Standardization and measurement of gamma-ray probability per decay of 177Lu

The procedure followed by the Nuclear Metrology Laboratory (LMN), at the Nuclear and Energy Research Institute (IPEN), for the primary standardization of 177Lu is described. This radionuclide is widely used in radiopharmacy due to its convenient half-life and emitted beta ray energies. The 177Lu solution was supplied during an international comparison sponsored by BIPM in 2009 and the primary standardization has been accomplished by the 4πβ-γ coincidence method using a proportional counter in 4π geometry coupled with two NaI(Tl) scintillation counters. The beta efficiency was varied by placing Collodion and aluminum absorbers over and under the radioactive source. The 177Lu calibrated sources were also measured in a previously calibrated HPGe spectrometer, in order to obtain the emission probability per decay for the selected gamma-ray transitions. The experimental extrapolation curves were also compared with Monte Carlo simulations by means of code ESQUEMA developed at the LMN.