γ線照射装置の照射野の自動制御

抄録

We constructed a γ-ray irradiation system with a commercial irradiation instrument, Sangyo Kagaku Co. Ltd., Model SK-951. The system is composed of an irradiator mounted with⁶⁰Co (3.7 GBq) and¹³⁷Cs (11.1 GBq and 111 GBq), and a mobile exposure deck having a lead shield sandwiched with iron (1200 mm (W) × 1200 mm (H) × 50 mm (D) ) at back side. This shield provides low exposure rate at wall, floor and ceiling in the present room. To limit irradiation field size within dimension of the shield, three kinds of square collimator (6.03°, 9.27° and 20.02°) were equipped around the irradiator beam, exit. The selection of collimators is automatically controlled. The abilities of shield and collimator were evaluated by calculation and measurement of exposure rate at points on the wall. By these improvements, exposure rate was lowered to the dose-equivalent limit in law.