Construction of a quartz OSL standardised growth curve (SGC) for aeolian samples from the Horqin dunefield in northeastern China

It has been suggested that the standardised growth curve (SGC) method can be used to de-terminate D_e accurately and reduce the measurement time. However, different opinions regarding the applicability of the SGC method exist. In this paper, we report the construction of quartz OSL SGC for 35 aeolian samples from different parts of the Horqin dunefield in northeastern China, and then test their applicability for D_e determination. Our results suggest that: 1) up to a regeneration dose of 80 Gy, the SGC of the Horqin dunefield can be fitted using the exponential plus linear equation, with the r² value of 0.97, and all the regeneration dose points closely stick to the fitting line, implying that all samples share a very similar dose-response curve; 2) for samples with Des ranging from 1 to 50 Gy, the ratios of SAR D_e to SGC D_e fall within the range of 0.9–1.1, and the average ratio of SAR D_e to SGC D_e is 1.01±0.01, close to unity. Therefore, the construction of SGC is correct, and the SGC is an effective procedure for accurate D_e determination for samples from the study area.     

Comparison of three K-feldspar luminescence dating methods for Holocene samples

The luminescence dating of the K-feldspar fraction is an alternative way for samples that cannot yield reasonable equivalent dose (D_e) from quartz fraction with very weak luminescence signal. For testing the reliability of the infrared stimulated luminescence (IRSL) dating of K-feldspar, luminescence dating was applied to quartz and K-feldspar fractions respectively for several Holocene samples in this study. K-feldspar apparent ages using routine single aliquot regenerative-dose (SAR) protocol, K-feldspar ages using g value correction method and ages from isochron dating method were compared with quartz ages. It is found that the g value correction method cannot give reliable ages due to the large errors induced during measurements. The isochron dating method is effective to the sample with problematically external dose rate. However, isochron dating may introduce a relatively greater error during grain sizes — D_e curve fitting, therefore this method could obtain low-resolution ages for Holocene samples. Even K-feldspar apparent age from routine SAR protocol is relatively younger by about 10% than the quartz age, it still could establish reasonable chronological framework for Holocene samples.     

Testing the standardized growth curve (SGC) to OSL dating coastal sediments from the south Bohai Sea, China

It has been suggested that the standardized growth curve (SGC) method can be used to accurately determinate equivalent dose (D_e) and reduce measurement time. However, different opinions regarding the applicability of the SGC method exist. In this paper, we evaluated quartz OSL SGCs of marine and coastal sediments of different grain sizes and different cores in the south Bohai Sea in China, and tested their applicability to the determination of D_e values. Our results suggested as follows: (1) The SGC method is applicable to both multiple- and single-aliquot regenerative-dose (MAR and SAR) protocols of OSL dating and efficiently provides reliable estimates of D_e. (2) Finesand quartz of different palaeodoses showed highly similar dose-response curves and an SGC was developed, but old samples using the SGC method have large uncertainties. (3) For coarse-silt quartz, two different types of dose-response curves were recorded: low-dose (≤60Gy) and high-dose (≥100Gy). The growth curves of low-dose quartz were similar to each other, facilitating the use of SGC in D_e estimations, but errors tended to be larger than those obtained in the SAR method. For high-dose (100–300Gy) quartz, the SGC was also found to be reliable, but there was large uncertainty in D_e (>300Gy) estimation. We suggest that SGC could be employed for the dating of marine and coastal sediments dating using either MAR or SAR OSL protocol and either fine-silt, coarse-silt or fine-sand quartz.     

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 D_e 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.     

Investigation of lime mortars and plasters from archaeological excavations in Hippos (Israel) using Electron Paramagnetic Resonance

This study presents the preliminary results of investigation of the lime mortars and plasters from archaeological excavations in Hippos (Israel), using Electron Paramagnetic Resonance (EPR) spectroscopy. The research was conducted in order to characterize the building material and its reaction to ionizing radiation. The ancient settlement Hippos, situated on the east shore of the Sea of Galilee, functioned from the 3^rd cent. BC until it was destroyed by the earthquake in 749 AD. Lime mortars and plasters show carbonate and locally gypsum character of binder and different kind of aggregate. Samples were γ-irradiated and measured using X-band EPR spectrometer. Computer Resolution Enhancement Method was applied to the complex spectra. Some of the γ-induced EPR signals were attributed to CO₂ ^? and CO₃ ^3? paramagnetic centres. Exponential growth of the dose response curve above 1 kGy and saturation for doses above 20 kGy was observed. For doses lower than 1 kGy the dose response curve has a linear character. The presence of γ-sensitive carbonate paramagnetic centres could indicate that, after further studies, well-chosen samples of mortars and plasters might be suitable for EPR dating, assuming the centres have been sufficiently bleached during the manufacturing process.     

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.     

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.     

ESR dose response of Al center measured in quartz samples from the Yellow River (China): Implications for the dating of Upper Pleistocene sediment

The ESR dating method requires to describe the evolution of the ESR signal intensities vs. increasing gamma doses, then to extrapolate the equivalent dose of radiation received by the sample since its deposition using mathematical fitting. The function classically used to describe the growth curves of ESR aluminium signal in quartz was recently discussed and challenged for Lower Pleistocene sediments. In the present work, some alluvial sediments sampled in Upper Pleistocene fluvial terraces of the Yellow River system (China) permit us to test the application of another extrapolation function (linear + exponential) recently proposed for Lower Pleistocene sediments. The equivalent doses obtained here for the recent deposits of the Yellow River system and the corresponding ages are promising and indicate the potential of ESR to date quartz deposits from Upper Pleistocene times.     

Optically stimulated luminescence (OSL) dating investigations of rock and underlying soil from three case studies

Three rock samples and associated underlying surface (floor) soils of geoarchaeological significance from Greece, Sweden and a modern surface stone-sample from a Danish site were investigated using OSL dating. Thin slice, sub-samples, from drilled core surfaces were prepared. A single-aliquot regenerative-dose (SAR) protocol was used on whole rock slices to estimate the laboratory equivalent dose. Laboratory tests showed that the SAR protocol successfully corrected for sensitivity changes and that a known laboratory dose could be measured accurately.     

Optically stimulated luminescence dating of young fluvial deposits of the Middle Elbe River Flood Plains using different age models

In the last few decades optically stimulated luminescence (OSL) dating has become an important tool in geochronological studies. The great advantage of the method, i.e. dating the depositional age of sediments directly, can be impaired by incomplete bleaching of grains. This can result in a scattered distribution of equivalent doses (D_E), leading to incorrect estimation of the depositional age. Thoroughly tested protocols as well as good data analysis with adequate statistical methods are important to overcome this problem. In this study, samples from young fluvial sand and flood plain deposits from the Elbe River in northern Germany were investigated to compare its depositional ages from different age models with well-known historical dates. Coarse grain quartz (100–200 μm and 150–250 μm) and polymineral fine grains (4–11 μm) were dated using the single aliquot regenerative (SAR) dose protocol. The paleodose (D_P) was calculated from the DE data set using different approaches. Results were compared with the development of the Elbe River, which is well-documented by historical records and maps covering the last 1,000 years. Depending on the statistical approach it can be demonstrated that depositional ages significantly differ from the most likely depositional age. For the investigated coarse grain quartz samples all ages calculated from the MAM-3_UL, including their uncertainties, are within the historical documented age. Results of the polymineral fine grain samples are overestimating the historically documented depositional age, indicating undetectable incomplete bleaching. This study shows the importance of using an adequate statistical approach to calculate reliable OSL ages from fluvial sediments.     

Luminescence dating of young coastal deposits from New Zealand using feldspar

A new measurement protocol has been tested on K-feldspars from Whanganui Inlet and Parengarenga Harbour, New Zealand. A Single Aliquot Regenerative (SAR) dose protocol, using two successive infrared (IR) stimulations (post-IR IR SAR protocol) is setup for these young (<1000 years) coastal sediments. Significant anomalous fading (g _2days =7 %/decade) is observed using the conventional IR signal measured at 50°C. In contrast, the fading rate of the IR signal measured at elevated temperature (150°C) after the IR stimulation at 50°C (a post-IR IR signal) is not significant (g _2days ≤ 1 %/decade). Surprisingly low residual infrared stimulated luminescence (IRSL) signals were observed for a surface sample, suggesting that accurate ages as young as ∼50 years can be obtained for these recent deposits. IRSL ages ranging between 48±6 years and 1050±50 years are obtained from six samples, indicating that sediment accumulation has occurred at the two sites during the last millennia, despite a falling trend in relative sea-level in Whanganui Inlet and a stable relative sea-level at Parengarenga Harbour.     

Examining quartz OSL age underestimation for loess samples from Luochuan in the Chinese Loess Plateau

When using quartz OSL to date loess samples from the Chinese Loess Plateau, it has been reported that the agreement between OSL ages and the independent ages is limited to the samples younger than ～70 ka with a corresponding D_e of ～230 Gy, and a sample with an expected age of 780 ka was dated to 107 ka, corresponding to 403 Gy. The growth curves of these samples do not saturate at doses of 700 Gy, and a linear growth part was observed for doses higher than 200 Gy. However, the maximum measured age of ～100 ka imply that the D_e determined using this linear part of a growth curve could be problematic, or that the quartz OSL signal is not as stable as previously thought and has a barrier age of ～100 ka. In the current study, we examine the reasons for the age underestimation. We examined the shape of growth curves, anomalous fading, thermal stability, etc. The results show that, for the loess samples examined, quartz OSL does not fade anomalously, and the barrier age of ～100 ka is due to the fact that the OSL signals are less thermally stable, the lifetime of 0.311 Ma at 20°C obtained is much smaller than those for quartz samples from other regions such as Australia (～100 Ma).     

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.     

OSL and TL dating of the Middle Stone Age sequence at Diepkloof Rock Shelter (South Africa): a clarification

Diepkloof Rock Shelter offers an exceptional opportunity to study the onset and evolution of both Still Bay (SB) and Howiesons Poort (HP) techno-complexes. However, previous age estimates based on luminescence dating of burnt quartzites (Tribolo et al., 2009) and of sediments (Jacobs et al., 2008) were not in agreement. Here, we present new luminescence ages for 17 rock samples (equivalent dose estimated with a SAR-ITL protocol instead of classical MAAD-TL) as well as for 5 sediment samples (equivalent dose estimated with SAR-single grain OSL protocol) and an update of the 22 previous age estimates for burnt lithics (modified calibration and beta dose estimates). While a good agreement between the rock and sediment ages is obtained, these estimates are still significantly older than those reported by Jacobs et al. (2008). After our own analyses of the sediment from Diepkloof, it is suspected that these authors did not correctly chose the parameters for the equivalent dose determination, leading to an underestimate of the equivalent doses, and thus of the ages.     

IRSL and post-IR IRSL residual doses recorded in modern dust samples from the Chinese Loess Plateau

Using a set of modern/young (0 to about 200 years old) dust samples collected from the Chinese Loess Plateau the bleachability of IRSL measured at 50°C (IR₅₀) and post-IR₅₀ elevated temperature IRSL (measured at 225°C and at 290°C) is investigated by measuring the apparent (residual) doses recorded by these signals. Doses recorded by quartz OSL are used as a reference. Allowing for differences in dose rates it seems that both IRSL and post-IR IRSL signals yield residual doses that are significantly larger than the doses measured in quartz. These residual doses can be largely explained by thermal transfer caused by preheating. Nevertheless, we advise against the use of a low temperature preheat (<200°C) with IR₅₀ to date loess samples because, as has been reported before, the signal appears to be thermally unstable. In general, we conclude that it may not be advisable to apply post-IR IRSL dating to Chinese loess samples where residuals of up to ∼20 Gy are a significant fraction of the total dose. However, these residuals quickly become unimportant when dating older samples, and this is the age range in which post-IR IRSL dating is likely to be most useful.     

Equivalent dose distributions from single grains of quartz at Sibudu,South Africa: context,causes and consequences for optical dating of archaeological deposits

Optical ages for 14 sediment samples collected from the post-Howiesons Poort, late Middle Stone Age (MSA) and final MSA deposits at Sibudu, KwaZulu-Natal, South Africa were reported in a companion paper (Jacobs, Z., Wintle, A.G., Duller, G.A.T., Roberts, R.G., Wadley, L. New ages for the post-Howiesons Poort, late and final Middle Stone Age at Sibudu, South Africa. Journal of Archaeological Science, 2008). These ages were based on equivalent dose (D_e) distributions that were overdispersed. In this paper, we investigate factors both internal and external to the grains that may contribute to such higher than expected overdispersion in single grain D_e values. Intrinsic factors accounted for some, but not all, of the observed scatter, and application of a set of rejection criteria filtered grains for which erroneous D_e values would otherwise be calculated. We investigated sediment mixing and differences in the beta dose received by individual grains in their burial environment as two likely reasons for the observed overdispersion. The scatter in D_e distributions for all the samples is best explained by grains that were deposited at the same time and which were well bleached, but that subsequently received a range of beta doses. A procedure is presented for adjusting the measured beta dose rate, and its associated error. We show that using a combination of single grain OSL measurements of D_e, the finite mixture model and adjustment of the beta dose rate, result in stratigraphically consistent ages. These ages are more consistent than the ages obtained from multiple grain aliquot D_e values and the average dose rates for each sample; the multiple grain ages are about 10% older, partly because of the variable dose rate and partly because these aliquots contained grains with undesirable OSL characteristics.     

Expectations of scatter in equivalent-dose distributions when using multi-grain aliquots for OSL dating

In the OSL dating of sediment, the scatter in equivalent dose (D _e) between grains is almost always larger than would be expected due to counting statistics alone. Some scatter may be caused by insufficient (partial) bleaching of some of the grains prior to deposition. In order to date partially bleached sediment, it is essential to estimate the amount of scatter caused by other processes (e.g. grain-to-grain variability in the natural dose rate). Measurements of such scatter are performed at the single-grain level; by contrast, most OSL dating is performed on multi-grain subsamples, for which grain-to-grain scatter is reduced through averaging.     

OSL and TL characteristics of fine grain quartz from Mongolian prehistoric pottery used for dating

The OSL, post-IR OSL and pulsed post-IR OSL applied to polymineral grains and calculated by fitting to the data the contributions from fast, medium and slow components revealed that the polymineral samples under study are dominated by the medium component. An increase in D _e ’s with increasing integration intervals was observed, which is considered as an indication of increasing medium and decayed fast component; and the equivalent doses obtained using different components or minerals reflect also the shape of the dose distributions. The identified fast component in polymineral sample has photoionization cross section of 1.2±0.02 × 10^?17 cm². The present study shows the usefulness of the application of different luminescence techniques combined with fitting procedures as a check which should be adopted in dating protocols. Based on luminescence ages obtained on poly-mineral grains from prehistoric pottery samples from the Boroo settlement, Mongolia, which are in agreement with independent age control by ¹⁴C on charcoal material, it is argued that the manufacturing of Xiongnu — pottery at this site lasted until ca. 130±75 AD.     

陶器古剂量线性回归方法和误差评估

陶器古剂量P包含等效剂量Q和超线性修正I两个部分,为了提高古剂量测量的准确性,正确地计算古剂量的测量误差,本工作测试了10个古陶片样品,利用线性回归方法计算等效剂量Q和超线性修正I,并对不同的古剂量计算方法进行误差分析和评估。研究表明,线性回归方法(包括归平法和平归法)计算陶器古剂量的准确性优于目前采用的常规法;通过几种不同方法的误差比较和分析,归平法所得误差较其它方法更严谨、合理。该研究在提高古剂量测量的准确性和正确计算古剂量的测量误差两方面具有重要的意义,使得古剂量的测量更加合理,符合数理统计规律。     

Thermally assisted OSL: A potent tool for improvement in minimum detectable dose and extension of dose range of Al2O3:C

The influence of electron-phonon interaction on the shape of the optically stimulated luminescence decay curve of Al₂O₃:C has been studied using thermally assisted optically stimulated luminescence (TA-OSL). The minimum detectable dose (MDD) of a phosphor depends on the standard deviation of the background signal which affects the signal-to-noise ratio. The standard deviation of the background signal reduces at lower stimulation light intensity while the readout time increases. Further, measurement at higher temperature enhances the OSL signal with faster decay due to the temperature dependence of photo-ionization cross-section. To achieve the same decay constant and more signal, the temperature of measurement was raised. As a result of lowering the stimulation in-tensity at higher temperature (85°C) the overall MDD of α-Al₂O₃:C was found to improve by 1.8 times. For extension of dose linearity in higher range, deeper traps were studied by simultaneous application of CW-OSL and thermal stimulation up to 400°C, using a linear heating rate of 4K/s. By using this method, two well defined peaks at 121°C and 232°C were observed. These TA-OSL peaks have been correlated with two deeper defects which can be thermally bleached at 650°C and 900°C respectively. These deeper defects are stable up to 500°C, so they can store absorbed dose information even if the sample is inadvertently exposed to light or heat. The dose vs. TA-OSL response from deep traps of α-Al₂O₃:C was found to be linear up to 10 kGy, thus extending its application for high dose dosimetry.