keV with respect to a medium-heavy nucleus
and the NeuLAND detector at 35 m distance to the target.
Multi-Neutron Configurations
The correct multi-neutron recognition is an essential improvement of NeuLAND over
the nowadays existing fast-neutron detectors. We detail here the response of NeuLAND
to a prime challenge of detector physics: the detection of 4 fast neutrons with a narrow
distribution in space and time. Four correlated neutrons may occur in the breakup of
four-neutron halo nuclei like 8 He and 14 Be. Their understanding is essential for the
study of, e.g. the 7 H system, as discussed in section 2.3.
Excellent 4-neutron detection efficiencies are expected, based on simulations, see section
4.5.3, i.e. table 4.5. In order to mimic the tetra-neutron case, we investigate the
detection capabilities of NeuLAND for a scenario, where 4 neutrons plus the projectile
fragment share a relative energy of only 100 keV. NeuLAND is situated at the maximum
distance of 35 m and we select 600 AMeV as a typical beam energy. Figure 4.22
displays the reconstructed relative energy spectrum for this scenario. We observe a
distribution, which has a gaussian-like peak plus an exponential tail to higher relative
energies. Fitting the gaussian part, as displayed in figure 4.22, results in σE = 42 keV.
We find 58% of all entries within a 2σ-interval. For an estimate on the fraction of correlated
4-neutron events, which will be resolved by NeuLAND, we must take the total
4-neutron-recognition probability of about 60% into account, see table 4.5. Therefore,
about one third of the impinging 4-neutron events can be resolved with good resolution
using the present neutron tracking algorithm. For the events in the exponential tail, see
figure 4.22, the first interactions have not been fully resolved for all four neutrons, thus
leading to a false reconstruction of the relative energy. This effect is observed similarly
in the case of multi-neutron contributions to the GDR, (we refer to the first example of
63

events
300
200
100
σ = 42 keV
0
0 0.5 1
Erel
(MeV)
Figure 4.22.: Relative energy spectrum for four-neutron events at 600 MeV, simulated
with a relative energy of 100 keV with respect to a projectile fragment and
the NeuLAND detector in 35 m distance to the origin.
this section). Again, from the further development of the neutron tracking algorithm,
the 4-neutron-response is expected to improve.
Quasi-Free Scattering
NeuLAND in use for quasi-free scattering reactions will detect single neutrons, but a
lower energies, see section 2.4. The detector will be located in close vicinity to the
target, at an angle around 45 degree. The high efficiencies even for low energies are
very important for this application. With a fully-active detector, we derive efficiencies
of 79% for 50 MeV neutrons, 94% for 100 MeV, 95% for 150 MeV and 90 % for 200 MeV
neutrons, respectively.
64

5. Technical Specifications and Design
Details of NeuLAND
5.1. Final Detector Parameters
Based on the simulations (chapter 4) and the prototype results (chapter 3), we select
scintillator bars with active sizes of 250 × 5 × 5 cm 3 as NeuLAND submodules. The
submodules in the standard configuration will be arranged in planes with face-sizes of
250 × 250 cm 2 . A total depth of 3 m guarantees a high efficiency combined with an
excellent multi-neutron recognition.
5.2. Structure of the NeuLAND Submodule
5.2.1. Material, Sizes and Wrapping
The rectangular length of the active part of each bar will be 250 cm, the outer cross
section 5 × 5 cm including wrapping. Together with the light-guides at the far sides, the
submodule will be 270 cm long (see section 5.2.2). As organic scintillator material we
select RP-408, a cost-effective material, using Polyvinyltoluene as polymer base [Rex-11].
It combines fast timing properties with a long optical attenuation length. The scintillator
bars should be provided including polishing, wrapping with a reflector material and with
adhesive black tape for light-tightness. The weight of one scintillator bar then amounts to
7.9 kg. A number of bars with precisely these specifications have already been obtained
from a commercial supplier (REXON Components, Inc.) and tested.
5.2.2. Light Guides
The light guide transforms the quadratical cross section of the scintillator bar to the
circular cross section of the entrance window of the photomultiplier. This tapered form,
as shown in the drawings in figure 5.1, is optimized for the readout with photomultipliers
with a diameter of 1 inch, enhancing the timing properties of the detector, see section 3.3
for prototype results and section 4.4 for simulations.
65

Figure 5.1.: Technical drawing of NeuLAND submodules together with its light guides.
In order to exclude possible losses at the optical borders between scintillator and light
guide, the scintillator bar and its light guides are produced in one piece from the RP-
408 material, as detailed in in the upper part of figure 5.1. This also simplifies the
mounting structure of the modules, because no dedicated holding device is needed for
the light guides. Another advantage of this one-piece solution is, that we can omit optical
coupling materials, which otherwise might lead to possible aging issues.
5.2.3. Light Readout
At the stage of writing of this Technical Design Report we propose a conventional photomultiplier
readout for the photons produced in the scintillator bars. However, as an
investment in the future we closely follow the fast development of semiconductor devices
for fast-timing readout, in particular so- called Silicon-Photomultipliers (SiPM). These
devices seem to fulfill the time resolution needs of NeuLAND. However, the currently
available SiPM sizes of up to 10×10 mm 2 are insufficient to fulfill the needs for Neu-
LAND, and their dark count rate is too high. Depending on the progress within this
field, a SiPM- based readout remains an option, either for the later phases of NeuLAND
66

construction, or for subsequent replacements of broken photomultipliers in a possible
refurbishing of NeuLAND.
In order to stay abreast of developments and to drive progress in the directions needed
for NeuLAND, we participate in the Nuclear Physics Network (NUPNET) ERA-Net, in
the NEDENSAA (NEutron DEtector developments for Nuclear Structure, Astrophysics
and Applications) project that runs from 2011-2014. NeuLAND is included in the NE-
DENSAA working package 4 on photon readout, concentrating on large area, and low
dark rate SiPM’s. This NeuLAND-oriented NUPNET work has strong synergies with the
NUPNET engagement of the CALIFA working group in the FATIMA (Advanced Fast
Timing Arrays with novel scintillators and photosensors) NUPNET. The work of the
CALIFA group within FATIMA also aims to improve the readout of SiPMs. Presently,
a read-out of NeuLAND with conventional photomultiplier tubes is not only viable but
also state of the art. However, we are actively participating in the development of a
promising, alternative that might become a cost-saving alternative in the future.
We select the R8619-Assembly photomultiplier from Hamamatsu [Ham-11], or equivalent,
for the readout of the NeuLAND submodules. This device with a diameter of
1 inch and a peak sensitivity of 420 nm fits well to the RP408 scintillator bars, via the
light-guide coupling discussed above. With a gain of 2 × 10 6 and an anode rise time of
2.6 ns it offers a cost-effective solution adapted to the needs of NeuLAND.
First tests of a final shape NeuLAND module with these photomultipliers in electron
beams (section 3.3) indicate a time resolution of σt = 125–135 ps, which is sufficient for
the resolutions aimed for with NeuLAND.
5.3. Full Detector Assembly
5.3.1. Grouping of Submodules — Double Planes
The scintillator bars will be grouped in double planes, each plane consisting of 50 submodules
to build up a face-size of 250 × 250 cm 2 . The orientation of the bars of the
second plane is rotated by 90 ◦ with respect to the first one. Two planes share a holding
structure, displayed in figure 5.2, the scintillator bars are locked into position via the
conical drill-holes, which support the light-guide part of the bars. The frame plates are
made from aluminium, about 265 cm long, 10 cm wide and 3 cm thick each.
Figure 5.3 details the attachment of read-out devices to the double planes. The photomultipliers
are mounted to the outside of the holding frame with a Mu-metal tube,
a Kapton foil inside serves for electrical insulation. A bayonet cap allows for an easy
access to the photomultiplier and attached voltage divider. The light-tightness is assured
by O-rings at both connection ends of the Mu-metal tube. The photomultiplier
window is pressed to the light-guide end of the scintillator bar through a spring included
in the bayonet cap. In figure 5.4 the sequence for building up the scintillator bars in
67

Figure 5.2.: Left: holding frame for NeuLAND double-planes. Right: detailed view of
the supporting conical drill-holes.
Figure 5.3.: Left: assembly of the photomultiplier housing, see text for details. Right:
detailed view of the mechanical connection of the photomultiplier to the far
end of the light-guide.
one double plane is broken down. The weight of one double plane amounts to about
950 kg, read-out and cabling not yet included. The lower frame plate of a double plane
is fortified with two aluminium plates, which form at the same time the cable channel.
For the cable channels on the other three sides standard PVC-modules are used.
68

positioning of 50 submodules mounting of two
on an assembly desk supporting rails
positioning second layer mountion of third and
of 50 submodules fourth supporting rails
complete attaching mounting of
of photomultipliers cabling box
insertion of sub-carrier view of full double plane 69
and cabling indicating frame for details
Figure 5.4.: Different stages of assembly for double planes of NeuLAND. The lower right
figure displays the full mounted double plane, the frame indicates the detail,
which is used in all other displays within this mounting protocol. The
sequence starts in the upper left part and ends in the lower left part.

For the supply and read-out of NeuLAND submodules, we foresee a modularized system,
connected to each double-plane, see section 5.4 (figure 5.10).
The assembly of double planes in the detector housing is described in the next subsection.
5.3.2. Full Detector Setup
For the NeuLAND detector two identical detector frames will be produced. Each housing
can host all 30 double planes. The second housing serves for the storage of planes during
assembly and maintenance and can be used for experiments where NeuLAND is used in
two separate parts at different locations. The frames are assembled from ready-made
steel parts, mostly hollow profiles, see figure 5.5. The weight of each frame amounts
5200
3275
3800 + 600
Freimaßtoleranzen: DIN 7168-m
Werkstoff
Gezeichnet 08.09.2011 Günter Ickert
Telefon: 06159-71-2441
E-Mail: G.Ickert@gsi.de
GSI
3250 + 600
Stahlprofil 220x120x10
EN 10219 (DIN 59411)
Maßstab
Tragestruktur für LAND 2
64291 Darmstadt
Planckstr. 1 Gewicht ca. 3500 kg
Blatt-Nr.
1
A4
\\WinfileSvG\LAND$Root\Ickert\Eigene Dateien\Inventor\Neu_LAND\Neu_LAND_V9\Zeichnungen\Trage-Struktur-LAND 2.idw
Figure 5.5.: Technical drawing of one of the two frames for NeuLAND.
to about 3.5 tons. The double planes are moved into the housing from the front side,
guided by four guide rails, see figure 5.6. The load transmission is provided via two
sub-carriers to the two lower guide rails, see the technical details of the sub-carriers in
figure 5.7.
The hollow structure of the sub-carriers, made from one piece of aluminium, allows at
the same time for the guidance of connecting lines from the photomultipliers to the
cable boxes. Figure 5.8 shows on the left hand side the lower right edge of a double
70

Figure 5.6.: Detector frame with first double plane inserted.
150
110
60
150
110
79
Rohling aus Aluminium-Guss
Außenflächen auf Maß geräst.
20
Druckbelastung pro 20x20-Säule ~ 125 kg
Freimaßtoleranzen:
Werkstoff
DIN 7168-m
Gezeichnet 08.09.2011 Günter Ickert Aluminium (Guss)
Telefon: 06159-71-2441
E-Mail: G.Ickert@gsi.de Ebenen-Träger
64291 Darmstadt
GSI Planckstr. 1
20
105
100
\\WinfileSvG\LAND$Root\Ickert\Eigene Dateien\Inventor\Neu_LAND\Neu_LAND_V9\Zeichnungen\Einzelteile.idw
Figure 5.7.: Specifications of dimensions for the sub-carriers, which carry the double
planes of NeuLAND.
alle R5
60
Maßstab
1:2
Blatt-Nr.
1
A4
71

plane together with its sub-carrier and the guide rail. The upper guide rails serve as tilt
prevention mostly, see exploded view in the right part of figure 5.8.
Figure 5.8.: Left: lower edge of one double plane together with its sub-carrier connection
to the guide rail. Right: Upper edge of one double plane, displaying its
connection to the upper guide rail.
Figure 5.9 illustrates the use of the second detector frame for maintenance purposes. The
front sides of both frames are constructed such, that the sliding rails of the both frames
can be connected easily. The double planes can be moved from one to the other frame
individually, thus giving space for maintenance purpose. When all 30 double planes
are inserted into one housing, the weight of NeuLAND amounts to about 32 tons. The
detector frames and the fully-assembled detector will be moved using air cushions.
Figure 5.9.: The two NeuLAND frames, arranged for moving double planes. On the left
hand side, the front-sides of both frames are put to minimum distance, on
the right part half of double planes have been moved to the second frame.
72

5.4. Peripheral Systems
5.4.1. Read-Out Electronics - TacQuila
NeuLAND will be built in a modular manner, composed of 30 double-planes. Each
double-plane will be independent with respect to its supply and read-out systems. In
figure 5.10 the present layout of the support boxes in the four corners of each double
plane is detailed.
6
5
4
A
D D
84
A ( 1 : 10 )
496
3275
C C
B B
t

Figure 5.11.: Shown is a fully assembled read-out chain, as currently in use for LAND:
on the left hand side, the TRIPLEX board on top of the frontend card,
in the middle the TacQuila main board with the QDC piggy-back, and on
the right hand side the connection for low-voltage supply.
For the implementation of TacQuila for NeuLAND two major further developments are
underway. First, the TAC stage shall be replaced by a high-resolution Time-to-Digital
Converter (TDC) [Bay-10] in a Field-Programmable-Gate-Array (FPGA). By that, we
overcome the limited availability of dedicated TAC-ASICs.
Second, the layout of the NeuLAND double-planes demands the read-out of 200 signals
in 4 corners of the frame structure. Thus an upgrade of the TacQuila board from
currently 16 to 50 channels is envisaged, in order to fulfill the space constraints, see
figure 5.10.
5.4.2. High-Voltage Distribution System
For NeuLAND 6000 photomultiplier need to be supplied with high voltages of typically
1 to 2 kV, with a maximum current of 2-3 mA per channel. For the first NeuLAND
submodules, conventional high voltage (HV) supplies are used, i.e. a Multichannel Power
Supply System SY1527, CAEN 1 , similarly to the supply of the existing LAND detector.
For the full detector solution, an optimized solution is under development, namely a HV
1 http://www.caen.it/csite/CaenProd.jsp?parent=20&idmod=122
74

Figure 5.12.: The photo shows the TacQuila-based read-out of the LAND detector, comprising
480 channels in 3 crates. In the lower part of the rack, the lowvoltage
supplies for TacQuila are hosted.
supply, which will be integrated into the socket of each photomultiplier voltage divider.
A similar supply has been realized earlier for the photomultipliers of the Crystal Ball
detector, which is part of the LAND setup 2 . An integrated solution is favoured for two
reasons, namely space and power consumption. First, compared to cables and connectors
required for the supply of high voltages, typical cables and connectors for the control of
the integrated HV supply inside the photomultiplier socket, are much smaller and more
flexible. Second, the power consumption and thus heat dissipation, are typically reduced
by one order of magnitude for integrated solutions.
2 http://www.iseg-hv.com/download.php/500/file url en/iseg PHQ.pdf
75

5.4.3. Controls
The NeuLAND controls will be based on EPICS (Experimental Physics and Industrial
Control System) [EPI-11], a real-time control system that is readily used in our current
R 3 B-Cave C setup and provides an easily scalable interface to the required amount of
process variables of NeuLAND.
76

6. Radiation Environment and Safety Issues
The radiation dose that NeuLAND will be exposed to is rather low. The detector will be
used for experiments with radioactive beams with maximum production rates of 10 8 to
10 9 particles/s. Assuming a target thickness corresponding to 1% interaction probability,
a maximum neutron flux of 10 6 to 10 7 /s is expected, distributed over the 19 m 3 volume
of the detector. Many of the experiments will deal with very rare ions (down to 100
particles/s), therefore for the estimation of the overall dose on the neutron detector, a
mean value of 10 6 ions/s and equivalent 10 4 neutrons/s are taken into account. With
an operation time of 2 months per year, 5×10 10 neutrons/year are deposited in the
detector volume, neglecting duty cycle. Radiation damages can therefore be excluded.
Also, with respect to aging the dose appears irrelevant. However, the long-term exposure
of NeuLAND to the direct ion beam should be avoided. This is done by the R 3 B-
GLAD Magnet, which serves to bend the charged particles out of the axis of the direct
beamline.
The photomultipliers used for NeuLAND need a high-voltage supply, up to 3 kV. Standard
operation procedures according to VDE 1 will be followed to guarantee the safety.
NeuLAND with its frame, weighs about 32 tons. With a contact area of about 2.3 m 2
of the NeuLAND detector frame, a floor load of about 15 tons/m 2 is obtained, which is
far below the foreseen floor loads for the experimental hall.
The detector can be moved on air cushions, which can be introduced at the bottom
of the four pillars of the frame. This means of transportation has proven very reliable
during the operation of the existing LAND, which weighs about 20 tons. The use of air
cushions requires an approriate flatness of the ground, see chapter 9 for further details.
In some cases, access to individual detector planes might be necessary for maintenance,
or the detector must be split due to experimental constraints. If so, the double-planes
can be moved smoothly on the guide rails from the first to the second detector frame,
see figure 5.9 in section 5.3. The guides on the four corners of the double-planes protect
against tilting.
The NeuLAND operation does not require the use of gases and cryogenic fluids.
1 VDE: Association for Electrical, Electronic & Information Technologies, german: Verband der Elek-
trotechnik Elektronik Informationstechnik e.V.
77

7. Production, Quality Assurance and
Acceptance Tests
NeuLAND will be assembled from ready-bought scintillator bars and photomultipliers.
The RP408 scintillator bars with its light-guides will be ready-made including wrapping
for reflection and light-tightness. The technical details are specified in sections 5.2.1
and 5.2.2. In-factory acceptance tests will ensure the specified quality for the mass
production for each supplier.
The choice of light readout is detailed in section 5.2.3. The selected photomultipliers
can be purchased including the voltage dividers. Here, as well, quality assurance will be
provided by in-factory acceptance tests.
The quality of the readout electronics TacQuila is assured by a in-factory acceptance
test, for which GSI provides a test setup for the involved company.
We foresee the assembly of scintillator bars and photomultipliers at the GSI/FAIR site,
for practical reasons. During and after assembly, the constant delivery quality of the
provided detector components will be proven by on-site tests. The light-tightness of the
NeuLAND submodules will be inspected after mounting of the read-out. Measurements
with radioactive sources will be utilized to characterize each submodule, partly with
its read-out electronics. As a result of these measurements parameters as the lightattenuation
length will serve for the quality control of each NeuLAND submodule.
In addition, samples will be drawn, for which a sophisticated test procedure will be
applied. These samples will be exposed to an electron beam, e.g. at the ELBE facility,
in order to check the time resolution of the selected modules, see section 3.3.
After the arrangement of 100 NeuLAND submodules into one double-plane, this doubleplane
with its final read-out electronics and its final high-voltage supply units will be
tested, either using radioactive sources, again, or cosmic rays, see also section 8.2.
79

8. Calibration
8.1. Calibration with Fast Neutrons
8.1.1. Calibration of a Subset of NeuLAND Modules
The calibration of a fast-timing neutron detector for high-energy neutrons is a difficult
task, since tagged neutron beams are rarely available. The experimental scheme, which
we elaborated in order to measure time resolution, efficiencies and data patterns at high
neutron energies, is detailed in the accepted GSI beam time proposal S406 [Bor-10].
The most important points are summarized in the following. The demands are precise
determinations of angle and energy of impinging neutrons on an event-by-event basis for
high-energy neutrons.
We will utilize neutrons stemming from a quasifree-scattering reaction of a deuteron
beam on protons. The deuteron beam is delivered from SIS18 at GSI with energies
between 200-1500 AMeV to the LAND reaction setup at Cave C, where the beam is
impinging on a CH2 target. Quasifree-scattering reactions are selected by detection of
both protons from the (p,2p) reaction in a wide angular range from 10 to 80 degrees. The
two protons stemming from the quasi-free p knockout reaction exhibit typical angular
correlations resulting in an opening angle ∆θ ∼ 90 ◦ and ∆Φ ∼ 180 ◦ . The angles are
measured with Si-strip detectors. The energy of the protons is measured with the Crystal
Ball detector. The transverse momentum of the spectator neutron is fixed by proton
kinematics, thus we know where the neutron detector is hit. Figure 8.1 shows the
angular distribution of protons for two incident beam energies. While for lower energies
a symmetric distribution in the proton polar angles peaking around 43 ◦ is observed,
an asymmetric distribution of angles is favored for beam energies above 500 AMeV,
resulting, e.g., in two strong peaks at around 15 ◦ and 70 ◦ for a reaction at 1000 AMeV.
Figure 8.2 shows exemplarily the spatial neutron distribution in 10 m distance from the
target for the neutrons stemming from the quasifree scattering reaction at 250 AMeV
deuterons on protons. In the following we detail how time resolution and efficiency of
a subset of NeuLAND submodules will be determined in an experiment scheduled for
the first half of 2012. Note, that the same beam time will be utilized as a calibration
experiment for the existing LAND detector for characterization of event patterns.
1. Time resolution:
Since the detection of a neutron is mostly of destructive character, at least with
respect to its momentum, studying the time resolution of neutron detectors is a
81

Figure 8.1.: Distribution of proton polar angles θ for both protons from the quasifreescattering
reaction for deuteron on proton at 250 AMeV (left panel) and
1015 AMeV (right panel).
Figure 8.2.: Spatial distribution of neutrons from quasifree scattering of deuterons at
250 AMeV on protons in 10 m distance to the target.
82

Figure 8.3.: ToF distribution in 10 m distance from the target for neutrons stemming
from the quasifree breakup of deuterons on protons at 1500 AMeV.
nontrivial task. We are missing a reference measurement telling us event-by-event
the energy of the neutron. When using the quasifree-scattering reaction at high
beam energies (approximately 1500 MeV) nevertheless the neutrons can be viewed
as nearly monoenergetic. Figure 8.3 shows exemplarily the time-of-flight (ToF)
distribution of the neutrons from the quasifree-scattering of deuterium on proton
at 1500 AMeV in 10 m distance to the target. The observed width of about 200 ps
results from the intrinsic momentum distribution of the knocked-out proton in the
deuteron. For a distance of 5 m from the target, the width of the ToF distribution
will thus be approximately 100 ps. First, from a measurement at two distances
to the target using the existing LAND we can disentangle the contribution from
the ToF resolution of the detector and the width related to the wave function of
the deuteron. Measurements will be performed in addition with a Carbon target
in order to quantitatively understand background stemming from reactions with
C-nuclei in the CH2 target which survive the kinematics conditions of the quasifree
breakup. From earlier measurements we know that this background is contributing
on a 10% level only. Second, after the width of the neutron momentum distribution
after breakup is determined as described above, we can derive the time resolution
from measurements on the subset of NeuLAND submodules which aim to be of
the order of ≤ 150 ps.
2. NeuLAND submodules efficiencies:
The second important quantity to study for the NeuLAND submodules is their
efficiency as a function of beam energy. We aim to measure at 5 energies, namely
at 200, 300, 500, 800, and 1500 MeV, thus providing excellent benchmark data for
further detailed simulations.
83

8.1.2. Characterization of Neutron Interactions with the Full-Size
Detector
After the installation of the fully-equipped NeuLAND, again, a calibration experiment
will be performed. The above-mentioned technique of quasi-free scattering of deuteron
beams will be applied. Time resolution and efficiency of the full system will be determined,
the latter as a function of neutron energy. Using the full detector volume, it
allows in addition a detailed study of the event patterns for real one-neutron events.
This is an important input for the development of tracking algorithms in order to optimize
the recognition capabilities. The measured one-neutron response can be used in
order to simulate the response of NeuLAND to multiple neutron events by overlaying
several one-neutron hit-patterns, taken from experimental data. This method relies on
the superposition principle for hit patterns on the NeuLAND detector.
Moreover, NeuLAND will be exposed to real and clearly characterized two-neutron
events, using the breakup of tritons as detailed in the following. Tritons provide a clean
source of correlated two neutron events, where the intrinsic wave function is known with
high precision. Quasifree proton knockout on the tritons with coincident detection of the
two protons from the (p,2p) reaction enables us to put strict cuts on the reaction kinematics,
in particular the transferred momentum to the removed proton. By requiring a
momentum transfer considerable larger than the proton’s Fermi momentum inside the
tritons we enhance events where the two neutrons act as spectators in the reaction, and
thus keep their original correlations. Using the known n-n scattering length, also finalstate
interaction can be taken into account precisely. The n-n relative-energy spectrum
can thus be calculated reliably and compared to the observed spectrum. The response
of the detector to 2n events is particularly important for low relative energy between the
two neutrons, En−n, for which the efficiency drops rapidly. In addition, the incident CM
angle of the two neutrons can be determined by the measurement of the angles of the
two protons. This measurement will, thus, allow for a detailed check of the simulation
procedure for the two neutron response.
8.2. Cosmic Ray Tracking in NeuLAND for Adjustment and
Calibration
For the internal calibration of NeuLAND before, during and after experiments, tracks
from cosmic rays will be used. The hard component of the cosmic ray flux at sea
level, mainly muons (97%), has sufficiently high energy (mean energy is 2 GeV) to
penetrate the concrete ceiling of the Cave C or the R 3 B Cave, respectively, and to
traverse NeuLAND with approximately the speed of light. The expected rates of incident
cosmic rays amount to about 1.5 kHz. That enables a full scan of the detector within
reasonable time scales. The tracks of muons, as displayed in a GEANT4 simulation in
figure 8.4, serve as a good time reference between the traversed submodules.
84

Figure 8.4.: Event display for several muons (cyan lines) traversing NeuLAND. The detector
is presented in a side view, simulated using GEANT4. Secondary
gamma rays (green) and electrons/positrons (yellow lines) can be seen as
well.
Within the calibration procedure, the distance of the two hits belonging to one muon
track is determined and their relative time difference has to satisfy the condition of a
particle traversing with speed of light. A minimization procedure can be applied to
match all 3000 submodules of NeuLAND. At the same time, this calibration also allows
an energy gain matching.
This procedure has been developed for LAND [Lei-93b], and proven very successful. A
more detailed description, can be found, e.g., in [Aks-09b] .
85

9. Infrastructure
Two identical detector frames are foreseen for NeuLAND, allowing to split the detector
for experimental reasons or for maintance purposes, see section 5.3 for details. Both
detector frams shall be located in the experimental hall (Cave C and later R 3 B hall).
Within the experimental hall the full-equipped detector is moved using air cushions. A
certain planarity of the floor is thus demanded within the hall.
The weight of one double-plane of NeuLAND amounts to about 1 ton. The doubleplanes
can be moved from one to the other frames utilizing the guide rails. In case, they
have to be taken out completely from the frame, this easily can be performed using the
crane installed in the experimental hall, which is laid out to carry up to 10 tons.
The power consumption, and thus the heat dissipation, for full NeuLAND amounts
to about 40 kW. This takes into account 4 W per photomultiplier and about 1.5 W
per Tacquila read-out channel. In addition about two racks of ancillary electronics are
required and taken into account. Air cooling will be used.
87

10. Installation procedure, its Time
Sequence, Necessary Logistics from A
to Z including Transportation
The parts for the NeuLAND submodules will be delivered to the GSI/FAIR site, where
the final assembly, testing and installation takes place. The detailed sequence and testing
procedures are described in chapter 7. For the mounting of submodules and the
arrangement of the submodules in double-planes a certain installation area has to be
allocated.
The area has to provide space for one NeuLAND detector frame, with a width of about
5.2 m, a height of about 3.3 m, and a depth of about 4.4 m (figure 5.5 in section 5.3).
In addition, space for storage of delivered scintillator bars and peripherals is required.
Racks for testing the submodules with their electronics and high voltage supplies need
to be installed. Two special mounting tables need to be provided, with an area of about
3×3 m 2 each. In total the required assembly space amounts to about 100 m 2 plus 50 m 2
for storage of submodules and peripherals close to the assembly location.
After full assembly and test of an double-plane, the double-plane has to be lifted from
the mounting table and inserted into the frame structure. This requires an indoor- or
mobile-crane for the transport of the double-plane with a weight of about 1 ton.
The time scheme foresees the production of one double-plane per month. First experiments
will be scheduled using a 20% detector, see chapter 12. We propose to move the
first detector frame from the assembly space to Cave C, after 20%, i.e. 6 double-planes
are ready to be installed. Depending on the location of the assembly area and its technical
equipment, we can either transport the double-planes and the frame individually
or all-together.
Starting with the 20% detector, NeuLAND will be gradually be built up with ready-built
and tested double-planes, while being located at Cave C. The supervened double-planes,
with their 200 read-out channels, each, will be integrated into the R 3 B DAQ system.
Ongoing cosmic calibrations, see section 8.2 will serve to monitor the implementation.
In the following we describe the procedure to move a fully mounted NeuLAND detector
from one experimental area to the other, i.e. from Cave C to the R 3 B hall. NeuLAND
with its frame can be moved to the outer area of the assembly hall using air cushions.
89

Outside the hall, it has to be lifted to a transporter. A special lifting beam 1 allows to
distribute the load to suspension points at the four pillars of the frame. One or two truckmounted
cranes will lift the fully equipped detector to a truck. After transportation to
the final destination and off-loading the detector is moved into the experimental hall
using air cushions again. This operation requires to (temporary) equip the floor space in
front of the experimental halls with a highly planar cover and a compressed air supply
close by. As well, a (temporary) opening of the building entrance and experimental hall
is demanded, which allows the passage of the NeuLAND detector frames.
1 german: Krantraverse
90

11. Cost and Funding
11.1. Cost Estimate
11.2. Funding Scheme
91

12. Time Schedule Table and Milestones
The NeuLAND production scheme comprises the full installation of one double-plane
per month. NeuLAND will be built from 30 planes, therefore, the full detector will be
ready three years after the beginning of production. This time scheme takes into account
three months for the startup of production lines for the supplying companies and three
months for the full system integration after building of the last double-plane. Another
three months will be needed for the invitation for tender and the order placing after the
financing commitments.
With the expected financing commitments in Q3/2012 we can define the following milestones,
which are visualized in figure 12.1:
1. 20%-detector readiness Q1/2014
2. first physics experiment with 20% detector in Q3/2014 in Cave C at GSI
3. NeuLAND readiness Q4/2015
4. first physics experiment with complete NeuLAND in Q3/Q4/2016 in Cave C at
GSI
Nr. Task Name
1 NeuLAND Construction Phase
2 invitation to tender / order placing
3 startup production lines at companies
4 production of NeuLAND submodules
5 20% detector produced
6 20% detector system integration
7 Milestone 1: 20% detector readiness
8 20% detector first experiment in Cave C
9 Milestone 2: first experiment using 20% detector performed
10 full detector produced
11 full detector system integration
12 Milestone 3: full detector readiness
13 full NeuLAND calibration and first physics experiment
14 Milestone 4: completion of first physics experiment with full NeuLAND
2012 2013 2014 2015 2016 2017
. Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt . Qt
Figure 12.1.: Graphical display of the time schedule of NeuLAND production including
dependencies and milestones.
31.12.
01.10.
01.10.
31.12.
93

The timeline for milestone 1 includes an elongated system integration time of 6 months
instead of 3 months. After the completion of milestone 3 and before milestone 4 a
calibration experiment using fast neutrons will be required.
94

13. Organization and Distribution of
Responsibilities
The detector design was developed from a subgroup of the R 3 B collaboration, called
the NeuLAND Working Group. The members, as of today, are listed in appendix A.
The NeuLAND Working Group, convened currently by Konstanze Boretzky, GSI, and
her deputy, Ushasi Datta Pramanik, SINP, will build the NeuLAND detector. A close
contact to the R 3 B Technical Coordinator and the Project Coordinator enables a smooth
embedding of the NeuLAND detector into the R 3 B’s full setup.
The responsibilities for the different subtasks are closely related to their associated funding
profile, as laid out in chapter 11. In table 13, we summarize the required tasks for
the construction phase of NeuLAND and assign the institutes with key responsibilities.
More details on the tasks are found in the numerated list below.
Item NeuLAND Task Short Description Responsible Institutes
1 Submodules purchase, assembly, test SINP, TU Darmstadt,
& double planes PNPI, TU Dresden,
HZDR, U Cologne,
U Frankfurt, GSI
2 Sample Tests using electron beams HZDR
3 Mechanics detector & double-plane frames GSI
full integration
4 Electronics quality control, integration GSI
5 HV System production, quality control, integration PNPI, GSI
Table 13.1.: Layout of the subtasks for the building phase of NeuLAND and the responsibity
distribution. The item numbers refer to the list in the text, accordingly.
1. NeuLAND Submodules and Double-Planes
This task comprises first, the purchase of scintillator bars, photomultipliers and
needed peripherals like voltage supplies and read-out channels, second, the assembly
of NeuLAND submodules and its acceptance tests, third, the arrangement of
NeuLAND submodules into double-planes. The work load is shared amongst the
partners according to the financial contributions. Since, for practical reasons, the
NeuLAND submodules will be built on-site at GSI/FAIR, the external partners
will send personnel to GSI/FAIR for the assembly and testing procedure.
95

96
2. Sample Tests
Random samples of NeuLAND submodules will be selected for a detailed investigation
of the response function, including determination of the time resolution
achieved with electron beams using the ELBE facility.
3. NeuLAND Mechanics
Included is the technical design of the mechanics of both the detector and holding
frames for the double-planes, the contract placing and the site acceptance test.
4. Electronics
This tasks comprises the production and quality control and the full system integration
of the foreseen read-out electronics for NeuLAND, a modified version of
TacQuila, see section 5.4.1.
5. High Voltage System
The necessary high voltage devices for the 6000 photomultiplier tubes of NeuLAND
have to be selected and ordered or produced in-house, tested and integrated into
the system including slow-control.

A. NeuLAND Working Group Members
Convener: Konstanze Boretzky, GSI Darmstadt, Germany
Deputy: Ushasi Datta Pramanik, SINP Kolkata, India
Germany
GSI Darmstadt: D. Bertini, K. Boretzky, J. Hehner, M. Heil, G. Ickert, Y. Leifels,
D. Rossi, H. Simon
HZDR Dresden-Rossendorf: D. Bemmerer, T. Cowan, Z. Elekes, M. Kempe, M. Sobiella,
D. Stach, A. Wagner, J. Wüstenfeld, D. Yakorev
TU Darmstadt: T. Aumann, C. Caesar, D. Gonzalez Diaz, A. Ignatov, D. Kresan,
H. Scheit
TU Dresden: T. Cowan, M. Röder, K. Zuber
U Cologne: J. Endres, A. Hennig, V. Maroussov, A. Zilges
U Frankfurt: R. Reifarth, M. Volknandt
India
SINP Kolkata: B. Agrawal, P. Basu, P. Bhattacharya, S. Bhattacharya, S. Chakraborty,
S. Chatterjee, U. Datta Pramanik, P. Kumar Das, J. Panja, A. Rahaman, J. Ray,
T. Sinha
Portugal
LIP Coimbra: A. Blanco, P. Fonte, L. Lopez
U Lisbon: D. Galaviz Redondo, J. Machado, P. Teubig
Romania
ISS Bucharest: M. Cherciu, M. Ciobanu, M. Haiduc, M. Potlog, E. Stan
Kurchatov Institute Moscow: L. Chulkov
Russia
97

PNPI St. Petersburg: G.D. Alkhazov, V.A. Andreev, A.A. Fetisov, V.L. Golovtsov,
E.A. Ivanov, A.G. Krivshich, L.N. Uvarov, V.V. Vikhrov, S.S. Volkov, A.A. Zhdanov
Chalmers Univ. of Technology: A. Heinz
98
Sweden

B. Neutron MRPC Results in Details
The final NeuLAND design is based on a fully active detector of organic scintillator
material. However, in the past also an alternative scheme using passive converters and
a multigap resistive plate chamber (MRPC) based detector had been investigated in
detail, including the construction and test of a fully operational 2 m long prototype.
The scintillator-based design shows significantly better performance than the MRPC option,
therefore it is adopted for the technical design of NeuLAND. The present appendix
summarizes the main results of the MRPC studies for reference.
B.1. Principle of Operation of an MRPC-Based Neutron
Detector with a Thick Iron Converter
The principle of operation for an MRPC-based neutron detector is derived from the
existing Large Area Neutron Detector (LAND) [Bla-92] at GSI, which has a face size of
2×2 m 2 . LAND converts neutrons into charged particles in 5 mm thick iron plates, and
subsequently detects the charged particles in plastic scintillators of the same thickness.
With LAND, typical detection efficiencies above 90% have been reached for 400 MeV
neutrons [Bor-03], see sections 4.2 and 4.1.2 for details.
Detectors that are similar to LAND have been used elsewhere, e.g. at Forschungszentrum
Jülich [Roz-05] and with the MONA detector at Michigan State University [Bau-05]. It
should be noted, however, that in the MONA case the converter is presently not used.
For the MRPC-based neutron-detector prototype, a setup similar to LAND is used,
but the scintillator is replaced with an MRPC. As converter material, stainless steel is
selected for practical reasons. In an MRPC, a charged particle passing through a gas
volume causes ionization. Owing to the electrical field strength of ≈100 mV/cm, an
avalanche is caused by this ionization. The mirror charge of the avalanche on a readout
electrode is used as signal.
MRPC’s are well-known for their excellent time resolution, as low as σt = 20 ps for special
configurations [An-08]. They are only weakly sensitive to γ-rays [Ali-07], eliminating
an important source of background. In the literature there are reports of successful
operation of large-scale MRPC structures on the scale of 1.5 m [Bla-02, Abb-09] for
minimum ionizing particles. However, besides the neutron MRPC option presented
here, to date no high-energy neutron detector involving MRPCs has been developed.
99

HV
1.$ mm
2$ mm
0+$1-2)-2'.%/
5%4'.6/
!"#$%&'(%)*+,-'.(/
78'(%)*+,-'.,/
5&%44'.-/
78'%$+,-'.9/
0+$1-2)-23
4"#$%&'%$+,-'.#/
Figure B.1.: Schematic cutout of a neutron detector MRPC module, as seen from one
of the sides where the signals are read out. From top to bottom, a 2 mm
thick stainless steel converter plate (a), a gas volume (b). Subsequently, the
signal cathode formed by copper strips applied on mylar foil (c), and the
high voltage cathode given by mylar foils with one-sided antistatic coating
(d). The 1 mm thick float glass sheets (e) form a symmetrical 2×2 gap
structure. The high voltage anode (f) is from the same material as the high
voltage cathode. The central 4 mm thick signal anode strips (g) also serve
as converter for the subsequent lower half of the MRPC structure. The
gas volumes (b) between signal cathode and outer converter serve to reduce
cross-talk between cathode strips.
Incident neutrons are converted to charged particles in a hadronic shower taking place
in the iron converter. This process takes place either in the 2+2=4 mm thick converter
on top of the 2×2 gap MRPC unit, or in the 4 mm thick converter and central anode
that is placed below the top 2 gaps (figure B.1). Subsequently, the secondary charged
particles are detected in the MRPC structure.
Different from LAND, each 2×2 gap MRPC structure is read out separately, giving a
granularity of 15 mm along the direction of propagation of the beam. Perpendicular to
the beam direction, a granularity of 26.5 mm (25 mm strip width, 1.5 mm gap between
strips) is obtained. Along each MRPC strip length, the spatial resolution, with the
interaction point determined from the time difference between the readout on both sides,
depends on the time resolution of the MRPC.
As each such module (figure B.1) has a low detection efficiency for 400 MeV neutrons,
many modules must be placed one after the other to reach 90% efficiency. For mechanical
reasons, each layer is divided into four modules of 2 m × 0.5 m each, leading to the
preliminary design sketched in figure B.2. In this scheme, the 2 mm thick steel outside
converter plates would also serve as housing and vacuum tight box for the MRPC structure
inside it and provide mechanical stability. In order to service individual modules,
100

! m
1%! m
&%' m
1 (e* neutron
Figure B.2.: Scheme of a possible implementation of a full MRPC-based neutron detector
with a 1 GeV neutron impinging. The 50 layers of four 2 m × 0.5 m
modules each are indicated by the the ellipsis points. See figure B.1 for
details of each MRPC module.
one can extract them from the top.
The MRPC part of such a composite detector has been extensively tested using an
electron beam of 30 MeV, close to minimum of ionization. The electron beam testing
facility is described in sec. B.2. A number of design issues have been studied using
smaller prototypes of 40 cm × 20 cm size [Yak-11, Dat-10]. The findings are presented
in detail in [Yak-11] and are reviewed in sec. B.3. Subsequently, a full-size prototype of
200 cm × 50 cm has been built and tested (sec. B.4). All of the aspects of the detector
have in addition been studied using extensive Monte Carlo simulations (sec. B.5). Some
preliminary results have also been obtained in experiments using quasi-monochromatic
neutrons [Cae-10].
B.2. 40 MeV Single Electron Test Facility at ELBE
For testing the response of the prototypes when irradiated with minimum ionizing particles,
the electron beam of the 40 MeV Electron Linac with high Brilliance and low Emittance
(ELBE) facility 1 at Helmholtz-Zentrum Dresden-Rossendorf, Dresden/Germany,
has been used. The tests were performed with a low-intensity electron beam of 30 MeV
kinetic energy, right above the energy for the minimum of ionization. As a time reference,
the radio frequency (RF) signal of the electron source was adopted. A new mode
1 Internet address http://www.hzdr.de/elbe
! m
101

Beamline
Be exit
window
P 6
P 3
P 4
MRPC
124.5 28.5 10
Figure B.3.: Experimental setup at the ELBE facility, with approximate distances in
cm. The MRPC unit is placed on a remote controlled moving table which
allows 50 cm movement both in horizontal and vertical direction. The sizes
of the plastic scintillators are (x/y/z) 20 mm × 20 mm × 5 mm (P3,4), 35 mm
× 35 mm × 5 mm (P6).
of operation of the ELBE accelerator was used, called one electron mode. In this mode,
the gate voltage of the electron gun is reduced much below usual operating parameters.
Then, most accelerated bunches are empty and the rest has only one electron per bunch
[Nau-08]. Two scintillators were used as trigger in coincidence with the RF signal. The
flux of single electrons was 5-20 Hz/cm 2 for the present measurements, much higher than
can be obtained with cosmic rays.
The electron beam first passes through 5 mm thick scintillator (P6) and then a thicker
20 mm scintillator (P3,4). The coincidence requirement defining an electron event is
formed by P6 ∧ P3 ∧ P4 ∧ RF, meaning both photomultipliers of scintillator P3,4 and
scintillator P6 detect a signal above threshold.
In order to determine the time resolution, the time signal from the MRPC under study
is compared with the reference time from the radio frequency signal (hereafter called RF
signal) of the electron source. The high precision RF signal is supplied by the accelerator,
with a jitter of less than 25 ps as measured with a digital oscilloscope. Therefore, no fast
start detector is needed and the time resolution of the scintillators included in the setup
is not critical. For the processing of the timing signal, two options are available:
1. FOPI FEE1-based readout: The RF signal is fed into a 25 ps per channel timeto-digital
converter (TDC, CAEN V1290 2 ). The signals from the readout strips
2 CAEN S.p.A., internet address http://www.caen.it
102

Counts
Counts
6000
5000
4000
3000
2000
1000
0
5000
4000
3000
2000
1000
0
0 10000 20000 30000
QDC scintillator P1,2 [25 fC]
Figure B.4.: Scintillator charge spectra (units equivalent to P3,4 in figure B.3) for two
different gate voltages of the electron gun: 9.5 V (top) and 6.5 V (bottom).
In the top panel, the peaks due to 1, 2, 3, 4, 5, and 6 electrons per bunch
are visible, as well as some low-charge background that is not correlated
in time. In the bottom panel, just the peak due to one electron per bunch
survives, due to the lower gate voltage and additional screens restricting the
beam envelope. The mode of operation for the detector tests corresponds
to the lower panel.
of the MRPC under study are amplified by a FOPI FEE1 [Cio-07] frontend and
fed into the subsequent TDC channels. The current signal is amplified by a factor
of 30-70 in the front-end electronics and a further factor of 10 in the amplifier.
The amplified charge signal is then fed into a 25 fC per channel charge-to-digital
converter (QDC, CAEN V965).
2. TACQUILA-based readout: The TACQUILA-based readout [Koc-05] was used
with the option for MRPC input. Since there was only one TACQUILA unit
available at the time of the ELBE test shown here, the distance between readout
ends was different, limiting the performance.
The logic for the trigger and also various programmable scalers are implemented via
software in a field programmable gate array (FPGA) unit that allows to change the trigger
conditions on the fly for debugging the setup. The entire VME-bus data acquisition
is controlled by a GSI multi-branch system (MBS) [Ess-00] unit. In order to reduce
complexity and save cable length, all the electronics units are sited in the experimental
cave, close to the setup. The experiment is then completely remote-controlled over the
institute intranet.
The beam quality is monitored during each experiment by checking the charge spectrum
of the initial scintillator P1,2 (figureB.4). In this way it was assured that it still fulfills
the single-electron per bunch mode.
103

B.3. Design Issues Addressed with 40 cm × 20 cm Prototypes
In order to test the salient design parameters of the planned MRPC units, in a first
step smaller prototypes have been built. Their structure follows exactly that of one full
MRPC module (figure B.1), only that the individual strips are 40 cm long (instead of
200 cm) and that the units are only 20 cm wide (instead of 50 cm).
For the central signal anode/converter strips, commercially available stainless steel strips
of 25 mm × 4 mm cross section have been used. They are fixed at the ends on a Durostone
strip that is held by pins on the housing of the prototype. In some cases, the anode
strips were additionally glued to one another with epoxy distance holders. The two
outer converters were made from 2 mm thick prefabricated stainless steel plates. They
are tightened together by springs, holding the whole stack and fixing them to the central
anode strips. The MRPC was implemented using 0.58 mm or 1.0 mm thick soda-lime
glass.
The gas gaps were 0.3 mm thick, maintained by standard fishing line, spaced by 5 cm
(omitted in figure B.1). For all studies reported here, no attempt at varying the gas
mixture was made [Lop-11], instead the standard mixture of 85% freon R134a, 10% SF6,
5% iso-butane [Fon-02] has been used. During the experiments, a gas flux of ≥50 ml/min
has been maintained.
The following design parameters have then been studied using the small prototypes, with
the adopted solution indicated:
• The number of gas gaps −→ 2×2,
• the width of the anode strips −→ 25 mm
• the interstrip spacing −→ 1.5 mm)
• the glass thickness −→ 1.0 mm
• the material for the high voltage electrode −→ semiconductive mylar film
• the effect of impedance matching transformers −→ none adopted
• the effect of different readout schemes −→ FOPI FEE1 [Cio-07], PADI-3 [Cio-09],
and TACQUILA [Koc-05] (the latter tested only with 200×50 cm 2 prototype) all
produce acceptable results.
Due to the high luminosity of the ELBE single-electron beam when compared to cosmic
rays, these design issues could be studied with high statistics and relatively quick
turnaround directly when they arose during the prototyping effort. As the ELBE facility
is also well suited for a study of the efficiency as a function of the flux of minimum
ionizing particles [Nau-11], this effect was also tested. Since standard float glass was
used instead of special ceramics [Nau-11], the typical drop of efficiency [Alv-04] for rates
≥ 300 Hz/cm 2 for this number of gas gaps was again observed. However, for the standard
application of NeuLAND a much lower counting rate is expected, therefore this question
104

is purely of academic interest. Further electrical and in-beam tests, aging issues, and
simulations are addressed in Ref. [Yak-11].
B.4. Construction and Test of a Full-Size 200 cm × 50 cm
Prototype
The center of the detector consists of 19 stainless steel anode strips (0.4×2.5× 200 cm 3 ),
which also serve as converters, converting the primary neutron to a secondary charged
particle.
On either side of the anode there is a standard MRPC glass-gap structure with two gas
gaps, in order to detect the secondary charged particle. Semiconductive mylar sheets
provide high voltage and ground to the glass. Further out on each side is the signal
cathode, made by copper strips. The covers of the box are made from 2 mm stainless
steel for conversion. For mechanical reasons, two such structures are built in one frame
with a common gas volume. There is a 2.5 mm gas gap between signal cathode and
converter plate box that is needed to increase cathode impedance. Rubber tubes with
fishing line inside keep the gas gap at its nominal width (figure B.2).
The strip impedance is about 13 Ω, defined by the geometry of detector and the limitation
on the adopted strip width of 25 mm. In order to reach 50 Ω impedance, the strips should
have a width of just 3-4 mm, which is unrealistic as the readout would require too
many electronic channels. Because of this impedance mismatch there is an unavoidable
reflection at twice the distance from the place of interaction to the far end (as seen from
the readout electrode) of the strip, i.e. 2×1 m for the case when the beam is in the center
and 2×7.5 cm for the case when the beam is on the left side.
Due to the large width of 50 cm and the relatively thin housing of just 2 mm steel, the
box bulges outward by 1.5 mm in the center. This can be a problem for the mechanical
stability of the inner structure. It is solved by a pump generating about 100 Pa
underpressure inside the chamber, compensating the deformation.
The ELBE in-beam tests of full size prototypes (200 × 50 cm) show satisfactory results
for efficiency (>90%) and time resolution (σ < 100 ps) for minimum ionizing particles,
for the whole area of the detector (figure B.6). It should be noted that the time resolution
aim can be reached both by the standard FOPI FEE1-based readout and also the
TACQUILA-based readout, even for the 2 m long prototype HZDR201b.
In 2012, a test with neutrons from the breakup of deuteron beams will be performed at
GSI (see section 8.1), including mainly scintillator-based NeuLAND solutions, but for
comparison also this prototype and the converter-less one are described in section B.7.
105

Time [ns]
Counts
41
40
39
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0 100 200 300 400 500 600 700
Charge [pC]
0
0 100 200 300 400 500 600 700
Charge [pC]
220
200
180
160
140
120
100
80
60
40
20
0
Counts
Counts
8000
7000
6000
5000
4000
3000
2000
1000
0
12000
10000
8000
6000
4000
2000
0
39 40 41
Time [ns]
Entries 113760
2
χ / ndf
1226 / 35
Constant 1.087e+04 ± 4.277e+01
Mean 0.006169 ± 0.000305
Sigma 0.1008 ± 0.0003
-1 -0.5 0
Time [ns]
0.5 1
Figure B.5.: Typical spectra for the 2 x 2 gap prototype HZDR201a at ∼100 kV/cm electrical
field strength (ELBE run 954). Top left: Time over charge for valid
MRPC hits. Bottom left: Charge spectrum. Top right: Uncorrected time
spectrum. Bottom right: Time spectrum, corrected for time walk. — The
measured efficiency for this run is 94%, the time resolution σt = 101 ps.
B.5. Monte Carlo Simulations
Extensive Monte-Carlo simulations have been performed in order to understand the
behavior of the small-size as well as the full-size prototypes at ELBE facility in the
testing phase. Furthermore, the simulations were used to predict the properties of a
possible, envisaged full-scale detector setup based on MRPC modules and converters.
As a tool, mainly the software package GEANT4 [Ago-03] was employed to track the
primary (electrons or neutrons) and the secondary particles produced in various reactions.
Nevertheless, as a cross-check of the produced particles and the energy deposition,
R 3 BRoot framework was also applied using GEANT4 and GEANT3 transportation
codes via Virtual Monte Carlo. Since no significant difference was observed, standalone
GEANT4 was chosen to simulate the details for practical reasons.
In the first step, the experimental setup at ELBE facility including the beam monitoring
scintillator detectors and the tested MRPC prototypes (small-size and full-size) were
106

Figure B.6.: ELBE test-beam results for the 200 cm × 50 cm prototype HZDR201b. —
Left panel: Using FOPI FEE1 readout, tests were done on several of the 19
strips of the device, with the electron beam incident either near the center
or near the left side of the prototype. — Right panel: One of the tests is
repeated with TACQUILA readout, with the beam near the center of the
prototype.
constructed in a realistic way taking into account all important materials and objects.
Since the beam particles were 30 MeV electrons in the testing phase the standard electromagnetic
physics list was used. These primary electrons were generated considering
the beam size.
However, the MRPCs are special gas detectors, and their principle of operation is not
implemented in GEANT4 by default. Therefore, additional coding has been done to
simulate the signal generation and propagation similar to the work by Lippmann and
Riegler [Lip-03, Rie-03].
The Monte Carlo simulation provides the energy deposit in the gas gaps, which is converted
into primary electron clusters governed by the ionization energy in the specific
gas. These clusters are randomly distributed in the gas gap along the primary track.
Due to the applied high electric field, electron avalanches are produced which are grown
and propagated in small steps toward the anode. The avalanche size and propagation
depends on the so-called Townsend and attachment coefficients (multiplication and recombination)
as well as the drift velocity which are known from the literature. The
space charge effect, i.e., a limit on the growth is also implemented as a parameter by
cutting the avalanche size at a certain value. The correlation between the avalanches
in the same gas gap is also taken into account with a parameter. If two avalanches are
closer than a certain value, they are further handled as a single avalanche.
The induced charge signal is calculated and propagated along the readout strip in each
step as the avalanches move. In order to match the experimentally observed efficiency
107

Efficiency
100
80
60
40
20
0
7.5 8 8.5 9 9.5 10 10.5 11
HV [kV]
Efficiency
100
80
60
40
20
200 MeV neutrons simulation
400 MeV neutrons simulation
1000 MeV neutrons simulation
fit
0
0 20 40 60 80 100
Number of layers
Figure B.7.: Monte Carlo simulations of the MRPC-based neutron-detector prototype.
— Left panel: Simulated (lines) and experimental (dots) efficiency for
30 MeV electrons from ELBE tests. — Right panel: Simulated efficiency
for high-energy neutrons, as a function of the number of MRPC layers.
at different high voltages, the parameters were adjusted and a threshold cut was applied
in the induced charge spectrum. The result of such comparison between experimental
data and simulation can be seen in the left panel of B.7. Excellent agreement could
be achieved and therefore the optimized parameters and threshold values were used to
predict the properties of the full-scale setup for neutron primary particles.
For neutrons as incoming particles, the QGSP BIC HP physics list was adopted. It
applies the quark gluon string model for high energy interactions of protons, neutrons,
pions, and Kaons and nuclei (QGSP) and uses GEANT4 Binary cascade for primary
protons and neutrons with energies below 10GeV (BIC). HP sub-package is to transport
neutrons below 20 MeV down to thermal energies. The results show that the desired 90%
efficiency for 400 MeV neutrons can be reached by using 50 layers of MRPC modules,
which corresponds to about 1.2 m total depth (figure B.7, right panel).
The design goal, however, is not only to detect single neutrons but also to be able to
disentangle multi-neutron events and reconstruct the relative energy of outgoing particles
with an excellent resolution in certain nuclear reactions. The resolution requirement
depends on the beam energy, the reaction and the relative energy in question. Therefore,
hypothetic eventfiles were produced using TGenPhaseSpace class of the Root framework.
The beam energy, the number of outgoing particles and their relative energy were varied
in order to cover all possible aspects of the setup.
108

events
1200
1000
800
600
400
200
σ = 17 keV
0
0 500 1000
E (keV)
rel
Figure B.8.: Reconstructed relative energy spectrum for the Neutron MRPC from a
Monte Carlo simulation. Simulated is the one-neutron emission from 132 Sn
for 600 AMeV energy with a relative energy of 100 keV. The detector is
placed at 35 m distance to the target.
In order to be able to reconstruct the relative energy, an algorithm was developed, which
selects those hits in the simulation that can be used to determine the momenta of the
incoming neutrons correctly. The hit multiplicity increases as the number of impinging
neutrons increases and there is a fair separation between the appearing peaks in the
spectrum as is seen in figure B.7. Therefore, this was used to determine the number of
incoming neutrons in an event (n). This provides us the so-called identification matrix
which contains correlation percentages between the expected and deduced number of
incoming neutron (see e.g., B.1). The hit selection algorithm is based on the clustering
of the hits with an adjustable distance parameter, which is combined with a causality
check between the clusters. The remaining hits were ordered according to their latent
speed calculated from the hit position and time of detection. The first n number of hits
were used for the momentum and relative energy reconstruction. As an example such a
reconstructed relative energy spectrum is shown in figure B.8.
According to the simulations, the MRPC-based setup is able to detect single neutrons
with high efficiency. There is some limited capability, as well, to disentangle multineutron
events and reconstruct the relative energy of nuclear reaction products. The
multi-neutron performance is, however, much worse than that of the scintillator-based
concept (see section 4.5).
109

200 AMeV, Erel = 100 keV
emitted
% 1n 2n 3n 4n
1n 49 25 12 4
2n 24 31 22 12
3n 7 23 25 20
4n 1 12 21 22
5n 0 4 12 19
6n 0 1 5 12
7n 0 0 2 7
8n 0 0 1 3
9n 0 0 0 1
reconstructed
1000 AMeV, Erel = 100 keV
emitted
% 1n 2n 3n 4n
1n 62 25 8 2
2n 25 39 24 11
3n 4 26 33 25
4n 0 8 23 29
5n 0 1 10 20
6n 0 0 2 10
7n 0 0 0 3
Table B.1.: Simulated multi-neutron hit capability for the MRPC-based neutron detector
with 50 layers, with the reconstruction algorithm described in the
text. Left side, 200 AMeV. Right side, 1000 AMeV. See figure B.9 for the
underlying multiplicity spectrum for 1000 AMeV.
B.6. Further MRPC Prototype and Offline Tests
The MRPC prototype SINP1 of size 40 cm × 20 cm has segmented anode strips, each strip
being 40 cm long and 2 cm wide (figure B.10). The anode strips are made of PCB with
a thin layer of gold coating and are thus almost converter free. The cathode plates were
made by introducing a thin layer of conducting material on 1 mm thick float glass. The
detector structure was housed in an aluminium chamber. Further details of the design
can be found in Ref. [Dat-10]. The detector volume of 1000 cm 3 was continuously flushed
with a gas mixture of 89% R134a, 4% sulfur hexafluoride (SF6) and 7% isobutane.
The response of the prototype has been studied extensively using cosmic-ray muons,
in coincidence with a fast inorganic scintillator detector, Cerium doped Lanthanum
Bromide (LaBr3:Ce). For the design as neutron detector we want to keep converter
material above and below the MRPC detector. List mode data of the MRPC and
LaBr3:Ce signals were taken corresponding for cosmic-ray muons and γ-rays. The master
trigger for the data acquisition was produced by a logical AND of time signals from the
MRPC and LaBr3:Ce detectors. Figure B.10 shows the TAC spectra of the MRPC in
coincidence with the LaBr3:Ce detector. The time resolution of the MRPC was measured
to be σt = 150±31 ps without slew correction. The time resolutions of the LaBr3:Ce
detector and electronics were 120 and 35 ps, respectively.
The same prototype was also studied with the ELBE pulsed electron beam. At ELBE,
after a specially designed slew correction a time resolution of σt = 92±3 ps was obtained.
All the above mentioned values for the time resolution correspond to experimental parameters
for which an absolute detection efficiency of more than 90% was obtained for
110
reconstructed

counts
500
400
300
200
100
1000 AMeV, 100 keV, 35m, 2x2x1.2
1n
2n
3n
4n
0
0 20 40 60 80 100
multiplicity
Figure B.9.: Monte Carlo simulations of the MRPC-based neutron detector prototype.
Multiplicity spectrum for one selected case (neutrons impinging at
1000 MeV/A, Erel = 100 keV).
Multi Strip
Anode Plate
Glass epoxy
Float glass
Gas gap
Signal
Cathode (ESD coated)
Figure B.10.: MRPC prototype SINP1. Left panel: Sectional view. Right panel: TAC
spectra of the prototype in coincidence with a LaBr3:Ce detector. The
solid line shows the data for cosmic-ray muons, the dashed line for 60 Co
γ-rays.
minimum ionizing particles. Further details are presented in Ref. [Dat-10].
111

B.7. MRPC Solution using Glass as Converter
As an alternative, a new concept for the detection of high energy neutrons based on
RPC’s was also proposed. This concept considers only glass as converter material.
There is no iron in the whole detector.
Based on a modular geometry, each RPC module contains a certain number of glass
electrodes separated by 300 µm, operated in a standard gas mixture. The gas gaps are
encapsulated in a gas tight plastic box, which only contains feed-throughs for the active
gas (a standard mixture of 90% freon and 10% SF6) and the high voltage. The readout
strips are allocated outside the plastic box. The whole system is electrically isolated by
a metallic shielding. Based on simulation studies using the R 3 BROOT framework, the
thickness of the glass plates has been chosen to be 3 mm [Mac-11]. A schematic view
of the iron-less RPC concept is shown in the left panel of figure B.11. A RPC module
(100 cm × 50 cm) based on the iron-less RPC concept already exists at LIP-Coimbra,
and it can be seen in the right panel of figure B.11.
Metallic shielding
Figure B.11.: Schematic drawing (left) and photograph (right) of the iron-less RPC module
with the readout electrodes.
A number of up to 8 modules with dimensions 200 × 50 cm is presently under construction
at LIP-Coimbra. The performance of this new concept in the detection of high
energy neutrons will be tested during the allocated deuteron break-up experiment at the
R 3 B setup during 2012.
B.8. Summary and Outlook
The development of the MRPC option for NeuLAND provided many valuable insights.
One of the largest area MRPC structures ever built was developed for the purpose, and
it was unambiguosly shown that the structure will even work as an MRPC in its strongly
modified form using thick passive converters.
The first MRPC-based neutron detector we are aware of has been built, and it was
shown that an MRPC-based detection concept can work for 1 GeV neutrons. Also, the
Neutron MRPC development for NeuLAND was an important driver in the development
112

of the single-electron capability at the ELBE accelerator, which can henceforth be used
for detector tests for many different detectors as a kind of benchmark.
The MRPC-based design was not adopted for building NeuLAND because of the much
superior performance of the pure scintillator based approach. However, it should not be
seen as a failed development effort, and it is presently under study whether this detection
concept can be applied in a different setting, where no multi-neutron hit capability is
demanded.
113

114

Bibliography
[Abb-09] M. Abbrescia et al., Nucl. Phys. B (Proc. Suppl.) 190, 38 (2009).
[Adr-05] P. Adrich et al., Phys. Rev. Lett. 95, 132501 (2005).
[Ago-03] S. Agostinelli et al., Nucl. Inst. Meth. A 506, 250 (2003).
[Aks-08] Y. Aksyutina et al., Phys. Lett. B 666, 430 (2008).
[Aks-09] Y. Aksyutina et al., Phys. Lett. B 679, 191 (2009).
[Aks-09b] Y. Aksyutina PhD Thesis, University Frankfurt, Germany, (2009).
[Ali-07] A. Alici et al., Nucl. Inst. Meth. A 579, 979 (2007).
[Alv-04] H. Alvarez et al., Nucl. Inst. Meth. A 535, 277 (2004).
[An-08] S. An et al., Nucl. Inst. Meth. A 594, 39 (2008).
[And-10] A.N. Andreyev et al., Phys. Rev. Lett. 105, 252502 (2010).
[Bau-05] T. Baumann et al., Nucl. Inst. Meth. A 543, 517 (2005).
[Bay-10] E. Bayer and M. Traxler, GSI Annual Report 2009 (2010)
http://www.gsi.de/informationen/wti/library/scientificreport2009
/PAPERS/INSTRUMENTS-METHODS-45.pdf.
[Ber-08] D. Bertini et al., Journal of Physics: Conference Series 119, 032011 (2008).
[Ber-85] C.A. Bertulani and G. Baur, Nucl. Phys. A 442, 739 (1985).
[Bet-76] G. Betti et al., Nucl. Inst. Meth. 135, 319 (1976).
[Bir-64] J.B. Birk, The theory and practice of scintillation counting, Pergamon Press,
Oxford, (1964).
[Bla-92] T. Blaich et al., Nucl. Inst. Meth. A 314, 136 (1992).
[Bla-02] A. Blanco et al., Nucl. Inst. Meth. A 485, 328 (2002).
[Bor-03] K. Boretzky et al., Phys. Rev. C 68, 024317 (2003).
[Bor-10] K. Boretzky et al., Characterization of NeuLAND prototypes and the LAND
detector using fast ”monoenergetic” neutrons, proposal for SIS experiment S406,
unpublished (2010).
115

[Bot-04] S. Botvina andI.N. Mishustin, Phys. Lett. B 584, 233 (2004), Nucl. Phys. A
843, 98 (2010).
[Bro-90] U. Brosa et al., Phys. Rep. 197, 167 (1990).
[Bro-00] B.A. Brown, Phys. Rev. Lett. 85, 5296 (2000).
S. Typel, and B.A. Brown, Phys. Rev. C 64, 027302 (2001).
[Bru-97] R. Brun and F. Rademakers, Nucl. Inst. Meth. A 389, 81 (1997).
[BTR-06] FAIR - Baseline Technical Report, Volume 4, Experiment Proposals on
Nuclear Structure and Astro Physics (NUSTAR) (2006)
http://www.fair-center.de/fileadmin/fair/publications FAIR/FAIR BTR 4.pdf
[Cae-10] C. Caesar et al., Nucl. Inst. Meth. A, doi:10.1016/j.nima.2010.09.163 (2010).
[Cam-07] M. Caamaño et al., Phys. Rev. Lett. 99, 062502 (2007).
[Car-10] A. Carbone et al., Phys. Rev. C 81, 041301(R) (2010).
[CDR-01] FAIR CDR - An International Accelerator Facility for Beams of Ions and
Antiprotons, Conceptual Design Report. (2001)
http://www.fair-center.de/fileadmin/fair/publications FAIR/FAIR CDR.pdf
[Cec-79] R.A. Cecil et al., Nucl. Inst. Meth. 161, 439 (1979).
[Cio-07] M. Ciobanu et al., IEEE Trans. Nucl. Sci. 54, 1201 (2007).
[Cio-09] M. Ciobanu et al., IEEE Nuclear Science Symposium Conference Record, 401
(2009).
[Coz-11] M.D. Cozma, Phys. Lett. B 700, 139 (2011).
[Dat-03] U. Datta Pramanik et al., Phys. Lett. B 551, 63 (2003).
[Dat-10] U. Datta Pramanik et al., Nucl. Inst. Meth. A, doi:10.1016/j.nima.2010.10.055
(2010).
[Dan-02] P. Danielewicz et al., Science 298, 1592 (2002).
[Ede-72] R.M. Edelstein et al., Nucl. Inst. Meth. 100, 355 (1972).
[EPI-11] A. Johnson et al., EPICS - Experimental Physics and Industrial Control System
http://www.aps.anl.gov/epics/index.php.
[Ess-00] H. Essel and N. Kurz IEEE Trans. Nucl. Sci. 47, 337 (2000).
[Evs-81] V.S. Evseev et al., Nucl. Phys. A 352, 379 (1981).
[FLU-05] A. Ferrari et al., CERN Report 10, (2005)
http://cdsweb.cern.ch/record/898301/files/CERN-2005-010.pdf
[FLU-07] G. Battistoni et al., AIP Conf. Proceedings 896, 31 (2007).
[Fon-02] P. Fonte and V. Peskov, Nucl. Inst. Meth. A 477, 17 (2002).
116

[Gad-08] A. Gade et al., Phys. Rev. C 77, 044306 (2008).
[GEA-93] GEANT, CERN Program Library Long Writeup W5013 , (1993)
http://wwwasdoc.web.cern.ch/wwwasdoc/geant/geantall.html
[Gor-98] S. Goriely, Phys. Lett. B 436, 10 (1998).
[Guo-11] C. Guo et al., preprint submitted to Science China (2011).
[Gur-07] Yu.B. Gurov et al., Eur. Phys. J. A 32, 261 (2007).
[Ham-10] F. Hammache et al., Phys. Rev. C 82, 065803 (2010).
[Ham-11] R8619 Photomultiplier Assembly Data Sheet
http://sales.hamamatsu.com/en/products/electron-tube-division
/detectors/photomultiplier-tubes/part-r8619.php .
[Han-87] P.G. Hansen and B. Jonson, Europhys. Lett. 4, 409 (1987).
[Har-01] M.N. Harakeh and A. van der Woude, Giant Resonances; Fundamental High-
Frequency Modes of Nuclear Excitations, Claredon Press, Oxford (2001).
[Hil-92] D. Hilscher and H. Rossner, Ann. Phys. Fr. 17, 471 (1992).
[Hol-11] J.D. Holt and A. Schwenk, arXiv:1108.2680v1(2011).
[Hor-01] C.J. Horowitz and J. Piekarewicz, Phys. Rev. Lett. 86, 5647 (2001).
[Ish-03] C. Ishizuka et al., Nucl. Phys. A 723, 517 (2003).
[Joh-10a] H.T. Johansson et al., Nucl. Phys. A 842, 15 (2010).
[Joh-10b] H.T. Johansson et al., Nucl. Phys. A 847, 66 (2010).
[Joh-87] J.O. Johnson et al., ORNL/TM-10196(1987).
[Kli-07] A. Klimkiewicz et al., Phys. Rev. C 76, 051603(R) (2007).
[Koc-05] K. Koch et al., IEEE Trans. Nucl. Sci. 52, 745 (2005).
[Koc-11] K. Koch et al., GSI Annual Report 2010 (2011)
http://www.gsi.de/informationen/wti/library/scientificreport2010
/PAPERS/PHN-IS-EE-07.pdf.
[Kor-03] A.A. Korsheninnikov et al., Phys. Rev. Lett. 90, 082501 (2003).
[Lei-93] Y. Leifels et al., Phys. Rev. Lett. 71, 963 (1993).
[Lem-09] R.C. Lemmon et al., proposal for SIS experiment S394, unpublished (2009).
[Lei-93b] Y. Leifels, PhD Thesis, University Bochum, Germany,(1993).
[Li-05] Q. Li et al., J. Phys. G 31, 1359 (2005).
[Li-08] B.-A. Li et al., Phys. Rep. 464, 113 (2008).
117

[Lip-03] C. Lippmann, PhD Thesis, University Frankfurt, Germany,(2003).
[Lit-09] E. Litvinova et al., Nucl. Phys. A 823, 26 (2009).
[Lop-11] L. Lopez et al., Nucl. Inst. Meth. A, in press (2011).
[Mac-11] J. Machado Master Thesis in Physics Engineering, University of Lisbon(2011).
[Mar-02] F.M. Marquez et al., Phys. Rev. C 65, 044006 (2002).
[Nau-08] L. Naumann, U. Lehnert, R. Kotte, and A. Wagner. Anordnung und Verfahren
zur Erzeugung einzelner relativistischer Elektronen. Patent pending: DE10 2008
054 676.3, 2008.
[Nau-11] L. Naumann et al., Nucl. Inst. Meth. A 628, 138 (2011).
[Nik-10] E.Yu. Nikolskii et al., Phys. Rev. C 81, 064606 (2010).
[Ogu-11] R. Ogul et al., Phys. Rev. C 83, 024608 (2011).
[Ots-10] T. Otsuka et al., Phys. Rev. Lett. 105, 032501 (2010).
[Paa-07] N. Paar et al., Rep. Prog. Phys. 70, 691 (2007).
[Pan-11] V. Panin et al., GSI Annual Report 2010 (2011)
http://www.gsi.de/informationen/wti/library/scientificreport2010
/PAPERS/PHN-NUSTAR-NR-05.pdf.
[Pie-06] J. Piekarewicz, Phys. Rev. C 73, 044325 (2006).
[R3B-05] Technical Proposal for the Design, Construction, Commissioning and Operation
of R 3 B (2005)
http://www.gsi.de/onTEAM/grafik/1130224398/13-PROP-R3B-TP-07Dez2005.pdf
[Rau-08] T. Rauscher, Phys. Rev. C 78, 032801 (2008).
[Rex-11] RP-408 PLASTIC SCINTILLATOR Data Sheet
(http://www.rexon.com/RP 408.pdf).
[Rie-03] R. Riegler et al., Nucl. Inst. Meth. A 500, 144 (2003).
[Roz-05] T. Rozek, Report Juel-4184, Forschungszentrum Jülich (2005).
[Rus-11] P. Russotto et al., Phys. Lett. B 697, 471 (2011).
[Sch-00] K.-H. Schmidt et al., Nucl. Phys. A 665, 221 (2000).
[Sch-03] F. Schümann et al., Phys. Rev. Lett. 90, 232501 (2003).
[Sch-06] F. Schümann et al., Phys. Rev. C 73, 015806 (2006).
[Sch-10] C. Schmitt et al., Phys. Rev. C 81, 064602 (2010).
[Sub-08] R. Subedi et al., Science 320, (5882) 1476 (2008).
[Sur-09] R. Surman et al., Phys. Rev. C 79, 045809 (2009).
118

[Tan-85] I. Tanihata et al., Phys. Rev. Lett. 55, 2676 (1985).
[Tay-11] PhD Thesis, University Liverpool, United Kingdom, (2011).
[Ter-07] G.M. Ter-Akopian et al., Eur. Phys. J. Special Topics 150, 61 (2007).
[VMC-03] I. H˘rivná˘cová et al., Computing in High Energy and Nuclear Physics (2003)
http://www.slac.stanford.edu/econf/C0303241/proc/papers/THJT006.PDF
[Wam-11] F. Wamers et al., GSI Annual Report 2010 (2011)
http://www.gsi.de/informationen/wti/library/scientificreport2010
/PAPERS/PHN-NUSTAR-NR-06.pdf
[Wie-09] O. Wieland et al., Phys. Rev. Lett. 102, 092502 (2009).
[Yak-11] D. Yakorev et al., Nucl. Inst. Meth. A 654, 79 (2011).
[Zei-94] C. Zeitnitz and T.A. Gabriel, Nucl. Inst. Meth. A 349, 106 (1994).
119