Thorium Isotope Content in River Water in Japan

Abstract

Concentrations of thorium isotopes 232Th,230Th and "sTh were determined in the river water collected at ten main rivers in Japan. The concentration of dissolved 232Th in river water was one order of magnitude higher than that in the Pacific surface waters. The weighted averages were 2.7x 10-8 g/l for 232Th and 2.8x 10-13 g/l for ""Th. The constancy in 232Th and 230Th concentration with time was observed, but the concentration of 228Th in river water was quite variable. Accordingly,228T h/232Th activity ratio showed a wide range of variation from 37 to 0.65 during the period of study.