Some empirical observations concerning the liquid scintillation counting of coloured solutions

Abstract

The colour quenching capabilities of nine dyes have been examined, and compared with the visible absorption spectra of the dyes in toluene solution. From these data an empirical relationship is derived, from which the liquid scintillation counting efficiency is estimated simply from the λmax (wavelength of maximum absorption) of the dye and its absorption, A, at that wavelength. For the particular instrument, window settings, and scintillator solutions used in this work the relationship was[Formula: see text]Colour quenching agents are classified as severe (λmax 380–480 nm), moderate (λmax 480–520 nm), light (λmax 520–560 nm), or zero (λmax > 560 nm).The normal external standard channels ratio method for obtaining counting efficiency of chemically quenched samples has been applied to samples that contain colour quenchers and various combinations of colour and chemical quench. The results are in excellent agreement with the actual counting efficiencies; this result is in direct contrast to current views on the matter. It appears, therefore, that the counting of samples quenched both chemically and by colour may not always be impossible and the user is well advised to investigate his own System to evaluate whether results within acceptable error may be obtained.