Measurement of peak and total efficiencies of low-energy gamma-ray detectors with sources emitting photons in cascade

A method for measurement of peak and total efficiencies for point sources measured on low-energy gamma-ray detectors is presented. The efficiencies are measured with radionuclides emitting gamma-rays in a two-step cascade or in a crossover transition. One of the photons emitted in the cascade must have an energy which is much lower than the other in order to attain stronger attenuation as compared to the higher energy photon. The method is illustrated by measurements of the efficiencies with 179Ta and 57Co.