LIQUID SCINTILLATION COUNTING METHODS FOR ACCURATE ASSAY OF BETA RADIOACTIVITY IN BIOLOGICAL EXPERIMENTS

Improvements in liquid scintillation spectrometer design allow considerable simplification of the sample preparation procedure; and some characteristics of two simple high-efficiency methods are described, particularly in relation to counting aqueous solutions in dioxane, or precipitates of macromolecular substances on filters. Problems of chemical, color, and self-absorption quenching are considered, and the external standard ratio technique for quench correction is investigated. External standard ratio is found particularly useful for multiple-isotope counting with wide nonoverlapping channel widths, and accurate resolution can be obtained by this method for mixtures of two or three isotopes having varying degrees of quenching. © 1968.