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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Strong metal–support bonding enhanced thermal stability in Au–Al 2 O 3 core–shell nanowires characterized by in situ transmission electron microscopy

In this study, the thermal stability of Au–Al 2 O 3 core–shell and Au nanowires was investigated by in situ scanning transmission electron microscopy and other techniques. Here, the nanowires were synthesized by the helium droplets method and deposited on various substrates. The in situ characterization of Au–Al 2 O 3 thermal stability demonstrated a substantially enhanced stability as compared to that of pure Au nanowires, which can be a transformative approach to design more durable Au-based nanocatalysts. Our study also revealed the existence of strong metal–support bonding in the Au/Al 2 O 3 system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Multi-MeV Electrons from Above-Threshold Ionization of the Neon K-Shell

We present measurements of integrated electron energies produced by above-threshold ionization (ATI) of neon in a laser field with intensity exceeding 10 20 W/cm 2 . We observe electrons with energy exceeding 10 MeV ejected in the laser forward direction above a threshold intensity of 2 ×10 20 W/cm 2 . Here, we compare to ATI models using both tunneling (ADK-PPT) and barrier suppression ionization and observe the onset of ATI at a higher threshold intensity than predicted by these 15 models.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1992

L-shell X-ray opacity of many-electron atoms

The study presents a formulation for obtaining the L-shell photoelectric cross section (sigma sub L) for many-electron atomic systems. A scaling law is suggested for the evaluation of the contribution to sigma sub L from 2s and 2p ejection from a general system in any ionization state. The formula is expressed in terms of the effective nuclear charge (Z sub 2s and Z sub 2p) seen by the corresponding bound electrons, with Z sub 2s and Z sub 2p, obtained from improved screening constants derived in a recent investigation. A comparison is made of Hartree-Fock and hydrogenic expressions for sigma sub L with experimental results for atomic neon at X-ray photon energies, providing the basis for the scaling law and an approximate energy dependence for the cross sections. The special case of sigma sub L for atomic Fe is considered in detail. This L edge has structure because of the different threshold for 2s and 2p photoejection; the latter has fine structure.

Jung, Young-Dae↗
DOE OSTI2024

Above-threshold ionization at laser intensity greater than 10 20 W / cm 2

Here we present experimental observation of above-threshold ionization (ATI) electrons produced by ionization of the neon K shell in a laser field where intensity exceeds 10 20 W/cm 2 . An array of plastic scintillating calorimeter detectors was used to measure the high-energy electrons at four angles in the laser forward direction. Coarse energy resolution was obtained using aluminum filters of several thicknesses to block lower-energy electrons. A threshold intensity around 2×10 20 W/cm 2 is observed for production of energetic ATI electrons in the laser forward direction, with maximum electron energy exceeding 10 MeV. L-shell electrons with energies <1.4 MeV are scattered farther forward along the laser direction than expected. We present comparisons of the measured total electron energies to the predictions of Monte Carlo models employing the ADK-PPT ionization model and the Augst barrier suppression ionization model.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Energy variation of double K -shell photoionization of Ne

Herein we report on an experimental and theoretical study of double K-shell photoionization of Ne over the 2.3–8.5 keV x-ray energy range. The ratio of double-to-single K-shell photoionization cross sections was determined experimentally by measuring the relative rates of the KK–KL 2,3 L 2,3 ( 2 D) Auger hypersatellite and the K–L 2,3 L 2,3 ( 1 D) diagram Auger transitions. By scaling the hypersatellite-diagram Auger-electron ratios to KK/K cross-section ratios, comparison was made with theoretical cross-section ratios of He-like Ne 8+ determined by the R matrix with pseudostates method. The experimental Ne and theoretical Ne 8+ cross-section ratios show similar variations with energy, but the experimental ratios systematically exceed the calculated ratios and also show a lower threshold energy for double K-shell photoionization onset compared to the computed Ne 8+ threshold. The discrepancy is attributed to effects of L-shell electrons not included in the He-like Ne 8+ calculations. Quantified scaling with nuclear charge Z along the He-like isoelectronic sequence indicates that the measured 10-electron Z = 10 double K-shell photoionization cross section behaves like the computed He-like Z = 8.9 cross section, suggesting an effective nuclear screening parameter of s L =1.1 by the additional eight outer L-shell electrons. Experimental results for the energy variations of Auger electron transitions from other multielectron hole states are also discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Observing the onset of pressure-driven K-shell delocalization

The gravitational pressure in many astrophysical objects exceeds one gigabar (one billion atmospheres), creating extreme conditions where the distance between nuclei approaches the size of the K shell. This close proximity modifies these tightly bound states and, above a certain pressure, drives them into a delocalized state. Both processes substantially affect the equation of state and radiation transport and, therefore, the structure and evolution of these objects. Still, our understanding of this transition is far from satisfactory and experimental data are sparse. Here, in this work, we report on experiments that create and diagnose matter at pressures exceeding three gigabars at the National Ignition Facility where 184 laser beams imploded a beryllium shell. Bright X-ray flashes enable precision radiography and X-ray Thomson scattering that reveal both the macroscopic conditions and the microscopic states. The data show clear signs of quantum-degenerate electrons in states reaching 30 times compression, and a temperature of around two million kelvins. At the most extreme conditions, we observe strongly reduced elastic scattering, which mainly originates from K-shell electrons. We attribute this reduction to the onset of delocalization of the remaining K-shell electron. With this interpretation, the ion charge inferred from the scattering data agrees well with ab initio simulations, but it is significantly higher than widely used analytical models predict.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Shell correction for the stopping power of K electrons

In view of the inapplicability of the asymptotic expressions for the stopping number available in the literature at high energies, an alternative approach is taken to compute the shell correction to the stopping number of K electrons. Anholt's formula for the K-shell ionization has been used to calculate the excitation function for longitudinal interaction and numerical integration over energy has been carried out to evaluate the shell correction. Comparison with other theoretical calculations is made. It is proposed that, with the inclusion of relativistic effects, an asymptotic expansion of the stopping number with a leading-term logarithmic in the energy of the incident particle would be more meaningful and might enable one to extract the relativistic contribution to the shell correction from it.

Leung, P. T.↗
NASA NTRS2018

An Engergetic Electron Flux Dropout Due to Magnetopause Shadowing on 1 June 2013

We examine the mechanisms responsible for the dropout of energetic electron flux during 31 May to 1 June 2013 using Van Allen Probe (Radiation Belt Storm Probes (RBSP)) electron flux data and simulations with the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. During the storm main phase, L-shells at RBSP locations are greater than ~8, which are connected to open drift shells. Consequently, diminished electron fluxes were observed over a wide range of energies. The combination of drift shell splitting, magnetopause shadowing, and drift loss all results in butterfly electron pitch angle distributions (PADs) at the nightside. During storm sudden commencement, RBSP observations display electron butterfly PADs over a wide range of energies. However, it is difficult to determine whether there are butterfly PADs during the storm main phase since the maximum observable equatorial pitch angle from RBSP is not larger than ~40° during this period. To investigate the causes of the dropout, the CIMI model is used as a global 4-D kinetic inner magnetosphere model. The CIMI model reproduces the dropout with very similar timing and flux levels and PADs along the RBSP trajectory for 593 keV. Furthermore, the CIMI simulation shows butterfly PADs for 593 keV during the storm main phase. Based on comparison of observations and simulations, we suggest that the dropout during this event mainly results from magnetopause shadowing.

Kang, Suk-Bin↗
DOE OSTI2025

Demonstration of closed shell breeding of cesium ions with an electron beam ion source

An electron beam ion source serves as a charge breeder for the Californium Rare Isotope Breeder Upgrade (CARIBU) at the Argonne Tandem Linac Accelerator System (ATLAS). The source accepts radioactive beams of 1+ or 2+ ions and raises their charge state for post-acceleration by ATLAS. The efficiency of this process impacts the length of each experiment and, hence, the type and number of experiments that can be run in each program cycle. Recent efforts to improve the charge breeding efficiency for the 80 < A < 160 species typical of CARIBU have focused on utilizing the closed shell breeding technique. Here, with this technique, the electron beam energy is manipulated to take advantage of the large gap in ionization energies at shell closures and selectively populate a single charge state. Charge breeding studies with stable cesium ions have demonstrated an absolute efficiency of 72% for Cs 27+ and a total efficiency of 93%. The Cs 27+ efficiency result represents a factor of 3 improvement over the previous best charge breeding result of 23% for Cs 27+ .

Vondrasek, R. [Argonne National Laboratory (ANL), ↗
NASA NTRS1984

A detailed X-ray and radio comparison of Kepler's supernova remnant

High-resolution radio images of Kepler's SNR (SNR (SN 1604) at 6 and 21 cm have been obtained using the VLA. The orientation of linear polarization in the SNR implies a substantial nonrandom radial component for the magnetic field of the remnant. Based on a new X-ray picture of the SNR, obtained using the Einstein Observatory, a detailed comparison of the X-ray and radio morphology is carried out. There is a good correlation between rotation measure, obtained from the radio maps, and emission measure, an X-ray-derived quantity in the SNR shell. From the mean electron density value infered from an analysis of X-ray fluxes, a mean radial magnetic field of 14 micro G and a total magnetic field of 70 microG are estimated. The energy density of relativistic electrons in Kepler's SNR in the shell comparable to the energy density in the magnetic field; the relativistic electron-pressure is 2 percent of the thermal gas pressure. The strong correlation between radio emissivity and X-ray emissivity found over the SNR in somewhat large scale can be ascribed to acceleration of thermal electrons at the shock wave and insignificant diffusion of resultant relativistic electrons.

Matsui, Y.↗
NASA NTRS1994

Second-Order Moller-Plesset Perturbation Theory for Molecular Dirac-Hartree-Fock Wave Functions

Moller-Plesset perturbation theory is developed to second order for a selection of Kramers restricted Dirac-Hartree-Fock closed and open-shell reference wave functions. The open-shell wave functions considered are limited to those with no more than two electrons in open shells, but include the case of a two-configuration SCF reference. Denominator shifts are included in the style of Davidson's OPT2 method. An implementation which uses unordered integrals with labels is presented, and results are given for a few test cases.

Dyall, Kenneth G.↗