Prog Med Phys.  2018 Dec;29(4):101-105. 10.14316/pmp.2018.29.4.101.

Assembly Neutron Moderation System for BNCT Based on a ²⁵²Cf Neutron Source

• Gheisari R
• Mohammadi

• KMID: 2434643
• DOI: http://doi.org/10.14316/pmp.2018.29.4.101

Abstract

In this paper, a neutron moderation system for boron neutron capture therapy (BNCT) based on a ²âµ²Cf 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 Alâ‚‚O₃, 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/Alâ‚‚O₃ 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.

Keyword

Epithermal neutron beam; Gamma ray contamination; MCNPX; BNCT; Neutron moderation system

MeSH Terms

Boron Neutron Capture Therapy
Fast Neutrons
Gamma Rays
Graphite
Neutrons*
Graphite

Figure

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  Fig. 1 A MCNP geometrical scheme of the proposed neutron moderation system.

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  Fig. 2 Total epithermal neutron flux versus the size of the twolayer filter of Ti+Pb with different reflectors.

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  Fig. 3 Neutron energy spectra at the output port of the proposed neutron moderation system.

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  Fig. 4 Total epithermal neutron flux versus filter thickness.

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  Fig. 5 Total flux of g-rays versus filter thickness.

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  Fig. 6 Epithermal neutron and g-rays flux reported by Ghassoun et al.6).

Reference

1.Dias AZ., Coderre JA., Chanana AD., Ma R. Ann Med. 2000. 213:81–85.

2.Fukuda H., Honda C., Wadabayashi N., Kobayashi T., Yoshino K., Hiratsuka K, et al. Melanoma Res. 1999. 9:75–83.

3.Nano R., Barni S., Chiari P., Pinelli T., Fossati F., Altieri S, et al. Efficacy of boron neutron capture therapy on liver metastases of colon adenocarcinoma: optical and ultrastructural study in the rat. Oncol Rep. 2004. 11:149–153.

4.Green S. Developments in accelerator based boron neutron capture therapy. Radiat Phys Chem. 1998. 51:561–569.

5.Ghassoun J., Chkillou B., Jehouani A. Spatial and spectral characteristics of a compact system neutron beam designed for BNCT facility. Appl Radiat Isot. 2009. 67:560–564.

6.Ghassoun J., Merzouki A., Morabiti AEl., Jehouani A. On the 252Cf primary and secondary gamma rays and epithermal neutron flux for BNCT. Nucl Instrum Method Phys Res B. 2007. 263:231–233.

7.Kiger III WS., Sakamoto S., Harling OK. Neutronic design of a fission converter-based epithermal neutron beam for neutron capture therapy. Nucl Sci Eng. 1999. 131:1–22.