A NEW METHOD FOR GAMMA-DOSE-RATE ESTIMATION OF HETEROGENEOUS MEDIA INTL DATING

In this paper we develop a new method for gamma dose rate estimation o f heterogeneous archaeological deposits. This method is based upon a c omputerised 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 e lectron 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 c omponent) 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 vol ume elements, contiguous and centred on the dared sample. Within each volume element, the proportion of each lithilogic component is estimat ed. The K, U and Th contents of each lithologic component are determin ed. This enables us to quantify the effective radiochemical compositio n of any lithologic component. The relative weight of each volume elem ent, which is related to the absorption properties of the gamma rays b y the radioactive system bring studied (i.e. the dated sample and the surrounding environment) is estimated by a computation whose potential ities and limitations are discussed. Both this reconstruction and in s itu radioactivity measurements were applied at the cave known as ''Gro tte XVI'' in Dordogne (southwestern France), in order to assess the ga mma 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 e nvironmental dose rate than the classical and/or simplified approaches . (C) 1998 Elsevier Science Ltd. All rights reserved.