On Optically Stimulated Luminescence Research Articles

Dynamic optical information encoding strategy of flexible thin films based on Ba2SiO4 phosphor for ultra-long storage time

Nowadays, state-of-the-art for optical data storage (ODS) have emerged as a leader in the competition of data storage technologies. However, the development of optical storage technology based on optically stimulated luminescence (OSL) encounter the serious problems, of single storage mode and easily decoding. In this study, a series of Ba2SiO4 (denoted as BS): Eu2+, Ln3+ (Ln = Dy, Ho) phosphors with adjustable trap distributions (trap depths of 0.6–0.8 eV) have been developed by high-temperature solid-phase method and exhibit intense green emission peak located at 504 nm under excitation of 360 nm. Typically, BS: 0.02Eu2+, 0.02Ho3+ phosphor owns a shallow trap depth of 0.696 eV and BS: 0.02Eu2+, 0.02Dy3+ phosphor shows a deep trap depth of 0.81 eV. Interestingly, the flexible optical information storage film prepared by BS: 0.02Eu2+, 0.02Ho3+ phosphor through spin-coating technique can storage the “National Water Conservation Logo” pattern under NUV irradiation and reappear even after more than 60 days at 75 °C. Subsequently, multimodal anti-counterfeiting strategy is proposed by BS: Eu2+, Ln3+ (Ln = Dy, Ho) phosphors with adjustable trap depths and the flexible information coding device with high transmittance has been developed, in which encrypted message of “HELLO” and “86068” can be recognized at 75 °C and 130 °C, respectively. This work not only lays the foundation for realizing the durability of optical information storage, but also provides high security with multiple levels of retrievability.

Fading correction for calibration of a novel 2D OSL-film dosimeter

A new film dosimeter based on optically stimulated luminescence (OSL) was calibrated for high-resolution 2D dosimetry in the context of radiotherapy patient-specific quality assurance (PSQA). The OSL-film signal is linear with the dose and decays with time, in a process called fading. Two models were proposed to characterize the fading: (1) a linear model independent from the delivery and of practical use thanks to the straightforward signal-to-dose conversion, and (2) a delivery-dependent model, to investigate whether a more simplified model may be sufficient to accurately determine the fading independently from the specific-irradiation conditions. The models were used in a nonlinear regression over an experimental dataset acquired with a 6MV photon beam in standard calibration settings. Both models were accurate and showed an adjusted-R 2 of 0.98 (1) and 0.99 (2). The residual analysis on both models allowed to define the minimum scanning time to have a discrepancies between the models <1%. Under this condition the OSL fading can be assumed independent on the irradiation parameters. As a consequence, within these boundary conditions, the linear model can be used for the OSL-film calibration.

Large floods on the lower Ohio River inferred from slackwater deposits

Slackwater deposits representing past flood events provide a robust means to extend systematic gage records further back in time, place historic floods in a longer-term context, and reduce uncertainties in flood hazard analysis. The identification and application of slackwater deposits in riverine paleoflood hydrology has traditionally been limited to arid bedrock-controlled environments and periglacial environments. In this study, we utilize methods developed in humid alluvial settings and apply them to slackwater deposits, one of the first studies to do so. This novel approach uses sediment texture and geochemistry to distinguish slackwater deposits from in situ material in a temperate alluvial setting. We identify multiple slackwater deposits in two rock shelters situated on bluffs adjacent to the lower Ohio River. Flood age estimates are based on optically stimulated luminescence (OSL) dating, and discharge estimates are based on a 1D HEC-RAS model. The uppermost slackwater deposit at both sites corresponds to the AD 1937 historic flood of record (∼31,400 m3/s), while another slackwater deposit identified only at the lower elevation site corresponds to a paleoflood that occurred around AD 1650 with a discharge of ∼23,900 m3/s. Our findings imply that the AD 1937 flood represents the largest magnitude flood on the lower Ohio River in at least the last 400 years. Inclusion of the paleoflood into a flood frequency analysis for the Ohio River at Louisville reduces uncertainties in large flood quantiles by ∼50%.

The effect of boron co-doping on thermoluminescence and optically stimulated luminescence properties of LiMgPO4:Tb,Sm

The effect of boron co-doping on optically stimulated luminescence (OSL) and thermoluminescence (TL) properties of LiMgPO4:Tb,Sm,B prepared by solid-state reaction was studied. The structure of the prepared materials was confirmed by X-ray diffraction. The TL glow curves of samples irradiated with different doses of β rays were tested. No matter how much B is doped, the peaks at 190 or 280 °C are for a first-order kinetic glow curve. The activation energy and frequency factor remained almost unchanged with the increase of boron doping concentration, which indicated the trap centers of LiMgPO4:Tb,Sm,B were independent of boron doping concentration. The E at 190 and 280 °C are around 1.16 eV and 1.55 eV. Photo-ionization cross-section showed significant changes and the sensitivity of OSL reached a maximum for a concentration of 4 mol% with increasing of boron doping concentration. B-doping enhanced the OSL-signal with a factor 2.6 when B concentration is 4 mol%. The repeatability of the powders for OSL were also studied and the relative standard deviation was less than 1.5%. The minimal detectable dose (MDD) of LiMgPO4:Tb,Sm,B with a boron doping concentration of 4 mol% was 8.2 μGy. This material has a fast decay time, good repeatability, low MDD and has further research value.

Fluvial Responses to Late Quaternary Climate Change in a Humid and Semi-Humid Transitional Area: Insights from the Upper Huaihe River, Eastern China

Research into river processes in different climatic and geomorphic areas is vital for a clearer understanding of the non-linear responses of rivers to climate change. The Huaihe River (HHR) Basin, located in China’s North–South Transition Zone (NSTZ), provides an ideal environment in which to explore river responses to climate change within a humid/semi-humid transitional area. Based on optically stimulated luminescence (OSL) and 14C dating, combined with sedimentary stratigraphic analyses, we reconstructed the river processes of three sedimentary sequences in the upper HHR since the Late Quaternary. Our results showed that the upper HHR was characterized by aggrading meandering channels from the Last Glacial Maximum (LGM) to 0.5 ka, and an aggrading wandering channel from 0.2 ka to the present. Two periods of downcutting occurred during 5.8–3.0 and 0.5–0.2 ka, respectively. The river incision is potentially linked to changes in the climate during the Mid–Late Holocene transition and the Little Ice Age (LIA). However, there have been no marked changes in channel patterns in the upper HHR since the LGM. This phenomenon reflects the influence of vegetation on channel patterns during climate change. Our results showed that the fluvial processes in different climatic and geomorphic areas are controlled by the local hydroclimatic regime.

Unlocking the effect of Li and Ce ions on the thermoluminescence and optically stimulated luminescence signals of the MgB4O7 compound.

Magnesium tetraborate (MgB4O7) is an example of a material that has attracted the attention of researchers in the field of ionising radiation dosimetry. Several challenges are present in order to achieve considerable advances in luminescence dosimetry. The incorporation of efficient dopants in the host matrix has been an experimentally useful but limited strategy. The lack of specific information about the introduced defects as well as their connection with the trapping and recombination processes associated with light emission may be quoted as challenging examples. Here, we demonstrate the influence of lithium incorporation on Optically Stimulated Luminescence (OSL)/Thermoluminescence (TL) signal modification/suppression of MgB4O7 by combining experimental and computational procedures. Li substitution into the Mg site leads to a signal suppression due to the probable quenching of the Fs and Fs+ centres in MgO and the formation of O''i, drastically reducing the possibility of MgO anti-Schottky defect formation in MgB4O7. When using Li-co-doped MgB4O7:Ce3+, the Li ions act as a charge balancer, facilitating the entry of Ce ions into the interstitial pores and making possible a positive synergistic effect on the luminescence and dosimetric properties. These findings provide new insights into designing more efficient dosimeters by tuning dopants.

Paleochannel of the Yellow River within the Zoige Basin and its environmental significance on the NE Tibetan Plateau

Paleochannel sedimentary sequences can provide abundant information on regional environmental changes. A typical paleochannel (paleo-oxbow lake type) section of the Yellow River was identified within the Zoige Basin on the NE Tibetan Plateau. A multi-index approach was used to accurately identify sediments of different genetic types, such as riverbed deposits of the Yellow River, paleo-oxbow lake deposits, and overbank flood deposits (OFD) in the section. Based on optically stimulated luminescence (OSL) and AMS 14C dates, we examined the environmental evolution recorded by the section. The results show that: (1) The section is a record of environmental change since 4.17 ± 0.49 ka. During 4.17 ± 0.49 to 3.24 ± 0.26 ka, the ancient Yellow River occupied the channel. At 3.24 ± 0.26 ka, the paleochannel experienced a neck cutoff, and the fluvial environment began to change into the oxbow lake environment. After 2.45 ± 0.11 ka, the paleo-oxbow lake gradually disappeared. Subalpine meadow soil has developed at this site since 1.31 ± 0.05 ka. (2) Paleoenvironmental proxies indicate that the Zoige Basin was warmer and wetter before ~3.00 ka, and became drier and colder after ~3.00 ka, which may be mainly related to the weakening of the East Asian summer monsoon (EASM) and the strengthening of the Westerlies. (3) Two episodes of extreme overbank flooding occurred at 2.96 ± 0.24 to 2.87 ± 0.27 ka and 1.84 ± 0.20 to 1.70 ± 0.16 ka, correlated with climate shift period from the mid-Holocene climatic optimum to the late Holocene and the Dark Age Cold Period (DACP), respectively. Due to the relatively cold and dry climate in these periods, glaciers generally advanced on the Tibetan Plateau, and the contribution of snow and ice meltwater weakened. Therefore, the strong rainfall caused by the abnormal atmospheric circulation may be the main cause of these extreme overbank flooding.

Impact of rare earth doping on the luminescence of lanthanum aluminum silicate glasses for radiation sensing

Large core soft glass fibers have been demonstrated to be promising candidates as intrinsic fiber sensors for radiation detection and dosimetry applications. Doping with rare earth ions enhanced their radiation sensitivity. SiO2-Al2O3-La2O3 (SAL) glasses offer easy fabrication of large core fibers with high rare earth concentration and higher mechanical strength than soft glasses. This paper evaluates the suitability of the SAL glass type for radiation dosimetry based on optically stimulated luminescence (OSL) via a comprehensive investigation of the spectroscopic and dosimetric properties of undoped and differently rare earth doped bulk SAL glass samples. Due to the low intensity of the rare earth luminescence peaks in the 250–400 nm OSL detection range, the OSL response for all the SAL glasses is not caused by the rare earth ions but by radiation-induced defects that act as intrinsic centers for the recombination of electrons and holes produced by the ionizing radiation, trapped in fabrication induced defect centers, and then released via stimulation with 470 nm light. The rare earth ions interfere with these processes involving intrinsic centers. This dosimetric behavior of highly rare earth doped SAL glasses suggests that enhancement of OSL response requires lower rare earth concentrations and/or longer wavelength OSL detection range.

A Novel Nanocomposite Material for Optically Stimulated Luminescence Dosimetry.

Radiotherapy is a well-established and important treatment for cancer tumors, and advanced technologies can deliver doses in complex three-dimensional geometries tailored to each patient's specific anatomy. A 3D dosimeter, based on optically stimulated luminescence (OSL), could provide a high accuracy and reusable tool for verifying such dose delivery. Nanoparticles of an OSL material embedded in a transparent matrix have previously been proposed as an inexpensive dosimeter, which can be read out using laser-based methods. Here, we show that Cu-doped LiF nanocubes (nano-LiF:Cu) are excellent candidates for 3D OSL dosimetry owing to their high sensitivity, dose linearity, and stability at ambient conditions. We demonstrate a scalable synthesis technique producing a material with the attractive properties of a single dosimetric trap and a single near-ultraviolet emission line well separated from visible-light stimulation sources. The observed transparency and light yield of silicone sheets with embedded nanocubes hold promise for future 3D OSL-based dosimetry.

Synthesis and structural characterization of AI2O3 nanoparticles: Towards 3D optically stimulated luminescence dosimetry

Advanced radiotherapy techniques, which plan and deliver a treatment in complicated 3D geometries with steep dose gradients, push 3D dosimetry with correspondingly high spatial resolution to the top of scientific and clinical agendas. This paper presents the first steps taken towards an inexpensive and reusable material for 3D dosimetry based on optically stimulated luminescence (OSL). Carbon-doped alumina (Al2O3:C) nanoparticles were synthesized using supercritical flow synthesis, in which product properties can be finely controlled. The particles were characterized using electron microscopy and powder x-ray diffraction. C-doping did not alter the crystallographic structure appreciably, and a high elemental signal from C could be measured. Nanoparticles of amorphous γ-Al2O3:C were achieved, however calcining these to produce the OSL-relevant α-phase yielded microparticles. Future work will aim at producing phase-pure α-Al2O3:C nanoparticles with a narrow size distribution below 10 nm, and controllable C-concentration and O-deficiency.

Chronostratigraphic and palaeogeographic interpretation of Nakdong deltaic sequences in the south-eastern Korean Peninsula

We investigated the chronostratigraphy of six boreholes in the Nakdong River delta area in South Korea based on optically stimulated luminescence (OSL) and 14C dating. The standardised growth curves (SGCs) produced from single and multiple boreholes performed well in determining low equivalent dose (De; < 40 Gy). 14C dates from shell and wood fragments were mostly representative of depositional time. Based on 14C and OSL ages, the lowermost fluvial sediments showed relatively low sediment accumulation rates (0.1–0.8 m/kyr−1) prior to 12 ka. A hiatal discontinuity ranging from 12 to a maximum of 50 ka resulted in a break in sedimentation between the Last Glacial Maximum and the Holocene. A thick fluvio-estuarine unit in the lower part indicated relatively high accumulation rates (3.3–9.4 m/kyr−1) from 12 to 9 ka, which corresponded to rapid sea level rise. In the middle part, decreased accumulation rates (1.7–5.5 m/kyr−1) from approximately 9 to 6 ka were interpreted as transgressive deepening. Lower accumulation rates (0.9–3.2 m/kyr−1) during the middle to late Holocene were caused by relative sea level fall and a horizontally extended sedimentation area. In the upper part, the highest sediment accumulation rates (3.5–8.3 m/kyr−1) and rapid delta progradation during the last 2.0 ka might have been caused by widespread human influence and monsoonal climatic change. Isochrons of 1-kyr scale were identified based on the lithologic boundary and age results for each borehole, which represent palaeoshoreline positions during the transgressive cycle and boundaries of considerable delta progradation.

Direct dating of lithic surface artifacts using luminescence.

Archaeological surface assemblages composed of lithic scatters comprise a large proportion of the archaeological record. Dating such surface artifacts has remained inherently difficult owing to the dynamic nature of Earth-surface processes affecting these assemblages and because no satisfactory chronometric dating technique exists that can be directly applied to constrain the timing of artifact manufacture, discard, and thus human use of the landscape. Here, we present a dating approach based on optically stimulated luminescence (OSL)-OSL rock-surface burial dating-and apply it to a lithic surface scatter in Tibet. We generate OSL burial ages (age-depth profiles) for each artifact, outline the methodological complexities, and consider the artifact burial ages in the context of local-scale Earth-surface dynamics. The oldest age cluster between 5.2 and 5.5 thousand years is likely related to quarrying activities at the site and thus represents the oldest chronometric age constraints for human presence on the south-central Tibetan plateau.

Last interglacial sea levels within the Gulf of Mexico and northwestern Caribbean Sea

Abstract. During the last interglacial (LIG) the volume of additional water in the world's oceans was large enough to raise global sea levels about 6–9 m higher than present levels. However, LIG sea levels vary regionally and those regional differences hold clues about the past distribution of ice sheets and local rates of subsidence and tectonic uplift. In this study, I used a standardized database template to review and summarize the existing constraints on LIG sea levels across the northern Gulf of Mexico and Caribbean shoreline of the Yucatán Peninsula. In total, I extracted 32 sea-level indicators including the insertion of 16 U-series ages on corals, 1 electron spin resonance age, 2 amino acid racemization ages, and 26 luminescence ages. Most dated sea-level indicators for the northern Gulf of Mexico are based on optically stimulated luminescence (OSL) ages of beach deposits of a mappable LIG shoreline. This shoreline extends from the Florida Panhandle through south Texas but is buried or removed by the Mississippi River across most of Louisiana. A similar feature is observed in satellite images south of the Rio Grande within the Mexican portions of the Gulf of Mexico but has yet to be dated. Elevations measured on portions of this feature close to the modern coast point to sea levels less than 1 m to ∼5 m higher than present for much of the northern Gulf of Mexico. However, a few, albeit undated, portions of the same shoreline located at more inland locations point to sea levels up to +7.2 m, attesting to up to 7 m of differential subsidence between the inland and coastal sites. Across the Yucatán Peninsula, U-series dating of corals has provided the main index points for LIG sea levels. Other carbonate coastal features such as beach ridges and eolianites have also been described but rely on corals for their dating. The maximum elevation of the LIG coral-based relative sea-level (RSL) estimates decrease from around +6 m across the Caribbean shoreline of the Yucatán Peninsula near Cancún, Mexico, to as low as −6 m to the south beneath the southern atolls of Belize, although discussion continues as to the validity of the ages for these southern corals. If these lower-elevation corals are LIG in age, their below-present elevations may be a result of vertical motion along faults dipping into the Cayman Trough. South of Belize only one purported LIG coral has been dated on the Isla de Roatán off the coast of Honduras at a likely tectonically uplifted elevation of 37.2 m. Thus the elevation of LIG sea levels within the inland siliciclastic shorelines of Guatemala and Honduras as well as the southwestern Gulf of Mexico remains poorly constrained and a potential venue for future research. The database described in this paper is available open access in spreadsheet format as Simms (2020), at this link: https://doi.org/10.5281/zenodo.4556163.

The ups and downs of the Missouri River from Pleistocene to present: Impact of climatic change and forebulge migration on river profiles, river course, and valley fill complexity

AbstractThe Missouri River is a continent-scale river that has thus far escaped a rigorous reporting of valley fill trends within its trunk system. This study summarizes evolution of the lower Missouri River profile from the time of outwash in the Last Glacial Maximum (LGM) until establishment of the modern dominantly precipitation-fed river. This work relies on optically stimulated luminescence (OSL) dating, water-well data, and a collection of surficial geological maps of the valley compiled from U.S. Geological Survey EDMAP and National Science Foundation Research Experience for Undergrads projects. Mapping reveals five traceable surfaces within valley fill between Yankton, South Dakota, USA, and Columbia, Missouri, USA, that record two cycles of incision and aggradation between ca. 23 ka and ca. 8 ka. The river aggraded during the LGM to form the Malta Bend surface by ca. 26 ka. The Malta Bend surface is buried and fragmented but presumed to record a braided outwash plain. The Malta Bend surface was incised up to 18 m between ca. 23 ka and ca. 16 ka to form the Carrolton surface (ca. 16 ka to ca. 14 ka). The Carrollton surface ghosts a braided outwash morphology locally through overlying mud. Aggradation followed (ca. 14 ka to ca. 13.5 ka) to within 4 m of the modern floodplain surface and generated the Salix surface (ca. 13.5 to ca. 12 ka). By Salix time, the Missouri River was no longer an outwash river and formed a single-thread meandering pattern. Reincision at ca. 12 ka followed Salix deposition to form the short-lived Vermillion surface at approximately the grade of the earlier Carrolton surface. Rapid aggradation from ca. 10 ka to ca. 8 ka followed and formed the modern Omaha surface (ca. 8 ka to Present). The higher Malta Bend and Omaha profiles are at roughly the same grade, as are the lower Carrolton and Vermillion surfaces. The Salix surface is in between. All surfaces converge downstream as they enter the narrow and shallow bedrock valley just before reaching Columbia, Missouri. The maximum departure of the profiles is 18 m near Sioux City, Iowa, USA, at ∼100 km downstream from the James Lobe glacial input near Yankton, South Dakota. Incision and aggradation appear to be driven by relative changes in input of sediment and water related to glacial advance and retreat and then later by climatic changes near the Holocene transition. The incision from the Malta Bend to the Carrolton surface records the initial breakdown of the cryosphere at the end of the LGM, and this same incisional event is found in both the Ohio and Mississippi valleys. This incisional event records a “big wash” that resulted in the evacuation of sediment from each of the major outwash rivers of North America. The direction and magnitude of incision from the LGM to the modern does not fit with modeled glacioisostatic adjustment trends for the Missouri Valley. Glaciotectonics likely influenced the magnitude of incision and aggradation secondarily but does not appear to have controlled the overall timing or magnitude of either. Glaciotectonic valley tilting during the Holocene, however, did likely cause the Holocene channel to consistently migrate away from the glacial front, which argues for a forebulge axis south of the Missouri Valley during the Holocene and, by inference, earlier. This is at least 200 km south of where models predict the Holocene forebulge axis. The Missouri Valley thus appears to reside in the tectonic low between the ice front and the forebulge crest. The buffer valley component of incision caused by profile variation could explain as much as 25 m of the total ∼40 m of valley incision at Sioux City, Iowa. The Missouri Valley also hosted a glacial lobe as far south as Sioux City, Iowa, in pre-Wisconsinan time, which is also a factor in valley excavation.

Reducing variability in OSL rock surface dating profiles

In recent years, rock surface dating has seen the emergence of a technique based on optically stimulated luminescence (OSL). This application translates the depth of OSL signal bleaching within a rock surface into an exposure age or erosion rate at 1-10 4 a timescales. Considerable effort has been undertaken to improve our understanding of OSL rock surface dating, yet a large amount of uncertainty associated with the method remains. Specifically, OSL profiles measured into rock surfaces can be highly scattered. Potential causes of this scatter could be lithological heterogeneity that modify bleaching rate throughout the rock, variability in surface erosion or experimental artefacts. Here, we report experiments that were conducted to explore whether experimental artefacts could contribute to the scatter in OSL profiles measured from rock surfaces exposed in Zermatt, Switzerland. This was done by varying the following parameters: (i) heating rate, (ii) isothermal holding time, (iii) luminescence signal detection filters, (iv) the sequential order of optical stimulations, and (v) core diameter. Our results indicate that sample temperature, for both preheating and stimulation, may exert a strong influence on the OSL profiles obtained. Thermal lag, i.e. the temporal offset between sample temperature and the instrument temperature, can be significant for rock slices if a heating rate of 5 °C s −1 is used and if rock slices are placed directly on the instrument carousel. To reduce this effect, our results suggest future studies place samples in metal cups, reduce the heating rate and increase preheating and holding times prior to optical stimulation, to allow samples to heat at the desired rate and reach the required temperatures. • Variability in heating increases noise in luminescence depth profiles. • Thermal lag causes heating to vary between rock slices. • Suggestions for the optimization of rock surface dating protocols are given.

A comparison of polymineral and K-feldspar post-infrared infrared stimulated luminescence ages of loess from Franconia, southern Germany

Abstract. Loess-paleosol sequences (LPSs) are essential records for reconstructing Quaternary paleoenvironments. No previous study has provided numerical chronologies of loess in Lower Franconia, southern Germany; their chronostratigraphic assumptions have relied mainly on German (pedo)stratigraphic schemes. In this study, we provide for the first time a chronology for LPSs in Lower Franconia based on optically stimulated luminescence (OSL) dating using quartz and a comparison of K-feldspar (63–100 µm) and the polymineral fraction (4–11 µm). Our results show that all obtained ages are in stratigraphic order, ranging from Holocene to late Pleistocene, and in general confirm the former stratigraphical interpretations. A good agreement of the obtained ages is observed between both feldspar grain size fractions; they also agree well with the quartz OSL ages up to ∼50 ka. However, a marked difference between the growth pattern of the dose response curves and consequently different saturation characteristics of fine and coarse grains is found. Even though in our samples the discrepancy in ages is not very significant, we suggest the use of coarse-grained K-feldspar whenever possible in order to not be confronted with unknowns such as the mineral composition of the polymineral fraction.

Boosted UV emission on the optically and thermally stimulated luminescence of CaB6O10:Gd,Ag phosphors excited by X-rays

The luminescent properties of X-ray phosphors based on optically stimulated luminescence (OSL) are quite fortuitous, since it demands the existence of both trapping and recombination (luminescent) centers. Nevertheless, lanthanide-doped materials have changed this paradigm by two main reasons: lanthanide doping provides the development of high efficient phosphors and allows for a relatively easy prediction of the energy-levels of the trapping centers involved in OSL phenomena. In view of that, this work reveals some luminescent and dosimetric properties of a phosphor never reported before, i.e., gadolinium and silver doped CaB6O10 polycrystalline samples. The phosphor synthesis followed a solid state reaction method and was optimized regarding the concentration of dopants for a better OSL response. Comparing to non-doped samples, the OSL showed an enhancement of ∼ 140x when doped with gadolinium and silver. The phosphor exhibited a high UV emission under blue stimulation (475 nm), with a linear dose-response for the range analyzed (1 mGy up to 2 Gy) and a minimum detectable dose of ∼ 40 μGy. The material exhibited a fading of ∼ 30% within the first 24 h after irradiation, which is attributed to shallow traps created by Ag+ incorporation. Wavelength-resolved thermoluminescence (TL) and OSL spectra revealed a sharp 317 nm emission, which is ascribed to 6PJ → 8S7/2 transition of Gd3+ centers, indicating that the Gd3+ has a crucial role in the luminescence mechanisms. In addition, the OSL spectrum exhibited also a broad emission at 350 nm attributed to 3DJ,1D2 → 1S0 transitions of Ag+ centers. Insights on the luminescent processes are given, including the role of Gd3+ and Ag+ centers in the trapping and recombination processes responsible for the TL and OSL. New mechanisms of luminescent enhancement by silver incorporation are suggested.

OSL Dating of Earthen Mortars from a Medieval Building in Northwestern Spain: Crypt of Basílica da AscensiÓn (Allariz, Ourense)

ABSTRACTThere are few papers that focus on optically stimulated luminescence (OSL) dating of earthen mortars. These mortars are abundant in historical buildings in northwestern Spain. The Basílica da AscensiónyForno da Santa building is an unfinished church built on a previous structure that was transformed into a crypt (Allariz, Ourense, NW Spain). Previous archaeological studies established a sequence of phases of construction, the first dating back to the Iron Age, with significant changes occurring in the Early and Late Medieval ages. The only datable material in the crypt is earthen mortar. Thus, eight mortar samples (seven joint mortars and one wall infill) were taken, seven of them dated by OSL. The dose rate was assessed, and the expected equivalent doses estimated based on the established archaeological age. Several grain sizes (from fine to coarse) were used in small multigrain aliquots to assess the equivalent doses and ages. No evidence of partial bleaching was observed in most samples and grain sizes. The resulting ages are younger than expected for most samples. This is explained by the fact that joints were repaired with new mortar from the 16th century onwards.

Hydrological Variations and the Ancient Silk Road in the Northern Tarim Basin between Han and Sui Dynasties

AbstractThe fluctuation pattern of China's civilization can be ascribed to climate change and historical geopolitical variations. The ancient Silk Road served as the most prosperous route connecting East Asia and Europe during Han Dynasty (206 BC–220 AD) and Sui‐Tang Dynasties (581–907 AD), but was deserted in Wei, Jin, Northern and Southern dynasties (220–580 AD), of which the Tarim Basin was a key area. However, our understanding about the decline of the route during this period remains limited. Here, we present an ~7‐year resolution record based on optically stimulated luminescence (OSL) age‐depth model (ca. 120 BC–750AD) from Luntai (LT) profile, about 5 km from the modern Tarim River, which fed the ancient oases, to assess the potential causes on the documented decline of the ancient Silk Road between Late Han and Sui dynasties. In this study, five episodes of hydrological change were identified by combining grain size, magnetic susceptibility, geochemistry and TOC/TN contents. Our reconstruction reveals that cold and wet climate dominated at 120BC–50 AD and 550–750AD, respectively, indicated by strong hydrodynamic conditions. Relatively warm and humid climate occurred at 120–550AD, between Eastern Han and Sui‐Tang dynasties, indicating a better and more suitable local environment. A comparison between the studied region and other areas of China demonstrates that the paleoclimatic variations in eastern and western China exhibit rough discrepancies, and the hydrological conditions in arid region is inconsistent with the decline of ancient Silk Road in the northern Tarim Basin. We suggest that political and societal factors are the key issues that caused the interruption of Silk Road during Wei, Jin, Northern and Southern dynasties, such as the co‐occurrence of societal crises, turmoil and division in eastern China, rather than the deteriorating climatic condition in the northern Tarim basin.

A new approach to the 2D radiation dosimetry based on optically stimulated luminescence of LiF:Mg,Cu,P

A new approach to the two-dimensional (2D) spatial radiation dosimetry based on optically stimulated luminescence (OSL) phenomena is presented. By investigating prototype dosimeters in form of flat and flexible sheets made of a polymer (PDMS), with the embedded OSL active grains (LiF:Mg,Cu,P), direct measurements of the 2D dose distribution using the OSL method and self-developed optical setup were verified. We have determined the response of 2D OSL prototype silicone foils, stimulated with the blue LEDs (470 nm) and read out using the CCD camera system, after doses of beta radiation ranging from less than 0.1 Gy up to 100 Gy. We have also verified the basic dosimetric parameters of the prototype sample foils, including the sensitivity (signal per dose), linearity, repeatability and fading effect. These encouraging results are the first step towards the practical use of LiF:Mg,Cu,P 2D OSL foils as a reusable spatial dosimeter system.