Activity standardisation of ¹⁷⁷Lu

Lu-177 decays through low-energy ss-and gamma-emissions in addition to conversion and Auger electrons. To support the use of this radiopharmaceutical in Switzerland, a Lu-177 solution was standardised using the ss-gamma coincidence technique, as well as the TDCR method. The solution had no Lu-177m impurity. Primary coincidence measurements, with plastic scintillators for beta detection, were carried out using both analogue and digital electronics. TDCR measurements using only defocusing were also made. Monte Carlo calculations were used to compute the detection efficiency. The coincidence measurements with both analogue and digital electronics are compatible within one standard uncertainty, but they are lower than (and discrepant with) the TDCR measurements. An ampoule of this solution was submitted to the BIPM as a contribution to the Systeme International de Reference.