Nuclear Environmental Engineering Sciences and Radioactive Waste Management (NEESRWM)

Current Research

Active Grants and Projects

Collapse Development of Coupled On-line and Hands-on Radiation Detection and Radiochemistry Laboratory Courses: NRC, 09/01/09-05/31/12

The goal of this project is to develop two courses: an on-line radiation detection and measurement laboratory and a hands-on radiochemistry laboratory. The curriculum design and classroom instruction for both courses will be a collaborative effort between professors at Clemson University and South Carolina State University (SCSU). Based on educational backgrounds, current research and teaching interests, and previous experience with similar courses, the Clemson/SCSU team has the teaching competencies and subject matter expertise to successfully build and offer the proposed courses. The objective of the on-line radiation detection and measurement course is for the students to experience working with the instruments as if they were in the laboratory. The on-line laboratory exercises will be unique in that students will be able control laboratory measurements in real-time through a broadband internet connection. The second course will be an intense hands-on radiochemistry laboratory which will build upon the knowledge students gained from the on-line course. The course will cover radiochemical separations processes that are “universal” in nuclear science fields such as environmental sampling, fuel processing, waste processing, and nuclear forensics. The course will be taught during the 2-week Maymester term at Clemson. The short, intense laboratory course will provide a relatively low cost alternative to obtaining hands-on radiochemistry experience. These courses will improve the nuclear education infrastructure by being offered to universities that want to offer radiation detection and radiochemistry laboratory experience to their students but do not have the instrumentation, the radioactive materials license, or the personnel to teach the course. Furthermore, the on-line radiation detection course will offer an alternative to traditional on-line courses where students must travel to campus several weekends per semester for the detection laboratory experience. The short 2-week timeframe for the hands-on radiochemistry course provides a reasonable balance between the required course time and the need for hands-on laboratory experience.


Collapse Development of a Self-Consistent Model of Plutonium Sorption: Quantification of Enthalpy and Ligand-promoted Dissolution: DOE, 06/15/2010-06/14/2013

Project Objectives: The goal of this research is to improve our ability to predict the environmental behavior of plutonium through the development of a mechanistic model of plutonium speciation in subsurface environments. The speciation model will be a thermodynamic surface complexation model of plutonium sorption to mineral surfaces that is self-consistent with macroscopic batch sorption data, X-ray absorption spectroscopy (XAS) measurements, electron microscopy analyses, and quantum-mechanical calculations. The novelty of the proposed work lies largely in the manner the information from these measurements and calculations will be combined into a model that will be used to evaluate the thermodynamics of plutonium sorption reactions as well as predict sorption of plutonium to sediments from DOE sites using a component additivity approach. Additional studies will incorporate effects of surface-mediated redox interactions as well as complexation with natural organic matter (NOM) into the model. Hypotheses: This research will test the hypotheses that 1) strong interactions of plutonium with mineral surfaces are due to formation of inner sphere Pu(IV) complexes which are mechanistically driven by displacement of solvating water molecules from the actinide and mineral surface during sorption and 2) under environmental conditions, desorption of these inner sphere complexes can only be accomplished by mineral surface-mediated oxidation to more soluble Pu(V) or Pu(VI) or through ligand-enhanced dissolution with NOM.

Proposed Experimental Design: Development of a mechanistic sorption model will require: 1) macro-scale sorption data, 2) measurement of chemical speciation and bonding environment both in the aqueous and solid phase, and 3) understanding of physical state of plutonium (i.e., present as a sorbed complex or as a surface precipitate). This project will consist of three main tasks to build a model which can meet the above criteria. The first task will measure sorption values and enthalpy of Pu(IV) and Pu(V) sorption to pure mineral phases as well as sediments from the Savannah River Site and the Hanford Site. The batch sorption data will be coupled with the results of XAS and electron microscopy. Task 2 will consist solely of quantum-mechanical calculations to determine sorption energies and activated states involved in adsorption, observe the electronic interactions between the adsorbate, co-adsorbate, and substrate, and possible reduction of actinide species. Both the computational studies and experimental studies will be used to build a surface complexation model of plutonium speciation that is consistent with experiments and atomistic simulations and based on actual reaction mechanisms. This model will evaluate the strength of plutonium surface interactions as noted in hypothesis 1. The third task of this project will test the second hypothesis by performing plutonium desorption tests under variable redox conditions and in the presence and absence of organic ligands intended to simulate NOM and microbial exudates.

Relevance to ERSD Mission: The proposed research will support the ERSD mission through development of a mechanistic model describing plutonium sorption to soils and sediments, including the role of redox transformations and NOM complexation. Our inability to understand the fundamental controls of plutonium subsurface mobility limits the effectiveness of current predictive transport models and has significant implications for DOE clean-up mission and their responsibility to estimate accurately the risk posed by long-term nuclear waste disposal. Products of the proposed research will include a qualitative conceptual model, a thermodynamically based sorption model, and kinetic parameters describing Pu desorption under variable redox conditions and in the presence of NOM.


Collapse Junior Nuclear Environmental Engineering and Science Faculty at Clemson University: NRC, 05/01/2010-04/30/2013

The objectives of this proposal are twofold: (1) to support the academic career of our radiochemistry assistant professor and (2) attract and support a new junior nuclear faculty in health physics.


Collapse Clemson University Nuclear Forensics Junior Faculty Award Program: DHS, 08/18/2011-08/17/2012

Under this grant Dr. Brian Powell’s educational and research experience in environmental radiochemistry will be directed at the field of technical nuclear forensics. Dr. Powell is an assistant professor in Environmental Engineering and Earth Sciences (EE&ES) at Clemson University. EE&ES has a Nuclear Environmental Engineering and Science program in which Dr. Powell oversees the radiochemistry educational/research track. The key educational highlight of this proposal will be enhancement of student laboratory training in radioanalytical chemistry. Dr. Powell teaches courses in environmental actinide chemistry and in low-level radiation detection of environmental samples. Dr. Powell will expand these courses to include nuclear forensics applications. Students are gaining laboratory experience that is available in only a few institutions so these courses are helping to generate the next generation of nuclear scientists who are needed in the field of nuclear forensics. The research highlight is a strong collaboration with Dr. Kersting, Dr. Shaughnessy, and Dr. Hutcheon at Lawrence Livermore National Laboratory. Through this collaboration, Dr. Powell will develop a research program examining advanced separations of actinides from large volume environmental samples and characterization of plutonium particles and nanoparticles. Collaboration with LLNL scientists with expertise in these research areas will ensure that a strong program results.


Collapse Evaluation of Nanoparticle Behavior during Transitions from Engineered to Natural Systems: NSF, 09/15/10-08/31/14

The objective of this proposal is to define the potential source term of nanoparticles in natural systems to be used in a quantitative risk assessment. This will be achieved by quantifying the rate and extent of physical and chemical changes in nanoparticles during transitions from engineered to natural systems as indicated by the behavior of nanoparticles when released into natural waters.

Approach: Specific objectives of this project will be to:

  1. Examine the rate and extent of exchange between naturally occurring ligands (NOM, carbonate, and phosphate) and anthropogenic ligands (insert ligands).
  2. Quantify the influence of pH, ionic strength, and NOM on the aggregation and morphology of nanoparticles introduced either as “bare” or ligand stabilized nanoparticles.
  3. Characterize the morphology of aggregated nanoparticles formed in natural systems via aggregation
  4. Characterize and quantify the interactions between nanoparticles and naturally occurring macroscale mineral phases
  5. Further develop analytical tools for the characterization of nanoparticle behavior in natural and engineered systems
  6. Use ligand exchange rates and aggregation kinetics to predict the fate of functionalized nanomaterials in waste treatment systems and experimentally verify results.
  7. Provide experimental evidence that exchange with natural ligands that stabilized nanoparticles (as determined in objective 1 and 2) will result in enhanced mobility through packed sediment column studies under advective flow.

Intellectual Merit:
The results of this work can be used to inform risk analysis by identifying the nanoparticles likely to be mobile in natural environments and biologically available in natural waters. In addition, the following tools will be developed to determine the fate of nanomaterials in natural systems:

  1. New technique for measuring ligand exchange on nanomaterials
  2. Models of ligand exchange on metal and metal oxide nanomaterials.
  3. Qualitative conceptual modeling and quantitative physical/chemical modeling of nanoparticle fate in natural systems.

All the data produced in this project will be released to public databases. The developed models will be automated for high throughput screening.

Broader Impacts:
As part of the broader impact of this work, we propose to create an Undergraduate Creative Inquiry (UCI) research group at Clemson. UCI is a Clemson wide focus on team-based undergraduate research that transcends both class and discipline. We shall recruit motivated undergraduate students from all disciplines, especially those in the PI’s departments of Environmental Engineering and Earth Science, Chemical and Biomolecular Engineering, and Material Science and Engineering. We will employ an application process to target a group of eight students at different stages in their education with priority given to women and minority students. Ideally we will have a diverse group of undergraduate researchers recruited as freshmen and sophomores and continuing up to their graduation.


Collapse Development of New Analytical Capabilities for the Measurement of Fundamental Thermodynamic Parameters Supporting Advanced Fuel Cycle Chemistry Clemson University: DOE, 08/31/2011-08/30/2012

The objective of this proposal is to develop new analytical capabilities improve the teaching and research efforts within the Nuclear Environmental Engineering and Science (NEES) program at Clemson University. Specifically, funds are requested for an Isothermal Titration Calorimeter. The calorimeter will be primarily utilized in two major research focus areas: 1) determination of aqueous stability constants of actinide-ligand systems to support advanced actinide separations processes and 2) determination of enthalpy of actinide interactions at solid-water interfaces. These properties will help to inform nuclear fuel processing activities, separations chemistry, and evaluation of actinide bearing materials during geologic disposition.

The NEES program is a graduate only academic program established in the early 1980’s within the Department of Environmental Engineering and Earth Sciences (EE&ES) at Clemson University. The program focuses on the environmental aspects of nuclear technologies, including environmental health physics, radioactive waste processing, environmental risk assessment, the nuclear fuel cycle, radiation detection and measurement, environmental radiochemistry, and environmental remediation. Having a nuclear focus within an EE&ES department is unique and allows students to develop the range of skills necessary to address contemporary issues in natural and anthropogenic radioactivity. The NEES educational program is a combination of classroom instruction, laboratory instruction, and research. NEES encompasses a two track program of study: Environmental Health Physics (Applied Science Accreditation Commission (ASAC) within the Accreditation Board for Engineering and Technology (ABET)) and Environmental Radiochemistry.

The primary benefit of this project will be an enhancement of the educational experience of students studying in the NEES program. Training students through hands-on laboratory teaching and research exercises, such as those which will be performed using the calorimeter requested in this proposal, will assist in training the next generation of scientists and technicians in nuclear chemistry and nuclear science fields (including health physics and radiochemistry). This is imperative due to the precipitous decline in the number of trained nuclear scientists in the current workforce. Through the use of the instruments requested in this proposal, students will gain hands on laboratory experience focusing on radiation detection and measurement, radiochemical separations, determination of thermodynamic constants for actinide complexes, and analysis of radionuclides in the environment. These instruments will be available for use by all EE&ES students and faculty as as well as other colleagues at Clemson University and our collaborators at other universities as noted in the proposal narrative.


Collapse Quantification of Cation Sorption to Engineered Barrier Materials Under Extreme Conditions: DOE,10/17/2011 - 09/30/2014

Objective: The objective of this work is to quantify interactions of risk driving radionuclides with engineered barrier materials used in radioactive waste repositories. The engineered solids to be examined will be iron oxide byproducts of steel corrosion and bentonite clays as representative backfill materials. Data examining sorption and ion exchange of various radionuclides to these materials are available. However, data are lacking for studies at high temperatures and high ionic strengths. The high ionic strength is expected to limit sorption of cations due to competition for a finite number of sorption and/or exchange sites. However, as temperature increases, sorption of actinide ions is hypothesized to increase based on an entropy driven displacement of solvating waters. Therefore studies at extremely high ionic strengths and at high temperatures are necessary. We will use a suite of actinide ions in these experiments to allow for a systematic and quantitative understanding of ion interactions with these materials as a function of ion size, hydration state, and charge. The deliverable will be a qualitative conceptual model and a quantitative thermodynamic aqueous/surface complexation speciation model describing actinide sorption to engineered barrier materials, which is based upon a mechanistic understanding of specific sorption processes as determined from both micro-scale and macro-scale experimental techniques.

Hypotheses:The overarching hypothesis of this research is that strong actinide interactions with metal (oxyhydr)oxide surfaces are manifested by large stability constants for the actinide surface complexes. These large stability constants are due to positive entropies which are mechanistically driven by displacement of solvating water molecules from the actinide ion and the mineral surface during sorption and/or surface precipitation. Such entropies are accessible through measurement of sorption enthalpies and stability constants using surface complexation modeling and calorimetric titration techniques. Additional specific hypotheses that are corollaries to this general hypothesis are:

  • Dehydration of metal ions upon sorption may provide an energetic barrier to desorption.
  • The ability of bentonite clay to sequester radionuclides can be enhanced via amendment of the clay with functionalized or redox active materials such as fly ash or zeolites.

Outcomes: This work directly addresses the expressed need in Technical Work Scope Identifier FC-6 for understanding “aqueous speciation and surface sorption at high temperature and high ionic strengths anticipated in near field conditions.” The primary deliverable will be a set of thermodynamically based sorption and ion exchange constants describing radionuclide sorption to engineered barrier materials. These data will provide an understanding of the fundamental reaction mechanisms occurring at the mineral-water interface. A greater understanding of these processes will reduce the uncertainty in strategies for sequestration of radionuclide bearing wastes. Overall this project will increase our understanding of radionuclide interfacial reactions and help to ensure human and environmental health are protected during treatment and disposal of radionuclide bearing wastes.


Collapse Technetium Sorption to Cementitious Materials: SRNS thru SCUREF, 05/05/2011-09/30/2012

In this work, Dr. Brian Powell and Dr. Yuji Arai will measure important geochemical parameters relevant to calculating the risk associated with disposing of low-level radioactive waste on the Savannah River Site. Specifically, technetium distribution coefficients (Kd values) or solubility values will be measured under a nitrogen gas environment. SRNL will provide the non-radioactive solid phases to be tested. Results will be presented in a detailed report no later than September 15, 2011.

Performance Assessments (PA) are risk calculations designed to determine: (1) the maximum amount of radioactivity that can be safely buried in a subsurface facility and (2) the potential human risk associated with disposing of radioactive waste in a subsurface facility. Special Analyses (SAs) are similar to PAs except that they are designed to address specific issues related to PAs, such as a new discovery since the PA was issued. Commonly, parameters describing the extent that a radionuclide interacts with solids at the source, vadose zone, and aquifer influences the extent of calculated human risk. The two parameters that the SRS use to represent radionuclide/solid interactions are Kd and apparent solubility values, together referred to as sorption values. Sorption values vary with radionuclides, groundwater chemistry, and the type of solid phase (and for cementitious materials, by the age of the material during the calculation).


Collapse Environmental Transport of Plutonium: Geochemical Processes at the Femtomolar Concentration and Nanometer Scale: DOE thru LLNL, 11/01/2011-09/30/2015

A major scientific challenge in environmental sciences is to gain the scientific knowledge needed to reliably predict and control the cycling and mobility of actinides (e.g.,. plutonium). Over 2000 metric tons of plutonium (Pu) have been deposited in the surface-subsurface worldwide. This along with its long-half life and toxicity, represents a significant long-term environmental risk. Currently, we cannot reliably predict how Pu will move once deposited in the subsurface preventing accurate assessment of risk to human health. Field measurements document Pu transport kilometers farther than models predict. Significant gaps in our current understanding of the dominant biogeochemical (inorganic, organic, and microbial) processes that control actinide transport exist. A mechanistic understanding of the surface structure and reactivity of coupled Pu-mineral, Pu-organic ligand, and Pu-microbe interfacial processes is needed to advance our understanding of the fate and transport of Pu in this complex subsurface system.

Our program focuses on identifying and quantifying the dominant biogeochemical processes that control the behavior of Pu in the subsurface. Despite the recognized importance of colloid-facilitated transport, very little is known about the mechanisms controlling the coupled Pu-colloid interfacial processes and associated reaction rates. Equally uncertain are the conditions under which colloid-facilitated transport is not significant. The objective of this research program is the identification and quantification of Pu-biogeochemical processes such as:

  • the role of binary association (Pu-mineral),
  • ternary complexes (Pu-inorganic + organic),
  • intrinsic colloid formation (Pu oxide),
  • co-precipitation/surface alteration of Pu,
  • and Pu- microbial interactions

on the affinity and sorption/desorption rates of Pu over a range of environmentally relevant concentrations (10-8 to 10-18 mol/L). With the use of unique capabilities at LLNL, such as accelerator mass spectrometry, an IsoProbe mass-spectrometer, a Titan Transmission Electron Microscope, a nano-secondary ion mass spectrometer, nuclear magnetic resonance facilities, and high-performance computing capabilities, we will test whether the biogeochemical processes identified, operate over a 10 order of magnitude range in concentration. New knowledge gained as a result of this work will provide foundational science for the prediction and control of Pu mobility in the surface/subsurface.


Collapse Alternative Sample Loading Preparation for Thermal Ionization Mass Spectrometry: NNSA, 07/01/2012 – 06/30/2015

The objectives of this project are to design and test an alternative sample loading method for thermal ionization mass spectrometry (TIMS) analysis. TIMS is one of the most sensitive analytical tools for determining isotopic ratios for plutonium and uranium and is used widely within the nuclear nonproliferation and safeguards communities. This work seeks to introduce a polymer thin film based method for loading samples that would replace the traditional ‘bead loading’ method. This thin film system has the potential to decrease sample preparation time, increase sensitivity, and minimize the risk of sample loss due to explosive decompression commonly observed using the current bead loading technique.

The project team has extensive experience in radioisotope detection and measurement, radiochemical separations, and the surface engineering technologies required to produce the thin films to be utilized in this work. Here is a summary of methods to be employed by this team:

Thin film coating: Degassed rhenium ribbons will be coated with a thin film of type 1 strong anion-exchange polymer. Polymer thin films will be deposited on the ribbons using a dip-coating method. The experiments will focus on elucidating the impacts of solvents, polymer solution concentration, and dip-coating withdrawal speed on film thickness. A theoretical framework for thin film formation will be used to guide experimental design. Characterization will verify uniform coating of rhenium ribbons by the polymer films and will determine their thickness values.

Sample loading: These experiments will examine methods for loading uranium and plutonium from solutions onto the ribbons, determine the uptake kinetics, and determine loading capacities. Three methods will be used to load uranium and plutonium onto the coated ribbons: Static batch uptake experiments, flow-through uptake in continuously stirred batch reactors, and microvolume additions directly to the ribbon.

TIMS analysis: A side-by-side comparison of traditional bead-loaded materials and thin film-loaded samples will be performed at SRNL. The analysis will be performed using a reference plutonium sample, examining both the isotopic ratios and the total counts obtained for each sample. These studies will allow determination of any signal enhancement created by the alternative loading method and potentially indicate reduction of sample loss due to explosive decompression.

Ribbon geometry: After optimal thin film formation and loading conditions have been determined, the research will focus on fabrication and testing of ribbons with novel rhenium physical geometry. The varying geometries may result in greater ionization of plutonium during the TIMS analysis.

The primary deliverable from this project will be a method for producing polymer thin film-coated rhenium ribbons to improve TIMS analyses. The knowledge gained from these studies has the potential to increase the sensitivity of TIMS analyses by one or more orders of magnitude. Increasing the sensitivity of TIMS analyses may lead to enhanced ability to detect proliferant isotopes. The results from this project will be disseminated to the scientific community in the form of progress reports to NNSA, technical presentations at national meetings, and publication of the results in peer-reviewed literature.


Collapse U.S. Nuclear Regulatory Commission Nuclear Education Program Scholarship and Fellowship: NRC, 08/01/08-07/31/12 and 08/01/2012-07/31/2016

Fellowships are requested to support three graduate students (MS/PhD) per year in nuclear environmental engineering and science (NEES) program within the Environmental Engineering and Earth Sciences Department at Clemson University. Fellowship students will pursue a course of study in either Environmental Health Physics (ABET-ASAC accredited at MS level) or Environmental Radiochemistry. Fellows will conduct their thesis/dissertation research in collaboration with an outside partner such as a national laboratory, utility, or regulatory agency. This will provide fellows with an opportunity both to interact with a practicing professional and to conduct research that contributes to the solution of a contemporary technical issue in the nuclear sector.

The NEES program is a graduate only academic program established in the early 1980’s. The program focuses on the environmental aspects of nuclear technologies, including environmental health physics, radioactive waste processing, environmental risk assessment, the nuclear fuel cycle, radiation detection and measurement, environmental radiochemistry, and environmental remediation. The average number of M.S. and Ph.D. students pursuing a program of study in the NEES focus area has been ~14 per year over the past 5 years. There has been a significant increase to where there are currently 23 M.S. and Ph.D. students within the NEES concentration.


Collapse Nuclear Forensics Education Award Program: DHS/DOE, 09/15/2010-09/30/2012

Nuclear Forensics involves, amongst other things, radiochemistry and radiation detection which are two strengths of the interdisciplinary Nuclear Environmental Engineering and Science (NEES) focus area within the Environmental Engineering and Earth Sciences (EE&ES) Department at Clemson University. The NEES focus area is a long-standing graduate-only academic program that is concerned with the environmental aspects of nuclear technologies including environmental health physics, radioactive waste management, environmental risk assessment, radiation detection and measurement, environmental radiochemistry, and environmental remediation. The NEES educational program is a combination of classroom instruction, laboratory instruction and research. The NEES focus area currently has two tracks that a student can follow: Environmental Health Physics (Accreditation Board for Engineering and Technology Applied Science Accreditation Commission(ABET ASAC) accredited at the MS level) or Environmental Radiochemistry. The proposed Nuclear Forensics track would be an outgrowth of our existing NEES focus area. The Nuclear Forensics track will integrate a new course in nuclear forensics along with existing nuclear courses, laboratory instruction and thesis research in collaboration with senior personnel at federal nuclear forensics facilities.


Collapse Technical Review and Comments on SRS Environmental Report: DOE-SRNL, 03/15/2007 - 03/14/2013

The objective of this project is to provide a scientific/technical review and comments of the eight primary chapters of the annual SRS Environmental Report.The objective of the technical review is to produce a clear and concise document regarding the releases of radioactive materials to the environment from the Department of Energy Savannah River Site.


Collapse Ultra-Trace-level Quantification of Alpha and Beta emitting Radionuclides with Extractive Scintillating Resin: DTRA, 05/06/2012-05/06/2015

The objective of this research is to advance scientific understanding in the development of high-selectivity sensor materials, high-sensitivity sensors, and data analysis techniques for ultra-trace-level quantification of radionuclides, particularly α- and β-emitting radionuclides. An on-line system for ultra-low-level detection of α- and β-emitting radionuclides in environmental media (water, air and sewage) would be a powerful nuclear forensics tool. Currently, no such system is available.

Scope:

  1. Design, synthesize, and characterize a new class of extractive scintillator resins that incorporate covalently bound scintillator molecules and selective ligands for α- and β-emitting radionuclides. We will prepare two resin platforms for comparative testing: one incorporates ligands continuously throughout the resin matrix and the other isolates ligands within a polymer nanolayer adjacent to the resin-solution interface. The second type of resin will be prepared by grafting ligand-rich nanolayers from the resin surface using surface-initiated atom transfer radical polymerization (ATRP). Study variables include scintillator and ligand type, monomer composition in the formulation, and polymerization time. Focus in Years 1-3 will be given to development of extractive scintillation resins for Sr, Tc, U. Years 4-5 would focus on the development of resins for Cs and Pu.
  2. Quantify the fundamental parameters that control the sensitivity of the extractive scintillator sensor. Using deterministic and Monte Carlo techniques, we will assess trade-offs among resin size, flow-cell diameter and geometry, energy deposition in the scintillator, light collection efficiency, radionuclide selectivity, type of radiation, and resin capacity. Preliminary calculations show that detection of alpha radiation below mBq/L levels is possible. The focus for the first 1.5 years will be on the charged particle modeling. From year 1.5 – 3.0 our team will work on the light collection model. While in year 3, we will begin to work on the combined energy deposition and light collection models. This effort will extend into years 4 and 5.
  3. Develop statistical control chart methods that will lower the detection limit of the sensors developed under Tasks 1 and 2. Preliminary tests indicate that some control chart methods are significantly more sensitive to detection of small changes in count rate over conventional paired analyses. The ability of the control chart to improvement the detection limit is expected to be an order of magnitude or better. During years 1 and 2 our team will concentrate on control chart data using count rate data. During year 2 and 3 our team will develop the control chart methods using the time-interval data.

Collapse Synthesis-Microstructure-Performance Relations in Oxide Ceramic Scintillators: NSF, 08/01/2012-07/31/2016

Scintillators are unique materials that transform high energy ionizing radiation into detectable visible light, being used for the detection and measurement of radiation in security, energy, medical diagnosis, and other strategic fields. Presently, there is a knowledge gap relating the fabrication and processing conditions of transparent ceramic scintillators with their scintillation output, a situation that negatively impacts the widespread use of these materials, as well as undermines their performance. We hypothesize that the intensities of scintillation and afterglow are related to the concentration of structural imperfections that generate electronic traps, and that it is possible to mitigate afterglow by identifying suitable rare earth (RE) dopants to drain charge carriers off the traps. In order to evaluate the above hypothesis, it is proposed to:

  1. Investigate the effect of grain boundary density on the scintillation efficiency and afterglow intensity and duration. Manipulation of grain size will be promoted by controlled thermal treatments in vacuum and characterized by electron microscopy,
  2. Investigate the effect of oxygen non-stoichiometry on the scintillation efficiency and afterglow intensity and duration. Systematic variation of the oxygen content will be promoted by controlled thermal treatments under O2 and reducing atmospheres and monitored by compositional analysis,
  3. Develop a predictive capability to identify suitable RE dopants to decrease afterglow intensity and duration. Traps energy depth will be determined by thermoluminescence measurements, and identification of suitable RE dopants to drain charge carriers off these traps will be based on Dorenbos model of RE energy levels within the band gap.

The innovative aspect of the proposed research is to go beyond the fabrication of transparent ceramics to establish relations between fabrication conditions, microstructure and defect characteristics with afterglow and scintillation performance, and to develop a predictive capability to identify RE dopants to mitigate afterglow. The project will focus on RE-doped Lu2O3, Y2O3, and Y3Al5O12 transparent ceramics.