Standardization of 109Cd by 4πe-x coincidence counting with a conventional gas flow counter and measurement of the 88-keV gamma-ray intensity

Standardization of 109Cd by two methods

¹⁰⁹Cd is quite a useful nuclide for the calibration of X-ray spectroscopy, gamma-ray spectroscopy or as an excitation source in X-ray fluorescence. In this work, 4π(PC)e-X coincidence counting and 4π(LS)ce counting were used to determine the activity of the ¹⁰⁹Cd solution. The two methods showed good agreement in their counting results. On the other hand, the mean value came from the results of the two methods was used to calibrate the well type ionization chambers to maintain the radioactivity measurement standard of ¹⁰⁹Cd at INER.

Activity standardization and nuclear decay data of 109Cd

The activity of a (109)Cd solution has been accurately determined without using (109)Cd nuclear decay data such as emission probabilities. An ampoule containing this calibrated (109)Cd 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 gamma-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 p(gamma)=0.03663(33) and a total internal conversion coefficient of alpha(t)=26.30(25) were determined.

The absolute counting of 125I

The Institute of Nuclear Energy Research (INER) participated in a comparison of activity organized by the Electrotechnical Laboratory (ETL, Japan). At this occasion, 125I was measured. Seven laboratories of the Asia Pacific region carried out measurements and ETL, at the same time, took part in BIPM SIR measurements. Two measurement methods developed by INER, the sum-peak coincidence counting with two 76 x 76 mm NaI(Tl) detectors and the 4pie-X coincidence counting technique with efficiency extrapolation, were used to standardize the activity of 125I. The results from the two methods are 2.6% different. INER's results agree with the results of the regional comparison and the BIPM SIR.