Behavior of uranium-238 and its daughter nuclides in the Masutomi spring, Yamanashi Prefecture, central Japan

The geochemical behavior of uranium, radium and radon in the Masutomi spring district, Yamanashi Prefecture, central Japan, was studied. The uranium concentrations in the spring waters range from 0.01 to 2.07 ppb (average 0.27 ppb). The 234U/238U activity ratios in the spring waters range from 0.98 to 2.42, and show an inverse correlation with the 238U concentrations. The measurement of redox potentials of the waters shows that the waters are reductive. This may be the reason for the low uranium concentrations. Alpha recoil dissolution of 234Th explains the behavior of 234U. Radioactive disequilibria are also observed in 226Ra/238U, 222Rn/238U, and 222Rn/226Ra ratios. Highly exess radon is attributed to both the source granite rocks and the radium rich precipitates near the surface. On the other hand, the behavior of raium as well as other general ions such as sodium is explained by mixing or dilution of a deep water with surface waters. (author)