²²⁸Ra/²²⁶Ra activity ratio in groundwater around Mount Fuji, Japan

Tomoko Ohta^1*, Yasunori Mahara¹, Kimio Miyakawa², Takumi Kubota¹, Keiko Tagami³ and Jun Sato⁴

¹ Research Reactor Institute, Kyoto University - Japan
² Civil Engineering Laboratory, Central Research Institute of Electric Power Industry - Chiba, Japan
³ Office of Biospheric Assessment for Waste Disposal, National Institute of Radiological Sciences - Chiba, Japan
⁴ School of Science and Technology, Meiji University - Japan

^* E-mail: nakano-o@rri.kyoto-u.ac.jp

Published online: 04 April 2012

Abstract

We estimated the groundwater age from ²²⁸Ra/²²⁶Ra ratios in young groundwater and relevant rocks in the volcanic area of the Kakitagawa River around Mount Fuji, Japan, and compared our results with those from ³H/³He age determination. The groundwater residence time estimated from the ²²⁸Ra/²²⁶Ra activity ratio in groundwater and relevant rocks agreed well with the ³H/³He age, suggesting that the ²²⁸Ra/²²⁶Ra ratio of groundwater can be used to estimate residence time of young groundwater in volcanic areas.