Determination of emission probabilities of gamma photons in the decay of 56Co

The emission probabilities of gamma photons in the decay of 56Co were determined at Czech Metrology Institute (CMI) by means of an HPGe detector. This detector was calibrated experimentally and by MCNP-computation in the energy range from 40 to 2754 keV for a point source geometry and source-to-detector distance of 25 cm. Experimental and computed peak and total efficiencies were compared and calibration curves were determined. Full-peak efficiencies were calculated for all 56Co γ-ray energies, and were used to calculate the emission probabilities. A set of point sources was prepared from a 56Co solution. The solution was standardized using the 4πβ–γ coincidence method, and an ampoule was sent to international reference system for activity measurement of γ-ray emitting radionuclides (SIR). Each point source was measured with the HPGe detector at a source-to-detector distance of 25 cm. Coincidence emission probabilities of all the gamma photons were calculated and used to determine the summing correction factors.