Ra isotopes in Na-Cl type groundwater in Japan

Radium isotopes (226Ra and 228Ra) were measured for Na-Cl type groundwater samples collected from Hokkaido, Aomori, Akita and Yamagata Prefectures in Japan. The 226Ra contents varied in the wide range from 9 - 5000 mBq kg-1 and their values were roughly correlated to the total dissolved solid (TDS). Activity ratios of 228Ra/226Ra in groundwater ranged from 0.3 – 4.2 and most of them clustered around those of 232Th/238U of common rocks in Japan. These observations agreed well with the previous results from Ishikawa, Toyama and Niigata Prefectures, and overall indicated that Ra was mainly transported into the groundwater by α-recoil process and its concentration in groundwater was constrained by adsorption-desorption reaction depending on salinity. (author)