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.
Precise measurement of dead time
Abstract Four methods are discussed by which dead times of the non-extending type can be determined experimentally. Two methods using statistical pulses were improved by eliminating uncertainties due to counting statistics. However, it was concluded from a comparison of the four methods that those using periodical pulses are not only less time-consuming but are preferable if high-precision values are aimed at. A dead-time unit with quartz oscillator-based dead times of the non-extending type was tested using all of the four methods. Measurements within a period of three years indicated that the unit investigated here has subnanosecond stability for each of the adjusted dead-time values.