Optically Stimulated Luminescence Measurements Research Articles

Luminescence properties of common salt (NaCl) available in Nigeria for use as accident dosimeter in radiological emergency situation

In the event of a radiological accident or attack, it is important to assess and quantify radiation dose to the population. This could be done using materials in the vicinity that are sensitive to ionizing radiation. Common salt (NaCl) is known to be a sensitive thermoluminescence (TL) phosphor. Luminescence properties of common salt (NaCl) used in Nigeria were investigated using an automated luminescence reader Risø TL/OSL-DA-15, with attention focused more on the Optically Stimulated Luminescence (OSL). Strong radiation-induced TL and OSL signals were observed. The TL peaks occurred at about 100 °C, 240 °C and 280 °C. The dose response of both the TL and OSL signals showed a linear relationship. From the OSL pulse anneal curve with TL curve, a preheat temperature of 190 °C for 10 s was found adequate for the OSL measurements. There was no significant difference in the OSL decay for stimulation temperatures of 100 and 120 °C. Fading experiment over a storage period of 14 days showed about 13 and 3% decrease in the OSL signal of sample 1 and sample 2, respectively. The ratios of measured to given dose for dose recovery test were within ±19% of unity. Within the limit of error the samples could be used as a complementary emergency dosimeter in radiological accident situation.

Recent development in the optical stimulation of luminescence

Both in thermoluminescence (TL) and in optically stimulated luminescence (OSL), the physical quantity that governs the luminescence process is the probability of electron release from a trap. Thanks to the usage of the temperature dependence of this quantity, the TL analysis enables estimation of the parameters that determine uniquely a trap. During TL measurements is possible to empty shallow traps without depopulating the deeper traps. This is not possible in the course of the standard OSL measurements that do not exploit the dependency of the optical cross-section (OCS) on experimental parameters. Moreover, the OCS, the only parameter that can be determined from these standard measurements, does not define the trap uniquely. It depends on at least three trap parameters and on the experimental conditions. Recently, investigations were undertaken to reduce this unfavourable for OSL unbalance between TL and OSL methods. The idea was to cause during optical stimulation the changes of the electron release probability similar to those exploited in TL measurements. The foundation of such a stimulation method is the proper expression that describes the OCS dependence on stimulation energy and temperature. Such expression was proposed previously and here it is shown how the three factors: the stimulation energy, the temperature and the shape of the stimulation band, may be used for generating the OCS changes during the optical stimulation. Results of computer modelling of adequate luminescence processes are presented together with a few simple experiments that were carried out for all kinds of stimulation.

A methodology for on‐board CBCT imaging dose using optically stimulated luminescence detectors

Cone‐beam computed tomography CBCT systems are used in radiation therapy for patient alignment and positioning. The CBCT imaging procedure for patient setup adds substantial radiation dose to patient's normal tissue. This study presents a complete procedure for the CBCT dosimetry using the InLight optically‐stimulated‐luminescence (OSL) nanoDots. We report five dose parameters: the mean slice dose (DMSD); the cone beam dose index (CBDIW); the mean volume dose (DMVD); point‐dose profile, D(FOV); and the off‐field Dose. In addition, CBCT skin doses for seven pelvic tumor patients are reported. CBCT‐dose measurement was performed on a custom‐made cylindrical acrylic body phantom (50 cm length, 32 cm diameter). We machined 25 circular disks (2 cm thick) with grooves and holes to hold OSL‐nanoDots. OSLs that showed similar sensitivities were selected and calibrated against a Farmer‐type ionization‐chamber (0.6 CT) before being inserted into the grooves and holes. For the phantom scan, a standard CBCT‐imaging protocol (pelvic sites: 125 kVp, 80 mA and 25 ms) was used. Five dose parameters were quantified: DMSD, CBDIW, DMVD, D(FOV), and the off‐field dose. The DMSD for the central slice was 31.1±0.85 mGy, and CBDIW was 34.5±0.6 mGy at 16 cm FOV. The DMVD was 25.6±1.1 mGy. The off‐field dose was 10.5 mGy. For patients, the anterior and lateral skin doses attributable to CBCT imaging were 39.04±4.4 and 27.1±1.3 mGy, respectively.OSL nanoDots were convenient to use in measuring CBCT dose. The method of selecting the nanoDots greatly reduced uncertainty in the OSL measurements. Our detailed calibration procedure and CBCT dose measurements and calculations could prove useful in developing OSL routines for CBCT quality assessment, which in turn gives them the property of high spatial resolution, meaning that they have the potential for measurement of dose in regions of severe dose‐gradients.PACS number(s): 87.57.‐s, 87.57.Q, 87.57.uq

Investigation of optically stimulated luminescence behavior of quartz from crystalline rock surfaces: A look forward

Abstract Optically stimulated luminescence (OSL) dating has recently been applied to crystalline (i.e. igneous and metamorphic) rock surfaces. With the advent of this technique, early studies can guide improvements to the methodology that will lead to more robust age constraints. Low OSL sensitivity, poor measurement reliability, and equivalent dose scatter are common problems with dating quartz from crystalline rock surfaces. We investigate OSL characteristics of quartz extracted from crystalline Antarctic beach cobbles. Comparison of OSL behavior with cathodoluminescene characteristics and mineral composition and texture does not show a distinct relationship, suggesting luminescence behavior results from the natural radiation environment and post-crystallization transport history, rather than provenance source and the nature of crystal defects. Elemental composition of processed samples used for OSL measurements indicates standard methods of chemical preparation are not always suitable to extract pure quartz samples. Additionally, heterogeneous radiation production and attenuation poses a problem for estimating dose rates, in particular regarding beta contributions that dominate effective dose rates. We determine the sensitivity of effective dose rates to water content parameters and crystal size needed to calculate dose rates for crystalline rock surfaces. An increase in the value of all modelled parameters serves to reduce effective dose rates and, thus increase OSL ages. Dose rates are most sensitive to crystal size, which can introduce large uncertainty in burial ages from crystalline rocks due to heterogeneous crystal morphology (i.e. size and shape). This study provides a step forward in understanding the challenges and improving the methodology of luminescence dating of quartz from crystalline rock surfaces.

SU-F-T-327: Total Body Irradiation In-Vivo Dose Measurements Using Optically Stimulated Luminescence (OSL) NanoDots and Farmer Type Ion Chamber

Purpose: This study was performed to analyze the agreement between optically stimulated luminescence (OSL) nanoDots measured doses and 0.6 cc Farmer type ionization chamber measured doses during total body irradiation (TBI). Methods: In-vivo dose measurements using OSL nanoDots and Farmer chamber were done in a total of twelve patients who received TBI at our center by bilateral parallel-opposed beams technique. In this technique, the patient is kept inside the TBI box which is filled with rice bags and irradiated using two bilateral parallel opposed beams of 40×40 cm2 size with 45° collimator rotation at an SSD of 333.5 cm in an Elekta Synergy linear accelerator. All patients received a dose of 2 Gy in single fraction as conditioning regimen. The beams were equally weighted at the midplane of the box. The nanoDots were placed over forehead, right and left neck, right and left lung, umbilicus, right and left abdomen, medial part of thigh, knee and toe. A 0.6 cc Farmer chamber was placed in between the thighs of the patient. Measured doses are reported along with the statistical comparisons using paired sample t-test. Results: For the above sites the mean doses were 212.2±21.1, 218.2±7.6, 218.7±9.3, 215.6±9.5, 217.5±11.5, 214.5±7.7, 218.3±6.8, 221.5±15, 229.1±11.0, 220.5±7.7 and 223.3±5.1 cGy respectively. For all OSL measurements the mean dose was 218.6±11.8 cGy. Farmer chamber measurements yielded a mean dose of 208.8±15.6 cGy. Statistical analysis revealed that there was no significant difference between OSL measured doses in forehead, right and left neck, right and left lung, umbilicus, right and left abdomen and toe and Farmer chamber measured doses (0.72≤p≤0.06). However the mean OSL doses at thigh and knee were statistically different (p<0.05) from the Farmer chamber measurements. Conclusion: OSL measurements were found to be in agreement with Farmer type ionization chamber measurements in in-vivo dosimetry of TBI.

Investigation of the applicability of standardised growth curves for OSL dating of quartz from Haua Fteah cave, Libya

Abstract The establishment of standardised growth curve (SGC) for equivalent dose (De) determination can substantially reduce the amount of instrument time required for OSL measurements. In this study, we investigated the applicability of SGC for the optically stimulated luminescence (OSL) signal from single grains and small aliquots of sedimentary quartz from Haua Fteah cave, in Libya. The samples exhibit large inter-grain and inter-aliquot variation in the shape of their single grain and small aliquot dose response curves (DRCs) constructed from a range of sensitivity-corrected regenerative dose signals (Lx/Tx), which prevents the establishment of a single common SGC among different grains or small aliquots. Instead, the DRCs for the small aliquots can be divided into a minimum of three groups using the Finite Mixture Model, with the DRC saturating at a different dose level for each group. In order to establish a common DRC, or SGC, for each group, we propose a new normalisation method, the so-called least-squares normalisation procedure (‘LS-normalisation’), which largely reduces the variation between aliquots within the same group and allows the establishment of a common DRC, or SGC, for each group. In order to apply the SGC method for these samples, two regenerative dose points are needed for each aliquot to attribute it to one of the groups based on the ratio of the Lx/Tx signals for two sensitivity-corrected regenerative dose points. Equivalent dose (De) values for each aliquot can be estimated using the fitting parameters calculated for the SGC of the relevant group to which it belongs, together with measurements of the natural signal (Ln), one regenerative dose signal (Lx1) and their corresponding test dose signals (Tn, Tx1). For the samples investigated from Haua Fteah, we found that De estimates obtained from the SGCs are consistent with those obtained using a full SAR procedure. Our results suggest that small single-aliquot and single-grain De values obtained from application of the SGC may be underestimated if there is a significant proportion of early-saturating grains present in the sample; such grains or aliquots are mostly rejected due to saturation when analysed using the full SAR procedure. In this case, it is necessary to calculate the De values based only on those grains or aliquots that have relatively high saturation levels.

Tectonically-controlled infilling of the eastern Nihewan Basin, North China, since the middle Pleistocene

There has been a significant debate about the nature and causes of the Pleistocene evolution of the Nihewan Basin, North China. We studied the eastern Nihewan Basin sedimentary facies at two main sites, Hutouliang and Donggou. A combination of field observations and measurements of sediment grain-size distribution was used to reconstruct the sequence of sedimentary environments since the middle Pleistocene, and optically-stimulated luminescence measurements were used to date the sediments. Our results indicate that a shallow lake occupied the basin center along the Sanggan River, probably lasting until ~440 kyr ago before disappearing completely ~340 kyr ago. It was succeeded by a phase of fluvial-dominated sediment accumulation which ended ~30 kyr ago. We suggest that the formation of the gorge resulted from the relative uplift of the Niuxin Mountain along the Liulengshan fault ~140 kyr ago. However, since ~30 kyr ago the fault may have become inactive and the river downcutting near Shixia was no longer offset by the relative uplift, which caused a shift from deposition to denudation in the Nihewan Basin from then on. The disappearance of the paleolake ~340 kyr ago may have been the culmination of the ongoing process of basin infilling.

The age of human remains and associated fauna from Zhiren Cave in Guangxi, southern China

Zhiren Cave in southern China is an important site for the study of the origin and the environmental background of early modern humans. The combination of Elephas kiangnanensis, Elephas maximus, and Megatapirus augustus, indicates an early representative of the typical Asian elephant fauna. Previous U-series dating of flowstone calcite has pinpointed an upper age limit for the fossils of about 100 ka. In order to achieve a better comprehension of the chronology of the modern human and contemporaneous faunal assemblage, paleomagnetic, stratigraphic, and optically stimulated luminescence (OSL) dating methods have been applied to the cave sediments. Paleomagnetic analyses reveal that there is a reversed polarity excursion below the fossiliferous layer. This excursion can be regarded as the Blake excursion event, given the U-series ages of the overlying flowstone calcite, the OSL measurements, the virtual geomagnetic pole (VGP) path of the excursion, the two reverse polarity zones within this excursion event, and the characteristic of the fauna assemblage. The human remains and mammalian fauna assemblage can be bracketed to 116–106 ka. Application of OSL dating leads to erroneous ages, largely due to the uncertainty associated with the estimation on the dose rates.

Influence of the infrared stimulation on the optically stimulated luminescence in four K-feldspar samples

Many dating protocols involve combined measurements of thermoluminescence (TL), optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL). Although the physics behind each stimulation mode is entirely different, it is possible that all of these stimulation modes act on the same set of electron trapping levels existing in dosimetric materials. Therefore, one might expect that the experimental results of the combined TL, OSL and IRSL measurements may be correlated. The present work deals with the correlation between IRSL and OSL signals. The experimental protocol involves an initial exposure of the irradiated sample to infrared radiation (IR) for various stimulation times, and then recording the continuous-wave OSL signal (CW-OSL) of the same sample. In this way one can follow how the exposure to IR influences the trapping levels responsible for the CW-OSL signal. The results of the experiments showed that the IR stimulation influences these trapping levels which are responsible for the fast components of the CW-OSL decay curve, and not the trapping levels responsible for the slow CW-OSL components. The IRSL decay curves are described by analytical equations derived from a localized tunneling recombination model. On the other hand, the CW-OSL decay curves were fitted successfully with either one of two following methods; Firstly they were fitted by using an analytical expression derived from the solution of the one trap one recombination center model (OTOR), which describes delocalized recombination processes. Secondly, the CW-OSL decay curves were also fitted successfully using the same analytical expressions used for fitting the IRSL decay curves, based on localized transition processes. A more detailed analysis of the CW-OSL signals for stimulation durations up to 100s, showed that the description of the CW-OSL using the localized tunneling recombination expression is superior to the description which uses the delocalized OTOR model.

Study of thermoluminescence (TL) and optically stimulated luminescence (OSL) from α-keratin protein found in human hairs and nails: potential use in radiation dosimetry.

The thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of human nails and hairs containing α-keratin proteins have been investigated. For the present studies, black hairs and finger nails were selectively collected from individuals with ages between 25 and 35 years. The collected hairs/nails were cut to a size of < 1 mm and cleaned with distilled water to remove dirt and other potential physical sources of contamination. All samples were optically beached with 470 nm of LED light at 60 mW/cm(2) intensity and irradiated by a (60)Co γ source. The hair and nail samples showed overlapping multiple TL glow peaks in the temperature range from 70 to 210 ° C. Continuous wave (CW)-OSL measurements of hair samples at a wavelength of 470 nm showed the presence of two distinct OSL components with photoionization cross section (PIC) values of about 1.65 × 10(-18) cm(2) and about 3.48 × 10(-19) cm(2), while measurements of nail samples showed PIC values of about 6.98 × 10(-18) cm(2) and about 8.7 × 10(-19) cm(2), respectively. This difference in PIC values for hair and nail samples from the same individual is attributed to different arrangement of α-keratin protein concentrations in the samples. The OSL sensitivity was found to vary ± 5 times among nail and hair samples from different individuals, with significant fading (60% in 11 h) at room temperature. The remaining signal (after fading) can be useful for dose estimation when a highly sensitive OSL reader is used. In the absorbed dose range of 100 mGy-100 Gy, both the TL and OSL signals of hair and nail samples showed linear dose dependence. The results obtained in the present study suggest that OSL using hair and nail samples may provide a supplementary method of dose estimation in radiological and nuclear emergencies.

Thermoluminescence and optically stimulated luminescence characteristics of Al2O3:C films annealed at different tempeartures

-Al2O3:C crystal is a high sensitive luminescence dosemeter, and it possesses a high thermoluminescence (TL) sensitivity, approximately 40-60 times greater than LiF: Mg, Ti. However, the crystal growth requires sophisticated laboratories, high temperatures and highly reducing atmosphere. The fluorescence and TL characteristics of -Al2O3:C ceramic are similar to those of -Al2O3:C crystal, however, it shows three TL peaks. In this work, porous alumina membranes are prepared by two-step anodization in 0.5 M/L oxalic acid at 5 ℃. We investigate the influence of annealing temperature ( 600 ℃) on thermoluminescence (TL) and optically stimulated luminescence (OSL) characteristics of Al2O3:C films and discuss the influence mechanism. The scanning electron microscopy measurement reveals that Al2O3:C film possesses highly ordered nanopores with homogeneous dimensions arranged in a closed-packed hexagonal pattern. The energy dispersive X ray spectroscopy and the Fourier transform infrared spectroscopy results indicate that oxalic acid impurity is incorporated into the porous alumina membrane in the synthesis process, after the annealing treatment, the oxalic acid impurity decomposes and C2+ replaces Al3+, which leads to the formation of F+and the C content of samples increasing with elevated annealing temperature. The X-ray diffraction measurement reveals that Al2O3:C films annealed at different temperatures are amorphous. TL measurements show that the dominated peak of Al2O3:C film is centered at around 310 ℃, owing to the number of F+increasing with the annealed temperature increasing, under the same irradiation dose, the sample annealed at 600 ℃ has the greatest TL intensity. With the increase of the irradiation dose, the TL intensity increases and the dominated peak gradually shifts to high temperature, which is consistent with the general order kinetic model. The sample annealed at 600 ℃ has the greatest TL sensitivity and its TL response shows excellent linear characteristic in as dose range of 1-10 Gy, but shows super-linear behavior in a dose range of 10-120 Gy. The OSL measurements show that with the increases of the annealed temperature and the irradiation dose, the OSL initial intensity increases and each of all samples shows a typical exponential decay. Compared with the case of -Al2O3:C crystal, the fast attenuation rate of film is dramatically accelerated. In a dose range of 1-200 Gy, the OSL responses of all samples each show an excellent linear characteristic, the sample annealed at 600 ℃ has the greatest OSL sensitivity. Compared with TL response, OSL response of Al2O3:C film shows a wider range of linear dose response. In this paper we have made a beneficial exploration for Al2O3:C films as OSL dosimerer.

Commissioning optically stimulated luminescence in vivo dosimeters for fast neutron therapy.

Clinical in vivo dosimeters intended for use with photon and electron therapies have not been utilized for fast neutron therapy because they are highly susceptible to neutron damage. The objective of this work was to determine if a commercial optically stimulated luminescence (OSL) in vivo dosimetry system could be adapted for use in fast neutron therapy. A 50.5 MeV fast neutron beam generated by a clinical neutron therapy cyclotron was used to irradiate carbon doped aluminum oxide (Al2O3:C) optically simulated luminescence dosimeters (OSLDs) in a solid water phantom under standard calibration conditions, 150 cm SAD, 1.7 cm depth, and 10.3 × 10.0 cm field size. OSLD fading and electron trap depletion studies were performed with the OSLDs irradiated with 20 and 50 cGy and monitored over a 24-h period to determine the optimal time for reading the dosimeters during calibration. Four OSLDs per group were calibrated over a clinical dose range of 0-150 cGy. OSLD measurement uncertainties were lowered to within ±2%-3% of the expected dose by minimizing the effect of transient fading that occurs with neutron irradiation and maintaining individual calibration factors for each dosimeter. Dose dependent luminescence fading extended beyond the manufacturer's recommended 10 min period for irradiation with photon or electron beams. To minimize OSL variances caused by inconsistent fading among dosimeters, the observed optimal time for reading the OSLDs postirradiation was between 30 and 90 min. No field size, wedge factor, or gantry angle dependencies were observed in the OSLDs irradiated by the studied fast neutron beam. Measurements demonstrated that uncertainties less than ±3% were attainable in OSLDs irradiated with fast neutrons under clinical conditions. Accuracy and precision comparable to clinical OSL measurements observed with photons can be achieved by maintaining individual OSLD calibration factors and minimizing transient fading effects.

Evaluation of equivalent dose from neutrons and activation products from a 15-MV X-ray LINAC.

A high-energy photon beam that is more than 10 MV can produce neutron contamination. Neutrons are generated by the [γ,n] reactions with a high-Z target material. The equivalent neutron dose and gamma dose from activation products have been estimated in a LINAC equipped with a 15-MV photon beam. A Monte Carlo simulation code was employed for neutron and photon dosimetry due to mixed beam. The neutron dose was also experimentally measured using the Optically Stimulated Luminescence (OSL) under various conditions to compare with the simulation. The activation products were measured by gamma spectrometer system. The average neutron energy was calculated to be 0.25 MeV. The equivalent neutron dose at the isocenter obtained from OSL measurement and MC calculation was 5.39 and 3.44 mSv/Gy, respectively. A gamma dose rate of 4.14 µSv/h was observed as a result of activations by neutron inside the treatment machine. The gamma spectrum analysis showed 28Al, 24Na, 54Mn and 60Co. The results confirm that neutrons and gamma rays are generated, and gamma rays remain inside the treatment room after the termination of X-ray irradiation. The source of neutrons is the product of the [γ,n] reactions in the machine head, whereas gamma rays are produced from the [n,γ] reactions (i.e. neutron activation) with materials inside the treatment room. The most activated nuclide is 28Al, which has a half life of 2.245 min. In practice, it is recommended that staff should wait for a few minutes (several 28Al half-lives) before entering the treatment room after the treatment finishes to minimize the dose received.

Optical dating in archaeology: thirty years in retrospect and grand challenges for the future

In 1982, when Richard Klein first became one of the Editors of this journal, the luminescence dating community was embarking on a new phase of exploratory research. Attention was turning from the use of thermoluminescence (TL) dating to estimate the time of last heating of archaeological objects, such as pottery and burnt flint, to the TL dating of unheated sediments that had been transported by wind and then deposited on the landscape. This revolutionary development enabled the extension of TL dating to sedimentary deposits in a variety of environmental settings and to the multitude of archaeological sites that lack suitably heated artefacts. In sediment dating, the age of most interest is usually the time elapsed since grains of quartz or feldspar were last exposed to sunlight, as the energy of the sun's rays is sufficient to evict electrons from their light-sensitive traps. These traps are steadily refilled after sediment deposition and the longer the grains remain buried, the more TL they will emit when measured. In 1985, Huntley and colleagues proposed ‘optical dating’ as a simpler and superior means of stimulating the light-sensitive traps in Quaternary sediments, and this is now the principal luminescence-based method of dating geological and archaeological deposits. Optical dating is an umbrella term for an armada of acronyms, the most common in archaeological contexts being OSL (optically stimulated luminescence), TT-OSL (thermally-transferred OSL), IRSL (infrared stimulated luminescence) and pIRIR (post-infrared IRSL). All of these variants are founded on the same basic tenet – measurement of a light-sensitive signal to determine (typically) the last time that sediment grains were sun-bleached – but each approach has its virtues and vices. In this paper, we review this ‘family’ of luminescence dating techniques and look back on 30 years of optical dating in archaeology. Some of the more interesting and important achievements are highlighted, including the critical insights gained in the last two decades from OSL measurements of individual grains of quartz. We also look to the future of optical dating in archaeological contexts. Efforts to extend the age limits of optical dating to older hominin and archaeological sites will remain a key goal, and understanding how archaeological sites – of all ages – form and evolve over time could be improved greatly by combining micromorphology analysis with optical dating of undisturbed (intact) sediments. The latter poses a series of particularly formidable technical challenges, but if the past is any guide to the future, then we can expect optical dating to illuminate much more of human history before celebrating its Golden Jubilee.

A short-lived aeolian event during the Early Holocene in southeastern Norway

The Starmoen dune field is part of a larger aeolian system in the Jømna and Glomma river valleys in southeastern Norway. It is believed to have formed just after the last deglaciation in the area, but no absolute ages have been available to support this. Here, we present a set of quartz optically stimulated luminescence (OSL) ages from the aeolian sediments and the underlying glacifluvial deposits. The results show that the main dune-building phase was a short-lived event ∼10ka ago, likely with a duration less than a few hundred years. This suggests a rapid stabilisation of an initially unstable environment in newly deglaciated terrain. A much younger event with limited and surficial reworking of sand is dated to 770±110 years ago, and the modern age of an active dune provide additional OSL quality control. Age overestimation is found for glacifluvial sediments, probably due to incomplete bleaching as indicated by e.g. scattered dose distributions from small aliquots. OSL measurements were conducted using coarse quartz grains (180–250m), which show a dominance of a fast signal component.

Application of newly developed NCF-SAR protocol to Quaternary sediments from Suncheon and Jeongok, South Korea

Present study is an attempt to test the applicability of recently developed natural sensitivity corrected single aliquot regeneration (NCF-SAR) protocol for samples from archaeological sites of South Korea. The protocol monitors the sensitivity change during measurement of natural OSL (Optically Stimulated Luminescence) signal and provides a methodology to correct for it. The natural OSL signals in the quartz samples from Suncheon (fluvial) and Jeongok (aeolian) sites were either in dose saturation region or lying well above the luminescence dose response curve, suggesting the possibility of sensitivity changes during natural OSL signal measurements. These samples thus provide opportunity to test the NCF-SAR protocol. The results suggest that, for the samples examined in this study, there are significant sensitivity changes during the natural OSL signal measurements. The ratio of TL (Thermoluminescence) peaks before and after natural OSL measurement was used to correct for the sensitivity changes. The dose distribution obtained using NCF had less scatter. However, in some cases, even the NCF correction could not resolve the issue of natural signal lying above saturation dose, indicating some other unidentified factors are also responsible for this oversaturation of quartz OSL signal.

Estimating the parameters of traps in quartz by the variable energy of stimulation optically stimulated luminescence (VES-OSL) method

Optical-cross section that is a trap parameter estimated from the measurements of optically stimulated luminescence (OSL) is not a uniquely determined physical quantity. It depends not only on temperature and the energy of stimulation light but also, in the simplest case, on the optical depth of trap, the frequency of vibration mode and on the Huang-Rhys factor, i.e. the average number of phonons involved in the process of optical excitation of electrons from trap to conduction band. Conventional OSL measurement techniques do not enable to determine directly these parameters but they could be estimated by applying the variable energy of stimulation optically stimulated luminescence (VES-OSL) method. Recently it was put in to practice and the first VES-OSL curves were presented. In this study the outcomes of VES-OSL experiments are presented together with the first attempt of direct estimating the optical depth of traps active in OSL process in quartz.

Age, soil-forming processes, and archaeology of the loess deposits at the Apennine margin of the Po plain (northern Italy): New insights from the Ghiardo area

The significance of two loess profiles located in the Ghiardo area (Reggio Emilia, northern Italy) along the southern margin of the Po Plain is discussed on the basis of sedimentary and pedological data, optically stimulated luminescence (OSL) dating, and archaeological context. Loess sedimentation occurred during cold and arid glacial and stadial periods of the Upper Pleistocene, between c. 70 and 35 ka. In the same time interval, loess sedimentation occurred at other localities at the northern margin of the Po Plain (Po Plain Loess Basin). The early period of loess sedimentation was contemporary with an intense frequentation of the area by Palaeolithic hunters, whose remains, consisting of clusters of flint artefacts, are found at the base of the loess sequences. Thermoluminescence dates on burned flints are consistent with OSL measurements on sediments where lithics were found and therefore the archaeological finds may be attributed to the Middle Palaeolithic lithic complexes of the Mousterian culture. Subsequent soil-forming processes on the loess deposits during the Holocene are suggested by changes in the proprieties of the profiles (clay illuviation, hydromorphic and vertic features, mukkara/gilgai microrelief). Degradation processes of the topsoil, leading to the formation of an eluvial top horizon, were eventually triggered by deforestation, which took place in the area since the Chalcolithic period (middle Holocene).

Investigation of OSL signal of resistors from mobile phones for accidental dosimetry

Resistors from mobile phones, usually located near the human body, are considered as individual dosimeters of ionizing radiation in emergency situations. The resistors contain Al2O3, which is optically stimulated luminescence (OSL) material sensitive to ionizing radiation. This work is focused on determination of dose homogeneity within mobile phones which was carried out by OSL measurements of resistors placed in different parts inside the mobile phone. Separate, commercially available resistors, similar in the shape and size to the resistors from circuit board of the studied mobile phone, were situated in different locations inside it. The irradiations were performed in uniform 60Co and 137Cs radiation fields, with the mobile phones connected and not connected to the cellular network. The dose decrease of 9% was measured for original resistors situated between circuit board and battery, in comparison to the dose at the front of the phone. The resistors showed the lower signal when the mobile phone was connected to the cellular network, due to higher temperature inside the housing. The profile of fading was investigated within 3 month period for resistors irradiated with 1 Gy of gamma rays to estimate of the fading coefficient.

The dependence of quartz OSL on stimulation energy

Quartz is the mineral most commonly used for sediment dating. In dating practice, the optically stimulated luminescence (OSL) of quartz is measured mainly using the stimulation light whose wavelength is 470 ± 30 nm. The parameters of traps active in the OSL process are also determined for this stimulation band. The zeroing of the OSL is the fundamental condition of applicability of the luminescence dating for specific sediment and takes place in sunlight whose spectrum differs significantly from the band 470 ± 30 nm. In order to be able to know the course of OSL process in nature, a wider knowledge of the dependency of the trap parameters on the stimulation band is needed. Here the results are presented for the OSL measurements carried out with different wavelengths of stimulation light. For each stimulation band the components of the OSL signal are determined by the fitting procedure, and in this way the wavelength dependence of an individual component is found. The experiment has been repeated for two temperatures of OSL detection – the room temperature, which corresponds to natural conditions, and for 125 °C, which is the temperature usually applied for OSL measurement in dating. Four OSL components are presented in both experimental series. The values of their optical cross-section changes along with stimulation energy and temperature, as it is predicted by the model of OSL process including crystal lattice vibrations.