A Polyethylene Moderator with Volumetric Bismuth Inclusions for Boron Neutron Capture Therapy

Abstract

Boron neutron capture therapy, a promising treatment for malignant tumors, requires intense neutron beams in the epithermal energy range. Nuclear reactors or particle accelerators generate higher-energy neutrons and slow them to the required energy through elastic and inelastic scattering of neutrons on the atomic nuclei of the moderator material. Neutrons with energies around 10 keV are optimal for treating deeply localized tumors, and a beam shaping assembly with a moderator made of crystalline or pressed magnesium fluoride is used to generate such a neutron beam. For research with cell cultures and laboratory animals, a hydrogen-containing moderator (plexiglass, polyethylene) is used; in this case, the neutron energy spectrum is shifted toward the thermal region. The authors have proposed using a moderator made of polyethylene with a volumetric inclusion of bismuth. This paper presents the results of measurements of the spatial distribution of the intensity of nuclear neutron absorption reactions by boron and the intensity of γ-radiation in a water phantom for three similar moderators made of plexiglass, polyethylene, and polyethylene with volumetric bismuth inclusions. The measurements were conducted using a compact sensor with a pair of injection-molded polystyrene scintillators, one of which is enriched with boron. It is shown that the use of polyethylene with volumetric bismuth inclusions, compared to plexiglass or polyethylene, reduces the unwanted γ-radiation dose while maintaining the neutron flux intensity.