Pulsed Optically Stimulated Luminescence Research Articles

Rock surface luminescence dating of gravel determines the age of a glacial outburst megaflood, Glacial Lake Missoula, Montana, USA

AbstractGiant gravel bars are important archives of megafloods; however, determining their depositional ages requires reliable geochronometric methods. Five gravel bars, reaching heights of 150–170 m, formed in the bedrock-lined Alberton Gorge along the Clark Fork River, Montana (USA), during draining of Glacial Lake Missoula (GLM). We report the first numerical ages for megaflood deposits in the GLM basin by successfully applying the novel optically stimulated luminescence (OSL) rock surface dating technique to date cobbles collected from three locations along one bar’s transport direction. Depth-dependent infrared stimulated luminescence and post-infrared pulsed OSL signals showed that exteriors of only 3 out of the 38 collected cobble samples were well bleached by exposure to daylight before burial, and hence suitable for dating. The cobbles provided ages of 16.5 ± 0.9, 18.5 ± 1.4, and 21.7 ± 1.1 ka, all of which are indistinguishable from the average cosmogenic nuclide age of 18.2 ± 1.5 ka (n = 4) for a large megaflood in the Channeled Scabland, eastern Washington State. The average of the two younger ages, 17.5 ± 1.0 ka, is our best estimate of the deposit age. We interpret the older age to be from a cobble that was reworked by the flood. Our results show that these techniques have great potential for providing reliable chronologies for paleofloods and other high-energy depositional events.

Testing the Applicability of Quartz and Feldspar for Luminescence Dating of Pleistocene Alluvial Sediments in the Tatra Mountain Foothills, Slovakia

Abstract Luminescence dating is a widely used method in combination with sedimentological analysis for reconstructing the landscape development of the Quaternary period. In this study, quartz and K-feldspar measurements were used to evaluate the luminescence characteristics with the aim of dating the deposits. The sediments were sampled from an abandoned gravel pit in the Biely Váh valley and eight sites in the lower part of the Velická dolina valley, High Tatra Mountains, Slovakia. Optically stimulated luminescence (OSL) showed that quartz had an unstable weak signal, and standard single aliquot regeneration (SAR) dose estimates were unreliable, as were doses from pulsed OSL and differential OSL. Infrared (IR50) and post-IR IR225 stimulation (pIRIR225) signals from K-feldspar grains, on the other hand, gave stronger signals but were, to various extents, influenced by incomplete bleaching, fading and uncertainty due to high (>2D0) doses. We find the uncorrected pIRIR225 ages most reliable, though modern analogues indicate that there may be significant residual from incomplete bleaching for some of the samples. The results of the luminescence analyses, ages and sedimentology are put in the context of landscape dynamics and compared to the known glacial history of the Tatra Mountains.

Improved simultaneous LET and dose measurements in proton therapy

The objective of this study was to improve the precision of linear energy transfer (LET) measurements using text {Al}_2text {O}_3text {:C} optically stimulated luminescence detectors (OSLDs) in proton beams, and, with that, improve OSL dosimetry by correcting the readout for the LET-dependent ionization quenching. The OSLDs were irradiated in spot-scanning proton beams at different doses for fluence-averaged LET values in the (0.4–6.5) hbox {keV}, upmu hbox {m}^{-1} range (in water). A commercial automated OSL reader with a built-in beta source was used for the readouts, which enabled a reference irradiation and readout of each OSLD to establish individual corrections. Pulsed OSL was used to separately measure the blue (F-center) and UV (F^+-center) emission bands of text {Al}_2text {O}_3text {:C} and the ratio between them (UV/blue signal) was used for the LET measurements. The average deviation between the simulated and measured LET values along the central beam axis amounts to 5.5% if both the dose and LET are varied, but the average deviation is reduced to 3.5% if the OSLDs are irradiated with the same doses. With the measurement procedure and automated equipment used here, the variation in the signals used for LET estimates and quenching-corrections is reduced from 0.9 to 0.6%. The quenching-corrected OSLD doses are in agreement with ionization chamber measurements within the uncertainties. The automated OSLD corrections are demonstrated to improve the LET estimates and the ionization quenching-corrections in proton dosimetry for a clinically relevant energy range up to 230 MeV. It is also for the first time demonstrated how the LET can be estimated for different doses.

The effect of shallow and deep traps on the determination of thermal quenching using pulsed optically stimulated luminescence: The case of Al2O3:C

The objective of this work is to apply a model that accounts for the presence of shallow traps to the analysis of pulsed optically stimulated luminescence (POSL) data, which is used to characterize the luminescence lifetime and thermal quenching of luminescent materials. In particular, we focus on the analysis of photon arrival time distribution (PATD) data obtained by POSL readouts of irradiated materials. To achieve this, we present the detailed analysis of a PATD experiment over a range of readout temperatures of a well-known dosimetric material, Al2O3:C. Hitherto, an exact model accounting for the previously observed luminescence lifetime over-estimation is missing. Herein, we apply a proposed model that accounts for the influence of shallow traps and show how this model corrects for the luminescence lifetime over-estimation and introduces the temperature-dependent shallow trap lifetime as a new parameter. We furthermore show that populated deep electron traps lead to a stronger shallow trap occupation, which could be quantified with our model. The results are relevant for both the interpretation of thermal quenching models of Al2O3:C and, more generally, for lifetime measurements in luminescent materials.

New correlation between PTTL and POSL components in Al2O3:C

We describe newly found correlations between thermoluminescence (TL), pulsed optically stimulated luminescence (POSL), and phototransfer TL (PTTL) signals in Al2O3:C. A set of Al2O3:C samples were characterized for their TL and OSL curve shapes, as well as TL/POSL integrals and correlated with their PTTL behavior. POSL was used to separate the contribution from fast UV emission (F+ centers) and slow blue emission (F centers) OSL components in Al2O3:C. The results show that samples with high PTTL exhibit TL curve shapes with a peak at higher temperatures and OSL curves that decay slower compared to samples with low PTTL. The ratio of the integral POSL components, the UV/B ratio, was found to inversely correlate with the PTTL. We discuss the possible causes of our observations and outline the limitations of commonly used luminescence models to explain our data. These correlations add yet another piece to the puzzle of the stimulated luminescence mechanisms of Al2O3:C.

On the analysis of photon arrival time distributions obtained using the pulsed optically stimulated luminescence technique

The objective of this work is to address the analysis of photon arrival time distributions (PATDs) obtained using the pulsed optically stimulated luminescence (POSL) technique in two particular situations: (a) when the interval between pulses is insufficient for the full decay of some of the luminescence components, and (b) in the presence of shallow traps. PATDs are important to characterize the luminescence lifetime of synthetic and natural optically stimulated luminescence (OSL) materials used for dosimetry and in luminescence dating, as well as to separate the OSL components from luminescence centers associated with different luminescence lifetimes. In this study we simulated numerically the PATDs that can be obtained in the presence of fast and slow luminescence centers, where “fast”/“slow” is relative to the pulse width and period, and show that the analysis of these PATDs using semi-empirical equations based on a simple model can lead to wrong results when certain conditions are not satisfied (e.g. full decay of luminescence component between pulses, presence of shallow traps). Modifications to the semi-empirical equations are derived to provide better estimates for the luminescence lifetimes in the conditions simulated. Experimental data on Al2O3:C OSL dosimeters are used to illustrate the relevance of the results.

Recombination lifetimes of LiF:Mg,Cu,P for pulsed optically stimulated luminescence

The well-known thermoluminescent material LiF:Mg,Cu,P (MCP) was previously shown to emit significant optically stimulated luminescence (OSL). In this paper, we investigate the rate of OSL recombination processes in MCP, expressed as effective lifetimes, using time-correlated single photon counting, in this context often referred to as time-resolved pulsed OSL. The recombination luminescence fell into two categories: (i) a dominant fast decaying luminescence described by the two lifetimes τ1=22.8(1.7)μs and τ2=60(5)μs and (ii) a slowly decaying part with indeterminate decay profile at a comparatively low signal level (we denote this as “offset luminescence”). The fast recombination channels corresponding to τ1 and τ2 are responsible for 71% of the total luminescence observed during test measurements. The luminescence associated with τ1 dominate the beginning of an experiment, but is depleted much quicker than the luminescence associated with τ2. We show that all recombination channels show similar response to preheating of the sample, which suggests that they are associated with the same trapping centers.

Pulsed optically stimulated luminescence for mechanisms studies in quartz

In this study we present pulsed optically stimulated luminescence (OSL) measurements in quartz, directed towards the generation of information relevant to mechanisms studies. Our measurement program covers the pulsed OSL emitted from a number of laboratory-irradiated South Australian quartz samples shone across a wide temperature range. We reveal that although the response is dominated by a single exponential component, it also includes several faint slow components and a temperature-dependent step component. We find that the room temperature time constant of 40.9 ± 0.2 μs measured from the pulse fall exceeds the corresponding value of 39.9 ± 0.2 μs measured from the rise. Further, application of the Mott-Seitz formula across the temperature range has enabled a value of 0.694 ± 0.004 eV to be derived for the activation energy associated with thermal quenching. Similar investigations yield a room temperature time constant of 1.60 ± 0.02 ms and an activation energy of 1.1 ± 0.05 eV for the strongest of the faint components. Regarding the step component, we find that it dominates the OSL as the temperature is increased. By applying linearly modulated OSL in the 300–450 °C high temperature region, we show that the step is generated even in the absence of applied ionising radiation.

Timing and development of sand dunes in the Golestan Province, northern Iran—Implications for the Late-Pleistocene history of the Caspian Sea

Abstract The Golestan Province, in northern Iran, presents a rich record of aeolian deposits, including thick loess-palaeosol sequences and prominent sand dunes. While the loess chronology in this area is relatively well constrained, the formation time of the dunes remains largely overlooked, despite their potential to provide valuable information in terms of palaeoclimate conditions and Caspian Sea level changes. In this study, we provide the first reconstruction of dune evolution in Golestan Province, based on geomorphic and sedimentological investigations, high resolution granulometric and microfossil analyses, and luminescence dating. Luminescence analysis includes quartz post-infrared pulsed optically stimulated luminescence (Post-IR pulsed OSL) and K-feldspar post-IR infrared stimulated luminescence (pIRIR) measurements. Luminescence ages indicate that the studied dunes accreted within a few thousand years ranging from 10.6 ± 1.6 ka to 8.4 ± 1.4 ka, during the Holocene. Based on the geomorphological evidence and geographical setting, the dunes observed in the Caspian lowland are of parabolic type, which would reflect arid to semi-arid palaeoenvironmental conditions with sparse vegetation and predominance of easterly winds at the time of dune formation. Grain size distribution analysis and sedimentological investigations indicate a clear influence of the Caspian coast environment on the dunes development, in addition to probable sediment input from nearby fluvial systems. The spatial and temporal distribution pattern of the studied dunes reflects a quick regression of the Caspian Sea during the Early Holocene, probably following the so-called Mangyshlak regression.

Quartz OSL dating of palaeosols intercalated with basaltic lava flows and scoria deposits from monogenetic volcanoes in northeastern Jeju Island, Korea

Jeju Island, which lies on the continental shelf in the southern Korean Peninsula, is the emergent portion of a basaltic volcanic field that has erupted since the Early Pleistocene (ca. 1.8 Ma). Volcanic activity that continued into historic times (ca. 1 ka) formed an elongated shield with a central edifice (Mt. Halla) and more than 300 monogenetic cones and rings. The establishment of a temporal framework for Jeju volcanism, particularly during the Late Pleistocene and Holocene activities, requires geochronological tools other than radiometric dating techniques, which are based on parent-daughter isotope pairs with geologically long half-lives, such as 40Ar/39Ar dating. In this study, we conducted quartz optically stimulated luminescence (OSL) dating of palaeosols intercalated with basaltic lava flows and scoria deposits, presumably ejected from three monogenetic volcanoes (Cheoreum, Darangsh and Dunjibong volcanoes) in the northeastern part of the island. Quartz extracts from the palaeosols had moderate to dim sensitivity to optical stimulation, but several prerequisite tests of the measurement protocols for equivalent dose estimation were successful. The coarse (63–250 μm) and fine (4–11 μm) quartz fractions yielded continuous wave (CW)-OSL ages of 19.9–7.0 and 18.6–6.7 ka, respectively, both of which were broadly consistent with the radiocarbon dates (10245–7440 Cal yr BP). These ages indicate that lava flows and scoria deposits covering the palaeosols are younger than ~7 ka. The pulsed OSL signals in coarse quartz extracts from the palaeosols suffered from poor counting statistics, thus it is recommended that they not be applied solely (i.e., without any other absolute ages to compare) to dating dim samples. From one of the sites investigated here, the averaged sedimentation rate of the palaeosol is estimated to be ~0.05 mm/yr, based on stratigraphically consistent CW-OSL ages. The OSL ages presented in this paper, together with previous OSL and radiocarbon ages, confirm that Jeju volcanic island was regionally active during the Holocene.

Time-resolved pulsed OSL of ceramic YAP:Mn phosphors

The paper deals with the results of comparative study on time-resolved pulsed optically stimulated luminescence (TR-OSL) response of ceramic YAP:Mn materials prepared by different methods. In particular, the ceramics prepared from the nanocrystalline material synthesized by the solution combustion method and ones obtained by the solid-state synthesis have been studied comparatively. These studies have revealed that the TR-OSL decay of both materials features a non-exponential behavior. The Becquerel decay function with three parameters fits quite well their decay responses recorded over wide time scale and dynamic range. The mean relaxation time estimated from fitting parameters differs significantly for samples fabricated by different technologies. This difference between two types of ceramics is discussed in the framework of the trap structure of the materials.

Late quaternary fluvial incision and aggradation in the Lesser Himalaya, India

Reconstructing how rivers respond to changes in runoff or sediment supply by incising or aggrading has been pivotal in gauging the role of the Indian Summer Monsoon (ISM) as a geomorphic driver in the Himalayas. Here we present new chronological data for fluvial aggradation and incision from the Donga alluvial fan and the upper Alaknanda River, as well as a compilation of previous work. In addition to conventional OSL-SAR (Single-Aliquot Regenerative-Dose) dating method, we have tested and applied pulsed OSL (POSL) dating for quartz samples that include K-rich feldspar inclusions, which is expected to improve the applicability and validity of OSL ages in the Lesser Himalaya. For previously dated deposits, our OSL ages are shown to be systematically older than previously reported ages. These results suggest periods of aggradation in the Alaknanda and Dehradun Valleys mainly between ∼25 and 35 ka. This most likely reflects decreased stream power during periods of weakened monsoon. In addition, in-situ cosmogenic beryllium-10 was used to infer bedrock surface exposure ages, which are interpreted as episodes of active fluvial erosion. Resulting exposure ages span from 3 to 6 ka, suggesting that strath terraces were exposed relatively recently, and incision was dominant through most of the Holocene. In combination, our results support precipitation-driven fluvial dynamics, which regulates the balance between stream power and sediment supply. On a larger spatial scale, however, fluvial dynamics are probably not spatially homogeneous as aggradation could have been taking place in adjacent catchments while incision dominated in the study area.

Optically stimulated luminescence ages for the Upper Palaeolithic site Krems-Wachtberg, Austria

Abstract The loess-paleosol profiles at Krems in central Europe (Lower Austria) are well known for the impressive output of Upper Palaeolithic remains as well as for their paleoclimate potential as terrestrial archives. Previous high-resolution sedimentological and environmental magnetic results documented a rather complex sedimentological setting at Krems-Wachtberg, an Early Gravettian site. The site has been previously dated by radiocarbon as well as luminescence methods. Here, optically stimulated luminescence dating (OSL) methods and sedimentological analyses are reported for new profiles previously not investigated. Continuous wave luminescence (CW-OSL) has been performed on 16 samples on fine (4-11 μm) and coarse (63-90 μm) quartz grains. Despite extensive sample preparation the quartz extracts proved to be highly contaminated with other minerals. The application of standard single aliquot regenerative (SAR) protocol intrinsic rigour tests (recycling, IR depletion and recuperation) resulted in almost half of the analysed aliquots being rejected. Albeit improving the precision of the equivalent doses, the application of these rejection criteria did not result in significantly different average values. Pulsed OSL (POSL) has been further employed in order to better separate quartz OSL signals, but resulted in no significant change in the determined equivalent doses. Obtaining a higher accuracy and precision for the chronology of the Krems-Wachtberg site using currently available luminescence dating methods remains a daunting task, despite the archaeological and paleoenvironmental significance of the site.

Optical dating of Holocene tidal deposits from the southwestern coast of the South Yellow Sea using different grain-size quartz fractions

The tidal flat deposit provides ideal sedimentary records for paleoenvironmental studies. Reliable chronology is crucial to utilize this archive for deciphering the history of environmental changes. In this study, we applied optically stimulated luminescence (OSL) dating method to a Holocene tidal flat sequence using both coarse-grained (CG, 90–200μm) and fine-grained (FG, 4–11μm) quartz extracts from a sedimentary core (YZ07) in western coast of the South Yellow Sea. The luminescence characteristics of the two grain-size fractions were investigated and then their resulting OSL ages were systematically compared. The results suggested that most tidal flat deposits are well bleached and their FG quartz ages are generally consistent with CG quartz ages, while some samples have CG ages underestimated compared with FG, likely resulted from the K-feldspar contamination for CG quartz. Hence, we applied post-IR OSL dating and pulsed OSL dating techniques; they could overcome the problems caused by feldspar contamination, and yielded identical dates as FG OSL ages. All OSL ages are generally in stratigraphic order; in contrast, the 14C ages are much more disorder and characterized with severe inversions. Finally, the age framework of the tidal flat sequence under this study was constructed based on the 30 OSL ages and one acceptable radiocarbon age. According to the age-depth model, three main periods of sedimentation-rate (SR) variation were identified. These SR changes are probably associated with sea-level rise/fall history, and the depocenter landward/seaward movement as well as the transition of depositional process within the Holocene delta initiation. The depositional environment changes were also reflected in sedimentological features of the tidal flat deposits in our study area.

Time-resolved OSL studies of YAlO3:Mn2+ crystals

Time-Resolved Optically Stimulated Luminescence (TR-OSL) from single crystalline YAlO3:Mn2+ samples was investigated using a green light emitting diode (λ ∼ 525 nm) as stimulation light source. The TR-OSL decay curve of the material can be described with a single exponential decay function with a lifetime about 80 ms that does not depend on irradiation dose in the range from 50 mGy to 1 kGy. This OSL decay is superposed on a photoluminescence signal with a much shorter (3.5 ms) decay lifetime. The Mn2+ photoluminescence decay with a lifetime of 3.5 ms can be easily eliminated by corresponding time resolution using pulsed OSL readout. Dose response and thermal stability of the OSL signal are consistent with the previous thermoluminescent (TL) studies of the material.

Performance of pulsed OSL stimulation for minimising the feldspar signal contamination in quartz samples

The use of pulsed optically stimulated luminescence (POSL) stimulation to remove contaminated feldspar OSL signal in quartz fractions has been tested either on artificial or natural mixtures of quartz and feldspar grains, using samples with good luminescence characteristics of quartz. The problem of feldspar contamination in quartz, however, is often accompanied by other undesirable luminescence characteristics such as a dim OSL signal and slow OSL decay. We report here, on the performance of POSL for nine sand-sized quartz samples from different parts of the Earth, which show severe feldspar contamination in the quartz OSL signal. The time resolved (TR)-OSL signal of these samples was measured to check the dominance of quartz OSL in their off-time signals. The fitting results of the off-time TR-OSL signal showed that the quartz OSL signal dominated during the off-time. The POSL De values for these quartz samples are on average ∼30% larger than the continuous wave (CW)-OSL De values due to the anomalous fading of the feldspar OSL signal. Furthermore the POSL ages were compared with post-infrared infrared stimulated luminescence (pIRIR) ages from K-feldspar for the samples and in most cases the two ages were consistent. These results indicate that POSL is an effective tool to remove feldspar contamination even for dim quartz samples. However, there are quartz samples which show severe anomalous fading in the quartz OSL signal itself. For such samples feldspar may be a better dosimeter.

Fundamental investigations of natural and laboratory generated SAR dose response curves for quartz OSL in the high dose range

SAR-OSL investigations on quartz from Romanian loess resulted in non concordant fine and coarse-grain ages for equivalent doses higher than ∼100 Gy. The laboratory dose response for both grain sizes is well represented by a sum of two saturating exponential functions, fine and coarse grains characterised by D01 and D02 values of ∼140 and ∼1400 Gy and ∼65 and ∼650 Gy respectively. Pulsed OSL experiments confirmed that this behaviour is almost certainly inherent to quartz and not caused by contamination with another mineral. Natural dose–response curves do not follow the same pattern and enter saturation much earlier. Analysis of time resolved spectra indicated similar luminescence lifetimes for both fine and coarse quartz grains, and natural and laboratory generated OSL signals seem to use the same non-dose-dependent recombination pathways. The natural signals of a sample with an expected equivalent dose of 2000–2500 Gy were found to be below the saturation level of the laboratory dose response curve for both grain sizes; this also applied to the luminescence signals measured after >5000 Gy given on top of natural doses.

Extending the area of investigation of fine versus coarse quartz optical ages from the Lower Danube to the Carpathian Basin

Despite the general satisfactory performance of quartz in the single aliquot regeneration protocol (SAR), previous optically stimulated luminescence (OSL) dating studies of key loess sections in Romania, Lower Danube region, revealed a disturbing disagreement among the ages obtained on fine (4–11 μm) grains and coarse (63–90 μm) grains respectively. The current study aims at expanding these investigations, both by extending the area of study from the Lower Danube Basin to the Carpathian Basin and by applying time-resolved optically stimulated luminescence (TR-OSL) on quartz, in order to gain further insights into the above mentioned behaviour. The samples from the Orlovat loess paleosol section (Vojvodina, Serbia) showed a similar behaviour to that previously reported on Romanian loess. A marked difference between the dose saturation characteristics of fine and coarse quartz OSL signals is observed for both continuous wave (CW-OSL) and pulsed OSL (POSL), where the dose response (up to 1000 Gy) is well described by a sum of two saturating exponential functions. TR-OSL measurements show one single, characteristic quartz lifetime for both natural as well as regenerative signals in the entire dose range investigated. A general disagreement between the ages obtained on the two grain sizes for samples with equivalent doses higher than about 100 Gy is reported as in the case of Romanian loess, inferring that the age discrepancy between the two grain sizes might be more widespread than previously thought.

Description of modular devices for the measurement of external dosimetry in radiation protection.

In 2002 the Group of Radiation Dosimetry and Calibration of the Belgian Nuclear Research Centre (SCK•CEN) has developed an experimental device based on the optically stimulated luminescence (OSL) working with Al2O3:C detectors (TLD-500 and Luxel) stimulated with an argon laser. A set of devices made from different modules have been developed to permit external dosimetry measurements with thermoluminescence (TL) and OSL techniques under different conditions. This study describes these measurement devices that can be made with these modules and some of the characteristics of the different systems. These devices present several advantages in terms of measurement possibilities: a small number of modules allow the use of different detection materials (Al2O3:C, BeO, quartz electronic components and tiles) and different measurement methods (TL, CW-OSL and pulsed OSL). Some applications are commented.

Fast assessment of retrospective dosimetry using the SAAD–POSL method with core disc samples from building materials

To establish a fast assessment method of accidental dose, core disc samples were extracted from a heated red brick, roof tile, ceramic tile, and toilet porcelain, which are commonly used building materials. We examined the physical characteristics of pulsed optically stimulated luminescence (POSL) signals from these samples, and tested the reliability of the single aliquot additive dose (SAAD)-POSL method over a range of 7 Gy. In addition, when the SAAD-POSL method was applied, the minimum detectable dose (MDD) was as low as 0.01 Gy for the heated red brick, and the calculation time for an equivalent dose was as short as 2 h. This result indicates that the SAAD-POSL method is more effective as a fast assessment method of accidental dose than the SAR-OSL method.