Investigations of uranium distribution in flints

Thermoluminescence (TL), which is commonly used to date burnt flints from Palaeolithic sites, sometimes yields ages which are younger than those obtained by other methods. Many reasons could explain such discrepancies and one concerns the evaluation of the dose-rate originating from the sample itself, i.e., the internal dose-rate. In order to refine the parameters used in the internal dose-rate estimation, we investigated the uranium (U) distribution by the induced fission track method in three archaeological flint specimens. This approach shows that the U distribution is roughly uniform on a scale of a millimetre but not on a smaller scale (<100 μm), because of the presence of quartz grains whose size is sample-dependent and because of relatively high local U concentrations. Therefore, the assumption of a homogeneous U distribution currently used to estimate the beta and alpha dose-rates may not be fully appropriate for all samples; in this case, this could lead to an underestimate of the TL age.