医用直線加速装置の高エネルギーX線による放射化の解析–短半減期放射化核種の推定－

概要

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In medical linear accelerators, radioactivation is induced on the target and neighborhood parts by photoneutrons accompanying a photo-nuclear reaction and leading to higher acceleration energy. We measured the residual radiation from the radioactivated materials according to the time, and tried to identify radioactivated nuclides and their relative quantities by means of measurement results. It was presumed that the main source of residual radiations was the Target, Flattening filter and Primary collimator in the linac head. Among those materials (copper, tungsten), we calculated decrement curves of residual radiations from radioactivated nuclides generated with photo-nuclear reaction or thermal neutron capture reaction by various ratios, and we investigated the ratio that best fit the measured data. Consequently, it was presumed that 66Cu generated with thermal neutron capture reaction contributed the most to residual radiation, followed by 62Cu generated with photo-nuclear reaction contributed. It is important to understand various characteristics of these nuclides and to undertake management of the device.