Equivalent Dose Distributions Research Articles

Analyzing complex single grain feldspar equivalent dose distributions for luminescence dating of glacially derived sediments

Overdeepened valleys are structures scoured into the underlying substrate by glaciers that have been subsequently filled with sediment, which recorded the environmental history of the adjacent landscape. Investigated here is an overdeepened structure that was formed beneath the Salzach Paleoglacier west of Freilassing, Bavaria (southern Germany). In a previous study, infinite infrared stimulated luminescence (IRSL) ages have been determined for the lower part of the core using a multi-grain approach. Applying single-grain feldspar luminescence dating allows to identify the unsaturated signals, previously masked by multi-grain signal averaging. Identification of the normally distributed leading edge in equivalent dose (De) distributions allows for the dismissal of low value De (LOVED) grains that appear to reflect underestimating outliers. Measurement of eleven samples distributed along the entire length of the core yielded two distinct age clusters, for which fading corrected IRSL50 and uncorrected pIRIR225 ages agree within uncertainties. Whereas the younger age cluster at the top of the sequence is attributed to Marine Isotope Stage (MIS) 3, the older age cluster is assigned to MIS 6. It is shown that single grain pIRIR measurements will allow to resolve the infill chronology of overdeepened structures in the Alps, at least for the last ca. 200 ka. Overall, the present study represents a further step towards understanding and handling complex De distributions often encountered in single grain feldspar luminescence dating. This contributes to better understand the frequently observed age offset between single grain and single-aliquot measurements.

Radiological impact assessment of a dirty bomb using Hotspot Code and AI: Insights from spent nuclear fuel isotopes

This study evaluates the potential radiological effects resulting from the use of a Radiological Dispersal Device (RDD), commonly known as a “dirty bomb,” in Dhamar City, Yemen, focusing on its impact on human health. Seasonal atmospheric variations were analyzed using the HotSpot Health Physics Code to model the Total Effective Dose Equivalent (TEDE) distribution following an explosion. The TEDE’s effect on different human organs was assessed, considering both external and internal radiation exposures. The study demonstrated that winter nights posed the highest radiation risk, with dose distribution areas of 0.018 km2, 0.14 km2, and 3.3 km2 for inner, middle, and outer zones, respectively, surpassing other seasonal and daily values. Conversely, summer recorded the lowest radiation spread. A detailed temporal analysis during winter nights showed an initial TEDE of 9.5 Sv at 0.1 min post-explosion, which decreased exponentially to 1.3 Sv after 2000 min (33.3 h) and further to 0.0038 Sv after 6500 min (108.3 h) with the aid of AI-enhanced “Long Short Term Memory Networks (LSTM)”. The highest radiation doses to human organs within a 100 m2 area during the initial 10 min post-detonation were significantly above permissible limits, with critical organs like the surface bone, liver, and red marrow receiving doses of 68 Sv, 12 Sv, and 5.5 Sv, respectively. These findings underline the need for robust emergency response strategies and long-term health monitoring to mitigate the adverse health impacts of RDDs. The comprehensive assessment presented in this study, enhanced by artificial intelligence, provides essential data for improving public health safety and emergency preparedness in regions susceptible to radiological threats.

Thin loess in Southwestern Sweden

ABSTRACT A thin (20–80 cm), patchy layer of silt-rich sediment occurs at the surface throughout Svartedalen, a nature reserve 30 km north of Gothenburg, Sweden. This surface silt mantles a bedrock-dominated, fracture-valley landscape. Using data from grain-size analysis, OSL dating and detrital-zircon U-Pb dating, we argue that the silt is loess sourced from glacial sediment that was eroded from local bedrock. The sediment has a grain-size distribution typical of wind-blown silt and is especially similar to thin deposits of loess overlying coarser material. OSL ages on five samples range from 1 to 8 ka, although analysis of equivalent dose distributions of one may suggest an age as old as 11 ka. The dates may represent true depositional ages and represent several Holocene eolian events. However, we consider as more likely that the loess was deposited during deglaciation, and quartz-grain signals have been partially reset during bioturbation. U-Pb ages on 273 zircon grains from the loess show prominent peaks at 1.6 and 1.8 Ga, as well as smaller numbers of grains from 1.0 to 1.6 Ga. These ages match dates from the Idefjord Terrane which comprises the bedrock of the study area. We argue that during ice-margin retreat, debris in the glacier was dominated by locally derived debris. This glacial sediment was left in thin patches uplands and particularly in large ice-marginal deltas. These deposits served as the proximal source for the loess. The presence of thin loess in Svartedalen suggests loess to be common in soils of southwest Sweden.

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.

Directional vector visualization of scattered rays in mobile c-arm fluoroscopy.

Previous radiation protection-measure studies for medical staff who perform X-ray fluoroscopy have employed simulations to investigate the use of protective plates and their shielding effectiveness. Incorporating directional information enables users to gain a clearer understanding of how to position protective plates effectively. Therefore, in this study, we propose the visualization of the directional vectors of scattered rays. X-ray fluoroscopy was performed; the particle and heavy-ion transport code system was used in Monte Carlo simulations to reproduce the behavior of scattered rays in an X-ray room by reproducing a C-arm X-ray fluoroscopy system. Using the calculated results of the scattered-ray behavior, the vectors of photons scattered from the phantom were visualized in three dimensions. A model of the physician was placed on the directional vectors and dose distribution maps to confirm the direction of the scattered rays toward the physician when the protective plate was in place. Simulation accuracy was confirmed by measuring the ambient dose equivalent and comparing the measured and calculated values (agreed within 10%). The directional vectors of the scattered rays radiated outward from the phantom, confirming a large amount of backscatter radiation. The use of a protective plate between the patient and the physician's head part increased the shielding effect, thereby enhancing radiation protection for the physicians compared to cases without the protective plate. The use of directional vectors and the surrounding dose-equivalent distribution of this method can elucidate the appropriate use of radiation protection plates.

Efficacy of the collapsed cone algorithm calculated radiotherapy plans in intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT): A comparative dosimetric study in tumors of thorax.

In this study, efficacy of collapsed cone algorithm-generated intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) were evaluated for treatment of thoracic esophageal cancer. Ten previously treated patients with VMAT were considered for evaluation. The planning parameters were evaluated in terms of max dose, mean dose, Homogeneity Index, Conformity Index for planning target volume, and organ at risk doses. Total monitor unit, treatment time, and gamma passing index were also reported. The target dose coverage of the VMAT and IMRT plans achieved the clinical dosimetric criteria for all ten patients in the evaluation. Under the condition of equivalent target dose distribution, the VMAT plan's Conformity Index, monitor unit, treatment time, and gamma passing index rate were superior than in the IMRT plan, and the result was statistically significant. Collapsed cone algorithm-based VMAT can have a more effective and better approach for esophageal cancer than IMRT.

IRSL and post-IR IRSL dating of multi-grains, single grains, and cobble surfaces to constrain fluvial responses to climate changes during the last glacial period in the Tokachi Plain, northern Japan

Accurate chronologies of fluvial terraces are necessary to understand fluvial responses to climate and sea-level changes and uplift. Although feldspar post-infrared infrared stimulated luminescence (post-IR IRSL, or pIRIR) dating has been used to establish chronologies for Pleistocene fluvial terraces, the signals can be partially bleached in short, high-gradient river systems typical of Japanese rivers, resulting in overestimated ages. This study investigated aggradational fluvial terraces formed on the Tokachi Plain, northern Japan, during the last glacial period, and true depositional ages of the deposits were estimated by comparing multi-grain IRSL50/150, pIRIR50/150, and pIRIR50/225 ages, with single-grain pIRIR50/225 ages. IRSL50/225 and pIRIR50/225 ages of granite cobbles were also obtained and compared with the ages of multi-grains to evaluate the reliability of cobble ages. Fading-corrected IRSL 50/150 ages of multi-grains were consistent with pIRIR50/150 ages, indicating that the fading correction of IRSL50/150 signal was successful. Although equivalent dose distributions of single grains suggest that the pIRIR50/225 signal was completely bleached at deposition, pIRIR50/225 ages were slightly older than fading-corrected IRSL 50/150 and pIRIR50/150 ages possibly because of small residual doses. Fading-corrected IRSL50/225 and fading-corrected pIRIR50/225 ages of granite cobbles were consistent with the fading-corrected IRSL50/150 and pIRIR50/150 ages of multi-grains. However, comparison of cobble ages with climate records seems difficult due to their large errors. The fading-corrected IRSL50/150 and pIRIR50/150 ages of multi-grains indicate that fluvial aggradation occurred at 70–60 ka, followed by incision. Changes in the strength of East Asian summer monsoon precipitation are sufficient to explain fluvial evolution in the Tokachi Plain. Although some previous studies have argued that the ages of fluvial terraces might not be simply correlated to climate changes because of complex fluvial responses, significant changes in precipitation in the study area might have dominated the evolution of the entire fluvial system. Comparison with other fluvial systems in Japan suggests that slight differences in the responses of different fluvial systems to climate changes might be due to the spatial variability of those changes.

Clinical Implementation of Weak Magnetic Field Generator in Radiation Therapy

The application of weak magnetic fields may improve radiation therapy efficacy by manipulating the free radical activity induced by radiation to optimize tumor death. Once the device is commercially available, we will conduct clinical trials to determine the clinical impact of the weak magnetic field. However, the magnetic field generator (MFG) restricts Linac gantry rotation to approximately 180° and this limitation may limit treatment plan quality. This work is a continuation of an ongoing study to determine if the gantry angle restrictions can be compensated for during treatment planning. Previous work has demonstrated the feasibility for GBM cases. For this work, 10 prostate cancer treatment plans were retrospectively replanned using only coplanar arcs that spanned from 90° to 270° (half-arcs). The prescriptions were 60 Gy for 6 patients, 55.8 Gy for 2 patients, 54 Gy for 1 patient, and 40.05 Gy for 1 patient. The prescription doses were delivered to 95% of the planning target volume (PTV = GTV + 2 cm). The critical structure doses were compared to determine if clinically equivalent plans could be delivered using half-arcs. The dose criteria that were met by the clinical plans were also met by the half-arc plans except for the cases shown in Table 1. Table 1: Doses that did not meet criteria CONCLUSION: The half-arc plans were able to deliver clinically equivalent dose distributions as the clinical treatment plans. This provides continuing evidence that clinical trials will be able to be developed to evaluate the use of weak magnetic fields for radiation therapy.

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.

Optical dating of sediments affected by post-depositional mixing: Modelling, synthesizing and implications

One of the biggest challenges in optically stimulated luminescence (OSL) dating is to deal with sediments that are affected by post-depositional mixing. Equivalent dose (De) distributions of such samples are commonly analysed using the finite mixture model (FMM), which can statistically identify dose components of grains derived from sedimentary layers with different ages. The FMM has been increasingly applied in OSL dating of sediments from key geological and archaeological sites that are critical for understanding the evolution of Quaternary environment and human history. The burial age of the dated layer is commonly determined by dividing the De value of the target dose component estimated using the FMM by the total dose rate of the bulk sample. However, a systematic investigation of the reliability of this method for different post-depositional mixing situations has not been conducted. This study aims to investigate the reliability of the burial ages so obtained, using simulated mixed single-grain De distributions. We assess the performances of two different protocols—a user-specified or an automatically estimated between-grain dispersion value, σb. A number of factors influencing the reliability of the determined burial age are investigated, including the inherent dispersion in different dose populations, the proportion of grains associated with the target layer, the sample size used, the difference in dose rates and burial ages between the mixing components, and the time when mixing occurred. Published single-grain samples affected by post-depositional mixing are synthesized and their FMM results are assessed. Our results show that the reliability of FMM is controlled by the analytical and the intrinsic errors and depends critically on the proportion of grains for the target layer. The simulation and synthesized results caution against using an arbitrarily specified σb as input for the FMM. The intrinsic accuracy of the burial age is controlled by multiple factors for both synchronously and asynchronously mixed samples. The FMM ages derived from sediment samples affected by serious post-depositional mixing should be constrained by independent chronological information.

Car-borne survey and dose assessment from external radiation exposure in Bangka Island.

With a history of more than 200years of tin mining, Bangka Island has brought along a byproduct of heavy minerals containing radionuclide elements. There are some concerns about this byproduct material contributing to natural radiation in the environment. In this study, a car-borne survey was conducted to accurately assess natural background radiation in Bangka Island. Indoor and outdoor ambient dose rates in 146 houses were also measured to assess the radiation dose from external exposure received by the public. Soil samples were collected and measured using a gamma spectroscopy system to evaluate the contributions of specific radionuclides to external terrestrial exposure. From 3790 measurement points during the car-borne survey, the highest ambient dose equivalent rate was 596 nSv h-1 measured in Muntok area, with a mean value of 101 nSv h-1 and a median value of 95 nSv h-1. The ambient dose equivalent rate distribution map showed a relatively higher value in the northern coastal area of the island, where the Pemali tin deposit is located. The annual effective dose received from external radiation in the 146 houses in Bangka Island ranged from 0.44 to 1.30mSvyear-1, with a median value of 0.66mSvyear-1. The soil contained a relatively high amount of thorium (232Th), which contributed 69% to external radiation exposure in Bangka Island.

Assessment of ambient dose equivalent rate distribution patterns in a forested-rugged terrain using field-measured and modeled dose equivalent rates

Measuring radioactivity in forested mountainous areas is challenging owing to the limited accessibility on foot and the canopy blocking of airborne survey signals. Meanwhile, the influence of multiple environmental factors on radioactivity, in particular on ambient dose equivalent rates (ADER) in a forested area, are not well understood. In this study, we surveyed the ADER using hand-held and backpack-type scintillators in a forest of deciduous and evergreen trees in Iitate Village, Fukushima Prefecture, Japan, on multiple dates. The village is located 35 km northwest of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP). The observations showed that, 7.5 years after the FNDPP accident, the ADER still exceeded the maximum permissible level (0.23 μSv h−1) of the Japanese standard limit. The ADERs were distributed unevenly in the forest, ranging from 1 μSv h−1 to 3.73 μSv h−1, with statistically significant variabilities among survey dates. The spatial variabilities of the ADER among the survey dates were depicted by semivariograms. The effects of the complex topography on the ADER were examined using multivariate adaptive regression splines against five selected topographic parameters. Although the topographic effect of individual parameters varied between survey dates, when all topographic parameters were considered, the model predictions yielded a positive correlation (R2 > 0.54). We discovered ground wetness as the source of ADER variations among survey dates based on climatic records. Additionally, we estimated the ADER from radiocesium concentrations in soil samples and checked their consistency with the measured ADER. It was found that about half of the ADER estimated from the soil samples were within the range of field measurements. Although challenges remain in the modeling of radioactivity pathways under natural conditions, this study shows that combining topographic features, meteorological factors, and near-ground and high-altitude surveys are the keys to understanding radiation behavior in the environment.

Dose assessment based on short-ranged computer simulation in a radioactive release event

This study describes the computational modeling of the atmospheric dispersion of radionuclides resulting from a hypothetical nuclear accident involving an off-site release of the inventory of a Small Modular Reactor (SMR). The inventory released was simulated with the aid of the SCALE software, considering 2 years of continuous operation. The radionuclide Cs-137 was selected due to its abilities to cause environmental damage. A simulation of the atmospheric dispersion of the radionuclide was performed using the codes HotSpot (analytical) and ANSYS (numerical). The distribution of concentrations and consequent equivalent total effective doses (TEDE) were estimated as a function of the distance from the point of release and the local atmospheric stability conditions. In the study, a hybrid computer simulation refers to the simultaneous application of the analytical and numerical models of the nuclear event. The results from the simulated conditions agree with the environmental Cs-137 concentration values, regardless of whether those values are from a numerical or analytical model. However, there is a disagreement about the location and distribution of these concentrations. It was also verified that the average percentage error of the results obtained in the two simulations was around 5%, considering the evaluation between 400 and 1500 m from the origin of the dispersion. For smaller distances in relation to the release point, the analytical and numerical models produce solutions that, although divergent, were shown to be complementary. The relevance of this investigation shows the importance of the convergence of isolated computing platforms in order to support decision-making.

A Novel Approach to Quantify Sediment Transfer and Storage in Rivers—Testing Feldspar Single‐Grain pIRIR Analysis and Numerical Simulations

AbstractQuantifying sediment transport and storage in fluvial systems is fundamental for understanding the transfer of eroded materials from source to sink. Here, we investigated the potential of a combined approach using a luminescence measured in modern fluvial sediments and numerical simulations to quantify transport and storage in rivers. We acquired luminescence data at the single‐grain scale on feldspar sediments of Waimakariri and Rakaia braided rivers (New Zealand) using a post infra‐red infra‐red stimulated luminescence protocol. We considered three metrics from the analysis of luminescence equivalent dose (De) distribution: the percentage of bleached and the percentage of saturated grains, and the meanDe. All three metrics show similar longitudinal trends along both rivers. To derive quantitative information on sediment transfer from these data, we developed a numerical model that simulates the longitudinal evolution ofDedistribution of a population of grains during transport and storage in floodplains. The model considers four main parameters: the transport length of grains during floods, their resting time between successive transport events, the bleaching probability (probability of the luminescence signal to be reset due to sunlight exposure during transport or rest), and the likelihood of partial bleaching. Identification of model parameters that best reproduce natural observations allowed estimating transit time of sediments between 2.1 and 10.3 Kyr (mean of 6.9 2.9 Kyr), corresponding to mean virtual transit velocity of 20–95 m.yr−1(mean of 46 28 m.yr−1). Our study illustrates the potential of the combined single‐grain luminescence and modeling approach to quantify sediment transfer in fluvial systems.

The Effect of Stereotactic Body Radiation Therapy for Hepatocellular Cancer on Regional Hepatic Liver Function

To investigate direct radiation dose-related and inflammation-mediated regional hepatic function losses after stereotactic body radiation therapy (SBRT) in patients with hepatocellular carcinoma (HCC) and poor liver function. Twenty-four patients with HCC enrolled on an IRB-approved adaptive SBRT trial had liver dynamic gadoxetic acid-enhanced magnetic resonance imaging and blood sample collections before and 1 month after SBRT. Gadoxetic acid uptake rate (k1) maps were quantified for regional hepatic function and coregistered to both 2-Gy equivalent dose and physical dose distributions. Regional k1 loss patterns from before to after SBRT were analyzed for effects of dose and patient using a mixed-effects model and logistic function and were associated with pretherapy liver-function albumin-bilirubin scores. Plasma levels of tumor necrosis factor α receptor 1 (TNFR1), an inflammation marker, were correlated with mean k1 losses in the lowest dose regions by Spearman rank correlation. The whole group had a k1 loss rate of 0.4%/Gy (2-Gy equivalent dose); however, there was a significant random effect of patient in the mixed-effect model (P < .05). Patients with poor and good liver functions lost 50% of k1 values at 12.5 and 57.2 Gy and 33% and 16% of k1 values at the lowest dose regions (<5 Gy), respectively. The k1 losses at the lowest dose regions of individual patients were significantly correlated with their TNFR1 levels after SBRT (P < .02). The findings suggest that regional hepatic function losses after SBRT in patients with HCC include both direct radiation dose-dependent and inflammation-mediated effects, which could influence how to manage these patients to preserve their liver function after SBRT.

Testing the potential of using coarse-grain feldspars for post-IR IRSL dating of calcium sulphate-wedge growth in the Atacama Desert

The growth of vertically laminated calcium-sulphate wedges in the Atacama Desert is assumed to be driven by the interaction of moisture supply and salt dynamics in the subsurface. Geochronological data of these wedge laminations is yet sparse but indispensable to resolve wedge-growth phases and episodes of moisture supply and to use these deposits as a palaeoclimate archive in the hyperarid environment. Our pilot study presents a first approach of dating a calcium-sulphate wedge from the Atacama Desert using coarse-grain feldspar luminescence dating. Our results show a widespread and clustered equivalent-dose distribution of two wedge samples from ∼20 Gy up to saturation. Optically stimulated luminescence (OSL) of quartz revealed unsuitable properties for dating wedge deposits. Consequently, we applied post-infrared infrared stimulated luminescence (post-IR IRSL) to coarse-grained feldspars. Since feldspar single-grain measurements yielded a low number of luminescent grains, we used 1 mm aliquots as reliable single-grain proxies for genuine single-grain measurements. Data from energy-dispersive x-ray spectroscopy (EDX) showed that the feldspar single grains have large differences in their internal K content, resulting in an averaged internal K content of 3.9 ± 1.0 % for all luminescent grains. This result was subsequently used for dose rate and age calculations. Our results of equivalent-dose distributions and palaeodoses derived from the minimum age model reveal most recent wedge-growth activities at 10.6 ± 2.2 ka and 7.9 ± 1.8 ka for the two wedge samples.

Luminescence age calculation through Bayesian convolution of equivalent dose and dose-rate distributions: the De_Dr model

Abstract. In nature, each mineral grain (quartz or feldspar) receives a dose rate (Dr) specific to its environment. The dose-rate distribution therefore reflects the micro-dosimetric context of grains of similar size. If all the grains were well bleached at deposition, this distribution is assumed to correspond, within uncertainties, with the distribution of equivalent doses (De). The combination of the De and Dr distributions in the De_Dr model proposed here would then allow calculation of the true depositional age. If grains whose De values are not representative of this age (hereafter called “outliers”) are present in the De distribution, this model allows them to be identified before the age is calculated, enabling their exclusion. As the De_Dr approach relies only on the Dr distribution to describe the De distribution, the model avoids any assumption about the shape of the De distribution, which can be difficult to justify. Herein, we outline the mathematical concepts of the De_Dr approach (more details are given in Galharret et al., 2021) and the exploitation of this Bayesian modelling based on an R code available in the R package “Luminescence”. We also present a series of tests using simulated Dr and De distributions with and without outliers and show that the De_Dr approach can be an alternative to available models for interpreting De distributions.

Illuminating past river incision, sediment source and pathways using luminescence signals of individual feldspar grains (Rangitikei River, New Zealand)

AbstractSingle‐grain post‐infrared infrared stimulated luminescence (SG‐pIRIR) of feldspar has recently been introduced as a method to date Quaternary deposits. The method is particularly appropriate for fluvial deposits that cannot be dated by more conventional quartz optically stimulated luminescence dating and that are heterogeneously bleached (i.e. where only part of the grains is exposed to sufficient light to remove the full luminescence signal). Besides age estimation, single grain equivalent dose (De) distributions also reflect the variable bleaching degree and origins of grains. Thereby, the SG‐pIRIR signal offers a valuable tool to reconstruct sediment pathways. This study builds upon these ideas and develops a dual aspect that combined river terrace dating and SG‐pIRIR sediment pathway reconstruction for fluvial deposits in terraces and modern river floodplain along the Rangitikei River (RR), New Zealand. We found that the RR last aggrading phase (17.4 ± 1.9 ka to 11.6 ± 1.5 ka) was followed by a first phase of fast incision related to knickpoint retreat followed by a steady incision and widening of the RR canyon. TheDedistribution of fluvial deposits varies accordingly, due in particular to variable input of bedrock particles with saturated pIRIR signal from landsliding of valley flanks. Our study illustrates that the SG‐pIRIR approach is well suited to date terraces and shows how SG‐pIRIRDedistributions provide proxies to reconstruct sediment sources and pathways.

Whole-body photoneutron 360° angular distribution dosimetry by novel “Sohrabi neutron dosimetry methods”

PurposeWhole-body photoneutron (PN) energy-specific dosimetry on phantom surfaces and 360°angular fast PN distribution dosimetry on and around polyethylene (PE) phantom organs for prostate cancer in 10 cm × 10 cm and 20 cm × 20 cm field sizes of 18 MV X-rays of Varian Clinac 2100C linear accelerator. MethodsNovel “Sohrabi neutron dosimetry methods” including “miniature passive neutron dosimeter/spectrometer” and “strip polycarbonate neutron dosimeters” were applied. Energy-specific PN dose equivalents on surface as well as 360°fast PN dose equivalent angular distributions on and around PE phantom organs; head, neck, thorax, arms, pelvis, thighs and legs were determined. ResultsMatrix of surface (skin) energy-specific PN dose equivalents including total thermal, total epithermal, total fast, sum total thermal + epithermal and sum total thermal + epithermal + fast, and 360°angular fast PN dose equivalent responses were determined. The results indicate that data matrix of 20 cm × 20 cm field size provides higher PN dose equivalent values than those of 10 cm × 10 cm field size for surface points even remote from the central axis and for all 360°angular fast PN dose equivalent distributions on organs studied. ConclusionsMatrix of energy-specific PN dose equivalents was obtained demonstrating that the Sohrabi neutron dosimetry methods applied are unique for energy-specific PN dose equivalent studies as well as for 360°angular PN dose equivalent distribution data for PN-SPC risk estimation. The dosimetry methods can be specifically applied to many other exotic applications in health physics, medical physics, space flight dosimetry, and nuclear science and technology.

Bayesian analysis of De distributions in optical dating: Towards a robust method for dealing with outliers

In optical dating, especially single-grain dating, various patterns of distributions in equivalent dose (D e ) are usually observed and analysed using different statistical models. None of these methods, however, is designed to deal with outliers that do not form part of the population of grains associated with the event of interest (the ‘target population’), despite outliers being commonly present in single-grain D e distributions. In this paper, we present a Bayesian method for detecting D e outliers and making allowance for them when estimating the D e value of the target population. We test this so-called Bayesian outlier model (BOM) using data sets obtained for individual grains of quartz from sediments deposited in a variety of settings, and in simulations. We find that the BOM is suitable for single-grain D e distributions containing outliers that, for a variety of reasons, do not form part of the target population. For example, D e outliers may be associated with grains that have undesirable luminescence properties (e.g., thermal instability, high rates of anomalous fading) or with contaminant grains incorporated into a sample when collected in the field or prepared in the laboratory. Grains that have much larger or smaller D e values than the target population, due to factors such as insufficient bleaching, beta-dose heterogeneity or post-depositional disturbance, may also be identified as outliers using the BOM, enabling these values to be weighted appropriately for final D e and age determination. • A Bayesian outlier model (BOM) for luminescence dating of sediments. • Outliers are identified in single-grain equivalent dose (D e ) distributions. • Outliers are weighted appropriately for final D e and age determination. • Three special cases (BOM central, minimum and maximum) for different contexts. • Tested on well-bleached, partially bleached and post-depositionally mixed samples.