| 摘要: | 本研究針對大屯火山區溫泉中U/Th系列核種（包括：²³⁸U, ²³⁴U, ²³⁰Th, ²²⁶Ra, ²³²Th, and ²²⁸Th）進行分析，並分析採樣點環境之化學特性（如：酸鹼度、氧化還原電位及溫泉水中之Cl⁻、SO₄²⁻濃度等），藉以探討放射性核種之遷移及其對放射性核種含量之變動的影響。研究結果顯示，溫泉水中U、Th之含量隨pH增加而遞減。²³⁴U/²³⁸U之放射活度比值(AR)可歸因於U(Ⅵ)之水解、α衰變核反跳及²³⁴U之選擇性瀝濾，然其不平衡現象並不明顯。而溫泉水中之²³⁰Th/²³⁴U, ²²⁶Ra/²³⁰Th和²²⁸Th/²³²Th及底泥中²³⁰Th/²³⁴U, ²²⁶Ra/²³⁰Th, ²²⁸Ra/²³²Th, ²²⁸Th/²²⁸Ra和²²⁸Th/²³²Th之放射活度比值均可見明顯之不平衡現象。溫泉水中之Cl⁻和SO₄²⁻離子可促進U和Th溶入水中。溫泉水中之²³⁰Th/²³⁴U AR小於1，而底泥中之²³⁰Th/²³⁴U AR (1.13-1.52)大於1，此可歸因於²³⁴U和²³⁰Th溶解度的迵異。溫泉水中²²⁶Ra/²³⁰Th的AR (0.60-34.8)隨Cl-和SO₄²⁻濃度增加而下降，而底泥中²²⁶Ra/²³⁰Th的AR (1.57-21.5)則有相反之趨勢；此結果可歸因於²³⁰Th與Cl⁻或SO₄²⁻的錯合及²²⁶Ra與(Ba, Pb)SO₄的共沉澱反應。²²⁸Th/²³²Th在溫泉水中之AR (1.01-12.0)和底泥中之AR (1.02-25.6)均偏離1，且與²⁸Ra和(Ba, Pb)SO₄之共沉澱及²²⁸Th之錯合有關。
The activity concentrations of ²³⁸U, ²³⁴U, ²³⁰Th, ²²⁶Ra, ²³²Th, and ²²⁸Th in hot springs in the Tatun volcanic area were determined. Factors including acidity, redox potential, and Cl⁻and SO₄²⁻concentrations in spring waters at the sampling sites have been investigated to allow interpretation of the migration of the radionuclides, and to elucidate the influence of these parameters on the variations of radionuclide contents. The contents of U and Th in water decrease with increasing pH. ²³⁴U/²³⁸U ARs were ascribed to alpha recoil and selective leaching of ²³⁴U, while the ²³⁴U/²³⁸U disequilibrium is not significant with regard to the statistical error. Radioactive disequilibria were found in ²³⁰Th/²³⁴U (0.04-0.63), ²²⁶Ra/²³⁰Th (0.60-34.8) and ²²⁸Th/²³²Th (1.01-12.0) in hot springs waters, and ²³⁰Th/²³⁴U (1.13-1.52), ²²⁶Ra/²³⁰Th (1.57-21.5), ²²⁸Ra/²³²Th (1.10-277.4), ²²⁸Th/²²⁸Ra (0.09-1.23) and ²²⁸Th/²³²Th (1.02-25.6) in sediments. The contents of uranium and thorium decreased with increasing pH. The Cl⁻ and SO₄²⁻ions promote the dissolution of uranium and thorium. The ²³⁰Th/²³⁴U ratio increased, while the ²²⁶Ra/²³⁰Th ratio decreased with the Cl⁻ or SO₄²⁻concentration, and was attributed to chemical difference between ²³⁰Th and ²³⁴U. ²²⁶Ra/²³⁰Th disequilibrium was attributed to the promotion of ²³⁰Th solubility by forming complexes with Cl⁻or SO₄²⁻ ions. All ²²⁸Th/²³²Th ratios deviated from unity due to the co-precipitation of ²²⁸Ra with barium and lead sulfate. |
