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-disc liquid scintillation spectrometry and pulse shape analysis, necessarily involves a correction for the mis-classification of a small fraction of the alpha-induced events. What has not been clear is how best to correct for the quenching associated with the (almost) unavoidable variability in source quality of discs prepared by electrodeposition in the course of the routine analysis of environmental samples. The latter results in a reduction in the detection efficiency for Pu-241 and an 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 paper, a novel approach is described in which the shift in the alpha peak, as measured by LS spectrometry, relative to that of an unquenched standard, represents the parameter by which both the alpha to beta cross-talk and the beta efficiency are determined using appropriate sets of quenched standards. The method has been tested with replicate samples of intercomparison materials and confirmed by thermal ionization mass spectrometry. Copyright (C) 1996 Elsevier Science Ltd.