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 238U, 234U, 232Th, 230Th and 228Th by α-spectrometry after separation and purification of the isotopes of interest by using anion-exchange chromatography and preparation of the samples for α-measurements by electrodeposition. The concentration varied from -1 and from -1 for 238U and 234U, respectively. Thorium isotope measurements varied from -1 from -1 and from -1 for 232Th, 230Th and 228Th, 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 234U/238U, 230Th/232Th and 228Th/232Th, respectively. The effective doses due to the intake of 238U and 234U present in these waters are expected to reach values up to 1.4 x 10-3 mSv y-1 and 8.0 x 10-3 mSv y-1, respectively.