search for




 

Assembly Neutron Moderation System for BNCT Based on a 252Cf Neutron Source
Prog. Med. Phys. 2018;29(4):101-105
Published online December 31, 2018
© 2018 Korean Society of Medical Physics.

Rouhollah Gheisari*,†, Habib Mohammadi

*Physics Departmentm, Persian Gulf University, Nuclear Energy Research Center, Persian Gulf University, Bushehr, Physics Group, Fars Education Administration Office, Fars, Iran
Correspondence to: Rouhollah Gheisari (gheisari@pgu.ac.ir)
Tel: 987731223342  Fax: 987733441494
Received August 13, 2018; Revised August 13, 2018; Accepted September 19, 2018.
This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
In this paper, a neutron moderation system for boron neutron capture therapy (BNCT) based on a 252Cf neutron source is proposed. Different materials have been studied in order to produce a high percentage of epithermal neutrons. A moderator with a construction mixture of AlF3 and Al, three reflectors of Al2O3, BeO, graphite, and seven filters (Bi, Cu, Fe, Pb, Ti, a two-layer filter of Ti+Bi, and a two-layer filter of Ti+Pb) is considered. The MCNPX simulation code has been used to calculate the neutron and gamma flux at the output window of the neutronic system. The results show that the epithermal neutron flux is relatively high for four filters: Ti+Pb, Ti+Bi, Bi, and Ti. However, a layer of Ti cannot reduce the contribution of γ-rays at the output window. Although the neutron spectra filtered by the Ti+Bi and Ti+Pb overlap, a large fraction of neutrons (74.95%) has epithermal energy when the Ti+Pb is used as a filter. However, the percentages of the fast and thermal neutrons are 25% and 0.5%, respectively. The Bi layer provides a relatively low epithermal neutron flux. Moreover, an assembly configuration of 30% AlF3+70% Al moderator/Al2O3 reflector/a two-layer filter of Ti+Pb reduces the fast neutron flux at the output port much more than other assembly combinations. In comparison with a recent model suggested by Ghassoun et al., the proposed neutron moderation system provides a higher epithermal flux with a relatively low contamination of gamma rays.
Keywords : Epithermal neutron beam, Gamma ray contamination, MCNPX, BNCT, Neutron moderation system


December 2018, 29 (4)