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Alpha-spectrometric technique is described as an independent method for determining mi-cro-contents of U~(238) and Th~(232).It is based on the comparison of alpha spectral activity ofU~(238) and Th~(232) in geological samples with that contributed by the U~(232)-Th~(228) spike of knownconcentration.The experiment procedure consists of dissolving fine powdered samples with acid andadding a given amount of U~(232)-Th~(228) 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~(232) and Th~(232) concent-rations can be calculated.The data obtained by the alpha-spectrometric method using U~(232)-Th~(228) 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~(238) and 0.97 for Th~(232).The accuracy of uranium and thorium analyses by this method depends primarily uponthe counting statistics of U~(232),U~(238) and Th~(228) and,to a certain extent,upon the calibrationof U~(232)-Th~(228) spike.Errors in uranium and thorium concentrations obtained by this methodare generally within 2 to 5%.
Alpha-spectrometric technique is described as an independent method for determining mi-cro-contents of U ~ (238) and Th ~ (232). It is based on the comparison of alpha spectral activity of U ~ (238) and Th ~ ) in geological samples with that contributed by U ~ (232) -Th ~ (228) spike of known concentration. The experiment procedure consists of dissolving fine powdered samples with acid and adding a given amount of U ~ (232) -Th ~ (228 ) spike.Uranium and thorium are then separated by ion exchange. After purification, each aliquot is mounted onto a separate stainless steel disk for measurement by alpha spectrometer, which consists essentially of a silicon surface barrier detector and a low noise amplification system connected to a multi-channel analyzer. Aftercorrections for the background, tail and other factors, the desired U ~ (232) and Th ~ (232) concentrations can be calculated. The data obtained by the alpha-spectrometric method using U ~ (232) (228) spike are compar-ed with colorimetric determinations.Excel lent agreement is obtained between the two sets of results. The coefficients of correlation are about 0.98 for U ~ (238) and 0.97 for Th ~ (232). The accuracy of uranium and thorium analyzes by this method depends on uponthe counting statistics of U ~ (232), U ~ (238) and Th ~ (228) and, to certain extent, upon the calibration of U ~ (232) -Th ~ (228) spike. Errors in uranium and Thorium spectra obtained by this method are generally within 2 to 5%.