Design of Moderator Assemblies for Fast, Epithermal, or Thermal Neutron–Dominated n-γ Mixed Fields Using a D-D Neutron Source

Abstract

The treatment field of boron neutron capture therapy (BNCT) is a n-γ mixed field. In the Osaka University BNCT project, a material-filtered radio-photoluminescence glass dosimeter (RPLGD) was proposed for the simultaneous measurement of neutron and gamma-ray doses. In this study, to validate the material-filtered RPLGD, various types of n-γ mixed fields are designed by irradiating different moderator assemblies with a D-D neutron source at the OKTAVIAN facility, Osaka University, Japan. The n-γ mixed fields are classified into fast neutron–, epithermal neutron–, or thermal neutron–dominated fields and a gamma-ray-only field with the specific characteristics as follows: (1) the dose ratios of gamma ray to neutron are 1.0% to 977.0% for the fast neutron–dominated field, 5.0% to 921.1% for the epithermal neutron–dominated field, 5.0% to 921.1% for the thermal neutron–dominated field, and 11880.6% for the gamma-ray-only field; (2) the proportions of fast, epithermal, and thermal neutron doses to total neutron dose are 98.4% to 100.0% for the fast neutron–dominated field, 74.0% to 85.4% for the epithermal neutron–dominated field, and 90.1% to 90.8% for the thermal neutron–dominated field, respectively; and (3) the maximum gamma-ray energy is up to 12 MeV.