Activity standardization and nuclear decay data of 109Cd

The activity of a 109Cd solution has been accurately determined without using 109Cd nuclear decay data such as emission probabilities. An ampoule containing this calibrated 109Cd solution was sent to the Bureau International des Poids et Mesures to include the activity result in the database of the International Reference System (SIR). The emission rate of conversion electrons was measured by means of pressurized proportional counters as well as by a liquid scintillation spectrometer. The combination of the results with the photon emission rate measured with the aid of γ-ray spectrometers yields the activity concentration. The measurement results were also used to deduce emission probabilities with high accuracy. For the 88 keV transition, a photon emission probability of pγ=0.03663(33) and a total internal conversion coefficient of αt=26.30(25) were determined.