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Investigation of microscopic radiation damage in waste forms using ODNMR and AEM techniques

Description: This report summarizes work done after 2 years of a 3-year project. Using analytic electron microscopic and selective laser spectroscopic techniques, the authors first examined lanthanide orthophosphate crystals of YPO{sub 4} and LuPO{sub 4} that accumulated self-radiation damage from dopant (1 wt.%) {sup 244}Cm ions for 17 years. Although the accumulated dose of radiation (> 10{sup 18} alpha-decay events/mg) is significantly high, the samples that they examined physically remain crystalline on a macroscopic scale. Amorphization is not evident, even though isolated defects of various sizes were observed. Microscopic radiation effects in the crystals were manifested by (1) individual defect clusters of 2 to 5 nm size, which resemble disordered fission tracks, and (2) bubbles of 5 to 20 nm that are attributed to accumulation of He atoms generated during alpha decay events. These bubbles are relatively mobile and easily coalesce in electron microscopy studies due to enhanced diffusion arising from electron irradiation. They have observed that, when exposed to an electron beam, the bubbles aggregated as a function of exposure time. This observation thus provides additional evidence that the bubbles developed from the aggregation of helium atoms that were created from alpha-decay of Cm-244, and the local lattice recovered from radiation damage. In addition to bubbles and fission tracks of nanometer sizes, there exist smaller scale structural defects and lattice strains that were revealed from selective laser excitation and fluorescence spectra. These defects are attributed to alpha-decay induced structural damage that occurred randomly throughout the lattice. Annealing of the samples at 773 K for 12 hours removed more of the residual defects.
Date: April 4, 2000
Creator: Liu, G.
Partner: UNT Libraries Government Documents Department

Investigation of microscopic radiation damage in waste forms using ODNMR and AEM techniques. 1998 annual progress report

Description: 'This project seeks to understand the microscopic effects of radiation damage in nuclear waste forms. The authors approach to this challenge encompasses studies of crystals and glass containing short-lived alpha- and beta-emitting actinides with electron microscopy, laser spectroscopy, and computational modeling and simulation. Much of the initial effort has focused on alpha-decay induced microscopic damage in 17-year old samples of crystalline yttrium and lutetium orthophosphates and thorium dioxide that initially contained {approximately}1% of the alpha-emitting isotope Cm-244 (18.1 y half life) or the beta-emitting isotope Bk-249 (0.88 y half life). Studies will also be conducted on borosilicate glasses that contain Cm-244 or Am-241, respectively. The goal is to gain clear insight into accumulated radiation damage and the influence of aging on such damage, which are critical factors in the long-term performance of high-level nuclear waste forms. Amorphization previously has been thought to be the most important effect of radiation damage in crystalline and ceramic materials. The studies show that for alpha-emitting actinide ions in certain crystalline phosphates, amorphization is not a significant effect of radiation damage. Instead, formation of microscopic cavities (bubbles) is an important consequence of alpha-decay events. This amorphization-resistant property makes orthophosphates a very attractive high level nuclear waste form. However, aggregation and mobilization of cavities (bubbles) might increase the leach rate of radionuclides and influence the long-term stability of the waste forms. Further research is needed before the authors can draw a final conclusion on the long-term effects of radiation damage in high level waste forms.'
Date: June 1, 1998
Creator: Liu, G.
Partner: UNT Libraries Government Documents Department

Investigation of microscopic radiation damage in waste forms using ODNMR and AEM techniques. 1997 annual progress report

Description: 'This project seeks to understand the microscopic effects of radiation damage in nuclear waste forms. The authors approach to this challenge encompasses studies in electron microscopy, laser spectroscopy, and computational modeling and simulation. During this first year of the project, efforts have focused on a-decay induced microscopic damage in crystalline orthophosphates (YPO{sub 4} and LuPO{sub 4}) that contain the short-lived a-emitting isotope {sup 244}Cm (t{sub 1/2} = 18.1 y). The samples that they studied were synthesized in 1980 and the initial {sup 244}Cm concentration was {approximately}1%. Studying these materials is of importance to nuclear waste management because of the opportunity to gain insight into accumulated radiation damage and the influence of aging on such damage. These factors are critical to the long-term performance of actual waste forms [1]. Lanthanide orthophosphates, including LuPO{sub 4} and YPO{sub 4}, have been suggested as waste forms for high level nuclear waste [2] and potential hosts for excess weapons plutonium [3,4]. The work is providing insight into the characteristics of these previously known radiation-resistant materials. They have observed loss of crystallinity (partial amorphization) as a direct consequence of prolonged exposure to intense alpha radiolysis in these materials. More importantly, the observation of microscopic cavities in these aged materials provides evidence of significant chemical decomposition that may be difficult to detect in the earlier stages of radiation damage. The preliminary results show that, in characterizing crystalline compounds as high level nuclear waste forms, chemical decomposition effects may be more important than lattice amorphization which has been the focus of many previous studies. More extensive studies, including in-situ analysis of the dynamics of thermal annealing of self-radiation induced amorphization and cavity formation, will be conducted on these aged {sup 244}Cm:LuPO{sub 4} and {sup 244}Cm:YPO{sub 4} samples, along with other related compounds and glasses, in next two years ...
Date: September 1, 1997
Creator: Liu, G.
Partner: UNT Libraries Government Documents Department

Modeling crystal-field interaction for f-elements in LaCl{sub 3}.

Description: The results of crystal field calculations in the framework of exchange charge model (ECM) are reported for trivalent lanthanide and actinide ions doped into LaCl{sub 3}. Whereas the scalar strength of the model crystal field parameters are consistent with that previously determined by fitting the experimental data, the sign of the second-order parameter is found to be negative, in contrast to previous reports. The contribution from long-range electrostatic interactions exceeds that from the nearest neighboring ligands and leads to the negative sign of the second-order crystal field parameter. Other interaction mechanisms including overlap, covalence, and charge exchange are less important to the second order parameter, but dominate the fourth- and sixth-order parameters. This work provides a consistent interpretation of the previously controversial experimental results for both lanthanide and actinide ions in this classical host.
Date: July 14, 1997
Creator: Liu, G. K. & Zhorin, V. V.
Partner: UNT Libraries Government Documents Department

The Dependence of Cloud Particle Size on Non-Aerosol-Loading Related Variables

Description: An enhanced concentration of aerosol may increase the number of cloud drops by providing more cloud condensation nuclei (CCN), which in turn results in a higher cloud albedo at a constant cloud liquid water path. This process is often referred to as the aerosol indirect effect (AIE). Many in situ and remote sensing observations support this hypothesis (Ramanathan et al. 2001). However, satellite observed relations between aerosol concentration and cloud drop size are not always in agreement with the AIE. Based on global analysis of cloud effective radius (r{sub e}) and aerosol number concentration (N{sub a}) derived from satellite data, Sekiguchi et al. (2003) found that the correlations between the two variables can be either negative, or positive, or none, depending on the location of the clouds. They discovered that significantly negative r{sub e} - N{sub a} correlation can only be identified along coastal regions of the continents where abundant continental aerosols inflow from land, whereas Feingold et al. (2001) found that the response of r{sub e} to aerosol loading is the greatest in the region where aerosol optical depth ({tau}{sub a}) is the smallest. The reason for the discrepancy is likely due to the variations in cloud macroscopic properties such as geometrical thickness (Brenguier et al. 2003). Since r{sub e} is modified not only by aerosol but also by cloud geometrical thickness (H), the correlation between re and {tau}{sub a} actually reflects both the aerosol indirect effect and dependence of H. Therefore, discussing AIE based on the r{sub e}-{tau}{sub a} correlation without taking into account variations in cloud geometrical thickness may be misleading. This paper is motivated to extract aerosols' effect from overall effects using the independent measurements of cloud geometrical thickness, {tau}{sub a} and r{sub e}.
Date: March 18, 2005
Creator: Shao, H. & Liu, G.
Partner: UNT Libraries Government Documents Department

Energy up-conversion and trapping: Dynamics of 5f states of Bk sup 4+ in CeF sub 4

Description: Energy transfer mechanisms of excited 5f states of Bk{sup 4+} (0.05 atom %) in CeF{sub 4} containing circa 0.95 atom % Cf{sup 4+} have been investigated at 4 K. The observed anti-Stokes fluorescence arises from both up-conversion and two-photon excitation. Nonexponential decays of Stokes fluorescence are ascribed to both excitation-excitation annihilation and site-dependent trapping processes and, therefore, are not describable by the Inokuti-Hirayama or exciton annihilation models. Based on the Forster-Dexter energy transfer theory, a new model is developed to fit the observed fluorescence decay data. 16 refs., 3 figs.
Date: January 1, 1991
Creator: Liu, G.K. & Beitz, J.V.
Partner: UNT Libraries Government Documents Department

An in situ transmission electron microscopy study of the thermalstability of near-surface microstructures induced by deep rolling andlaser-shock peening

Description: Mechanical surface treatments are known to be effective at improving the fatigue resistance of metallic alloys at elevated temperatures ({approx}550-600 C), even though the near-surface compressive residual stress fields have been annealed out. We have investigated the thermal stability of near-surface microstructures induced by deep rolling and laser-shock peening in an austentic stainless steel (AISI 304) and a titanium alloy (Ti-6Al-4V) using in situ hot-stage transmission electron microscopy. It is found that the improvements in fatigue resistance at elevated temperature are related to the high-temperature stability of the work-hardened near-surface microstructure in each case.
Date: February 24, 2003
Creator: Altenberger, I.; Stach, E.A.; Liu, G.Y.; Nalla, R.K. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Photon avalanche up-conversion in holmium doped fluoride glasses

Description: Photon avalanche green up-conversion emission centered at 545 nm has been observed in Ho{sup 3+} doped and Ho{sup 3+}, Tm{sup 3+} co-doped ZrF{sub 4}-based fluoride glasses when excited near 585 nm which is off resonance with any ground state absorption bands of either Ho{sup 3+} or Tm{sup 3+} ions. Detailed spectral measurements and analysis suggest that the 545 nm emission occurs from the {sup 5}S{sub 2},{sup 5}F{sub 4} states of Ho{sup 3+} that are populated by excited state absorption from the {sup 5}I{sub 7} state of Ho{sup 3+}. Strong cross-relaxation that efficiently populates the {sup 5}I{sub 7} state makes the photon avalanche process possible in this system.
Date: August 1, 1996
Creator: Chen, Y.H.; Liu, G.K.; Beitz, J.V. & Jie Wang
Partner: UNT Libraries Government Documents Department

Spectroscopy and dynamics of 5f states of Es{sup 3+} in LaF{sub 3}

Description: Using time- and wavelength-resolved laser-induced fluorescence methods, the 5f state spectroscopy and photodynamics of {sup 253}Es{sup 3+} in LaF{sub 3} have been investigated. Based on an effective operator Hamiltonian model and approximating the metal ion site symmetry as C{sub 2V}, a set of crystal field parameters has been obtained that fit the 56 assigned levels associated with the 7 states of Es{sup 3+} that were observed. The {sup 5}F{sub 5} emitting state of Es{sup 3+} exhibited a decay rate that approached the expected purely radiative decay of the state. This suggests that the shorter lifetime previously found for this state of Es{sup 3+} in LaCl{sub 3} arose from radiation damage induced by alpha decay of {sup 253}Es.
Date: November 1, 1997
Creator: Beitz, J.V.; Williams, C.W. & Liu, G.K.
Partner: UNT Libraries Government Documents Department

Modelling crystal-field interaction for f-elements in LaCl{sub 3}

Description: The results of crystal field calculations in the framework of exchange charge model (ECM) are reported for trivalent lanthanide and actinide ions doped into LaCl{sub 3}. Whereas the scalar strength of the model crystal field parameters are consistent with that previously determined by fitting the experimental data, the sign of the second-order parameter is found to be negative, in contrast to previous reports. The contribution from long-range electrostatic interactions exceeds that from the nearest neighboring ligands and leads to the negative sign of the second-order crystal field parameter. Other interaction mechanisms including overlap, covalence, and charge exchange are less important to the second order parameter, but dominate the fourth-and sixth-order parameters. This work provides a consistent interpretation of the previously controversial experimental results for both lanthanide and actinide ions in this classical host.
Date: September 1, 1997
Creator: Zhorin, V.V. & Liu, G.K.
Partner: UNT Libraries Government Documents Department

Molecular dynamics simulation of local structure and vibrational spectrum of uranyl (UO{sub 2}){sup 2+} in vitreous B{sub 2}O{sub 3}.

Description: Laser spectroscopic and extended X-ray absorption fine structure (EXAFS) spectra have shown that uranium in B{sub 2}O{sub 3} glass matrix forms uranyl in the electronic configuration of (UO{sub 2}){sup 2+},but its surrounding structure is not well known. Understanding of uranyl local structure, ion-ligand interaction, and chemical stability on the nanometer scale in glasses is essential in management of long-term performance of high-level nuclear wastes after disposal in a geologic repository. In the present work, the structure, phonon density of states, and vibrational spectrum of vitreous B{sub 2}O{sub 3} and the surrounding environment that contains a uranyl ion have been studied using a molecular dynamics (MD) simulation method that utilizes the Born-Mayer-Huggins and Coulomb pair potentials and the Stillinger-Weber three-body potential. A system of 406 ions was considered in our calculation. Simulation of a thermal quenching from 3000 K to 300 K was performed to generate a uniform and equilibrium model glass matrix before structure configuration and vibrational frequencies were obtained from the system. The structure of the simulated glass is in agreement with that reported by Krogh-Moe and Mozzi et al. The characteristic network of planar boroxol (B{sub 3}O{sub 6}) rings is evident in the simulated system. A configuration of a U{sup 6+} cation in the vitreous B{sub 2}O{sub 3} matrix is shown in Fig. 1. It is shown that a nearly linear (UO{sub 2}){sup 2+} uranyl ion is coordinated by four equatorial oxygen anions in an approximately planar arrangement. The U-O bond length is approximately 0.178 nm for the axial oxygen and 0.254 nm for the equatorial oxygen, which is in good agreement with the U-O distances obtained from fitting EXAFS spectra. Based on the simulated model structure, the uranyl vibrational spectrum is simulated and compared with experimental results obtained using site-selective fluorescence line narrowing (FLN) techniques.
Date: November 3, 2000
Creator: Zhuang, Z.-H.; Liu, G. K. & Beitz, J. V.
Partner: UNT Libraries Government Documents Department

Investigation of microscopic radiation damage in waste forms using ODNMR and AEM techniques. (EMSP Project Final Report)

Description: This project seeks to understand the microscopic effects of radiation damage in nuclear waste forms. The authors' approach to this challenge encompasses studies of ceramics and glasses containing short-lived alpha- and beta-emitting actinides with electron microscopy, laser and X-ray spectroscopic techniques, and computational modeling and simulations. In order to obtain information on long-term radiation effects on waste forms, much of the effort is to investigate {alpha}-decay induced microscopic damage in 18-year old samples of crystalline yttrium and lutetium orthophosphates that initially contained {approximately} 1(wt)% of the alpha-emitting isotope {sup 244}Cm (18.1 y half life). Studies also are conducted on borosilicate glasses that contain {sup 244}Cm, {sup 241}Am, or {sup 249}Bk, respectively. The authors attempt to gain clear insights into the properties of radiation-induced structure defects and the consequences of collective defect-environment interactions, which are critical factors in assessing the long-term performance of high-level nuclear waste forms.
Date: April 21, 2000
Creator: Liu, G.; Luo, J.; Beitz, J.; Li, S.; Williams, C. & Zhorin, V.
Partner: UNT Libraries Government Documents Department

A laser spectroscopic study of Nd-doped Zirconia

Description: High-surface-area rare-earth (RE) modified zirconia powders prepared by solution methods can be used as catalytic support of noble metals and as electrolyte oxygen sensors in automobile exhaust-emission- control systems. Previous neutron-scattering study showed that substituting Zr with trivalent RE ions not only stabilizes the cubic and tetrgonal phases over a wide range of temperatures but also creates oxygen vacancies in the RE-Zr oxide solid solution. This work focuses on Nd fluorescence in Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} powders under laser excitation of the Nd{sup 3+} ground state to the {sup 4}G{sub 7.2} states. Distinct features were found at 8K in the {sup 4}I{sub 9/2}{r_arrow}{sup 4}G{sub 7/2} excitation and {sup 4}F{sub 3.2}{r_arrow}{sup 4}I{sub 9/2} emission spectra using two sets of incident and emission frequencies, respectively. Results are discussed in terms of site-sensitive local structures surrounding the Nd ions in the two-phased oxide structure.
Date: June 1, 1996
Creator: Loong, C.-K.; Liu, G.K.; Ozawa, M. & Suzuki, S.
Partner: UNT Libraries Government Documents Department

Molecular dynamics simulation of lattice structure, radiation damage, and vibrational spectra of zircon (ZrSiO{sub 4}).

Description: The lattice structure, phonon density of states, and infrared spectrum for crystalline zircon, ZrSiO{sub 4}, have been studied using a molecular dynamics (MD) simulation method that utilizes the Born-Mayer-Huggins and Coulomb pair potentials and the Stillinger-Weber three-body potential. A lattice block of ZrSiO{sub 4}, which contains 343 unit cells with dimensions of 4.6249 x 4.6249 x 4.1874 nm{sub 3} and containing 8232 ions, was considered in our calculations. The simulated lattice structure agreed with that determined from x-ray and neutron diffraction experiments. The vibrational modes and absorption spectrum were calculated based on the simulated lattice and compared with infrared absorption spectra. Characteristic lines in infrared spectra obtained from previous experiments on natural and synthetic zircon were assigned to specific bond structures by interactive MD simulations with variation of selected potential parameters. It is shown that the O-Si-O three-body correlations in the SiO{sub 4} tetrahedron significantly influence the spectrum. It is demonstrated that the oxygen ions that are parallel and perpendicular to the c-axis in the SiO{sub 4} tetrahedron are inequivalent and make different contributions to the vibration spectrum. The energy distribution among 24 atoms in a unit cell in the 1011-cm{sup {minus}1} vibrational mode is shown in Fig. 1. Comparison between the simulated infrared absorption spectrum and that from experiments on synthetic zircon is shown in Fig. 2. The interactive method of fitting simulated results to those determined from experiments may be used as a tool for studying nanostructure and thermodynamics properties of materials. The model potentials for the ZrSiO{sub 4} lattice are refined and further applied to MD simulation of lattice disordering and line broadening that are induced by radiation damage processes and amorphization. We have further simulated alpha-decay-induced damage and dynamical recovery in the lattice of ZrSiO{sub 4}. The simulated lattice with structure damage is used for reproducing ...
Date: November 3, 2000
Creator: Liu, G. K.; Zhuang, H.-Z. & Beitz, J. V.
Partner: UNT Libraries Government Documents Department

Retrieval of Cloud Ice Water Content Profiles from Advanced Microwave Sounding Unit-B Brightness Temperatures Near the Atmospheric Radiation Measurement Southern Great Plains Site

Description: One of the Atmospheric Radiation Measurement (ARM) Program important goals is to develop and test radiation and cloud parameterizations of climate models using single column modeling (SCMs) (Randall et al. 1996). As forcing terms, SCMs need advection tendency of cloud condensates besides the tendencies of temperature, moisture and momentum. To compute the tendency terms of cloud condensates, 3D distribution of cloud condensates over a scale much larger than the climate model's grid scale is needed. Since they can cover a large area within a short time period, satellite measurements are useful utilities to provide advection tendency of cloud condensates for SCMs. However, so far, most satellite retrieval algorithms only retrieve vertically integrated quantities, for example, in the case of cloud ice, ice water path (IWP). To fulfill the requirement of 3D ice water content field for computing ice water advection, in this study, we develop an ice water content profile retrieval algorithm by combining the vertical distribution characteristics obtained from long-term surface radar observations and satellite high-frequency microwave observations that cover a large area. The algorithm is based on the Bayesian theorem using a priori database derived from analyzing cloud radar observations at the Southern Great Plains (SGP) site. The end product of the algorithm is a 3D ice water content covering 10{sup o} x 10{sup o} surrounding the SGP site during the passage of the satellite. This 3D ice water content, together with wind field analysis, can be used to compute the advection tendency of ice water for SCMs.
Date: March 18, 2005
Creator: Seo, E-K. & Liu, G.
Partner: UNT Libraries Government Documents Department

Vibronic interaction and crystal structure distortion in Cm sup 4+ :CeF sub 4

Description: We have applied selective excitation to unravel the complex 5f state spectra of Cm{sup 4+} in CeF{sub 4} which arises from multiple metal ion sites and vibronic interactions. An unusual laser-induced site distortion on one of the two ion-sites has been studied. Distinct spectral lines of the distorted ion site were detected. The site distortion was found to be stable below 45 K and reverted, via a thermally activated process, at higher temperatures. Below 45 K, persistent spectral holes were burnt in the absorption lines of Cm{sup 4+} on distorted site. Site distortion and hole burning are interpreted based on excited-state vibronic coupling and the assumption of an asymmetric two-minimum potential surface. 15 refs., 2 figs.
Date: January 1, 1990
Creator: Liu, G.K.; Beitz, J.V. & Carnall, W.T.
Partner: UNT Libraries Government Documents Department

Development and testing of underbalanced drilling products. Topical report, September 1994--September 1995

Description: Underbalanced drilling is experiencing growth at a rate that rivals that of horizontal drilling in the mid-1980s. Problems remain, however, for applying underbalanced drilling in a wider range of geological settings and drilling environments. This report addresses the development and testing of two products designed to advance the application of underbalanced drilling techniques. A user-friendly foam fluid hydraulics model (FOAM) was developed for a PC Windows environment. The program predicts pressure and flow characteristics of foam fluids used in underbalanced drilling operations. FOAM is based on the best available mathematical models, and was validated through comparison to existing models, laboratory test well measurements, and field data. This model does not handle air or mist drilling where the foam quality is above 0.97. An incompressible drilling fluid was developed that utilizes lightweight solid additives (hollow glass spheres) to reduce the density of the mud to less than that of water. This fluid is designed for underbalanced drilling situations where compressible lightweight fluids are inadequate. In addition to development of these new products, an analysis was performed to determine the market potential of lightweight fluids, and a forecast of underbalanced drilling in the USA over the next decade was developed. This analysis indicated that up to 12,000 wells per year (i.e., 30 percent of all wells) will be drilled underbalanced in the USA within the next ten years.
Date: September 1, 1995
Creator: Medley, G. H., Jr; Maurer, W. C.; Liu, G. & Garkasi, A. Y.
Partner: UNT Libraries Government Documents Department

Ion-ion interaction and energy transfer of 4+ transuranium ions in cerium tetrafluoride

Description: Dynamics of excited 5f electron states of the transuranium ions Cm{sup 4+} and Bk{sup 4+} in CeF{sub 4} are compared. Based on time- and wavelength-resolved laser-induced fluorescence, excitation energy transfer processes have been probed. Depending on concentration and electronic energy level structure of the studied 4+ transuranium ion, the dominant energy transfer mechanisms were identified as cross relaxation, exciton-exciton annihilation, and trapping. Energy transfer rates derived from the fitting of the observed fluorescence decays to theoretical models, based on electric multipolar ion-ion interactions, are contrasted with prior studies of 4f states of 3+ lanthanide and 3d states of transition metal ions. 16 refs., 1 tab.
Date: January 1, 1990
Creator: Liu, G.K. & Beitz, J.V.
Partner: UNT Libraries Government Documents Department

Fluorescence dynamics and cross relaxation of 4+ curium in cerium tetrafluoride

Description: Fluorescence from Cm{sup 4+} has been observed for the first time. The dynamics of its emitting 5f state have been probed using time- and frequency-resolved laser-induced fluorescence. Nonexponential fluorescence decays were found from Cm{sub 0.001}Ce{sub 0.999}F{sub 4} and Cm{sub 0.05}Ce{sub 0.95}F{sub 4} at temperatures from 4.2 K to 300 K. A simple cross-relaxation model was found to fit the excited f-state dynamics of the Cm{sub 0.001}Ce{sub 0.999}F{sub 4} sample at low excitation intensity whereas an exciton-exciton annihilation model was necessary to model the observed fluorescence decay as exciton number density increased at higher excitation intensity. The annihilation model, modified to account for a small amount of trap site emission, was required to fit all the observed decays from the Cm{sub 0.05}Ce{sub 0.95}F{sub 4} sample. 15 refs., 2 figs.
Date: January 1, 1989
Creator: Liu, G.K. & Beitz, J.V.
Partner: UNT Libraries Government Documents Department

Examination of Potential Benefits of an Energy Imbalance Market in the Western Interconnection

Description: In the Western Interconnection, there is significant interest in improving approaches to wide-area coordinated operations of the bulk electric power system, in part because of the increasing penetration of variable generation. One proposed solution is an energy imbalance market. This study focused on that approach alone, with the goal of identifying the potential benefits of an energy imbalance market in the year 2020.
Date: March 1, 2013
Creator: Milligan, M.; Clark, K.; King, J.; Kirby, B.; Guo, T. & Liu, G.
Partner: UNT Libraries Government Documents Department

Effects of self-radiation damage on electronic properties of {sup 244}Cm{sup 3+} in an orthophosphate crystal of YPO{sub 4}

Description: Electronic energy level of alpha-emitting isotope {sup 244}Cm{sup 3+} (t{sub {1/2}}=18.1 y) doped into single crystals of YPO{sub 4} has been studied using site-selected laser spectroscopic methods. Electronic transitions between the nominal {sup 8}S{sub 7/2} state of Cm{sup 3+} were utilized to characterize the effects of alpha-decay induced structural damage. The total splitting of the four crystal field doublets in the ground multiplet is 12.5 cm{sup -1} and that of the excited multiplet is 611 cm{sup -1}. Due to radiation damage accumulated in 17 years since the crystals were grown, the inhomogeneous line width of the {sup 8}S{sub 7/2} {leftrightarrow} {sup 6}D{sub 7/2} transitions in broader than 50 cm{sup -1} as measured without site selection. The line width of resonant fluorescence line narrowing (RFLN) is less than 1 cm{sup -1} at 4 K. A total of 12 satellite lines were observed symmetrically spacing about the RFLN line. The position, width, and intensity of these satellite lines have been analyzed to gain information on the electronic and structural properties of the actinide ions in the metamict phases of Cm{sup 3+}:YPO{sub 4}.
Date: October 1, 1997
Creator: Liu, G.K.; Li, S.T.; Beitz, J.V. & Abraham, M.M.
Partner: UNT Libraries Government Documents Department

Optimization of Acetylene Black Conductive Additive andPolyvinylidene Difluoride Composition for High Power RechargeableLithium-Ion Cells

Description: Fundamental electrochemical methods were applied to study the effect of the acetylene black (AB) and the polyvinylidene difluoride (PVDF) polymer binder on the performance of high-power designed rechargeable lithium ion cells. A systematic study of the AB/PVDF long-range electronic conductivity at different weight ratios is performed using four-probe direct current tests and the results reported. There is a wide range of AB/PVDF ratios that satisfy the long-range electronic conductivity requirement of the lithium-ion cathode electrode; however, a significant cell power performance improvement is observed at small AB/PVDF composition ratios that are far from the long-range conductivity optimum of 1 to 1.25. Electrochemical impedance spectroscopy (EIS) tests indicate that the interfacial impedance decreases significantly with increase in binder content. The hybrid power pulse characterization results agree with the EIS tests and also show improvement for cells with a high PVDF content. The AB to PVDF composition plays a significant role in the interfacial resistance. We believe the higher binder contents lead to a more cohesive conductive carbon particle network that results in better overall all local electronic conductivity on the active material surface and hence reduced charge transfer impedance.
Date: July 1, 2007
Creator: Liu, G.; Zheng, H.; Battaglia, V.S.; Simens, A.S.; Minor, A.M. & Song, X.
Partner: UNT Libraries Government Documents Department