External exposure from 137Cs deposited on surface soil is one of the important exposure pathways during an accident at nuclear facilities. In this study, a validation of a dose assessment model of that pathway was carried out by using the monitoring data of the concentration of 137Cs in the surface soil layers around the Chernobyl nuclear power plant. It was obtained that the dose estimation by using the 2-component removal model from soil surface, which is generally used for dose assessment, is useful as the results of comparison with a compartment model in which the effect of vertical migration of nuclides in soil layers is considered. It was found that the ratio of rapid component is the most important parameter in the model, and that the values change from about 0.09 to 0.69 in the monitoring area.
It has been reported by the authors that priming X-irradiation of mice (ICR strain) with 0.3-0.5Gy two weeks before challenging irradiation induces radio-resistance (decrease in bone marrow death). This study was carried out to elucidate the mechanisms of the acquired radio-resistance. After challenging irradiation, peripheral blood cell counts were examined first, since bone marrow death has been thought to result from a functional disorder of bone marrow, suppression of hematopoiesis. But the blood cell counts of the thrombocytes, leukocytes and erythrocytes on days 14 and 15 after 5.5Gy were not influenced by the pre-irradiation. We next measured hemorrhage in the feces. It is reported to serve as a good indicator for evaluating the effectiveness of test therapeutic treatments on animals exposed to midlethal or sublethal doses. The pre-irradiation diminished the hemorrhage measured by quantitative determination of occult blood in the feces collected on days 10-12 after both 6.12 and 6.66Gy. On the other hand, coagulation time on day 12 was elongated by about 30% after challenging exposure to 5.2Gy, but the prolonged coagulation time was not recovered by the pre-irradiation. These studies suggest that some factor(s) that can possibly suppress hemorrhage might be produced in mice by pre-irradiation, but neither accelerates the recovery of hematopoiesis nor affects the coagulation time after the challenging irradiation.
This paper discusses the threshold of carcinogen risk from the viewpoint of social psychology. First, the results of a survey suggesting that renunciation of the Linear No-Threshold (LNT) hypothesis would have no influence on the public acceptance (PA) of nuclear power plants are reported. Second, the relationship between the adoption of the LNT hypothesis and the standardization of management for various risks are discussed.