Ecological half-lives of radiocesium on Izu-Oshima Island related with the Fukushima Daiichi nuclear power plant accident

DISTRIBUTION OF RADIOCESIUM CONCENTRATIONS OF SOILS IN THE EIGHT IZU ISLANDS AFTER THE FUKUSHIMA DAIICHI NUCLEAR POWER PLANT ACCIDENT

Large amounts of anthropogenic radionuclides, such as 134Cs and 137Cs(radiocesium), were released into the atmosphere due to the Fukushima Daiichi Nuclear Power Plant (F1-NPP) accident and were transported into various environments. The soil accumulations of diffused radionuclides are marked by large differences in their horizontal distributions, and the vertical air dose rates vary depending on the topography, altitude and other factors. In this study, soil activity concentrations of eight islands in the Izu Islands, ~334-563 km south of the F1-NPP, were analyzed from both horizontal and vertical perspectives. Soil samples were collected over a 4-y period from 2012 to 2016, and their activity concentrations of radiocesium were measured. The activity concentrations in the soil were categorized for intervals of a 100-m altitude above sea level, and the relationship between the maximum activity concentration in each category and the distance from the F1-NPP was analyzed. The correlation was good at the lower altitudes.

Distribution of gamma radiation dose rate related with natural radionuclides in all of Vietnam and radiological risk assessment of the built-up environment

A built-up environment utilizes building materials containing natural radionuclides that will change radiological risks. While radiological risks have been estimated from the activity concentrations of natural radionuclides in soil, it is important to evaluate the changes of these risks for the built-up environment using these building materials. Based on the direct measurements of absorbed dose rate in air and calculation of absorbed dose rate in air from activity concentrations in soil for all of Vietnam which has undergone significant economic growth in recent decades, the changes of absorbed dose rate in air and radiological risks before and after construction of many artificial structures were investigated. The results showed that the absorbed dose rates in air were clearly changed by the urbanization, and the difference ratio for all of Vietnam ranged from 0.5 to 2.1, meaning that the artificial structures have been acting as shielding materials to terrestrial gamma-rays or radiation sources. However, changes in annual effective dose in the built-up environment were small, and there was no new radiation risk from the built-up environment for Vietnam.