NeuLAND - FAIR

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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
Page 1 and 2: FAIR/NUSTAR/R 3 B/TDR NeuLAND Techn
Page 3 and 4: Germany EMMI and FIAS: Enrico Fiori
Page 5 and 6: INR Moscow: Alexander Botvina Russi
Page 7 and 8: Contents Executive Summary 11 1. In
Page 9: B.7. MRPC Solution using Glass as C
Page 12 and 13: Apart from the excellent energy res
Page 14 and 15: processes in the universe, such as
Page 19 and 20: 2. Physics Scenarios: Requirements
Page 21 and 22: e studied at R 3 B at FAIR include
Page 23 and 24: all theoretical calculations predic
Page 25 and 26: at the surface of the nucleus. The
Page 27 and 28: the evolution of fission channels (
Page 29 and 30: 3. Summary of NeuLAND Prototype Res
Page 31 and 32: counts 70 60 50 40 30 20 10 0 15 15
Page 33 and 34: Figure 3.4.: Shown is the time reso
Page 35 and 36: 4. Monte Carlo Simulations Within t
Page 37 and 38: normalized counts normalized counts
Page 39 and 40: GEANT3 interface. Here, we compare
Page 41 and 42: Counts 1000 900 800 700 600 500 400
Page 43 and 44: counts 5 10 4 10 3 10 2 10 10 LAND
Page 45 and 46: incident neutron fully active detec
Page 47 and 48: investigated. Three values for the
Page 49 and 50: spectrum, absorption length, refrac
Page 51 and 52: Counts 600 500 400 300 200 100 with
Page 53 and 54: Since, as discussed above, several
Page 55 and 56: events 800 600 400 200 0 0 200 400
Page 57 and 58: clusters N 100 50 0 0 500 1000 1500
Page 59 and 60: In the following section we discuss
Page 61 and 62: events 15000 10000 5000 input outpu
Page 63 and 64: events 2000 1500 1000 500 σ = 15 k
Page 65 and 66: 5. Technical Specifications and Des
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construction, or for subsequent rep
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positioning of 50 submodules mounti
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Figure 5.6.: Detector frame with fi
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5.4. Peripheral Systems 5.4.1. Read
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Figure 5.12.: The photo shows the T
Page 77:
6. Radiation Environment and Safety
Page 81 and 82:
8. Calibration 8.1. Calibration wit
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Figure 8.3.: ToF distribution in 10
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Figure 8.4.: Event display for seve
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10. Installation procedure, its Tim
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11. Cost and Funding 11.1. Cost Est
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The timeline for milestone 1 includ
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96 2. Sample Tests Random samples o
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PNPI St. Petersburg: G.D. Alkhazov,
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HV 1.$ mm 2$ mm 0+$1-2)-2'.%/ 5%4'.
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Beamline Be exit window P 6 P 3 P 4
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B.3. Design Issues Addressed with 4
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Time [ns] Counts 41 40 39 2200 2000
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Efficiency 100 80 60 40 20 0 7.5 8
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200 AMeV, Erel = 100 keV emitted %
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B.7. MRPC Solution using Glass as C
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114
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[Bot-04] S. Botvina andI.N. Mishust
Page 118 and 119:
[Lip-03] C. Lippmann, PhD Thesis, U
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NeuLAND - FAIR

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