A natural calibration source for determining germanium detector efficiencies

In many applications of gamma-ray spectroscopy one is faced with the task of efficiency determinations for large and/or unusually shaped samples. We propose an efficiency calibration technique that takes advantage of the well-understood decays of the long-lived naturally occurring radioisotopes, 176Lu, 138La and 40K. Mixtures of known amounts of chemical compounds like Lu2O3, LuCl3, La2O3, La(NO3)3, K2SO4 and KCl provide efficiency values for six gamma lines ranging from 88 to 1461 keV. We present results of this procedure in different samples.