ALPHA-LIQUID-SCINTILLATION SPECTROMETRY USED FOR THE MEASUREMENT OF URANIUM THORIUM-DISEQUILIBRIA IN SOIL SAMPLES/

For the measurements of low-level radioactivity of natural samples, it is of interest to have a system with high counting efficiency. Alpha liquid-scintillation spectrometry is attractive, because it offers a 4 pi geometry. Some chemical separation can be obtained using extractiv e scintillators. Due to quenching problems for natural samples, additi onal separation power is needed. A new sample preparation method was d eveloped employing extraction chromatographic resin for measuring U-23 8, U-234, Th-232, Th-230, Th-228,, and Ra-226 in, soil samples, withou t using any uranium-or thorium-tracer for determining the chemical yie lds. This method was tested by analyzing the two different reference m aterials, IAEA-375, soil from Tschernobyl, as well as IAEA SDA-1, a de ep-sea sediment with a high calcium content. For all analyzed radionuc lides the recoveries were better than 90% with errors (confidence leve l of 95%) smaller than 5%. The minimal detectable concentration ranges between 0.2 and 0.8 Bq/kg, based on a one gram aliquot of sample and 80'000 seconds counting time.