Digital Radiographyシステムで発生した黒点の放射能の推定 : 輝尽性蛍光体板表面に直接付着した低濃度放射性同位元素起源の黒点の解析

Because of an accident of the nuclear power plants in the Fukushima, many radioisotopes (RI) have been diffused to the environment. As a result, black spots were appearing on the medical images which were taken by the phosphor plate. The aim of this study is to evaluate the activity (Bq) of radioactive contaminated IP based on the experiment using RI. The radioactive material (134Cs and/or 137Cs) in the form of liquid was dropped on filter paper (25 mm2), and radioactive sources having 40–240 Bq activities were made. These sources were closely attached to the IP with irradiation times of 2–22 h. Then, we obtained the relationship between pixel values and products of activities and irradiation times. Using these relationships, we evaluated the activity in the contaminated IP. The evaluated value of approximately 7 Bq was in good agreement with a value which was inhered in a chemical wiper used for the decontamination of the IP. Based on the results, we summarized that almost all black spots were created by the RI adhered directly to the IP.