Plutonium concentration and isotopic ratio in soil samples from central-eastern Japan collected around the 1970s

Abstract

Obtaining Pu background data in the environment is essential for contamination source identification and assessment of environmental impact of Pu released from the Fukushima Daiichi nuclear power plant (FDNPP) accident. However, no baseline information on Pu isotopes in Fukushima Prefecture has been reported. Here we analyzed 80 surface soil samples collected from the central-eastern Japan during 1969-1977 for 239+240 Pu activity concentration and 240 Pu/ 239 Pu atom ratio to establish the baseline before the FDNPP accident. We found that 239+240 Pu activity concentrations ranged from 0.004 -1.46 mBq g â '1, and 240 Pu/ 239 Pu atom ratios varied narrowly from 0.148 to 0.229 with a mean of 0.186 ± 0.015. We also reconstructed the surface deposition density of 241 Pu using the 241 Pu/ 239 Pu atom ratio in the Japanese fallout reference material. The obtained results indicated that, for the FDNPP-accident released 241 Pu, a similar radiation impact can be estimated as was seen for the global fallout deposited 241 Pu in the last decades.