Activity determination of 68Ge/68Ga by means of 4πβ(Č)-γ coincidence counting

Highlights: • The 4πβ(Č)-γ coincidence counting was used to measure ⁶⁸Ge/⁶⁸Ga. • A new custom-built 4π(LS)β-γ coincidence system was used. • The β efficiency variation was accomplished by grey filters. • A relative uncertainty of the activity concentration of only 0.82% was obtained. - Abstract: Germanium-68 is an important radionuclide since it is used to generate its daughter ⁶⁸Ga which is frequently used for positron emission tomography (PET). In addition, ⁶⁸Ge/⁶⁸Ga sources are often used as surrogates for short-lived PET isotopes when calibrating instruments. In this work, 4πβ(Č)-γ coincidence counting was used to determine the activity concentration of a ⁶⁸Ge/⁶⁸Ga solution. The presented measurements were made by means of a new PTB-custom-built 4π(LS)β-γ coincidence counting system, where a liquid scintillation detector in the β channel can also be used as a Čerenkov counter, and a NaI(Tl) crystal detects annihilation radiation. The arithmetic mean of two results (from double N_D and triple N_T coincidences in the β channel) was adopted as the final result for the activity concentration of the solution under study. The overall relative uncertainty was estimated to be 0.82% and the uncertainty consideration as well as details about the measurement and the analysis are discussed. The measurements were carried out within the scope of the international CCRI(II)-K2.Ge-68 comparison.