ESTIMATION OF SECULAR CHANGE OF AIR DOSE RATE CAUSED BY RADIOACTIVE CESIUM POLLUTION IN URBAN LAND

Abstract

 Field investigation in Fukushima showed that mobility of radioactive cesium was low in soil, and wetdry cycle experiment showed that quantity of bioavailable radioactive cesium in soil decreased with time. Convection-dispersion equation and point attenuation kernel integration method are used for modeling the secular change of air dose rate caused by radioactive cesium in soil. Here, two-step variation model of distribution coefficient for radioactive cesium in soil could well explain its distribution profile in depth and change of monitored air dose rate. This model showed that air dose rate at urban flat area in August of 2011 would decrease to less than half in two years and that of 1μSv/h would decrease to 0.19μSv/h before 10 years have passed. It was also showed that weeding didn't have significant effect to air dose rate.