66Ga: a standard for high-energy calibration of Ge detectors

Two independent measurements of the relative emission probabilities for the strongest transitions in 66Ga electron capture decay are reported here. The results of these measurements are in excellent agreement with each other and with those from another recent measurement. Consequently, 66Ga emission probabilities for 18 strong lines, from 834 to 4806 keV, are now known to better than 1% accuracy. Thus, 66Ga can now be considered a suitable radionuclide for Ge detector efficiency calibration up to an energy of 4806 keV, the highest energy attainable with radioactive calibration sources. We have also provided an empirical function for correcting earlier incorrect emission probability results for Eγ greater than about 3 MeV which were produced using an inappropriate efficiency curve extrapolation.