Physics Commons^™

The High Pressure Dependence Of X-Ray Induced Decomposition Of Cadmium Oxalate, Adrian F. Lua Sanchez, Petrika Cifligu, Marc Graff, Michael Pravica, Pradip K. Bhowmik, Changyong Park, Egor Evlyukhin

Physics & Astronomy Faculty Research

The high proclivity of x rays to destabilize and distort molecular structures has been previously utilized in the synthesis of novel compounds. Here, we show that x-ray induced decomposition of cadmium oxalate induces chemical and structural transformations only at 0.5 and 1 GPa. Using x-ray diffraction and Raman spectroscopy, the synthesized product is identified as cadmium carbonate with cadmium oxalate remnants, which is stable under ambient conditions. At ambient and >1 GPa pressures, only degradation of the electronic density distribution is observed. The transformation kinetics are examined in terms of Avrami’s model, which demonstrates that despite the necessity of high …

Recovery Of High Specific Activity Molybdenum-99 From Accelerator-Induced Fission On Low-Enriched Uranium For Technetium-99m Generators, M. Alex Brown, Nathan Johnson, Artem V. Gelis, Milan Stika, Anna G. Servis, Alex Bakken, Christine Krizmanich, Kristin Shannon, Peter Kozak, Amanda Barnhart, Chad Denbrock, Nicolas Luciani, Terry Grimm, Peter Tkac

Chemistry and Biochemistry Faculty Research

A new process was developed to recover high specific activity (no carrier added) 99Mo from electron-accelerator irradiated U3O8 or uranyl sulfate targets. The process leverages a novel solvent extraction scheme to recover Mo using di(2-ethylhexyl) phosphoric acid following uranium and transuranics removal with tri-n-butyl phosphate. An anion-exchange concentration column step provides a final purification, generating pure 99Mo intended for making 99Mo/99mTc generators. The process was demonstrated with irradiated uranium targets resulting in more than 95% 99Mo recovery and without presence of fission products or actinides in the product.

Β -Technetium: An Allotrope With A Nonstandard Volume-Pressure Relationship, Emily Siska, Dean Smith, Christian Childs, Daniel Koury, Paul M. Forster, Keith V. Lawler, Ashkan Salamat

Chemistry and Biochemistry Faculty Research

We report the synthesis and structure of the second allotrope of technetium, β-Tc. Transformative pathways are accessed at extreme conditions using the laser-heated diamond anvil cell and confirmed with in situ synchrotron x-ray diffraction and Raman spectroscopy. β-Tc is fully recoverable to ambient conditions, although counter to our DFT calculations predicting a face-centered-cubic lattice, we observe a tetragonal structure (I4/mmm) that exhibits further tetragonal distortion with pressure. β-Tc has an expanded volume relative to the hcp ground state phase, that when doped with nitrogen has an unexpected volume lowering. Such anomalous behavior is possibly indicative of a rare electronic phase …

Colossal Density-Driven Resistance Response In The Negative Charge Transfer Insulator Mns2, Dylan Durkee, Nathan Dasenbrock-Gammon, G. Alexander Smith, Elliot Snider, Dean Smith, Christian Childs, Simon A.J. Kimber, Keith V. Lawler, Ranga P. Dias, Ashkan Salamat

Chemistry and Biochemistry Faculty Research

A reversible density driven insulator to metal to insulator transition in high-spin MnS2 is experimentally observed, leading with a colossal electrical resistance drop of 108 ω by 12 GPa. Density functional theory simulations reveal the metallization to be unexpectedly driven by previously unoccupied S22- σ3p∗ antibonding states crossing the Fermi level. This is a unique variant of the charge transfer insulator to metal transition for negative charge transfer insulators having anions with an unsaturated valence. By 36 GPa the emergence of the low-spin insulating arsenopyrite (P21/c) is confirmed, and the bulk metallicity is broken with the system returning to an …

Pressure- And Temperature-Dependent Inelastic Neutron Scattering Study Of The Phase Transition And Phonon Lattice Dynamics In Para-Terphenyl, Qingan Cai, Michael Mcintire, Luke L. Daemen, Chen Li, Eric Chronister

Chemistry and Biochemistry Faculty Research

Inelastic neutron scattering has been performed on para-terphenyl at temperatures from 10 to 200 K and under pressures from the ambient pressure to 1.51 kbar. The temperature dependence of phonons, especially low-frequency librational bands, indicates strong anharmonic phonon dynamics. The pressure- and temperature-dependence of the phonon modes suggest a lack of phase transition in the region of 0-1.51 kbar and 10-30 K. Additionally, the overall lattice dynamics remains similar up to 200 K under the ambient pressure. The results suggest that the boundary between the ordered triclinic phase and the third solid phase, reported at lower temperatures and higher pressures, …

Author Correction: Closing The Nuclear Fuel Cycle With A Simplified Minor Actinide Lanthanide Separation Process (Alsep) And Additive Manufacturing, Artem V. Gelis, Peter Kozak, Andrew T. Breshears, M. Alex Brown, Cari Launiere, Emily L. Campbell, Gabriel B. Hall, Tatiana G. Levitskaia, Vanessa E. Holfeltz, Gregg J. Lumetta

Chemistry and Biochemistry Faculty Research

No abstract provided.

Closing The Nuclear Fuel Cycle With A Simplified Minor Actinide Lanthanide Separation Process (Alsep) And Additive Manufacturing, Artem V. Gelis, Peter Kozak, Andrew T. Breshears, M. Alex Brown, Cari Launiere, Emily L. Campbell, Gabreil B. Hall, Tatiana G. Levitskaia, Vanessa E. Holfeltz, Gregg J. Lumetta

Chemistry and Biochemistry Faculty Research

Expanded low-carbon baseload power production through the use of nuclear fission can be enabled by recycling long-lived actinide isotopes within the nuclear fuel cycle. This approach provides the benefits of (a) more completely utilizing the energy potential of mined uranium, (b) reducing the footprint of nuclear geological repositories, and (c) reducing the time required for the radiotoxicity of the disposed waste to decrease to the level of uranium ore from one hundred thousand years to a few hundred years. A key step in achieving this goal is the separation of long-lived isotopes of americium (Am) and curium (Cm) for recycle …

Stereodynamical Control Of A Quantum Scattering Resonance In Cold Molecular Collisions, Pablo G. Jambrina, James F.E. Croft, Hua Guo, Mark Brouard, Balakrishnan Naduvalath, F. Javier Aoiz

Chemistry and Biochemistry Faculty Research

Cold collisions of light molecules are often dominated by a single partial wave resonance. For the rotational quenching of HD (v=1, j=2) by collisions with ground state para-H2, the process is dominated by a single L=2 partial wave resonance centered around 0.1 K. Here, we show that this resonance can be switched on or off simply by appropriate alignment of the HD rotational angular momentum relative to the initial velocity vector, thereby enabling complete control of the collision outcome.

Superconductivity In The Van Der Waals Layered Compound Ps2, Yan-Ling Li, Elissaios Stavrou, Qiang Zhu, Samantha M. Clarke, Yunguo Li, Hong-Mei Huang

Physics & Astronomy Faculty Research

van der Waals (vdW) layered compounds provided a fruitful research platform for the realization of superconductivity. However, a vdW layered superconductor with a high transition temperature (Tc) at ambient conditions is still rare. Here, using variable-composition evolutionary structure predictions, we systematically explored the stable compounds in the P-S system up to 20 GPa. Opposed to the complex stoichiometries at ambient conditions, only one compound, PS2, is predicted to be thermodynamically stable above 8 GPa. Strikingly, PS2 is a vdW layered material isostructural to 3R−MoS2 exhibiting a predicted Tc of around 11 K at ambient pressure, both in the bulk and …

Unraveling The Stereodynamics Of Cold Controlled Hd−H2 Collisions, James F. E. Croft, Naduvalath Balakrishnan, Meng Huang, Hua Guo

Chemistry and Biochemistry Faculty Research

Measuring inelastic rates with partial-wave resolution requires temperatures close to a Kelvin or below, even for the lightest molecule. In a recent experiment, Perreault, Mukherjee, and Zare [Nat. Chem. 10, 561 (2018).] studied collisional relaxation of excited HD molecules in the v=1, j=2 state by para- and ortho-H2 at a temperature of about 1 K, extracting the angular distribution of scattered HD in the v=1, j=0 state. By state preparation of the HD molecules, control of the angular distribution of scattered HD was demonstrated. Here, we report a first-principles simulation of that experiment which enables us to attribute the main …

Mcnair Research Journal - Summer 2015, Kelly Abuali, Starr Bailey, Krystal Courtney D. Belmonte, Brittaney Benson-Townsend, Jennifer Bolick, Mihaela A. Ciulei, Ashley Crisp, Daniel N. Erosa, Richard V. Foster, Gisele Braga Goertz, Michael A. Langhardt, Kara Osborne, Julienne Jochel Paraiso, Shawn M. Rosen, Bella V. Smith, Jeevake Attapattu, Ernesto H. Bedoy, Michael G. Curtis, Wanda Inthavong, Marielle Leo, Primrose Martin, Tamieka Meadows, Rosa Perez, Jessica Recarey, Shea Silver, Linda Tompkins

McNair Journal

Journal articles based on research conducted by undergraduate students in the McNair Scholars Program

Table of Contents

Biography of Dr. Ronald E. McNair

Statements:

Dr. Neal J. Smatresk, UNLV President

Dr. Juanita P. Fain, Vice President of Student Affairs

Dr. William W. Sullivan, Associate Vice President for Retention and Outreach

Mr. Keith Rogers, Deputy Executive Director of the Center for Academic Enrichment and Outreach

McNair Scholars Institute Staff

Angular And Dynamical Properties In Resonant Inelastic X-Ray Scattering: Case Study Of Chlorine-Containing Molecules, Renaud Guillemin, Wayne C. Stolte, Loic Journel, Stephane Carniato, Maria Novella Piancastelli, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

Polarization-dependent resonant inelastic x-ray scattering (RIXS) has been shown to be a probe of molecular-field effects on the electronic structure of isolated molecules. In this experimental analysis we explain the linear dichroism observed in Cl 2p polarized RIXS following Cl 1s excitation of a series of chlorofluoromethanes (CF3Cl, CF2Cl2, CFCl3, and CCl4) as due to molecular-field effects, including singlet-triplet exchange. We present an approach to extract directly the 2p inner-shell electronic state populations from the experimental measurements. Using the angular properties of the measured KV emission we also are able to determine the value of the polarization anisotropy parameter βp …

Hrc Enews — 2012 Summer, Megan M. Iudice

Publications (HRC)

This issue contains staff accomplishments and announcements, event listings, and a "new faces" listing for new staff, affiliates, and researchers.

Hrc Enews — 2012 Spring, Megan M. Iudice

Publications (HRC)

This issue contains staff accomplishments and announcements, event listings, and a "new faces" listing for new staff, affiliates, and researchers.

K-Shell X-Ray Spectroscopy Of Atomic Nitrogen, M. M. Sant'anna, Gunnar Ohrwall, Wayne C. Stolte, Alfred S. Schlachter, Dennis W. Lindle, B. M. Mclaughlin

Chemistry and Biochemistry Faculty Research

Absolute K-shell photoionization cross sections for atomic nitrogen have been obtained from both experiment and state-of-the-art theoretical techniques. Because of the difficulty of creating a target of neutral atomic nitrogen, no high-resolution K-edge spectroscopy measurements have been reported for this important atom. Interplay between theory and experiment enabled identification and characterization of the strong 1s → np resonance features throughout the threshold region. An experimental value of 409.64 ± 0.02 eV was determined for the K-shell binding energy.

Hrc Enews — 2012 Winter, Megan M. Iudice

Publications (HRC)

This issue contains staff accomplishments and announcements, event listings, and a "new faces" listing for new staff, affiliates, and researchers.

Resonant Inelastic X-Ray Scattering Of Methyl Chloride At The Chlorine K Edge, L. El Khoury, Loic Journel, Renaud Guillemin, Stephane Carniato, Wayne C. Stolte, T. Marin, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

We present a combined experimental and theoretical study of isolated CH3Cl molecules using resonant inelastic x-ray scattering (RIXS). The high-resolution spectra allow extraction of information about nuclear dynamics in the core-excited molecule. Polarization-resolved RIXS spectra exhibit linear dichroism in the spin-orbit intensities, a result interpreted as due to chemical environment and singlet-triplet exchange in the molecular core levels. From analysis of the polarization-resolved data, Cl 2px, y and 2pz electronic populations can be determined.

A New Method To Derive Electronegativity From Resonant Inelastic X-Ray Scattering, Stephane Carniato, Loic Journel, Renaud Guillemin, Maria Novella Piancastelli, Wayne C. Stolte, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

Electronegativity is a well-known property of atoms and substituent groups. Because there is no direct way to measure it, establishing a useful scale for electronegativity often entails correlating it to another chemical parameter; a wide variety of methods have been proposed over the past 80 years to do just that. This work reports a new approach that connects electronegativity to a spectroscopic parameter derived from resonant inelastic x-ray scattering. The new method is demonstrated using a series of chlorine-containing compounds, focusing on the Cl 2p−1LUMO1 electronic states reached after Cl 1s→LUMO core excitation and subsequent KL radiative decay. Based on …

Thomson-Resonant Interference Effects In Elastic X-Ray Scattering Near The Cl K Edge Of Hcl, Stephane Carniato, P. Selles, Loic Journel, Renaud Guillemin, Wayne C. Stolte, L. El Khoury, T. Marin, Faris Gel'mukhanov, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

We experimentally observed interference effects in elastic x-ray scattering from gas-phase HCl in the vicinity of the Cl K edge. Comparison to theory identifies these effects as interference effects between non-resonant elastic Thomson scattering and resonant Raman scattering. The results indicate the non-resonant Thomson and resonant Raman contributions are of comparable strength. The measurements also exhibit strong polarization dependence, allowing an easy identification of the resonant and non-resonant contributions.

Jahn-Teller Coupling And Fragmentation After Core-Shell Excitation Ini Cf4 Investigated By Partial-Ion-Yield Spectroscopy, Renaud Guillemin, Wayne C. Stolte, Maria Novella Piancastelli, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We investigate fragmentation processes induced by core-level photoexcitation in CF4 at both the carbon and fluorine K edges by means of partial-ion-yield spectroscopy. The molecule CF₄ is a textbook example of systems in which Jahn-Teller coupling strongly manifests itself in the photoabsorption spectrum. Spectral features related to Jahn-Teller and quasi-Jahn-Teller splitting are observed, and important differences in the fragmentation pathways are revealed depending on the symmetries of the core-excited states. We interpret these experimental observations on the grounds of symmetry lowering from the Td to the C3v point group as well as preferential orientation with respect …

Full Multiple Scattering Analysis Of Xanes At The Cd L 3- And O K- Edges In Cdo Films Combined With A Soft-X-Ray Emission Investigation, I. N. Demchenko, J. D. Denlinger, M. Chernyshova, K. M. Yu, D. T. Speaks, P. Olalde-Velasco, Oliver Hemmers, W. Walukiewicz, A. Derkachova, K. Lawniczak-Jablonska

Environmental Studies Faculty Publications

X-ray absorption near edge structure (XANES) at the cadmium L3 and oxygen K edges for CdO thin films grown by pulsed laser deposition method, is interpreted within the real-space multiple scattering formalism, FEFF code. The features in the experimental spectra are well reproduced by calculations for a cluster of about six and ten coordination shells around the absorber for L3 edge of Cd and K edge of O, respectively. The calculated projected electronic density of states is found to be in good agreement with unoccupied electronic states in experimental data and allows to conclude that the orbital character of the …

Sulfur K-Edge Photo-Fragmentation Of Ethylene Sulfide, Wayne C. Stolte, Gunnar Ohrwall

Chemistry and Biochemistry Faculty Research

We have investigated the photofragmentation properties of the three-membered ring heterocyclic molecule ethylene sulfide or thiirane, C₂H₄S, by time-of-flight mass spectroscopy. Positive ions have been collected as a function of photon energy around the S K ionization threshold. Branching ratios were derived for all detected ions, which are informative of the decay dynamics and photofragmentation patterns of the core-excited species. We present a new assignment of the spectral features around the S K-edge.

Fragmentation Properties Of Three-Membered Ring Heterocyclic Molecules By Partial Ion Yield Spectroscopy: C2h4o And C2h4s, Wayne C. Stolte, I. Dumitriu, S-W Yu, Gunnar Ohrwall, Maria Novella Piancastelli, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We investigated the photofragmentation properties of two three-membered ring heterocyclic molecules, C₂H₄O and C₂H₄S, by total and partial ion yield spectroscopy. Positive and negative ions have been collected as a function of photon energy around the C 1s and O 1s ionization thresholds in C₂H₄O, and around the S 2p and C 1s thresholds in C₂H₄S. We underline similarities and differences between these two analogous systems. We present a new assignment of the spectral features around the C K-edge and the sulfur L_{2 …}

Experimental And Theoretical Investigation Of Molecular Field Effects By Polarization-Resolved Resonant Inelastic X-Ray Scattering, Stephane Carniato, Renaud Guillemin, Wayne C. Stolte, Loic Journel, Richard Taieb, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

We present a combined theoretical and experimental study of molecular field effects on molecular core levels. Polarization-dependent resonant inelastic x-ray scattering is observed experimentally after resonant K-shell excitation of CF₃Cl and HCl. We explain the linear dichroism observed in spin-orbit level intensities as due to molecular field effects, including singlet-triplet exchange, and interpret this behavior in terms of population differences in the 2p_x,y,z inner-shell orbitals. We investigate theoretically the different factors that can affect the electronic populations and the dynamical R dependence of the spin-orbit ratio. Finally, the results obtained are used to interpret the L-shell …

Partial Ion Yield Sspectroscopy Around The Cl 2p And C 1s Ionization Thresholds In Cf3cl, D. Ceolin, Maria Novella Piancastelli, Wayne C. Stolte, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We present a partial ion yield experiment on freon 13, CF₃Cl, excited in the vicinity of the C 1s and Cl 2p ionization thresholds. We have collected a large amount of cationic fragments and a few anionic fragments at both edges. We have observed a strong intensity dependence of Rydberg transitions with ion fragment size for the CF_nCl⁺ and CF_n⁺/F⁺ (n=0–3) series at both the Cl 2p and C 1s ionization edges. Selectivity in the fragmentation processes involving the C–Cl and C–F bonds are highlighted by the intensities of the C …

Yttrium And Hydrogen Superstructure And Correlation Of Lattice Expansion And Proton Conductivity In The Bazr0.9y0.1o2.95 Proton Conductor, A. Braun, A. Ovalle, V. Pomjakushin, A. Cervellino, S. Erat, Wayne C. Stolte, T. Graule

Chemistry and Biochemistry Faculty Research

Bragg reflections in Y-resonant x-ray diffractograms of BaZr_0.9Y_0.1O_2.95 (BZY10) reveal that Y is organized in a superstructure. Comparison with neutron diffraction superstructure reflections in protonated/deuterated BZY10 suggests that both superstructures are linked, and that protons move in the landscape imposed by the Y. The thermal lattice expansion decreases abruptly for protonated BZY10 at T≥648±20 K, coinciding with the onset of lateral proton diffusion and suggesting a correlation of structural changes and proton conductivity. The chemical shift in the Y L₁-shell x-ray absorption spectra reveals a reduction from Y³⁺ toward Y²⁺ upon …

Linear Dichroism In Resonant Inelastic X-Ray Scattering To Molecular Spin-Orbit States, Renaud Guillemin, Stephane Carniato, Wayne C. Stolte, Loic Journel, Richard Taieb, Dennis W. Lindle, Marc Simon

Chemistry and Biochemistry Faculty Research

Polarization-dependent resonant inelastic x-ray scattering (RIXS) is shown to be a new probe of molecular-field effects on the electronic structure of isolated molecules. A combined experimental and theoretical analysis explains the linear dichroism observed in Cl 2p RIXS following Cl 1s excitation in HCl and CF₃Cl as due to molecular-field effects, including singlet-triplet exchange, indicating polarized-RIXS provides a direct probe of spin-orbit-state populations applicable to any molecule.

Stability And Equation Of State Of A Nanocrystalline Ga-Ge Mullite In A Vitroceramic Composite: A Synchrotron X-Ray Iffraction Study, Kristina E. Lipinska-Kalita, Patricia Kalita, Cedric Gobin, Oliver Hemmers, Thomas Hartmann, Gino Mariotto

Environmental Studies Faculty Publications

Synchrotron x-ray diffraction and diamond anvil cell techniques were used to characterize the phase transformations and to evaluate the structural stability at elevated pressures of a developed nanocrystalline composite. The optically transparent material was built of a germanium oxide-based amorphous host matrix with homogeneously dispersed 13±3 nm Ga-Ge mullite-type nanocrystals, which had a structure similar to the conventional Al₂O₃-SiO₂ mullite. The equation of state of the nanocrystals and the overall structural integrity of the nanocomposite were investigated in quasihydrostatic conditions on compression to 36 GPa and on the following decompression to ambient conditions. The overall …

Equation Of State Of Gallium Oxide To 70 Gpa: Comparison Of Quasihydrostatic And Nonhydrostatic Compression, Kristina E. Lipinska-Kalita, Patricia Kalita, Oliver Hemmers, Thomas Hartmann

Environmental Studies Faculty Publications

Synchrotron x-ray diffraction and diamond-anvil cell techniques were used to characterize pressure induced structural modifications in gallium oxide. Gallium oxide was studied on compression up to 70 GPa and on the following decompression. The effect of the pressure-transmitting medium on the structural transformations was investigated in two sets of compression and decompression runs, one with nitrogen as a quasihydrostatic pressure-transmitting medium and the other in nonhydrostatic pressure conditions. The x-ray diffraction data showed gradual phase transition from a low-density, monoclinic β-Ga₂O₃ to a high-density, rhombohedral α-Ga₂O₃. With the use of nitrogen as a …

Evaluation Of Cs/Sr Waste Form For Long Term Storage And Disposal, Gary Cerefice

Waste Forms Campaign (TRP)

The goal of this project is to examine the potential long term performance of the proposed aluminosilicate waste/storage form for the isolation and eventual direct disposal of the cesium and strontium separated from recycled nuclear fuel. In the first phase of this work, researchers will investigate the sintering procedure to prepare the drum-like aluminosilicate waste/storage form from the as-received aluminosilicate powder, and then examine the basic physical properties, phase structure and microstructure of the sintered aluminosilicate with /without mixing solution with several ppm Cs/Sr. In the second phase, researchers will evaluate the interaction of the proposed waste form with structural …