Effect of secondary radiation from lead shielding during liquid scintillation counting

In this study, the effects of secondary radiation from the lead shielding on the efficiency calculation were estimated, using the MICELLE2 program and the EGS5MPI Monte Carlo code. The results show that the counting efficiency values for ⁵⁴Mn (which decays via electron capture and emits gamma rays) were increased by approximately 0.5% due to the effect of the lead shield. Thus, secondary radiation was found to be non-negligible during the standardization of this radionuclide, leading to an standard uncertainty in the range of 0.6-1.2%. Henceforth, secondary radiation should be taken into account during the standardization of nuclides that decay by electron capture and emit gamma rays when using liquid scintillation counters. (author)