Development of dose rate simulation code in consideration of displacement in a forest of radioactive cesium and development of high precision measurement technique for low-concentrated environmental radioactivity samples. Part 2

The following studies have been conducted: (1) Development and improvement of a simulation tool for quantitatively evaluating the concentration distribution and displacement of radioactive cesium, (2) development of a method for back-calculating the spatial distribution of radiation source from the distribution of air dose rates, (3) verification of the model, and (4) effectiveness assessment of quantitative microanalysis of radioactive cesium. Tokyo City University measured the radioactivity concentration of soil and fallen litter as the samples that were collected for space dose rate measurement and surface contamination density measurement for forest survey. This survey has been carried out in the 'Long-term assessment of transport of radioactive contaminant in the environment of Fukushima' project as the Fukushima long-term environmental dynamics research being conducted by JAEA. This university compared these data with the past air dose rates and the radioactivity concentration of soil and fallen litter, and investigated the changes with time. It was confirmed that the space dose rates and a difference in trends of radioactivity distribution due to altitude in the sloped lands was appropriate. The spatial dose rates measured at the time of sample collection was useful for developing the air dose rate distribution simulation technique considering the contribution of the spatial distribution of radiation sources. In the method for quantitatively determining a low concentration of radioactive cesium, concentrating techniques such as solid-liquid separation and ammonium phosphomolybdate co-precipitation were developed and verified. (A.O.)