The measured dependence of laboratory beta dose rates on sample grain size

The dependence of laboratory beta dose rate on grain size was measured using a Risø TL-DA-15 reader with the latest model of source housing (Radiat. Meas. 27(2) (1997) 83). In comparisons of optically stimulated luminescence signals due to laboratory beta-irradiation to similar signals due to external gamma-irradiations, no dependence of laboratory dose rate was observed for sample grain sizes between ∼55 and 250μm. Below 40μm there is a clear dependence on grain size, with the dose rate to 4-11μm grains being ∼12% lower than that for 55-250μm grains. The strength of dependence on grain size is less than that observed by Wintle and Aitken (Int. J. Appl. Radiat. Isot. 28 (1977) 625) and this difference is attributed to source geometry (specifically the sample-to-source spacing). For fine grains (4-11μm), there appears to be little dependence on mounted sample mass, over the range 0.1-1.5 mg (sample evenly mounted on aluminium discs, 10 mm in diameter).