Physics Commons^™

Spectroscopy Of 88Y By The (P,Dγ) Reaction, T. J. Ross, C. W. Beausang, R. O. Hughes, N. D. Scielzo, J. T. Burke, J. M. Allmond, C. Angell, M. S. Basunia, D. L. Bleuel, R. J. Casperson, J. Escher, P. Fallon, R. Hatarik, J. Munson, S. Paschalis, M. Petri, L. Phair, J. J. Ressler

Physics Faculty Publications

Low-spin, high-excitation energy states in ⁸⁸Y have been studied using the ⁸⁹Y(p,dγ) reaction. For this experiment a 25 MeV proton beam was incident upon a monoisotopic ⁸⁹Y target. A silicon telescope array was used to detect deuterons, and coincident γ rays were detected using a germanium clover array. Most of the known low-excitation-energy low-spin states populated strongly via the (p,d) reaction mechanism are confirmed. Two states are seen for the first time and seven new transitions, including one which bypasses the two low-lying isomeric states, are observed.

Logistic Curves, Extraction Costs And Peak Oil, Robert J. Brecha

Physics Faculty Publications

Debates about the possibility of a near-term maximum in world oil production have become increasingly prominent over the past decade, with the focus often being on the quantification of geologically available and technologically recoverable amounts of oil in the ground. Economically, the important parameter is not a physical limit to resources in the ground, but whether market price signals and costs of extraction will indicate the efficiency of extracting conventional or nonconventional resources as opposed to making substitutions over time for other fuels and technologies. We present a hybrid approach to the peak-oil question with two models in which the …

Saturation-Dependence Of Dispersion In Porous Media, B. Ghanbarian-Alavijeh, Thomas E. Skinner, Allen Hunt

Physics Faculty Publications

In this study, we develop a saturation-dependent treatment of dispersion in porous media using concepts from critical path analysis, cluster statistics of percolation, and fractal scaling of percolation clusters. We calculate spatial solute distributions as a function of time and calculate arrival time distributions as a function of system size. Our previous results correctly predict the range of observed dispersivity values over ten orders of magnitude in experimental length scale, but that theory contains no explicit dependence on porosity or relative saturation. This omission complicates comparisons with experimental results for dispersion, which are often conducted at saturation less than 1. …

Triaxial Deformation And Nuclear Shape Transition In 192Au, Y. Oktem, D. L. Balabanski, B. Akkus, L. Amon Susam, L. Atanasova, C. W. Beausang, R. Cakirli, R. F. Casten, M. Danchev, M. Djongolov, E. Ganioglu, K. A. Gladnishki, J. Tm. Goon, D. J. Hartley, A. A. Hecht, R. Krucken, J. R. Novak, G. Rainovski, L. L. Riedinger, T. Venkova, I. Yigitoglu, N. V. Zamfir, O. Zeidan

Physics Faculty Publications

Background: Nuclei in the A≈190 mass region show gradual shape changes from prolate through nonaxial deformed shapes and ultimately towards spherical shapes as the Pb region is approached. Exploring how this shape evolution occurs will help us understand the evolution of collectivity in this region.

Purpose: The level scheme of the ¹⁹²Au nucleus in A ≈ 190 region was studied in order to deduce its deformations.

Methods: High-spin states of ¹⁹²Au have been populated in the ¹⁸⁶W(¹¹B, 5n) reaction at a beam energy of 68 MeV and their γ decay was studied …

"Tuning Hole Mobility In Inp Nanowires", Mariama Rebello Sousa Dias, A. Picinin, V. Lopez-Richard, S. E. Ulloa, L. K. Castelano, J. P. Rino, G. E. Marques

Physics Faculty Publications

Transport properties of holes in InP nanowires (NWs) were calculated considering electron-phonon interaction via deformation potentials, the effect of temperature, and strain fields. Using molecular dynamics, we simulate NW structures, the longitudinal optical phonon (LO-phonon) energy renormalization, and lifetime. The valence band ground state changes between light- and heavy-hole character, as the strain fields and the NW size vary. Drastic changes in the mobility arise with the onset of resonance between the LO-phonons and the separation between valence subbands.

A Modular Fibrinogen Model That Captures The Stress-Strain Behavior Of Fibrin Fibers, Rodney D. Averett, Bryant Menn, Eric H. Lee, Christine C. Helms, Thomas Barker, Martin Guthold

Physics Faculty Publications

We tested what to our knowledge is a new computational model for fibrin fiber mechanical behavior. The model is composed of three distinct elements: the folded fibrinogen core as seen in the crystal structure, the unstructured α-C connector, and the partially folded α-C domain. Previous studies have highlighted the importance of all three regions and how they may contribute to fibrin fiber stress-strain behavior. Yet no molecular model has been computationally tested that takes into account the individual contributions of all these regions. Constant velocity, steered molecular dynamics studies at 0.025 Å/ps were conducted on the folded fibrinogen …

Economics Of Nuclear Power And Climate Change Mitigation Policies, Nico Bauer, Robert J. Brecha, Gunnar Luderer

Physics Faculty Publications

The events of March 2011 at the nuclear power complex in Fukushima, Japan, raised questions about the safe operation of nuclear power plants, with early retirement of existing nuclear power plants being debated in the policy arena and considered by regulators. Also, the future of building new nuclear power plants is highly uncertain. Should nuclear power policies become more restrictive, one potential option for climate change mitigation will be less available. However, a systematic analysis of nuclear power policies, including early retirement, has been missing in the climate change mitigation literature. We apply an energy economy model framework to derive …

Experimental Study Of The P11(1440) And D13(1520) Resonances From The Clas Data On Ep→E′Π+Π−P′, V. I. Mokeev, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

The transition helicity amplitudes from the proton ground state to the P₁₁(1440) and D₁₃(1520) excited states (v_γpN* electrocouplings) were determined from the analysis of nine independent one-fold differential π⁺π⁻p electroproduction cross sections off a proton target, taken with CLAS at photon virtualities of 0.25 < Q² < 0.60 GeV². The phenomenological reaction model was employed for separation of the resonant and nonresonant contributions to the final state. The P₁₁(1440) and D₁₃(1520) electrocouplings were obtained from the resonant amplitudes parametrized within the framework of a unitarized …

Continuous Single-Column Model Evaluation At A Permanent Meteorological Supersite, Roel A.J. Neggers, A. Pier Siebesma, Thijs Heus

Physics Faculty Publications

Uncertainties in numerical predictions of weather and climate are often linked to the representation of unresolved processes that act relatively quickly compared to the resolved general circulation. These processes include turbulence, convection, clouds, and radiation. Single-column model (SCM) simulation of idealized cases and the subsequent evaluation against large-eddy simulation (LES) results has become an often used and relied on method to obtain insight at process level into the behavior of such parameterization schemes; benefits of SCM simulation are the enhanced model transparency and the high computational efficiency. Although this approach has achieved demonstrable success, some shortcomings have been identified; among …

Geometric Constructions For Image Formation By A Converging Lens, Ulrich Zürcher

Physics Faculty Publications

Light rays emerge from an object in all directions. In introductory texts, three 'special' rays are selected to draw the image produced by lenses and mirrors. This presentation may suggest to students that these three rays are necessary for the formation of an image. We discuss that the three rays attain their 'special status' from the geometric solution of the equation of a hyperbola x−1 + y−1 = c−1 (mirror/lens equation). The material is suitable for use in introductory courses for science majors.

Effect Of Disorder On Quantum Phase Transition In The Double Layered Ruthenates (Sr1−Xcax)3ru2o7effect Of Disorder On Quantum Phase Transition In The Double Layered Ruthenates (Sr1−Xcax)3ru2o7, Leonard Spinu, Zhe Qu, Jin Peng, Tijang Liu, David Forbes, Vkad Dobrosavljevic, Z Q. Mao

Physics Faculty Publications

(Sr_1−xCa_x)₃Ru₂O₇ is characterized by complex magnetic states, spanning from a long-range antiferromagnetically ordered state over an unusual heavy-mass nearly ferromagnetic (NFM) state to an itinerant metamagnetic (IMM) state. The NFM state, which occurs in the 0.4 > x > 0.08 composition range, freezes into a clusterspin glass (CSG) phase at low temperatures [Z. Qu et al., Phys. Rev. B 78, 180407(R) (2008)]. In this article, we present the scaling analyses of magnetization and the specific heat for (Sr_1−xCa_x)₃Ru₂O₇ in the 0.4 > x > 0.08 composition …

The Helium-Rich Subdwarf Cpd−20°1123: A Post-Common-Envelope Binary Evolving On To The Extended Horizontal Branch, Naslim N., S. Geier, C. S. Jeffery, N. T. Behara, V. M. Woolf, L. Classen

Physics Faculty Publications

Subluminous B stars come in a variety of flavours including single stars, close and wide binaries, and pulsating and non-pulsating variables. A majority have helium-poor surfaces (helium by number n_He < 1 per cent), whilst a minority have extremely helium rich surfaces (n_He > 90 per cent). A small number have an intermediate surface helium abundance (≈10–30 per cent), accompanied by peculiar abundances of other elements. The questions posed are (i) whether these abundance peculiarities are associated with radiatively driven and time-dependent stratification of elements within the photosphere as the star evolves from a helium-enriched progenitor to become a normal helium-poor sdB star and (ii) whether these phenomena occur only in …

Comparison Of Forward And Backward Pp Pair Knockout In 3He(E,E′Pp)N, H. Baghdasaryan, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

Measuring nucleon-nucleon short range correlations (SRCs) has been a goal of the nuclear physics community for many years. They are an important part of the nuclear wave function, accounting for almost all of the high-momentum strength. They are closely related to the EMC effect. While their overall probability has been measured, measuring their momentum distributions is more difficult. In order to determine the best configuration for studying SRC momentum distributions, we measured the ³He(e,e’ pp)n reaction, looking at events with high-momentum protons (p_p > 0.35 GeV/c) and a low-momentum neutron ( …

Extraordinary Optical Transmission And Extinction In A Terahertz Wire-Grid Polarizer, J. S. Cetnar, J. R. Middendorf, Elliott R. Brown

Physics Faculty Publications

A THz wire grid polarizer is simulated and demonstrated consisting of 40-μm periodic aluminum strips mounted on a polycarbonate substrate with a variable metal-to-gap ratio. Full-wave numerical simulations were performed from 100 GHz to 550 GHz predicting that the transmission in perpendicular (parallel) polarization is much higher (lower) than that predicted by geometric optics, leading to a very high extinction ratio of ∼60 dB between 100 and 550 GHz when the gaps become very small (<5 >μm). This behavior is confirmed qualitatively in experiments between 100 and 530 GHz where extinction ratios exceeding 40 dB are achieved. …

Quasielastic Scattering In The Interaction Of Ultracold Neutrons With A Liquid Wall And Application In A Reanalysis Of The Mambo I Neutron-Lifetime Experiment, Albert Steyerl, J. M. Pendlebury, Charles Kaufman, Surendra S. Malik, A. M. Desai

Physics Faculty Publications

We develop a theory of ultracold and very cold neutron scattering on viscoelastic surface waves up to second-order perturbation theory. The results are applied to reanalyze the 1989 neutron-lifetime experiment using ultracold neutron storage in a Fomblin-coated vessel by Mampe et al. [Phys. Rev. Lett. 63, 593 (1989)]. Inclusion of this theory of the quasielastic scattering process in the data analysis shifts the neutron lifetime value from 887.6 ± 3 to 882.5 ± 2.1 s.

Measurement Of The Entry-Spin Distribution Imparted To The High Excitation Continuum Region Of Gadolinium Nuclei Via (P,D) And (P,T) Reactions, T. J. Ross, C. W. Beausang, R. O. Hughes, J. M. Allmond, C. Angell, M. S. Basunia, D. L. Bleuel, J. T. Burke, R. J. Casperson, J. Escher, P. Fallon, R. Hatarik, J. Munson, S. Paschalis, M. Petri, L. Phair, J. J. Ressler, N. D. Scielzo, I. Thompson

Physics Faculty Publications

Over the last several years, the surrogate reaction technique has been successfully employed to extract (n,f) and (n,γ) cross sections in the actinide region to a precision of ∼5% and ∼20%, respectively. However, attempts to apply the technique in the rare earth region have shown large (factors of 2–3) discrepancies between the directly measured (n,γ) and extracted surrogate cross sections. One possible origin of this discrepancy lies in differences between the initial spin-parity population distribution in the neutron induced and surrogate reactions. To address this issue, the angular …

Statistical Γ Rays In The Analysis Of Surrogate Nuclear Reactions, N. D. Scielzo, J. Escher, J. M. Allmond, M. S. Basunia, C. W. Beausang, L. A. Bernstein, D. L. Bleuel, J. T. Burke, R. M. Clark, F. S. Dietrich, P. Fallon, J. Gibelin, B. L. Goldblum, S. R. Lesher, M. A. Mcmahan, E. B. Norman, L. Phair, E. Rodriguez-Vieitez, S. A. Sheets, I. Thompson, M. Wiedeking

Physics Faculty Publications

The surrogate nuclear reaction method is being applied in many efforts to indirectly determine neutron-induced reaction cross sections on short-lived isotopes. This technique aims to extract accurate (n,γ) cross sections from measured decay properties of the compound nucleus of interest (created using a different reaction). The advantages and limitations of a method that identifies the γ-ray decay channel by detecting any high-energy (“statistical”) γ ray emitted during the relaxation of the compound nucleus were investigated. Data collected using the Silicon Telescope Array for Reaction Studies and Livermore-Berkeley Array for Collaborative Experiments silicon and germanium detector arrays were used …

Information Transfer By Vector Spin Chirality In Finite Magnetic Chains, Matthias Menzel, Yuriy Mokrousov, Robert Wieser, Jessica E. Bickel, Elena Vedmedenko, Stefan Blügel, Stefan Heinze, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger

Physics Faculty Publications

Vector spin chirality is one of the fundamental characteristics of complex magnets. For a one-dimensional spin-spiral state it can be interpreted as the handedness, or rotational sense of the spiral. Here, using spin-polarized scanning tunneling microscopy, we demonstrate the occurrence of an atomic-scale spin spiral in finite individual bi-atomic Fe chains on the (5×1)−Ir(001) surface. We show that the broken inversion symmetry at the surface promotes one direction of the vector spin chirality, leading to a unique rotational sense of the spiral in all chains. Correspondingly, changes in the spin direction of one chain end can be probed tens of …

Ion Acceleration In A Helicon Source Due To The Self-Bias Effect, Matt Wiebold, Yung-Ta Sung, John E. Scharer

Physics Faculty Publications

Time-averaged plasma potential differences up to 165 V over several hundred Debye lengths are observed in low pressure (p_n < 1 mTorr) expanding argon plasmas in the Madison Helicon eXperiment (MadHeX). The potential gradient leads to ion acceleration greater than that predicted by ambipolar expansion, exceeding E_i≈7 kT_e in some cases. RF power up to 500 W at 13.56 MHz is supplied to a half-turn, double-helix antenna in the presence of a nozzle magnetic field, adjustable up to 1 kG. A retarding potential analyzer (RPA) measures the ion energy distribution function (IEDF) and a swept emissive probe measures the plasma potential. Single and double probes measure the electron density and temperature. Two distinct mode hops, the capacitive-inductive (E-H) and inductive-helicon (H-W) transitions, …

The M Dwarf Problem In The Galaxy, Vincent M. Woolf, Andrew A. West

Physics Faculty Publications

We present evidence that there is an M dwarf problem similar to the previously identified G dwarf and K dwarf problems: the number of low-metallicity M dwarfs is not sufficient to match simple closed-box models of local Galactic chemical evolution. We estimated the metallicity of 4141 M dwarf stars with spectra from the Sloan Digital Sky Survey (SDSS) using a molecular band strength versus metallicity calibration developed using high resolution spectra of nearby M dwarfs. Using a sample of M dwarfs with measured magnitudes, parallaxes and metallicities, we derived a relation that describes the absolute magnitude variation as a function …

Measurement Of The Neutron F2 Structure Function Via Spectator Tagging With Clas, N. Baillie, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We report on the first measurement of the F₂ structure function of the neutron from semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to ≲ 100° MeV/c and their angles to ≳ 100° relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The Fⁿ₂ data collected cover the nucleon-resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 < Q² < 4.52 GeV², with uncertainties from nuclear corrections estimated to be less than …

Mid-Infrared Upconversion Spectroscopy Based On A Yb:Fiber Femtosecond Laser, Todd Johnson, Scott A. Diddams

Physics Faculty Publications

We present a system for molecular spectroscopy using a broadband mid-infrared laser with near-infrared detection. Difference frequency generation of a Yb:fiber femtosecond laser produced a mid-infrared (MIR) source tunable from 2100–3700 cm^-1 (2.7–4.7 μm) with average power up to 40 mW. The MIR spectrum was upconverted to near-infrared wavelengths for broadband detection using a two-dimensional dispersion imaging technique. Absorption measurements were performed over bandwidths of 240 cm^-1 (7.2 THz) with 0.048 cm^-1 (1.4 GHz) resolution, and absolute frequency scale uncertainty was better than 0.005 cm^-1 (150 MHz). The minimum detectable absorption coefficient per spectral element was …

Measurement Of The Neutron F2 Structure Function Via Spectator Tagging With Clas, N. Baillie, S. Tkachenko, J. Zhang, P. Bosted, S. Bültmann, M. E. Christy, H. Fenker, K. A. Griffioen, C. E. Keppel, S. E. Kuhn, K. P. Adhikari, D. Adikaram, M. J. Amaryan, H. Baghdasaryan, G. Dodge, N. Guler, C. E. Hyde, A. Klein, A. Klimenko, L. B. Weinstein

Physics Faculty Publications

We report on the first measurement of the F₂ structure function of the neutron from the semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to ≲ 100MeV/c and their angles to ≳ 100° relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The Fⁿ₂ data collected cover the nucleon-resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 < Q² < 4.52 GeV², with uncertainties from nuclear corrections estimated to be less …

Measurement Of The Generalized Form Factors Near Threshold Via Γ*P→Nπ+ At High Q2, K. Park, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We report the first extraction of the pion-nucleon multipoles near the production threshold for the nπ⁺ channel at relatively high momentum transfer (Q² up to 4.2 GeV²). The dominance of the s-wave transverse multipole (E₀₊), expected in this region, allowed us to access the generalized form factor G₁ within the light-cone sum-rule (LCSR) framework as well as the axial form factor G_A. The data analyzed in this work were collected by the nearly 4π CEBAF Large Acceptance Spectrometer (CLAS) using a 5.754-GeV electron beam on a proton …

Utilizing (P,D) And (P,T) Reactions To Obtain (N,F) Cross Sections In Uranium Nuclei Via The Surrogate-Ratio Method, R. O. Hughes, C. W. Beausang, T. J. Ross, J. T. Burke, N. D. Scielzo, M. S. Basunia, C. M. Campbell, R. J. Casperson, H. L. Crawford, J. Escher, J. Munson, L. Phair, J. J. Ressler

Physics Faculty Publications

The surrogate ratio method has been tested for (p,d) and (p,t) reactions on uranium nuclei. ²³⁶U and ²³⁸U targets were bombarded with 28-MeV protons and the light ion recoils and fission fragments were detected using the Silicon Telescope Array for Reaction Studies detector array at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. The (p,df) reaction channels on ²³⁶U and ²³⁸U targets were used as a surrogate to determine the σ[²³⁶U(n,f)]/σ[²³⁴U(n, …

Upper Limits For The Photoproduction Cross Section For The Φ−−(1860) Pentaquark State Off The Deuteron, H. Egiyan, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We searched for the Φ^--(1860) pentaquark in the photoproduction process off the deuteron in the Ξ^-π^--decay channel using CLAS. The invariant-mass spectrum of the Ξ^-π^- system does not indicate any statistically significant enhancement near the reported mass M = 1.860 GeV. The statistical analysis of the sideband-subtracted mass spectrum yields a 90%-confidence-level upper limit of 0.7 nb for the photoproduction cross section of Φ^--(1860) with a consecutive decay into Ξ^-π^- in the photon-energy range 4.5 GeV < E_γ < 5.5 GeV.

Practicality Of Compensating The Loss In The Plasmonic Waveguides Using Semiconductor Gain Medium, Jacob B. Khurgin, Greg Sun

Physics Faculty Publications

We consider the issue of compensating the loss in plasmonic waveguides with semiconductor gain material and show that, independent of specific geometry, full loss compensation in plasmonic waveguides with significantly sub-wavelength light confinement (less than λ/4n) requires current density well in excess of 100 kA/cm². This high current density is attributed to the unavoidable shortening of recombination time caused by the Purcell effect inherent to sub-wavelength confinement. Consequently, an injection-pumped plasmonic laser that is truly sub-wavelength in all three dimensions (“spaser”) would have threshold current densities that are hard to obtain in any conceivable semiconductor device.

Α−Α Cross-Links Increase Fibrin Fiber Elasticity And Stiffness, Christine C. Helms, Robert A.S. Ariens, S. Uitte De Willige, Kristina F. Standeven, Martin Guthold

Physics Faculty Publications

Fibrin fibers, which are ∼100 nm in diameter, are the major structural component of a blood clot. The mechanical properties of single fibrin fibers determine the behavior of a blood clot and, thus, have a critical influence on heart attacks, strokes, and embolisms. Cross-linking is thought to fortify blood clots; though, the role of α–α cross-links in fibrin fiber assembly and their effect on the mechanical properties of single fibrin fibers are poorly understood. To address this knowledge gap, we used a combined fluorescence and atomic force microscope technique to determine the stiffness (modulus), extensibility, and elasticity of …

Chiral Magnetization Configurations In Magnetic Nanostructures In The Presence Of Dzyaloshinski-Moriya Interactions, Naoise Grisewood, John Eves, Timothy Usher, Hans-Benjamin Braun

Physics Faculty Publications

Many low-dimensional systems, such as nanoscale islands, thin films, and multilayers, as well as bulk systems, such as multiferroics, are characterized by the lack of inversion symmetry, a fact that may give rise to a Dzyaloshinskii-Moriya (DM) interaction. For sufficient strength, the DM interaction will favor spiral spin configurations of definite chirality. In order to harness such systems for applications, it is important to understand the conditions under which these spiral spin configurations form and how they can be controlled via an external field. Here, we present exact solutions of the 1D magnetization profiles in such systems for arbitrary material …

To The Continuum And Beyond: Structure Of U Nuclei, R. O. Hughes, C. W. Beausang, T. J. Ross, J. T. Burke, N. D. Scielzo, M. S. Basunia, C. M. Campbell, R. J. Casperson, H. L. Crawford, J. Munson, L. Phair, J. J. Ressler

Physics Faculty Publications

An experiment was performed at the 88-inch cyclotron at LBNL to investigate the structure of uranium isotopes and concurrently test the so-called surrogate ratio method. A 28 MeV proton beam was used to bombard ²³⁶U and ²³⁸U targets and the outgoing light ions were detected using the STARS silicon telescope allowing isotopic assignments and the excitation energy of the compound nucleus to be measured. A fission detector was placed at backward angles to give particle-fission coincidences, while the six clover germanium detectors of the LIBERACE array were used for particle-γ coincidences. The (p,d) reaction channels on ²³⁶U …