中性子捕捉療法のためのハイパー熱中性子発生装置:試作機の設計および製作ならびにシミュレーション計算による特性評価

概要

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With hyper-thermal neutron incidence, both of the depth dose distribution and the beam controllability are expected to be improved for neutron capture therapy (NCT). In order to clarify the irradiation characteristics of hyper-thermal neutrons and the feasibility of hyper-thermal neutron irradiation field for NCT, a "test-type" hyper-thermal neutron generator was designed and produced. Hyper-thermal neutron can be made of thermal neutrons by up-scatter with a high temperature material. Graphite of 6 cm thickness and 21 cm diameter was selected as the high temperature scatterer. The scatterer is heated up to 1200°C in maximum using molybdenum heaters. The radiation heat is shielded by reflectors of molybdenum and stainless steal. The temperature is measured using three R-type thermo-couples and controlled by a program controller. The total thickness of the generator is designed to be as thin as possible,20 cm in maximum, in the standing point of the neutron beam intensity. The thermal stability, controllability and safety of the generator at high temperature were confirmed by the heating tests. From the simulation calculations, it was confirmed that the neutron temperature shifted to be higher as the scatterer temperature was higher.