A new method for gamma dose-rate estimation of heterogeneous media in TL dating

In this paper we develop a new method for gamma dose rate estimation of heterogeneous archaeological deposits. This method is based upon a computerised reconstruction of the gamma irradiating environment of the sample to be dated when applying any paleodosimetric methods such as thermoluminescence (TL), optically stimulated luminescence (OSL) and electron spin resonance (ESR). If the deposits overlying the sample to be dated have already been excavated, the missing upper environment (i.e. the relative position, the shape and the size of each lithologic component) is graphically reconstructed using the information recorded in field documents. For this purpose, the space surrounding the dated sample, within a 50 cm radius sphere, is decomposed into spherical volume elements, contiguous and centred on the dared sample. Within each volume element, the proportion of each lithilogic component is estimated. The K, U and Th contents of each lithologic component are determined. This enables us to quantify the effective radiochemical composition of any lithologic component. The relative weight of each volume element, which is related to the absorption properties of the gamma rays by the radioactive system bring studied (i.e. the dated sample and the surrounding environment) is estimated by a computation whose potentialities and limitations are discussed. Both this reconstruction and in situ radioactivity measurements were applied at the cave known as "Grotte XVI" in Dordogne (southwestern France), in order to assess the gamma dose-rate of TL dated burnt sediments extracted from a Mousterian combustion structure. In spite of its complexity, this reconstruction method yields a more suitable and more accurate determination of the environmental dose rate than the classical and/or simplified approaches. (C) 1998 Elsevier Science Ltd. All rights reserved.