Significance of the correction for accidental coincidences in liquid scintillation counting measurements

International audienceMethods for the evaluation of the accidental coincidences counting rates in Triple-to-Double Coincidences Ratio (TDCR) Liquid Scintillation (LS) measurements have been proposed recently [1]. The methods were used in this study where the corrections for accidental coincidences are applied to TDCR measurements of different radionuclides with a wide range of activities and in different measurement conditions. The contribution of the accidental coincidences to the true coincidences counting rates is evaluated. The corrections for accidental coincidences are also applied to TDCR measurements of 18F with counting rates from 430000 s-1 to 150 s-1. The contribution of the accidental coincidences for each order of magnitude of the counting rate is presented. The effect of the accidental coincidences to the evaluated half-life of 18F is presented and discussed.This study also shows how the corrections can be extended to a four-detector system as used in the Compton Source Efficiency Tracing (CSET) method [2] or the Zombies method [3]. For such detector systems, employing an external gamma-ray source and a Compton spectrometer, the counting rate in the LS must be very high to observe a reasonable counting rate in the gamma-ray detector. In this case the correction for accidental coincidences is far from negligible