An examination of beta dose attenuation effects in coarse grains located in sliced samples

Abstract

Previous work has demonstrated the feasibility of performing spatially resolved luminescence measurements with sliced solid materials (e.g., rock and ceramic) to determine the cumulative absorbed dose to individual luminescent grains in situ. In the present study, aspects of the dosimetry of individual grains that are truncated during slicing were examined using radiation transport simulations employing simplified geometries. The results of the simulations were applied to model the effect of grain truncation on the dosimetry of grains, in particular the beta attenuation factor and the laboratory beta source dose rate for whole and partial volumes of individual spherical grains. Where a material contains a wide range of coarse grain sizes there is the potential for misinterpreting the size of the parent grain on the basis of an examination of the shape and size of the truncated grain section exposed in the slice surface. If the original grain size is underestimated, which is likely, the simulations predict an overestimation of both the beta attenuation factor and the laboratory source beta dose rate, the maximum extent of which depends on the range of grain sizes present in the material. The simulations also indicate that by limiting the depth from the surface within which the average absorbed dose is determined, approximating the effects of opacity of the mineral, the magnitude of these deviations is reduced. However, a consequence of particular interest deriving from these results is that, when evaluating the age equation, the changes in the two quantities compensate, acting to moderate the overall effect on the calculated age for an individual grain, depending on the geometry of the grain and the composition of the sample material.