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Recent Publications

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2018 Publications

  • Anay, R., Soltangharaei, V., Assi, L., DeVol, T., Ziehl, P., 2018. Identification of damage mechanisms in cement paste based on acoustic emission. Constr. Build. Mater. 164, 286–296. doi:10.1016/J.CONBUILDMAT.2017.12.207
    Acoustic emission (AE) monitoring during compressive loading was employed to investigate micro-crack formation and coalescence in cement paste specimens. To establish a correlation between damage and AE activity, the data was categorized on the basis of amplitude and cumulative signal strength (CSS). Three distinct stages of crack behavior, illuminated by changes in the slope of the cumulative signal strength versus time relationship, were identified. Micro-crack initiation, crack extension, and unstable crack growth (crack coalescence) were assigned to these stages. An unsupervised pattern recognition approach was employed to separate the data into signal subsets which were then classified and assigned to differing mechanisms. To gain further insight into the crack growth network and behavior, specimens were loaded to varying levels of ultimate capacity and micro-CT scanning was employed to investigate the dimensional extent of micro-cracking and to correlate the images with AE data.
  • Bliznyuk, V.N., Conroy, N.A., Xie, Y., Podila, R., Rao, A.M., Powell, B.A., 2018. Increase in the reduction potential of uranyl upon interaction with graphene oxide surfaces. Phys. Chem. Chem. Phys. 20, 1752–1760. doi:10.1039/C7CP04197G
    Coordination of uranyl (U(VI)) with carboxylate groups on functionalized graphene oxide (GO) surfaces has been shown to alter the reduction potential of the sorbed uranium ion. A quantitative measure of the reduction potential and qualitative estimation of sorption/desorption processes were conducted using cyclic voltammetry, and the proposed coordination environment was determined using the surface sensitive attenuated total reflection mode of infrared spectroscopy (ATR-FTIR). GO is a nanostructured material possessing a large amount of oxygen-containing functional groups both on basal planes and at the edges, which can form strong surface complexes with radionuclides. The presence of these functional groups on the surface of GO allows efficient immobilization of uranium due to sorption of uranyl (UO22+) to carboxylate, hydroxide, or sulfonate functional groups and the potential for enhanced reduction of U(VI) to more strongly sorbing and insoluble U(IV). Herein, binding of U(VI) to carboxylate groups on the GO surface is proposed as the primary sorption mechanism based on the FTIR study. Furthermore, the coordination of uranium with the surface increases the reduction potential of the U(VI)/U(IV) redox couple as compared to the case of the aqueous U(VI)/U(IV) species. This is consistent with the alteration of the electronic structure of the sorbed ion, which can be determined in our case due to the use of a GO-coated working electrode. Thus, GO-coated glassy carbon electrodes and other semi-conducting electrodes with high ion sorption capacities may provide a means of examining the oxidation/reduction potentials of sorbed ions.
  • Bliznyuk, V.N., Seliman, A.F., Husson, S.M., Lvov, Y.M., DeVol, T.A., 2018. Hybrid Nanoparticle-Polymer Brush Composites for Detection of Low-Level Radiostrontium in Water. Macromol. Mater. Eng. 303, 1700651. doi:10.1002/mame.201700651
    Combining extraction and scintillation properties within the same material is a relatively new approach in development of sensors for detection of radioactive elements. Structural organization of such materials at a nanoscale typically offers higher efficiency of detection and shorter response time. In this contribution, several new protocols are discussed for fabrication of stable extractive scintillating systems based on commercial Superlig 620 (SL) material with high affinity to radiostrontium. Application of hybrid organic–inorganic beads with SL particles used as core and halloysite clay nanotubes (HNT) modified with a polyvinyltoluene (PVT) brush as a permeable shell combines high‐performance extracting properties of the SL material with efficient light emission properties of the polymer scintillator. The developed SL–HNT–PVT hybrid extractive scintillating material allows real‐time detection of low‐level concentrations of radiostrontium in water. Moreover, the suggested approach is not limited to detection of Sr but can find broader application in development of chemical, biological, or radioluminescent sensors and multifunctional materials.
  • Cho, K.-W., Cantone, M.-C., Kurihara-Saio, C., Le Guen, B., Martinez, N., Oughton, D., Schneider, T., Toohey, R., ZöLzer, F., Authors on behalf of ICRP, 2018. ICRP Publication 138: Ethical Foundations of the System of Radiological Protection. Ann. ICRP 47, 1–65. doi:10.1177/0146645317746010
    Despite a longstanding recognition that radiological protection is not only a matter of science, but also ethics, ICRP publications have rarely addressed the ethical foundations of the system of radiological protection explicitly. The purpose of this publication is to describe how the Commission has relied on ethical values, either intentionally or indirectly, in developing the system of radiological protection with the objective of presenting a coherent view of how ethics is part of this system. In so doing, it helps to clarify the inherent value judgements made in achieving the aim of the radiological protection system as underlined by the Commission in Publication 103. Although primarily addressed to the radiological protection community, this publication is also intended to address authorities, operators, workers, medical professionals, patients, the public, and its representatives (e.g. NGOs) acting in the interest of the protection of people and the environment. This publication provides the key steps concerning the scientific, ethical, and practical evolutions of the system of radiological protection since the first ICRP publication in 1928. It then describes the four core ethical values underpinning the present system: beneficence/ non-maleficence, prudence, justice, and dignity. It also discusses how these core ethical values relate to the principles of radiological protection, namely justification, optimisation, and limitation. The publication finally addresses key procedural values that are required for the practical implementation of the system, focusing on accountability, transparency, and inclusiveness. The Commission sees this publication as a founding document to be elaborated further in different situations and circumstances.
  • Duval, C.E., Darge, A.W., Ruff, C., DeVol, T.A., Husson, S.M., 2018. Rapid Sample Preparation for Alpha Spectroscopy with Ultrafiltration Membranes. Anal. Chem. 90, 4144–4149. doi:10.1021/acs.analchem.8b00135
    This contribution describes a rapid, fieldable alpha spectroscopy sample preparation technique that minimizes consumables and decreases the nuclear forensics timeline. Functional ultrafiltration membranes are presented that selectively concentrate uranium directly from pH 6 groundwater and serve as the alpha spectroscopy substrate. Membranes were prepared by ultraviolet grafting of uranium-selective polymer chains from the membrane surface. Membranes were characterized by Fourier-transform infrared spectroscopy before and after modification to support functionalization. Membrane performance was evaluated using uranium-233 or depleted uranium in both deionized and simulated groundwater at pH 6. Functionalized membranes achieved peak energy resolutions of 31 ± 2 keV and recoveries of 81 ± 4% when prepared directly from pH 6 simulated groundwater. For simulated groundwater spiked with depleted uranium, baseline energy resolution was achieved for both isotopes (uranium-238 and uranium-234). The porous, uranium-selective substrate designs can process liters per hour of uranium-contaminated groundwater using low-pressure (<150 kpa="" filtration="" and="" a="" 45="" mm="" diameter="" membrane="" filter="" leading="" to="" high-throughput="" one-step="" concentration="" purification="" sample="" mounting="" process="" div="">
  • Edayilam, N., Montgomery, D., Ferguson, B., Maroli, A.S., Martinez, N., Powell, B.A., Tharayil, N., 2018. Phosphorus Stress-Induced Changes in Plant Root Exudation Could Potentially Facilitate Uranium Mobilization from Stable Mineral Forms. Environ. Sci. Technol. acs.est.7b05836. doi:10.1021/acs.est.7b05836
    Apparent deficiency of soil mineral nutrients often triggers specific physio-morphological changes in plants, and some of these changes could also inadvertently increase the ability of plants to mobilize radionuclides from stable mineral forms. This work, through a series of sand-culture, hydroponics, and batch-equilibration experiments, investigated the differential ability of root exudates of Andropogon virginicus grown under conditions with variable phosphorus (P) availability (KH2PO4, FePO4, Ca3(PO4)2, and no P) to solubilize uranium (U) from the uranyl phosphate mineral Chernikovite. The mineral form of P, and hence the bioavailability of P, affected the overall composition of the root exudates. The lower bioavailable forms of P (FePO4 and Ca3(PO4)2), but not the complete absence of P, resulted in a higher abundance of root metabolites with chelating capacity at 72 hrs after treatment application. In treatments with lower P-bioavailability, the physiological amino acid concentration inside of the roots increased, whereas the concentration of organic acids in the roots decreased due to the active exudation. In batch dissolution experiments, the organic acids, but not amino acids, increase the dissolution U from Chernikovite. The root exudate matrix of plants exposed to low available forms of P induced a >60% increase in U dissolution from Chernikovite due to 5-16 times greater abundance of organic acids in these treatments. However, this was ca. 70% of the theoretical dissolution achievable by this exudate matrix. These results highlight the potential of using active management of soil P as an effective tool to alter the plant-mediated mobilization of U in contaminated soil.
  • Erdmann, B.J., Powell, B.A., Kaplan, D.I., DeVol, T.A., 2018. One-dimensional Spatial Distributions of Gamma-ray Emitting Contaminants in Field Lysimeters Using a Collimated Gamma-ray Spectroscopy System. Health Phys. 114, 1. doi:10.1097/HP.0000000000000799
    One-dimensional scans of gamma-ray emitting contaminants were conducted on lysimeters from the RadFLEX facility at the Savannah River Nationals Laboratory (SRNL). The lysimeters each contained a contamination source that was buried in SRNL soil. A source consisted of Cs, Co, Ba, and Eu incorporated either into a solid waste form (Portland cement and reducing grout) or applied to a filter paper for direct soil exposure. The lysimeters were exposed to natural environmental conditions for 3 to 4 y. The initial contaminant activities range from 4.0 to 9.0 MBq for the solid wasteforms and 0.25 to 0.47 MBq for the soil-incorporated source. The measurements were performed using a collimated high-purity germanium gamma-ray spectrometer with a spatial resolution of 2.5 mm. These scans showed downward mobility of Co and Ba when the radionuclides were incorporated directly into the SRNL soil. When radionuclides were incorporated into the solid waste forms positioned in the SRNL soil, Cs exhibited both upward and downward dispersion while the other radionuclides showed no movement. This dispersion was more significant for the Portland cement than the reducing grout wasteform. Europium-152 was the only radionuclide of those studied that showed no movement within the spatial resolution of the scanner from the original placement within the lysimeter. Understanding radionuclide movement in the environment is important for developing strategies for waste management and disposal.
  • Pales, A.R., Li, B., Clifford, H.M., Kupis, S., Edayilam, N., Montgomery, D., Liang, W., Dogan, M., Tharayil, N., Martinez, N., Moysey, S., Powell, B., Darnault, C.J.G., 2018. Preferential flow systems amended with biogeochemical components: imaging of a two-dimensional study. Hydrol. Earth Syst. Sci. 22, 2487–2509. doi:10.5194/hess-22-2487-2018
    The vadose zone is a highly interactive heterogeneous system through which water enters the subsurface system by infiltration. This paper details the effects of simulated plant exudate and soil component solutions upon unstable flow patterns in a porous medium (ASTM silica sand; US Silica, Ottawa, IL, USA) through the use of two-dimensional tank light transmission method (LTM). The contact angle (θ) and surface tension (γ) of two simulated plant exudate solutions (i.e., oxalate and citrate) and two soil component solutions (i.e., tannic acid and Suwannee River natural organic matter, SRNOM) were analyzed to determine the liquid–gas and liquid–solid interface characteristics of each. To determine if the unstable flow formations were dependent on the type and concentration of the simulated plant exudates and soil components, the analysis of the effects of the simulated plant exudate and soil component solutions were compared to a control solution (Hoagland nutrient solution with 0.01 M NaCl). Fingering flow patterns, vertical and horizontal water saturation profiles, water saturation at the fingertips, finger dimensions and velocity, and number of fingers were obtained using the light transmission method. Significant differences in the interface properties indicated a decrease between the control and the plant exudate and soil component solutions tested; specifically, the control (θ = 64.5° and γ = 75.75mNm−1) samples exhibited a higher contact angle and surface tension than the low concentration of citrate (θ = 52.6° and γ = 70.8mNm−1). Wetting front instability and fingering flow phenomena were reported in all infiltration experiments. The results showed that the plant exudates and soil components influenced the soil infiltration as differences in finger geometries, velocities, and water saturation profiles were detected when compared to the control. Among the tested solutions and concentrations of soil components, the largest finger width (10.19cm) was generated by the lowest tannic acid solution concentration (0.1mgL−1), and the lowest finger width (6.00cm) was induced by the highest SRNOM concentration (10mgL−1). Similarly, for the plant exudate solutions, the largest finger width (8.36cm) was generated by the lowest oxalate solution concentration (0.1mgL−1), and the lowest finger width (6.63cm) was induced by the lowest citrate concentration (0.1mgL−1). The control solution produced fingers with average width of 8.30cm. Additionally, the wettability of the medium for the citrate, oxalate, and SRNOM solutions increased with an increase in concentration. Our research demonstrates that the plant exudates and soil components which are biochemical compounds produced and released in soil are capable of influencing the process of infiltration in soils. The results of this research also indicate that soil wettability, expressed as cosθ1∕2, should be included in the scaling of the finger dimension, i.e., finger width, when using the Miller and Miller (1956) scaling theory for the scaling of flow in porous media.
  • Wen, Y., Xu, Y., Brinkman, K.S., Shuller-Nickles, L., 2018. Atomistic scale investigation of cation ordering and phase stability in Cs-substituted Ba1.33Zn1.33Ti6.67O16, Ba1.33Ga2.66Ti5.67O16 and Ba1.33Al2.66Ti5.33O16 hollandite. Sci. Rep. 8, 5003. doi:10.1038/s41598-018-22982-7
    The titanate-based hollandite structure is proposed as an effective ceramic waste form for Cs-immobilization. In this study, quantum-mechanical calculations were used to quantify the impact of A-site and B-site ordering on the structural stability of hollandite with compositions BaxCsy(MzTi8-z)O16, where M = Zn2+, Ga3+, and Al3+. The calculated enthalpy of formation agrees with experimental measurements of related hollandite phases from melt solution calorimetry. Ground state geometry optimizations show that, for intermediate compositions (e.g., CsBaGa6Ti18O48), the presence of both Cs and Ba in the A-site tunnels is not energetically favored. However, the decay heat generated during storage of the Cs-containing waste form may overcome the energetics of Ba and Cs mixing in the tunnel structure of hollandite. The ability of the hollandite structure to accommodate the radioparagenesis of Cs to Ba is critical for long term performance of the waste. For the first time, B-site ordering was observed along the tunnel direction ([001] zone axis) for the Ga-hollandite compositions, as well as the intermediate Al-hollandite composition. These compositionally dependent structural features, and associated formation enthalpies, are of importance to the stability and radiation damage tolerance of ceramic waste forms.

2017 Publications

  • Montgomery, D., Barber, K., Edayilam, N., Oqujiuba, K., Young, S., Biotidara, T., Gathers, A., Danjaji, M., Tharayil, N., Martinez, N., Powell, B., 2017. The influence of citrate and oxalate on 99TcVII, Cs, NpV and UVI sorption to a Savannah River Site soil. J. Environ. Radioact. 172, 130–142. doi:10.1016/j.jenvrad.2017.03.017
    Batch sorption experiments were conducted with 0.5–50 ppb 99Tc, 133Cs, 237Np and U in the presence and absence of citrate and/or oxalate in a 25 g/L Savannah River Site (SRS) soil suspension. Citrate and oxalate were the ligands of choice due to their relevancy to plant exudates, the nuclides were selected for their wide range of biogeochemical behavior, and the soil from SRS was selected as a model Department of Energy (DOE) site soil. Batch samples were continually mixed on a rotary shaker and maintained at a pH of approximately 5. Analysis via ICP-MS indicated that sorption of 237Np increased with ligand concentration compared to baseline studies, as did sorption of 99Tc although to a lesser extent. The increased sorption of 237Np is proposed to be due to a combination of factors that are dependent on the ligand(s) present in the specific system including, ligand dissolution of the soil by citrate and formation of tertiary soil-oxalate-Np complexes. The increased 99Tc sorption is attributed to the dissolution of the soil by the ligands, leading to an increase in the number of available sorption sites for 99Tc. Uranium sorption decreased and dissolution of native uranium was also observed with increasing ligand concentration, thought to be a result of the formation of strong U-ligand complexes remaining in the aqueous phase. The majority of these effects were observed at the highest ligand concentrations of 50 mgC/L. No notable changes were observed for the 133Cs system which is ascribed to the minimal interaction of Cs+ with these organic ligands.
  • Gillenwalters, E., Martinez, N., 2017. Review of Gender and Racial Diversity in Radiation Protection. Health Phys. 112, 384–391. doi:10.1097/HP.0000000000000640
    The rapidly changing demographics of the United States workforce include a large number of women and members of minority groups that are currently underrepresented in science and engineering-related education and careers. Recent research indicates that while singular incidents of sexism do exist, gender bias more often affects women in various subtle ways. The effects of stereotype threat and the lack of appropriate mentoring and female role models are samples of the possible factors contributing to performance and longevity for women in math-intensive fields. To address how this issue affects those in radiation protection, the current status of women in the field is reviewed as a progression through the scientific pipeline, from education and employment to positions in scientific bodies and professional recognition, with primary focus on American women and institutions. Racial diversity demographics are reviewed where available. Findings indicate women and minority racial groups are underrepresented in multiple aspects of education, research, and leadership. While gender diversity across the field has not yet reached gender parity, trending indicates that the percentage of women earning degrees in radiation protection has consistently increased over the last four decades. Diversity of racial groups, however, has remained fairly consistent and is well below national averages. Diverse perspectives have been documented in collective problem-solving to lead to more innovative solutions. Health Phys. 112(4):384–391; 2017
  • Dogan, M., Moysey, S.M.J., Ramakers, R.M., DeVol, T.A., Beekman, F.J., Groen, H.C., Powell, B.A., 2017. High-resolution 4D pre-clinical SPECT/CT imaging of technetium transport within a heterogeneous porous media. Environ. Sci. Technol. acs.est.6b04172. doi:10.1021/acs.est.6b04172
    A dynamic 99mTc tracer experiment was performed to investigate the capabilities of combined preclinical single photon emission computed tomography (SPECT) and X-ray computed tomography (CT) for investigating transport in a heterogeneous porous medium. The experiment was conducted by continuously injecting a 99mTc solution into a column packed with eight layers (i.e., soil, silica gel, and 0.2–4 mm glass beads). Within the imaging results it was possible to correlate observed features with objects as small as 2 mm for the SPECT and 0.2 mm for the CT. Time-lapse SPECT imaging results illustrated both local and global nonuniform transport phenomena and the high-resolution CT data were found to be useful for interpreting the cause of variations in the 99mTc concentration associated with structural features within the materials, such as macropores. The results of this study demonstrate SPECT/CT as a novel tool for 4D (i.e., transient three-dimensional) noninvasive imaging of fate and transport processes in porous media. Despite its small scale, an experiment with such high resolution data allows us to better understand the pore scale transport which can then be used to inform larger scale studies.
  • Thies, S.R., Duval, C.E., DeVol, T.A., Husson, S.M., 2017. Creating monodisperse polymer microspheres using membrane emulsification. J. Appl. Polym. Sci. 134. doi:10.1002/app.44593
    This study used membrane emulsification (ME) as a pre-treatment step to suspension polymerization to produce polystyrene microspheres with diameters from 200 to 300 µm and coefficient of variation (CV) as low 20%. Limited scientific information is available on utilizing suspension polymerization to prepare monodisperse polystyrene microspheres with diameters greater than 100 µm. Microspheres were produced by pumping monomer solution through uniform pores of nickel membranes to form dispersed phase droplets that were transferred to a reactor for suspension polymerization. Systematic studies were done to understand the roles of continuous phase composition, ME unit process parameters, and polymerization reactor stir speed on microsphere size and CV. For a specific microsphere size, there were particular stir speeds in each unit that minimized CV. The methodology developed in this study is being used to prepare monodisperse polymer resin beads to improve detection efficiency and accuracy in flow-cell sensors for quantifying waterborne radioactivity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44593
  • Martinez, N.E., 2017. Contributions from Women to the Radiation Sciences. Health Phys. 112, 376–383. doi:10.1097/HP.0000000000000646
    Contributions from men to radiation science are well known, particularly the early contributions from such luminaries as William Roentgen, James Chadwick, Niels Bohr, Robert Oppenheimer, and the like. Although not ignored per se, beyond Marie Curie and Lise Meitner, the contributions of female nuclear scientists are not as widely recognized. This paper provides a concise historical summary of contributions to radiation science from the discovery of radiation through the current status of international leadership within the radiation protection community. Beyond lead scientists and academics, this paper also considers support personnel as well as the role women have played in the advancement of radiation epidemiology.
  • Mannion, J.M., Shick, C.R., Fugate, G.A., Powell, B.A., Husson, S.M., 2017. Anion-Exchange Fibers for Improved Sample Loading in Ultra-Trace Analysis of Plutonium by Thermal Ionization Mass Spectrometry. Anal. Chem. acs.analchem.7b01455. doi:10.1021/acs.analchem.7b01455
    A new sample loading procedure was developed for isotope ratio measurements of ultratrace amounts of plutonium with thermal ionization mass spectrometry (TIMS). The goal was to determine the efficacy of a polymer fiber architecture for TIMS sample loading by following similar sample loading procedures as those used in bead loading. Fibers with diameter of approximately 100 μm were prepared from triethylamine-quaternized-poly(vinylbenzyl chloride) cross-linked with diazabicyclo[2.2.2]octane. Fiber sections (2.5 mm) were loaded with 10 pg of New Brunswick Laboratory certified reference material (NBL CRM) 128 from an 8 M HNO3 matrix and affixed to rhenium filaments with collodion. A single filament assembly was used for these analyses. Total ion counts (239Pu + 242Pu) and isotope ratios obtained from fiber-loaded filaments were compared to those measured by depositing Pu amended resin beads on the filament. Fiber loading was found to improve sensitivity, accuracy, and precision of isotope ratio measurements of plutonium when compared to the established resin bead loading method, while maintaining its simplicity. The average number of detected Pu+ counts was 180% greater, and there was a 72% reduction in standard deviation of ratio measurements when using fiber loading. An average deviation of 0.0012 (0.117%) from the certified isotope ratio value of NBL CRM Pu128 was measured when fiber loading versus a deviation of 0.0028 (0.284%) when bead loading. The fiber formation method presented in this study can be extended to other anion-exchange polymer chemistries and, therefore, offers a convenient platform to investigate the efficacy of novel polymer chemistries in sample loading for TIMS.
  • Conroy, N.A., Zavarin, M., Kersting, A.B., Powell, B.A., 2017. Effect of Natural Organic Matter on Plutonium Sorption to Goethite. Environ. Sci. Technol. 51, 699–708. doi:10.1021/acs.est.6b03587
    The effect of citric acid (CA), desferrioxamine B (DFOB), fulvic acid (FA), and humic acid (HA) on plutonium (Pu) sorption to goethite was studied as a function of organic carbon concentration and pH using batch sorption experiments at 5 mgC·L–1 and 50 mgC·L–1 natural organic matter (NOM), 10–9–10–10 M 238Pu, and 0.1 g·L–1 goethite concentrations, at pH 3, 5, 7, and 9. Low sorption of ligands coupled with strong Pu complexation decreased Pu sorption at pH 5 and 7, relative to a ligand-free system. Conversely, CA, FA, and HA increased Pu sorption to goethite at pH 3, suggesting ternary complex formation or, in the case of humic acid, incorporation into HA aggregates. Mechanisms for ternary complex formation were characterized by Fourier transform infrared spectroscopy in the absence of Pu. CA and FA demonstrated clear surface interactions at pH 3, HA appeared unchanged suggesting HA aggregates had formed, and no DFOB interactions were observed. Plutonium sorption decreased in the presence of DFOB (relative to a ligand free system) at all pH values examined. Thus, DFOB does not appear to facilitate formation of ternary Pu-DFOB-goethite complexes. At pH 9, Pu sorption in the presence of all NOM increased relative to pH 5 and 7; speciation models attributed this to Pu(IV) hydrolysis competing with ligand complexation, increasing sorption. The results indicate that in simple Pu-NOM-goethite ternary batch systems, NOM will decrease Pu sorption to goethite at all but particularly low pH conditions.
  • Arail, Y., Powell, B.A., Kaplan, D.I., 2017. Sulfur speciation in untreated and alkali treated ground-granulated blast furnace slag. Sci. Total Environ. 589, 117–121. doi:10.1016/j.scitotenv.2017.02.163
    Reduced sulfur species in ground-granulated blast furnace slag (GGBFS) play an important role in immobilizing radionuclide contaminants in caustic cement-GGBFS mixtures via reductive precipitation reaction. However, sulfur (S) speciation and its stability in GGBFS have not been clearly understood. In this study, S speciation of GGBSF in alkaline radionuclide liquid waste simulant solutions was investigated using S K-edge X-ray absorption near edge structure spectroscopy (XANES) and powder X-ray diffraction (XRD) measurements. Although S mineralogy was not detectable by XRD due to the amorphous nature in GGBFS, XANES analysis revealed that GGBSF contained high concentration of sulfoxide (~57%), followed by S(0) (~37%), sulfate (~3.81%), and sulfonate (~2.33%). When GGBFS was reacted with anoxic or oxygenated alkali solutions, it retained most of sulfoxide with some changes in the fraction of elemental S, sulfonate and sulfate, indicating the involvement of reduced S species in the reductive precipitation of radionuclides. This study shows the presence of intermediate S valence species in GGBFS.
  • Mannion, J.M., Shick, Jr., C.R., Fugate, G.A., Wellons, M.S., Powell, B.A., Husson, S.M., 2017. Rhenium filament oxidation: Effect on TIMS performance and the roles of carburization and humidity. Talanta 168, 183–187. doi:10.1016/j.talanta.2017.03.036
    This communication presents findings on the effect of rhenium filament oxidation on thermal ionization mass spectrometry (TIMS) analyses of plutonium. Additionally, the roles of atmospheric humidity and carburization on the oxidation characteristics (i.e. aging) of rhenium filaments were studied. Degassed and carburized filaments were aged for up to 79 days under dry and humid conditions, and the growth of oxo-rhenium crystallites was investigated intermittently by scanning electron microscopy (SEM) to construct growth profiles. SEM images were analyzed to determine average crystallite size, number density, and percent surface coverage. Crystallite growth was found to be suppressed by both filament carburization and dry storage conditions (~13% relative humidity). Under humid conditions (75% relative humidity), crystallite growth progressed steadily over the investigatory period, reaching >2.3% surface coverage within 79 days of aging. Atomic ion production of Pu (Pu+) was suppressed by approximately 20% and the standard deviation of isotope ratio measurements was increased by 170% when filaments with 1% oxide surface coverage were used in sample loading. Measurement sensitivity and reproducibility are imperative for applications involving ultra-trace analysis of plutonium by TIMS. These findings offer validation for observations regarding the detrimental effect of excessive filament aging post-degassing, improve the understanding of conditions that impel the oxidation of rhenium filaments, and provide practical means to suppress the growth of oxides.
  • Arai, Y., Meena, A.H., Lenell, B., Powell, B.A., Kaplan, D.I., 2017. Spatial distribution, chemical state, solubility of rhenium in a reducing cement waste form: Implications for predicting technetium mobility in saltstone. Appl. Geochemistry. doi:10.1016/j.apgeochem.2017.02.001
    Reducing cementitious materials (RCMs) are presently being developed for the long-term, subsurface disposal of low-level radioactive waste within the United States Department of Energy complex.
  • Mannion, J.M., Wellons, M.S., Shick, C.R., Fugate, G.A., Powell, B.A., Husson, S.M., 2017. Ambient aging of rhenium filaments used in thermal ionization mass spectrometry: Growth of oxo-rhenium crystallites and anti-aging strategies. Heliyon 3, e00232. doi:10.1016/j.heliyon.2017.e00232
    Degassing is a common preparation technique for rhenium filaments used for thermal ionization mass spectrometric analysis of actinides, including plutonium. Although optimization studies regarding degassing conditions have been reported, little work has been done to characterize filament aging after degassing. In this study, the effects of filament aging after degassing were explored to determine a “shelf-life” for degassed rhenium filaments, and methods to limit filament aging were investigated. Zone-refined rhenium filaments were degassed by resistance heating under high vacuum before exposure to ambient atmosphere for up to 2 months. After degassing the nucleation and preferential growth of oxo-rhenium crystallites on the surface of polycrystalline rhenium filaments was observed by atomic force microscopy and scanning electron microscopy (SEM). Compositional analysis of the crystallites was conducted using SEM-Raman spectroscopy and SEM energy dispersive X-ray spectroscopy, and grain orientation at the metal surface was investigated by electron back-scatter diffraction mapping. Spectra collected by SEM-Raman suggest crystallites are composed primarily of perrhenic acid. The relative extent of growth and crystallite morphology were found to be grain dependent and affected by the dissolution of carbon into filaments during annealing (often referred to as carbonization or carburization). Crystallites were observed to nucleate in region specific modes and grow over time through transfer of material from the surface. Factors most likely to affect the rates of crystallite growth include rhenium substrate properties such as grain size, orientation, levels of dissolved carbon, and relative abundance of defect sites; as well as environmental factors such as length of exposure to oxygen and relative humidity. Thin (∼180 nm) hydrophobic films of poly(vinylbenzyl chloride) were found to slow the growth of oxo-rhenium crystallites on the filament surfaces and may serve as an alternative carbon source for filament carburization.
  • Yuan, K., Taylor, S.D., Powell, B.A., Becker, U., 2017. An ab initio study of the adsorption of Eu 3+ , Pu 3+ , Am 3+ , and Cm 3+ hydroxide complexes on hematite (001) surface: Role of magnetism on adsorption. Surf. Sci. 664, 120–128. doi:10.1016/j.susc.2017.06.007
    Inner-sphere hydroxide complexes of Eu3+, Pu3+, Am3+, and Cm3+ adsorbed to antiferromagnetic and ferromagnetic hematite (001) surfaces were modeled by using DFT (GGA + U) calculations in order to compare the electronic properties, atomic structures, and adsorption energies between the trivalent actinide analog Eu3+ and the corresponding actinides An3+. Eu3+ forms a tridentate–binuclear surface complex on the hematite surface with an Eu–Fe distance of 3.4–3.8 Å. Eu3+ is partially reduced upon adsorption, as indicated by the increase of original Eu3+ spin value from 6 to ∼7. Eu3+ adsorption on the ferromagnetic surface is energetically more favorable than on the antiferromagnetic surface, while the opposite is the case for all actinides An3+. When retaining a similar adsorption configuration (e.g., coordination number = 6), An3+ cations are adsorbed ∼0.2 Å closer to the surface compared to Eu3+. Partial density of states analyses indicate ionic bonding between O ions on the hematite surface and the Eu3+/An3+ adsorbates. An increasing number of bands above the Fermi energy were found when Eu3+ and An3+ were adsorbed to the ferromagnetic surface but not on the antiferromagnetic surface, indicating the ferromagnetic substrate becomes more semiconducting upon cation adsorption. These results show that the spin configurations of the hematite (001) surface have a weak but distinct influence on the cation adsorption energy. Although the antiferromagnetic spin configuration of hematite is dominant in nature, metastable ferromagnetic domains on nanohematite grains may influence the energetics of certain cation adsorption reactions.

2016 Publications

  • Bliznyuk, V.N., Seliman, A.F., Ishchenko, A.A., Derevyanko, N.A., DeVol, T.A., 2016. New Efficient Organic Scintillators Derived from Pyrazoline. ACS Appl. Mater. Interfaces 8, 12843–12851. doi:10.1021/acsami.6b02719
    We report on the synthesis, spectroscopic and scintillation properties of three new pyrazoline core based fluorophores. Fluorescence properties of the fluorophores have been studied both in a solution state and in a solid polyvinyltoluene (PVT) resin matrix of different porosity. The synthesized fluorophores were found to be promising candidates for application in plastic scintillators for detection of ionizing radiation (alpha, beta particles, γ rays and neutrons) and demonstrated superior efficiency in comparison to the existing commercially used fluorophores (2-(1-naphthyl)-5-phenyloxazole (αNPO), 9,10-diphenylanthracene, etc.). Moreover, the suggested synthetic route allows functionalization of the fluorophores with a vinyl group for further covalent bound to the PVT or other vinyl polymer matrices, which dramatically improves chemical stability of the system simultaneously improving the photoluminescence quantum yield. Possible mechanisms of the enhanced scintillation properties are discussed based on preliminary quantum mechanical calculations and spectroscopic characteristics of the fluorophores under study.
  • Chapman, M.G., Walker, R.C., Schmitt, J.M., McPherson, C.L., Ameena, F., Kucera, C.J., Quarles, C.A., DeVol, T.A., Ballato, J., Jacobsohn, L.G., 2016. Effects of Sintering Temperature on Open-Volume Defects and Thermoluminescence of Yttria and Lutetia Ceramics. J. Am. Ceram. Soc. 99, 1449–1454. doi:10.1111/jace.14119
    The effects of different processing steps and processing conditions for the fabrication of Y2O3 and Lu2O3 ceramics were investigated, particularly the effects of calcination, and sintering temperature on the content of open-volume and electronic defects. Ceramic bodies were prepared from calcined powders by sintering from 1400°C to 1700°C for 20 h. Density was determined by the Archimedes method and showed pellets reached about 99% of Y2O3 density for temperatures ≥1450°C, and reached 98% for sintering at 1700°C for Lu2O3. The content of open-volume defects was followed by positron annihilation lifetime (PAL) measurements. For both materials, two lifetimes were obtained. The faster lifetime, 211 ps for Y2O3 and 204 ps for Lu2O3, was assigned to bulk annihilation with possible contribution of grain boundaries. The longer lifetime was assigned to positronium annihilation in open-volume defects with radii of 2–4 Å. Doppler broadening analysis revealed the same type of defect in Lu2O3 ceramics for all sintering temperatures. PAL analysis results showed that densification was achieved through the elimination and agglomeration of open-volume defects. Thermoluminescence (TL) measurements of Y2O3 showed that sintering is beneficial in eliminating traps and/or recombination centers, and that higher sintering temperatures increase TL signal.
  • Duval, C.E., DeVol, T.A., Wade, E.C., Seliman, A.F., Bliznyuk, V.N., Husson, S.M., 2016. Stability of polymeric scintillating resins developed for ultra-trace level detection of alpha- and beta-emitting radionuclides. J. Radioanal. Nucl. Chem. 310, 583–588. doi:10.1007/s10967-016-4913-3
    This contribution characterizes the stability of scintillating resins for ionizing radiation detection that were synthesized with 2-(1-naphthyl)-5-phenyloxazole (α-NPO) or 2-(1-naphthyl)-4-vinyl-5-phenyloxazole (v-NPO) fluor in polystyrene (PS) or poly(4-methyl styrene) (PVT) matrices. Leaching studies of the PS and PVT resins with methyl acetate show a 60 % reduction in luminosity and 80 % reduction in detection efficiency for α-NPO samples; while v-NPO resins retained detection properties. Degradation studies indicate the nitration of PS resins and the fluors after nitric acid exposure, resulting in a 100 % reduction in optical properties; whereas PVT resins with v-NPO fluor maintained 20 % detection efficiency. Heuristics are reported for designing stable scintillating resins.
  • Duval, C.E., DeVol, T.A., Husson, S.M., 2016. Evaluation of resin radius and column diameter for the implementation of extractive scintillating resin in flow-cell detectors. J. Radioanal. Nucl. Chem. 307, 2253–2258. doi:10.1007/s10967-015-4494-6
    This contribution characterizes the stability of scintillating resins for ionizing radiation detection that were synthesized with 2-(1-naphthyl)-5-phenyloxazole (α-NPO) or 2-(1-naphthyl)-4-vinyl-5-phenyloxazole (v-NPO) fluor in polystyrene (PS) or poly(4-methyl styrene) (PVT) matrices. Leaching studies of the PS and PVT resins with methyl acetate show a 60 % reduction in luminosity and 80 % reduction in detection efficiency for α-NPO samples; while v-NPO resins retained detection properties. Degradation studies indicate the nitration of PS resins and the fluors after nitric acid exposure, resulting in a 100 % reduction in optical properties; whereas PVT resins with v-NPO fluor maintained 20 % detection efficiency. Heuristics are reported for designing stable scintillating resins.
  • Duval, C.E., DeVol, T.A., Husson, S.M., 2016. Extractive scintillating polymer sensors for trace-level detection of uranium in contaminated ground water. Anal. Chim. Acta 947, 1–8. doi:10.1016/j.aca.2016.09.029
    This contribution describes the synthesis of robust extractive scintillating resin and its use in a flow-cell detector for the direct detection of uranium in environmental waters. The base poly[(4-methyl styrene)-co-(4-vinylbenzyl chloride)-co-(divinylbenzene)-co-(2-(1-napthyl)-4-vinyl-5-phenyloxazole)] resin contains covalently bound fluorophores. Uranium-binding functionality was added to the resin by an Arbuzov reaction followed by hydrolysis via strong acid or trimethylsilyl bromide (TMSBr)-mediated methanolysis. The resin was characterized by Fourier-transform infrared spectroscopy and spectrofluorometry. Fluorophore degradation was observed in the resin hydrolyzed by strong acid, while the resin hydrolyzed by TMSBr-mediated methanolysis maintained luminosity and showed hydrogen bonding-induced Stokes' shift of ∼100 nm. The flow cell detection efficiency for uranium of the TMSBr-mediated methanolysis resin was evaluated at pH 4, 5 and 6 in DI water containing 500 Bq L-1 uranium-233 and demonstrated flow cell detection efficiencies of 23%, 16% and 7%. Experiments with pH 4, synthetic groundwater with 50 Bq L-1 uranium-233 exhibited a flow cell detection efficiency of 17%. The groundwater measurements show that the resins can concentrate the uranyl cation from waters with high concentrations of competitor ions at near-neutral pH. Findings from this research will lay the groundwork for development of materials for real-time environmental sensing of alpha- and beta-emitting radionuclides.
  • Martinez, N.E., Johnson, T.E., Pinder, J.E., 2016. Application of computational models to estimate organ radiation dose in rainbow trout from uptake of molybdenum-99 with comparison to iodine-131. J. Environ. Radioact. 151, 468–479. doi:10.1016/j.jenvrad.2015.05.021
    This study compares three anatomical phantoms for rainbow trout (Oncorhynchus mykiss) for the purpose of estimating organ radiation dose and dose rates from molybdenum-99 ((99)Mo) uptake in the liver and GI tract. Model comparison and refinement is important to the process of determining accurate doses and dose rates to the whole body and the various organs. Accurate and consistent dosimetry is crucial to the determination of appropriate dose-effect relationships for use in environmental risk assessment. The computational phantoms considered are (1) a geometrically defined model employing anatomically relevant organ size and location, (2) voxel reconstruction of internal anatomy obtained from CT imaging, and (3) a new model utilizing NURBS surfaces to refine the model in (2). Dose Conversion Factors (DCFs) for whole body as well as selected organs of O. mykiss were computed using Monte Carlo modeling and combined with empirical models for predicting activity concentration to estimate dose rates and ultimately determine cumulative radiation dose (μGy) to selected organs after several half-lives of (99)Mo. The computational models provided similar results, especially for organs that were both the source and target of radiation (less than 30% difference between all models). Values in the empirical model as well as the 14 day cumulative organ doses determined from (99)Mo uptake are compared to similar models developed previously for (131)I. Finally, consideration is given to treating the GI tract as a solid organ compared to partitioning it into gut contents and GI wall, which resulted in an order of magnitude difference in estimated dose for most organs.
  • Martinez, N., Wueste, D., 2016. Balancing theory and practicality: engaging non-ethicists in ethical decision making related to radiological protection. J. Radiol. Prot. 36, 832–841. doi:10.1088/0952-4746/36/4/832
    This paper discusses an approach for engaging radiation protection professionals in the ethical aspects of decision-making, with discussion on how this approach fits in with the existing system of radiological protection. It explores finding common ground between ethical and scientific theory, how to present relevant moral theory in accessible language, and provides a practical framework for dealing with real-world problems. Although establishing the ethical theory behind the system of radiological protection is an important ongoing endeavour within the community, it is equally important to communicate this information in a way that is useful to non-ethicists. Discussion of both ethical theory and a useful strategy for applying the theory makes ethics more accessible to those working in the field by providing them with the knowledge and confidence to apply ethical principles in decisions and practice.
  • Xie, Y., Helvenston, E.M., Shuller-Nickles, L.C., Powell, B.A., 2016. Surface Complexation Modeling of Eu(III) and U(VI) Interactions with Graphene Oxide. Environ. Sci. Technol. 50, 1821–1827. doi:10.1021/acs.est.5b05307
    Graphene oxide (GO) has great potential for actinide removal due to its extremely high sorption capacity, but the mechanism of sorption remains unclear. In this study, the carboxylic functional group and an unexpected sulfonate functional group on GO were characterized as the reactive surface sites and quantified via diffuse layer modeling of the GO acid/base titrations. The presence of sulfonate functional group on GO was confirmed using elemental analysis and X-ray photoelectron spectroscopy. Batch experiments of Eu(III) and U(VI) sorption to GO as the function of pH (1-8) and as the function of analyte concentration (10-100, 000 ppb) at a constant pH ≈ 5 were conducted; the batch sorption results were modeled simultaneously using surface complexation modeling (SCM). The SCM indicated that Eu(III) and U(VI) complexation to carboxylate functional group is the main mechanism for their sorption to GO; their complexation to the sulfonate site occurred at the lower pH range and the complexation of Eu(III) to sulfonate site are more significant than that of U(VI). Eu(III) and U(VI) facilitated GO aggregation was observed with high Eu(III) and U(VI) concentration and may be caused by surface charge neutralization of GO after sorption.
  • Xu, Y., Wen, Y., Grote, R., Amoroso, J., Shuller-Nickles, L.C., Brinkman, K.S., 2016. A-site compositional effects in Ga-doped hollandite materials of the form Ba x Cs y Ga 2x + y Ti 8 − 2x − y O 16 : implications for Cs immobilization in crystalline ceramic waste forms. Nat. Publ. Gr. 6, 1–8. doi:10.1038/srep27412
    The hollandite structure is a promising crystalline host for Cs immobilization. A series of Ga-doped hollandite BaxCsyGa2x+yTi8−2x−yO16 (x = 0, 0.667, 1.04, 1.33; y = 1.33, 0.667, 0.24, 0) was synthesized through a solid oxide reaction method resulting in a tetragonal hollandite structure (space group I4/m). The lattice parameter associated with the tunnel dimension was found to increases as Cs substitution in the tunnel increased. A direct investigation of cation mobility in tunnels using electrochemical impedance spectroscopy was conducted to evaluate the ability of the hollandite structure to immobilize cations over a wide compositional range. Hollandite with the largest tunnel size and highest aspect ratio grain morphology resulting in rod-like microstructural features exhibited the highest ionic conductivity. The results indicate that grain size and optimized Cs stoichiometry control cation motion and by extension, the propensity for Cs release from hollandite.
  • Xu, Y., Feygenson, M., Page, K., Shuller-Nickles, L.C., Brinkman, K.S., Vanderah, T., 2016. Structural Evolution in Hollandite Solid Solutions Across the A-Site Compositional Range from Ba1.33Ga2.66Ti5.34O16 to Cs1.33Ga1.33Ti6.67O16. J. Am. Ceram. Soc. 99, 4100–4106. doi:10.1111/jace.14443
    Hollandite solid solutions along the A-site compositional range from the pure barium end-member Ba1.33Ga2.66Ti5.34O16 to the pure cesium end-member Cs1.33Ga1.33Ti6.67O16 have been synthesized using a solid-state reaction technique. The crystal structure of the hollandite across the entire compositional range remained in the I4/m space group. Structural evolution was resolved by neutron diffraction, total scattering data, and density functional theory calculations. A trend of decreasing thermodynamic stability with smaller tunnel cations was attributed to increased structural distortion observed in the system. In addition, the tunnel cations' local environment was studied in the eightfold coordinated oxygen cavities. Local binding features of the tunnel cations reveals that the hollandite structure can strongly stabilize tunnel cations, even at elevated temperatures up to 500 K.
  • Xu, Y., Grote, R., Wen, Y., Shuller-Nickles, L., Brinkman, K.S., Pfeifer, T., Matyáš, J., Balaya, P., Singh, D., Wei, J., 2016. Development of Ga Doped Hollandites Ba x Cs y (Ga 2x+y Ti 8-2x-y )O 6 for Cs Immobilization, in: Ceramics for Energy Conversion, Storage, and Distribution Systems. John Wiley & Sons, Inc., Hoboken, NJ, USA, pp. 157–164. doi:10.1002/9781119234531.ch14
    Among the many proposed hollandites compositions (Bax,Csy)(M,Ti)8O16, Ga substituted hollandite has been studied to a limited extent. By substituting Ti with Ga, hollandite can be synthesized with a standard sintering process producing dense ceramics at relatively low temperature of 1250°C. In the present work, Ga substituted hollandites containing different levels of Cs, from a pure Cs end-member to a pure Ba end-member were synthesized with a fixed A site occupancy level. X-ray diffraction patterns coupled with SEM-EDX mapping confirmed hollandite formation as a primary homogenous phase. Density functional theory calculations were performed on selected compositions to evaluate the energetics of the hollandite system. Computational results showed favorable formation of hollandite for these samples based on negative formation enthalpies.
  • Hao, N., Moysey, S.M.J., Powell, B.A., Ntarlagiannis, D., 2016. Comparison of the surface ion density of silica gel evaluated via spectral induced polarization versus acid–base titration. J. Appl. Geophys. 135, 427–435. doi:10.1016/j.jappgeo.2016.01.014
    Surface complexation models are widely used with batch adsorption experiments to characterize and predict surface geochemical processes in porous media. In contrast, the spectral induced polarization (SIP) method has recently been used to non-invasively monitor in situ subsurface chemical reactions in porous media, such as ion adsorption processes on mineral surfaces. Here we compare these tools for investigating surface site density changes during pH-dependent sodium adsorption on a silica gel. Continuous SIP measurements were conducted using a lab scale column packed with silica gel. A constant inflow of 0.05 M NaCl solution was introduced to the column while the influent pH was changed from 7.0 to 10.0 over the course of the experiment. The SIP measurements indicate that the pH change caused a 38.49 ± 0.30 μS cm− 1 increase in the imaginary conductivity of the silica gel. This increase is thought to result from deprotonation of silanol groups on the silica gel surface caused by the rise in pH, followed by sorption of Na+ cations. Fitting the SIP data using the mechanistic model of Leroy et al. (Leroyet al., 2008), which is based on the triple layer model of a mineral surface, we estimated an increase in the silica gel surface site density of 26.9 × 1016 sites m− 2. We independently used a potentiometric acid–base titration data for the silica gel to calibrate the triple layer model using the software FITEQL and observed a total increase in the surface site density for sodium sorption of 11.2 × 1016 sites m− 2, which is approximately 2.4 times smaller than the value estimated using the SIP model. By simulating the SIP response based on the calibrated surface complexation model, we found a moderate association between the measured and estimated imaginary conductivity (R2 = 0.65). These results suggest that the surface complexation model used here does not capture all mechanisms contributing to polarization of the silica gel captured by the SIP data.
  • Emerson, H.P., Hickok, K.A., Powell, B.A., 2016. Experimental evidence for ternary colloid-facilitated transport of Th(IV) with hematite (α-Fe2O3) colloids and Suwannee River fulvic acid. J. Environ. Radioact. 165, 168–181. doi:10.1016/j.jenvrad.2016.10.001
    Previous field experiments have suggested colloid-facilitated transport via inorganic and organic colloids as the primary mechanism of enhanced actinide transport in the subsurface at former nuclear weapons facilities. In this work, research was guided by the hypothesis that humic substances can enhance tetravalent actinide (An(IV)) migration by coating and mobilizing natural colloids in environmental systems and increasing An(IV) sorption to colloids. This mechanism is expected to occur under relatively acidic conditions where organic matter can sorb and coat colloid surfaces and facilitate formation of ternary colloid-ligand-actinide complexes. The objective of this work was to examine Th transport through packed columns in the presence of hematite colloids and/or Suwannee River fulvic acid (SRFA). In the presence of SRFA, with or without hematite colloids, significant transport (>60% recovery within the effluent) of thorium occurred through quartz columns. It is notable that the SRFA contributed to increased transport of both Th and hematite colloids, while insignificant transport occurred in the absence of fulvic acid. Further, in the presence of a natural sandy sediment (as opposed to pure quartz), transport is negligible in the presence of SRFA due to interactions with natural, clay-sized sediment coatings. Moreover, this data shows that the transport of Th through quartz columns is enhanced in ternary Th-colloid-SRFA and binary Th-SRFA systems as compared to a system containing only Th.
  • Gillens, A.R., Powell, B.A., 2016. A novel technique for the rapid determination of tributyl phosphate degradation from alkaline hydrolysis in aqueous and organic phases using FTIR–ATR and verification of this technique by gas chromatography. J. Radioanal. Nucl. Chem. 307, 1891–1899. doi:10.1007/s10967-015-4434-5
    This paper details a semi-quantitative method for determining tributyl phosphate (TBP) degradation from alkaline hydrolysis using FTIR–ATR accompanied by GC verification and it provides a method to extract TBP from aqueous media associated with its use in nuclear reprocessing. The amount of TBP determined by GC decreases from 95 to 36 % after approximately 4½ h in the reaction. TBP present in the organic phase predicted by the FTIR–ATR technique shows that TBP decreases from 97 to 42 %. Up to 15 % of TBP and 40 % of DBP were extracted from the precipitate based on the extraction recoveries determined.
  • Locklair, W.D., Mannion, J.M., Husson, S.M., Powell, B.A., 2016. Uptake of plutonium on a novel thin film for use in spectrometry. J. Radioanal. Nucl. Chem. 307, 2333–2338. doi:10.1007/s10967-015-4493-7
    Trace elemental and isotopic analysis of actinides via Thermal Ionization Mass Spectrometry (TIMS) is often difficult and time consuming due to intensive sample preparation. Polymer thin films show strong potential for rapid concentration of radionuclides from solution that may prove as suitable substrates for TIMS analyses. In this work, a polymer thin film (~180 nm) was coated onto a silicon substrate and utilized for rapid radioanalytical analysis. The polymer is composed of poly(vinyl benzyl chloride) functionalized with triethyl amine (TEA) to produce an anion-exchange site for concentrating anionic actinide complexes (i.e. PuCl62-, Pu(NO3)62-) from solution. In addition, selectively functionalizing “spots” with TEA creates hydrophilic regions and allows for concentration of an aqueous drop when surrounded by the hydrophobic polymeric backbone. Batch uptake studies were performed using inductively coupled plasma mass spectrometry, liquid scintillation counting and alpha spectrometry to determine uptake kinetics and anion-exchange capacities of the polymer thin film. Results indicated that along with a potential for utilization as a TIMS substrate, the polymer thin film yields high resolution alpha spectra, comparable to samples produced via electrodeposition. An apparent equilibrium constant (Kd) for the functionalized polymer was found to be approximately 9060 L/kg from 9M HCl. The anion exchange capacity of the film was determined using 36Cl uptake studies and found to be 1.25 x 10-1 ± 1.07 × 10-2 meq/gpolymer. Thus, the rapid uptake kinetics, good anion-exchange capacity, and high-resolution alpha spectra show good promise for the use of this thin film for rapid radioanalytical analyses.
  • Mannion, J.M., Locklair, W.D., Powell, B.A., Husson, S.M., 2016. Alpha spectroscopy substrates based on thin polymer films. J. Radioanal. Nucl. Chem. 307, 2339–2345. doi:10.1007/s10967-015-4498-2
    The objective of this work was to prepare a novel substrate for the simultaneous concentration of actinides and sample preparation for alpha spectroscopy. Substrate preparation involved forming ultrathin films (10–180 nm) of quaternary amine anion-exchange polymers on glass and silicon by dip-coating. Samples were loaded by submerging the polymer-coated substrates into acidified solutions of 238Pu or natural water with elevated uranium concentrations. High resolution (25–30 keV) alpha spectra were acquired from these substrates under certain loading conditions indicating that through further development they may be a useful, inexpensive, and potentially field deployable platform serving national security and environmental sampling applications.
  • Taylor, S.D., Powell, B.A., Becker, U., 2016. Influence of the goethite (α-FeOOH) surface on the stability of distorted PuO2 and PuO2–x phases. Radiochim. Acta 104, 821–841. doi:10.1515/ract-2015-2515
    Experiments by [Powell, B. A., Dai, Z. R., Zavarin, M., Zhao, P. H., Kersting, A. B.: Stabilization of plutonium nano-colloids by epitaxial distortion on mineral surfaces. Environ. Sci. Technol. 45, 2698 (2011).] deduced the heteroepitaxial growth of a bcc Pu4O7 phase when sorbed onto goethite from d-spacing measurements obtained from selected-area electron diffraction (SAED) patterns. The structural and/or chemical modification of Pu(IV) oxide (PO) nanocolloids upon sorption to goethite, in turn, affects colloidal-transport of Pu in the subsurface. In this study, molecular simulations were applied to investigate mechanisms affecting the formation of non-fcc PO phases and to understand the influence of goethite in stabilizing the non-fcc PO phase. Analyses of the structure, chemistry, and formation energetics for several bulk PuO2 and PuO2–x phases, using ab initio methods, show that the formation of a non-fcc PO can occur from the lattice distortion (LD) of fcc PuO2 upon sorption and formation of a PO–goethite interface. To strain and non-uniformly distort the PuO2 lattice to match that of the goethite substrate at ambient conditions would require 88 kJ/mol Pu4O8. The formation of a hypostoichiometric PuO2–x phase, such as the experimentally-deduced bcc, Ia3̅ Pu4O7 phase, requires more O-poor conditions and/or high energetic inputs (> +365 kJ/mol Pu4O7 at O-rich conditions). Empirical methods were also applied to study the effect of lattice distortion on sorption energetics and adsorbate particle growth using simple heterointerfaces between cubic salts, where KCl clusters (notated as KClLD) of varying size and lattice mismatch (LM) were sorbed to a NaCl cluster. When the lattice of a KClLD cluster has <15% LM with that of a NaCl substrate, the sorption of KClLD onto NaCl is exothermic (<–80 kJ/mol) and the KClLD cluster can reach sizes of ~2–5 nm on the NaCl substrate. These models suggest that the lattice of a fcc PuO2 particle can distort upon formation of a heterointerface with goethite to lower LM, in turn better enabling the growth of the PO adsorbates and yielding more exothermic adsorption energies. A more detailed understanding of the interfacial environment between PO and goethite is obtained through structural, chemical, and energetic analyses on modeled PuO2 (110)– and PuO2–x (110)–goethite (001) heterointerfaces. Structural analyses of the heterointerfaces continue to support that the lattice of PO is strained to better match that of goethite and thus lead to the formation of a non-fcc PO phase. When the lattice of the PO (110) surface is distorted to match that of the goethite (001) surface, the alignment and d-spacings from simulated electron diffraction patterns for the PO–goethite heterointerfaces reproduce experimental observations. Non-fcc PO thin-films are also found to be stabilized through the formation of an interface with goethite, as the work of adhesion for the PuO2– and PuO2–x–goethite interfaces are 1.4 J/m2 and 2.0 J/m2, respectively. Analyses of electron and charge density of the heterointerfaces also show that covalent- to polar-covalent bonding at the interface promotes the stabilization of a PO–goethite interface. The results from these models contribute to experimental observations, providing further understanding of how the goethite substrate influences the formation and stabilization of a non-fcc PO phase. Furthermore, the information from this study aids in better understanding processes at mineral–water interfaces that influence actinide transport.
  • Wylie, E.M., Olive, D.T., Powell, B.A., 2016. Effects of Titanium Doping in Titanomagnetite on Neptunium Sorption and Speciation. Environ. Sci. Technol. 50, 1853–1858. doi:10.1021/acs.est.5b05339
    Neptunium-237 is a radionuclide of great interest owing to its long half-life (2.14 × 106 years) and relative mobility as the neptunyl ion (NpO2+) under many surface and groundwater conditions. Reduction to tetravalent neptunium (NpIV) effectively immobilizes the actinide in many instances due to its low solubility and strong interactions with natural minerals. One such mineral that may facilitate the reduction of neptunium is magnetite (Fe2+Fe3+2O4). Natural magnetites often contain titanium impurities which have been shown to enhance radionuclide sorption via titanium’s influence on the Fe2+/Fe3+ ratio (R) in the absence of oxidation. Here, we provide evidence that Ti-substituted magnetite reduces neptunyl species to NpIV. Titanium-substituted magnetite nanoparticles were synthesized and reacted with NpO2+ under reducing conditions. Batch sorption experiments indicate that increasing Ti concentration results in higher Np sorption/reduction values at low pH. High-resolution transmission electron microscopy of the Ti-magnetite particles provides no evidence of NpO2 nanoparticle precipitation. Additionally, X-ray absorption spectroscopy confirms the nearly exclusive presence of NpIV on the titanomagnetite surface and provides supporting data indicating preferential binding of Np to terminal Ti—O sites as opposed to Fe—O sites.

2015 Publications

  • Chapman, M.G., Marchewka, M.R., Roberts, S.A., Schmitt, J.M., McMillen, C., Kucera, C.J., DeVol, T.A., Ballato, J., Jacobsohn, L.G., 2015. Luminescence and scintillation enhancement of Y2O3:Tm transparent ceramic through post-fabrication thermal processing. J. Lumin. 165, 56–61.
    The effects of post-fabrication thermal processing in O2 flux on the luminescence and scintillation of a Y2O3:Tm transparent ceramic were investigated. The results showed that the strategy of post-fabrication processing can be beneficial to the performance of the ceramics, depending on the cumulative processing time. After the first hour of processing, about 40% enhancement in the luminescence output together with about 20% enhancement in the scintillation light yield were obtained. The enhancements were tentatively assigned to the incorporation of oxygen into vacancy sites. Longer cumulative processing times lead to the incorporation of oxygen as interstitials that is detrimental to scintillation light yield but not to luminescence output. This work also revealed that thermoluminescence measurements are a useful tool to predict scintillation light yield of Y2O3:Tm.
  • Bliznyuk, V.N., Seliman, A.F., Husson, S.M., Chumanov, G., DeVol, T.A., 2015. Fluorescence properties of fluor molecules confined within nanoscale pores in a polymer matrix. MRS Commun. 5, 347–352. doi:10.1557/mrc.2015.38
    We demonstrate that fluorescence properties of organic fluors embedded in a porous polystyrene matrix are highly sensitive to the average pore size and pore-size distribution of the matrix. The effect can be understood as two different types of confinement imposed to the fluor molecules by the matrix. First, there is geometrical confinement that restricts the fluor oscillations due to its physical contact with a pore wall. Second, there is an electronic confinement due to a local polarization of the wall material by molecular dipoles. The effects lead to a spectral shift and enhancement of the fluorescence intensity of the material.
  • Bliznyuk, V.N., Duval, C.E., Apul, O.G., Seliman, A.F., Husson, S.M., DeVol, T.A., 2015. High porosity scintillating polymer resins for ionizing radiation sensor applications. Polymer (Guildf). 56, 271–279. doi:10.1016/j.polymer.2014.10.076
    Due to their high sorption capacity, nanoporous polymer resins can be used as an active material for ionizing radiation sensor applications. This contribution reports on the molecular design and synthesis of scintillating styrene-based resins with controlled bead size, porosity and surface functionality. In a working sensor device, the adsorption of radioactive analyte species on the resin can be monitored via incorporation of specially designed fluor molecules to convert ionizing radiation (specifically, α-particles and β-particles) into light. Porous polystyrene (PS) and poly(4-methylstyrene) resins of various compositions and structure were synthesized via suspension polymerization technique. 1,4-Bis(4-methyl-5-phenyl-oxazol-2-yl)benzene (DM-POPOP) was incorporated into the resin by adding it to the dispersed phase. Polymerization conditions were adjusted to achieve a desirable range of polymer beads size and porosity (pore size distribution, specific surface area). The porosity of the resin beads could be controlled by the type and concentration of the porogen, as well as by the degree of PS matrix crosslinking with divinylbenzene. Three different porogens (toluene, n-heptane or span-80 nonionic surfactant) were used to achieve a broad variation of the nanopore size distribution within the same matrix. The structure, porosity and optical fluorescence properties of the synthesized PS beads were analyzed with nitrogen adsorption porosimetry, optical/UV confocal, scanning electron and helium ion microscopy, and fluorescence spectroscopy. A broad variation of the pore size distribution, specific surface area and optical properties within the same system were demonstrated. Findings from this study can be used for the development of more efficient environmental sensors to monitor contamination of ground water with trace amounts of radioactive materials.
  • Seliman, A.F., Bliznyuk, V.N., Husson, S.M., DeVol, T.A., 2015. Development of polymerizable 2-(1-naphthyl)-5-phenyloxazole scintillators for ionizing radiation detection. J. Mater. Chem. C 3, 7053–7061. doi:10.1039/C5TC00308C
    The synthesis, chemical characterization and optical properties of 2-(1-naphthyl)-4-vinyl-5-phenyloxazole (vNPO) and 2-(1-naphthyl)-4-allyl-5-phenyloxazole (allylNPO) monomers are reported. Starting with the organic fluor 2-(1-naphthyl)-5-phenyloxazole (αNPO), the vNPO and allylNPO monomers were synthesized using Stille coupling followed by purification. The final products were obtained with yields of ∼95% and ∼55% for vNPO and allylNPO. The absorption/emission spectra of αNPO, vNPO and allylNPO revealed that vNPO has the largest red-shifted in emission with an average wavelength of ∼420 nm, which is an advantage for increasing photomultiplier tube sensitivity without the need to add a wavelength shifter. Stable scintillating resin beads were prepared through copolymerization of the newly synthesized fluor monomers with styrene or 4-methylstyrene and divinylbenzene in the presence of toluene porogen. The resin beads were chemically stable and retained the ability to scintillate efficiently after energy deposition of beta particles from 99Tc. This result indicates efficient energy transfer occurs from the base polymer to the covalently attached fluors with subsequent fluorescence in the presence of ionizing radiation.
  • Seliman, A.F., Bliznyuk, V.N., Husson, S.M., DeVol, T.A., 2015. Development of polymerizable 2-(1-naphthyl)-5-phenyloxazole scintillators for ionizing radiation detection. J. Mater. Chem. C 3, 7053–7061. doi:10.1039/C5TC00308C
    The synthesis, chemical characterization and optical properties of 2-(1-naphthyl)-4-vinyl-5-phenyloxazole (vNPO) and 2-(1-naphthyl)-4-allyl-5-phenyloxazole (allylNPO) monomers are reported. Starting with the organic fluor 2-(1-naphthyl)-5-phenyloxazole (αNPO), the vNPO and allylNPO monomers were synthesized using Stille coupling followed by purification. The final products were obtained with yields of ∼95% and ∼55% for vNPO and allylNPO. The absorption/emission spectra of αNPO, vNPO and allylNPO revealed that vNPO has the largest red-shifted in emission with an average wavelength of ∼420 nm, which is an advantage for increasing photomultiplier tube sensitivity without the need to add a wavelength shifter. Stable scintillating resin beads were prepared through copolymerization of the newly synthesized fluor monomers with styrene or 4-methylstyrene and divinylbenzene in the presence of toluene porogen. The resin beads were chemically stable and retained the ability to scintillate efficiently after energy deposition of beta particles from 99Tc. This result indicates efficient energy transfer occurs from the base polymer to the covalently attached fluors with subsequent fluorescence in the presence of ionizing radiation.
  • Martinez, N.E., Sharp, J.L., Kuhne, W.W., Johnson, T.E., Stafford, C.T., Duff, M.C., 2015. Assessing the use of reflectance spectroscopy in determining CsCl stress in the model species Arabidopsis thaliana. Int. J. Remote Sens. 36, 5887–5915. doi:10.1080/01431161.2015.1110258
    Reflectance spectroscopy is a rapid and non-destructive analytical technique that may be used for assessing plant stress, and has potential applications for use in remediation. Changes in reflectance such as that due to metal stress may occur before damage is visible, and existing studies have shown that metal stress does cause changes in plant reflectance. To further investigate the potential use of reflectance spectroscopy as a method for assessing metal stress in plants, an exploratory study was conducted in which Arabidopsis thaliana plants were treated twice weekly in a laboratory setting with varying levels (0, 0.5, or 5 mM (millimolar)) of caesium chloride (CsCl) solution, and reflectance spectra were collected every week for three weeks using an Analytical Spectral Devices FieldSpec Pro spectroradiometer with both a contact probe (CP) and a field of view (FOV) probe at 36.8 and 66.7 cm, respectively, above the plant. Plants were harvested each week after spectra collection for determination of relative water content and chlorophyll content. A visual assessment of the plants was also conducted using point observations on a uniform grid of 81 points. A mixed-effects model analysis was conducted for each vegetation index (VI) considered to determine the effects of length of treatment, treatment level, view with which spectra were acquired, and the interactions of these terms. Two-way analyses of variance (ANOVAs) were performed on the aforementioned endpoints (e.g. chlorophyll content) to determine the significance of the effects of treatment level and length of treatment. Multiple linear regression (MLR) was used to develop a predictive model for each endpoint, considering VI acquired at each view (CP, high FOV, and low FOV). Of the 14 VI considered, 8 were included in the MLR models. Contact probe readings and FOV readings differed significantly, but FOV measurements were generally consistent at each height.
  • Renock, D., Shuller-Nickles, L.C., 2015. Predicting Geologic Corrosion with Electrodes. Elements 11.
    Ever since humans discovered how to separate metal from its ore mineral, preserving its metallic luster has been a driving force in the advancement of materials science. In modern times, developing materials that will contain and isolate nuclear waste has pushed corrosion science to new limits. We must now predict corrosion rates over geologic time scales, upwards of a million years. This article reviews the electrochemical basics that underpin metal and mineral corrosion and uses that to understand the case study of copper corrosion in nuclear-waste containers. Electrochemistry can also explain electron-transfer processes on mineral surfaces and so offer insight into weathering and environmentally relevant natural redox processes, such as those forming supergene metal deposits.
  • Lynn X. Zhang, Benjamin T. Manard, Brian A. Powell, and R. Kenneth Marcus, “Preliminary Assessment of Potential for Metal-Ligand Speciation in Aqueous Solution via the Liquid Sampling-Atmospheric Pressure Glow Discharge (LS-APGD) Ionization Source: Uranyl Acetate”, Anal. Chem., 87, 7218-7225, 2015.
    The determination of metals, including the generation of metal–ligand speciation information, is essential across a myriad of biochemical, environmental, and industrial systems. Metal speciation is generally affected by the combination of some form of chromatographic separation (reflective of the metal–ligand chemistry) with element-specific detection for the quantification of the metal composing the chromatographic eluent. Thus, the identity of the metal–ligand is assigned by inference. Presented here, the liquid sampling–atmospheric pressure glow discharge (LS-APGD) is assessed as an ionization source for metal speciation, with the uranyl ion–acetate system used as a test system. Molecular mass spectra can be obtained from the same source by simple modification of the sustaining electrolyte solution. Specifically, chemical information pertaining to the degree of acetate complexation of uranyl ion (UO22+) is assessed as a function of pH in the spectral abundance of three metallic species: inorganic (nonligated) uranyl, UO2Ac(H2O)n(MeOH)m+, and UO2Ac2(H2O)n(MeOH)mH+ (n = 1, 2, 3, ...; m = 1, 2, 3, ...). The product mass spectra are different from what are obtained from electrospray ionization sources that have been applied to this system. The resulting relationships between the speciation and pH values have been compared to calculated concentrations of the corresponding uranyl species: UO22+, UO2Ac+, UO2Ac2. The capacity for the LS-APGD to affect both atomic mass spectra and structurally significant spectra for organometallic complexes is a unique and potentially powerful combination.
  • Cross, R.B., L.B. McCarty, N. Tharayil. J.S. McElroy, S. Chen, P.E. McCullough, R.A. Powell, and W. C. Bridges, Jr. 2015. A Pro106 to Ala Substitution is Associated with Resistance to Glyphosate in Annual Bluegrass (Poa annua). Weed Science 63:613-622.
    Glyphosate is used in the transition zone to control annual bluegrass in fully dormant warm-season grasses. A suspected resistant (R) biotype of annual bluegrass was identified on a golf course in South Carolina after at least 10 consecutive years of glyphosate application. Greenhouse bioassays revealed the R biotype was 4.4-fold resistant to glyphosate compared with a standard susceptible (S) biotype. Further studies were conducted to investigate the mechanism conferring glyphosate resistance in the R biotype. Leaf discs of both biotypes accumulated shikimate in response to increasing glyphosate concentration, but the glyphosate concentration resulting in 50% EPSP synthase inhibition as a result of shikimate accumulation (I50) was 4.2-fold higher in the R biotype compared with the S biotype. At the whole plant level, similar levels of shikimate accumulation were observed between biotypes at 6 and 24 h after treatment (HAT) with glyphosate, but greater shikimate accumulation occurred in the S biotype at 72, 120, and 168 HAT. Shikimate levels decreased in the R biotype after 72 HAT. There were no differences in 14C-glyphosate absorption between biotypes. However, more 14C-glyphosate translocated out of the treated leaf in the R biotype and into root tissues over time compared with the S biotype. Partial sequencing of the EPSP synthase gene revealed a point mutation that resulted in an Ala substitution at Pro106. Although other mechanisms may contribute to glyphosate resistance, these results confirm a Pro106 to Ala substitution is associated with resistance to glyphosate in the R annual bluegrass biotype.
  • Hao, N., Moysey, S.M., Powell, B.A., Ntarlagiannis, D. "An evaluation of surface sorption processes using spectral induced polarization and a 22Na tracer" Environmental Science and Technology, 49: 9866-9873, doi: 10.1021/acs.est.5b01327, 2015.
    We investigate mechanisms controlling the complex electrical conductivity of a porous media using noninvasive spectral induced polarization (SIP) measurements of a silica gel during a pH dependent surface adsorption experiment. Sorption of sodium on silica gel surfaces was monitored as the pH of a column was equilibrated at 5.0 and then successively raised to 6.5 and 8.0, but the composition of the 0.01 M NaCl solution was otherwise unchanged. SIP measurements show an increase in the imaginary conductivity of the sample (17.82 ± 0.07 μS/cm) in response to the pH change, interpreted as deprotonation of silanol groups on the silica gel surface followed by sorption of sodium cations. Independent measurements of Na+ accumulation on grain surfaces performed using a radioactive 22Na tracer support the interpretation of pH-dependent sorption as a dominant process controlling the electrical properties of the silica gel (R2= 0.99) and confirms the importance of grain polarization (versus membrane polarization) in influencing SIP measurements of silicate minerals. The number of surface sorption sites estimated by fitting a mechanistic, triple-layer model for the complex conductivity to the SIP data (13.22 × 1016 sites/m2) was 2.8 times larger than that estimated directly by a 22Na mass balance (5.13 × 1016 sites/m2), suggesting additional contributions to polarization exist.
  • Emerson, H.P., and Powell, B. A., “Observations of surface-mediated reduction of Pu(VI) to Pu(IV) on hematite nanoparticles using FTIR-ATR, Radiochimica Acta, 103(8), 553-563, 2015.
    Previous studies have shown that mineral surfaces may facilitate the reduction of plutonium though the mechanisms of the reduction are still unknown. The objective of this study is to use batch sorption and attenuated total reflectance Fourier transform infrared spectroscopy experiments to observe the surface-mediated reduction of plutonium on hematite nanoparticles. These techniques allow for in situ measurement of reduction of plutonium with time and may lead to a better understanding of the mechanisms of surface mediated reduction of plutonium. For the first time, ATR FT-IR peaks for Pu(VI) sorbed to hematite are measured at ∼ 916 cm–1, respectively. The decrease in peak intensity with time provides a real-time, direct measurement of Pu(VI) reduction on the hematite surface. In this work pseudo first order rate constants estimated at the high loadings (22 mgPu/ghematite, 1.34 · 10–6 MPu/m2) for ATR FT-IR are approximately 10 × slower than at trace concentrations based on previous work. It is proposed that the reduced rate constant at higher Pu loadings occurs after the reduction capacity due to trace Fe(II) has been exhausted and is dependent on the oxidation of water and possibly electron shuttling based on the semiconducting nature of hematite. Therefore, the reduction rate at higher loadings is possibly due to the thermodynamic favorability of Pu(IV)-hydroxide complexes.
  • Yang, C., Powell, B. A., Zhang, Shengdong, Z., Rao, L., “Surface complexation modeling of Neptunium(V) sorption to lepidocrocite (-FeOOH)” Radiochimica Acta, 103(10), 707-717, 2015.
    Lepidocrocite (γ-FeOOH), an important iron-bearing mineral found to exist with a relatively high abundance in the soils of the Chinese nuclear test sites, has rarely been studied for its sorption of transuranic elements from the nuclear wastes. This work develops a quantitative surface complexation model describing the sorption and speciation of Np(V) on synthetic lepidocrocite (γ-FeOOH). Batch sorption experiments on γ-FeOOH were performed under a range of conditions (25 ℃, 0.1 M NaClO4, pH = 4 – 11, 5 μM Np(V), and atmospheric conditions). The Diffuse Layer Model (DLM) was applied to describe the surface-complexation reaction. The data were best-fitted with a single surface-complexation reaction, (≡XOH + NpO2+ = XONpO20 + H+) that occurred at the lepidocrocite/water interface to form an inner-sphere Np(V) complex with lepidocrocite. The results are complemented by the Np LIII-edge EXAFS data that show that Np(V) was absorbed on γ-FeOOH as monomeric neptunyl ions, with no observations of multinuclear surface complexes or surface precipitates. A prominent peak at ∼3 Å in the EXAFS Fourier Transform spectra can be attributed to a Np-Fe scattering path, consistent with the formation of an inner sphere Np(V)-lepidocrocite surface complex. Formation of aqueous NpO2(CO3)x1–2x complexes prevents Np(V) sorption at higher pH values but it is unclear if ternary lepidocrocite-Np-carbonate complexes may also form. These data indicate that there are subtle differences in Np(V) interactions with hematite, goethite, and lepidocrocite which is likely a manifestation of the differences in surface reactivity of the three minerals.
  • Wong, J. C., Zavarin, M., Begg, J. C., Kersting, A. B., Powell, B. A. “Effect of Equilibration Time on Pu Desorption from Goethite” Radiochimica Acta, 103(10), 695-705, 2015.
    It has been suggested that strongly sorbing ions such as plutonium may become irreversibly bound to mineral surfaces over time which has implications for near- and far-field transport of Pu. Batch adsorption–desorption data were collected as a function of time and pH to study the surface stability of Pu on goethite. Pu(IV) was adsorbed to goethite over the pH range 4.2 to 6.6 for different periods of time (1, 6, 15, 34 and 116 d). Following adsorption, Pu was leached from the mineral surface with desferrioxamine B (DFOB), a complexant capable of effectively competing with the goethite surface for Pu. The amount of Pu desorbed from the goethite was found to vary as a function of the adsorption equilibration time, with less Pu removed from the goethite following longer adsorption periods. This effect was most pronounced at low pH. Logarithmic desorption distribution ratios for each adsorption equilibration time were fit to a pH-dependent model. Model slopes decreased between 1 and 116 d adsorption time, indicating that overall Pu(IV) surface stability on goethite surfaces becomes less dependent on pH with greater adsorption equilibration time. The combination of adsorption and desorption kinetic data suggest that non-redox aging processes affect Pu sorption behavior on goethite.
  • Tinnacher, R. M., Begg, J. D., Mason, H., Ranville, J., Powell, B. A., Wong, J. C., Kersting, A. B., Zavarin, M. “Effect of fulvic acid surface coatings on plutonium sorption and desorption kinetics on goethite” Environmental Science and Technology, 49(5), 2776-2785, 2015.
    The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presence of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu–FA–mineral complexes could enhance colloid-facilitated Pu transport. However, more representative natural conditions need to be investigated to quantify the relevance of these findings.
  • Shannahan, J. H., Podila, R., Aldossari, A. A., Emerson, H. P., Powell, B. A., Ke, P., Brown, J. M., “Formation of a Protein Corona on Silver Nanoparticles Mediates Cellular Toxicity via Scavenger Receptors” Toxicological Sciences, 143(1), 136-146, 2015.
    Addition of a protein corona (PC) or protein adsorption layer on the surface of nanomaterials following their introduction into physiological environments may modify their activity, bio-distribution, cellular uptake, clearance, and toxicity. We hypothesize that silver nanoparticles (AgNPs) will associate with proteins common to human serum and cell culture media forming a PC that will impact cell activation and cytotoxicity. Furthermore, the role of scavenger receptor BI (SR-BI) in mediating this toxicity was evaluated. Citrate-suspended 20 nm AgNPs were incubated with human serum albumin (HSA), bovine serum albumin (BSA), high-density lipoprotein (HDL), or water (control) to form a PC. AgNPs associated with each protein (HSA, BSA, and HDL) forming PCs as assessed by electron microscopy, hyperspectral analysis, ζ-potential, and hydrodynamic size. Addition of the PC decreased uptake of AgNPs by rat lung epithelial and rat aortic endothelial cells. Hyperspectral analysis demonstrated a loss of the AgNP PC following internalization. Cells demonstrated concentration-dependent cytotoxicity following exposure to AgNPs with or without PCs (0, 6.25, 12.5, 25 or 50 μg/ml). All PC-coated AgNPs were found to activate cells by inducing IL-6 mRNA expression. A small molecule SR-BI inhibitor was utilized to determine the role of SR-BI in the observed effects. Pretreatment with the SR-BI inhibitor decreased internalization of AgNPs with or without PCs, and reduced both cytotoxicity and IL-6 mRNA expression. This study characterizes the formation of a PC on AgNPs and demonstrates its influence on cytotoxicity and cell activation through a cell surface receptor.
  • Powell, B. A., Miller, T., Kaplan, D. I. “On the influence of ionic strength on radium and strontium sorption to sandy loam soils” Journal of the South Carolina Academy of Science, 13(1), 4, 2015.
    Models which can estimate environmental transport of radioactive contaminants in natural and engineered systems are required to 1) deploy effective remediation strategies for contaminated sites, 2) design waste repositories for future waste streams, and 3) ensure protection of human and environmental health in all cases. These models require accurate transport parameters in order to correctly predict how these contaminants will move in the subsurface. This work aimed to determine more accurately the distribution coefficients for radium and strontium sorption to Savannah River Site (SRS) soils. Radium and strontium sorption to the soils was found to be highly dependent upon ionic strength due to competition for ion exchange sites. Radium distribution coefficients (Kd) for the clayey soil were determined to be 185.1 ± 25.63 L kg-1 and 30.35 ± 0.66 L kg-1 for ionic strengths of 0.02M and 0.1M as NaCl which is the approximate ionic strength of groundwater at the SRS. Radium distribution coefficients for the sandy soil were determined to be 24.95 ± 2.97 L kg-1 and 9.05 ± 0.36 L kg-1 for ionic strengths of 0.02M and 0.1M as NaCl. Sorption of Ra2+ was generally greater than Sr2+, consistent with the frequent use of higher distribution coefficients for Ra in performance assessments.
  • Meena, A.H., Kaplan,, D.I., Powell,, B.A., Arai., Y., Chemical stabilization of chromate in blast furnace slag mixed cementitious materials. Chemosphere. 138, 247-252, 2015
    Cement waste form (CWF) technology is among the leading approaches to disposing of metals and liquid low-level nuclear waste in the United States. One such material, saltstone, includes slag, fly ash and Portland cement to enhance the immobilization of contaminants (e.g., Cr, 99Tc) in alkaline liquid wastes. To evaluate the stability of such redox sensitive contaminants in saltstone, the effects of slag as a source of reductant on Cr immobilization was evaluated in aged

2014 Publications

  • Shuller-Nickles, L., Bender, W., Walker, S., Becker, U., 2014. Quantum-Mechanical Methods for Quantifying Incorporation of Contaminants in Proximal Minerals. Minerals 4, 690–715. doi:10.3390/min4030690
    Incorporation reactions play an important role in dictating immobilization and release pathways for chemical species in low-temperature geologic environments. Quantum-mechanical investigations of incorporation seek to characterize the stability and geometry of incorporated structures, as well as the thermodynamics and kinetics of the reactions themselves. For a thermodynamic treatment of incorporation reactions, a source of the incorporated ion and a sink for the released ion is necessary. These sources/sinks in a real geochemical system can be solids, but more commonly, they are charged aqueous species. In this contribution, we review the current methods for ab initio calculations of incorporation reactions, many of which do not consider incorporation from aqueous species. We detail a recently-developed approach for the calculation of incorporation reactions and expand on the part that is modeling the interaction of periodic solids with aqueous source and sink phases and present new research using this approach. To model these interactions, a systematic series of calculations must be done to transform periodic solid source and sink phases to aqueous-phase clusters. Examples of this process are provided for three case studies: (1) neptunyl incorporation into studtite and boltwoodite: for the layered boltwoodite, the incorporation energies are smaller (more favorable) for reactions using environmentally relevant source and sink phases (i.e., ΔErxn(oxides) > ΔErxn(silicates) > ΔErxn(aqueous)). Estimates of the solid-solution behavior of Np5+/P5+- and U6+/Si4+-boltwoodite and Np5+/Ca2+- and U6+/K+-boltwoodite solid solutions are used to predict the limit of Np-incorporation into boltwoodite (172 and 768 ppm at 300 °C, respectively); (2) uranyl and neptunyl incorporation into carbonates and sulfates: for both carbonates and sulfates, it was found that actinyl incorporation into a defect site is more favorable than incorporation into defect-free periodic structures. In addition, actinyl incorporation into carbonates with aragonite structure is more favorable than into carbonates with calcite structure; and (3) uranium incorporation into magnetite: within the configurations tested that preserve charge neutrality (U6+ → 2Fe3+oct/tet or U4+ → Fe2+oct), uranium incorporation into magnetite is most favorable when U6+ replaces octahedral Fe3+ with charge balancing accomplished by an octahedral Fe3+ iron vacancy. At the end of this article, the limitations of this method and important sources of error inherent in these calculations (e.g., hydration energies) are discussed. Overall, this method and examples may serve as a guide for future studies of incorporation in a variety of contexts.
  • Martinez, N.E., Johnson, T.E., Capello, K., Pinder, J.E., 2014. Development and comparison of computational models for estimation of absorbed organ radiation dose in rainbow trout (Oncorhynchus mykiss) from uptake of iodine-131. J. Environ. Radioact. 138, 50–59. doi:10.1016/j.jenvrad.2014.08.001
    This study develops and compares different, increasingly detailed anatomical phantoms for rainbow trout (Oncorhynchus mykiss) for the purpose of estimating organ absorbed radiation dose and dose rates from 131I uptake in multiple organs. The models considered are: a simplistic geometry considering a single organ, a more specific geometry employing additional organs with anatomically relevant size and location, and voxel reconstruction of internal anatomy obtained from CT imaging (referred to as CSUTROUT). Dose Conversion Factors (DCFs) for whole body as well as selected organs of O. mykiss were computed using Monte Carlo modeling, and combined with estimated activity concentrations, to approximate dose rates and ultimately determine cumulative radiation dose (μGy) to selected organs after several half-lives of 131I. The different computational models provided similar results, especially for source organs (less than 30% difference between estimated doses), and whole body DCFs for each model (∼3 × 10−3 μGy d−1 per Bq kg−1) were comparable to DCFs listed in ICRP 108 for 131I. The main benefit provided by the computational models developed here is the ability to accurately determine organ dose. A conservative mass-ratio approach may provide reasonable results for sufficiently large organs, but is only applicable to individual source organs. Although CSUTROUT is the more anatomically realistic phantom, it required much more resource dedication to develop and is less flexible than the stylized phantom for similar results. There may be instances where a detailed phantom such as CSUTROUT is appropriate, but generally the stylized phantom appears to be the best choice for an ideal balance between accuracy and resource requirements.
  • Duff, M.C., Kuhne, W.W., Halverson, N.V., Chang, C.-S., Kitamura, E., Hawthorn, L., Martinez, N.E., Stafford, C., Milliken, C.E., Caldwell, E.F., Stieve-Caldwell, E., 2014. mRNA Transcript abundance during plant growth and the influence of Li+ exposure. Plant Sci. 229, 262–279. doi:10.1016/j.plantsci.2014.10.004
    This study develops and compares different, increasingly detailed anatomical phantoms for rainbow trout (Oncorhynchus mykiss) for the purpose of estimating organ absorbed radiation dose and dose rates from 131I uptake in multiple organs. The models considered are: a simplistic geometry considering a single organ, a more specific geometry employing additional organs with anatomically relevant size and location, and voxel reconstruction of internal anatomy obtained from CT imaging (referred to as CSUTROUT). Dose Conversion Factors (DCFs) for whole body as well as selected organs of O. mykiss were computed using Monte Carlo modeling, and combined with estimated activity concentrations, to approximate dose rates and ultimately determine cumulative radiation dose (μGy) to selected organs after several half-lives of 131I. The different computational models provided similar results, especially for source organs (less than 30% difference between estimated doses), and whole body DCFs for each model (∼3 × 10−3 μGy d−1 per Bq kg−1) were comparable to DCFs listed in ICRP 108 for 131I. The main benefit provided by the computational models developed here is the ability to accurately determine organ dose. A conservative mass-ratio approach may provide reasonable results for sufficiently large organs, but is only applicable to individual source organs. Although CSUTROUT is the more anatomically realistic phantom, it required much more resource dedication to develop and is less flexible than the stylized phantom for similar results. There may be instances where a detailed phantom such as CSUTROUT is appropriate, but generally the stylized phantom appears to be the best choice for an ideal balance between accuracy and resource requirements.
  • Martinez, N.E., Kraft, S.L., Johnson, T.E., 2014. A Proposed Simple Model for Estimating Occupational Radiation Dose to Staff from Veterinary 18F-FDG Pet Procedures. Health Phys. 106, 583–591. doi:10.1097/HP.0000000000000037
    Several studies have been conducted concerning the radiation dose to hospital personnel from positron emission tomography (PET) radiopharmaceuticals, but to date only one parallel study has been conducted for veterinary staff. Veterinary patients present challenges not encountered with human patients, as they require anesthesia and therefore more intensive monitoring than human patients. This paper presents a simple model for estimating the effective radiation dose to veterinary staff using occupational dose data from PET studies at Colorado State University's (CSU) James L. Voss Veterinary Teaching Hospital. The model consists of three point sources within a soft tissue cylinder, and sample calculations are provided for estimating dose to nuclear medicine technologists and an anesthesia technologist based on four different sized dogs. The estimated doses are within the range of actual occupational doses published previously. There are different protocols for the sequence of events in veterinary PET, specifically the order of anesthesia induction and radiopharmaceutical injection. When F-FDG injection is performed prior to anesthesia induction, the estimated dose is between 1.5 and 3.6 times higher than the doses received if injection is done after anesthesia induction, although expected doses for both protocols are below occupational dose limits based on a case load of 100 veterinary patients per year. The model is based on the techniques used at CSU, but it can be modified for different hospitals as well as differently sized animals.
  • Martinez, N.E., Johnson, T.E., Pinder, J.E., 2014. Influence of Lake Trophic Structure on Iodine-131 Accumulation and Subsequent Cumulative Radiation Dose to Trout Thyroids. J. Environ. Radioact. 131, 62–71. doi:10.1016/j.jenvrad.2013.10.015
    Iodine-131 is a major component of the atmospheric releases following reactor accidents, and the passage of (131)I through food chains from grass to human thyroids has been extensively studied. By comparison, the fate and effects of (131)I deposition onto lakes and other aquatic systems have been less studied. In this study we: (1) reanalyze 1960s data from experimental releases of (131)I into two small lakes; (2) compare the effects of differences in lake trophic structures on the accumulation of (131)I by fish; (3) relate concentrations in fish and fish tissues to that in the water column using empirically estimated uptake (L kg(-1) d(-1)) and loss (d(-1)) parameters; and (4) show that the largest concentrations in the thyroids of trout (Oncorhynchus mykiss) may occur from 8 to 32 days after initial release. Iodine-131 concentration in trout thyroids at 30-days post release may be >1000 times that in the water. Estimates of cumulative radiation dose (mGy) to thyroids computed using an anatomically-appropriate model of trout thyroid structure within the Monte Carlo N-particle modeling software predicted cumulative thyroid doses that increased approximately linearly after the first 8 days and resulted in 32-day cumulative thyroid doses that ranged from 6 mGy g(-1) to 18 mGy g(-1) per 1 Bq mL(-1) of initial (131)I in the water depending upon fish size. The majority of this dose is due to beta emissions, and the dose varies with positions in the thyroid tissue.
  • Martinez, N.E., Johnson, T.E., Pinder, J.E., 2014. Influence of Lake Trophic Structure on Iodine-131 Accumulation and Subsequent Cumulative Radiation Dose to Trout Thyroids. J. Environ. Radioact. 131, 62–71. doi:10.1016/j.jenvrad.2013.10.015
    Iodine-131 is a major component of the atmospheric releases following reactor accidents, and the passage of (131)I through food chains from grass to human thyroids has been extensively studied. By comparison, the fate and effects of (131)I deposition onto lakes and other aquatic systems have been less studied. In this study we: (1) reanalyze 1960s data from experimental releases of (131)I into two small lakes; (2) compare the effects of differences in lake trophic structures on the accumulation of (131)I by fish; (3) relate concentrations in fish and fish tissues to that in the water column using empirically estimated uptake (L kg(-1) d(-1)) and loss (d(-1)) parameters; and (4) show that the largest concentrations in the thyroids of trout (Oncorhynchus mykiss) may occur from 8 to 32 days after initial release. Iodine-131 concentration in trout thyroids at 30-days post release may be >1000 times that in the water. Estimates of cumulative radiation dose (mGy) to thyroids computed using an anatomically-appropriate model of trout thyroid structure within the Monte Carlo N-particle modeling software predicted cumulative thyroid doses that increased approximately linearly after the first 8 days and resulted in 32-day cumulative thyroid doses that ranged from 6 mGy g(-1) to 18 mGy g(-1) per 1 Bq mL(-1) of initial (131)I in the water depending upon fish size. The majority of this dose is due to beta emissions, and the dose varies with positions in the thyroid tissue.
  • Hixon, A. E., and Powell, B. A., “Observed changes in the mechanism and rates of Pu(V) reduction on hematite as a function of total plutonium concentration” Environmental Science and Technology, 48, 9255-9262, 2014
    Changes in aqueous- and solid-phase plutonium oxidation states were monitored as a function of time and plutonium concentration in hematite (α-Fe2O3) suspensions containing initially Pu(V). Batch kinetic experiments were conducted at plutonium concentrations between 10–8 and 10–6 M at pH 5 and 0.3 g/L (9.3 m2/L) hematite. Surface-mediated reduction of Pu(V) was observed under all conditions studied. However, differences in the reaction kinetics demonstrate that the mechanism of Pu(V) reduction changes as a function of plutonium concentration. Adsorption of Pu(V) was found to be the rate-limiting step at plutonium concentrations less than approximately 10–7 M Pu(V). Plutonium reduction in these systems was attributed to trace amounts of Fe(II) in the hematite structure. Reduction of Pu(V) was found to be the rate-limiting step at concentrations higher than approximately 10–6 M Pu(V) and is attributed to the formation of PuO2+x·nH2O nanoparticles and the Nernstian favorability of Pu(IV) surface complexes. The reaction order with respect to plutonium concentration was found to be −0.68 ± 0.09, indicating that there is a concentration dependence in these systems. This work strongly suggests that the kinetics of experiments carried out under high plutonium concentrations (i.e., >10–7 M Pu) cannot be directly extrapolated to environmental concentrations of plutonium.
  • Kaplan, D. I., Miller, T. J., Diprete, D., Powell, B. A., “Long-term radiostrontium interactions and transport through sediment” Environmental Science and Technology, 48, 8919-8925, 2014
    Radioactive strontium is one of the most common radiological contaminants in groundwater and soil. Objectives of this study were to (1) evaluate Sr transport through an 11-year-long field lysimeter study and (2) quantify secondary aging effects between Sr and sediment that may need to be considered for long-term transport modeling. Batch sorption/desorption tests were conducted with 85Sr, 88Sr, and 90Sr using a sediment recovered from a field lysimeter containing a glass pellet amended with high-level nuclear waste for 24 years. Sr was largely reversibly and linearly sorbed. 85Sr sorption coefficients (Kd, concentration ratios of solids/liquids) after a 23-day contact period were about the same as the 90Sr desorption Kd values after a 24-year contact period: sorption Kd = 32.1 ± 3.62 mL g–1 and desorption Kd = 43.1 ± 11.4 mL g–1. Numerical modeling of the lysimeter 90Sr depth profile indicated that a Kd value of 32 mL g–1 fit the data best. The Kdconstruct captured most of the data trends above and below the source term, except for immediately below the source where the model clearly overestimated Sr mobility. 90Sr desorption tests suggested that the overestimated mobility may be attributed to a second, slower sorption reaction that occurs over a course of months to decades.
  • Zimmerman, T., Zavarin, M., Powell, B. A., “Influence of humic acid on plutonium sorption to gibbsite: Determination of Pu-humic acid complexation constants and ternary sorption studies” Radiochimica Acta, 102(7), 629-643, 2014
    In this work stability constants describing Pu(IV), Th(IV), and Np(V) binding to Leonardite humic acid (HA) were determined using a discrete pKa model. A hybrid ultra-filtration/equilibrium dialysis, ligand exchange technique was used to generate the partitioning data. Ethylenediaminetetraacetic acid (EDTA) was used as a reference ligand to allow the aqueous chemistry of the Pu(IV)-HA system to be examined over a range of pH values, while minimizing the possibility of precipitation of Pu(IV). The conditional stability constant for Pu(IV) complexation with HA determined as part of this work is logβ112 = 6.76 ± 0.14 based on the equation: Pu4+ + HL3 + 2H2O <-> Pu(OH)2L3+ + 3H+ where HA is represented by HL3 (a binding site on the HA with a pKa value of 7). This value is three orders of magnitude higher than the Th(IV)-HA constant and between six and eight orders of magnitude higher than the Np(V)-HA complex. The magnitude of the stability constants and the general trend of increasing complexation strength with increasing pH is consistent with previous observations. The Pu(IV)-HA stability constants were used to model sorption of Pu(IV) to gibbsite in the presence of HA. Assuming only aqueous Pu-HA complexes and AlOH-Pu surface complexes, the model was unable to predict the observed data which exhibited greater sorption at pH 4 relative to pH 6; a phenomenon which does not occur in the absence of HA. Therefore, this study demonstrates that ternary Pu-HA-gibbsite complexes may form under low pH conditions and exhibit greater sorption than that observed in the absence of HA. Although the presence of HA may increase the solubility/aqueous concentrations of Pu in the absence of a solid phase, formation of ternary complexes may indeed retard the subsurface migration of Pu. The corollary to this finding is that increased mobility may occur if the ternary surface complex forms on a mobile colloid rather than part of the subsurface matrix.

2013 Publications

  • Grogan, K.P., DeVol, T.A., 2013. Development of a novel method for the determination of aqueous inorganic 129I speciation. Anal. Chem. 85, 4658–4665. doi:10.1021/ac4003084
    The objective of this research was to develop a method suitable for the determination of aqueous concentrations of radioactive iodine as I2, I–, and IO3–. As one of the primary risk-drivers and contaminants of concern at nuclear waste repositories, the accurate determination of 129I in aqueous systems is of significant concern. The redox-active nature of iodine makes its mobility and fate in the environment difficult to predict, thus underscoring the importance of species-specific determination of iodine concentrations. The developed method couples solid phase extraction with liquid scintillation counting, and scintillating anion exchange with a flow-cell detection system for a sequential measurement of each iodine species. Solid phase extraction disks were impregnated with polyvinylpyrrolidone for the selective extraction and stabilization of I2 with subsequent analysis by liquid scintillation counting. Aqueous I– was concentrated and measured by a previously developed flow-cell system utilizing scintillating anion-exchange resin. A subsequent chemical reduction of IO3– to I– in the effluent was used to quantify IO3– by the same flow-cell system. Nearly quantitative results were found for standardized single-species samples of I2 (95%), I– (101%), and IO3– (91%), respectively, while consistent measurements were obtained for multispecies samples using the developed method and algorithm.
  • Shuller-Nickles, L.C., Ewing, R.C., Becker, U., 2013. Atomistic calculations of the thermodynamic properties of mixing for tetravalent metal dioxide solid solutions: (Zr, Th, Ce)O2. J. Solid State Chem. 197, 550–559. doi:10.1016/j.jssc.2012.08.033
    The thermodynamic mixing properties for isometric ThxCe1−xO2, CexZr1−xO2, and ThxZr1−xO2 were determined using quantum-mechanical calculations and subsequent Monte-Carlo simulations. Although the ThxCe1−xO2 binary indicates exsolution below 600 K, the energy gain due to exsolution is small (Eexsoln=1.5 kJ/(mol cations) at 200 K). The energy gain for exsolution is significant for the binaries containing Zr; at 1000 K, Eexsoln=6 kJ/(mol cations) for the CexZr1−xO2 binary, and Eexsoln=17 kJ/(mol cations) for the ThxZr1−xO2 binary. The binaries containing Zr have limited miscibility and cation ordering (at 200 K for x=0.5). At 1673 K, only 4.0 and 0.25 mol% ZrO2 can be incorporated into CeO2 and ThO2, respectively. Solid-solution calculations for the tetragonal ThxZr1−xO2 binary show decreased mixing enthalpy due to the increased end-member stability of tetragonal ZrO2. Inclusion of the monoclinic ZrO2 is predicted to further reduce the mixing enthalpy for binaries containing Zr.
  • Shuller, L.C., Ewing, R.C., Becker, U., 2013. Np-incorporation into uranyl phases: A quantum–mechanical evaluation. J. Nucl. Mater. 434, 440–450. doi:10.1016/j.jnucmat.2011.04.016
    Density functional theory calculations are used to compare mechanisms of charge-balanced Np5+-incorporation into boltwoodite [K(UO2)(SiO3OH)(H2O)1.5]. The charge-balancing mechanisms considered include: (i) H+ addition (Np5+ + H+ ↔ U6+), (ii) interlayer substitution (Np5+ + Ca2+/Mg2+ ↔ U6+ + K+), and (iii) intra-layer substitution (Np5+ + P5+ ↔ U6+ + Si4+). The choice of the source (of Np5+, H+, Ca2+, Mg2+, P5+) and sink (of substituted U6+, K+, Si4+) phases, the reference phases, for the cations involved in the incorporation reaction greatly affects the final calculated incorporation energy (ΔErxn). The incorporation energies using oxide (ΔErxn = 183.5 kJ/mol) and silicate (ΔErxn = 67.5 kJ/mol) reference phases are compared for the interlayer substitution mechanism. Since both the source of Np in environmental systems and the cations released are typically aqueous complexes, a newly-developed approach of combining cluster and periodic simulations was employed to model exchange with aqueous complexes. For the H+ addition mechanism, incorporation from oxides reference phases (ΔErxn = 93.6 kJ/mol) is less favorable than from aqueous (ΔErxn = 12.5 kJ/mol) reference species. Estimates of the solid-solution behavior of Np5+/P5+- and U6+/Si4+-boltwoodite and Np5+/Ca2+- and U6+/K+-boltwoodite solid solutions are used to predict the limit of Np-incorporation into boltwoodite. For the interlayer and intra-layer substitution mechanisms, the substitution energies are 67.5 and −2.9 kJ/mol, respectively, resulting in a maximum amount of incorporation at 300 °C of 172 ppm and 768 ppm, respectively.
  • Gillens, A. and Powell, B. A., “Rapid quantification of TBP and TBP degradation product ratios by FTIR-ATR” Journal of Radioanalytical and Nuclear Chemistry, 296(2), 859-868, 2013
    Tri-n-butyl phosphate (TBP) is the key complexant within the plutonium and uranium reduction extraction process used to extract uranium and plutonium from used nuclear fuel. During reprocessing TBP degrades to dibutyl phosphate (DBP), butyl acid phosphate (MBP), butanol, and phosphoric acid over time. A method for rapidly monitoring TBP degradation is needed for the support of nuclear forensics. Therefore, a Fourier transform infrared spectrometry-attenuated total reflectance (FTIR-ATR) technique was developed to determine approximate peak intensity ratios of TBP and its degradation products. The technique was developed by combining variable concentrations of TBP, DBP, and MBP to simulate TBP degradation. This method is achieved by analyzing selected peak positions and peak intensity ratios of TBP and DBP at different stages of degradation. The developed technique was tested on TBP samples degraded with nitric acid. In mock degradation samples, the 1,235 cm−1 peak position shifts to 1,220 cm−1 as the concentration of TBP decreases and DBP increases. Peak intensity ratios of TBP positions at 1,279 and 1,020 cm−1 relative to DBP positions at 909 and 1,003 cm−1 demonstrate an increasing trend as the concentration of DBP increases. The same peak intensity ratios were used to analyze DBP relative to MBP whereas a decreasing trend is seen with increasing DBP concentrations. The technique developed from this study may be used as a tool to determine TBP degradation in nuclear reprocessing via a rapid FTIR-ATR measurement without gas chromatography analysis.
  • Begg, J. D., Zavarin, M., Zhao, P., Tumey, S. J., Powell, B. A., Kersting, A. B., “Pu(V) and Pu(IV) sorption to montmorillonite” Environmental Science and Technology, 47(10), 5146-5153, 2013.
    Plutonium (Pu) adsorption to and desorption from mineral phases plays a key role in controlling the environmental mobility of Pu. Here we assess whether the adsorption behavior of Pu at concentrations used in typical laboratory studies (≥10–10 [Pu] ≤ 10–6 M) are representative of adsorption behavior at concentrations measured in natural subsurface waters (generally <10–12M). Pu(V) sorption to Na-montmorillonite was examined over a wide range of initial Pu concentrations (10–6–10–16 M). Pu(V) adsorption after 30 days was linear over the wide range of concentrations studied, indicating that Pu sorption behavior from laboratory studies at higher concentrations can be extrapolated to sorption behavior at low, environmentally relevant concentrations. Pu(IV) sorption to montmorillonite was studied at initial concentrations of 10–6–10–11 M and was much faster than Pu(V) sorption over the 30 day equilibration period. However, after one year of equilibration, the extent of Pu(V) adsorption was similar to that observed for Pu(IV) after 30 days. The continued uptake of Pu(V) is attributed to a slow, surface-mediated reduction of Pu(V) to Pu(IV). Comparison between rates of adsorption of Pu(V) to montmorillonite and a range of other minerals (hematite, goethite, magnetite, groutite, corundum, diaspore, and quartz) found that minerals containing significant Fe and Mn (hematite, goethite, magnetite, and groutite) adsorbed Pu(V) faster than those which did not, highlighting the potential importance of minerals with redox couples in increasing the rate of Pu(V) removal from solution.
  • Estes, S. L., Arai, Y., Becker, U., Fernando, S., Yuan, K., Ewing, R. C., Zhang, J., Shibata, T., Powell, B. A. “A Self-Consistent Model Describing the Thermodynamics of Eu(III) Adsorption onto Hematite” Geochimica et Cosmochimica Acta, 122, 430-447, 2013.
    The environmental fate of actinides is greatly influenced by interfacial reactions, including adsorption onto solid surfaces where the adsorption of trivalent and tetravalent actinides is generally a very strong and potentially irreversible reaction. Changes in the primary hydration sphere of the actinide during inner-sphere adsorption could greatly influence the thermodynamics of these reactions. However, few researchers have studied actinide adsorption thermodynamics. Therefore, using Eu(III) as an analog for trivalent actinides, we examined the thermodynamics of Eu(III) adsorption onto hematite, with particular emphasis on changes in the Eu(III) coordination number and the influence of temperature upon sorption. Our working hypothesis was that a decrease in hydration number upon adsorption, as indicated by a decrease in coordination number and an increase in adsorption with increasing temperature, results in energetically favorable sorption reactions, which are driven by a large, positive entropy term. To perform these studies, we applied the diffuse layer model to describe Eu(III) adsorption onto hematite at pH values ranging from ∼3 to 7 and at 15, 25, 35, and 50 °C. Additionally, we characterized the Eu(III)–hematite surface complex and changes in the Eu(III) primary hydration sphere using extended X-ray absorption fine structure spectroscopy (EXAFS) and computational modeling. High-resolution transmission electron microscopy (HRTEM) was used to identify possible europium surface precipitates or morphological changes in the hematite. The data indicate that the adsorption reaction (1) is endothermic, (2) proceeds with a decrease in the Eu(III) coordination number, and (3) results in the formation of a bidentate mononuclear surface complex, ( FeO)2Eu+. The enthalpy and entropy values for the formation of this surface complex, which were estimated using a van’t Hoff plot, were 131 ± 8 kJ mol−1 and 439 ± 26 J K−1 mol−1, respectively, indicating that adsorption of Eu(III) onto hematite is entropically driven. Additionally, we suggest that the decrease in Eu(III) coordination number and the large entropy term are due to the loss of coordinating water molecules from the Eu(III) hydration sphere.
  • Hixon, A.E.; Arai, Y.; Powell, B.A., “Examination of the effect of alpha radiolysis of plutonium(V) sorption to quartz using multiple plutonium isotopes,” Journal of Colloid and Interface Science, 403, 105-112, 2013.
    The objective of this research was to determine if radiolysis at the mineral surface was a plausible mechanism for surface-mediated reduction of plutonium. Batch sorption experiments were used to monitor the amount of plutonium sorbed to high-purity quartz as a function of time, pH, and total alpha radioactivity. Three systems were prepared using both 238Pu and 242Pu in order to increase the total alpha radioactivity of the mineral suspensions while maintaining a constant plutonium concentration. The fraction of sorbed plutonium increased with increasing time and pH regardless of the total alpha radioactivity of the system. Increasing the total alpha radioactivity of the solution had a negligible effect on the sorption rate. This indicated that surface-mediated reduction of Pu(V) in these systems was not due to radiolysis. Additionally, literature values for the Pu(V) disproportionation rate constant did not describe the experimental results. Therefore, Pu(V) disproportionation was also not a main driver for surface-mediated reduction of plutonium. Batch desorption experiments and X-ray absorption near edge structure spectroscopy were used to show that Pu(IV) was the dominant oxidation state of sorbed plutonium. Thus, it appears that the observed surface-mediated reduction of Pu(V) in the presence of high-purity quartz was based on the thermodynamic favorability of a Pu(IV) surface complex.
  • Hixon, A.E., DiPrete, D.P., DeVol, T.A., “Development of a Colorimetric Test for Quantification of Uranium in Drinking Water,” Journal of Radioanalytical and Nuclear Chemistry, V 298, #1, 419-427, 2013.
    A colorimetric method was developed for the determination of uranium in groundwater. The detection limit for the method is approximately 25 μg/L uranium, which is below the maximum contaminant level for uranium in drinking water, 30 μg/L. The method is rapid and requires little technical training to conduct, allowing it to be used by consumers, in the laboratory, or in the field. The two-step technique involves preconcentrating uranium using a U/TEVA-2 extraction chromatographic resin followed by complexation with a pyridylazo indicator dye, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol. If color change is visible to the eye, the concentration of uranium in groundwater is above the detection limit. Preconcentration using U/TEVA-2 also serves to eliminate metals that may interfere with the quantification of uranium.
  • Lolap, G.N., DeVol T.A., “Correlating the Luminosity Parameters to Pulse Shape Discrimination,” IEEE Transactions on Nuclear Science, 60 (4) 2958-2965, 2013.
    Monte Carlo simulations were used to investigate the correlation between luminosity parameters and pulse shape discrimination (PSD) and subsequently compared with experimental results from CsI:Tl. Luminosity intensity parameters Af, As (fast and slow initial luminosities) and temporal luminosity parameters τf, τs (fast and slow decay time constants) of a dual decay mode scintillator were applied to create a dynamic model with Crystal Ball simulation system. The simulated pulses were analyzed with charge comparison (CC) and constant time discrimination (CTD) PSD methods followed by quantification of the histogrammed pulse data with Figure of Merit (FoM) and spillover (pulse misclassification). Performance in terms of FoM and spillover is compared with that of fixed reference pulses set at (Af τf/As τs)γ = 1 and (Af τf/As τs)γ = 0.1. For the CC method, independent of the reference pulse characteristics [(Af τf/As τs)γ = 1 or = 0.1], τs is the most influential parameter for PSD as compared with Af, As, and τf. For the CTD method, Af and As are seen to have less influence over the PSD compared to τf and τs when (Af τf/As τs)γ = 1 and τf is the most influential parameter for both reference pulses. Using both methods with either reference pulse applied, the scintillator having luminosity parameters such that is classified as having poor PSD. Excellent correlation is observed between the simulation and the experimental results with CsI:Tl, which is known for very good α/β(γ) pulse shape discrimination. This study is useful for describing how the luminosity parameters affects PSD.
  • Luo, P., Sharp, J.L., DeVol, T.A., “Bayesian Analyses of Time-Interval Data for Environmental Radiation Monitoring,” Health Physics Journal, 104 (1), 15-25, 2013.
    Time-interval (time difference between two consecutive pulses) analysis based on the principles of Bayesian inference was investigated for online radiation monitoring. Using experimental and simulated data, Bayesian analysis of time-interval data [Bayesian (ti)] was compared with Bayesian and a conventional frequentist analysis of counts in a fixed count time [Bayesian (cnt) and single interval test (SIT), respectively]. The performances of the three methods were compared in terms of average run length (ARL) and detection probability for several simulated detection scenarios. Experimental data were acquired with a DGF-4C system in list mode. Simulated data were obtained using Monte Carlo techniques to obtain a random sampling of the Poisson distribution. All statistical algorithms were developed using the R Project for statistical computing. Bayesian analysis of time-interval information provided a similar detection probability as Bayesian analysis of count information, but the authors were able to make a decision with fewer pulses at relatively higher radiation levels. In addition, for the cases with very short presence of the source (< count time), time-interval information is more sensitive to detect a change than count information since the source data is averaged by the background data over the entire count time. The relationships of the source time, change points, and modifications to the Bayesian approach for increasing detection probability are presented.

NEESRWM Director: Dr. Tim DeVol
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