International Conference on Nuclear Data for Science and Technology 2007
DOI: 10.1051/ndata:07330

A full characterisation of the GELINA neutron flux distributions and resolution functions with the Monte Carlo code MCNP5

D. Ene¹, C. Borcea^{1, 2}, M. Flaska³, S. Kopecky¹, A. Negret^{1, 4}, W. Mondelaers¹ and A.J.M. Plompen<sup>1

1</sup>  European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, 2440 Geel, Belgium
²  National Institute for Physics and Nuclear Engineering "Horia Hulubei'', P.O. Box MG-6, Bucharest, Romania
³  Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge Tennessee, USA
⁴  IFIN-HH, Bucharest, Romania

Arjan.Plompen@ec.europa.eu.

Published online: 21 May 2008

Abstract
A numerical analysis of the GELINA target-moderator assembly has been conducted with the MCNP5 code to completely characterise the facility's neutron and gamma flux distributions as well as the neutron resolution functions. The aim of the work is to provide reference flux distributions for all flight paths for the benefit of external users, improved resolution functions for resonance analysis, and a general purpose calculational tool that may be used as a starting point for the optimisation of experimental arrangements. This work is based on an earlier study in which the suitability of the use of the MCNP code was demonstrated for the purposes discussed here. This detailed neutronic study with the MCNP5 code was performed for all flight paths of the facility. The following parameters characterising the performance of a neutron time-of-flight facility were investigated for the fast and for the moderated flux configurations:

-the energy distribution of the time-integrated neutron flux,

-the resolution function in dependence of the neutron energy and flight path angle,

-the gamma background at the detector position,

-the time distribution of neutrons and photons at the detector location.

The quality of the facility was also summarised by means of the energy-dependent figure of merit. Results of these calculations are presented and discussed. A better understanding of the correlations between the energy and the time of flight as well as of the origin of the components contributing to the spectra has been achieved by analysing time of flight spectra of both neutrons and photons with respect to the time at which the electron burst hits the target. Based on this work, the accuracy of the determination of the nuclear resonance parameters from time-of-flight measurements was further improved by implementing the detailed description of the resolution functions in the analysis code REFIT. Implementation and testing in the REFIT code of the obtained resolution functions is discussed.

© CEA 2008