Sedimentary Quartz Research Articles

Ultrafast component effects on quartz single grains dose estimation from Khutagt Uul Mountains, Mongolia

Abstract This study presents single-grain optically stimulated luminescence (OSL) results from pottery and sediments from the archaeological site “The burials in Khutag Uul Mountains (Mongolia)”. A global fitting procedure was used on a selection of single grains from pottery, D0 values obtained were between 16 to 40 Gy and 25 to 82 Gy and the equivalent doses De ranged from ~8 to 12 Gy and from 4.2 ± 0.4 Gy to 37.3 ± 2.5 Gy for pottery and sedimentary quartz, correspondingly. For pottery, the relative spread in CAM De values increases as higher precision constraints are applied and lead to significant increases in the relative standard error from 2.7% to ~7.5%. The number of accepted grains which passed acceptance criteria reduced from 180 to 65. For sedimentary quartz, there is a trend observed that both MAM De and FMM De values increase as higher precision in De is applied, and the number of accepted grains reduces from 146 to 53. The detailed study of the OSL decay curves identified an ultrafast OSL component with the decay rates of 53 ± 1 s–1 in addition to the fast and medium components and its effect on De was examined.

The compensation effect (Meyer–Neldel rule) on [AlO4/h+] and [TiO4/M+] paramagnetic centers in irradiated sedimentary quartz

The effect of thermal excitation on paramagnetic defects in natural sedimentary quartz irradiated with different doses of gamma radiation was studied using electron spin resonance (ESR) spectroscopy. We report a variation in the activation energy and the frequency factor for [AlO4/h+]0 and [TiO4/M+]0 paramagnetic defects with the gamma dose, for a dose range investigated between ∼100 Gy and ∼40 000 Gy. Our results indicate that both [AlO4/h+]0 and [TiO4/M+]0 defects are less thermally stable above 1 kGy–2 kGy than below this dose range. The correlation between the two kinetic parameters (activation energy and frequency factor) satisfies the Meyer–Neldel rule. A linear correlation was found between the amplitude of the ESR signals of [AlO4/h+]0 and [TiO4/M+]0 paramagnetic defects corresponding to different doses after the application of thermal treatments in the pulse annealing procedure. We propose a mechanism involving the exchange of the cation, assigned mainly to Li+ here, between the two defects. Under irradiation, the cation is removed from [AlO4/M+]0 (forming [AlO4/h+]0) to [TiO4]− (forming [TiO4/M+]0), while under heating, the reverse mechanism takes place. The migration energy of the cation from one defect to another was found to be about 51 meV, corresponding to a temperature of about 325 °C.

Insights into the relationship between luminescence and ESR dating signals from Spanish sedimentary quartz samples of different geologic origins

Trapped charge dating of optically bleached quartz deposits that lie beyond the dose-saturation limits of conventional optically stimulated luminescence (OSL) has typically focused on two main techniques over the last decade: electron spin resonance (ESR) and thermally transferred optically stimulated luminescence (TT-OSL). In spite of a clear association between these two dating techniques through their shared dose rate terms, the exact relationships between the various ESR centre (i.e., Al and Ti) and TT-OSL dating signals remain largely unexplored. In this study we undertake ESR and luminescence signal comparisons on paired sedimentary quartz samples from two Middle Pleistocene Spanish archaeological sites (Porto Maior in northwest Spain and Cuesta de la Bajada in northeast Spain) to examine the empirical relationships between quartz dating signals across different geological provinces. For this purpose we undertake 3-dimensional (3D) thermoluminescence (TL) spectral measurements, single-grain TT-OSL dating and signal analyses, normalised multiple centre (MC) ESR signal characterisation (ESR intensities, signal composition, dose-response curve properties), MC ESR De evaluation, and ICP-OES analysis of quartz extracts to evaluate potential correlations between elemental impurity concentrations and Al, Li–Ti and Li–H centre signals. The ESR samples from Cuesta de la Bajada and Porto Maior display similar Al centre signal intensities and dose-response behaviour, but they exhibit major differences in their Ti centre properties. Geochemical analysis reveals that the Cuesta de la Bajada quartz extracts contain higher concentrations of Al and Ti impurities (15 and 21% higher, respectively) when compared with the Porto Maior quartz extracts. These compositional differences appear correlated with the relative Ti–H signal intensities for the two sample datasets but not with the relative Al and Ti–Li signal intensities. The luminescence characterisation comparisons reveal a higher proportion of TT-OSL-producing grains in the Cuesta de la Bajada samples (6.2% versus ~1.6% for Porto Maior), and single-grain TT-OSL signal intensities that are almost an order of magnitude higher than for the Porto Maior samples. The 3D TL spectra for the Cuesta de la Bajada quartz are dominated by two major TL peaks in the red emission band (620 nm) at 265–310 °C and 365 °C (when using a heating rate of 1 °C/s), which are up to seven times more intense than the corresponding signals observed for the Porto Maior quartz. However, no major inter-sample differences were observed in the blue and UV-blue bands of the 3D TL spectra. These contrasting luminescence characteristics may be indicative of variable signal sensitisation histories related to dissimilar sedimentary recycling or geological origins between the two sites. Our results provide a useful baseline dataset for future comparative ESR and luminescence characterisation studies, and indicate a potentially close relationship between the quartz ESR Ti centre and single-grain TT-OSL signals. There is significant potential to refine understanding of these signal relationships in the future by expanding the number, and geographic coverage, of paired ESR–luminescence comparison studies, and by incorporating comparative 3D TL spectral investigations that focus exclusively on TT-OSL-producing grains (as opposed to bulk grain populations) to better elucidate luminescence trapping and recombination characteristics.

Assessing the Dating Potential of Violet Stimulated Luminescence Protocols

Violet stimulation is a new development in optical dating which has been suggested to extend the upper age limit of optically simulated luminescence (OSL) dating of quartz. Despite the reported advantage, few validation tests and applications have been published so far. The present study investigated the violet stimulated luminescence (VSL) using a single aliquot regenerative dose (SAR) protocol and a multiple aliquot additive dose (MAAD) protocol. Sedimentary quartz samples from four archaeological sites in Europe with independent age controls spanning 40–900 ka were used, including Grotte Mandrin (France), Brooksby Quarry (UK), Cueva Negra del Estrecho del Río Quípar (Spain) and Sima de las Palomas del Cabezo Gordo (Spain). The equivalent dose of a relatively young sample (∼40 ka) was successfully determined. However, significant underestimations were observed for older samples with higher doses. These findings indicate the need for further development of the measurement protocol to date high-dose natural samples.

On the dose dependence prior and after stimulation with visible light of E' and Al-hole centres in sedimentary quartz: correlation and mechanisms

On the dose dependence prior and after stimulation with visible light of E' and Al-hole centres in sedimentary quartz: correlation and mechanisms

Bleaching studies on Al-hole ([AlO4/h]0) electron spin resonance (ESR) signal in sedimentary quartz

Electron spin resonance (ESR) dating of sediments using quartz is most commonly used for older sediments (>100 ka), since large residuals render the ESR signal unsuitable for dating young sediments. The multiple-centre approach (utilising both Ti and [AlO4/h]0 signals) is usually used to test the resetting of the signals used for ESR dating. Here we work towards a better understanding of, and correction for, the residual signal in ESR samples of sedimentary quartz. We undertook multiple-centre ESR measurements using quartz [AlO4/h]0 and Ti signals on young aeolian samples of different grain sizes which have been independently dated using optically stimulated luminescence (OSL). Our results demonstrate that [AlO4/h]0 signal yields residuals indicating equivalent doses of about 500 Gy, substantially older than expected for the known OSL equivalent doses in the range of 8–37 Gy. The decay of [AlO4/h]0 signal as function of bleaching time can be represented by an exponential function. We investigate the dependence of the residual magnitude of the ESR signal as a function of the previous given dose and observe an exponential increase in the residual signal with dose. Such observations are consistent with the results of luminescence process modelling conducted for a model comprising two luminescence centres and several traps, one of which is a so-called deep disconnected trap that cannot be emptied during optical stimulation. We propose that bleaching occurs through an electron-hole recombination process with electrons released from optically sensitive traps. In addition to our new insights into the bleaching mechanisms of the [AlO4/h]0 ESR signal, we discuss the implications for the procedures used for performing residual dose corrections in ESR dating. We recommend that modern analogues be used in addition to laboratory-bleached samples when performing residual dose corrections.

Reassessing the timeframe of Upper Palaeolithic deposits in the Ceahlău Basin (Eastern Carpathians, Romania): Geochronological and archaeological implications

Abstract The Pleistocene deposits capping fluvial terraces in the Bistrita valley (Eastern Carpathians, Romania) host a high density of Upper Palaeolithic (UP) settlements, rendering this area a type-region for Late Pleistocene cultural evolution in eastern Romania and beyond. Despite its archaeological significance, site formation, palaeoenvironmental contextualisation and chronostratigraphy are still insufficiently resolved to draw a consistent picture of UP cultural dynamics. In the frame of recent excavations at the sites Bistricioara-Lutarie I and III (BLI, BLIII), we aimed at establishing a comprehensive multi-method (TL on heated flints, OSL on sedimentary quartz, radiocarbon dating of charcoal) chronology of the pluristratified archaeological records contained in the loess-like sediments on the lower and middle terraces of the Bistrița river. Therefore, new chronometric data are reviewed in conjunction with OSL ages and radiocarbon dates of a precursor study (Trandafir et al., 2015). Multi-emission TL ages of four heated flints, OSL sediment ages and radiocarbon dates are consistent within 2σ throughout the investigated archaeological profiles and allow a much more precise chronological framing of the identified lithostratigraphic units within the last glacial cycle. However, the silt-sized and sand-sized quartz fractions of a luminescence sample do not always produce identical results at 1σ. Numerical ages and field observations indicate that the geological record reaches back to Marine Isotope Stage 5 and is preserved on a lower terrace. Depending on their location, the investigated terrace cover beds represent genetically independent geomorphological units, and up to three palaeosols (cambisols) developed in the cover beds, of which at this stage of research only the youngest (PS1) can be traced unequivocally within all profiles. In archaeological terms, the new chronological framing confirms that the currently identified cultural layers belong to the Late Gravettian (28–25 ka BP), and to several Epigravettian stages (24–15 ka BP), leaving limited chronological space for the previously suspected Aurignacian presence at BLI and at other settlements nearby.

Phenomenological model of aluminium-hole ([AlO4/h+]0) defect formation in sedimentary quartz upon room temperature irradiation: electron spin resonance (ESR) study

The mechanism governing the production of the paramagnetic [AlO4/h+]0 centres (denoted also as Al-hole or Al-h) in quartz as a function of given dose is of great importance in electron spin resonance (ESR) dating, as the analytical function used to characterise the evolution of this centre with accumulated dose is used to derive the equivalent dose by extrapolation to the abscissa-axis. The single saturating exponential model fails to accurately represent the dose response curve especially at high doses, and consequently, empirical functions, such as a saturating exponential plus a linear term, are widely used in the dating community. Herein, a physical phenomenological model is presented to describe the Al-hole formation under gamma irradiation in sedimentary quartz. Based on previous studies it is known that the Al-hole centre is formed via the dissociation of the Al centres compensated with alkali ions [AlO4/M+]0 (generally denoted as Al-M) where M+ could be Li+, Na+ or K+, as well as by the dissociation of Al compensated with hydrogen ions [AlO4/H+]0, (denoted as Al–H). When irradiation moves interstitial alkali ions away from the aluminium ions, they can be replaced by H+ ions beside the conversion to Al-hole centres. By assuming that the rate of the dissociation process is proportional to the concentration of the defects themselves, a sum of saturating exponential functions is obtained for describing the growth of Al-hole with dose. The model is applied on data obtained on sedimentary quartz specimens of different origins for describing the dose response of the paramagnetic Al-hole ESR signal. We are showing that the signal of Al-hole does not reach full saturation at doses even as high as 100 kGy and can it be well represented by two exponential components as predicted by the model. As such, the additional linear term reported by other works when describing the dose response is just a first order approximation of one of the saturating exponential functions.

Bleaching studies on Al-hole Electron Spin Resonance (ESR) signals in sedimentary quartz

Bleaching studies on Al-hole Electron Spin Resonance (ESR) signals in sedimentary quartz

Deconvolution of isothermal TA – OSL decay curves from sedimentary quartz using combinations of various contemporary models

Thermally assisted optıcally stimulated luminescence (TA – OSL) stands as an experimental technique which encompasses the simultaneous use of optical and thermal stimulation. The technique can effectively stimulate electrons from traps with delocalization temperatures beyond 500 °C, also known as very deep traps (VDTs). For the case of quartz, TA – OSL is usually measured isothermally, at constant elevated temperature, yielding a decaying shape similar to that reported for the cases of conventional OSL. This feature is prevalent for all quartz samples. In the framework of the present study, a deconvolution analysis was attempted on the corresponding isothermal TA – OSL decay curves of 5 different quartz samples collected from the Aegean Anatolia region, Turkey. Deconvolution was performed on isothermal TA – OSL signals measured at a wide range of stimulation temperatures. Combinations of three different, well established, contemporary luminescence models were applied, two involving delocalized recombination via the conduction band, namely general order kinetics and photo-transfer models, along with one involving both tunneling recombination and delocalized recombination pathways. The use of the model of general order kinetics alone gives physically meaningless results, as the photo-ionization cross section of a specific component indicates a behavior which contradicts the luminescence models, yielding inverse Arrhenius law behavior. A combination of the general order kinetics and the photo-transfer models yields results without major physical inconsistencies. However, the thermal quenching parameters obtained according to the deconvolution procedure do not agree with the corresponding prevalent or even representative values for quartz. This latter feature, in conjunction to (a) the shapes of the residual thermoluminescence signal after TA – OSL, (b) the shapes of the TA – OSL with linear heating and (c) the shapes of the isothermal TA – OSL curves normalized over the initial intensity, suggest that the major part of the TA – OSL signal recombines via tunneling. The use of a combination of tunneling plus general order kinetic models has also been applied for the deconvolution analysis. The physically meaningful corresponding results indicate that in the absence of any other specific luminescence model for the isothermal TA – OSL decay curves, the latter combination of these two models provides the optimum case, not only for deconvolving the isothermal TA – OSL in quartz, but also for providing further insight to the physics of the phenomenon.

Calculating or simulating the dose rate? A comparison

Accurate determination of the environmental radiation dose-rate is crucial for dosimetric dating methods. Two approaches for dose-rate estimation are currently employed: (1) calculating and summing up individual dose-rate components, including propagation of uncertainties and (2) simulating the radiation field and calculating the absorbed dose using a Monte Carlo approach. Here we compare dose-rate estimation using the two aforementioned approaches, applied to six sedimentary quartz samples with differing radionuclide concentrations, chemical composition, grain-size distribution and water content and to one heterogeneous archaeological sample. For approach (1) two web-based, freely accessible calculators, “Dose-Rate calculator” (DRc), “Dose Rate and Age Calculator” (DRAC) and a bespoke spreadsheet were used. For approach (2) DosiVox, a Geant4 Monte Carlo simulation toolkit was employed which allows the definition of material properties such as chemical composition, density and porosity in addition to radionuclide concentrations and water content in a three dimensional geometry. The sensitivity of dose rate to material properties, usually assumed to be constant over the burial time scale, was also tested.The results obtained using the three dose-rate calculators for sedimentary quartz samples are consistent within uncertainties, mainly because the conversion and correction factors are all taken from the same references. Comparing these results with those obtained from DosiVox simulations show grain-size dependent dose-rate differences, caused by the charge build-up and attenuation of the irradiated grain-size fraction. Moreover, it reveals that the effect of porosity and moisture on dose rate is grain-size dependent. For the heterogeneous archaeological sample the total dose rate determined by a calculator is inaccurate for the alpha- and too precise for the beta dose-rate. We conclude that the standard approach to dose-rate estimation is robust and that DosiVox is an important diagnostic tool for samples originating from complex environments.

Electron spin resonance characterisation of sedimentary quartz of different grain sizes

Different optically stimulated luminescence (OSL) single aliquot regenerative (SAR) saturation characteristics have been previously reported for quartz of diverse grain sizes. This preliminary electron spin resonance (ESR) study documents on paramagnetic signals in natural sedimentary quartz extracts of different grain sizes (4–11 μm, 63–90 μm, 90–125 μm, 125–180 μm, 180–250 μm) extracted from loess and sand samples that are amendable to OSL and ESR dating. Spectra recorded at room temperature and low power (<1 mW) are dominated by the E1’ centre, whose intensity in natural samples was found to decreases with increasing grain size. The signature of titanium centre could not be detected in fine (4–11 μm) quartz. For coarse fractions (>63 μm) titanium-lithium [TiO4/Li+]0 signals increase with increasing grain size. Aluminium-hole ([AlO4]0) signals are observed in all natural and laboratory irradiated investigated samples when spectra are recorded at low temperature (90 K). The intensity of these signals appears to decrease with increasing grain size, however, room temperature measurements show that these signals are highly interfered by a variety of signals tentatively attributed to peroxy (g ≈ 2.007 and g ≈ 2.004) with significantly higher intensities in fine grains (4–11 μm). A decrease of their intensity is reported when grain size increases and partial evidence that these defects are preferentially located in damaged regions of the grains is presented. A dose dependent paramagnetic signal at g ≈ 2.011 was detected only in 4–11 μm quartz. The stronger signature of the [TiO4/Li+]0 signals in larger grains coupled with the weaker signals of peroxy signals interfering with [AlO4]0 signal measurement is suggesting that coarser fractions should be preferred for conventional ESR dating using aluminium-hole and titanium signals. The understanding of the implication of these defects in OSL dating alongside with their concentration dependency on grain size requires further investigations.

On the potential of the Electron Spin Resonance (ESR) dating method in geoarchaeological contexts: an overview of 30 years of investigation in the Iberian Peninsula

ESR dating is a palaeodosimetric method based on the detection and quantification of the trapped charges accumulated over time in the crystal lattice of some materials due to their exposure to natural radioactivity. Like any chronometric dating methods, ESR has strengths and weaknesses. In particular, whilst the precision achieved with ESR is not as good as that of radiometric methods (e.g. radiocarbon, Ar-Ar or U-Th), it does have the advantage to being able to be used on a wide range of materials, covering thus almost any geological contexts during the last 2.6 Ma. Amongst them, the ESR dating of fossil tooth enamel and optically bleached sedimentary quartz grains are probably the most interesting applications in archaeology. This study mainly aims at showing an updated overview of the potential -and current limitations- of the ESR dating method used in geoarcheological contexts, through a synthesis of the previous studies carried out on various sites of the Iberian Peninsula that have been published over the last 30 years.

Contribution des méthodes ESR et ESR/U-Th à la datation de quelques gisements pléistocènes de Chine

Since the beginning of the 2000s, studies concerning the chronology of the first human settlements in China were conducted by electron spin resonance (ESR) on sedimentary quartz and electron spin resonance coupled with U-series (ESR/U-series) on teeth in collaboration by French and Chinese teams on some Chinese archaeological or geological sites: Yunxian, Dali, Tangshan, Zongwei, Nihewan, Longgupo and several Giganthopithecus sites in Guangxi. After a quick overview of the used dating methods, some of the major results obtained during this collaboration will be briefly presented and discussed.

ESR dating of sedimentary quartz grains: some basic guidelines to ensure optimal sampling conditions

Electron Spin Resonance (ESR) applied to optically bleached quartz grains extracted from sediment provides an age estimate for the last exposure of sediment to sunlight. This method has been increasingly used in archaeological, geological and geomorphological contexts for the last 30 years. However, its successful application is highly dependent on the geological context and the type and quality of the material sampled. Therefore, appropriate sampling strategy and conditions are crucial to ensure reliable ESR ages. The aim of this paper is to provide basic background information on the best way to collect samples and select the most suitable materials for ESR dating. It is nevertheless highly recommended to contact an ESR geochronologist prior to fieldwork sampling.

Testing the suitability of dim sedimentary quartz from northern Switzerland for OSL burial dose estimation

We investigate the suitability of sedimentary quartz associated with former glacial advances in northern Switzerland to provide reliable burial dose estimates using Optically Stimulated Luminescence (OSL). Previous studies on northern alpine quartz show that its signal characteristics can be poor and potentially problematic. We analyse quartz signals of small aliquots, which reveal the presence of a prominent medium or slow component in the initial part of some signals. Nonetheless, rejection of aliquots with unfavourable signal composition does not alter the burial dose estimates, but significantly reduces the data set for D&lt;sub&gt;e&lt;/sub&gt; determination. Signal lifetimes from isothermal decay measurements cover a wide range of values, yet the lowest lifetimes are high enough to guarantee a reliable burial dose estimate for samples of &lt; 400 ka. Comparison of small aliquot and single grain burial dose distributions reveals that signal averaging masks partial bleaching in some of the samples. We therefore strongly recommend single grain measurements for samples from this setting and area, in order to exclude age overestimation due to partial bleaching.

Dose recovery and residual dose of quartz ESR signals using modern sediments: Implications for single aliquot ESR dating

Electron spin resonance (ESR) dating is a promising method for dating sedimentary quartz beyond a million years. Here we investigate the use of modern quartz samples with well bleached optically stimulated luminescence (OSL) signals to study the bleachability of the ESR signals, and to further check the applicability of the ESR single aliquot regenerative dose (SAR) protocol. The residual doses from five samples using both the Al- and Ti-centres were in general found to be large and, especially for the Al-centre, with a large variability. Although it is known that the Ti-centre is fully bleachable in nature, a subtraction of the residual dose using a modern analogue should be considered. Dose recovery tests were performed by using the single aliquot regenerative and added dose (SARA) method, and the dose recovery ratio (measured-to-added dose ratio) was obtained from the slope of the added vs. measured dose plot. The dose recovery ratio from the Ti-centre was satisfactory for all five samples indicating the validity of the proposed ESR SAR protocol. However, only one sample yielded a SARA plot for the Al-centre. This could be explained by the decrease in sensitivity caused by the annealing step in the SAR protocol and/or to the erroneous subtraction of the intensity of the peroxy centre, which overlaps with the Al-centre.

Chronology of the Pleistocene deposits at Elands Bay Cave (South Africa) based on charcoals, burnt lithics, and sedimentary quartz and feldspar grains

In 2011 we conducted a field campaign at the site of Elands Bay Cave (EBC), on the West coast of South Africa, with the aim of clarifying the nature and chronology of its human Pleistocene occupations. In the present paper, we present the results of a chronology based on various materials and methods: radiocarbon (C14) dating was applied to 8 fragments of charcoal whereas luminescence dating methods (OSL, IRSL and TL) were applied to quartz and feldspar grains extracted from 5 sediment samples and to 4 burnt fragments of quartzite rock. For the upper part of the sequence, the luminescence ages are either in agreement with or slightly younger than the C14 ages. The results suggest that the upper part of the EBC sequence extends from MIS3 to MIS2, including successively late Middle Stone Age (starting from 38 ± 3 ka), Early Later Stone Age (ending 22 ka ago) and Robberg occupations (starting 19.1 ± 0.3 ka ago). The lower part of the EBC sequence, associated with Early Middle Stone Age assemblages, remains poorly constrained: the sediment sample taken above could be a mixture of different layers and could not be dated, whereas OSL ages for sediments below are 236 ± 23 ka and only one stone sample could be dated within this layer (83 ± 14 ka). Considering both the chronological and techno-cultural points of view, the EBC sequence is complementary to the Diepkloof sequence, located less than 20 km eastward.

Chronology of the Pleistocene deposits at Elands Bay Cave (South Africa) based on charcoals, burnt lithics, and sedimentary quartz and feldspar grains

In 2011 we conducted a field campaign at the site of Elands Bay Cave (EBC), on the West coast of South Africa, with the aim of clarifying the nature and chronology of its human Pleistocene occupations. In the present paper, we present the results of a chronology based on various materials and methods: radiocarbon (C14) dating was applied to 8 fragments of charcoal whereas luminescence dating methods (OSL, IRSL and TL) were applied to quartz and feldspar grains extracted from 5 sediment samples and to 4 burnt fragments of quartzite rock. For the upper part of the sequence, the luminescence ages are either in agreement with or slightly younger than the C14 ages. The results suggest that the upper part of the EBC sequence extends from MIS3 to MIS2, including successively late Middle Stone Age (starting from 38 ± 3 ka), Early Later Stone Age (ending 22 ka ago) and Robberg occupations (starting 19.1 ± 0.3 ka ago). The lower part of the EBC sequence, associated with Early Middle Stone Age assemblages, remains poorly constrained: the sediment sample taken above could be a mixture of different layers and could not be dated, whereas OSL ages for sediments below are 236 ± 23 ka and only one stone sample could be dated within this layer (83 ± 14 ka). Considering both the chronological and techno-cultural points of view, the EBC sequence is complementary to the Diepkloof sequence, located less than 20 km eastward.

Non‐Destructive or Noninvasive? The Potential Effect of X‐Ray Fluorescence Spectrometers on Luminescence Age Estimates of Archaeological Samples

The non‐destructive nature of X‐ray fluorescence (XRF) spectrometers is a principal reason for an increase in their use in archaeological science over the last 15 years, especially for analyzing museum‐curated artifacts and in situ site fabrics. Here, we show that low‐power XRF spectrometry can be detrimental for luminescence dating (surface applications such as mud‐wasp nest dating in particular). We investigated the effects of irradiation by X‐rays emitted from handheld and benchtop spectrometers on optically stimulated luminescence (OSL) signals. Measurements were taken using a portable OSL (pOSL) unit on the following unprepared archaeological materials: sedimentary quartz grains, pottery, a mud‐wasp nest, stone tools, and a rock flake with anthropogenically applied pigment and natural pigmentation (iron oxides). We observed an increase in luminescence compared to initial background counts for all materials tested, which could lead to overestimation of age determinations in some situations. Our experiment provides a reminder of the potential effects of X‐ray radiation, and the need for thorough documentation of all recording and analytical techniques applied to archaeological materials.