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Monte Carlo Simulations of the Energy Resolution Function of n_TOF at CERN

C. Carrapiço, E. Berthoumieux, I. F. Gonçalves, F. Gunsing, A. Mengoni, P. Vaz, V. Vlachoudis, The n_TOF Collaboration

Nuclear Technology / Volume 168 / Number 3 / December 2009 / Pages 837-842

MC Calculations / Special Issue on the 11th International Conference on Radiation Shielding and the 15th Topical Meeting of the Radiation Protection and Shielding Division (PART 3) / Radiation Measurements and Instrumentation /

The n_TOF facility is a time-of-flight (TOF) spectrometer dedicated to studying neutron-induced reactions, mainly neutron capture and fission cross sections. The spectrometer consists of a pulsed proton beam (7 × 1012 protons/pulse, 6-ns width, 20 GeV/c) impinging on an 80 × 80 × 60 cm3 lead target. The neutrons produced by spallation reactions reach the detector station at 185 m through an evacuated tube. There, neutron-induced reactions are studied by using the TOF technique. The facility is unique for its high instantaneous neutron flux (of the order 106 neutrons/cm2 per proton pulse at 185 m), an excellent energy resolution, low background conditions, and a very low duty cycle. This combination allows one to measure neutron capture and fission cross sections in the energy range from 1 eV to 250 MeV with high precision.

For the analysis of the data in the resolved resonance region up 1 MeV, a precise and accurate knowledge of the distribution of the energy resolution is mandatory. The only way to obtain the resolution function in a detailed way is to use Monte Carlo simulations together with the experimental verification with well-known resonance reactions at selected energies. Such calculations and an analytical fit of the results have been performed for the target setup of the first phase of data taking.

Monte Carlo simulations performed for the assessment and comparison of the resolution function for different target configurations are reported. The different resolution functions are compared and discussed.

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