Beta Dose Research Articles

Synthesis and Thermoluminescence Characterization of Ba₆Y₂W₃O₁₈ Perovskite Nanosensors for Dosimetry

Through the citrate-assisted sol-gel method, barium gadolinium tungstate (Ba6Y2W3O18) perovskite samples were synthesized, and their luminescence properties were investigated. Through X-ray diffraction (XRD) the crystal structure of the prepared samples was examined. The tunnelling electron microscopy (TEM) analysis has confirmed the agglomeration of the nanoparticles into rods with an average diameter and length of 71 and 214 nm, respectively. The thermoluminescence (TL) properties were investigated by; first, estimating the number of composing TL components using both experimental and computational methods; second, studying the dose-response of the glow curves in response to the irradiated beta dose. The third step in the study of the TL properties was to assess the reusability of the prepared samples in TL dosimetry and the fourth step was to estimate the minimum detectable dose of the phosphor samples. The Computerized Glow Curve Deconvolution (CGCD) method was then used to extract the kinetic parameters of the composing TL peaks.

Thermoluminescence and optically stimulated luminescence studies of Gypsum for retrospective dosimetry

This study examines the use of gypsum for radiation dosimetry using Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) techniques. It is observed that gypsum preserves the information of radiation dose despite the loss of water upon heating in a laboratory. Deconvolution of the thermoluminescence glow curve suggests thermoluminescence glow peaks at 125, 150, 280, 320, and 440 °C. The glow peak at 440 °C has a minimum detectable dose of 200 mGy, and it bleaches to approximately 50% with 300 min of daylight exposure. The Blue Light Stimulated Luminescence (BLSL) comprises a slow component and is correlated to 255 °C TL glow peak. The alpha efficiency of luminescence production per unit Gy of alpha dose with respect to the beta dose for the TL glow peaks at 440 °C is calculated at 0.18 ± 0.01. For BLSL, the value is calculated at 0.15 ± 0.01. A measurement protocol for the use of gypsum for retrospective dosimetry is also presented.

Photoluminescence and beta-ray irradiation induced thermoluminescence of Er(III) doped tungstate double perovskite

A luminescent double perovskite Ca3WO6 doped with Er3+ was successfully synthesized via traditional solid-state reaction. Structural analysis was performed through X-ray diffraction (XRD) patterns utilizing Rietveld refinement. When excited at 380 nm, the Ca3WO6:Er3+ phosphors displayed green spectral emission, corresponds to 2H11/2, 4S3/2 to 4I15/2 transitions of Er3+. The influence of Er3+ concentrations on photoluminescence (PL) intensity and concentration quenching was discussed, ascribing multipolar interaction as a cause of intensity quenching. The temperature-dependent PL analysis revealed the phosphor's excellent thermal stability, retaining approximately 79.6 % of its PL intensity at 150 °C. Furthermore, the Ca3WO6:Er3+ phosphors exhibited high-quality thermoluminescence (TL) after beta irradiation. The impact of Er3+ concentrations and beta dose on TL intensity was investigated comprehensively. The reproducibility of the phosphor was checked after several TL readouts. The various heating rate (VHR) experiments were conducted to examine the effect of HR and to determine the trapping parameters.

Contribution of coupled ESR/U-series fossil dating to a Paleolithic-Neolithic transition site - Naminan, Southwest China

The coupled ESR and U-series (ESR/U-series) method has been increasingly utilized for dating fossil teeth from Early to Middle Pleistocene hominid sites. One significant advantage of this method is its ability to directly analyze fossil animal or human teeth. However, compared with other radiometric methods such as 14C charcoal dating, U-series carbonate dating, and OSL sediment dating, this dating method is rarely employed for Late Pleistocene or younger sites. In this study, we present an ESR/U-series dating investigation conducted at the Naminan site, a Paleolithic-Neolithic transition (P–N transition) site situated on the Sino-Myanmar border. The ESR/U-series analysis of eleven dental samples yields an age range of 18.1–13.2 ka for the fossils. These obtained ages are generally consistent with the 14C chronology of the site. When dealing with young fossil samples, it was observed that due to relatively low uranium concentration in dental tissues, internal dose rate plays a less significant role compared to external beta and gamma dose rates in the total dose rate of the fossil samples. Consequently, evaluating the dose rate of surrounding sediment becomes a primary source of uncertainty. Additionally, in this study we attempted to employ the standardized growth curve (SGC) and representative dose response curve method for determining Equivalent Dose (DE), which was then compared with values obtained using additive dose method (ADM). Although the precision of DE estimated by two methods are comparatively lower than that of ADM, it demonstrates the potential to efficiently determine a more rational Dmax for irradiation, identify samples with stratigraphic disturbances, and analyze small or valuable fossil specimens.

Thermally stable luminescence and dosimetric features of Ho(III) activated tungstate double perovskite

Luminescent efficient tungstate double perovskites Ca3WO6 doped with Ho3+ were synthesized via the solid-state reaction at 1200 C°. The resulting phosphors were analyzed using Rietveld refinement of X-ray diffraction (XRD) data, confirming a monoclinic crystal structure with crystallite sizes ranging between 50 and 55 nm. Optical bandgap determination was facilitated by diffusion reflectance spectra (DRS). Fourier transform infrared (FTIR) studies were conducted to identify functional group vibrations. The optical excitation of the Ca3WO6:Ho3+ phosphors under different excitation conditions resulted in intense green photoluminescence (PL) emission at 545 nm, indicative of the 5F4–5I8 transition of Ho3+ ions. Thermal stability assessment of Ca3WO6:1 % Ho3+ phosphor under blue excitation (454 nm) revealed good thermally stable luminescence about 85.32 % at LED working temperature (150 °C). PL decay studies were conducted to analyze fluorescent behaviour, wherein by means of PL decay lifetime, the PL quantum efficiency of Ca3WO6:1 % Ho3+ phosphor is computed to be 91.1 %. The CIE color coordinates of the phosphors being investigated reside within the green spectral region, with a calculated color purity of 93.25 % observed for Ca3WO6:1%Ho3+. Furthermore, the phosphors under study exhibited high-quality thermoluminescence (TL) after beta irradiation. The detailed TL characterization conducted to assess dosimetric properties. The impact of Ho3+ concentrations and beta dose on TL intensity are two major aspects that have been investigated in detail. TL fading experiments were performed to determine dose storage capacity over a month after beta irradiation. Additionally, the various heating rate (VHR) experiments are conducted to determine the TL kinetic parameters. Besides, the glow curve deconvolution (GCD) for trap parameter determination is also applied, where the results obtained are comparable with the VHR results.

Beta dose rate estimation of soil samples with CW-OSL technique using LiCaAlF6:Eu,Y phosphor for retrospective dosimetry

Retrospective dosimetry technique makes use of commonly available materials such as soil, brick, electronic components etc. for dose estimation. The measurement of internal component of annual dose is necessary for estimating the background dose received by the sample. This dose is then subtracted from the cumulative dose received by the sample in order to estimate the accident dose received by the sample retrospectively. In most of the cases it is sufficient to determine only the beta dose for the internal component of the annual dose. For the annual beta dose in soil/pottery thermoluminescence (TL) technique is widely used. However, in recent years Optically Stimulated Luminescence (OSL) dosimetry is gaining importance due to its various advantages over TL dosimetry. LiCaAlF6:Eu,Y (LCAF) is one of the promising OSL phosphor having remarkable dosimetric characteristics and sensitivity. By varying the stimulation parameters, the minimum detectable dose (MDD) of LCAF could be achieved in the range of 0.1–0.2 μGy. Leveraging this advancement, LCAF based dosimeters were successfully utilized for assessing the beta dose originating from various soil samples. The obtained results exhibit notable concurrence with Monte Carlo-based computations, validating the accuracy and reliability of LCAF dosimeters.

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

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

Monte Carlo dosimetry of Y-90 and Ru-106 /Rh-106 disk sources for ocular melanoma treatment: beta dose falloff study

Monte Carlo dosimetry of Y-90 and Ru-106 /Rh-106 disk sources for ocular melanoma treatment: beta dose falloff study

Comparison of De values from Late Pleistocene alluvial deposits on the coast of Galicia (NW Spain) using BayLum or Analyst-based procedures

The coastal sedimentary record of Galicia (NW Spain) is important to study sea-level oscillations during the Late Quaternary. The alluvial deposits preserved in the Ria de Coruña and Ria de Arousa are remnants of fluvial valleys flooded by the sea during the successive Pleistocene and Holocene transgressions. A first chronological study by Optical Stimulated Luminescence (OSL)- revealed a fast-component dominated, but dim OSL signal emitted by quartz from this area. Equivalent dose distributions, as obtained with the Analyst software, yielded large overdispersion values, which were negatively correlated to the potassium concentration in the sediment, thus suggesting the influence of beta dose rate heterogeneities. Nevertheless, for most samples many aliquots were considered in saturation, leading to a palaeodose and age underestimation – regardless of the model choice for age calculation. In this paper, we present new analyses using the open-source R package BayLum, as the so-called saturated aliquots may be incorporated in age calculation. Thus, we test this model performance and more commonly used models in retrieving large doses. Then, we discuss the implications for age calculation for these continental sediments formed during the Late Pleistocene.

The radioactivity levels and beta dose rate assessment from dental ceramic materials in Egypt

There is a lack of available data on the radioactivity levels of these materials, despite the potential risks they may pose to patients, dental technicians, and dentists. A total of forty samples were collected from different dental markets in Egypt. Using an NaI(Tl) detector, the gamma-ray spectrometer measured the activity levels of uranium-238, radium-226, thorium-232, and potassium-40. The findings revealed that the mean concentration of 238U (below the minimum detectable activity, MDA), 226Ra (135 ± 5 and 132 ± 5 Bq/kg), 232Th (187 ± 4 and 243 ± 8 Bq/kg), and 40K (1560 ± 52 and 2501 ± 89 Bq/kg) in feldspar and zirconia (ZrO2) dental ceramic samples, respectively, were all within the limits established by the International Organization for Standardization (ISO) and the European Commission (EC). The use of feldspar and zirconia dental ceramics to restore all teeth would result in an estimated maximum beta dose of 1.5 mGy/year to the oral tissue. The results suggest that there is no cause for concern regarding any additional beta dose to the oral cavity from the use of feldspar and zirconia dental ceramics.

Kinetic analysis and dosimetric characteristics of the thermoluminescent glow curve of aquamarine (Be3Al2(SiO3)6:Fe)

Kinetic analysis of the thermoluminescent (TL) glow curve of aquamarine, a cyan variety of beryl (Be3Al2(SiO3)6), is reported. Samples were irradiated at room temperature using a90Sr/90Y β source at a rate of 0.10 Gy-1. Measurements made at 1 °C/s after irradiation from 1 to 100 Gy show a high intensity peak at 75 °C followed by three secondary peaks at 115, 189 and 302 °C respectively. The dose response of the high intensity peak (called the main peak) is linear within the first 20 Gy, but tends towards sub-linearity as the dose is close to 100 Gy. The signal decays with the time delay between irradiation and reading. It decays about 14% of its initial value, 600 s after irradiation. Reproducibility analysis shows that the material reproduces its response under identical experimental conditions with an uncertainty of 0.8% after 10 Gy beta dose irradiation. The kinetic analysis of the TL glow curve was carried out using the curve fitting method. The results show that the main peak follows first order kinetics, its activation energy is of the order of 1 eV and the frequency factor is between 1012 and 1014 s−1, while some secondary peaks follow general order kinetics.

Synthesis and thermoluminescence characteristics of beta irradiated nanocrystalline calcium aluminate doped with lanthanum oxides

This study investigated the thermoluminescence (TL) characteristics of calcium, a nano-phosphor doped with a rare earth element (lanthanum, La). Six different concentrations of dopants were prepared by the sol-gel method. The XRD data displayed that the particle size was 52.48 nm. The surface morphology was examined by SEM analysis. The highest TL response of the nano-phosphor CaAl2O4 was found with a dopant of 0.1 % La, which has the most intense TL peak. The Computerized Glow Curve Deconvolution (CGCD) and Variable Heating Rate (VHR) methods were carried out for trap-level analyses and activation energy determination. The deconvolution of the glow curves displayed thirteen superimposed TL glow peaks located between 362 and 717 K. The TL response of CaAl2O4:0.1 % La nano-phosphor showed linearity in the beta dose range from 2.2 Gy up to 330 Gy for all the deconvoluted glow peaks. The minimum detectable dose of the prepared samples is 284 μGy. Other parameters, such as the sensitivity and reproducibility of the prepared samples, were determined. It is concluded that CaAl2O4 with a dopant of 0.1 % La is a good material for dosimetry applications.

Luminescence dating of sand matrices within gravelly fluvial deposits: Assessing the plausibility of beta dose rate calculation

Dating of gravelly fluvial deposits is typically hampered by the absence of suitable plant fragments for radiocarbon dating or sand layers for luminescence dating. Although gravelly fluvial deposits generally contain sand-sized quartz and feldspar that could be used for luminescence dating, the considerable grain-to-grain variability in beta dose rate, coupled with the lack of methods for routine dose rate estimation, presents challenges. In this study, a recently proposed model for calculating average beta dose rates in granular matrices was modified to be applicable to sand-sized dosimeter grains within gravelly deposits. We applied the modified model to sand-sized K-rich feldspars within sand matrices obtained from gravelly fluvial deposits in the Tokachi Plain, northern Japan, and compared the ages of samples obtained from sand matrices with those from sand lenses. Although the weight of <2 mm grains accounted for only 20%–35% of the bulk sediment, these grains were estimated to contribute approximately 70% of the external beta dose rate according to the model, because larger grains have a larger self-dose. Taking into account that the beta dose to dosimeter grains is mainly derived from smaller matrices (e.g. <2 mm), beta dose rates were also calculated based on the infinite matrix dose rate of the <2 mm fraction, along with the conventional water correction method. The ages of sand matrices calculated based on the beta dose rates derived from both the model and the infinite matrix dose rate of the <2 mm fraction were generally consistent with those of sand lenses. The dose rate calculated based on the model might be more accurate than that calculated using the infinite matrix dose rate of <2 mm fraction, but calculating the beta dose rate using the infinite matrix dose rate of <2 mm fraction is useful as a simple approach.

Low Rebleed Incidence with Eptacog Beta Treatment through 24 and 48 Hours in Children (

Introduction Persons with hemophilia A or B and inhibitors (PwHABI) who are not on prophylaxis may have high rates of bleeding, and, if not treated effectively, may have significant morbidity related to rebleeding. Dosing strategies of bypassing agents (BPAs) are variable in clinical practice, and following a period of initial bleed control, rebleeding may occur. The development of additional bypassing agents that can minimize the incidence of rebleeding in this patient population is an important medical need. Eptacog beta is a recombinant activated human factor VII approved in the US and Mexico (Sevenfact®, 2020), as well as the EU and UK (Cevenfacta®, 2022) as a BPA for the treatment of bleeding episodes (BEs) in PwHABI aged 12 years and older using two initial dose regimens (IDRs) of 75 or 225 µg/kg. In the EU and UK, eptacog beta is also indicated for preventing bleeding in the setting of surgery and other invasive procedures. Approval in the US and Mexico was based on demonstrated efficacy in the pivotal phase 3 PERSEPT 1 trial (NCT02020369), which included 27 adolescent and adult PwHABI who treated 465 mild or moderate BEs. Bleed resolution at 24 hours post-initial infusion was 96.7% and 99.5% for 75 and 225 µg/kg IDRs, respectively, with a single bleed recurrence observed before 24 hours. The subsequent phase 3 PERSEPT 2 trial (NCT02448680) enrolled 25 PwHABI &amp;lt;12 years of age who treated 546 mild or moderate BEs. Bleed resolution at 24 hours post-initial infusion in these pediatric patients was 97.4% and 98.0% for 75 and 225 µg/kg IDRs, respectively. The objective of this analysis is to evaluate the incidence of rebleeding when treating mild or moderate BEs in PwHABI &amp;lt;12 years of age with eptacog beta during PERSEPT 2 at 24 and 48 hours post-initial dose. Methods PwHABI in PERSEPT 2 were randomized to either the 75 or the 225 µg/kg IDR to treat BEs and were crossed over to the alternate IDR every 3 months. No subjects in PERSEPT 2 were using prophylaxis. Subjects assigned to the 75 µg/kg IDR treated BEs with initial doses of 75 µg/kg eptacog beta followed by 75 µg/kg q3h as needed. Subjects assigned to the 225 µg/kg IDR treated BEs with an initial 225 µg/kg eptacog beta dose, followed after 9 hours by 75 µg/kg q3h as needed. Mild or moderate BE treatment success at a given time point was assessed by the patient or caregiver and was defined as obtaining a hemostasis evaluation of “excellent” or “good” on a 4-point scale with no additional eptacog beta being infused, no alternative hemostatic agents or blood products being used, and no increase in pain following the first “excellent” or “good” assessment. For this analysis, a BE was considered a rebleed if occurring at the same anatomical location as the original bleed, and within 24 or 48 hours of the initial infusion for the original bleed. Results During the study, subjects treated 546 BEs. Nine rebleeds occurred among 4 of the 25 children within 24 hours, and 13 rebleeds occurred among 6 children within 48 hours. The rebleed incidence and 95% confidence intervals (CIs) through 24 hours was 1.3% [95% CI: 0.0%, 3.6%] for the 75 µg/kg IDR and 2.0% [95% CI: 0.0%, 3.9%] for the 225 µg/kg IDR. The corresponding rebleed incidence and 95% CIs through 48 hours for the 75 and 225 µg/kg IDRs were 2.1% [95% CI: 0.0%, 4.5%] and 2.6% [95% CI: 0.4%, 4.9%], respectively. The differences in rebleed incidence between the two IDRs were not statistically significant at either 24 or 48 hours (Figure 1). The overall rebleed incidence in PERSEPT 2 was 1.6% [95% CI: 0.0%, 3.7%] through 24 hours and 2.4% [95% CI: 0.2%, 4.5%] through 48 hours. No treatment-related adverse events or thrombotic complications were observed. Conclusions Eptacog beta demonstrated a low overall incidence of rebleeding through 24 hours (1.6%) and 48 hours (2.4%) in PwHABI &amp;lt;12 years of age during PERSEPT 2. Rebleeding was similarly low for either IDR at both time points. These findings align with those previously reported for PERSEPT 1 in adolescent and adult patients. Combined with the high efficacy at 24 hours (&amp;gt;96%) observed in both trials and both IDRs, these results suggest that eptacog beta can provide clinicians and caregivers with a treatment option that can establish and maintain hemostatic control of mild or moderate BEs in PwHABI of all ages.

Processing biological samples from simulated radiological terrorist events using Rapid DNA instruments

Two commercially available portable Rapid DNA instruments were evaluated for their ability to process 1 µL and 10 µL saliva samples deposited on metal and plastic surfaces and contaminated with surrogates of cesium (Cs)-137, strontium (Sr)-90 and cobalt (Co)-60; radioactive materials potentially released during a nuclear weapon accident or a radiological dispersal device detonation. A comparable success rate was noted for both Rapid DNA instruments when considering the number of complete and balanced DNA profiles, the number of profiles with a minimum of 10 autosomal STR loci (out of 23 [FlexPlex™ 27] or 21 [GlobalFiler™ Express]), and the possibility to search a national DNA database in Canada and the United States. Cobalt had an adverse impact on the quality of the megaplex short tandem repeat (STR) DNA profiles derived on each instrument for two of the three contamination levels tested in this study, i.e., 0.05 M and 0.1 M as reflected by a reduced number of detected alleles and decreased profile peak heights. Strontium exhibited some adverse effect on the Rapid DNA results when used at the highest contamination level (0.1 M) whereas cesium had none. No new artifacts were observed in the Rapid DNA profiles of samples spiked with the non-radiogenic surrogates. Importantly, in the context of a radiological/nuclear (RN) event, the ANDE™ 6C offers the possibility to dispose of all radioactive materials associated with contaminated samples quickly using a chip on which all steps of the Rapid DNA process are performed whereas the RapidHIT™ ID accumulates radioactive materials for many days before disposal. An individual handling 25 samples in a week (5 per day) on the RapidHIT™ ID at a 30.5 cm distance with a 5 min exposure to the radioactive source estimated at every run would exceed the 0.042 µSv/5 min limit with gamma dose rates for Cs at 0.13 mSv and for Co at 3.8 mSv. Beta dose rates calculated for the surrogate isotopes at the three concentrations tested were also above the recommended radiation exposure limit of 1 mSv/yr (0.042 µSv/5 min). Various potential mechanisms of action behind the interference noted for Sr and Co at high concentrations are presented. These elements may play a role in the steps prior to PCR (at the DNA molecule by binding to bases or to phosphate groups), during PCR (at the DNA polymerase as cofactors for catalytic sites), or even during amplified DNA fragment detection (as fluorescence quenchers).

Luminescence and dosimetry approach in terbium(III)-activated tungstate double perovskite.

A series of tungstate double perovskite Ca3 WO6 doped with Tb3+ was prepared by a combustion process using urea as a flux. The crystal structure identification of Ca3 WO6 :Tb3+ phosphors was done using X-ray diffraction patterns, and a monoclinic structure was discovered. The Fourier transform infrared spectrum of Ca3 WO6 :Tb3+ displayed characteristic vibrations of tungstate bonds. Under 278 nm excitation, Ca3 WO6 :Tb3+ exhibited intense downconversion green emission, which corresponded to the 5 D4 -7 FJ (J = 4,5) transitions of Tb3+ . The phosphor exhibited the highest photoluminescence (PL) intensity when it was doped with 1mol% of Tb3+ ; later intensity quenching appeared to be due to the multipolar interaction at higher dopant concentrations. Moreover, high-quality thermoluminescence (TL) was detected when phosphors were irradiated using beta rays. The effects of Tb3+ concentration and beta dose on TL intensity were the two major aspects studied in detail. The TL intensity demonstrated excellent linear response to the applied range of beta dose. The trap parameters of the studied phosphors were computed by the peak shape approach and glow curve deconvolution. The fading effect on TL intensity was studied by recording the TL glow curves after 1 month of beta irradiation. Obtained results from the PL and TL characterizations showed that the phosphors under study have the potential to be used in lighting displays and in thermoluminescence dosimetry.

Thermoluminescent glow curve of Gd1-xRExAlO3 (RE=Dy or Pr) beta irradiated phosphors

Phosphors composed of Gd1-xRExAlO3 (0≤x ≤ 5 RE = Dy or Pr) stoichiometries were synthesized using the reverse coprecipitation pathway. The thermoluminescent responses of all phosphors were studied under beta radiation exposure. Doping the gadolinium aluminate host improved the thermoluminescent response of the phosphors, with the phosphors composed of Gd0.99Dy0.01AlO3 and Gd0.95Pr0.05AlO3 being the most sensitive. The Dy3+ ions produced a higher improvement of the thermoluminescent signal than the Pr3+ ions. Additionally, a proportional relationship between the similarity of the atomic numbers of the dopant and replaced ions and the sensitivity to thermoluminescence was confirmed. Besides, a slight shift of the thermoluminescent peaks toward lower temperatures was detected for doped phosphors. In the repeatability tests applied to the phosphor composed of Gd0.99Dy0.01AlO3, an anomalous increase in sensitization was observed. The observed sensitization was associated with the formation of electron trap clusters resulting from the continuous exposure to beta radiation. Furthermore, another sensitization phenomenon was detected in the phosphor with Gd0.95Pr0.05AlO3 stoichiometry when it was heated at low temperatures. The aforementioned striking behavior was related to quasi-continuous distributions of electron traps and the tunneling effect. In regard to linearity, the phosphor composed of Gd0.99Dy0.01AlO3 exhibited a linear response with the dose across the entire range of beta doses. However, the response of the Gd0.95Pr0.05AlO3 phosphor lost linearity beyond 26.4 Gy of beta dose. The results obtained through the use of the Tmax-Tstop method and deconvolutions suggested an enhancement in the efficiency of the thermoluminescent mechanisms due to the incorporation of activators.

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

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

Thermoluminescence dosimetric characteristics of natural zircon

The dosimetric characteristics were studied for natural zircon extracted from beach sand of grain size 106 micron to assess whether it can be used as a retrospective dosimeter. Zircon was extracted from the beach sand of Tirunelveli district, Tamilnadu. By analyzing the TL peaks between the room temperature and 450°C it was found to consist of two low temperature peaks (LTP) at 99 and 128°C and the high temperature broad peak (HTP) at 270°C when read at a heating rate of 5°C/sec. The initial rise method, Tm–Tstop, various heating rate method (VHR), Beta dose response and fading studies were carried out for the HTP. From the initial rise method the activation energy levels were found to vary from 0.8 to 1.6 eV. By the Tm–Tstop method it was found that the high temperature broad peak (HTP) at 270°C was a superposition of 6 TL peaks. The Im− Tm dependence curve was plotted and the value of the kinetic order was found to be 1.3. Beta irradiation between the dose levels 0.5 Gy to 100 Gy was used to study the linearity of dose response. It's observed that the zircon sample shows linear dose response up to 100 Gy of beta dose. Fading of the high temperature peak within 1 hour under bright sunlight was found to be ∼21% and after 24 hours the sample exhibited a fading of 47%. Repeatability test were also carried out for the HTP.

Characterising and correcting for a previously unconsidered source of scatter in measurements of equivalent dose

Single aliquot methods make it feasible to routinely determine multiple estimates of equivalent dose (De) for a sample. The scatter in De values observed within a sample has been used previously to make inferences about the resetting of the luminescence signal being measured prior to the event dated, about post-depositional processes that may have affected the sample, and about spatial variations in environmental dose rate on a small (millimetre) scale. However, in addition to processes associated with deposition and burial, scatter in the De values generated may also arise if the dose rate from the beta source used as part of the De determination method varies between grains or aliquots. Spatial variation in the beta dose arising from 90Sr plaque beta sources has been known for more than 20 years. What has not previously been described is variation in beta dose rate between different sample positions on the Risø TL/OSL instruments, one of the most widely used commercial systems used for luminescence dating. The variation arises from misalignment of the carousel used to hold samples with respect to the lid upon which the beta source is mounted. For one instrument in this study, this misalignment led to variations in apparent dose between different carousel positions of 14%. For most instruments the variability was lower (0.15–∼2%), but still detectable. A method for assessing the severity of this problem for individual instruments is described, along with a procedure for correcting for the effect and thus reducing the impact of this hitherto undescribed source of scatter in De.