Determination of micelle size in some commercial liquid scintillation cocktails

Dynamic light scattering measurements were performed on commercially available liquid scintillation (LS) cocktails over a range of aqueous and acid contents. In all cases, measured hydrodynamic diameters were substantially smaller than the current de facto canonical value of 8 nm. Cocktail compositions that yield stable micelles are described and the observed diameters are reported. Calculations of the magnitude of the "micelle effect" on LS counting efficiencies and the error introduced by adopting an incorrect value for the micelle size are also discussed. - Highlights: ► Micelles in cocktails prepared from commercial scintillants are smaller than previously held. ► The micelle effect on LS counting efficiencies will thus be smaller than previously estimated. ► Dependence of micelle size on aqueous or acid fraction depends on the cocktail formulation. ► Micelle diameter changes little over a period of 1.5 months. ► Calculations indicate that the micelle effect is insignificant for most common formulations.