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Abstract: If high-energy beta particles are required for the efficiency determination of surface contamination monitors, wide area filtered 90Sr/90Y sources are commonly used instead of short-lived pure 90Y sources. In this work we show how the instrument efficiencies are dependent on filtering. Significant difference in the instrument efficiencies between filtered 90Sr/90Y and pure 90Y source was obtained due to spectral degradation of the beta emission spectrum. Changes in the β-particle spectra were investigated by the use of a plastic scintillation spectrometer and the anisotropy of β-particle fluences was examined to clarify the possible reason of such discrepancy. [Copyright &y& Elsevier]

Abstract: Calibrations of instrument efficiency of surface contamination meters are usually made with extended reference sources which are standardized in terms of 2π surface β-particle emission rates from the source surface including backscattered particles. Extended sources supplied from various metrology institutes or calibration laboratories, but the source-types such as structure, preparation method, backing and covering materials vary between manufacturers. In this work first we show how the calibration results are dependent on the source type. Second, in order to clarify the possible reason of such discrepancy, we examined the isotropy of β-particle fluences by the use of a proportional counter and also observed the angular dependence of β-particle spectra by the use of small plastic scintillation spectrometer, where the source mount can rotate relative to the detector window at various obliquities. The discrepancy in the instrument-calibration of surface contamination meters, which are mainly used under the conditions of large source-to-detector geometry, can be explained. [Copyright &y& Elsevier]