Characteristic evaluation of the thermal neutron irradiation field using a 30 MeV cyclotron accelerator for basic research on neutron capture therapy

Abstract The development of a new boron compound for boron neutron capture therapy (BNCT) requires a high-intensity thermal neutron beam and the construction of thermal neutron fields in place of research reactors scheduled for suspension in the future. A thermal neutron irradiation field was produced by combining a cyclotron-based epithermal neutron source with a moderator to form an irradiation field for mice and cells, and its characteristics were evaluated. Our study confirmed that the lower limbs of the mouse could be sufficiently irradiated with a thermal neutron intensity of 4.83 × 108 n cm−2 s−1. The neutron dose rate and gamma ray dose rate per thermal neutron flux were 8.3 × 10−13 and 1.4 × 10−12 Gy cm2, respectively. In addition, by using a water phantom, irradiation with a maximum thermal neutron flux of 1.35 × 109 n cm−2 s−1 was achieved. In this case, the neutron dose rate and gamma ray dose rate per thermal neutron flux were 2.7 × 10−13 and 8.3 × 10−13 Gy cm2, respectively. An irradiation field capable of irradiating mice and cells was successfully produced and compared favorably with the irradiation fields from research reactors currently in use.