Radionuclide, scintillation cocktail and chemical/color quench influence on discriminator setting in gross alpha/beta measurements by LSC

Gross alpha/beta measurements in drinking waters enable radiochemical composition analysis in environmental studies providing efficient screening method that can indicate whether water contains elevated levels of any radionuclide. Routine gross alpha/beta activity monitoring in drinking waters has been carried out for a few years in laboratory for low-level radioactivity measurements in Novi Sad according to ASTM method, performing measurements on liquid scintillation counter Quantulus 1220 which can simultaneously generate alpha/beta spectra of samples by Pulse Shape Analysis (PSA circuit). In this paper, PSA discriminator impact was investigated to ensure obtaining of accurate and reliable alpha/beta activities. One novelty of presented work is PSA parameter setup with two combinations of radionuclides (Am-241, Ra-226 and Sr-90/Y-90) with varying activity concentrations. Performed experiments also make contribution to investigations on the manner in which chemical and color quench affect optimal PSA parameter setting and further on, their altogether influence on gross alpha/beta activity measurements. Nitromethane, 15.8 M nitric acid and water, as well as yellow and yellow-orange dye, were used as quenching agents in order to test PSA/interference factor behavior in the presence of quenchers with different quenching strengths. Variation of PSA setting in quenched samples with two different commercially available cocktails (Ultima Gold LLT and OptiPhase HiSafe 3) was also tested. Lastly, application i.e. assessment of obtained PSA-SQP(E) correlation on the obtained results of activity concentrations of few artesian well water samples and colored spiked samples, based on the measured SQP(E) value of samples, has been demonstrated. (C) 2015 Published by Elsevier Ltd.