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The interlaboratory comparison that 148 laboratories participated was performed to understand the validity and variability of measurements with NaI(Tl) scintillation detectors for samples near the standard limit for radioactive cesium in general foods in Japan. Brown rice grains with certified massic activity of radioactive cesium were used as test samples. The medians of the reported massic activities of radioactive cesium, 134Cs, and 137Cs in brown rice grains agreed with the reference values. On the point of view for inspection, more than 92% of the reported values were within the acceptable range. [ABSTRACT FROM AUTHOR]

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]