The analysis of naturally-occurring radionuclides from uranium and thorium decay series in table mineral waters.

This project required the highly sensitive analysis of low-level alpha- and beta-emitters naturally occurring in table mineral water sold on the Swiss market. These radionuclides occur in the three major decay series-uranium-238, uranium-235, and thorium-232. The radionuclides analysed were 238U, 235U, 234U, 232Th, 230Th, 228Th, 210Po, 210Pb, and 226Ra. Many other radionuclides were determinable as a result of their equilibrium with an analysed nuclide. Efficient, element specific separation techniques were developed, allowing for the spectral analysis of each element without interference from other radioactive elements. Radioactive tracers, 232U, 230Th, and 209Po, were necessary to determine the percentage yield. These yields often varied greatly between different mineral waters, especially for thorium, ranging from 30 to 100%. Uranium, thorium and polonium isotopes could be directly analysed for by alpha-spectrometry. 226Ra was determined through the ingrowth of its daughter 222Rn by liquid scintillation counting. From the samples remaining after 210Po removal, the isotope's re-ingrowth from 210Pb determined the original 210Pb content. Limits of detection ranged from 0.1 to 2.0 mBq/l. The following contents were determined 234U + 238U 30-720 mBq/l; 232Th + 230Th < 1-5 mBq/l; 228Th 2-40 mBq/l; 226Ra 5-370 mBq/l; 210Po 1-90 mBq/l; 2,0Pb 1-90 mBq/l.