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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Proof-of-concept Talbot–Lau x-ray interferometry with a high-intensity, high-repetition-rate, laser-driven K-alpha source

Talbot–Lau x-ray interferometry is a grating-based phase-contrast technique, which enables measurement of refractive index changes in matter with micrometric spatial resolution. The technique has been established using a variety of hard x-ray sources, including synchrotron, free-electron lasers, and x-ray tubes, and could be used in the optical range for low-density plasmas. The tremendous development of table-top high-power lasers makes the use of high-intensity, laser-driven K-alpha sources appealing for Talbot–Lau interferometer applications in both high-energy-density plasma experiments and biological imaging. To this end, we present the first, to the best of our knowledge, feasibility study of Talbot–Lau phase-contrast imaging using a high-repetition-rate laser of moderate energy (100 mJ at a repetition rate of 10 Hz) to irradiate a copper backlighter foil. The results from up to 900 laser pulses were integrated to form interferometric images. A constant fringe contrast of 20% is demonstrated over 100 accumulations, while the signal-to-noise ratio continued to increase with the number of shots. Phase retrieval is demonstrated without prior ex-situ phase stepping. Instead, correlation matrices are used to compensate for the displacement between reference acquisition and the probing of a PMMA target rod. The steps for improved measurements with more energetic laser systems are discussed. The final results are in good agreement with the theoretically predicted outcomes, demonstrating the applicability of this diagnostic to a range of laser facilities for use across several disciplines.

Bouffetier, V. (ORCID:0000000160791260)↗
DOE OSTI2021

High Pressure Brillouin Spectroscopy and X-ray Diffraction of Cerium Dioxide

Simultaneous high-pressure Brillouin spectroscopy and powder X-ray diffraction of cerium dioxide powders are presented at room temperature to a pressure of 45 GPa. Micro- and nanocrystalline powders are studied and the density, acoustic velocities and elastic moduli determined. In contrast to recent reports of anomalous compressibility and strength in nanocrystalline cerium dioxide, the acoustic velocities are found to be insensitive to grain size and enhanced strength is not observed in nanocrystalline CeO 2 . Discrepancies in the bulk moduli derived from Brillouin and powder X-ray diffraction studies suggest that the properties of CeO 2 are sensitive to the hydrostaticity of its environment. Our Brillouin data give the shear modulus, G 0 = 63 (3) GPa, and adiabatic bulk modulus, K S0 = 142 (9) GPa, which is considerably lower than the isothermal bulk modulus, K T0 ~ 230 GPa, determined by high-pressure X-ray diffraction experiments.

36 MATERIALS SCIENCE↗
NASA NTRS1971

Development of a position sensitive X-ray detector for use in a light weight X-ray diffractometer

A position sensitive proportional counter for use in an X-ray diffractometer is developed to permit drastic reductions in the power and weight requirements of the X-ray source and the elimination of the power, weight, and complexity of a moving slit. The final detector constructed and tested has a window spanning 138 and a free standing anode curved along an arc of 7.1 cm radius. Demonstration spectra of a quartz sample in a Debye-Sherrer geometry indicate a spatial resolution of 0.4 - 0.5 mm (0.3 - 0.4 theta). The lunar diffractometer consumed 25 watts in the X-ray generator and weighed about 20 pounds.

Semmler, R. A.↗
NASA NTRS1971

The MIT OSO-7 X-ray experiment. A five color survey of the positions and time variations of cosmic X-ray sources

The all-sky, X-ray measurements are made in five broad energy bands from 0.5 to 60 keV with X-ray collimators of one and three degree FWHM response. Working with the onboard star sensor source locations may be determined to a precision of plus or minus 0.1 deg. The experiment is located in wheel compartment number three of the spacecraft. A time division logic system divides each wheel rotation into 256 data bins in each of which X-ray counts are accumulated over a 190 second interval. Measurement chain circuits include provision for both geometric and risetime anticoincidence. A detailed description of the instrument is included as is pertinent operating information.

Taylor, R. S.↗
NASA NTRS1972

X-ray and gamma-ray imaging with multiple-pinhole cameras using a posteriori image synthesis.

In 1968, Dicke had suggested that multiple-pinhole camera systems would have significant advantages concerning the SNR in X-ray and gamma-ray astronomy if the multiple images could be somehow synthesized into a single image. The practical development of an image-synthesis method based on these suggestions is discussed. A formulation of the SNR gain theory which is particularly suited for dealing with the proposal by Dicke is considered. It is found that the SNR gain is by no means uniform in all X-ray astronomy applications.

Groh, G.↗
NASA NTRS1973

Galactic X-ray polarimetry and high-resolution X-ray spectroscopy.

Stellar X-ray spectroscopy and polarimetry are discussed in terms of the source parameters that can be determined through such studies and in terms of the constraints that these studies will place on theoretical models. The spectroscopic and polarimetric results that have been obtained to date are reviewed. These include the recent discovery of X-ray polarization in the Crab Nebula and the recent evidence for X-ray coronal line emission in the Cygnus Loop. Finally, the properties and predicted performance of a number of satellite-borne spectrometers and polarimeters are presented.

Novick, R.↗
NASA NTRS1973

The astrophysics of the diffuse background of X-rays and gamma rays

The orgin of diffuse X-ray and gamma ray background and some of the astrophysical implications of such a radiation background are discussed. Data show that gamma and X-rays come from thermal bremsstrahlung, neutral pion decay, and compton scattering of thermal protons. The range of energies studied extend from approximately 10 0 eV to approximately 10 to the 8th power eV.

Cowsik, R.↗
NASA NTRS1973

A study of cosmic-ray positron and electron spectra in interplanetary and interstellar space and the solar modulation of cosmic rays

The differential energy spectra of cosmic-ray positrons and negatrons with energies between approximately 11 and 1500 MeV was measured during the period 1968-1971 using a balloon-borne magnetic spectrometer. These measurements fill a gap in the previously existing data and permit the determination of the interstellar spectra of cosmic-ray positrons and electrons. Knowledge of these spectra provides a crucial tool for studies of the distribution and density of matter and magnetic fields in the interstellar medium and the origin and dynamics of energetic particles contained in the fields. The differential energy spectrum of interstellar electrons may be represented as a power-law, j alpha T to the -1.8 power for 100 MeV approximately T approximately 2 GeV, but must flatten considerably at lower energies. From the measured electron charge composition, it is concluded that the majority of cosmic-ray electrons with energies above approximately 10 MeV originate in primary sources.

Cummings, A. C.↗
NASA NTRS1974

Measurements of the cosmic-ray Be/B ratio and the age of cosmic rays

The ratio Be/B depends on whether the confinement time of cosmic rays in the Galaxy is long or short compared to the radioactive half-life of Be-10. We report observations of this ratio which were obtained with a dE/dx-Cerenkov detector launched into a polar orbit on OGO-6 as part of the Caltech Solar and Galactic Cosmic Ray Experiment. Be/B ratios were determined for various rigidity thresholds up to 15 GV. We find no statistically significant rigidity dependence of the ratio, which is 0.41 plus or minus 0.02 when averaged over all observed cutoffs. Additional calculations suggest that if the present fragmentation parameters are correct, then the lifetime of cosmic rays in the Galaxy is less then 10 m.y.

Brown, J. W.↗
NASA NTRS1974

Limits on rapid X-ray pulsing in X-ray binaries

A recent sounding rocket experiment in which the X-ray variations of Cir X-1 and Vela X-1 were investigated at time resolutions down to 1 msecond is described. Sporadic flaring activity in the X-ray sources was observed on time scales from 1 to several seconds, corresponding to intensity changes of about 20% in Cir X-1 and up to 100% in Vela X-1. Periodic, aperiodic, or quasi-periodic pulsations were not detected with time constants less than 1 second. The limits of rapid X-ray pulsations are shown to range from 3 to 15% for Cir X-1, Cyg X-1, Vela X-1, and 3U 1700-37.

Spada, G.↗
NASA NTRS1975

Cosmic ray diffusion: Report of the Workshop in Cosmic Ray Diffusion Theory

A workshop in cosmic ray diffusion theory was held at Goddard Space Flight Center on May 16-17, 1974. Topics discussed and summarized are: (1) cosmic ray measurements as related to diffusion theory; (2) quasi-linear theory, nonlinear theory, and computer simulation of cosmic ray pitch-angle diffusion; and (3) magnetic field fluctuation measurements as related to diffusion theory.

Birmingham, T. J.↗
NASA NTRS1975

K-alpha X-rays from cosmic-ray oxygen

Equilibrium charge fractions are calculated for subrelativistic cosmic-ray oxygen ions in the interstellar medium. These are used to determine the expected flux of K-alpha rays arising from atomic processes for a number of different postulated interstellar oxygen spectra. Relation of these results to the diffuse X-ray background measured at the appropriate energy (about 0.6 keV) suggests an observable broadened line feature.

Pravdo, S. H.↗
NASA NTRS1978

Low-intensity x-ray and gamma-ray imaging device

Low-dosage, low-power X-ray system can be made completely self-contained, allowing fluoroscopy and radiography to be carried out in field and remote locations. New device, known as "lixiscope," can be used with conventional X-ray machine turned down to low level, or, it can be operated with radioisotope source for hand-held portable applications. Originally developed for X-ray astronomy, lixiscope obtains high sensitivity by using intermediate stages of photoelectron conversion and electron amplification to generate image suitable for direct viewing or for recording on film.

Yin, L. I.↗
NASA NTRS1977

X-ray clusters of galaxies - Correlation of X-ray luminosity with galactic content

All 14 X-ray clusters of galaxies detected by the Ariel 5 satellite at high galactic latitudes with redshifts of less than 0.05 are analyzed optically for galaxy content. A strong correlation is found between cluster X-ray luminosity and galaxy type: the fraction of spiral galaxies in a cluster decreases rapidly with increasing X-ray luminosity. The observed correlation is consistent with a combined model of thermal bremsstrahlung emission from a hot intracluster gas and stripping of the spiral galaxies caused by the ram pressure of the same intracluster gas.

Bahcall, N. A.↗
NASA NTRS1978

The Comptonization of iron X-ray features in compact X-ray sources

The formation of X-ray spectral features due to iron in a relatively cool cloud of gas with a Thomson depth greater than 1 surrounding a compact source of continuum X-rays is described. Coupled equations are solved for the ionization structure of the cloud and for the radiative transfer of the X-rays. Photoionization suppresses the strength of emission lines and absorption edges. Comptonization of the radiation broadens emission lines, fills in absorption edges, and produces a high-energy cutoff. In order to describe multiple scattering, a Fokker-Planck equation is derived which includes an important modification of the Kompaneets equation. Narrow resonance lines are treated with an escape probability formalism.

Ross, R. R.↗