Experimental-theoretical response of ZnS(Ag) scintillating disc for gross α-measurements of aqueous radioactivity

ZnS(Ag) scintillating discs coupled to a photomultiplier window tube were used to determine the percent differences between experimental and theoretical detector efficiencies. The experimental detection efficiencies were determined at various concentrations of ²³³U and ²³⁷NP spiked wastewaters to be ∼17-18% The theoretical detection efficiency was calculated using an analytical model for an infinitely thick alpha source and were within 7% of the experimental values. In addition to these static measurements, on-line dynamic experiments were conducted. In these dynamic experiments, four concentrations of ²³³U wastewater (14.2 to 86.8 Bq/mL) were quantified using the experimental detection efficiency and determined to be within 17-18% of the expected concentrations. Pulse height analyses were performed for ²³³U spiked wastewater and for a 3700 Bq ⁹⁰Sr solid point source. For a very low discriminator setting the ⁹⁰Sr/⁹⁰Y detection efficiency was about 3.5%, which was reduced to essentially zero by slightly raising the discriminator setting. The effect on the alpha detection efficiency from raising the discriminator level was minimal.