Liquid-Scintillation Energy and Pulse-Shape Detection Applied to Low-Level Alpha Radioassay

Abstract

MCKLVEEN, J. W. Liquid-Scintillation Energy and Pulse-Shape Detection Applied to Low-Level Alpha Radioassay. Radiat. Res. 66, 199-214 (1976). The efficacy for rapid, low-level alpha-particle assay by liquid scintillation may be extended to routine environmental surveillance situations. Commercial liquid-scintillation counting systems, using energy discrimination, yield detection efficiencies up to 100% for alpha decay with backgrounds of the order of 5 to 10 cpm. However, consideration must be given to possible beta-particle interference. Alpha- and beta-energy conversion efficiencies were compared for numerous solvent-solute combinations. Whereas no single recipe emerged as a distinct favorite, a toluene-10 g/liter BBD scintillator is recommended on the basis of economics and material availability. Poor energy resolution, the result of numerous liquid scintillation statistical processes and energy spectrum quench, precluded, in general positive alpha-particle isotopic identification. Liquid-scintillation pulse-shape discrimination schemes use characteristic light pulses to furnish positive identification of alpha- or beta-particle decay. Alpha-detection efficiencies are unchanged but background count rates may be reduced to around 0.1 cpm. Applications of both energy and pulse-shape assay to selected environmental situations are presented.