Considerations for achieving low level radioactivity measurements with liquid scintillation counters

Low level LS counting requires that the most rigorous standards be maintained in sample preparation, instrument stability and low background operation. In order to achieve these goals, one must pay particular attention to sample chemistry and cocktail selection in order to minimize quench and obtain the highest counting efficiency. The use of special low volume vials, fabricated for positive seal and with material of low cocktail permeability and low natural radioactivity, is one of the most economical means for lowering background and reducing sample loss during long counting periods. Acquisition of select high quantum yield low noise PMT's is an excellent way to achieve high counting efficiency and lower electronic-generated background. Radiation shielding both by massive and electronic guards is the most important means for reducing background caused by external radiation sources. Pulse height discrimination and fast pulse time circuitry can both be applied with fast coincidence counting for background reduction. PSA can be applied to β, γ and β-γ counting and as a means for background reduction. 8 figures, 3 tables