Primary standardization of ⁶⁴Cu and ¹⁶⁶Ho radionuclides in the 4πβ(PC)-γ coincidence system and determination of its gamma-ray emission probability per decay

The procedure followed by the Nuclear Metrology Laboratory (LMN) at the Nuclear and Energy Research Institute (IPEN) for the primary standardization of ⁶⁴Cu and ¹⁶⁶Ho is described. These radionuclides are widely applied to Nuclear Medicine such as in diagnostic investigations and in radiotherapy. The absolute activity of both radionuclides were determined by the efficiency extrapolation method applied to 4πβ(PC)-γ coincidence counting system using a proportional counter in 4π geometry coupled with NaI(Tl) scintillation counter. The primary standardisation of ⁶⁴Cu for the conventional coincidence counting, the events were registered using a Time to Amplitude Converter (TAC) system associated with a multi-channel analyzer and by a software coincidence counting system, SCS, a digital method for primary activity measurements that simplifies the setting of optimal coincidence parameters. For performing the standardization of ⁶⁴Cu in the TAC system, the efficiency of the 4πβ(PC)-γ detector was varied using external absorbers and in order to correct the beta efficiency, the Kawada factor was applied. In the SCS counting, the events were registered by means of pulse digitization and the efficiencies (εEC and εβ) were varied through electronic discrimination. The biparametric method was used for determining the absolute activity and the result was in good agreement with the ones obtained with TAC system. The standardization of ¹⁶⁶Ho in the primary system was performed using the software coincidence counting, SCS. The gamma-ray emission probability per decay of the main transitions of both radionuclides were determined using the results obtained from the primary method, the 4πβ(PC)-γ coincidence system, associated with a calibrated HPGe gamma-ray spectrometer with standard ampoules of ¹⁵²Eu, ⁶⁰Co, ¹³³Ba, ¹³⁷Cs e ²⁴¹Am, previously standardized in the 4πβ(PC)-γ system. The gamma-ray emission probability per decay of the 1345,7 keV transition of ⁶⁴Cu was 0,472 (10) %, in good agreement with the literature. The gamma-ray emission probability per decay of the 1379,45 keV transition of ¹⁶⁶Ho was 0,936 (4) %. It were also determined the relative gamma ray emission probability of other gamma rays for this nuclide . All the results obtained were in good agreement with the literature. (author). (author)