Radiocesium Inventory on the Campus of Nihon University, Koriyama, Fukushima, Japan

Abstract

We have collected surface soil samples on the campus of Nihon University, Koriyama, Fukushima, Japan, after the Fukushima Dai-ichi Nuclear Power Plant accident for three years and measured their radiocesium (¹³⁴Cs and ¹³⁷Cs) concentrations to understand the behavior of deposited radiocesium on soil surfaces in the campus. In 2011, the inventory of ¹³⁴Cs and ¹³⁷Cs ranged from 73 to 164 kBq m^-2 with the arithmetic mean value of 110 ± 33 kBq m^-2, and from 83 to 203 kBq m^-2 with the arithmetic mean value of 134 ± 42 kBq m^-2, respectively. In 2012 and 2013, we found radiocesium inventories were rapidly decreasing at most sampling stations because of university decontamination work programs to remove the surface soil to a depth of 5 cm. Slightly increasing radiocesium inventories were observed at some stations, however, where soil and grass covered soil areas met. We considered that the elevated radiocesium inventories were affected by resuspension of soil dust. The ¹³⁷Cs residual rate at areas that had not been decontaminated was estimated at approximately 50% during 2012 to 2013.