Neutron irradiation field produced by 25Â MeV deuterons bombarding on thick beryllium target for radiobiological study

A fast neutron irradiation field for biological studies was established at the cyclotron facility in the National Institute of Radiological Sciences. Neutron spatial distributions and absorbed dose distributions were measured to characterize the neutron field. By using a simple technique that an aluminum plate activated by neutrons was exposed to the imaging plates, the width of the neutron-irradiated area was measured to be 23.6 cm with 2.5 mm spatial resolution. The absorbed dose distributions of neutrons and γ rays were obtained separately by using a tissue-equivalent plastic- and a graphite-walled low-pressure proportional counter. The neutron absorbed dose in a tissue-equivalent plastic was measured to be 144.6 (Gy/C). It was confirmed that this neutron field has only 1.8% contamination of γ-ray dose and has good quality for neutron irradiation to biological samples.