THERMOLUMINESCENCE DATING OF POTTERY: AN ASSESSMENT OF THE DOSE-RATE FROM RUBIDIUM

The naturally occurring radioisotope ⁸⁷Rb makes a small contribution to the total dose-rate. Assuming an average potassium:rubidium ratio of 200:1 the contribution is estimated at 2.9% of the B dose-rate From potassium. The effect will be negligible in quartz inclusion dating because of the strong attenuation of the B- emission from ⁸⁷Rb. In fine-grain dating the omission of the ⁸⁷Rb contribution will overestimate the age of a pottery sherd by not more than 2% and this is regarded as of minor importance when the total error in the technique is at least 15%.     

THERMOLUMINESCENCE DATING: RADIOACTIVITY IN QUARTZ

Alpha activities measured for four quartz extracts indicate that, in some samples, the alpha dose-rate to the quartz due to radioactivity within the quartz can be significant. Uranium mapping of the quartz by neutroninduced fission tracks shows that the radioactivity is not homogeneously distributed.     

THERMOLUMINESCENCE DATING OF STALAGMITIC CALCITE

The thermoluminescence (TL) method of dating stalagmitic calcite has been applied to twenty-seven samples from two paleolithic cave sites; Pontnewydd, Wales, and Caune de l'Arago, Tautavel, France. Environmental dose-rates were evaluated mainly by means of CaF₂ capsule burials. The ages of the stalagmitic samples were independently determined by means of the uranium series disequilibrium method. In general, good agreement is found between the TL and uranium series dates, which cover a range from approximately 15 000 to 300 000 years B.P. It is estimated that the TL method should extend to the order of a million years in good circumstances.     

AUTO-REGENERATIVE THERMOLUMINESCENCE DATING USING ZIRCON INCLUSIONS

Fired ceramics containing zircon inclusions have been dated by allowing the zircons to regenerate their own thermoluminescence (TL) signal, hence auto-regenerative TL dating. The technique is conceptually straightforward. One first measures the TL accrued since the last heating of the material. The zircon grains are then stored for six months and the TL signal regenerated through self-irradiation is measured. Since the internal dose-rate for zircon is dominated by the internal component the age of the sample is simply given by the ratio of the natural to auto-regenerated signal times the laboratory storage period. The technique, however, requires the measurement of a very small auto-regenerated signal, which introduces a number of experimental and physical complications. The methods for overcoming these problems and successfully dating zircons by auto-regeneration are described.     

DATING ARCHAEOMETALLURGICAL SLAGS USING THERMOLUMINESCENCE*

Thermoluminescence has a great potential for dating archaeometallurgical slags, because the smelting process leads to a well‐defined resetting of the ‘luminescence clock’. However, the complex compositions of slags have unpleasant consequences for TL measurements if the bulk slag substance is used. To overcome this problem, quartz has been separated out of slag matrices by chemical and physical procedures. The TL measurements were carried out on this defined mineral phase. This method was tested with seven slag samples from different locations and ages. In most cases, the TL ages determined show good agreement with reference data.     

SUPRALINEARITY CORRECTIONS IN FINE-GRAIN THERMOLUMINESCENCE DATING: A RE-APPRAISAL

Supralinearity correction in the routine ‘fine-grain’ technique of thermoluminescence dating of pottery has previously been regarded as empirical, but can now be shown to depend in many cases upon the previous radiation history of the material. The likely impact of this effect upon ceramic and bronze dating is considered and illustrated.     

THERMOLUMINESCENCE DATING OF BURNT FLINT AND QUARTZ: COMPARATIVE RESULTS

Thermoluminescence dates obtained from burnt flints and quartz recovered from the same sites are compared. For the Upper Perigordian level at la Vigne Brun (Loire, France), four quartz specimens and three flints yielded average ages of 27 400 ± 2300 and 26 900 ± 2200 years respectively, which are 15% greater than the radiocarbon age obtained for the same site (Evin 1982). For the neolithic site of la Vallée aux Fleurs (Loir et Cher, France), the respective averages of three flints and three ceramic sherds were 6830 ± 560 and 6570 ± 520 years.     

THERMOLUMINESCENCE DATING OF MATERIALS WHICH EXHIBIT ANOMALOUS FADING

This article reports a generalised and systematic approach to the thermoluminescence (TL) dating of samples which suffer from anomalous fading. We hypothesise that the TL signal from each mineral phase is composed of a stable and an unstable portion. The decay of the unstable TL is accelerated thermally, until only stable TL remains. The dating is then carried out on this stable signal. The results, on four known-age, coeval samples, exhibiting gross anomalous fading (25-50% loss over a few days), indicate that many, if not all, samples may successfully be dated with this approach.     

A NEW THERMOLUMINESCENCE DATING TECHNIQUE FOR HEATED FLINT*

A new thermoluminescence (TL) technique for determining the age of heated flint artefacts from archaeological sites is presented. It is a variant of the SAR protocol, which is usually used for OSL dating of sediment, but it is not based on a presumed model for fitting the dose–response curve. Dose recovery tests as well as comparisons with standard protocols show the accuracy of the new technique. It is found that the sensitivity of the thermoluminescence (TL) signal of flint in the orange–red waveband does not show severe changes due to the heating process while measuring the TL. This allows the application of a short SAR procedure, which requires only two dose points. The technique does not require as much instrument time as other SAR techniques, and thus is advantageous for dating very old samples. The major advantage of this new technique is the small amount of sample material required, which allows the dating of samples that are too small for standard TL dating techniques.     

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.     

CHARACTERIZATION AND THERMOLUMINESCENCE DATING OF PREHISTORIC POTTERY SHERDS FROM MILENA

This paper reports the results obtained applying absolute dating methodologies and mineralogical, petrographical and micropalaeontological characterization techniques to prehistoric pottery sherds varying in age from the Sicilian Middle Neolithic to Bronze Age. All samples came from the archaeological area of Milena (Caltanissetta, Sicily); those of the Bronze Age were found on a site with a precise stratigraphic succession. The investigation has contributed to the determination of an absolute chronology for the Milena prehistoric period. The data provide, for the first time in Sicily, absolute dates covering a wide spectrum of cultures following one another in the same area and, for the Bronze Age site, correlated to the precise stratigraphic succession. The petrographical and mineralogical analyses allowed not only the identification of the principal constituents of the pottery, but also the formulation of some hypotheses regarding the specific manufacturing techniques of different epochs. The microfacies, obtained from the presence of fossils in the groundmass of the pottery, were also analysed and compared with the microfauna present in the Miocene clays outcropping in the area. The data identified local Messinian clay as the raw material probably used in the manufacture of the pottery and also support the presence, already assumed by archaeologists, of imported Mycenaean pottery, thus supporting the dates obtained on pottery taken from the same stratum.