Production of reference sources of radioactive aerosols in filters for proficiency testing.

In the framework of the organization of proficiency testing, filters with deposits of 137Cs and 90Sr+90Y radioactive aerosols have been submitted to laboratories for radionuclide measurement. Procedures for the special preparation and characterization of filters have been developed. The different steps of filter preparation, determination of the deposited radionuclide activity and characterization of the homogeneity of these deposits are presented. This method of filter preparation can also be used in the production of secondary standards, whose properties are more adapted to the needs of laboratories measuring radioactivity in filters than are the solid sources that they typically use.

Standardization of 222Rn by LSC and comparison with alpha- and gamma-spectrometry.

Liquid scintillation counting (LSC) was used for the measurement of 222Rn in equilibrium with its daughters, with detection efficiency close to 5. The appropriate corrections were considered, including one related to the probability that the 165-micros half-life 214Po decays during the dead time of the counter initiated by the disintegration of his parent nuclide, 214Bi. The dead-time determination of a commercial LS counter is also presented using a 222Rn standard source. The LSC 222Rn sources were prepared by transfer of 222Rn produced by a solid 226Ra source into LSC cocktail frozen at 77K, flame-sealed afterwards. They were measured using the LNHB triple coincidence counter with adjustable extending-type dead-time unit, between 8 and 100 micros; two different procedures were used to calculate an effective dead time and then to deduce the counting rate extrapolated to zero dead-time value. The LSC results were compared with those obtained by cryogenic alpha-particle spectrometry (LNHB system) and by gamma-ray spectrometry for the same radon source in the LSC vial; the geometry transfer coefficient was calculated using the ETNA software. Measurement results and uncertainties are discussed.

A novel method for large-area sources preparation for the calibration of beta- and alpha-contamination monitors.

A method is proposed for the preparation of large-area reference sources for the calibration of beta- and alpha-contamination monitors. It is based on the incorporation, by the ion-exchange mechanism, of the radionuclide in a thin film of a conducting polymer ion-exchanger preliminarily grown on a metal support. Conducting pyrrole-based polymer functionalized by carboxylic cation-exchange groups is used to prepare 60Co and 90Sr-90Y beta-particle sources. Electrochemical polymerization of the corresponding monomer on different conducting supports is studied and a special electrochemical equipment developed permitting the preparation of large-area polymer films of controlled and reproducible thickness. The ion-exchanger obtained is characterized in terms of chemical affinity for cations Co2+ and Sr2+. Incorporation of the radionuclides in the large-area ion-exchanger films thus obtained is studied and optimized with respect to the uniform distribution of the radionuclide. The performance of the procedure is demonstrated using the example of circular sources 44 mm in diameter prepared on stainless steel supports. The sources obtained are characterized in terms of activity, beta-particle flux, uniformity and source efficiency.

Analytical calculations of counting losses in internal gas proportional counting.

In internal gas proportional counting, the evaluation of counting losses is important in order to obtain high accuracy measurement results. In this paper, counting losses due to the wall effect and not counted beta particles with very low energy are evaluated by analytical calculations. The calculated and experimental results are compared and a very good agreement is found.

A radon 222 traceability chain from primary standard to field detectors.

The development of a primary standard from a method for measuring the absolute activity of 222Rn has also made it possible to establish secondary standards. Detailed procedures to obtain these secondary standards are given. These standards are, in particular, adapted to the requirements of laboratories that have developed equipment for the calibration and comparison of instruments measuring the concentration of radon and its daughters. An example of the implementation of these new resources applied to the qualification of field detectors is given. The propagation of measurement uncertainties at each level (primary, secondary, test radon chamber) is described.