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

In the framework of an international BIPM comparison (Bureau International des Poids et Mesures), the activity standardization of Ge in a solution of Ge/Ga in equilibrium provided by NIST was carried out at LNHB. This exercise was organized to meet the growing interest in Ga as a radiopharmaceutical in nuclear medicine services (e.g. as a surrogate of F for PET imaging). Due to the volatility of germanium, the activity standardization of Ge 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 (~ 260keV in aqueous solutions) in order to prevent counting from electron-capture events associated with Ge 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.