Equivalent Dose Determination Research Articles

Optical dating of charcoal kiln remains from WWII: A test of accuracy

The majority of relic charcoal kilns in Europe are more recent than 1650 CE and cannot be precisely dated using radiocarbon dating (14C). Quartz-based optically stimulated luminescence (OSL) dating of the sediments associated with the kiln remains has been suggested as a viable alternative. Owing to the lack of reliable and sufficiently precise independent age information, however, it remains to be established whether OSL dating can yield accurate ages for post-1650 CE features. This is explicitly investigated in this study by applying a commonly adopted quartz OSL methodology to three relic charcoal kilns which are known to have been constructed and operated between December 1941 and March/April 1942 CE.We first document the quartz luminescence characteristics and show through procedural tests that the adopted single-aliquot regenerative dose procedure should be appropriate for equivalent dose determination. Four samples collected from the uppermost part of the charcoal-rich layers in the three features yield the youngest optical ages and are considered coeval. Their average age is 1928 ± 13 CE (95% probability), which matches the independent age reasonably well. The precision associated with the individual OSL ages ranges between 7 and 14% (1 sigma total uncertainty) and it might ideally be possible to establish relative chronologies with a higher time resolution. Finally, we briefly discuss our entire set of OSL ages in relation to future strategies for sampling charcoal kilns remains. In general, we conclude that OSL dating can be particularly advantageous to help resolving chronometric issues that pertain to post-1650 CE relic charcoal kilns.

Evaluation of the modified single-aliquot regenerative-dose procedure for equivalent dose determination

A common optically stimulated luminescence (OSL) method for dating sediments is the single-aliquot regenerative-dose (SAR) protocol, which is widely applied to measure the equivalent dose (De) in various sedimentary samples. The modified SAR protocol is distinguished from the conventional SAR protocol by the application of additional high-temperature (e.g. 280 °C) optical stimulation at the end of the procedure. In this study, we performed a dose recovery test using fine-grained (4–11 μm) quartz sample derived from coastal sediments and found that the De values recovered using the modified SAR protocol were significantly overestimated by ∼30% compared with the given dose, except for a preheating temperature of 160 °C. In contrast, De values recovered using the conventional SAR protocol showed good agreement with the given dose (within ±10%) over a large preheating temperature range (160–260 °C). Differences in the dose-response curves between the conventional and modified SAR protocols may have led to the overestimation of De values recovered using the latter approach. The lack of proportionality between Lx and Tx in the modified SAR protocol complicated the construction of the SAR dose-response curve and dose recovery. To avoid these phenomena, which may be highly sample dependent, modified SAR for OSL dating should be applied only to samples dominated by the slow OSL component and with high recuperation levels.

Время достижения радиологической эквивалентности РАО и природного уранового сырья при реализации ЗЯТЦ на базе РБН с учётом основных факторов неопределённости расчёта радиационных рисков

One of the most important problems in the large-scale development of nuclear energy is the management and disposal of radioactive waste (RW). The potential biological hazard of RW for human health considerably exceeds the health hazard from uranium feedstock. Due to the natural processes of radioactive decay, the potential biological hazard of RW decreases over time. However, long-term storage and disposal of long-lived RW leads to an increase in the health and environmental hazard of nuclear energy. Recently, to reduce the hazard effects, the novel ap-proach based on the principle that hazard of RW should not exceed the hazard of natural urani-um raw materials has been used. This principle is called as "radiation equivalence" if the hazards levels are assessed by the radiation dose magnitude, and "radiological equivalence" is used if the hazards are assessed by the magnitudes of lifetime radiation risks of malignant neoplasms development. Earlier papers have already given point estimates of the time to reach “radiation” or “radiological” equivalence when analyzing a scenario based on a closed nuclear fuel cycle. This article proposes a method for estimating the uncertainties in the time to achieve radiation and ra-diological equivalence. The results of these estimates are presented for a model scenario for the development of nuclear power, in which thermal neutron reactors are gradually being replaced by fast neutron reactors by 2100. The numerical simulation method is used. Modern radiation risk models proposed by the International Commission on Radiological Protection (ICRP) and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) are applied. The determination of equivalent radiation doses to organs and tissues was based on dose factors for radioactive substances provided for wide use by the US Environmental Protection Agency (EPA). If we assume that the maximum relative error of the initial values of the potential biologi-cal hazard of RW is about 246%, then the 95% confidence limit for achieving radiological equiva-lence was less than 340 years. The results of the study of the scenario for the development of nuclear energy in Russia, calculations show that since the integrity of containers with RW is main-tained for 1000 years, the safety of RW for future generations will be ensured.

Characterization of the collimated output fluence , in a thermal neutron field, in terms of ambient equivalent dose H*(10,0)

The Brazilian Neutron Laboratory at the Institute of Radioprotection and Dosimetry (IRD) developed and built a new standard facility for thermal neutron flux, seeking to provide a new homogeneous fluence to calibrate neutron detectors and personal dosimeters. The purpose of this work is therefore to characterize the collimated output fluence, in a thermal neutron field, in terms of ambient equivalent dose H*(10,0) for calibration and irradiation of personal monitors and neutron survey meters. The neutron fluence in the system irradiation field needs to be well known for personal monitors and neutron survey meters calibrated used in nuclear reactors in addition to studies and development of new materials for neutron dosimetry. The characterization of neutron thermal energy fields at the usual calibration points is one of the recommendations of the International Organization for Standardization ISO 8529, 2001 for international intercomparison of neutron fluence measurements. The determination of the ambient equivalent dose of the new facility was estimated based on a secondary transfer standard internationally known as Long Counter and properly characterized and traced back to the Neutron Laboratory primary standards.

Testing the applicability of standardised growth curves (SGCs) for OSL signals of quartz grains from the Yangtze Delta, China

The standardised growth curve (SGC) technique has the potential to save instrument time for equivalent dose (D e ) determination when applying single-aliquot regenerative-dose (SAR) protocol during optically stimulated luminescence (OSL) measurements. In this study, we test the applicability of two commonly used SGC procedures for OSL signals of quartz grains from aqueous deposits of the Yangtze Delta in China, which have been reported for weak luminescence signals and suffering from partial bleaching. Multiple silt-sized and sand-sized fractions of quartz samples from eight cores are used to construct SGCs by test dose standardisation (TD-SGC) and least-squares normalisation (LS-SGC), respectively. Three strategies, i.e. region-specific (SGC R ), region with core-specific (SGC R + C ) and core-specific (SGC C ), are adopted to categorise these normalised data into different SGC datasets. The large variability of dose response signals is substantially reduced by the SGC procedures for most of these datasets. Hence, common SGCs for a variety of samples from the Yangtze Delta can be established, irrespective of their distinctive particle sizes and luminescence characteristics. The D e values are then estimated using both TD-SGC and LS-SGC procedures for samples from a specific core. Comparing to the full SAR protocol, the TD-SGC procedure roughly gives reproducible D e estimates lower than ∼100 Gy while the LS-SGC procedure derives generally consistent D e estimates of up to ∼230 Gy. Although LS-SGC C and LS-SGC R + C procedures replicate the most consistent D e values, the LS-SGC R procedure performs better in efficiency with a slightly less accuracy. In addition to careful comparison of LS-SGC and full SAR procedures, we suggest that a synchronous ratio derived by the chosen regenerative dose and its response signal for re-normalisation can be used to predict the LS-SGC D e reliability on samples from similar sedimentary environments. • Standardised growth curves (SGCs) are applied to quartz samples from the Yangtze Delta. • SGC procedures are compared using three strategies. • Least-squares (LS) SGC D e values are consistent with those obtained by full SAR. • LS-SGC D e reliability is predicted by the chosen regenerative dose and signal.

Rapid assessment of beta dose variation inside cobbles, and implications for rock luminescence dating

Variation in beta dose rate within rocks may impact the results of rock surface luminescence dating, for both the burial age of cobbles and exposure age of rock surfaces. Current methods of rock surface luminescence dating assume that radionuclides are homogeneously distributed inside rocks. In this study, two rapid methods based on beta counting and on a portable XRF instrument were developed to measure the radioactivity of rock slices. These methods were applied to rock slices from four glaciofluvial granite cobbles that had previously been used for equivalent dose determination to test whether beta dose variation could be observed. Results from beta counting and K content from XRF show similar patterns and both vary along the depth profiles, but the magnitude of this variability is very different amongst the four cobbles. In rocks where the dose rate is highly variable, bleaching may not be the only source of variation of Ln/Tn or equivalent dose (De) along the luminescence-depth profile of cobbles, and it may be necessary to measure the beta dose rate for every single slice to determine whether multiple bleaching events are recorded or variations in De are due to dose rate heterogeneity.

High-content imaging analyses of the effects of bisphenols and organophosphate esters on TM4 mouse Sertoli cells†.

The endocrine disruptive effects of bisphenol A (BPA) and brominated flame retardants (BDE-47) have led to restrictions on their use and increased the pressure to identify safe replacements for these chemicals. Although there is evidence that some of these alternatives may be toxic to spermatogonial and Leydig cells, little is known about the toxicity of emerging replacements on Sertoli cells. We used high-content imaging to compare the effects of legacy chemicals, BPA and BDE-47, to their corresponding replacements. TM4 Sertoli cells were exposed for 48h to each chemical (0.001-100μM) followed by cytotoxicity and phenotypic endpoint assessment. The benchmark concentration potency ranking for bisphenols based on cytotoxicity was BPTMC > bisphenol M > BPAF>BPF > BPS > BPA. Human administered equivalent dose (AED) determination ranked BPS as the most potent alternative replacement. The benchmark concentration potency ranking of BDE-47 and organophosphate esters based on cytotoxicity was TDtBPP>BDMPP>TBOEP>TDCPP>TMPP>TPHP>BDE47>IPPP=BPDP=TCPP. Additionally, TM4 cell exposure to BDE-47 increased Calcein intensity (57.9μM) and affected lysosomes (21.6μM), while exposure to TPHP and TMPP resulted in cellular oxidative stress changes at benchmark concentration values as low as 0.01 and 0.4μM, respectively. Overall bioactivity considerations of the chemicals on TM4 via ToxPi analyses and AED modeling further validated emerging replacements as highly potent chemicals in comparison to BPA and BDE-47. These findings demonstrate that many bisphenol and flame retardant replacements are more potent in Sertoli cells than the legacy chemical they are replacing and that phenotypic parameter assessment is an effective tool in chemical toxicity assessment.

Advancing dosimetry for Dating Environmental Materials: Development of an ultra-sensitive beta dosimeter system and potential for beta autoradiography

Beta Dose Rate heterogeneity is a recognized source of uncertainty when applying luminescence dating to heterogeneous samples, such as coarse crystalline rocks and clast-rich sediments. Simulations have shown that a combination of a heterogeneous distribution of minerals and radioactive elements can lead to complex dose distributions, overdispersion and potentially to bias in equivalent dose determinations. However setting realistic conditions for such simulations remains difficult, and there are at present only a few experimental validation cases for such simulated systems. Project ADDEM is investigating means of linking Monte Carlo simulations of dose rate to specific minerals with direct observations using high sensitivity phosphor plates and laser scanning imaging systems in combination with phase mapping. To overcome some of the limitations of autoradiographic imaging of low level beta dose distributions work has been undertaken using Landauer alumina OSL phosphor screens in combination with a laser scanning system developed at the Scottish Universities Environmental Research Centre (SUERC). Preliminary excitation spectra, emission band characterization and time resolved measurements were undertaken, confirming the potential to recording low doses using asynchronous stimulation at 635 nm coupled with blue band detection. Taking advantage of the slow decay of the luminescence signal the scanning equipment has been configured for pulsed stimulation and asynchronous detection to maximise signal to background ratios. Exploratory work was calibrated using a 60Co facility capable of calibrating doses in the μGy to mGy range. A series of powdered granulite/basalt mixtures of known mean activity and dose rate (Dr) have also been used to calibrate the phosphor screens. To reduce background levels during autoradiographic signal accumulation rock slices are being exposed in the Zeplin shield of the STFC Boulby Underground Laboratory, in an environment which is essentially free from cosmic ray muon background.Simulations have been conducted providing preliminary deconvolution parameters in order to either reconstruct the beta dose rate (β Dr) distribution received by the grains in the sample, or retrieve the radioactive element distributions in the minerals of the sample, providing the data required for representative simulations of β Dr.This paper outlines the spectroscopy and sensitivity verification of the autoradiography system, confirming its prospects for measuring spatially resolved β Dr distributions with single pixel lower detection limit of 130 μGy and spatial resolution of 150 μm. Prospects are outlined.

Test of high sampling density OSL dating of aeolian samples from the south margin of the Tengger Desert using the global standardised growth curve (gSGC) method

Chronostratigraphic records in the drylands of north China provide basic archives to reveal the dynamic connections between climate changes and the behaviour of aeolian systems. However, the interpretation of aeolian chronostratigraphy is not straightforward and may be associated with significant uncertainty due to a number of external and localised forces. Taking into account this complexity of aeolian systems, excluding preservation and sampling bias from palaeoclimatic signals requires that the interpretation of chronostratigraphic records be based on as many dates from as many sites as possible. Optically stimulated luminescence (OSL) dating provides a direct way to date aeolian sediments. However, the determination of equivalent dose (D e ) using the commonly applied single-aliquot regenerative dose (SAR) protocol is relatively time-consuming for samples with burial doses exceeding 50 or 100 Gy. In this study, the global standardised growth curve (gSGC) method is applied to multi-grain aliquots of coarse quartz from various sites covering a wide region of the south margin of the Tengger Desert in north China to rapidly determine D e for a large number of aliquots and samples. The large between-aliquot variability in the shape of the dose response curve (DRC) is significantly reduced using a least-squares normalisation procedure. The results of a leave-one-out cross-validation (LOOCV) protocol demonstrates that D e values determined using the gSGC and SAR methods are very consistent with each other up to at least 200 Gy and 400 Gy, for the 90–150 μm and 63–90 μm fractions, respectively. It suggests that the gSGC protocol can be used as an efficient procedure for D e determination of a large number of aeolian samples from multiple sites. This in turn provides a better constraint for the interpretation of Late Quaternary aeolian chronostratigraphic records in drylands of north China.

The variability of single grain quartz luminescence properties investigated using EMCCD imaging

Optically stimulated luminescence (OSL) signals from individual quartz grains are frequently used for equivalent dose and age determination in luminescence dating. Typically, signals from individual grains are stimulated with a focussed solid-state laser and detected via a photomultiplier tube. In contrast to the light-emitting diodes (LEDs) usually used when stimulating multiple-grain aliquots, the laser has a much higher stimulation power density. An absolute value for the effective stimulation power cannot easily be quantified, and the power delivered to each grain cannot be considered consistent throughout a measurement sequence. Both intra- and inter-sample variability in single grain luminescence signals parameters such as dose response form, decay rate, and sensitivity have long been recognised, however there remains uncertainty over how much of this variability is intrinsic to quartz grains or whether some should be attributed to variation in the effective stimulation power associated with the laser system. To better characterise intrinsic variability of single quartz OSL signals, an electron multiplier charge coupled device (EMCCD) attachment for the Risø reader was used for detecting and imaging luminescence signals. Whilst the EMCCD system currently offers a lower detection sensitivity when compared to the laser system, the ability to use LEDs for stimulation of the OSL signal circumvents the power variability associated with the laser system and allows an investigation of intrinsic variability to be made. In this paper, signal intensity and the composition of components in single grain luminescence signals are considered, and curve deconvolution is undertaken to calculate photo ionisation cross-sections for single grain quartz signals. For the samples considered, intra-sample variability in these characteristics is observed in single grain quartz luminescence signals imaged using an EMCCD.

Программный модуль оценки достижения радиологической эквивалентности (РОЗА-РАО)

The main problem of the large-scale development of nuclear energy in the world is the safe dis-posal of accumulated radioactive waste (RW). The hazard of RW at the time of their formation to human health far exceeds the hazard of the source natural uranium ore, after the use of which these wastes were formed. Due to the natural processes of radioactive decay, the hazard of radi-oactive waste decreases over time. The hazard of waste can also be reduced by artificial trans-mutation or incineration of the radionuclides that make up RW composition. For uranium nuclear fuel cycles, the natural reference level of RW hazard is the hazard level of the uranium ore, upon reaching which decisions can be made on the final disposal of RW. The article presents a meth-od for estimating the time of achieving radiological equivalence of the mass of accumulated RW of nuclear energy and the source mass of natural uranium raw materials used in this case. A de-scription of the software module "Radiological support of protection – radioactive waste" (PM ROZA-RAO), which implements this method, is also presented. Radiological equivalence herein refers to the equality of the corresponding radiation risks for the population. The methodology used is determined by the current recommendations of the International Commission on Radio-logical Protection (ICRP) and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) on the calculation of human radiation risks from internal exposure based on equivalent doses in organs and tissues. The determination of equivalent doses to organs and tissues was based on dose coefficients of radioactive substances provided for widespread use by the United States Environmental Protection Agency (EPA). Calculations by means of the PM ROZA-RAO showed that within the framework of the most likely scenario for the development of two-component nuclear energy system in Russia, for radioactive waste accumulated by 2100, the time of onset of radiological equivalence is less than 100 years (98.8 years). With the help of the developed software module, for the first time in the nuclear industry, the parameters of the processing of exposed nuclear fuel (the composition and activity of radionuclides for controlled storage, combustion and transmutation) and the management of RW can be determined, minimizing the potential radiation risks of the population, which corresponds to the best practice of developed countries in the field of radiation protection.

Response of the Ti and Al electron spin resonance signals in quartz to X-ray irradiation

Equivalent dose determination with electron spin resonance (ESR) involves laboratory irradiation of samples using a calibrated source. In this study, we investigated the response of the quartz ESR signals to irradiations from 50 kV or 200 kV X-ray sources by inter-comparison with 60Co gamma irradiation using seven quartz samples of different origins. For each sample, the equivalent X-ray irradiation time required to create the same concentration of defects as a known dose of 60Co gamma-ray was calculated. The effective dose rate was obtained from the given gamma dose (188 Gy) divided by the equivalent X-ray irradiation time; this is referred to as the ‘X-ray dose rate’ in this study. The X-ray dose rate estimates from different samples were relatively uniform. However, the dose rate calculated from the Al centre was on average ∼10% higher than that of the Ti centre, and more scattered among different samples especially for the low-energy X-ray source. The ratio of the dose rates, obtained from the two centres (Al/Ti) varied significantly between the samples; four sediment samples from Tajikistan, China, Chile and Greece yielded consistent dose rates from both centres for both sources, whereas the remaining three samples from Japan and Taiwan showed a dose rate up to 26% higher from the Al centre compared to the Ti centre. The cause of the higher effective dose rate for the Al centre for these three samples requires further investigations.

Mesenchymal stem cells versus their extracellular vesicles in treatment of liver fibrosis: Is it possible to compare?

Liver fibrosis (LF) is a worldwide health problem that is associated with a range of complications and high mortality. Due to the scarcity of liver donors, mesenchymal stem cell (MSC) therapy emerged as an alternative therapeutic strategy. However, it is widely accepted that most of the transplanted MSCs exhibit their therapeutic impact mainly via a bystander paracrine (medicinal) capacity. In addition to their secretory proteins, MSCs also produce various types of extracellular vesicles (EVs) that are classified into three main subtypes: microvesicles, exosomes and apoptotic bodies. Thanks to their peculiar cargo composition (e.g., proteins, lipids, and nucleic acids), EVs serve as an advantageous candidate for cell-free therapy. Recently, MSC-derived EVs (MSC-EVs) have gained the podium due to their regenerative and immunomodulatory effect. In mitigation/treatment of LF, a plethora of recent studies have shown the anti-inflammatory, anti-fibrotic and cytoprotective effects of both MSCs and MSC-EVs in various in vitro and in vivo models of LF. However, despite the limited evidence, we sought in this mini review to sort out the established data and formulate several challenging questions that must be answered to pave the way for further clinical applications. One of the major questions to ask is “Which is the best therapeutic approach, MSCs or MSC-EVs?” We tried to highlight how difficult it might be to compare the two approaches while our understanding of both candidates is still deficient. Among the major obstacles against such comparison is the inaccurate equivalent dose determination, the unknown in vivo behavior, and the undetermined lifespan/fate of each. Currently, the fields of MSCs and MSC-EVs seem to be rich in ideas but lacking in appropriate technologies to test these ideas. Nevertheless, continuous efforts are likely to help resolve some of the challenges listed here.

A New Application of Sohrabi Albedo Neutron Dosimeters around a Plasma Focus Device.

A new application of the Sohrabi albedo neutron dosimeters is reported for the first time for determination of very low-level neutron ambient dose equivalents on and around a 3.5 kJ plasma focus device (PFD). The Sohrabi dosimeters basically use a polycarbonate track detector as bare and/or in contact with B convertor(s) under special cadmium cover arrangements. Its sensitivity was improved by using enriched B under new cadmium arrangements in order to detect epithermal neutrons in addition to fast and thermal neutrons. Results of 12 dosimeters installed externally around the PFD at different azimuthal (φ) and polar (θ) angles showed that azimuthal (φ) fast, epithermal, thermal, and total neutron ambient dose equivalents were symmetric and isotropic, respectively, with values 55.15 ± 8.36, 1.36 ± 02, 0.53 ± 03, and 57.04 ± 8.62 μSv/shot at ~25 cm from anode top. Polar (θ) neutron ambient dose equivalent values on z-axis relative to 90 angle were relatively higher. Results of 38 dosimeters placed on PFD facility walls for workplace monitoring and on a BOMAB phantom at operator's location for personal dose equivalent determination showed values below minimum detection limits after exposure to 130 PFD shots. However, an operator's personal dose equivalents at ~1.0 and ~3.0 m from the anode top were estimated to be, respectively, ~13.7 and ~1.52 mSv y using azimuthal angle (φ) values if the PFD operates, for example, up to 20 shots per day for 200 d y. Even under such an extreme assumption, annual personal dose equivalent is still much below 20 mSv, the annual ICRP dose limit for workers.

Quartz optically stimulated luminescence dating of loess in Tajikistan and its paleoclimatic implications for arid Central Asia since the Lateglacial

Thick and widespread loess deposits in southern Tajikistan provide insight into the regional climatic changes in arid Central Asia (ACA) during the Quaternary. However, because of the lack of robust chronological constraints, the environmental implications of these deposits are not yet fully understood. Here, we report a detailed medium-grained quartz optically stimulated luminescence (OSL) dating analysis on a loess sequence deposited since the Lateglacial in southern Tajikistan. The single-aliquot regeneration (SAR) and standardized growth curve (SGC) methods were used for equivalent dose determination. Quartz OSL measurements showed that both the SAR and SGC methods can be used for equivalent dose determination for Tajik loess. On the basis of the obtained OSL ages, we reconstructed the dust accumulation rates and mass accumulation rates. Our results show that the dust flux continued to decline whereas the precipitation increased stepwise after the end of the Last Glacial Maximum. Changes in the dust flux and precipitation in ACA were sensitive to the gradual warming since the Lateglacial.

Quartz OSL dating of loess deposits since the late glacial in the Southeast of Caspian Sea

Here we present loess deposits since the late glacial dated by OSL technique in the southeast of the Caspian Sea, bordering continents of Asia and Europe. Chronology of Holocene loess deposits are rarely reported in Eastern Europe and Western Asia, especially for their spacious mid-latitude adjacent region, between Balkans to the west and Pamirs to the east. In this study, an OSL-based chronology was developed for loess deposits in northern Iranian Plateau, based on the YBD loess profile which locates close to center of hilly Iranian Loess Plateau in the southeast of the Caspian Sea and on the northern slope of the Alborz Mountains. The OSL characteristics and their reliability were investigated on coarse-grained quartz (63–90 μm) of the profile, a preheat plateau test and dose recovery test of which reveal that the lower preheat is suitable for loess equivalent dose determination in the area. In addition, the SAR-OSL is an appropriate methodology for dating loess deposited since the late glacial in situ. With preservation of a complete record of loess accumulation since the late glacial, YBD section contains a potentially valuable paleoclimatic record for Caspian region and hence the vast transitional region between Asia and Europe.

Визначення колективних ефективних та еквівалентних доз та радіаційних ризиків населення україни за рахунок рентгенодіагностичних досліджень

Визначення колективних ефективних та еквівалентних доз та радіаційних ризиків населення україни за рахунок рентгенодіагностичних досліджень

A method for routinely monitoring the reproducibility of thermal pretreatment prior to optically stimulated luminescence measurements

Thermal pretreatments are used prior to optically stimulated luminescence (OSL) measurements in methods of dose determination, but the reproducibility of such heating appears to be poor within laboratories, and between laboratories. Monitoring the position of the 110 °C thermoluminescence (TL) peak in quartz can be used to routinely assess the reproducibility of heating within a repeated set of measurements on an aliquot (e.g. during the single aliquot regenerative dose protocol) providing feedback on whether changes in sample preparation can improve reproducibility. Poor reproducibility between measurements from a single aliquot are likely to arise from grains between the hotplate and sample holder. Variability between aliquots may also be affected by deformed sample holders. Differences between readers may also be caused by differences in the calibration of the hotplate. Reproducibility of heating can be improved within runs, and between instruments, by taking care to avoid loose grains, by removing deformed sample holders, and if necessary by calibrating hotplates. It is suggested that individual aliquots should only be accepted if the apparent 110 °C TL peak temperature within a sequence of measurements varies by 5 °C or less. Improving the reproducibility of thermal treatment is important in reducing scatter in equivalent dose determinations based on OSL from quartz, but also for signals such as TT-OSL from quartz, and the various feldspar luminescence signals. Temperature control is also critical for accurate kinetic analyses.

Luminescence chronology of the northeastern Bulgarian loess-paleosol sequences (Viatovo and Kaolinovo)

The key reference loess sequence of Viatovo in NE Bulgaria, lying within the lower Danube basin, records climatic and environmental changes over the last 800 ka. This 20 m thick loess sequence consists of seven loess units (L1 to L7) intercalated by six paleosols (S1 to S6) below the modern soil (S0). The Matuyama-Brunhes palaeomagnetic boundary has been identified in the lowest loess unit (L7). This reference loess sequence remains so far undated by radiometric techniques. Its chronostratigraphy relies only on pedostratigraphic and magnetostratigraphic evidence. This contrasts with the adjacent reference loess sequences of SE Romania (Tuzla, Mostistea, Mircea Vodă) whose luminescence chronology is now securely established up to MIS 8.The aim of this study is to validate the chronostratigraphic framework of the Viatovo loess sequence using the luminescence dating method. For this purpose, the luminescence method is applied to the three upper loess units (L1, L2, L3) from two adjacent sites: the reference site of Viatovo and the nearby site of Kaolinovo, both located in the Ludogorie region (NE Bulgaria) and showing the same superposition of loess (L1 to L7) and interbedded paleosols. Luminescence dating (Infrared stimulated luminescence; IRSL) was carried out using the feldspar fine sand-size grain fraction (60–80 μm), applying the IRSL50 and the pIRIR290 dating techniques. For the equivalent dose (De) determination we used both the SAR post-infrared infrared (pIRIR290) protocol on single aliquots and the multiple-aliquot additive dose (MAAD IRSL50) protocol. The pIRIR290 ages and the fading corrected MAAD-IRSL50 ages are self-consistent. It demonstrates for the first time, that the three upper loess layers (L1, L2, L3) at Viatovo and Kaolinovo were deposited during the marine isotope stages (MIS) 2–4, 6 and 8, thus constraining the youngest well-developed paleosol (S1, a chernozem) to the Last Interglacial. These IRSL50 and pIRIR290 ages are in good agreement with the luminescence ages obtained for (1) the two upper loess layers (L1, L2) from the Harletz sequence in NW Bulgaria and (2) the three upper loess units (L1, L2, L3) from the adjacent SE Romanian loess sequences.The luminescence chronology of the loess sequences is presented along with the pedogenic and magnetic property data. The pedostratigraphic records of the NE Bulgarian and SE Romanian loess sequences show the same palaeoclimatic trends, with progressive aridification during interglacial periods (from S6 to S0).

Analysis of uncertainties associated with different factors used to determine the age of sediments with the Optically Stimulated Luminescence method

In this work, a sediment sample from an excavated paleoseismological trench was collected and dated following the Optically Stimulated Luminescence (OSL) dating method, using the Riso TL/OSL DA-20 reader. Chemically purified quartz, from the sample, was analysed following a single-aliquot regenerative-dose (SAR) protocol for the equivalent dose (De) determination. Also, to estimate dose rates, the natural radioactivity of soil from the surroundings of the original sample location was measured, using gamma spectrometry. Since the application of the OSL dating method involves a number of intermediary factors and processes, all being the sources of uncertainties propagating to the total uncertainty, an exhaustive analysis of the involved uncertainties is presented and the implications to the derivation of the final ages are discussed.