OSL Measurement Research Articles

Study of non-exponential OSL decay curve within critical physical conditions of synthetic quartz material and their resolution by selection of suitable protocol

Researchers had reported that synthetic quartz which was annealed either at 400 °C irradiated by 75.6 Gy beta doses or at 600 °C irradiated by 25.2 Gy beta doses showed better rise in OSL intensity at room temperature depicting the change from non-exponential to exponential shape of the decay curve. Under these conditions, the non-exponential shape of decay curve with weaker OSL intensity was observed. It was due to re-trapping of optically released electrons by shallow traps corresponding to 110 °C TL glow peak and it was later verified by ESR spectra.In order to eliminate the non-exponential behaviour of decay curve, the researchers suggested OSL measurement at elevated temperature so as to further remove the contribution of shallow traps. However, in the present work, the OSL decay curves are recorded at 160 °C for 400 °C and 600 °C annealed samples irradiated by 2.52 Gy, 5.04 Gy, 25.2 Gy and 75.6 Gy beta doses. Both the samples show non-exponential shape of OSL decay curve up to 25.2 Gy beta doses. However, it gradually changes to exponential shape with better OSL intensity at higher beta doses. Additionally, few attempts were made to examine the non-exponential pattern of OSL decay at room temperature as well as elevated temperature within respective critical conditions by using fitting equations. It reports that various mode of non-exponential patterns of curve and their changes were influenced by strength of physical conditions. Further, a new protocol of cyclic sequence of doses, pre-heat up to 200 °C, test dose and stimulation at 125 °C for 40 s stimulation time was implemented to identical treated samples. It shows disappearance of non-exponential shape of OSL decay by growth in OSL intensity. These changes in OSL pattern were further justified by the contribution of annealing, irradiation, thermal transfer and thermal assistance process and TL measurements before and after OSL.

Quantitative beta autoradiography of a heterogeneous granulite sample and implications for luminescence dating

Beta dose rate heterogeneity is a known source of scatter in OSL measurement and equivalent dose distributions. Without proper methods to describe and account for it, it can contribute significantly to the uncertainties in OSL ages. For this reason, investigating the beta dose rate (β Dr) distribution is necessary to improve the dating of heterogeneous samples. Here we present a method for quantitative and high sensitivity autoradiographic imaging of beta dose rates. It is demonstrated using highly heterogeneous granulite rock samples. The accuracy and sensitivity of this method is improved using pulsed laser stimulation, and by underground exposure of samples in an ultra-low background environment. Results are calibrated using gamma (γ)irradiation and Monte Carlo simulation and have been validated using homogeneous dose rate standards. Combining analysis of autoradiography results and SEM backscattered images of the same samples allows determination of the dose rate distributions in the different mineral phases. A significant difference between the dose rate of K-feldspar grains obtained from the imaging and the dose rates calculated using methods commonly used in OSL dating is noted because of the clustering of grains in the sample. This represents a risk of bias in age determination in coarse grained rock samples which can be analysed using dose rate imaging methods. The beta Dr spatial distributions result in a significant dose scattering received by single grains, even compared to the total dose rate. The effect of such beta dose rate distributions on OSL dating of coarse-grained crystalline materials is discussed.

TL -OSL properties of nanosized BaMg2Al6Si9O30:Ce3+/ Dy3+ phosphor

In this article we have reported Ce3+ / Dy3+ activated BaMg2Al6Si9O30 nanosized phosphor synthesized by the combustion method. Prepared phosphors was initially irradiated by Sr-Y90β-emitting source and then it was used for the Thermoluminescence- Optically Stimulated Luminescence (TL-OSL) measurement. Here, BaMg2Al6Si9O30:Ce3+/ Dy3+ phosphor exhibits an isolated broad TL glow curve at around 2010 C. And further, it was well resolved into two sub-bands to estimate the trap depth and TL parameters of the individual glow curve. Along with this, we have carried out the OSL measurement of BaMg2Al6Si9O30:0.1Ce3+,yDy3+ phosphor which is well fitted into third order exponential. The micro and nanostructure of the phosphors product has been confirmed from SEM, TEM analysis. Again the phase purity of the materials was confirmed by XRD, which has hexagonal structure. Also diffraction pattern of the prepared phosphor is indexed well using theoretical tools of XRD. Hence from the investigation of TL-OSL properties, it is seen that synthesized thermoluminescent materials may be a promising candidate for the irradiation of foods and seeds.

Thermally modulated optically stimulated luminescence (TM-OSL) of quartz

It has recently been shown in computer simulations of the OSL process that increasing the temperature during optical stimulation allows the probability of electron excitation from traps to the conduction band to be modulated. This, in turn, facilitates the efficient separation of individual OSL components. A result of the thermally modulated OSL (TM-OSL) measurement method is a peak shaped curve. In addition, the position of the TM-OSL peak on the temperature axis can be controlled by the stimulation energy, heating rate and photon flux used for optical stimulation. Here, the results of a TM-OSL study for natural quartz samples are presented. The basic features of the TM-OSL curves of quartz are shown for different parameters that control their shape. The investigation is focused on traps that are most sensitive to light and which are the source of the OSL signal that is the most useful in retrospective dosimetry. A method by which it can be measured separately from the slower components is presented. The very first attempt at directly estimating the optical depth and the parameters determining the strength of the electron-phonon coupling for the traps responsible for the fast OSL component in quartz has been made.

P.2.d.022 - Inflammatory cytokines influence cortical thickness in bipolar disorder

It has recently been shown in computer simulations of the OSL process that increasing the temperature during optical stimulation allows the probability of electron excitation from traps to the conduction band to be modulated. This, in turn, facilitates the efficient separation of individual OSL components. A result of the thermally modulated OSL (TM-OSL) measurement method is a peak shaped curve. In addition, the position of the TM-OSL peak on the temperature axis can be controlled by the stimulation energy, heating rate and photon flux used for optical stimulation. Here, the results of a TM-OSL study for natural quartz samples are presented. The basic features of the TM-OSL curves of quartz are shown for different parameters that control their shape. The investigation is focused on traps that are most sensitive to light and which are the source of the OSL signal that is the most useful in retrospective dosimetry. A method by which it can be measured separately from the slower components is presented. The very first attempt at directly estimating the optical depth and the parameters determining the strength of the electron-phonon coupling for the traps responsible for the fast OSL component in quartz has been made.

Development and Performance Testing of a Time-resolved OSL Measurement System

Development and Performance Testing of a Time-resolved OSL Measurement System

The effect of test dose and first IR stimulation temperature on post-IR IRSL measurements of rock slices

Optically stimulated luminescence (OSL) is increasingly applied to the dating of rock surfaces. There is at present no practical way of separating pure minerals (quartz and feldspar) from hard rocks for OSL measurement without losing the grain-size dependent dosimetric information and there is little information about the performance of the single-aliquot regeneration-dose (SAR) measurement protocol on the post-infrared infrared stimulated luminescence (pIRIR) signals from rock slices. The latter is investigated here. Our data indicate that there is a systematic increase in dose response curve saturation (or <i>D</i><sub>o</sub>) with test dose size when the regeneration doses are first given in increasing order, and then decreasing order. This trend disappears if these orders are reversed. The reproducibility of dose response curves is dependent on the size of the test dose (poorer for small test dose). For rock slices given a saturation dose in the laboratory, it is observed that the sensitivity corrected pIRIR<sub>290</sub> signal lies close to saturation level of the dose response curve, for first IR stimulation at temperatures between 50 and 250°C. However, the pIRIR<sub>290</sub> signal from naturally saturated slices lies close to the laboratory saturation levels only for higher first IR stimulation temperatures e.g. 200°C or 250°C. Our data confirm earlier suggestions based on sand-grain measurements that, for older samples, accurate measurements close to saturation require that a higher first IR temperature is used.

OSL at elevated temperatures: Towards the simultaneous thermal and optical stimulation

In routine OSL dating measurements, a preheat procedure at high temperatures is used to empty the shallow traps. Thus no contribution from shallow traps was expected as each OSL measurement is subsequently performed at moderately high temperatures, around 110–125°C. The present work attempts to consider the OSL measurements performed at elevated temperatures without any previous preheat as a case of simultaneous thermal and optical stimulation of the same trap. Towards this direction, a set of proposed equations is derived for all three different cases of optical stimulation modes, namely CW-OSL, LM-OSL as well as PS-LM-OSL. According to these equations, indicative features of thermally activated OSL processes are expected, such as the steepening of CW-OSL decay curves as either stimulation temperature or intensity increases, as well as the shifting of the stimulation time of the maximum intensity for both LM-OSL and PS-LM-OSL curves towards shorter times with increasing temperatures. Experimentally, specific measurement sequences after varying stimulation temperature and/or intensity were applied in order to estimate the values of associated trap parameters, such as activation energy and photo-ionization cross-section. Experimental OSL data from a milky natural quartz sample stand in good agreement of these theoretical considerations in the case of 110°C TL peak and the intense OSL component C2 monitored at RT.

OSL measurement of 3.11 tsunami and offshore deposits

OSL measurement of 3.11 tsunami and offshore deposits

Influence of spectral width of stimulation band on the shape of OSL curve

In the practice of OSL measurements stimulation light sources with finite spectral band are used. Till now, however, this fact was not taken into account in the analysis of OSL measurement results. Here the simulation of OSL process under the stimulation with light of a defined spectral band is performed and the results of standard OSL analysis of the simulated curves are compared with optical cross-section values assumed in the kinetics model.

Improvement in dose threshold of α-Al2O3:C using thermally assisted OSL

Abstract α-Al 2 O 3 :C phosphor was studied for improvement of its dose threshold using thermally assisted optically stimulated luminescence (TA-OSL) phenomenon. The dose threshold of phosphor depends on the standard deviation of the background signal which affects the signal-to-noise ratio of the instrument. In case of OSL measurement, the background signal is due to the scattering of the stimulation light intensity from the planchet. On reducing the stimulation light intensity, the scattering component and thus the standard deviation of the background signal reduces considerably. The reduction in stimulation light intensity increases the readout time due to the dependence of decay constant of OSL signal on the former. The decay constant depends on the photo-ionization cross-section of the OSL active traps in the phosphor participating in OSL phenomenon and thus on the readout temperature due to the temperature dependence of photo-ionization cross-section. In order to achieve the same decay constant for two sets of measurements for α-Al 2 O 3 :C i.e. to take the OSL measurement in the same time at lower stimulation light intensity as that taken for higher light intensity, the temperature of measurement for α-Al 2 O 3 :C for the former was raised. Moreover, the increase of readout temperature does not affect the standard deviation in the background signal of OSL readout. The optimized elevated temperature for α-Al 2 O 3 :C was found to be 85 °C as the main dosimetric peak starts giving signal due to depletion of its filled traps, at temperatures higher than 90 °C. As a result of lowering the stimulation intensity at higher temperature (85 °C), the standard deviation in the background signal and thus the overall dose threshold of α-Al 2 O 3 :C was found to improve by 1.8 times.

Application of pulsed OSL to polymineral fine-grained samples

Abstract Pulsed OSL is applied to nine fine-grained sediment samples from Sichuan province, China, using stimulating pulses of 10 μs on and 240 μs off, with an infrared exposure prior to each OSL measurement. Comparison of fading rates between pulsed and non-pulsed signals, the latter also obtained with a preceding IR exposure, shows that fading is significant for mainly the non-pulsed signals. Presence of a pulsed IRSL and the magnitudes of b -value to correct for lower alpha efficiency suggest that pulsing does not fully remove a significant feldspar signal, only a fading component. Comparison with ages of quartz extracts shows that pulsed OSL ages are consistent, while CW-OSL ages are slightly older and CW-IRSL ages are much older. The older ages suggest a less well-bleached feldspar component.

Analysis of OSL intensity increase with temperature and its consequences for dating applications

OSL dependence on temperature in the range from RT to 230 °C has been investigated in quartz separated from sediments in order to determinate the main OSL component responsible for the OSL intensity increase with temperature. The optical cross section spectra have been found and four OSL components have been recognized. The significant changes of the relative contributions of individual components in the total signal with temperature have been observed. The share of fast and medium components decreases with temperature. The characteristic behaviour of the intensities of these components, found also in the computer simulations of equivalent OSL process, indicates that both components can be related to one trap. The share of the slow component increases clearly above 150 °C. Because of the increase of the unstable super fast component above 80 °C, the temperature range below this temperature has been indicated as the most safe for OSL measurement in OSL dating.

On some fundamental features of optically stimulated luminescence measurements

Abstract The influence of electron–phonon interaction on the shape of the optically stimulated luminescence decay curve has been examined. The formula describing the dependence of optical cross-section on stimulation energy and temperature has been applied in a computer simulation of optically stimulated luminescence process. Computer simulations have been carried out for different temperatures using both one-trap and two-trap models. The ideas of an OSL measurement with continuously increasing energy of stimulation have been tested via computer simulations. The outcomes of this technique have been presented for a wide range of material parameters.

The dependence of dose recovery experiments on the bleaching of natural quartz OSL using different light sources

In this paper, the dependence of dose recovery tests on the different bleaching light sources (blue-LEDs, solar simulator, natural sunlight) is investigated with a variety of sedimentary quartz samples, selected so that their OSL signals are dominated by the fast OSL component. We observed that when long solar simulator bleaching was applied, various known doses were underestimated in an SAR-based dose recovery test. However, when blue-LEDs and short solar simulator bleaching were used (10 s and 60 s) the known doses were accurately recovered. In repeated measurement of the OSL signals induced by the same regeneration and test dose, we observed a considerable increase in quartz OSL sensitivity during or after the first OSL measurement when long solar simulator bleaching was used; this seems to provide a possible explanation for the observed underestimation of the laboratory known doses. A series of experimental results using a sample from a modern aeolian dune surface shows that there are no subsequent sensitivity changes when the naturally zeroed samples are bleached with sunlight for long time. It seems that there is a dependence of the sensitivity change on the amount of dose administered before solar simulator bleaching and on the light intensity of solar simulator. When small doses were given to the naturally zeroed sample, the sensitivity change during or after the first OSL measurement was not significant. However, when a considerable amount of beta dose (∼4000 Gy) is administered to the sample, a clear sensitivity change during or after the first OSL measurement (∼20%) was observed. Such a sensitivity change was not observed when the bleaching light intensity of solar simulator was reduced by increasing the distance between samples and the UV lamp. Our results show that, at least for the samples described here, the outcomes of dose recovery experiments are dependent on the bleaching conditions.

The source of D e variability in periglacial sand wedges: Depositional processes versus measurement issues

Relict periglacial wedge structures are widespread in mid-latitude and polar regions. The wedges have a high preservation potential and are often infilled with quartz-rich aeolian sand, making them potentially suitable for luminescence dating. This paper presents initial work from an anti-syngenetic sand wedge in the Tuktoyaktuk Coastlands, Arctic Canada. When samples were measured at the single grain level they showed poor palaeodose (D e) reproducibility and consequent high age uncertainties. The aim of the study was to determine whether this intra-sample D e scatter reflected methodological issues arising from OSL measurement or processes of wedge development. Initial single grain dose recovery tests show that D e scatter was not easily explained by poor recycling, sensitivity changes, variable OSL components, recuperation problems, or large D e uncertainties from dim grains. Single grain preheating tests did show that some D e scatter might be attributable to individual grains requiring different preheat temperatures, whilst dose recovery tests revealed that highly sensitive grains showed less scatter than dim grains. However, selection of these bright grains from natural samples still resulted in scattered D e values. An alternative explanation for the D e scatter relates to the formation of anti-syngenetic sand wedges by thermal contraction cracking over thousands of years in an eroding landscape, which may result in sediment of very different ages being deposited in adjacent cracks. Finite mixture modelling was used to identify D e components within each sample. Ages calculated from these components suggest sand wedge formation at ca. 5, 8.5, 12.5 and 18 ka which correlate well with known cooling events over the last 18 ka and support a multiple phase activity model for anti-syngenetic sand wedges.

LM-OSL thermal activation curves of quartz: Relevance to the thermal activation of the 110 °C TL glow-peak

The thermally activated characteristics (TAC) of the linearly modulated optically stimulated luminescence (LM-OSL) signals of seven quartz samples from different origin were studied relative to the TAC of their respective thermoluminescence (TL) glow-peaks at 110 °C. Within the framework of the study the TAC behavior of the LM-OSL was investigated by measuring the OSL signal at room temperature (RT) with the 110 °C glow-peak present during OSL measurements, as well as, at 125 °C without the glow-peak at 110 °C removed by a cut-heat at 180 °C prior to OSL measurement. The LM-OSL curves were analyzed into individual components using a computerized deconvolution procedure. It was found that all individual LM-OSL components of each kind of quartz follow the TAC behavior of the respective TL glow-peak at 110 °C. The fourth component of the LM-OSL curve, centered at about t m = 400 s , appeared when the OSL measurements were performed at RT, whereas it was absent when the OSL measurement were performed at 180 °C. It is suggested that this component is closely related with the TL glow-peak at 110 °C.

Optimization of the ‘double SAR’ procedure for polymineral fine grains

The “double SAR” protocol has been used to measure the equivalent dose of polymineral grains from fine-grained samples. However, the optical ages obtained with this protocol using the different luminescence signals from a sample are not always consistent. Quartz optical ages are believed to be more reliable than feldspar ages. The post-IR OSL signals from polymineral fine grains are believed to be dominated by the signal from quartz. The ages obtained with the “double SAR” protocol using the post-IR OSL signals from polymineral fine grains are therefore considered to be more reliable than those obtained using the IRSL signals. Thus, the feldspar contribution to the post-IR OSL signals should be reduced as much as possible. In this paper, the effects of IR-stimulation temperature and duration before OSL measurement on the post-IR OSL signals from quartz extracts and polymineral grains, and their equivalent dose values were tested. The results show that the IR stimulation causes the quartz post-IR OSL signals to be reduced even at room temperature if the IR stimulation lasts long enough, but does not affect quartz equivalent dose estimation using post-IR OSL signals. In the ‘double SAR’ procedure, the IR-stimulation time should be determined by an IR-bleaching D e plateau test, and the bleaching should preferably be performed at room temperature.

New aspects of a BeO-based optically stimulated luminescence dosimeter

The optical sensitivity of BeO-based luminophors is well known for many years. A simple OSL treatment, the equipment and resulting dosimetric properties of BeO will be described. In contrast to most OSL measurement techniques, detector stimulation and luminescence light recording are performed from opposite sides of the detector. This gives rise to a very short distance between detector surface and light sensor, and consequently an optimum of light yield. Dosimetric properties of various available forms of BeO sinter pellets were examined for a broad range of conditions. The dosimeters show linear dose response between less than 5 μ Gy and 5 Gy. Long time fading of the signal is negligible. It amounts to less than 1% over six months. Other environmental factors like humidity neither influence the response. The greatest advantage of BeO is its very low photon energy dependence. Because of its effective atomic number the luminophor is nearly tissue equivalent. This fact and all other excellent dosimetric properties make BeO of interest for all applications in medicine, personal and environmental dosimetry.

Utilization of LED to OSL measurement

Utilization of LED to OSL measurement