Bias in the measurement of radon gas using ionization chambers: Application to SIR.
Two main non-destructive techniques can be used to measure standard 222Rn gas ampoules: well-type ionization chambers and gamma-ray spectrometry, the former being used in the Système International de Référence (SIR) for international comparison purposes. The reliability of these techniques requires that the variability of the flame-sealed gas glass ampoules used have a negligible influence on the detector response. This variability is studied in this work by considering three parameters: the volume of the ampoule, the position of the sealing point and the thickness of the glass. Results showed that variability of the gas ampoules induced measurement bias larger than the uncertainty of the standard sources.
The Système International de Référence and its application in key comparisons
The paper begins with the reasons which led to the installation of the Système International de Référence (SIR) more than 30 years ago, describes its main features and presents briefly the way it works. Then more detail is given on the treatment of impurities and on the determination of the efficiency curve. The improvements, which have been made recently to update the SIR and make it more efficient, are also discussed. A brief survey of the status of the present SIR is then given before focusing on the new developments which are in progress to enlarge the scope of the SIR towards measurements of radiopharmaceuticals with short half-lives and of α- and β-particle emitters.
Influence of radioactive impurities on SIR measurements
The correction usually applied to an SIR measurement in the presence of a gamma-ray emitting impurity is presented and explained. The method of calibration of a Ge(Li) spectrometer is briefly described. It is used to look for impurities when SIR measurements show inconsistencies. An example is presented where a 103Ru impurity was discovered in a 99Mo solution. The correction applied compensates for the decrease of around 0.2% per day observed in the SIR measurements of this 99Mo ampoule.