Simultaneous determination of 226Ra, 233U and 237Np by liquid scintillation spectrometry

A method has been developed for the simultaneous determination of Ra-226, U-211 and Np-217 by liquid-scintillation (LS) spectrometry. This method consists of the evaluation of the alpha-spectrum that is composed of the strongly overlapping peaks of Ra-226, U-233, Np-237, Rn-222 and Po-218 in the energy range of 4.60-6.00 MeV and the single Po-214 peak at 7.69 MeV. The a-peaks are analysed by a special peak fit function that considers the deviation of the a-peak at the low energy side from the pure Gaussian shape. First Np-237 is determined using its daughter Pa-233 by analysing the beta-spectrum in the range 150-570 keV. Ra-226 follows from the alpha-spectrum that is measured 6 weeks after sample preparation, i.e., Ra-226 is determined from the radioactive equilibrium with its short-lived daughters Rn-222, Po-218 and Po-214. Finally the 233 U activity results from the fitted spectrum in the range of 4.4-4.8 MeV by subtracting the activity of Ra-226 and Np-237. Knowing the exact energy position of the LS-peaks an alternative evaluation consists in the accurate deconvolution of the first three peaks that are formed by Ra-226 and U-233 (maximum of both at channel 700), Np-237 (maxima at channels 700 and 725) and Rn-222 (maximum at channel 737). In these two ways Ra-226, U-233 and Np-237 can be determined in mutual activity ratios of 1:50 with a relative standard deviation of less than 4% for the major activity and 9% for the minor activity. (c) 2006 Elsevier Ltd. All rights reserved.