Program - Brookhaven National Laboratory

on its surface. The amplification that takes place in the amplification region significantly improves the
signal-to-noise ratio of the detector. A chamber capable of holding up to 10 sample-detector modules was
constructed and used to house the plutonium samples (4× 240 PuO2, 4× 242 PuO2, with a total mass of 3.1
and 3.6 mg respectively for each isotope) and a reference 235 U sample (3.3 mg). The detector was operated
with an Ar:CF4:isoC4H10 gas mixture. The behaviour of the detectors was studied in detail by means of
Monte Carlo simulations performed with the FLUKA code [6], focusing particularly on the reproduction
of the pulse height spectra for α-particles and fission fragments for the evaluation of the detector efficiency
and the quality of the peak-search routine.
[1] Generation-IV International Forum, http://www.gen-4.org, International Framework for Nuclear Energy
Cooperation (IFNEC), http://www.ifnec.org [2] NEA Nuclear Data High Priority Request List,
http://www.nea.fr/html/dbdata/hprl [3] OECD/NEA Working Party on Evaluation and Co-operation
(WPEC) Subgroup 26 Final Report: Uncertainty and Target Accuracy Assessment for Innovative Systems
Using Recent Covariance Data Evaluations, http://www.nea.fr/html/science/wpec/volume26/volume26.pdf
[4] U. Abbondanno et al., CERN n TOF Facility: Performance Report, CERN-SL-2002-053 ECT. [5] Y.
Giomataris, Ph. Rebourgeard, J.P. Robert, G. Charpak, MICROMEGAS: a high-granularity positionsensitive
gaseous detector for high particle-flux environments, Nucl. Instr. Meth. A, 376 29-35, 1996
[6] G. Battistoni et al., The FLUKA code: Description and benchmarking, Proceedings of the Hadronic
Shower Simulation Workshop 2006, FERMILAB 6–8 September 2006, AIP Conf. Proc. 896, pages 31–49
and A. Fasso, A. Ferrari, J. Ranft, and P.R. Sala, FLUKA: A multi-particle transport code, Tech. Rep.
CERN-2005-10, INFN/TC 05/11, SLAC-R-73, 2005.
HA 5 5:00 PM
A Micromegas Detector for Neutron Beam Imaging at the n TOF Facility at CERN
F. Belloni, S. Andriamonje, E. Berthoumieux, M. Calviani, E. Chiaveri, N. Colonna, Y. Giomataris, C.
Guerrero, F. Gunsing, F. J. Iguaz, M. Kebbiri, J. Pancin, T. Papaevangelou, A. Tzinganis, V. Vlachoudis
and the n TOF Collaboration
CEA - Saclay, Irfu, F-91191, Gif Sur Yvette, France
Micromegas (Micro-MEsh Gaseous Structure) detectors are gas detectors consisting of a stack of one ionization
and one proportional chamber. A micromesh separates the two communicating regions, where two
different electric fields establish respectively a charge drift and a charge multiplication regime. The n TOF
facility at CERN provides a white neutron beam (from thermal up to GeV neutrons) for neutron induced
cross section measurements. These measurements need a perfect knowlodge of the incident neutron beam,
in particular regarding its spatial profile. A position sensitive micromegas detector equipped with a 10 B
based neutron/charged particle converter has been extensively used at the n TOF facility for characterizing
the neutron beam profile and extracting the beam interception factor for samples of different size. The
boron converter allowed to scan the energy region of interest for neutron induced capture reactions as a
function of the neutron energy, determined by the time of flight. Experimental results will be presented
and compared to simulations, performed by means of the FLUKA code.
HA 6 5:15 PM
Measurement of the 241 Am and the 243 Am Neutron Capture Cross Sections at the n TOF
Facility at CERN
E. Mendoza, D. Cano-Ott
106