PROGRESS IN TL DATING AT RISÖ

This article outlines the thermoluminescent dating technique employed at Risö. The intensity of beta and gamma radiation is determined by means of the TL phosphors CaSO₄:Mn and CaSO₄:Dy, and the determination of accumulated exposure is based on quartz and feldspar inclusions with a size of 0.3–0.5 mm. Results are presented of a dating programme comprising sherds, bricks, burned stones and burned clay (from kilns) from seventeen excavation sites. The age of the sites ranged from a.d. 1600 to 4000 b.c.     

COMPOSITIONAL INHOMOGENEITY OF SEDIMENTS AND ITS POTENTIAL EFFECTS ON DOSE RATE ESTIMATION FOR ELECTRON SPIN RESONANCE DATING OF TOOTH ENAMEL

We present results of particle size and radioactivity analyses of sediment samples collected from five sites with different burial environments. The uranium, thorium and potassium concentrations in the five sample sets are shown to vary with particle size. The potential effects of the observed size-dependent variations on electron spin resonance (ESR) dating of tooth enamel are assessed using two hypothetical models. Our results show that any bias to relatively fine fractions could result in a significant overestimation of the total environmental dose rate, leading to an underestimation of the calculated ESR age.     

FACTORS AFFECTING THE VIABILITY OF THERMOLUMINESCENCE DATING OF GLASS

The aim of this study is to achieve a better understanding of some of the factors that limit the thermoluminescence (TL) dating of glass. Using a‘model system’(lithium-disilicate samples having different levels of crystallinity from 0 to 100%), we show, first, that the TL of glass is reproducible only if the glass is not heated above its temperature glass transition and second, that there is a clear connection between the TL sensitivity and the degree of crvstallinity of the sample. We conclude that thermoluminescence is not a general dating method for archaeological glass, but it can be applied to particular glass samples that haue specified characteristics.     

OPTICAL DATING RESULTS FOR BRITISH ARCHAEOLOGICAL SEDIMENTS

In this paper optical dating results for a range of British archaeological sediments are presented to illustrate the potential this method offers for archaeologists. The optical dating is shown to offer an absolute method for directly dating the deposition of sediments for an age range of approximately 1–300ka. Problems have been found with recuperation of the optically stimulated luminescence signal and insufficient bleaching at deposition of the sediment. A suitable correction method for the recuperation has been found and a method of identifying insufficient bleaching is suggested.     

EVAPORITES OF THE WADI NATRUN: SEASONAL AND ANNUAL VARIATION AND ITS IMPLICATION FOR ANCIENT EXPLOITATION*

The evaporitic deposits of the Wadi Natrun on the edge of the Western Desert of Egypt have been used in variety of crafts and industries for over 6000 years. This paper reviews the formation processes of the evaporitic deposits between the different lakes in the wadi and for the wadi as a whole. It shows that the precipitation of sodium carbonate minerals within the lakes is seasonal and probably subject to long‐term fluctuation as climate varies. This has a significant impact on the use of the lakes for ancient industries, particularly the manufacture of glass.     

USE OF A WIRE SAW FOR SLICING CERTAIN SAMPLE MATERIALS FOR THERMOLUMINESCENT DATING

A method is described for obtaining accurate thin slices for thermoluminescence measurement of uniform materials, in particular burnt flint, which does not subject these materials to heat during the cutting process. Cutting is by means of a fine wire impregnated with diamond grit and gives a high standard of surface finish such that very little further preparation is needed. Thus, by the use of this method, there is a considerable saving in time as well as minimal risk of damage to the TL record of the materials during sampling.     

THERMOLUMINESCENT AUTHENTICITY STUDY AND DATING OF RENAISSANCE TERRACOTTAS

A comparative study is made of the thermoluminescence (TL) of terracottas of the Renaissance era and some known limitations of such ware dating to the middle of the last century. The data shows that conclusions on authenticity of an unknown work can be reliably obtained using this scientific method. Also examples are presented of accurate dating of genuine terracottas despite a lack of knowledge about the environmental circumstances of each piece's archaeological past.     

LUMINESCENCE DATING OF SEDIMENTS—THE DETECTION OF HIGH EQUIVALENT DOSE GRAINS USING AN IMAGING PHOTON DETECTOR*

In this paper we describe quantitative measurements on the thermoluminescence of many single grains, made with an imaging photon detector. In several of the sediments examined a few bright grains were found which had a high equivalent dose (ED). Physical measurements made on these grains using binocular microscopy and analytical scanning microscopy enabled several possible explanations for the causes of the high ED grains to be rejected. Insufficient bleaching at deposition or the intrusion of grains from an older sediment were identified as the most probable explanation for these grains.