Application of α/β discrimination in liquid scintillation counting for the purity control of 99mTc medical solutions

99mTc is a widely used nuclide in nuclear medicine for diagnosis. 99mTc solutions are eluted from 99Mo/99mTc generators as sodium chloride solutions. As the 99Mo source is a fission product extracted from the reprocessing of nuclear fuel, one might expect the presence of radioactive impurities. One point of special concern described in the 1997 European Pharmacopoeia (1996) is the possible contamination in α-impurities (U, Pu, Am, Cm, …) which must be very low. In order to check this impurity concentration, we used liquid scintillation counting (LSC) with α/β discrimination and a commercial extractive scintillator, Alphaex®. We first made measurements using synthetic mixtures of α and β-emitters and then using the real effluent. This paper describes the measurement procedure used with the optimum chemical conditions for a correct extraction of the α-emitting nuclides. The sensitivity of the method is also described from the measurements made using the real effluent with an addition of a quantitative amount of α particle contamination.