LES VERRES ANCIENS: LA QUESTION DE LA DATABILITÉ PAR THERMOLUMINESCENCE

La plupart des échantillons de verres archéologiques ne sont pas datables par thermoluminescence. Une analyse des causes limitant l'extension de la datation par thermoluminescence aux verres anciens montre que celles-ci sont directement issues de caracteristiques de l'etat vitreux. Toutefois. dans certains cas particuliers, la datation est possible. Most archaeological glass samples cannot be dated using thermoluminescence (TL). An analysis of the causes which limit the extension of the TL dating method to ancient glass shows that these causes come from the vitreous state characteristics. Nevertheless in some cases, dating is still possible.     

Luminescence dating studies of Ye?ilova Hoyuk

Ceramic findings collected from Ye?ilova Hoyuk located in Izmir were dated using the thermoluminescence dating technique. The area is of significant archaeological importance since it is the first prehistoric settlement in Izmir. Recent archeological observations suggest that human occupation of the region took place about 8500 years ago comparing to previously determined dates of 5000 years. Three samples collected from the same archaeological layer (Neolithic period) in Ye?ilova Hoyuk were dated using the thermoluminescence method. Archaeological doses (AD) were obtained by single aliquot regenerative dose method (SAR) for thermoluminescence (TL) using coarse grain quartz minerals extracted from samples. Thick and thin Al₂O₃:C thermoluminescence dosimeters (TLD) were used to determine the annual dose rate. The archaeological doses were found to vary from 25.91±0.78 to 26.82±0.68 Gy, and the annual doses were found to be between 3.34±0.24 and 3.47±0.24 mGy/a. The ages obtained for the samples were determined to be 6000±830 BC, 5740±670 BC and 5460±740 years for samples ND1, ND2 and ND3, respectively, which supports the prediction of archeologist that the sampling layer dates from the Neolithic period.     

瓷器热释光测定年代研究

本工作从标准的(即线性的)前剂量技术着手,研究了瓷器热释光测定年代的方法。在这个研究中,发现了瓷器的灵敏度对剂量的非线性响应和灵敏度随剂量变化的指数模式。因此,一个用饱和指数拟合的方法被提了出来。实验表明,这是一个测定瓷器年代的成功方法。另外,还对一些与测定年代有关的复杂因素进行了讨论。例如,当少数瓷器的灵敏度与剂量不呈指数关系时,就要改变拟合模式或采用B的平均值方法等。     

A contribution to the study of post-depositional alterations of pottery using TL dating analysis

In luminescence dating, the potassium concentration significantly contributes to the dose rate value in the age estimation. Within this study, fine-grain thermoluminescence dating has been applied on sherds of calcareous pottery of known age, excavated at a Roman site in Mallorca, Spain. For those of the samples that showed signs of severe potassium leaching, according to chemical and mineralogical examination, the thermoluminescence analysis provided overestimated dates. By using the known archaeological age of the samples, a corrected dose rate value can be estimated which provides the potassium concentration averaged for the burial period. Finally, a step-like model can then be used to estimate the fraction of the burial period after which most of the alteration effects took place.     

用热释光测年方法鉴定唐三彩真伪

本文从唐三彩文物真伪鉴定的实际要求出发,以石英热释光测年方法为基础,在实验中对只取十几毫克洋品进行真伪鉴定的实验方法进行了探索.给出了不同出处的唐三彩进行中子活化后得到的 U、Th、K 含量与年剂量值,以及用上述方法对十八个唐三彩样品进行热释光实验得到的测定结果.     

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.     

Optically stimulated luminescence dating of heated materials using single-aliquot regenerative-dose procedure: a feasibility study using archaeological artefacts from India

Optically stimulated luminescence (OSL) dating of heated/fired materials of archaeological importance from various parts of India was attempted. A single-aliquot regenerative-dose (SAR) procedure was used for palaeodose determination in the quartz grains extracted from the heated materials using the luminescence produced by blue light stimulation. In most pottery samples, the palaeodose obtained using SAR-OSL is ∼6% lower than the palaeodose measured using thermoluminescence (TL) method. Broadly, there is good agreement between the SAR-OSL and TL ages of the artefacts and their archaeologically expected ages. The results suggest that routine dating of heated/fired materials using the SAR-OSL procedure is more practicable, especially when the TL sensitivity of the quartz grains is poor and availability of datable material is limited.     

THE EFFECT OF HF ACID ETCHING ON THE MORPHOLOGY OF QUARTZ INCLUSIONS FOR THERMOLUMINESCENCE DATING

The assumption of isotropic etching in hydrofluoric acid of quartz grains prepared for thermoluminescence dating has been tested by optical and scanning electron microscopy. We have found that the rate of etch is very irregular over the surface of many grains and that some grains are attacked much more severely than others. The uncertainty introduced into TL dating by this effect is discussed.     

Thermoluminescence as a technique for determining the nature and history of small solar system particles

The thermoluminescence phenomenon has been used for pottery dating and radiation dosimetry for sixty years and for forty years has been applied to the study of meteorites, being successful in quantifying metamorphic histories and providing new insights into terrestrial age and orbits. Here we review some of the fundamental properties of thermoluminescence with particular focus on the study of small extraterrestrial particles. We suggest that natural TL data can be used to identify the burial and release history of cometary particles and that induced TL measurements can provide in-sights into the mineralogy of particles (even when largely amorphous) and the metamorphic history of those particles. We illustrate the use of TL to study small particles by describing recent studies on micrometeorites and 10–100 μm fragments taken from the matrix of a meteorite Semarkona which is type 3.0 ordinary chondrite.     

前剂量热释光测定年代方法

分析了三种测量方法──多次激活、加剂量法和钉子技术的优缺点,并对细粒石英前剂量方法进行了专门研究。结果表明,细粒五英前剂量方法测量简便,减少了来自多次激活、试验剂量和归一引起的误差,最小可测年龄能达到几十年。     

ESTIMATION OF THE AGE OF A PRE‐INDUSTRIAL IRON SITE IN KOREA*

A pre‐industrial iron‐smelting site in Korea, whose period of active use is placed on typological grounds between the eighth and 18th centuries ad , has been dated using accelerator mass spectrometry and thermoluminescence. The ages of two charcoal samples were 77 ± 25 and 81 ± 25 years bp , with the calibrated date for both ranging from ad 1700 to ad 1955, while a clay fragment dated to ad 1650 ± 50. The results from typology and radiocarbon seem insignificant due to the considerable uncertainties involved, but in combination with the thermoluminescence result they place the most probable date of the site at around ad 1700.     

On the intrinsic accuracy and precision of luminescence dating techniques for fired ceramics

Luminescence dating techniques have been used extensively for archaeological and geological samples. Such techniques are based on thermally or optically stimulated signals. This paper presents simulations of several luminescence techniques for equivalent dose (ED) estimation for ceramic materials containing quartz. The simulations are carried out using a recently published comprehensive kinetic model for quartz, consisting of 11 electron and hole traps and centers. The complete sequence of the experimental protocols for several thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques are simulated using the same set of kinetic parameters. The specific simulated protocols are: additive dose TL protocol, predose technique (both additive and multiple activation versions), phototransfer protocol, single aliquot regenerative optically stimulated luminescence (SAR-OSL) protocol, and SAR thermoluminescence protocol (SAR-TL). One hundred random variants of the natural samples were generated by keeping the transition probabilities between energy levels fixed, while allowing simultaneous random variations of the concentrations of the 11 energy levels. The relative intrinsic accuracy and precision of the protocols are simulated by calculating the equivalent dose (ED) within the model, for a given natural burial dose of the sample. The intrinsic accuracy of these techniques is estimated by simulating natural irradiation of the samples with a known burial dose, followed by simulation of the luminescence method used to recover the estimated dose ED. The percent difference between the burial dose and the ED value represents the simulated accuracy of the luminescence technique. The relative intrinsic precision of these techniques is estimated by fitting Gaussian probability functions to the ED values obtained with the 100 model variants. It is found that the various techniques can reproduce natural paleodoses in the range 10 mGy–10 Gy with a typical intrinsic accuracy of +1 to 10%. Techniques based on single aliquot protocols were found in general to be more precise than techniques requiring the use of multiple aliquots. In addition, techniques based on interpolation of experimental data were found to be consistently both more precise and accurate than those based on extrapolation of experimental data.     

Stability of IRSL signals from sedimentary K-feldspar samples

Recent work has identified IR stimulated luminescence signals at elevated temperature from both potassium- and sodium-rich feldspars that have much lower anomalous fading rates than the conventional signal measured using IR stimulation at 50°C. This paper examines the stability of these signals for potassium-rich sedimentary feldspars. We show that the natural post-IR IRSL (pIRIR) signal from a 3.6 Ma old sample is in apparent saturation on a laboratory generated dose response curve, i.e. it does not show detectable fading in nature although a low fading rate is observed on laboratory time scales. We show that the pIRIR signal has a greater thermal stability than the IRSL signal and that the trend in increasing thermal stability is mirrored by a decreasing fading rate. We also investigate the effect of preheat temperature and IR stimulation power on the decay shape and conclude that the data can be explained in terms of either a single- or multiple-trap model. We present evidence that may suggest that at least part of pIRIR signal is derived from a high temperature trap (∼550°C thermoluminescence (TL) peak), although again the data can also be explained in terms of a single-trap model. Finally, we present dose response curves and characteristic curvature constants (D₀) values for various IRSL signals and conclude that the more stable signals saturate more quickly than the less stable signals and that the initial and final signals saturate at approximately the same level.     

THE ASSESSMENT OF RADIONUCLIDE DISTRIBUTION IN SILEX BY AUTORADIOGRAPHY IN THE CONTEXT OF DOSE RATE DETERMINATION FOR THERMOLUMINESCENCE DATING

A combination of two autoradiography methods was applied to investigate the radionuclide distribution patterns in a range of different silices. We obtained greyscale images (β‐radiation) and α‐track patterns for qualitative assessment, and used a statistical approach to quantify the degree of uniformity of the radiation fields. It was found that almost all samples are poor in potassium, thorium and uranium, and that locally high concentrations are present only in dark‐coloured veins and inclusions. Statistical analyses reveal evidence of radionuclide clustering in more than half of the 21 specimens. Concerning thermoluminescence dating of burnt lithics, such gradients should be taken into account to improve precision and accuracy in cases where the external radiation is not strongly dominating for the sample under consideration.     

DETECTION OF ANCIENT MARBLE FORGERY: TECHNIQUES AND LIMITATIONS*

Since 1960, scientific results have replaced aesthetic judgements in marble authentication studies and the technology to perform analytical tests on micro‐samples has developed rapidly. However, no single method can be used to determine the authenticity of a piece of marble. A ‘detective‐like’ investigation is usually adopted by using optical microscopy, ultraviolet‐induced fluorescence, provenance determination techniques and mineralogical, chemical and morphological analyses of the patina. A newly proposed thermoluminescence methodology calculates the ‘burial age’ of recently excavated objects or distinguishes artefacts exposed to sunlight since antiquity from those exposed recently. The technique shows a lot of potential; however, much work remains to be done.     

THERMOLUMINESCENCE AUTHENTICITY MEASUREMENTS ON CORE MATERIAL FROM THE BRONZE HORSE OF THE NEW YORK METROPOLITAN MUSEUM OF ART

The Bronze Horse of the Metropolitan Museum of Art, New York, suspected in recent years of being a modern forgery, is shown by thermoluminescence to have been made in antiquity. Besides the standard thermoluminescence measurements, a new technique was used, utilizing single, highly radioactive grains of zircon separated from the core material of the horse. The zircon grains, because of their high radioactivities (100–200 ppm) and subsequent large internal alpha doses (60–170 krad), are negligibly affected by γ irradiations given to the horse during previous examination. The results show the horse was made 2000 to 4000 years ago, consistent with a work of classical antiquity.     

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.     

Combined archaeomagnetic and thermoluminescence study of a brick kiln excavated at Fontanetto Po (Vercelli,Northern Italy)

A combined archaeomagnetic and thermoluminescence study was carried out as part of a rescue archaeological excavation on a kiln discovered during the installation of methane gas pipelines beneath a rice field, along the southern border of Fontanetto Po village (Vercelli province, Italy). A total of 23 independent brick samples have been collected, oriented in situ with an inclinometer; the use of magnetic and sun compass was not possible due to the existence of metallic tubes beneath the kiln and a plastic cover above it. Standard archaeomagnetic procedures have been used for the determination of the archaeomagnetic inclination and absolute geomagnetic intensity. Stepwise thermal demagnetization shows a very stable characteristic remanent magnetization and the calculated mean inclination of the 23 samples is I = 65.3° with α₉₅ = 2.4° and k = 156. Archaeointensity experiments have been performed using the classical Thellier method as modified by Coe, with regular partial thermoremanent magnetization (pTRM) checks. The cooling rate and remanence anisotropy effects upon thermoremanent magnetization (TRM) have been investigated in all the specimens. A total of 19 archaeointensity determinations (at specimen level) that correspond to linear NRM–TRM plots were used for the calculation of the site mean archaeointensity that is 46.4 ± 2.9 μT. Archaeomagnetic dating results show two possible dating intervals for the last 1000 years, calculated at 95% confidence interval: a first one from 1511 to 1614 AD, and a second one from 1768 to 1872 AD. Thermoluminescence (TL) study has been also performed on two brick samples from the kiln's internal wall, using conventional laboratory procedures. According to the thermoluminescence results the kiln's last usage lies between 1796 and 1914 AD. This age is in good agreement with the second dating interval obtained by the archaeomagnetic analysis. The combined archaeomagnetic and thermoluminescence results suggest that the last firing of the kiln could have occurred between the end of the 18th century and the beginning of 20th century.     

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.     

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.