Multiple Aliquot Additive Dose Research Articles

Extending the ESR and OSL dating comparison on coastal dune deposits from the Wilderness-Knysna area (South Africa)

Our work follows up on the initial methodological ESR dating study by Ben Arous et al. (2022) on several quartz samples from the Plio-Pleistocene to Holocene aeolian coastal dune deposits of the Wilderness-Knysna area (South Africa) that were previously dated by optically stimulated luminescence (OSL). Here, we extend this first ESR-OSL comparison with five additional optically-bleached quartz samples. We used the Multiple Aliquot Additive Dose (MAAD) method to specifically (i) evaluate the influence of the irradiation dose steps on the determination of low De values (<100 Gy) and (ii) obtain finite ESR ages for older samples that sometimes show saturated OSL signals. Following the Multiple Centre ESR dating approach, the Aluminium (Al) and Titanium (Ti) signals (Ti–H and Ti–Li–H, the latter resulting from a mixture of Ti centres) were systematically measured in all samples, and resulting De values and age estimates were compared with the corresponding OSL data. Our results show that for young samples (<50 ka) showing De values of a few tens of Grays (Gy), the use of smaller irradiation steps spaced by < 100 Gy has a noticeable impact on the MAAD dose evaluation from the Ti centres, usually leading to De results closer to the expected values (for 2/3 samples). However, this also makes the ESR measurements somewhat more challenging, with higher experimental uncertainties, lower measurement repeatability and lower goodness-of-fit resulting from the relatively weak Ti ESR intensities, ultimately impacting the robustness of the ESR data collected. In this sense, our study illustrates the limitations of the ESR method to detect very low dose irradiation values < 30 Gy with our experimental conditions (i.e., using MAAD procedure, a standard resonator and a measurement temperature of ∼90 K). On the contrary, it also highlights the greater potential of the Ti–H signal to date Late Pleistocene samples, confirming previous studies. Moreover, our results suggest that the transport and bleaching conditions of these aeolianite deposits may not be ideal for the reset of the radiation-induced Al and Ti ESR signals, which is consistent with the very few existing studies specifically focused on this type of samples, but contrasts with other previous dating applications centered on fluvial environments. Finally, we also provide additional chronological constraints to the Landward barrier complex and Coversands deposits, two of the oldest Plio-Quaternary formations in the Wilderness-Knysna area.

Thermoluminescence dating of gypsum in loess deposits

Gypsum deposits within loess deposits are an important indicator of weathering processes and climate change. We conducted a thermoluminescence (TL) dating study of the gypsum from loess deposits of the Jiuzhoutai section in the western Chinese Loess Plateau. Determination of the equivalent doses (De) of gypsum samples was conducted using several protocols, including single-aliquot regenerative-dose (SAR-TL), multiple-aliquot additive dose (MAAD-TL), and Isothermal TL of SAR (SAR-ITL). The TL glow peak at 280 °C was targeted because of its reported stable signals. The test dose check, estimation of sensitivity changes, and the dose recovery test were applied to assess the applicability of the different protocols, and the characteristics of the thermoluminescence signals for gypsum were evaluated. The De results for the SAR-TL, MAAD-TL, and SAR-ITL protocols were within the error ranges. Among the three protocols, SAR-ITL did not involve high-temperature heating and it provided a more accurate De value, and thus it was used for De determinations for gypsum dating. With a dose rate of 1.74 ± 0.07 Gy/ka, the minimum TL age of the gypsum veins was ∼182 ± 7 ka. U-series dating was also applied to the same samples for comparison. However, the extremely low ratio of 230Th/232Th (≤4 × 10−6) of the gypsum veins deposited within the loess resulted in a large error of the U-series dates. We conclude that TL dating is more appropriate for the dating of gypsum in loess deposits.

ESR dating of optically-bleached quartz grains: Evaluating measurement repeatability and reproducibility

The true random uncertainty associated with ESR measurements of quartz grains at cryogenic temperature is currently unknown, as well as its impact on resulting equivalent dose (DE) estimates for ESR dating purpose. We provide here the results from the first quantitative evaluation study based on experimental data. Repeated single aliquot and multiple aliquot measurements of 100–200 μm quartz grains show that the random uncertainty (1σ) on the measurement of an individual aliquot usually lies in the range of 1–2%, 2–3 and 3–6% for the Al, Ti and Ti–H signals, respectively. These values are strongly sample and laboratory dependent, as they directly correlate with the signal-to-noise ratio associated with each signal, and may also be influenced by the stability of the experimental setup. The resulting variability of the DE values obtained from the multiple aliquot additive dose method over repeated measurements is estimated to 9%, 11% and 24% (1σ) on average for the Al, Ti and Ti–H signals, respectively.In the light of this outcome, the reliability of a dose estimate derived from one single measurement may be reasonably questioned, and we strongly advocate for the necessity to systematically carry out repeated measurements of a given quartz sample, a procedure that is far from being systematic within the community. Finally, our reproducibility experiments suggest that the experimental setup, measurement temperature or operator do not induce a significant bias in the dose evaluation, provided that repeated measurement are carried out. Our small-scale interlaboratory comparison shows consistent DE results for the Al and Ti signals, giving us some general confidence for the comparison of the dating results obtained by independent laboratories. We nevertheless acknowledge that a larger intercomparison study should be performed within the ESR dating community in order to confirm these initial results.

Characteristics of the quartz isothermal thermoluminescence (ITL) signal from the 375 °C peak and its potential for extending the age limit of quartz dating

The quartz isothermal thermoluminescence (ITL) signal measured at 330 °C (ITL330) has been proposed as a method to measure deep traps in quartz, i.e., 375 °C TL peak, therefore offering the potential to extend the dating limit of quartz. However, little is known about the applicability of this signal for dating. We therefore investigate the characteristics of the ITL330 signal, in terms of the origin of the signal, thermal stability, and bleachability. Since the trapping sensitivity changes induced by high temperature treatments undermine the application of the single aliquot regenerative dose (SAR) protocol, here we evaluate the reliability and applicability of the multiple aliquot methods, i.e., multiple aliquot additive dose (MAAD) and multiple aliquot regenerative dose (MAR) protocols, using samples from the Luochuan section on the Chinese Loess Plateau with the independent age control. Results indicate that the ITL330 signal is closely associated with the 375 °C peak of the glow curve, originating from a deep trap at about 1.8 eV with a thermal lifetime of ∼1010 years at 10 °C. The natural ITL330 dose response curve (DRC) indicates the signal has a theoretical dating range up to ∼800 Gy, equivalent to ∼230 ka. When the natural DRC is compared with the laboratory generated DRCs using MAR and MAAD protocols, they start to diverge in shape after ∼200 Gy, resulting in significant ITL330 age underestimation beyond ∼70 ka. However, application of the pulsed-irradiation (PI) method for the MAAD protocol reveals that the shape of the natural DRC can mostly be reproduced with the PI-MAAD protocol and thus it can provide reliable ages up to natural saturation at ∼230 ka. While further investigations are required to assess the impact of the repeated pulse irradiation and heating on the signal and determine the optimal pulsed irradiation conditions, it appears that this approach can be a promising step forward to provide a better simulation of the trapping conditions in nature.

Equivalent dose estimation of calcite using isothermal thermoluminescence signals

Thermoluminescence (TL) signals of calcite can be used to potentially date geological and archaeological events back to several million years. However, several issues, such as spurious TL signals appearing at temperatures above 300 °C, have hindered its application to a wide range of samples. A single-aliquot regenerative-dose (SAR) protocol for calcite with low-temperature measurements is proposed to measure the equivalent dose (D e ). It uses the isothermal TL (ITL) signals measured at around 225-240 °C, where a D e vs. ITL temperature (D e -T) plateau can be observed. The width of the temperature range of such a plateau can be sample dependent, as it relates to the proportional contributions of the signals from corresponding TL peaks. The signal at the ITL temperature plateau range largely corresponds to the TL signals of the 280 °C TL peak. D e values obtained by the SAR-ITL protocol are in agreement with those of the multiple-aliquot additive-dose (MAA)-TL and MAA-ITL protocols. The absence of detectable anomalous fading of ITL signals at 235 °C in this and previous studies indicates that the signal is free of fading. Dose recovery tests confirm the suitability of the SAR-ITL protocol for D e estimation. The SAR-ITL protocol measured with temperatures below 300 °C avoids the effects of spurious luminescence signals induced by high-temperature heating. The dose-response curves for ITL signals at 230-235 °C have large characteristic saturation doses (D 0 ) of ∼2000-2400 Gy. The SAR-ITL protocol for calcite thus has the potential to date geological and archaeological samples spanning the entire Quaternary period. • Thermoluminescence (TL) and isothermal TL properties of calcite are investigated. • Equivalent dose plateau using isothermal TL signals is identified within ∼225-240 °C. • SAR-ITL protocol avoids the influence of spurious signals appearing at >300 °C. • Isothermal TL signals of calcite at ∼230-235 °C saturate at ∼4800 Gy.

ESR dating of optically bleached quartz grains from Plio-Pleistocene to Holocene coastal dune deposits (Wilderness-Knysna area, South Africa): a comparison with luminescence

Five Plio-Pleistocene to Holocene aeolian quartz samples from the coastal dune deposits of the Wilderness-Knysna area (South Africa) previously dated by OSL were selected for ESR dating. Samples were processed following the Multiple Centre approach and using the Multiple Aliquot Additive dose method. Aluminium (Al) and Titanium (Ti) signals were systematically measured in all samples. Our study shows that ESR results obtained for Middle Pleistocene to Holocene samples may be strongly impacted by (i) the presence of a significant high frequency noise in the ESR spectra acquired for the Ti signals and (ii) the choice of the fitting function employed. In particular, if not taken into account, very noisy spectra can lead to a significant overestimation of the true ESR intensity measured for the Ti–H signal. These sources of uncertainty are however not sufficient to remove the ESR age overestimations. Consequently, our results indicate that the Al and Ti ESR signals of these quartz samples have not been fully reset during their aeolian transport. While this work contributes to improve our understanding of the ESR method applied to quartz grains, and especially of the potential and limitations of the Ti signals, it also provides additional baseline data to illustrate the existing variability among quartz samples of different origins or sedimentary context. Our results are consistent with previous studies by confirming that the Ti–H signal shows the best potential for the evaluation of low dose values (<100 Gy for these samples), whereas it becomes inappropriate for the higher dose range, and the Ti–Li–H (option D sensu Duval and Guilarte, 2015) should be used instead. Beyond the methodological outcome, this ESR dating study also provides a useful addition to the existing chronology of the aeolian deposits in this region. In particular, new (and possibly) finite numerical age results were obtained for the two oldest samples, constraining the aeolianite landward barrier dune and the coversand formations to the MIS 10-8 and Pliocene, respectively.

Developing an internally consistent methodology for K-feldspar MAAD TL thermochronology

Luminescence thermochronology and thermometry can quantify recent changes in rock exhumation rates and rock surface temperatures, but these methods require accurate determination of several kinetic parameters. For K-feldspar thermoluminescence (TL) glow curves, which comprise overlapping signals of different thermal stability, it is challenging to develop measurements that capture these parameter values. Here, we present multiple-aliquot additive-dose (MAAD) TL dose–response and fading measurements from bedrock-extracted K-feldspars. These measurements are compared with Monte Carlo simulations to identify best-fit values for recombination center density (ρ) and activation energy (ΔE). This is done for each dataset separately, and then by combining dose–response and fading misfits to yield more precise ρ and ΔE values consistent with both experiments. Finally, these values are used to estimate the characteristic dose (D0) of samples. This approach produces kinetic parameter values consistent with comparable studies and results in expected fractional saturation differences between samples.

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.

Luminescence chronology of the northeastern Bulgarian loess-paleosol sequences (Viatovo and Kaolinovo)

The key reference loess sequence of Viatovo in NE Bulgaria, lying within the lower Danube basin, records climatic and environmental changes over the last 800 ka. This 20 m thick loess sequence consists of seven loess units (L1 to L7) intercalated by six paleosols (S1 to S6) below the modern soil (S0). The Matuyama-Brunhes palaeomagnetic boundary has been identified in the lowest loess unit (L7). This reference loess sequence remains so far undated by radiometric techniques. Its chronostratigraphy relies only on pedostratigraphic and magnetostratigraphic evidence. This contrasts with the adjacent reference loess sequences of SE Romania (Tuzla, Mostistea, Mircea Vodă) whose luminescence chronology is now securely established up to MIS 8.The aim of this study is to validate the chronostratigraphic framework of the Viatovo loess sequence using the luminescence dating method. For this purpose, the luminescence method is applied to the three upper loess units (L1, L2, L3) from two adjacent sites: the reference site of Viatovo and the nearby site of Kaolinovo, both located in the Ludogorie region (NE Bulgaria) and showing the same superposition of loess (L1 to L7) and interbedded paleosols. Luminescence dating (Infrared stimulated luminescence; IRSL) was carried out using the feldspar fine sand-size grain fraction (60–80 μm), applying the IRSL50 and the pIRIR290 dating techniques. For the equivalent dose (De) determination we used both the SAR post-infrared infrared (pIRIR290) protocol on single aliquots and the multiple-aliquot additive dose (MAAD IRSL50) protocol. The pIRIR290 ages and the fading corrected MAAD-IRSL50 ages are self-consistent. It demonstrates for the first time, that the three upper loess layers (L1, L2, L3) at Viatovo and Kaolinovo were deposited during the marine isotope stages (MIS) 2–4, 6 and 8, thus constraining the youngest well-developed paleosol (S1, a chernozem) to the Last Interglacial. These IRSL50 and pIRIR290 ages are in good agreement with the luminescence ages obtained for (1) the two upper loess layers (L1, L2) from the Harletz sequence in NW Bulgaria and (2) the three upper loess units (L1, L2, L3) from the adjacent SE Romanian loess sequences.The luminescence chronology of the loess sequences is presented along with the pedogenic and magnetic property data. The pedostratigraphic records of the NE Bulgarian and SE Romanian loess sequences show the same palaeoclimatic trends, with progressive aridification during interglacial periods (from S6 to S0).

ESR dating of Chinese loess using the quartz Ti centre: A comparison with independent age control

The reliability of quartz electron spin resonance (ESR) dating using the Ti centre was tested through a comparison of the ESR ages of loess from the Luochuan site, Chinese loess plateau, with reference ages. Instead of the commonly used multiple-aliquot additive dose (MAAD) protocol, the single-aliquot regenerative dose (SAR) protocol was used to calculate the equivalent dose (De) values of five samples, with expected ages ranging from 28.5±2.9 ka (unit L1) to 646±65 ka (unit L6). The apparent ages, ranging from 59.4±3.8 to 517±42 ka, were then corrected for thermal signal loss, using the lifetime of the Ti centre, ∼1.7 × 106 years, previously calculated for a sample from the same site. The corrected ages ranged from 60.4±3.8 ka to 617±50 ka. For the youngest two samples both apparent and corrected ages overestimated the expected ages, which was presumably caused by incomplete signal resetting before burial. The apparent age of the oldest sample showed an age underestimation of ∼20%, but after the thermal signal loss from the Ti centre was corrected for, the age was consistent with the reference age. Both apparent and corrected ages of L3 and L4 are in good agreement with expected ages. We show, that with careful consideration of the thermal stability and bleachability of samples, reliable age calculation using the Ti centre is possible.

Roman traces in Germania magna: New thermoluminescence and pIRIR290 data from a lime kiln at Bergisch Gladbach, Germany

The applicability of a post‐infrared infrared stimulated luminescence (pIRIR290) protocol and two different thermoluminescence (TL) protocols—a single aliquot regeneration (SAR) and a multiple aliquot additive dose (MAAD)—was tested on six polymineral fine‐grain (4–11 μm) samples extracted from the wall remains of a Roman lime kiln and a Roman roof tile. These remains had been excavated close to Bergisch Gladbach, which was at that time part of Germania magna. For the pIRIR290 measurements, no dependence of De on first‐stimulation temperature was detectable, and the standard first stimulation temperature at 50°C was adopted. Fading tests and dose‐recovery tests were made for all samples. Background subtracted glow curves were recorded up to 480°C for TL after a preheat of 220°C for 120 s. A‐values were determined for all TL and pIRIR measurements. The results for all three protocols were fairly consistent, and TL and pIRIR290 protocols are shown to be suitable to estimate reliable equivalent doses for the fired kiln walls. The resulting ages are in agreement with the expected time range—Roman Iron Age—and with independent age control provided by radiocarbon ages of animal bones and charcoal from the firing chamber.

Electron spin resonance dating of optically bleached quartz grains from the Middle Palaeolithic site of Cuesta de la Bajada (Spain) using the multiple centres approach

Electron spin resonance (ESR) dating of optically bleached quartz grains was performed on three sediment samples collected from the Middle Palaeolithic site of Cuesta de la Bajada (Spain). A standard multiple grain and multiple aliquot additive dose procedure was employed, and both the Al and Ti centres were measured as part of the multiple centres approach. ESR age estimates obtained for the three samples indicate that the Al centre provides a maximum possible chronology, as the Ti centres show that the Al signal was likely not systematically reset to its residual level during sediment transport. A direct comparison between ESR ages based on the Ti centres and single grain optically stimulated luminescence (OSL) ages from samples collected nearby shows broadly consistent results. The Ti-H centre also appears to provide suitable chronologies for at least two of the three Middle Pleistocene samples studied here. Surprisingly, the only sample showing consistent ESR ages between the Al and Ti centres appears to be overestimated in comparison with the Ti-centre and OSL ages derived from the other two samples. This indicates either incomplete bleaching of both the Al and Ti centres for this sample, or unexpected impacts of other sources of De uncertainty, such as multi-grain averaging effects. The ESR dating results overall indicate that the archaeological sequence of Cuesta de la Bajada CB-3 is most likely correlated to either MIS 7 or 9.

Application of radioisotope XRF and thermoluminescence (TL) dating in investigation of pottery from Tell AL-Kasra archaeological site, Syria

Statistical analysis based on chemical composition, using radioisotope X-ray fluorescence, have been applied on 39 ancient pottery fragments coming from the excavation at Tell Al-Kasra archaeological site, Syria. Three groups were defined by applying Cluster and Factor analysis statistical methods. Thermoluminescence (TL) dating was investigated on three sherds taken from the bathroom (hammam) on the site. Multiple aliquot additive dose (MAAD) was used to estimate the paleodose value, and the gamma spectrometry was used to estimate the dose rate. The average age was found to be 715±36 year.

Single aliquot regenerative dose method for ESR dating using X-ray irradiation and preheat

Equivalent dose (De) estimations in electron spin resonance (ESR) dating have mostly been done by the multiple aliquot additive dose (MAAD) method despite disadvantages. In this study, we used X-ray irradiations and applied the single aliquot regenerative dose (SAR) technique to ESR De measurements of a volcanic quartz with independent age control. As the SAR protocol involves multiple steps of irradiations and readouts during a short period of time using a single aliquot, the thermal stabilities of the Al and Ti centres from natural and X-ray irradiated aliquots were compared by a pulse annealing test. The thermal stability of natural and regenerated ESR signals is significantly different for both Al and Ti centres and preheats are therefore considered necessary after artificial irradiations. The X-ray dose rate for quartz was calibrated using the same sample which was heated and irradiated with a known gamma dose. The SAR De values using the natural sample were obtained by means of a preheat plateau test. To check and correct for possible sensitivity change induced by the annealing used to reset the natural ESR signals, the single aliquot regeneration and added dose (SARA) method was applied. The SARA De values for the Al and Ti centres were in agreement, however, this De value overestimated the expected De from the independent age control, possibly because our sample was too old for the SARA method.

Multiple approaches to date Japanese marker tephras using optical and ESR methods

The present study aimed to test reliability of luminescence and electron spin resonance (ESR) methods to date tephra. We investigated on three Japanese marker tephras, Ikeda-ko (6.4 ka), Aira-Tn (30 ka) and Aira-Iwato (45–50 ka). A systematic studies were performed using different minerals (quartz and feldspar), different grain fractions (75–250 and 250–500 μm), different luminescence and ESR signals, like optically stimulated luminescence (OSL) of quartz, infrared stimulated luminescence (IRSL) of feldspar, including recently developed least faded post infrared IRSL (pIR-IRSL), and ESR signals from paramagnetic centers Al and Ti–Li of quartz. Ages obtained using pIR-IRSL signal of plagioclase with preheat of 320 °C, 60 s and stimulation at 300 °C are consistent with the reference ages. High dose detection range (up to ∼600 Gy) and accurate age estimation enable pIR-IRSL of feldspar a promising methodology to date quaternary tephra. ESR ages from quartz are grossly correlated with the reference ages but large deviation and large associated errors are observed, possibly due to either low signal to noise ratio or heterogenous dose response of different aliquot in multiple aliquot additive dose (MAAD) approach.

Our oldest children: Age constraints for the Krems-Wachtberg site obtained from various thermoluminescence dating approaches

We present several approaches to directly date the prehistoric human activity of lighting a fire at the Early Gravettian infant burial site of Krems-Wachtberg (Austria) by thermoluminescence (TL) methods. Blue thermoluminescence (B-TL) from polymineral fine grain and orange-red thermoluminescence (R-TL) from fine-grained quartz separates, both extracted from the baked loess immediately underlying the hearth were employed. The B-TL dating followed the “classic” multiple aliquot-additive dose (MAAD) protocol. For R-TL dating, the multiple aliquot-regenerative (MAR) and a shortened single-aliquot-regeneration (SAR) protocol were tested. All thermoluminescence ages obtained agree within 1-σ uncertainties and assign a weighted mean age of 33.9 ± 2.3 ka to the last use of the hearth and by inference to the infant burial. Anomalous fading is precluded due to the agreement of results from all luminescence protocols as well as with independent dating methods. The TL ages are consistent with calibrated radiocarbon ages on associated charcoal, OSL dating of the sediment deposition and with age estimates obtained by two magnetic dating approaches.

Luminescence (IRSL) dating of Yeni Rabat church in Artvin, Turkey

Luminescence dating is a chronological method that has been used extensively in terrestrial materials. In this study, we present Infrared Stimulated Luminescence (IRSL) dating results obtained for sediment and pottery samples taken from Yeni Rabat Church, Ardanuç, Artvin, Turkey. For this purpose, equivalent dose (ED) and annual dose rate (AD) of samples were measured. For annual dose rate, concentrations of radioactive isotopes (U, Th, K) were determined by using a high-purity germanium detector. For the equivalent dose, polymineral fine grain SAR (Single Aliquot Regenerative Dose) and MAAD (Multiple Aliquot Additive Dose) procedures were used. The optimal preheat temperature was determined for sediment and pottery samples. Ages were calculated by Aitken's luminescence age calculation method, which found 710±190 years for the pottery sample and 1450±370 years, 1390±420 years, 1430±310 years, 2210±520 years and 1640±390 years for different sediment samples, respectively. These estimated age ranges support the theory that Yeni Rabat Church could have been constructed in medieval times.

Dose estimation and dating of pottery from Turkey

The luminescence method is a widely used technique for environmental dosimetry and dating archaeological, geological materials. In this study, equivalent dose (ED) and annual dose rate (AD) of an archaeological sample were measured. The age of the material was calculated by means of equivalent dose divided by the annual dose rate. The archaeological sample was taken from Antalya, Turkey. Samples were prepared by the fine grain technique and equivalent dose was found using multiple-aliquot-additive-dose (MAAD) and single aliquot regeneration (SAR) techniques. Also the short shine normalization-MAAD and long shine normalization-MAAD were applied and the results of the methods were compared with each other. The optimal preheat temperature was found to be 200°C for 10min. The annual doses of concentrations of the major radioactive isotopes were determined using a high-purity germanium detector and a low-level alpha counter. The age of the sample was found to be 510±40 years.

A comparison of single and multiple aliquot TT-OSL data sets for sand-sized quartz from the Arabian Peninsula

Abstract The quartz OSL signal from dune sands from Saudi Arabia and Oman start to saturate at doses of about 100 Gy. In order to try to date dune sands with greater expected doses, a previously published, single-aliquot, regenerative-dose protocol (SAR) for thermally-transferred optically stimulated luminescence (TT-OSL) was tested. Dose recovery tests, recycling and recuperation ratios showed robust functioning and dose response curves demonstrated the potential to extend the dose range to beyond 600 Gy. Multiple aliquot additive dose (MAAD) TT-OSL protocols were used to test for sensitivity changes in the SAR TT-OSL protocol up to doses of 1200 Gy. A strong dose dependent deviation of the SAR TT-OSL relative to the MAAD TT-OSL dose response is observed. Comparison of the TT-OSL and OSL sensitivity data obtained from the MAAD and SAR data sets shows a lack of proportionality between TT-OSL and OSL for the SAR data which will result in a problem when SAR dose response curves are constructed using many regeneration points with doses above 300 Gy.

ESR dating of calcrete nodules from Bala, Ankara (Turkey): Preliminary results

The age of two calcrete nodules (C1 and C2) from the Bala section in the region of Ankara, Turkey, is determined by the Electron Spin Resonance (ESR) method. Three radiation-induced ESR signals at g=2.0056 (A signal), g=2.0006 (C signal) and g=2.0038 (broad signal, BL) were observed. The broad signal (BL) intensity was used as a dating signal. The properties of this dating signal are described in this manuscript. The calcrete nodules were irradiated with a (60)Co gamma source and measured with an ESR spectrometer (X-band) to obtain the signal intensity vs. dose curve and fitted well with the single exponential saturation functions. Based on this model, accumulated dose (D(E)) values for dating are obtained using the multiple-aliquot additive dose method. The D(E) values of C1 and C2 calcretes are 1880±207 and 671±67 Gy, respectively. The ESR ages of the two calcrete samples are obtained by assessing the annual dose rate (D) from the content of (238)U, (232)Th and K(2)O determined by wavelength dispersive X-ray fluorescence (XRF) spectrometry. The results are 761±120 and 419±64 ka, respectively, falling into the Middle Pleistocene Epoch in the geological time scale in agreement with the positions of the stratigraphical record.