Alpha-spectrometric Determination of Uranium and Thorium in Geological Samples

Alpha-spectrometric technique is described as an independent method for determining mi-cro-contents of U;and Th;.It is based on the comparison of alpha spectral activity ofU;and Th;in geological samples with that contributed by the U;-Th;spike of knownconcentration.The experiment procedure consists of dissolving fine powdered samples with acid andadding a given amount of U;-Th;spike.Uranium and thorium are then separated byion exchange.After purification,each aliquot is mounted onto a separate stainless steel diskfor measurement by alpha spectrometer,which consists essentially of a silicon surface barrierdetector and a low noise amplification system connected to a multi-channel analyzer.Aftercorrections for the background,tail and other factors,the desired U;and Th;concent-rations can be calculated.The data obtained by the alpha-spectrometric method using U;-Th;spike are compar-ed with colorimetric determinations.Excellent agreement is obtained between the two setsof results.The coefficients of correlation are about 0.98 for U;and 0.97 for Th;.The accuracy of uranium and thorium analyses by this method depends primarily uponthe counting statistics of U;,U;and Th;and,to a certain extent,upon the calibrationof U;-Th;spike.Errors in uranium and thorium concentrations obtained by this methodare generally within 2 to 5%.