Development of an on-line scintillation flow-cell detection system with pulse shape discrimination for quantification of actinides

A flow-cell detection system was developed utilizing pulse shape discrimination as a means of reducing the beta (gamma-ray) background when quantifying alpha emitters. Flow-cells consisting of 63-90 μm particles of CaF₂:Eu, scintillating glass (GS-20), and BaF ₂ were each packed into translucent Teflon tubing. CaF₂ :Eu and GS-20 exhibited only marginal pulse shape resolution, achieving figures of merit, (FOM) of 0.46 and 0.27, respectively. BaF ₂ exhibited reasonable pulse shape resolution, FOM=0.75. Unfortunately, the presence of intrinsic alpha emitters in CaF₂ :Eu and BaF₂ resulted in an elevated background count rate in the alpha window. Coupled with a detection efficiency of ~50% for ²³³U (E_α=4.8 MeV) alpha particles, minimum detectable activities at the optimal pulse shape time discriminator setting were 0.6 Bq for CaFa₂:Eu and BaF₂ and 1.1 Bq for GS-20