RI中性子線源

A Radioisotope neutron source and its application for dosimetry

古渡 意彦

Kowatari, Munehiko

中性子の発見以降、種々の放射性同位元素(RI)を用いる中性子線源が利用されてきた。RIを用いる中性子発生では、(,n)反応、(,n)反応及び核分裂反応が利用され、これらの核反応で生じた中性子を用いる。現在のところ、Am-Be線源及びCf線源のみが市販で利用可能なRI中性子線源であり、線源ごとの個体差の少ない中性子放出、比較的長い半減期による中性子放出の安定性、及び中性子放出に伴う混在線の割合が少ないことが特徴である。本稿においては、これらのRI中性子線源を用いる中性子標準の構築について述べ、中性子標準で不可欠となる、全中性子放出量及び中性子放出の角度依存の測定について概説する。

A various kinds of radioactive neutron sources have been developed since neutron had been first discovered. The reactions which are mainly taken advantage for generating neutrons as radioactive neutron source are (,n) reaction, (,n) reaction and nuclear fission reaction. Only Am-Be and Cf neutron sources are now available due to reliable reproducibility of neutron emission, long half-lives and less disturbing ray emission. Both are designated as a "reference neutron source" by ISO 8529 series describing principle of establishment of neutron calibration field. Total neutron emission rate from neutron source must be well defined in terms of sophisticated method by national metrological laboratory. Correction factor for anisotropic emission from cylindrical-shaped neutron source must be experimentally determined for neutron fluence rate at a point of test in the calibration laboratory.