A NEW APPROACH TO QUENCH CORRECTION WHEN MEASURING PU-241 IN THE PRESENCE OF PU-ALPHA BY SUPPORTED-DISC LIQUID SCINTILLATION SPECTROMETRY

It is widely recognized that the accurate measurement of beta-emitting Pu-241 in the presence of alpha-emitting Pu nuclides, by supported-di sc liquid scintillation spectrometry and pulse shape analysis, necessa rily involves a correction for the mis-classification of a small fract ion of the alpha-induced events. What has not been clear is how best t o correct for the quenching associated with the (almost) unavoidable v ariability in source quality of discs prepared by electrodeposition in the course of the routine analysis of environmental samples. The latt er results in a reduction in the detection efficiency for Pu-241 and a n increase in the mis-classification of cc events. It also gives rise to a shift of the alpha and beta spectra to lower energies. In this pa per, a novel approach is described in which the shift in the alpha pea k, as measured by LS spectrometry, relative to that of an unquenched s tandard, represents the parameter by which both the alpha to beta cros s-talk and the beta efficiency are determined using appropriate sets o f quenched standards. The method has been tested with replicate sample s of intercomparison materials and confirmed by thermal ionization mas s spectrometry. Copyright (C) 1996 Elsevier Science Ltd.