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

Abstract

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 (Kd) using the data on hot spring water or river water and hokutolite indicated that Th (Kd = 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 (Kd = 106-107).