Radionuclide metrology using liquid scintillation counting

Liquid scintillation counting ( LSC) techniques can be used for radionuclide standardization when the calculation of detection efficiency is possible. This is done using a model of the physicochemical processes involved in light emission and also of the statistics of photon emission: the free parameter model. This model can then be applied in two ways: by deducing the free parameter from the measurement of a tracer ( the CIEMAT/ NIST method) or by calculating this free parameter from coincidence ratio in a specific LS counter ( the TDCR method). The purpose of this paper is to describe both these models and some practical issues that need to be addressed if LSC is to be effectively used in radionuclide metrology.