Host: The Japan Radiation Research Society, Chairman of the 52nd Annual Meeting, Toshiteru Okubo (Radiation Effects Research Foundation)
Purpose: At present, the radioactivities in the environmental materials are monitored at many spots in Japan. The data is useful for estimating the radiation doses received by people. However, such environmental monitoring and study have not been conducted at Shobara City in the northern part of Hiroshima Prefecture. So, we started on accumulating the data of environmental radioactivity and studying how the radioactivities originated. First of all, we are measuring the radioactivities in airborne particulate matter (APM) in order to estimate where the radioactivity in APM is derived from.
Material and Methods: Every sampling of APM was performed using an air-dust sampler (Aloka,DMS-205) for six hours with absorption rate of 80 little per minute. After the sampling, the filter (ADVANTEC, HE-40T) was covered with polyethylene film. The gamma rays from the samples were measured with a high purity Ge-detector (Oxford, CPVDS30-0190, volume of 160 cm3). Each sample was measured three months after the sampling in order to determine the activities in the uranium and thorium series. In order to study how the rocks and soils around the sampling position influenced to the air dusts, the natural radioactivities in these materials were also determined with gamma-ray spectroscopy. The gamma-ray detection efficiencies for the powdered rock or dried soil samples were determined by using the rock reference samples from the Geological Survey of Japan.
Results and Discussion: Several natural radioactivities such as 212Pb and 40K were clearly observed in the APM collected in winter or spring. However, APM in summer included few natural radioactivities. This implied that the APM in winter and spring might have included the yellow sands or small particles from the east part of the Asian continent. The weathered rocks and dried soils around the sampling position also have a possibility to produce the natural radioactivities in the APM. The results of the present measurements will be used for studying how the near and distant sources related to the APM in the sampling spot.
