A tri-nuclide calibration standard for HPGe gamma spectrometry

High-resolution gamma spectrometry using high-purity germanium (HPGe) crystal provides identification and quantification of radionuclides at high confidence. However, it is critical for these HPGe spectrometry system to be robustly calibrated for energy, detection efficiency and peak-shape. Calibration of the spectrometer generally requires mixed gamma standards that contain as many as eleven radionuclides. Unfortunately, some of these radionuclides are short-lived with relatively short half-lives e.g. 27.7 and 64.8 days for Cr-51 and Sr-85, respectively. The short-lived nuclides limit the effectiveness of such calibration standards to only a few months. In this work, we report the development of a tri-nuclide calibration standard containing relatively long-lived Eu-154, Eu-155 and Sb-125 that allows it to remain effective for at least two years. The key to using the tri-nuclide as a calibration standard for HPGe spectrometry is to remove interferences resulting from coincidence summations.