Development of a homogeneous pulse shape discriminating flow-cell radiation detection system

A homogeneous flow-cell radiation detection system which utilizes coinciden ce counting and pulse shape discrimination circuitry was assembled and test ed with five commercially available liquid scintillation cocktails. Two of the cocktails, Ultima Flo (Packard) and Mono Flow 5 (National Diagnostics) have low viscosities and are intended for flow applications; and three of t he cocktails, Optiphase HiSafe 3 (Wallac), Ultima Gold AB (Packard), and Re ady Safe (Beckman), have higher viscosities and are intended for static app lications. The low viscosity cocktails were modified with l-methylnaphthale ne to increase their capability for alpha/beta pulse shape discrimination. The sample loading and pulse shape discriminator setting were optimized to give the lowest minimum detectable concentration for alpha radiation in a 3 0 a count time. Of the higher viscosity cocktails, Optiphase HiSafe 3 had t he lowest minimum detectable activities for alpha and beta radiation, 0.2 a nd 0.4 Bq/ml for U-233 and Sr-90/Y-90, respectively, for a 30 s count time. The sample loading was 70% and the corresponding alpha/beta spillover was 5.5%. Of the low viscosity cocktails, Mono Flow 5 modified with 2.5% (by vo lume) 1-methylnaphtharene resulted in the lowest minimum detectable activit ies for alpha and beta radiation; 0.3 and 0.5 Bq/ml for U-233 and Sr-90/Y-9 0, respectively; for a 30 s count time. The sample loading was 50%, and the corresponding alpha/beta spillover was 16.6%. HiSafe 3 at a 10% sample loa ding was used to evaluate the system under simulated flow conditions. (C) 1 999 Published by Elsevier Science B.V. All rights reserved.