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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]

When conducting uniformity measurements of a wide area reference source with a detector having a window of a size similar to that of a gridded individual portion area on the source, it is important to carefully consider neighbor effects on measuring emission rates of the individual target portion resulting from the gap between the source and detector window. Optimization of the uniformity measurement conditions was studied for beta-emitting wide area reference sources in this study. A measurement system consisting of a PR-gas (Ar: 90%+CH 4 : 10%) flow type windowed proportional counter and a motorized XY stage was installed. This system is adapted to the uniformity measurement of two different types of 36 Cl sources made by different manufacturers. Uniformity measurement of a 100 mm×100 mm source divided into 16 portions of 6.25 cm 2 (25 mm squared) each could be conducted using our system under the present conditions with a neighbor effect of around 15% or less. The measurement results by use of this system were also compared with those using the imaging plate technique. [ABSTRACT FROM AUTHOR]