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

A ZnS(Ag) scintillating disc coupled to a photomultiplier window tube was used to quantify the experimental detection efficiency of thick alpha sources and compare it with the theoretical detection efficiency. The experimental detection efficiencies were determined to be /spl sim/17%-18% for /sup 233/U and /sup 237/Np positioned 5.4 mm below the ZnS(Ag). The theoretical detection efficiency was calculated using an analytical model for an infinitely thick alpha source and was within 7% of the experimental values. In addition to these static measurements, online flow experiments were conducted. In these flow experiments, /sup 233/U wastewaters at three concentrations (14.19-53.65 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 /sup 233/U spiked wastewater and for a 3700-Bq /sup 90/Sr solid point source. For a very low discriminator setting, the /sup 90/Sr//sup 90/Y detection efficiency was about 3.5%, which was reduced to essentially zero by raising the discriminator level by a minimal amount that did not effect the alpha detection efficiency. Additional experiments, which included /sup 233/U (34.66 Bq/mL) on MnO/sub 2/-coated glass fiber filter resulted in a detection efficiency of 22%-23%.