Hokutolite collected from riverbed at Peitou Hot Spring in Taiwan: With emphasis on radiochemical studies

Summary

Hokutolite, and hot spring water and river water collected recently at Peitou Hot Spring in Taiwan were analyzed for U, Th, Ra and ²¹⁰Pb isotopes. Concentrations of major chemical elements were also measured. Hokutolite had its typical chemical composition make-up for this area. The concentrations of ²³⁸U, ²³⁴U, ²³²   Th, ²³⁰   Th, ²²⁸   Th, ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb in samples scrapped into 7 layers from the surface to the bottom of a hokutolite specimen were 0.0021-0.0068, 0.0022-0.0075, 1.47-2.07, 1.00-1.29, 1.56-1.97, 56.7-68.6, 1.46-2.06 and 25.9-36.0 Bq/g, respectively. All the radionuclides exhibited a relatively uniform distribution, and radioequilibrium was confirmed among ²³²   Th, ²²⁸Ra and ²²⁸   Th. From the relationship between the decay and growth of Th-series nuclides it was considered that the hokutolite studied was isolated from the stream water at least 70-80 years ago. The U/Th-series radionuclides in the hot spring water were in rather high concentrations and the enrichment of ²²⁸Ra and ²²⁸   Th to ²³²   Th was the most prominent feature. Evaluation of the distribution coefficients (K_d) using the data on hot spring water or river water and hokutolite indicated that Th (K_d = 10⁴-10⁵) in water was likely to be precipitated (and/or co-precipitated) with BaSO₄ as Th(SO₄)₂ with a relatively high concentration into hokutolite, together with Ra (K_d = 10⁶-10⁷).