Radioactive Disequilihrium of Uranium and Thorium Nuclide Series in Hot Spring and River Water from Peitou Hot Spring Basin in Taipei

Abstract

The distributions of the naturally occurring radionuclides ²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th, ²²⁸Th, ²²⁸Ra, and ²²⁶Ra in river and hot spring water within the Peitou hot spring basin at the northern part of Taiwan were studied by using alph-and gamma-spectrometric methods and liquid scintillation counting method. The respective concentration ranges of ²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th, ²²⁸Th, and ²²⁶Ra in river and hot spring water were 0.80-48, 1.2-51, 0.05-44, 0.09-39, 0.19-342, 3.0-22.5 mBq/L and 2.3-85, 2.9-91, 0.67-73, 1.14-66, 1.01-630, and 4. 5-36.5 mBq/L, respectively. In general, the distributions of uranium-series and thorium-series nuclides in river water, hot spring water were all pH dependent. The respective radioactivity ratios of ²³⁴U/²³⁸U in river and hot spring water are observed to be 1. 0-1.5 and 1.03-1.5, however, the radioactivity ratios of ²²⁸Th/²³²Th in river and hot spring water are 1.4-19 and 1.5-8.8, respectively. The high ²²⁸Th/²³²Th activity ratios showed that besides the recoil effect, enrichment of ²²⁸Ra to ²³²Th in the waters was another possible factor causing an excess of ²²⁸Th. Because radium may exist as (Pb, Ba, Ra) (SO₄) _x pseudo-colloid in hot spring water, which is the same as the more famous mineral of Peitoustone (Hukutolite), therefore, ²²⁸Ra and ²²⁶Ra are more abundant in the hot spring sediments, which radioactivity arel8-3010 and 16-230 Bq/kg (dry), respectively.