Investigation of the possible effect of the accidental coincidences correction on the determination of optimal kB value by efficiency variation with gray filters

Overview & Synopsis

Recently, analytical and experimental methods for evaluating accidental coincidences in TDCR measurements were proposed. It was shown that the correction for accidental coincidences depends on the experimental counting rates and that it is significant not only for measurements of high-activity sources but also in low-level LSC measurements. The efficiency variation by optical grey filters, on the other hand, is widely used for determining the optimal value of the Birks’ ionization quenching parameter kB, which has the major contribution to the uncertainty in the TDCR standardization of low-energy β-emitters like 3H. Since there is a change in the counting rates between measurements of a sample with different grey filters, it is interesting to investigate the effect of accidental coincidences on the choice of the proper kB value. This question is of practical relevance because it is interesting to assess the correctness of the estimates of kB applied in the past when no accidental coincidence corrections have been applied. To achieve this goal, we have re-analyzed a large set of experimental data of kB determinations by applying and not applying analytical accidental coincidence corrections. Examples of the obtained results are shown in Fig. 1. Overall, at this point, we do not see a statistically significant effect of the accidental coincidence correction on the optimal kB value. These results verify the choices of kB by efficiency variation by grey filters made in the past. More results for different nuclides and TDCR systems will be presented.