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Results for “POTENTIAL SCATTERING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Optical spectral singularities as threshold resonances

Spectral singularities are among generic mathematical features of complex scattering potentials. Physically they correspond to scattering states that behave like zero-width resonances. For a simple optical system, we show that a spectral singularity appears whenever the gain coefficient coincides with its threshold value and other parameters of the system are selected properly. We explore a concrete realization of spectral singularities for a typical semiconductor gain medium and propose a method of constructing a tunable laser that operates at threshold gain.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Analysis of {sup 4}He+{sup 40}Ca and {sup 4}He+{sup 44}Ti scattering using different optical model potentials

Elastic scattering of {sup 4}He+{sup 40}Ca and {sup 4}He+{sup 44}Ti reactions at backward angles has been analyzed using two different models, microscopic and semimicroscopic folding potentials. The derived real potentials supplemented with phenomenological Woods–Saxon imaginary potentials, provide good agreement with the experimental data at energy E{sub c.m.} = 21.8 MeV without need to renormalize the potentials. Coupled channels calculations are used to extract the inelastic scattering cross section to the low-lying state 2+ (1.083 MeV) of {sup 44}Ti. The deformation length is obtained and compared with the electromagnetic measurement values as well as those obtained from previous studies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Electron impact ionization of cycloalkanes, aldehydes, and ketones

The theoretical calculations of electron impact total ionization cross section for cycloalkane, aldehyde, and ketone group molecules are undertaken from ionization threshold to 2 keV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionization contribution method. The results of most of the targets studied compare fairly well with the recent measurements, wherever available and the cross sections for many targets are predicted for the first time. The correlation between the peak of ionization cross sections with number of target electrons and target parameters is also reported. It was found that the cross sections at their maximum depend linearly with the number of target electrons and with other target parameters, confirming the consistency of the values reported here.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1977

Comment of fitting ab initio intermolecular potentials for scattering calculations

The angular dependence of the interaction between two rigid linear rotors is considered, and one of the two expansions in current use is shown to be inappropriate. Interpolation of tabulated radial interactions is also discussed, and numerical tests are presented which demonstrate the accuracy of Lagrange and spline algorithms as a function of the spacing between points.

Green, S.↗
DOE OSTI2014

A dynamical formulation of one-dimensional scattering theory and its applications in optics

We develop a dynamical formulation of one-dimensional scattering theory where the reflection and transmission amplitudes for a general, possibly complex and energy-dependent, scattering potential are given as solutions of a set of dynamical equations. By decoupling and partially integrating these equations, we reduce the scattering problem to a second order linear differential equation with universal initial conditions that is equivalent to an initial-value time-independent Schrödinger equation. We give explicit formulas for the reflection and transmission amplitudes in terms of the solution of either of these equations and employ them to outline an inverse-scattering method for constructing finite-range potentials with desirable scattering properties at any prescribed wavelength. In particular, we construct optical potentials displaying threshold lasing, antilasing, and unidirectional invisibility. -- Highlights: • Proposes a dynamical theory of scattering in one dimension. • Derives and solves dynamical equations for scattering data. • Gives a new inverse scattering prescription. • Constructs optical potentials with desired scattering properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Scattering theory with path integrals

Starting from well-known expressions for the T-matrix and its derivative in standard nonrelativistic potential scattering, I rederive recent path-integral formulations due to Efimov and Barbashov et al. Some new relations follow immediately.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Role of {sup 8}Be heavy stripping mechanism in the {alpha} + {sup 12}C inelastic scattering to the near-3{alpha}-threshold states in {sup 12}C

The angular distributions of {alpha} + {sup 12}C elastic and inelastic (to the 4.44 MeV, 2{sup +}; 7.65MeV, 0{sup +}; and 9.64MeV, 3{sup -} states) scattering at 110 MeV are characterized by pronounced enhancement and strong oscillations at large angles. We performed calculations of the differential cross sections of these reactions assuming a potential scattering in the forward hemisphere and the direct transfer of {sup 8}Be cluster {theta}{sub c.m.} > 90 Degree-Sign . We showed that the {alpha} + {sup 8}Be cluster configuration with relative angular momentum L = 0 dominates in the Hoyle state being 4.4 times larger than that in the ground state. This result also contributes to the verification of {alpha}BEC hypothesis and is consistent with the conjecture of a dilute 3{alpha} structure of the Hoyle state. In the 9.64 MeV, 3{sup -} state, a positive interference of all allowed {alpha} + {sup 8}Be configurations with a dominance of the p-orbital (49%) {alpha}-{sup 8}Be relative motion is found. This finding manifests the exotic 3{alpha}, but hardly condensed structure of the 9.64-MeV 3{sup -} state in {sup 12}C.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Strong spin-orbit interaction and quadratic temperature dependence of electron-phonon scattering in disorder V{sub 75}X{sub 25} (X = Pd, Al) alloys at low temperature

The results of a comprehensive study of weak electron localization (WEL) and electron-electron interaction (EEI) effects in disordered V{sub 75}X{sub 25} (X = Pd, Al) alloys has been reported. The resistivity in absence of magnetic field shows a minimum at temperature T = T{sub m} and follows T{sup 1/2} law within the temperature range 5 K ≤ T ≤ T{sub m}, which suggests predominant EEI effect. Magnetoresistivity is positive due to strong spin-orbit interaction. The dephasing scattering time is dominated by the electron-phonon scattering. The electron-phonon scattering rate shows quadratic temperature dependence behavior, which is explained by the theory of incomplete dragging at the random scattering potential by phonons. The zero temperature scattering time strongly depends on the disorder and its magnitude decreases with increasing disorder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

First-principles mode-by-mode analysis for electron-phonon scattering channels and mean free path spectra in GaAs

We present a first-principles framework to investigate the electron scattering channels and transport properties for polar materials by combining the exact solution of the linearized electron-phonon (e-ph) Boltzmann transport equation in its integral-differential form associated with the e-ph coupling matrices obtained from the polar Wannier interpolation scheme. No ad hoc parameter is required throughout this calculation, and GaAs, a well-studied polar material, is used as an example to demonstrate this method. In this work, the long-range and short-range contributions as well as the intravalley and intervalley transitions in the e-ph interactions (EPIs) have been quantitatively addressed. Promoted by such mode-by-mode analysis, we find that in GaAs, the piezoelectric scattering is comparable to deformation-potential scattering for electron scatterings by acoustic phonons in EPI even at room temperature, and it makes a significant contribution to mobility. Furthermore, we achieved good agreement with experimental data for the mobility, and we identified that electrons with mean free paths between 130 and 210 nm provide the dominant contribution to the electron transport at 300 K. As a result, such information provides a deeper understanding of the electron transport in GaAs, and the presented framework can be readily applied to other polar materials.

36 MATERIALS SCIENCE↗
NASA NTRS1997

Re-Analysis of the Solar Phase Curves of the Icy Galilean Satellites

Re-analysis of the solar phase curves of the icy Galilean satellites demonstrates that the quantitative results are dependent on the single particle scattering function incorporated into the photometric model; however, the qualitative properties are independent. The results presented here show that the general physical characteristics predicted by a Hapke model (B. Hapke, 1986, Icarus 67, 264-280) incorporating a two parameter double Henyey-Greenstein scattering function are similar to the predictions given by the same model incorporating a three parameter double Henyey-Greenstein scattering function as long as the data set being modeled has adequate coverage in phase angle. Conflicting results occur when the large phase angle coverage is inadequate. Analysis of the role of isotropic versus anisotropic multiple scattering shows that for surfaces as bright as Europa the two models predict very similar results over phase angles covered by the data. Differences arise only at those phase angles for which there are no data. The single particle scattering behavior between the leading and trailing hemispheres of Europa and Ganymede is commensurate with magnetospheric alterations of their surfaces. Ion bombardment will produce more forward scattering single scattering functions due to annealing of potential scattering centers within regolith particles (N. J. Sack et al., 1992, Icarus 100, 534-540). Both leading and trailing hemispheres of Europa are consistent with a high porosity model and commensurate with a frost surface. There are no strong differences in predicted porosity between the two hemispheres of Callisto, both are consistent with model porosities midway between that deduced for Europa and the Moon. Surface roughness model estimates predict that surface roughness increases with satellite distance from Jupiter, with lunar surface roughness values falling midway between those measured for Ganymede and Callisto. There is no obvious variation in predicted surface roughness with hemisphere for any of the Galilean satellites.

Domingue, Deborah↗
DOE OSTI2010

Large-angle {alpha}-particle scattering on {sup 12}C and search for signatures of {alpha}-particle Bose condensation

Evidence of the 3{alpha}-particle condensate character of the Hoyle state (the 0{sub 2}{sup +} state at 7.65 MeV in {sup 12}C) implies not only an enhanced radius of {sup 12}C in this state, which was established by many theoretical calculations and confirmed by the recent diffraction model analysis, but also zero relative angular momenta between clusters. We performed coupled-channels model calculations of the angular distributions of {alpha}+{sup 12}C elastic and inelastic (to the 4.44-MeV 2{sup +}, 7.65-MeV 0{sub 2}{sup +}, and 9.65-MeV 3{sub 1}{sup -} states) scattering at 110 MeV and found the ratio of the empirical spectroscopic factors S(L). As the differential cross sections of these reactions are characterized by pronounced enhancement and strong oscillations at large angles, we assumed a potential scattering in the forward hemisphere and the direct transfer of a {sup 8}Be cluster at {theta}{sub c.m.}>90 deg. and took into account the direct transfer of {sup 8}Be in the ground state and in the first excited 2{sup +} and 4{sup +} states. We found that the cluster configuration with L=0 dominates in the 0{sub 2}{sup +} state, being more than three times larger than that in the ground state. This result provides additional evidence of the condensed structure of the Hoyle state in {sup 12}C with a dominance of zero relative angular momentum. The negative-parity 3{sub 1}{sup -} excited state in {sup 12}C observed above the 3{alpha} threshold is also considered to have the 3{alpha}-cluster structure. The present calculations described well the structure of the large-angle cross section on this state. We found a positive interference for all allowed {alpha}+{sup 8}Be configurations with a dominance of the p-orbital (69%){alpha}+{sup 8}Be motion and confirmed the exotic, but hardly a condensed, structure of this state.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Inversion of Many-Beam Bragg Intensities for Phasing by Iterated Projections: Removal of Multiple Scattering Artifacts from Diffraction Data

An iterated projection algorithm (N-Phaser) is developed that reconstructs a scattering potential from N-beam multiple Bragg scattered intensities. The method may be used to eliminate multiple scattering artifacts from electron diffraction data, solving the phase problem and increasing the thicknesses of samples used in materials science, solid-state chemistry, and small molecule crystallography. For high-energy transmission electron diffraction, we show that the algorithm recovers accurate complex structure factors from a wide range of thicknesses, orientations, and relativistic beam energies, and does not require known thickness or atomic-resolution data if sufficient multiple scattering occurs. Furthermore, extensions to Cryo-electron microscopy and Micro-electron diffraction are suggested.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Precise calculations in simulations of the interaction of low energy neutrons with nano-dispersed media

We discuss properties of the interaction of slow neutrons with nano-dispersed media and their application for neutron reflectors. In order to increase the accuracy of model simulation of the interaction of neutrons with nanopowders, we perform precise quantum mechanical calculation of potential scattering of neutrons on single nanoparticles using the method of phase functions. We compare results of precise calculations with those performed within first Born approximation for nanodiamonds with the radius of 2–5 nm and for neutron energies 3 × 10{sup -7}–10{sup -3} eV. Born approximation overestimates the probability of scattering to large angles, while the accuracy of evaluation of integral characteristics (cross sections, albedo) is acceptable. Using Monte-Carlo method, we calculate albedo of neutrons from different layers of piled up diamond nanopowder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Orbital Motion of the Wide Planetary-mass Companion GSC 6214-210 b: No Evidence for Dynamical Scattering

Direct-imaging exoplanet surveys have discovered a class of 5–20 M{sub Jup} substellar companions at separations >100 au from their host stars, which present a challenge to planet and star formation models. Detailed analysis of the orbital architecture of these systems can provide constraints on possible formation mechanisms, including the possibility that they were dynamically ejected onto a wide orbit. We present astrometry for the wide planetary-mass companion GSC 6214-210 b (240 au; ≈14 M{sub Jup}) obtained using NIRC2 with adaptive optics at the Keck telescope over 10 years. Our measurements achieved astrometric uncertainties of ≈1 mas per epoch. We determined a relative motion of 1.12 ± 0.15 mas yr{sup −1} (0.61 ± 0.09 km s{sup −1}), the first detection of orbital motion for this companion. We compute the minimum periastron for the companion due to our measured velocity vector and derive constraints on the orbital parameters through our modified implementation of the Orbits for the Impatient rejection sampling algorithm. We find that close periastron orbits, which could indicate that the companion was dynamically scattered, are present in our posterior but have low likelihoods. For all orbits in our posterior, we assess the detectability of close-in companions that could have scattered GSC 6214-210 b from a closer orbit, and find that most potential scatterers would have been detected in previous imaging. We conclude that formation at small orbital separation and subsequent dynamical scattering through interaction with another potential close-in object is an unlikely formation pathway for this companion. We also update stellar and substellar properties for the system using the new parallax from Gaia DR2.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

SU-E-I-64: X-Ray Coherent Scatter Mammography Simulation

Purpose: Conventional mammography has poor contrast between healthy and cancerous tissues due to the small difference in attenuation properties. Coherent scatter potentially provides more information because interference of coherently scattered radiation depends on the average intermolecular spacing, and can be used to characterize tissue types. However, typical coherent scatter analysis techniques are not compatible with rapid low dose screening modalities. Coherent scatter slot scan imaging is a novel imaging technique which provides new information with higher contrast. In this work a simulation was performed of coherent scatter slot scan imaging to assess its performance and provide system optimization. Methods: In coherent scatter imaging, the coherent scatter is exploited using a conventional slot scan mammography system with anti-scatter grids tilted at the characteristic angle of cancerous tissues. A Monte Carlo simulation was used to simulate the coherent scatter imaging. System optimization was performed across several parameters, including source voltage and filtration, tilt angle, source and grid distances, grid ratio, and shielding geometry. Results: The contrast was high and increased as the grid tilt angle was increased beyond the characteristic angle for the modeled carcinoma, and as the source voltage increased. Source filtration did not have a significant effect on contrast. Increasing grid ratio improved contrast at the expense of decreasing the signal to noise ratio (SNR). As the tumor size is decreased, additional shields to block the fat signal are necessary in order to detect the cancer signal. Conclusion: Coherent scatter analysis using a wide slot setup is promising as an enhancement for screening mammography. This work was supported by National Institutes of Health, # 7 R01EB009715.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Quantum Simulation of the Klein Paradox with Trapped Ions

We report on quantum simulations of relativistic scattering dynamics using trapped ions. The simulated state of a scattering particle is encoded in both the electronic and vibrational state of an ion, representing the discrete and continuous components of relativistic wave functions. Multiple laser fields and an auxiliary ion simulate the dynamics generated by the Dirac equation in the presence of a scattering potential. Measurement and reconstruction of the particle wave packet enables a frame-by-frame visualization of the scattering processes. By precisely engineering a range of external potentials we are able to simulate text book relativistic scattering experiments and study Klein tunneling in an analogue quantum simulator. We describe extensions to solve problems that are beyond current classical computing capabilities.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Impurity states and indirect exchange interaction in irradiated graphene

We theoretically investigate the impurity levels and exchange interaction between magnetic impurities in graphene driven by an off-resonant circularly polarized light field. Our analysis captures the non-perturbative effects resulting from scattering with magnetic impurities with a strong onsite potential. Under irradiation, a dynamical band gap opens up at the Dirac point, allowing impurity levels to exist inside the gap. These impurity levels are shown to give rise to a resonance feature in the exchange energy for impurities located either at the same or different sublattices. The exchange interaction also shows a wider spatial range of antiferromagnetic behavior due to irradiation. Furthermore, our work demonstrates that the exchange energy of magnetic impurities in graphene is extensively tunable by light irradiation in the presence of strong potential scattering.

2-dimensional systems↗