Determination of uranium and thorium isotopes in mineral spring waters

Concentrations levels of uranium and thorium isotopes have been analyzed in the mineral spring waters of a high background region of Brazil: Pocos de Caldas and Aguas da Prata. The procedure was based on the determination of U-238, U-234, Th-232, Th-230 and Th-228 by alpha-spectrometry after separation and purification of the isotopes of interest by using anion-exchange chromatography and preparation of the samples for alpha-measurements by electrodeposition, The concentration varied from <1.1 to 28.4 mBs.l(-1) and from <1.6 to 141 mBq.l(-1) for U-238 and U-234, respectively. Thorium isotope measurements varied from <0.2 to 1.8 mBq.l(-1) from <0.3 to 4.9 mBq.l(-1) and from <0.8 to 19.9 mBq.l(-1) for Th-232, Th-230 and Th, respectively. Calculations of thorium and uranium isotopic activity ratios were carried out giving values ranging from 1.9 to 7.2, from 1.2 to 3.0 and from 7.7 to 15.3 for U-234/U-238, Th-230/Th-232 and Th-228/Th-232, respectively. The effective doses due to the intake of U-238 and U-234 present in these waters are expected to reach values up to 1.4x10(-3) mSv y(-1) and 8.0x10(-3) mSv y(-1), respectively.