Optically Stimulated Luminescence Signal Research Articles

Luminescence and thermometry studies of plant opal phytoliths

We have investigated the luminescence properties of plant opal phytoliths to assess their suitability for determination of age and/or thermometric information from soil and sediment sequences. This study examined a <2.37 gcm−3 density fraction in parallel with quartz grains from samples collected from alluvial terraces. We observed comparable optically stimulated luminescence (OSL) from the phytolith fraction to the quartz, and thermoluminescence (TL) with broader peaks and continuum to higher temperatures. Scanning electron microscopy (SEM) data suggested the presence of opal clasts and contaminant minerals. To better understand the luminescence from opal phytoliths we analyzed a suite of biogenic materials including very pure diatoms, phytoliths, and quartz reference materials. We observe low sensitivity but measurable OSL signals in all the materials analyzed, and infrared stimulated luminescence (IRSL) signals with fast decay rates exceeding those of more typical feldspars in some of the purer materials. TL signals are similar to those observed for glasses and suggests dose response might extend beyond quartz saturation levels. Preliminary investigations of OSL dose response show very promising growth characteristics for opal phytolith samples and all other biogenic silica materials analyzed.

Fading performance on optically stimulated luminescence of LiMgPO4:Tb,Sm,B

This study aimed to investigate the fading of the optically stimulated luminescence (OSL) of LiMgPO4:Tb,Sm,B. Thermoluminescence (TL) glow curves were recorded immediately and 24 h after irradiation, as well as after OSL. Peaks 2 and 3 did not contribute to the fading of the TL signal, while peak 1 was identified as the primary source of TL signal fading in LiMgPO4:Tb,Sm,B. The fading was calculated by considering the OSL signal measured immediately after irradiation as the first measurement point. About 70% of the OSL signal was measured 30 days after irradiation if the pre-heat procedure was not applied. The intensity of LiMgPO4:Tb,Sm,B remains stable at 93.1% with a preheating program of 160 °C for 30 s.

Luminescence properties of SrB6O10:Ce,Gd phosphor for applications in OSL dosimetry and lighting

Strontium hexaborate (SrB6O10) doped with different metals and/or lanthanides has been studied widely as the thermoluminescence (TL) dosimeter. However, there is almost no dosimetry study concerning the utility of Optically Stimulated Luminescence (OSL) on SrB6O10. This preliminary study aims to examine the luminescence properties of SrB6O10 phosphor for their application in the areas of dosimetry and lighting technologies. Undoped and doped material to get an OSL dosimeter were synthesized by incorporating the dopants Ce3+, in the range of 0.1–0.7 % wt, and Gd3+, in the range of 0.1–1 % wt into the SrB6O10 structure using the solution combustion (SCS) method. The structural and morphological characterizations were performed using X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) methods, respectively. Two TL peaks of SrB6O10:Ce0.1%,Gd0.5% occurred at 70 °C and 182 °C after 1 Gy exposure to beta rays with a heating rate of 2 °C/s. The step annealing measurements were carried out to determine the traps responsible for the OSL signal. Various properties of the luminophore including dose-response and reusability were investigated using blue light stimulation. The phosphor showed a little variation of response up to 20 cycles within 2 % deviation (STD) from the first OSL readout. The OSL output within the range of 2–20 Gy was determined as linear. Radioluminescence (RL) measurement was investigated by emission in the range λem = 200–1000 nm. The parent compound displayed UV emission subdivided into UVA (315–400 nm), and UVB (280–315 nm) emissions at room temperature. The Chromaticity Coordinates (CIE) of SrB6O10:Ce0.1%,Gd0.5% were calculated as x = 0.2165, y = 0.1767. These remarkable characteristics show that, if developed, SrB6O10 could be used as an OSL dosimeter.

A formation record of modern Nitraria tangutorum nebkhas on the Ordos Plateau of northern China based on optically stimulated luminescence dating

Nebkhas, as special biologically mediated aeolian landforms, play an important role in indicating regional aeolian activities and aeolian environmental changes. The Ordos Plateau is located in arid and semiarid regions of northern China that have a wide distribution of Nitraria tangutorum nebkhas. There are few chronological records of nebkha formation, so the history of the formation and evolution of nebkhas in the plateau is still unclear. In addition, the optically stimulated luminescence (OSL) dating method, which has been widely used in the dating of Holocene aeolian sediments, has not yet been applied to the dating of nebkha sediments in the Ordos Plateau. In this study, OSL methods were used to discuss the formation age and relevant aeolian activities of Nitraria tangutorum nebkhas in the Ordos Plateau. The results demonstrated that (1) the coarse-grained quartz OSL signals of nebkha sediments were insensitive and thus were inapplicable by the single aliquot regenerative (SAR) protocol. (2) The luminescence characteristics of the K-feldspar fraction and internal checks of the post-infrared infrared-stimulated (pIRIR) dating indicated that the pIR50IR170 protocol with 200 °C of preheating was applicable for De determinations of nebkha sediments. (3) The residual doses of the pIRIR170 signals ranging from 0.02 to 0.14 Gy should be considered when calculating De values. (4) Bayesian age-depth models were used for the Nitraria tangutorum nebkha sedimentary sequences. The formation of nebkhas occurred during a relatively dry climate period accompanied by strong aeolian activity. That ∼0.38 ka was the main growth period of Nitraria tangutorum nebkhas. This study is the first report of the formation age of nebkhas of more than one hundred years in the region.

OSL dating of very young aeolian sediments of NW Spain to assess dune erosion and accretion periods

Optically stimulated luminescence (OSL) ages of young coastal dune ridges have allowed getting more knowledge on the deposition, erosion and evolution of coastal dune systems in Northern Europe during historical times. However, there is a lack of knowledge of the evolution of the same systems in SW Europe. The studies published in the last years about fossil dunes in NW Spain have allowed the reconstruction of the coastal evolution of this area from the Marine Isotopic Stage (MIS 8) until the Middle Holocene. However, there is still a poor knowledge for the Late Holocene and namely the last centuries. Dating young sediments is challenging due to the low signal to noise ratio of the natural OSL signal and because young samples are very sensitive to thermal transfer or partial bleaching of the luminescence signal during transport. In the last century, erosion and accretion events are better known because remote sensing methods allowed to model some coastal dune systems. However, OSL dating has also been particularly useful in NW Europe to get a better knowledge on the coastal dune evolution. In this work, seven samples from dune ridges and a climbing dune of a coastal system in Playa de Trece (NW Spain) were dated by OSL, as they record the last accretion events occurred in the last two centuries, and above all the 20th Century. For assessing the ages we have compared the results from both parametric central age models and Bayesian statistic using R package BayLum.

Chronology by luminescence and radiocarbon on core sediments from the northeastern pearl river plain and implications for delta process

Accurate dating is the basis for deciphering eustatic and climatic changes on deltaic sedimentary processes. In the Pearl River Delta (PRD) plain of south China, scarce robust chronology hinders the detailed interpretation of sedimentary history. In this study, quartz optically stimulated luminescence (OSL) (21 samples), feldspar post-IR IRSL (pIRIR) (4 samples) and radiocarbon (14C) (2 samples) dating were applied to obtain detailed chronological framework of core SXG06 (23-m long to bedrock) from the northeastern PRD. SXG06 consists an upper marine unit (M1) and a lower marine unit (M2), separated by a terrestrial unit (mottled clay, T1). For M1, quartz OSL and 14C samples yielded ages from 5.2 ± 0.3 to 0.32 ± 0.02 ka. The sample on top of T1 produced a quartz OSL age of 35 ± 2 ka. For other 12 samples in T1 and M2, quartz OSL signals reached saturation and generated minimum ages (>51 ka). For these the saturated quartz OSL samples, feldspar pIR50IR250 provides an age range of 123 ± 7–105 ± 7 ka. The compilation of all the above ages and previous sedimentology data reveals that: (1) M2 was formed during marine transgression of Marine Isotope Stage (MIS) 5; (2) A hiatus with an age gap of between ∼35 ka and ∼5 ka was observed, which might be due to the low sea level and resultant weathering scouring; (3) Initial M1 deposits from the northeastern PRD postdated the central and southern PRD by ∼3 ka, indicating delayed delta development in the northeastern PRD during the Holocene. (4) SXG06 experienced slow deposition 0.3 m/ka in ∼5–3 ka because of the coevally decreased sediment supply, followed by accelerated deposition rate of 3 m/ka after ∼3 ka associated with strengthen human activity.

Chronology of core sediments from the south coastal Bohai Sea of eastern Asia and its implications for sedimentary history

The Shandong Peninsula along the coastal Bohai Sea in China is a vast alluvial plain formed by the Yellow River. It is an ideal place for investigating the evolution of landform in a river–sea interaction area where chronology is key. However, detailed optically stimulated luminescence (OSL) chronology studies of cores are still limited and have mainly concentrated on the Yellow River Delta, while they are scarce on the south coast of the Bohai Sea. In this study 16 OSL samples were collected from the upper 32 m of core DZK01 (192 m in depth) to establish a chronological framework using quartz OSL. Results indicated that the quartz OSL ages ranged from 217 ± 19 ka to 1.63 ± 0.14 ka, and we believe they were the minimum ages when De > ca. 200 Gy owing to OSL signal saturation. Our dating results reveal two sedimentary hiatuses with age gaps of 71–37 ka and 37–9.5 ka. Holocene sediments are located above a depth of 11.8 m with an onset age of approximately 9.5 ± 0.6 ka. Based on the sedimentary facies and dating results, no transgression sediment has been observed during marine isotopic stage (MIS) 3. This sedimentary sequence pattern is consistent with global sea-level change. We also summarized the extents of three transgressions around the Bohai Sea, and found very different patterns for different part of the coasts, e.g., in the north, the west, and the south. This requires further investigation.

Underestimated single-aliquot quartz OSL ages of Late-Pleistocene sediments due to the dominance of medium component

Optically stimulated luminescence (OSL) dating technique has increasingly been employed to establish chronologies for coastal deposits since the Late Pleistocene. However, the commonly used single-aliquot quartz OSL dating method may yield inaccurate ages due to factors such as partial bleaching, luminescence characteristics, and the age limit of quartz. In this study, taking the Yangtze River Delta (YRD) as an example, single-aliquot and single-grain OSL dating using varying grain-sized quartz and K-feldspar were cross-checked to establish appropriate dating method for Late-Pleistocene sediments in coastal areas. The quartz OSL signals of the upper 24 m Holocene sediments were dominated by the fast component, and the ages obtained through OSL and AMS 14C ages agree. Conversely, the lower 24–91 m section, representing the last glacial-interglacial cycle, reveals a notable underestimation of quartz OSL ages, with a maximum underestimation of 250%, attributed to the influence of signal components. For samples within the dating limit of quartz (less than 70 ka), the single-grain method effectively mitigates the issue associated with the signal component. Single-grain K-feldspar technique proves valuable for accurately determining the age of those older sediments exceeding 70 ka. Through cross-checking between different OSL dating methods, sediments initially attributed to marine isotope stage (MIS) 3 (36–60 ka) are re-identified as deposited during MIS 5 (80–130 ka). This study highlights the necessity of assessing the variability in luminescence characteristics before applying a single OSL dating protocol to all samples from different sedimentary facies within a single core.

OSL and PTOSL of dosimetric materials: Observation of the luminescence after exposure to 90Sr+90Y source and LEDs in ultraviolet range

The study of luminescence phenomena by crystal-based radiation detectors is suitable for radiation dosimetry, once the light emitted by them enables the quantification of their deposited radiation energy. The light emission can be promoted when a material is illuminated with a certain wavelength and time interval, as in the optically stimulated luminescence (OSL) and photo-transferred OSL (PTOSL) processes. The objective of this work is to evaluate the OSL and PTOSL responses of commercial dosimeters (LiF:Mg,Ti, CaF2:Dy, CaF2:Mn and CaSO4:Dy) in order to study their luminescence and the possibility of use in radiation dosimetry with the PTOSL technique. OSL and PTOSL responses of LiF:Mg,Ti, CaF2:Dy, CaF2:Mn and CaSO4:Dy dosimeters, commercially sold as TLD-100, TLD-200, TLD-400 e TLD-900, respectively, by Thermo Fischer Scientific, were studied. The samples were irradiated with the 90Sr+90Y source of the TL/OSL reader system Risø, and the measurements were taken using the same system and blue LEDs. For the PTOSL signal, the dosimeters were irradiated, thermally treated and illuminated with LEDs with wavelengths between 265 nm and 420 nm. The most intense OSL signal occurred for TLD-100. Comparing the OSL and PTOSL results, it is possible to observe clearly the photo-transferred effect for TLD-100. For TLD-200 and TLD-400, no effects were noted. In the case of TLD-900, it presented a PTOSL signal in a small-scale when analyzing the curve integral.

Optically stimulated luminescence of Durolon polycarbonate

This paper reports for the first time the study of optically stimulated luminescence (OSL) of amorphous Brazilian bisphenol-A polycarbonate (Durolon) exposed to beta radiation. The OSL was studied from two perspectives: characterizing the luminescent signal as a function of radiation dose and examining repeatability. Computational analyses are applied to OSL curves via the deconvolution method. Fluorescence measurements employing the emission - excitation matrix (EEM) technique and optical absorption (OA) are incorporated to characterize the polymer defects and color centers. OSL measurements were carried out in a commercial reader Risø (model DA-20) coupled with a90Sr/90Y beta source. The sample was illuminated using 470 nm blue LEDs. The OSL response exhibited an exponential decay signal after 1 Gy, with linear dose-response and consistent repeatability. The continuous-wave-OSL curve was well adjusted with two distinct components. As result, Durolon promising potential as a luminescent dosimeter, supported by its desirable OSL signal characteristics.

Alluvial-lacustrine record of Mid- to Late-Holocene moisture variations trend verified by multiple proxies in the middle and lower reaches of the Hutubi River, northwest China

Alluvial-lacustrine deposits are important carriers for studying paleo-hydrological information and the evolution of paleo-environments. In this study, a total of 6 optically stimulated luminescence (OSL) samples from 2 profiles in the lower and middle reaches of the Hutubi River in the North Tianshan Mountains were dated, and a comprehensive analysis was conducted by integrating sedimentary structures, grain sizes, and magnetic susceptibility characteristics to explore the sedimentary environment patterns and regional evolution processes during the Mid to late Holocene. The results revealed the following findings: (1) The OSL signal of quartz samples indicates the predominance of fast components, allowing reliable dating of regional fluvial sediments using the appropriate condition-tested coarse-grained quartz single-aliquot regenerative dose (SAR) protocol within the 90–125 μm range. (2) Analysis of sedimentary structures, grain sizes, and magnetic susceptibility characteristics reveals lithofacies of heterotopic synchronous or homotopic asynchronous in exposed profiles, with predominantly poorly sorted fine and very fine sand. Magnetic susceptibility is primarily controlled by the content of magnetic minerals in the coarse particles, while also being influenced by the combined effects of provenance input and depositional environment, indicating a complex regional sedimentary environment influenced by variable hydrodynamic conditions driven by fluvial processes. (3) Based on OSL dating results and the analysis of various environmental proxy indicators, it is determined that the climatic environment in the Middle and Late-Holocene in the downstream areas of the northern piedmonts of the Tianshan Mountains demonstrates a fluctuating pattern of wet and dry alternations. The sedimentary environment shifted from a stable state in the Mid-Holocene to an unstable state in the Late-Holocene. The intermittent appearance of wet records may be associated with increased river activity caused presumably by the release of high-altitude ice due to rising temperatures and warming conditions.

Dose Rate Calibration of β Radiation Source in Risø TL/OSL-DA-20 Reader Device

This research is focused on determining the dose rate calibration of beta irradiation source in the Risø brand TL/OSL-DA-20 model thermoluminescence (TL) and optically stimulated luminescence (OSL) reader device manufactured by DTU Physics which is an integral component of the Technical University of Denmark (DTU). The beta radiation source of this device comprises a pellet-shaped Strontium ceramic made from the 90Sr/90Y radionuclide, with a half-life of approximately 29.1 years. This investigation provides a thorough examination of reproducing equivalent dose levels by comparing reproduced OSL signals with the OSL signals of calibration quartz crystals which were previously exposed to a 5 Gy beta radiation emission. Throughout this process, dose durations and equivalent dose levels were analysed on optically stimulated luminescence signals. The collected OSL data aims to ensure the precise calibration of the radioactive source, contributing to reliable results in dosimetric measurements. This calibrated device is utilized in the Luminescence Laboratory co-run by the Physics Department and Nuclear Materials Research and Application Center of Selçuk University. The determined dose rate of the beta radiation source is found as 0.065 Gy/second.

Short-term fading studies on optically stimulated luminescence in LiMgPO4:Er

The main drawback of LiMgPO4 is high fading. In order to improve the time stability of the optically stimulated luminescence (OSL) signal of LiMgPO4 after irradiation, five preparation processes had been adopted to prepare five kinds of LiMgPO4:Er phosphor. The structure of the prepared samples was analyzed by X-ray diffraction. The OSL decay curves, thermoluminescence (TL) glow curves, OSL sensitivity, minimum detectable dose (MDD) and the fading properties after irradiation for the five kinds of LiMgPO4:Er phosphors were investigated. Considering minimizing fading 24 h after irradiation, the preparation process for samples heated at 900 °C for 10 h is optimal. The OSL fading of LiMgPO4 phosphor is improved significantly by changing the preparation processes. The less than 5% loss of the OSL signal was measured after 24 h of the irradiation for samples heated at 900 °C for 10 h when the integration time is more than 0.5 s, and the sensitivity by taking the total area under the OSL curve of this samples is about half that of TLD-500k. There is a loss of less than or equal to 5% of the OSL signal for samples heated at 900 °C for 10 h when the integration time is greater than or equal to 20 s within 30 days after irradiation. LiMgPO4:Er samples heated at 900 °C for 10 h is the LiMgPO4 phosphor with the lowest fading so far. It is possible to prepare a LiMgPO4 phosphor with a low fading after irradiation and a moderate sensitivity by further investigating the preparation processes.

Insight into the dynamics of a long-runout mass movement using single-grain feldspar luminescence in the Pokhara Valley, Nepal

Abstract. Mass movements play an important role in landscape evolution of high mountain areas such as the Himalayas. Yet, establishing numerical age control and reconstructing transport dynamics of past events is challenging. To fill this research gap, we bring luminescence dating to the test in an extremely challenging environment: the Pokhara Valley in Nepal. This is challenging for two reasons: (i) the optically stimulated luminescence (OSL) sensitivity of quartz, typically the mineral of choice for dating sediments younger than 100 ka, is poor, and (ii) highly rapid and turbid conditions during mass movement transport hamper sufficient OSL signal resetting prior to deposition, which eventually results in age overestimation. Here, we first assess the applicability of single-grain feldspar dating of medieval mass movement deposits catastrophically emplaced in the Pokhara Valley. Second, we exploit the poor bleaching mechanisms to get insight into the sediment dynamics of this paleo-mass movement through bleaching proxies. The Pokhara Valley is a unique setting for our case study, considering the availability of an extensive independent radiocarbon dataset as a geochronological benchmark. Single-grain infrared stimulated luminescence (IRSL) signals were measured at 50 ∘C (IRSL-50) and post-infrared infrared stimulated luminescence signals at 150 ∘C (pIRIR-150). Our results show that the IRSL-50 signal is better bleached than the pIRIR-150 signal. A bootstrapped minimum age model (bMAM) is applied to retrieve the youngest subpopulation to estimate the paleodose. However, burial ages calculated with this paleodose overestimate the radiocarbon ages by an average factor of ∼23 (IRSL-50) and ∼72 (pIRIR-150), showing that dating of the Pokhara Formation with a single-grain approach was not successful for most samples. Some samples, however, only slightly overestimate the true emplacement age and thus could be used for a rough age estimation. Large inheritances in combination with the scatter in the single-grain dose distributions show that the sediments have been transported under extremely limited light exposure prior to deposition, which is consistent with the highly turbid nature of the sediment-laden flood and debris flows depositing the Pokhara gravels. To investigate the sediment transport dynamics in more detail, we studied three bleaching proxies: the percentage of grains in saturation 2D0 criteria, the percentage of best-bleached grains (2σ range of bMAM-De) and the overdispersion (OD). None of the three bleaching proxies indicate a spatial relationship with runout distance of the mass movement deposits. We interpret this as evidence for the lack of bleaching during transport, which reflects the catastrophic nature of the event. While not providing reliable burial ages of the Pokhara mass movement deposits, single-grain feldspar dating can potentially be used as an age range finder method. Our approach shows the potential of luminescence techniques to provide insights in sediment transport dynamics of extreme and rare mass movement events in mountainous regions.

Correlation between thermoluminescence and optically stimulated luminescence signal in BeO

Beryllium Oxide (BeO) is a promising dosimetric material that is rapidly becoming an essential instrument in Optically Stimulated Luminescence (OSL) dosimetry applications. Despite the potential of BeO as a luminescence dosimeter, gaps remain in understanding how its Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) signals are connected. Our study aimed at examining Residual Thermoluminescence (R-TL) glow curves after various bleaching times to find an association between TL traps and OSL components across a wide range of doses, at 40 mGy and from 10 to 100 Gy. OSL decay curves and intensities of R-TL glow curves were fitted to either pure exponential decay functions or to stretched exponential decay functions, due to optical attenuation, to determine the OSL components and the bleaching decay rates of each TL peak, respectively. A good correlation between the decay rates of the OSL components and bleaching decay rates of each TL peak for both high and low-dose irradiations was found only for the model functions considering optical attenuation in the material. Taken together, this qualitative method helped to identify various traps, and results revealed a more consistent luminescence mechanism between TL and OSL signals than was previously assumed. Further support for the correlation between TL and OSL was derived from thermal stability studies of the OSL signal and from the dose response of the TL peaks and the OSL signal after different thermal pretreatments. Different bleaching models were discussed to define the appropriate one for BeO. These results may enhance our understanding of BeO as a dosimeter.

The sensitisation of quartz extracted from andesite

Low quartz sensitivities have been reported in several studies in Iran, and in part this is presumed to be a result of the volcanic provenance of many of the sediments in the study areas. In this study we test experimentally whether a quartz sample, extracted from an andesitic rock and showing an insensitive fast component in the Optically Stimulated Luminescence (OSL) signal, can be sensitised using optical and thermal methods.The luminescence characteristics of quartz extracted from a rock sample from a landslide in Iran (Rudbar-Manjil) are compared to those of a well-characterised quartz sample. We find that very few of aliquots prepared from extracted quartz grains show any sensitivity of the most easily stimulated part of the OSL signal, but that ∼23% of aliquots give detectable initial signals after repeated dosing and bleaching. Surprisingly, a large fraction of the most easily stimulated quartz OSL is removed by infra-red stimulation, even though there is no significant IRSL signal in the UV. However thermal annealing at 700 °C gives rise to a test-dose response that is unaffected by IR. This annealing sensitises all aliquots to some degree and induces a signal which is stable up to 260 °C, in contrast to that following optical sensitisation, which begins to decrease when heated to 140 °C. The implications of these observations are discussed, both in terms of luminescence process and potential for dating.

Testing new kinetic models and calibration methods for Rock Surface Luminescence Exposure dating using controlled experiments

Rock surface luminescence exposure dating (RSLED) is an evolving tool in dating prehistoric rock surfaces. In this study, we explore and compare current and new models and calibration methods using optically stimulated luminescence (OSL) depth profiles from quartz grains and Infrared Stimulated Luminescence (IRSL; IR50, pIRIR225, and MET290) from feldspar grains found in granite and sandstone samples.This study shows that, although correct model assumptions improve the quality of exposure age estimates, significant discrepancies between observed and expected fitting parameter values remain, and these discrepancies leads to inaccurate age estimation. This is particularly the case when post-IR signals from feldspar are used. Here, the spectral dependency of luminescence signals is examined to better understand these problems. The demonstrated depth dependency of fitting parameters, previously assumed to be constant with depth, also gives rise to discrepancies in parameter values. The surprising observation that, in rocks, the IR50 signal is apparently more easily bleached than the quartz fast-component OSL signal is explained in terms of the wavelength dependence of light attenuation increasing the effective path length for shorter wavelengths, and so changing the shape of the light spectrum with penetration depth. This complicates parameter estimates in exposure dating even more.Alternative approaches (rather than parameter estimation) for estimating how long a rock surface has been exposed to light are considered, based on modelling the shape and position of the measured luminescence-depth profile. It is concluded that the most accurate exposure age is derived by interpolating the depth of an unknown profile onto a curve of profile depths from known age profiles (the Exposure Response Curve, or ERC, approach).

Towards the optically stimulated luminescence dating of unheated flint

Flint tools are important archaeological finds, but unheated specimens remain challenging to date. The optical luminescence properties of the microcrystalline flint differ from sedimentary quartz grains, and optically stimulated luminescence (OSL) has, therefore, only occasionally been used to date heated flint specimens. However, if OSL dating could be used on unheated samples, this should expand the number of dateable flint samples from the archaeological record. This study investigates the luminescence sensitivity to blue, green, and infrared stimulation in flints collected from four sites in eastern Denmark. While stimulations at each wavelength yielded some luminescence emissions, blue OSL provided the strongest emission, and subsequent investigations here focus on measurements using this signal. The shape of the decay curves and the photo-ionising cross-sections for the blue OSL signal components are similar between natural and irradiated OSL and are also comparable to decay curves from calibration quartz. Dose–response curves show characteristic doses of ∽400 Gy, and dose recovery tests demonstrate that a SAR protocol can recover laboratory doses. The measured laboratory fading rates are considerable, where flint slices stored for up to six weeks provide average g-values of up to 9 % per decade. Also, the flint is less thermally stable compared to calibration quartz. However, a natural OSL signal remains in Cretaceous flints (albeit at 50 % or less of laboratory saturation), showing that signal loss did not outpace the electron trapping rate. The presence of a dose-dependent, natural OSL signal and acceptable dose recovery indicate that optical dating of flint surfaces could be feasible, at least in the flints from eastern Denmark, and that flint from other regions should be investigated.

Dating (early) modern hearths on a decadal to multi-annual timescale using OSL signals from heated sedimentary quartz

Archaeological excavations at “Doorn Noord” (Ninove, East Flanders, Belgium) revealed a complex of traces of human activity and occupation, spanning several millennia. The youngest finds consist of a vast number of surficial hearths and hearth pits, that are interpreted as the remnants of military camps. Based on direct and indirect historical information, as well as a few diagnostic finds, these traces were originally assigned to possible phases of encampment in 1692 CE, 1693 CE, 1745 CE and/or 1831–1838 CE. Although widely used in archaeological research, it is well-known that radiocarbon (14C) dating lacks precision for post-1650 CE features and therefore does not allow allocating a particular trace to a distinct phase of military presence.In this study, we report on the potential of optically stimulated luminescence (OSL) signals of quartz for directly dating the heated sedimentary remains of the hearths. We consider it a test of both accuracy and precision given the availability of independent age information (historical sources and archaeomagnetic dating). Six samples from three features yielded indistinguishable optical ages, with an average age of 1748 ± 39 CE (95% probability). This OSL date coincides with historical and archaeological evidence for the presence of a large army in this area in 1745 CE. As sources of systematic uncertainty are (largely) shared, it is possible to distinguish between comparable features with a relative time-resolution of ∼2%. For hearths from the last few centuries (post-1650 CE), this implies that numerical and relative chronologies can be established on decadal and multi-annual timescales with 95% confidence.

Analysis probes and statistical parameters affecting the OSL ages of mortar samples; a case study from Italy

Mortars stand among the very few materials that theoretically cannot be reused due to irreversible hardening processes. Among the various dating techniques, radiocarbon and Optically Stimulated Luminescence (OSL) struggle for being selected as the most robust and reliable dating technique for the specific material. The principle of mortar OSL dating depends on the bleaching of the quartz grains of the sandy aggregate while mixing and laying the mortar to daylight. Thus, the OSL ages strongly depend on the effective bleaching of the quartz. Here, we deal with OSL ages from the old Roman Theatre of Padua. Preliminary OSL results based on Single Aliquot Regeneration (SAR) protocol using three regenerated doses to multigrain (MG) quartz aliquots, indicated distributions of ED (Equivalent Dose) leading to significant mismatch of these results compared to the expected ages. The present work attempts to discuss the influence of various data analysis approaches such as (a) exclusion criteria like recycling ratio and recuperation values, (b) selection of the suitable region of interest in the signal's integral along with the correct background (late or early) subtraction technique and (c) appropriate statistical analysis by selecting the suitable age model (descriptive statistics, Central Age Model, Minimum Age Model) on the final distribution as well as both value and precision of the ED, enabling thus to obtain ages that are not only more accurate, but also closer to what was expected. Alternative statistical indicators of either the symmetry of the ED distributions (like skewness, kurtosis, etc) or the OSL signal itself (residual distribution analysis, kinetic parameters and percentage contribution of each OSL component to the overall signal) will be assessed in an effort to investigate possible correlations.