Abstract: Method to determine the degree of chemical quench and the degree of color quench in liquid scintillation samples in order to find the correct counting efficiency for the samples. Scintillation pulses produced by the liquid scintillation solution as a result of an isotopic decay or in response to radiation from an external .gamma.-radiating source, are counted in a counter comprising two photodetectors working in coincidence, means for determining the value of one quench parameter dependent on the overall level of quench in the solution, and means for determining the value of another quench parameter predominantly dependent on the level of color quench in the solution. The counting efficiency for the sample can be determined on the basis of these two quench parameters.

Abstract: Method for calibrating a liquid scintillation counter comprising, for a number of reference solutions containing isotopes of known decay rates, the counting of a number of coincident pulses caused in at least two photodetectors by photons produced by the decay of the isotopes within a first known time interval, for obtaining the scintillation pulse frequency of each reference solution and the calculating of the counting efficiency for each reference solution by dividing said scintillation pulse frequency by the known decay rate.