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X-ray diffuse scattering measurements of nickel- palladium, iron-aluminum, and nickel-tungsten alloy systems
Diffuse X-ray scattering measurements from iron-aluminum alloys and electrical resistivity of niobium-tungsten alloys
Diffuse X-ray scattering measurements from nickel-palladium single crystals to determine relation between physical and thermal properties and local atomic arrangements
Calculations are reported for the ionic structure factor and X-ray scattering cross section of sodium (at T=0 K and 90 K) and lithium (both isotopes at T=0 K) within the harmonic approximation. An evaluation of the appropriate displacement- displacement correlation function by the special point method circumvents the need for a multiphonon expansion. In the case of sodium, the structure in the one-phonon scattering was straightforwardly accounted for, and an approximate expansion was obtained for all multiphonon scattering. By treating core and conduction electrons on an equal footing, it is shown that information on the conduction electron system is present in the forward scattering component. In lithium the one-phonon cross section at small angles aids in the determination of the effective electron-ion interaction.
Von Laue and Cowley diffraction theories of coherent diffuse X-ray scattering from random alloys, predicting diffuse intensity singularities at reciprocal lattice points
Recent Monte Carlo computations, based on a speculative extrapolation of the electron spectrum, suggested that repeated scatterings contribute most of the extragalactic X-ray background around 3 MeV in a Compton model. We have redone this calculation analytically with a similar electron spectrum, but with very different results. The double-scatter contribution near 3 MeV does not exceed 1 percent and cannot improve the fit to data. The effect is largest near 1 keV but will probably not be observable.
Integrated Bragg X ray scattering intensities for monatomic crystalline lattices, considering thermal diffuse component contribution
Relativistic electron energy loss due to inverse Compton scattering from cosmological blackbody radiation, noting diffuse X ray background implication for electron source strength
Fe rich Fe-Al alloys single crystals, determining three dimensional order and atomic displacements coefficients by X ray diffuse scattering
The spatial distribution of radio and X-ray fluxes from rich and regular clusters of galaxies is discussed. A diffusion model is investigated in which high-energy electrons are ejected from a point source at the center of the cluster. While diffusing out, the electrons lose energy by Compton scattering with the universal blackbody photons, thus producing the X-ray emission. Traversing intracluster magnetic fields, the electrons emit synchrotron radio emission. For the Coma cluster of galaxies good agreement is found between the observed and predicted X-ray counting-rate distribution for the Compton model. From the observed radio data a value of about 3 by 10 to the -8th power gauss is deduced for the average magnetic-field strength in the central region of Coma.
It is shown that the shape and spectral evolution of the giant X-ray bursts from the source 3U 1820-30 can be explained by Compton scattering of a short, intense X-ray pulse in a cloud surrounding the source. Pulse shapes due to Thomson scattering of an X-ray burst in an electron cloud were calculated for the (1) optically thin case on the assumption of one scattering per photon, (2) intermediate case with optical depth of about unity, and (3) optically thick case where the process is regarded as diffusion of photons through a uniform sphere. For the intermediate case, the effects of the reverberation were determined explicitly by Monte Carlo calculation. For an optical depth of 3, square pulse duration of 2 sec, characteristic cloud radius of 70,000 km, characteristic cloud density of 4 times 10 to the 14th per cu cm, and temperature of 5-30 keV, the calculations give a reasonably accurate description of X-ray bursts from 3U 1820-30. The scattering model does not imply the existence of a supermassive, central black hole.
Since the first balloon observation of the Crab Nebula balloon data have provided much information on the positions, spectra, time variability and pulsed nature of localized sources, and on the spectrum and isotropy of diffuse galactic and universal components. Measurements are limited to energies above about 20 keV by atmospheric attenuation at 2 to 3 g/sq cm depth and to below several hundred keV by detector sensitivity. Detectors usually consist of large-area Na I or Cs I scintillation counters with anticoincidence collimators for rejection of charged particles and scattered X-rays. Proportional counters are occasionally used at lower energies and solid-state detectors are used where extreme energy resolution is important. The instruments require a pointing capability on the order of 1.0 to 0.1 deg, depending on the collimator aperture. Digital data is either recorded on board or telemetered using a PCM technique.
A description of diffuse celestial X-ray flux is drawn from data taken by rocket borne detectors. It was concluded that the diffuse flux is intra- and extra-galactic in origin and is caused by Compton scattering of .052 rad black body photons of relativistic electrons leaking out of the galaxies.
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.
This paper investigates the radiative transfer of X-rays through a shell that is optically thick to Compton scattering, surrounding a point source of continuum X-rays. The emission and absorption of X-rays due to K-shell transitions of iron are included. The calculations are done in two entirely independent ways: by Monte Carlo simulation and by solving a Fokker-Planck diffusion equation. The emergent spectra agree very well for Thomson depths of at least about 2. The validity is confirmed of the modification to the Fokker-Planck equation of Kompaneets (1957) that is required when the photon energy is large compared with the average thermal energy of the electrons. A procedure is also developed for treating models of compact X-ray sources consisting of incomplete shells.
Summary of both the direct spacecraft observations of nonrelativistic solar electrons, and observations of the X-ray and radio emission generated by these particles at the sun and in the interplanetary medium. These observations bear on three physical processes basic to energetic particle phenomena: (1) the acceleration of particles in tenuous plasmas; (2) the propagation of energetic charged particles in a disordered magnetic field, and (3) the interaction of energetic charged particles with tenuous plasmas to produce electromagnetic radiation. Because these electrons are frequently accelerated and emitted by the sun, mostly in small and relatively simple flares, it is possible to define a detailed physical picture of these processes. In many small solar flares nonrelativistic electrons accelerated during flash phase constitute the bulk of the total flare energy. Thus the basic flare mechanism in these flares essentially converts the available flare energy into fast electrons. Nonrelativistic electrons exhibit a wide variety of propagation modes in the interplanetary medium, ranging from diffusive to essentially scatter-free. This variability in the propagation may be explained in terms of the distribution of interplanetary magnetic field fluctuations.
Single crystal growth for X-ray scattering experiments in determination of binary alloy physical and mechanical alloy
Diffuse cosmic X rays produced by Compton scattering of far IR radiation on cosmic ray electrons