Two-Dimensional Temperature Analysis of Nuclear Fireballs Using Digitized Film

Researchers at Lawrence Livermore National Laboratory have begun digitizing technical films spanning the atmospheric nuclear testing operations conducted by the United States from 1945 through 1962. Each atmospheric nuclear test was filmed by Edgerton, Germeshausen, and Grier, Inc., using between 20 to 40 cameras per test. These technical film test data represent a primary source for advancing the knowledge of nuclear weapon output as well as the understanding of nonnuclear high-temperature gases. This manuscript outlines the procedures followed in order to perform two-dimensional temperature calculations for early time nuclear fireballs using digitized film. The digitized optical densities of the film were converted into irradiance on the film that was then used to determine an effective power temperature. The events Wasp Prime and Tesla of Operation Teapot were analyzed using this technique. Film temperature results agreed within uncertainties with historic data collected by calorimeters. Results were also validated by comparison to a thermal heat flux solution that utilizes historic thermal yield values to normalize radiant flux. Additionally, digital imaging and remote sensing image generation was used to demonstrate that the two-dimensional temperature calculation was self-consistent

The effective surface Debye temperature of Yb:GaN

The effective Debye temperature of ytterbium and gallium in Yb:GaN thin films has been obtained using X-ray photoemission spectroscopy. The vibrational motion normal to the surface results in a dimunition of photoemission intensities from which we have estimated the effective Debye temperatures of 221±30 K and 308±30 K for Yb and Ga, respectively. The difference between the measured values for Yb and Ga suggests that the Debye temperatures are influenced by the local environment. The smaller effective surface Debye temperature for Yb correlates to a soft, strained surface, possibly due to an increased Yb―N bond length as compared to the Ga―N bond length

Schottky barrier formation at the Au to rare earth doped GaN thin film interface

The Schottky barriers formed at the interface between gold and various rare earth doped GaN thin films (RE = Yb, Er, Gd) were investigated in situ using synchrotron photoemission spectroscopy. The resultant Schottky barrier heights were measured as 1.68 ± 0.1 eV (Yb:GaN), 1.64 ± 0.1 eV (Er:GaN), and 1.33 ± 0.1 eV (Gd:GaN). We find compelling evidence that thin layers of gold do not wet and uniformly cover the GaN surface, even with rare earth doping of the GaN. Furthermore, the trend of the Schottky barrier heights follows the trend of the rare earth metal work function

Acquiring and modeling of Si solar cell transient response to pulsed X-ray

We report on the acquisition and modeling of the transient response of a commercial silicon (Si) solar cell using a benchtop pulsed X-ray source. The solar-cell transient output to the X-ray pulses was acquired under the dark and steady-state light illumination to mimic the practical operation of a solar cell under different light illumination levels. A solar-cell circuit model was created to develop a fundamental understanding of the transient current/voltage response of solar cell at read-out circuit level. The model was validated by a good agreement between the simulation and experimental results. It was found that the solar-cell resistance ( R ) and capacitance ( C ) depend on the light illumination, and the resulting variation in RC time constant significantly affects the solar-cell transient response. Thus, the solar cell produced different transient signals under different illumination intensities in response to the same X-ray pulse. The experimental data acquired in this work proves the feasibility of using solar panels for prompt detection of nuclear detonations, which also builds a practical mode of X-ray detection using a low-cost self-powered detector

Dual Role of Sb Ions as Electron Traps and Hole Traps in Photorefractive Sn2P2S6 Crystals

Doping photorefractive single crystals of Sn2P2S6 with antimony introduces both electron and hole traps. In as-grown crystals, Sb3+ (5s2 ) ions replace Sn2+ ions. These Sb3+ ions are either isolated (with no nearby perturbing defects) or they have a chargecompensating Sn2+ vacancy at a nearest-neighbor Sn site. When illuminated with 633 nm laser light, isolated Sb3+ ions trap electrons and become Sb2+ (5s2 5p1 ) ions. In contrast, Sb3+ ions with an adjacent Sn vacancy trap holes during illumination. The hole is primarily localized on the (P2S6) 4− anionic unit next to the Sb3+ ion and Sn2+ vacancy. These trapped electrons and holes are thermally stable below ∼200 K, and they are observed with electron paramagnetic resonance (EPR) at temperatures below 150 K. Resolved hyperfine interactions with 31P, 121Sb, and 123Sb nuclei are used to establish the defect models

Dual Role of Sb Ions as Electron Traps and Hole Traps in Photorefractive Sn\u3csub\u3e2\u3c/sub\u3eP\u3csub\u3e2\u3c/sub\u3eS\u3csub\u3e6\u3c/sub\u3e Crystals

Doping photorefractive single crystals of Sn2P2S6 with antimony introduces both electron and hole traps. In as-grown crystals, Sb3+ (5s2) ions replace Sn2+ ions. These Sb3+ ions are either isolated (with no nearby perturbing defects) or they have a charge-compensating Sn2+ vacancy at a nearest-neighbor Sn site. When illuminated with 633 nm laser light, isolated Sb3+ ions trap electrons and become Sb2+ (5s25p1) ions. In contrast, Sb3+ ions with an adjacent Sn vacancy trap holes during illumination. The hole is primarily localized on the (P2S6)4− anionic unit next to the Sb3+ ion and Sn2+ vacancy. These trapped electrons and holes are thermally stable below ∼200 K, and they are observed with electron paramagnetic resonance (EPR) at temperatures below 150 K. Resolved hyperfine interactions with 31P, 121Sb, and 123Sb nuclei are used to establish the defect models. Abstract © 2016 Optical Society of Americ

The local metallicity of gadolinium doped compound semiconductors

The local metallicities of Hf0:97Gd0:03O2, Ga0:97Gd0:03N, Eu0:97Gd0:04O and EuO films were studied through a comparison of the findings from constant initial state spectroscopy using synchrotron light. Resonant enhancements, corresponding to the 4d→4f transitions of Eu and Gd, were observed in some of the valence band photoemission features. The resonant photoemission intensity enhancements for the Gd 4f photoemission features are far stronger for the more insulating host systems than for the metallic system Eu0:96Gd0:04O. The evidence seems to suggest a correlation between the effective screening in the films and the resonant photoemission process

Investigation of \u3csup\u3e186\u3c/sup\u3eRe via radiative thermal-neutron capture on \u3csup\u3e185\u3c/sup\u3eRe

Partial -ray production cross sections and the total radiative thermal-neutron capture cross section for the 185Re(n,)186Re reaction were measured using the Prompt Gamma Activation Analysis facility at the Budapest Research Reactor with an enriched 185Re target. The 186Re cross sections were standardized using well-known 35Cl(n,)36Cl cross sections from irradiation of a stoichiometric natReCl3 target. The resulting cross sections for transitions feeding the 186Re ground state from low-lying levels below a cutoff energy of Ec=746keV were combined with a modeled probability of ground-state feeding from levels above Ec to arrive at a total cross section of σ0=111(6)b for radiative thermal-neutron capture on 185Re. A comparison of modeled discrete-level populations with measured transition intensities led to proposed revisions for seven tentative spin-parity assignments in the adopted level scheme for 186Re. Additionally, 102 primary rays were measured, including 50 previously unknown. A neutron-separation energy of Sn=6179.59(5)keV was determined from a global least-squares fit of the measured -ray energies to the known 186Re decay scheme. The total capture cross section and separation energy results are comparable to earlier measurements of these values

Particle-in-cell Simulations of Ion Dynamics in a Pinched-beam Diode

article-in-cell simulations of a 1.6 MV, 800 kA, and 50 ns pinched-beam diode have been completed with emphasis placed on the quality of the ion beams produced. Simulations show the formation of multiple regions in the electron beam flow characterized by locally high charge and current density (“hot spots”). As ions flow through the electron-space-charge cloud, these hot spots electrostatically attract ions to produce a non-uniform ion current distribution. The length of the cavity extending beyond the anode-to-cathode gap (i.e., behind the cathode tip) influences both the number and amplitude of hot spots. A longer cavity length increases the number of hot spots yet significantly reduces the amplitude producing a smoother, more uniform ion beam than for shorter cavities. The net current and the ion bending angles are also significantly smaller with long cavities

Approximating Mexican highways with slime mould

Plasmodium of Physarum polycephalum is a single cell visible by unaided eye. During its foraging behavior the cell spans spatially distributed sources of nutrients with a protoplasmic network. Geometrical structure of the protoplasmic networks allows the plasmodium to optimize transport of nutrients between remote parts of its body. Assuming major Mexican cities are sources of nutrients how much structure of Physarum protoplasmic network correspond to structure of Mexican Federal highway network? To find an answer undertook a series of laboratory experiments with living Physarum polycephalum. We represent geographical locations of major cities by oat flakes, place a piece of plasmodium in Mexico city area, record the plasmodium's foraging behavior and extract topology of nutrient transport networks. Results of our experiments show that the protoplasmic network formed by Physarum is isomorphic, subject to limitations imposed, to a network of principle highways. Ideas and results of the paper may contribute towards future developments in bio-inspired road planning