A comparative study of 234U/238U alpha-activity ratios determined by alpha-spectrometry and calculated from mass spectrometric data

U-234/U-238 alpha-activity ratios determined by alpha-spectrometry (AS) and those calculated from the atom ratio data using the half-life values are compared in some of the isotopic reference materials of uranium and a few other uranium samples. For alpha-spectrometry, electrodeposited sources were prepared and a large area passivated ion implanted (IPE) detector (450 mm(2)) was used for recording the alpha-spectra. The isotopic composition of U was determined by thermal ionisation mass spectrometry (TIMS) and the recommended half-life values of U-234 and U-238 were used to calculate the alpha-activity ratio. It is observed that U-234/U-238 alpha-activity ratios calculated from the atom ratio data are consistently high, with a mean difference of about 5%, when compared to the alpha-spectrometry results. This discrepancy warrants confirmation by a few more laboratories and suggests redetermination of the half-life values of U-234 and U-238.