Standardization of 68Ge/68Ga using the 4πβ−γ coincidence method based on Cherenkov counting

Highlights: • The standardization of ⁶⁸Ga was carried out in the framework of an international comparison. • The activity was assessed using the 4πβ−γ method based on LS and Cherenkov counting. • Activity measurements obtained by LS and Cherenkov counting are in good agreement. • The efficiency-extrapolation curve given by Cherenkov counting is compared with a Geant4 simulation. - Abstract: In the framework of an international BIPM comparison (Bureau International des Poids et Mesures), the activity standardization of ⁶⁸Ge in a solution of ⁶⁸Ge/⁶⁸Ga in equilibrium provided by NIST was carried out at LNHB. This exercise was organized to meet the growing interest in ⁶⁸Ga as a radiopharmaceutical in nuclear medicine services (e.g. as a surrogate of ¹⁸F for PET imaging). Due to the volatility of germanium, the activity standardization of ⁶⁸Ge was investigated at LNHB by means of 4πβ−γ coincidence counting based on Cherenkov measurements. This technique was applied to take advantage of the Cherenkov threshold (~ 260 keV in aqueous solutions) in order to prevent counting from electron-capture events associated with ⁶⁸Ge disintegrations. Cherenkov counting was performed using glass and polyethylene vials and the resulting activity concentrations were compared with 4πβ−γ coincidence measurements based on liquid scintillation. The efficiency-extrapolation curve obtained with Cherenkov measurements in glass vials was compared to Monte Carlo simulations based on the Geant4 code.