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At least 217 records · Page 12
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DOE OSTI2024

Comprehensive Study of Carrier Recombination in High‐Efficiency CdTe Solar Cells Using Transient Photovoltage

Cadmium telluride (CdTe) solar cells represent a commercially successful photovoltaic technology, with an annual production capacity approaching 20 GW. However, improving the open-circuit voltage (V OC ) remains challenging. This study aims to deepen the understanding of charge carrier recombination in CdTe solar cells and to explore alternative dynamical characterization methods that address the limitations found in conventionally used time-resolved photoluminescence for CdTe solar cells. Transient photovoltage and transient photocurrent techniques are utilized to investigate charge carrier dynamics under conditions resembling real-world solar cell operation. The results reveal that an effective nonradiative recombination lifetime of 580 ns dominates the charge dynamics at VOC values below 850 mV. Above this threshold, radiative recombination becomes significant, with a radiative recombination coefficient of 1.1 × 10 −9 cm 3 s −1 . Additionally, the stationary charge carrier density at 1 sun is determined to be around 1 × 10 14 cm −3 . By accurately determining both radiative and nonradiative recombination, this work provides a comprehensive understanding of carrier dynamics in high-performing CdTe devices and paves the way for improving the V OC and performance of CdTe solar cells.

CdTe solar cells↗
DOE OSTI2022

Environmental Benefits of Closing the Solar Manufacturing and Recycling Loop: Preparation of Solar Manufacturing Inventories

The cumulative global solar panel waste stream is projected to reach between 60 and 78 million tonnes by 2050. Steps towards developing, demonstrating, and implementing processes that recover glass, metals, and semiconductor materials from end-of-life solar panels have already been taken. However, these processes result in the downcycling of most secondary solar materials. Critically, the costs and benefits of capturing these secondary materials for use in new solar panels are unknown. To evaluate the environmental benefit associated with solar material recycling and reuse in next generation panels, prior inventories must be updated and prepared for integration with recycling processes to examine the benefit of closing the material loop between solar panel end-of-life and new panel manufacturing. This current work describes steps taken to upgrade existing inventories that detail the manufacturing of cadmium-telluride (CdTe) panels from the Ecoinvent -v2.2 life cycle inventory database to Ecoinvent -v3. During this update, material inventories were modified to capture different realistic material supply chains within the constraints of Ecoinvent -v3. Materials discussed in detail in this work include primary flat glass, aluminum, steel, copper, and CdTe. This work demonstrated that environmental indicators such as embodied carbon, acidification, and terrestrial eutrophication associated with solar panel production can be reduced by 25% to over 40% through improved primary material sourcing.

CdTe solar panels↗
DOE OSTI2024

Role of Selenium in CdZnTeSe as a Defect Engineering Agent

Cadmium zinc telluride (CdZnTe) with 10 atomic % Zn has been the material of choice for room-temperature semiconductor compact X- and gamma-ray detector applications for over three decades. Despite its commercial success as the most desirable room-temperature semiconductor radiation detection material, CdZnTe (CZT) suffers from a lack of compositional homogeneity on both the micro- and macroscales and the presence of high concentrations of performance-limiting defects such as subgrain boundary networks (dislocation walls) and secondary phases (Te-rich inclusions). Random distributions of these defects in the CZT matrix result in the spatial inhomogeneity of the material’s charge-transport properties. The recently discovered quaternary Cd x Zn 1-x Te 1-y Se y (CZTS) has experienced remarkable advances in its material properties, with highly reduced defects and higher compositional homogeneity. This book chapter focuses on the presence of performance-limiting defects in CZT that have thus far hindered the yield and cost of high-quality detectors and restricted their widespread deployment for a variety of potential applications, particularly for their use as large-volume gamma detectors, where the demands on material perfection are significantly greater. This chapter also provides an overview of the recent developments in the quaternary material CZTS, particularly the effects of selenium (Se) in the CZTS matrix on the defect engineering of the quaternary alloy material and the advancement of CZTS as a potential next-generation detector operable at room temperature.

Roy, Utpal N.↗
DOE OSTI2024

Structural and Electronic Properties of Indium-Doped n-type Cd-Se-Te Crystals

Here, we present a comprehensive investigation into the potential of n-type indium-doped cadmium selenide telluride (CST:In) as a high-performance candidate for solar cell applications, without the need for resource-intensive post-growth treatments that are required for CdTe:In. We compared undoped CST and CST:In crystals under different growth conditions, analyzing their structural and electronic properties using x-ray diffraction (XRD), electron probe microanalysis (EPMA), current-voltage (IV) and Hall effect measurements, time-resolved photoluminescence (TRPL), optical transmission, and photoluminescence (PL) mapping. The results reveal that as-grown CST:In crystals achieve nearly 100% carrier activation, yielding an electron concentration of 9.5x1018 cm -3 , mobility of 653 cm 2 /V.s and a 5 ns lifetime which approaches the radiative limit. Furthermore, comparison of PL maps from crystal growths having different cooling profiles suggests a strong effect of cooling rate on selenium segregation and cubic/hexagonal/polytype phase distribution. Slower cooling leads to a more homogeneous cubic structure with lower Se segregation, while a faster cooling rate results in increased Se segregation, and twin boundaries and stacking faults with polytypic and hexagonal character.

14 SOLAR ENERGY↗
DOE OSTI2023

On silica's roles in controlling americium migration in contaminated sediments

Two studies in the early 1980s described the leaching behavior of americium (Am) disposed as part of acidic high-salt processing wastes from the Hanford Site’s Plutonium Finishing Plant to nearby ground sediments. Here these batch leach experiments showed that the Am concentrations followed a linear log [Am] versus pH relationship with a slope of –1. Column leach experiments in the second study, however, did not follow this relationship and only ~30% of the americium desorbed even after extensive column leaching. Here, the 1980s research is re-examined along with previously unpublished information and, in light of recent published work, a plausible mechanism is proposed to explain these phenomena. Amorphous silica in the contaminated sediments is postulated to be the substrate responsible for both the exchangeable Am available for leaching and the retained low-leachable Am made evident in the column leach experiments. The exchangeable Am 3+ in the contaminated sediment leach experiments behaves with pH dependence similar to that observed for uptake onto amorphous silica of sodium (Na + ), calcium (Ca 2+ ), barium (Ba 2+ ), cadmium (Cd 2+ ), uranyl (UO 2 2+ ), ferric (Fe 3+ ), chromic (Cr 3+ ), cupric (Cu 2+ ), plumbous (Pb 2+ ), uranium(IV) (U 4+ ), plutonium(IV) (Pu 4+ ), zirconium (Zr 4+ ), analogue lanthanide (gadolinium, Gd 3+ , europium, Eu 3+ , and lutetium, Lu 3+ ) and curium (Cm 3+ ) ions as well as other studies with Am 3+ . Correspondingly, the residual low-leachable Am 3+ revealed in the column leach experiments is attributed to incorporation of Am 3+ within amorphous silica by dynamic Am 3+ sorption and silica precipitation processes.

58 GEOSCIENCES↗
DOE OSTI2021

Nuclear data for reactor production of 131 Ba and 133 Ba

The newest radioisotope for brachytherapy treatment of prostate cancer is 131 Cs (t 1/2 = 9.69 d, 100% EC). Generated via electron capture decay of 131 Ba (t 1/2 = 11.6 d, 100% EC), 131 Cs has been used in brachytherapy for prostate cancer since 2004. The 131 Ba parent is produced through neutron capture of enriched 130 Ba in a nuclear reactor. For large-scale production of 131 Ba, an accurate knowledge of production and burnup cross sections of 131 Ba are essential. Here, we report two group cross sections (thermal and resonance integrals) for 130 Ba and 131 Ba and a new measure of the half-life of 131 Ba. Targets consisting of milligram quantities of enriched 130Ba (~35%) were irradiated in Oak Ridge National Laboratory's High Flux Isotope Reactor at thermal and resonance neutron fluxes of (1.9–2.1) × 10 15 and (5.8–7.0) × 10 13 neutrons·cm -2 s -1 , respectively, for durations ranging from 3 to 26 days. In addition, cadmium covered samples of 130 Ba were irradiated for 1 hour at 12.6% full reactor power (10.7 MW). The yield of 131 Ba approaches a saturation value of ~60 GBq (~1.6 Ci) per mg of 130 Ba for 20 days irradiation at a thermal neutron flux of 1.8 × 10 15 n·s -1 ·cm -2 , with a thermal/epithermal ratio of ~30. Under the above experimental conditions, the two group cross sections of 130 Ba are 6.9 ± 0.5 b (thermal, σ 0 ) and 173 ± 7 b (resonance, I 0 ). These values represent the sum of cross sections to metastable and ground states of 131 Ba. For 131 Ba, the empirically measured thermal cross section is 200 ± 50 b assuming an I 0 /σ 0 of 10. This cross section is reported for the first time. Further, the half-life of 131 Ba was remeasured to be 11.657 ± 0.008 d. Lastly, this study also resulted in the co-production of 133 Ba (t 1/2 = 10.52 y, 100% EC). The experimental yield of 133 Ba is ~370 MBq (~10 mCi) per mg of 132 Ba (thin target) for one cycle irradiation in the High Flux Isotope Reactor, and measured two-group 132 Ba cross sections are 7.2 ± 0.2 b and 39.9 ± 1.3 b. These values also represent the sum of cross sections to metastable and ground states of 133 Ba.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2025

LABQ3: Bayesian method for quantification of mineral compositions and nano-scale elemental mapping of 3D synchrotron XCT data

Quantitative analysis of mineral compositions is essential in understanding geochemical, mineralogical and environmental processes. Fine-resolution 3D imaging is widely done using synchrotron X-ray computed tomography (XCT), but existing analyses are limited to visualization and segmentation. This paper presents a new method, Linear Attenuation Bayesian Quantitative 3D-mapper (LABQ3), based on the linearity of X-ray attenuation with respect to elemental concentrations. To address the random variability in attenuation measurements, LABQ3 employs Bayesian decision theory to minimize classification error, using reference attenuation distributions from scans of pure mineral standards. To demonstrate LABQ3 and test its performance, we studied precipitated carbonate samples. XCT scans were done at multiple energies using the transmission X-ray microscope (TXM) at beamline 32-ID-C of the Advanced Photon Source at Argonne National Laboratory. The reconstructed 3D images have a voxel size of 20 nm. Analyses revealed rich nano-scale compositional heterogeneity within individual particles. A mixture of calcium and cadmium produced an overall stoichiometric composition of (Ca 0.78 ,Cd 0.22 )CO 3 , with some voxels containing nearly pure CdCO 3 . The addition of zinc led to an overall stoichiometric composition of 33% Ca, 28% Cd, 39% Zn, with a nearly pure CaCO 3 core and compositional zonation through the rim. These compositional gradients are related to temporal sequences of carbonate mineral formation where Cd precipitated at the beginning in (Ca,Cd)CO 3 , while Cd and Zn precipitated at the end in (Ca, Cd,Zn)CO 3 . Results differ from bulk analyses using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), showing that LABQ3 provides particle-specific insights. LABQ3 distinguishes itself by quantifying chemical compositions along a continuum, making it different from XCT analyses based on segmentation. LABQ3 allows simultaneous acquisition of morphology and chemical composition in 3D, facilitating the interpretation of chemical gradients of trace elements, quantification of solid solution compositions, inferences about temporal sequences of mineral precipitation, and addressing other concerns about solid-phase chemistry.

58 GEOSCIENCES↗
DOE OSTI2021

Application of spectroscopic evidence to diffuse layer model (DLM) parameter estimation for cation adsorption onto ferrihydrite in single- and bi-solute systems

The diffuse layer model (DLM) is one of the most frequently used surface complexation models (SCM) for predicting cation adsorption onto ferrihydrite. However, the DLM with its existing database sometimes fails to predict cation adsorption, especially in multi-solute systems. Notably, the failure is often attributed to inaccurate selection of the surface complexes and/or underestimation of the site density for DLM formulation. DLM simulations of batch adsorption data conducted with cadmium, copper, lead, and zinc on ferrihydrite in CO2 free systems demonstrates the ability of the DLM to fit single-solute data reasonably well but highlights its limitations with respect to predicting bi-solute data. Modifications to the DLM were made in two steps. First, spectroscopic evidence was used to guide cation complexation reactions at the ferrihydrite surface. Second, surface characteristics (reactive site density, specific surface area, and acidity constants) of ferrihydrite were updated according to recent literature. The results from this study suggest that when spectroscopic verification is employed and surface site density is increased, a simple two-site DLM can predict cation adsorption on ferrihydrite in single-solute systems for pH data above 3.5 and in most of the bi-solute systems tested.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Impact of soiling on Si and CdTe PV modules: Case study in different Brazil climate zones

Soiling, particulate accumulation on photovoltaic (PV) module surfaces, reduces the available solar resource and the resulting generated device power. This case-study summarizes initial results of 5-year research on the contrasting soiling conditions in the tropical, subtropical, and semi-arid climates in Brazil. A major objective is to present a case study of the effects of soiling on PV module performance in different Brazil climate zones that represent the primary areas for the current and expanding Brazil solar installations. For this, the paper presents methodologies to quantify the soiling ratio (SRatio) and soiling rate (SRate) for two representative commercial technologies, polycrystalline or multicrystalline silicon (mc-Si) and thin-film cadmium telluride (CdTe) modules, through soiling monitoring stations deployed in the selected climate regions. An aim is to add to the growing soiling-research knowledge base through addressing these key factors and their relationships to critical electrical, solar resource, thermal, and local meteorological and environmental parameters. This paper presents, evaluates, and compares soiling rates and losses in Belo Horizonte, Minas Gerais (Equatorial Tropical: 19.92° S, 43.99° W), Porto Alegre, Rio Grande do Sul (Humid-Subtropical: 30.05° S, 51.17° W), and Brotas de Macaúbas, Bahia (Semi-Arid: 12.00° S, 42.63° W). The results show that soiling is moderate in all 3-regions, for example with 0.1%/day < SRate < 0.2%/day for Belo Horizonte. Precipitation dominates the cleaning of the modules in the summertime in this climate zone, while it is the major factor year-round in Rio Grande do Sul. Wind is the major issue mitigating the soiling accumulation for the Bahia installation. The methodology incorporates several key refinements, including the normalization and adjustment for the meteorological parameters (temperature, irradiance, wind, precipitation). The evaluations include the region-specific differing effects of non-uniform soiling, natural cleaning, and ambient temperatures.

14 SOLAR ENERGY↗
DOE OSTI2022

Morphological and crystallographic controls in the replacement of calcite and aragonite by cerussite and otavite

Mineral replacement reactions are essential solid-fluid interactions in natural and industrial processes including metasomatism, diagenesis, and metamorphism, and sequestration of metal toxins from polluted water. In this paper, we explore the morphological evolution of aragonite and calcite (polymorphs of CaCO 3 ) during their replacement by cerussite (PbCO 3 , an isomorph of aragonite) and otavite (CdCO 3 , an isomorph of calcite) in acidic aqueous solutions (with initial pH 3 to 4). Observations using scanning electron and synchrotron-based transmission X-ray microscopies reveal the formation of pseudomorphic shells (~5 to 10 µm thick) of cerussite and otavite when Pb 2+ is reacted with either calcite or aragonite and when Cd 2+ is reacted with aragonite. The formation of pore space at the substrate-precipitate interface and within the precipitate is found to be key in promoting chemical exchange between the dissolving phase and the solution. In contrast, minimal reactivity is observed when Cd 2+ is reacted with calcite. These results demonstrate that the lack of substrate-precipitate epitaxy (either because of inconsistent symmetries or due to large lattice constant mismatch) is a critical factor that enables replacement of primary CaCO 3 minerals by Pb- or Cd-bearing secondary minerals while the presence of epitaxial relationships inhibit those reactions. When calcite and aragonite coexist, the replacement of aragonite by cerussite and otavite occurs preferentially over calcite. We postulate that the relative reactivity of calcite and aragonite to Pb 2+ and Cd 2+ can be determined by interplay between morphological and crystallographic properties of CaCO 3 materials as well as solution chemistry. Our results demonstrate that coupled dissolution-precipitation processes of carbonate minerals play an important role in controlling mobility and bioavailability of lead and cadmium in environments where acidic metal-contaminated water interacts with carbonate-rich rocks and soils.

58 GEOSCIENCES↗
DOE OSTI2021

The effects of ACRT on melt undercooling during the growth of CZT via the traveling heater method: Ekman versus Taylor-Görtler flows

For the first time, a comprehensive model for the traveling heater method, including detailed species transport and phase-change thermodynamics, is applied to understand the effects of accelerated crucible rotation (ACRT) on the growth of cadmium zinc telluride. Here, a rotation schedule that is designed from classical considerations does not completely mix the melt, rather undercooled regions of localized melt are swept periodically across the growth interface. Even without melt homogenization, these ACRT-driven flows disrupt the persistent undercooling that occurs during THM growth without rotation. An ACRT schedule designed to promote Ekman flows results in lower levels of melt undercooling than a schedule designed to promote Taylor-Görtler flows and greater mixing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Stability-based optimization of ACRT for the growth of CZT by the traveling heater method

Numerical modeling is employed to study the effects of several accelerated crucible rotation technique (ACRT) rotation schedules on the growth of cadmium zinc telluride (CZT) by the traveling heater method (THM). In conjunction with these analyses, a measure is developed to estimate the amplitude of disturbances associated with cellular interface growth morphologies that develop over time and across the melt-solid interface. Furthermore, this disturbance amplitude measure is used to assess the ability of ACRT to stabilize the growth interface and thereby minimize inclusion formation processes. Notably, our analyses reveal that interfacial instability is not well correlated with melt undercooling, explaining why classical ACRT approaches to reduce undercooling by mixing may not stabilize growth. Computations show that interface stability is best achieved via rotation schedules that accentuate outward Ekman flows during spin-up and, during spin-down, eliminate Taylor-Görtler flows and minimize inward Ekman flows.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A combined management scheme to simultaneously mitigate As and Cd concentrations in rice cultivated in contaminated paddy soil

Paddy soils in southern China are heavily co-polluted by arsenic (As) and cadmium (Cd). The accumulation of these contaminants in rice grains may pose a high health risk. We evaluated the impact of adjusted water management practice (i.e., conventional irrigation and aerobic treatment after heading stage) and the application of two immobilization agents (i.e., CaO and Fe2O3) on the accumulation of As and Cd in rice grains of three rice varieties (i.e., Jinyou-463, Jinyou-268, and Mabayouzhan). The different schemes were tested via conducting a field experiment in paddy soil in Shaoguan, Guangdong Province, China. The results showed that the combined scheme (selecting Jinyou-268, aerobic water management after the heading stage, and 0.09% CaO and 0.5% Fe2O3 amendments) exhibited the best performance in the reduction of As and Cd accumulation in rice grains. This combined scheme decreased the grain As concentration by 26.19% and maintained the Cd at a low level (0.056 mg/kg) as compared to the use of local conventional irrigation patterns. Moreover, health risk assessment demonstrated that by applying the optimal scheme, neither As nor Cd content in rice had carcinogenic risk. However, the grain As remains at a high non-carcinogenic risk. We suggest that future field study design should fully incorporate the uncertainty of the natural environment to make the research conclusions more feasible for popularization and utilization. This study demonstrated an approach of utilizing the synergy effects of various measures for safe rice production in fields subjected to As and Cd contaminations.

Yang, Xiao↗
DOE OSTI2020

Irradiation performance of nonfertile (Pu-MA-Zr) fast reactor metal fuels

This work was part of a program begun in 2001 to develop advanced nuclear fuels, originally as carriers for plutonium and minor actinides (neptunium, curium, and americium) taken from spent commercial light-water reactors (LWR) so that the plutonium and minor actinides could be ‘burned’ or transmuted in an accelerator or a fast nuclear reactor. A central part of these experiment programs has been the development of advanced fast reactor fuels, because a fast reactor was considered the most efficient vehicle to transmute the actinide waste products, and metallic fuels is a central focus of these tests. An experiment design was developed in which a thermal test reactor, the Advanced Test Reactor (ATR), was used to test small fuel pin prototypes, by creating areas in the core shielded by cadmium filters to produce a largely epithermal and fast neutron spectrum environment in which the pins could be irradiated. The results of non-fertile metallic fuel (no uranium) tests are presented here. Pu-Am-Np-Zr fuels were irradiated to fission densities up to 33 × 10 20 fission/cm 3 and Pu-239 depletions of up to 39%. The depletions were created by roughly 2/3 by fission and 1/3 by transmutation neutron capture. Up to five fuel ‘rodlets’ were irradiated in three sealed capsules stacked axially in the core, and the peak cladding temperatures ranged from 300°C to 500°C, depending on axial location as those near the core centerline are operating hotter and to higher fission densities. Several post-irradiation examinations (precision gamma scanning and fission gas release) were similar to other historical metal fuel experiments in fast reactors. However, optical metallography indicated that two of the rodlets had breached. The exact reasons are unclear. Due to the design of this irradiation experiment a rodlet breach could have increased the temperature in others in the same capsule by contaminating the thermal gap helium with heavier and less conductive fission product gases. Finally, some of those rodlets showed high amounts of fuel/cladding chemical interaction (FCCI).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Testing fast reactor fuels in a thermal reactor: Comparison of transmutation metallic fuel alloys behavior by scanning electron microscopy

To optimize nuclear waste repository performance, the destruction of minor actinide elements, particularly Np and Am, in a neutron fast spectrum reactor is possible by incorporating these elements into nuclear fuel. Evaluating the performance of minor actinide containing fuel is of paramount importance to enabling this technology. However, such a task is challenging without an available domestic fast spectrum test reactor. A comparison of fuel performance tested in an available domestic thermal reactor at the Idaho National Laboratory, the Advanced Test Reactor, and in a fast spectrum reactor in France (Phénix) is presented here in this study. This study evaluates the capability of using a cadmium shrouded test position to mimic the power profile along the fuel radius present in fast spectrum reactors so that thermally driven phenomenon (e.g., constituent redistribution) can be evaluated in a thermal reactor and determined to be prototypical of a fast reactor. Thus, optical microscopy and scanning electron microscopy has been performed on irradiated 35U-29Pu-4Am-2Np-30Zr fuel samples (where the number preceding the element is the weight percent concentration) from the two mentioned reactors that present similar irradiation temperatures and power conditions. The results indicate that fuel performance phenomena are reproducible in the two irradiation conditions. The redistribution of Zr occurred in the same manner for the two samples. Similar partitioning of U-Pu-Zr phases was observed, and the behavior of Am was similar in the analyzed specimens. Finally, the overall microstructure evolution seems not to be affected by minor actinides addition compared to expected behavior of conventional U-19Pu-10Zr ternary metal fuels for both specimens. Slight differences in fuel cladding chemical interaction were, however, observed. This difference is likely driven by difference in cladding composition rather than irradiation conditions.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Photometric sensing of heavy metal ions using a naphthoquinodimethyl- bis -thioamide dye: Selectivity & photophysics of the metal organic complexes

As Mother Nature is experiencing catastrophic environmental pollutions from both natural sources and anthropogenic activities, many scientists have been working around the clock to develop environmentally benign and cost-effective, yet sensitive, detection techniques for pollutants, especially heavy metal species (e.g. lead, cadmium, mercury, among others) that are deleterious to human health. Herein, we report a novel sulfur-containing small organic dye/sensor naphthoquinodimethyl-bis-thioamide (QDM), which was found to be particularly selective toward mercury ion (Hg 2+ ). Using a combination of UV-vis absorption, photoluminescence, and time-resolved pump-probe techniques, we established that QDM and Hg 2+ can form stable complex(es) due to the strong affinity of sulfur toward mercury. In this investigation, while a higher ratio of QDM:Hg 2+ was necessary to fully quench the fluorescence emission of QDM, only 1 equiv of the Hg 2+ ion was necessary to observe the sensing effect on the excited state photo-behavior(s) of QDM. Furthermore, the present results highlight a synergy between molecular sensors' selectivity/sensitivity and sensor-analytes dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Radiation hardness characterization of LKH-5 scintillating glass

Radiation hardness is an important property to examine in scintillators to help determine their expected lifetime in application cases where significant radiation dose is expected. Industrial imaging systems using 9 MV linear accelerators for x-ray radiography are one such application where significant radiation doses are expected to the scintillators used. Cadmium tungstate scintillators (CWO) and Thallium doped Cesium Iodide scintillators (CsI(Tl)) are used in some high energy cargo x-ray radiography systems. However, CWO has a high manufacturing cost for adequately uniform crystals and CsI(Tl) does not have sufficient radiation hardness. LKH-5 glass is being investigated as a potential low cost replacement for CWO and CsI(Tl). In this experiment 36 samples of a terbium doped silicate glass called LKH-5 were irradiated at doses up to 5 MRad using a 9 MV linear accelerator, and the change in their transmission properties was observed. Additionally, the glass was discovered to be a radiation hard glass due to the relatively small change in the transmission of the glass: less than 3% per cm at its emission peak of 550 nm and 5 MRad. This is similar to CWO which has a reported reduction in transmitted light of 2% per cm at 5 MRad and the emission peak of 475 nm and better than CsI(Tl) which is reported to have a reduction in transmitted light of 5% per cm at the emission peak of 550 nm and 4.2 MRad dose. Furthermore, an annealing procedure is described that returned the transmission of the glass to pre-irradiation values.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Performance characterization of the Radionuclide Aerosol Sampler/Analyzer air sampler during a high-activity release event

The performance of the Radionuclide Aerosol Sampler/Analyzer (RASA) under high-activity conditions has been evaluated to maintain and protect the operations of International Monitoring System (IMS) radionuclide stations. Station measurements following the Fukushima Daichi accident of 11 March 2011 have been combined with laboratory measurements to understand how the quality of the measurements made using the RASA High-Purity Germanium (HPGe) gamma-spectrometer are impacted by increased sample activity and detector dead-time. Detector saturation has been identified to occur at a count rate of 175,000 counts s-1, at which level there are significant impacts to the sample live-time and detector resolution in addition to a system contamination risk. To safeguard against these effects, a dead-time limit of 16.6% is proposed that could be maintained by monitoring the activity collecting on the filter using a Cadmium Zinc Telluride (CZT) detector installed into the particulate collection area of the RASA. This limit would ensure that the IMS technical specifications for measurement time (> 20 h) and detector resolution (2.5 keV at 1332 keV) are met. The CZT would dynamically control the RASA air flow to limit the collection of particulate activity beneath the HPGe dead-time threshold and would also provide measurements useful for CTBT verification purposes and dose assessments.

Burnett, Jonathan L.↗