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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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The AXAF telescope was analytically investigated during the period from September 1979 to March 1980. The results of a performance evaluation in the presence of aligment errors and surface defects, a sensitivity analysis of every individual subsystem, and a diffraction analysis of the telescope assembly are presented.
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Condensation of metallic iron or the iron carbide cohenite Fe3C is proposed as the source of the approximately 1000 K dust condensate in nova shells, Wolf-Rayet stars, and other objects. Iron grains may serve as nucleation sites for carbon in carbon-star ejecta; however, nucleation of graphite at its equilibrium saturation temperature is almost certainly kinetically inhibited. A gas phase rich in CO, C2H2, and HCN is produced instead.
The development of a charge coupled device (CCD) X-ray imager for a large aperture, high angular resolution X-ray telescope is discussed. Existing CCDs were surveyed and three candidate concepts were identified. An electronic camera control and computer interface, including software to drive a Fairchild 211 CCD, is described. In addition a vacuum mounting and cooling system is discussed. Performance data for the various components are given.
The sensitivity of CR-39 is a strong function of catalyst concentration during its polymerization. Normal CR-39 will detect vertically incident particles with Z/beta as low as 10. An extrapolation suggests that CR-39 with a high catalyst concentration and sensitivity to within approximate 5% can be made by a suitable choice of cure cycle and mold material. CR-39 is less sensitive than Lexan to thermal annealing of tracks but cannot tolerate background radiation levels greater than a few Mrad.
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Upper limits to astronomical photon backgrounds are used to derive constraints on the radiative lifetime of neutrinos. With the assumption that the radiative decay dominates the decay routes available, comparisons with predicted fluxes exclude radiative lifetimes between 10 to the 13th and 10 to the 22nd-23rd sec for neutrinos which decay to lighter neutrinos and 5-50 eV photons. For a secondary neutrino mass much less than the parent neutrino mass, this photon-energy range corresponds to a parent-neutrino-mass range of 10-100 eV/c-squared.
Electron-capture cross sections are calculated and compared with existing experimental data. It is noted that the good agreement of the results with experimental data for the oxygen process suggests that the method given here can be successfully used for multielectron shell capture processes for intermediate and large incident energies. An explanation is given for the departure of the calculated cross sections from the experimental results for one of the processes at low relative energies. The theoretical results are seen as providing reasonably accurate cross sections for detailed modeling of Io's atmosphere.
Cosmic-ray antiprotons have been detected by a new balloon-borne experiment which covers the energy range between 130 and 320 MeV. Fourteen detected events yield a measured flux of 1.7 plus or minus 0.5 x 10 to the -4th antiprotons/sq m sr s MeV. The corresponding antiproton/proton ratio is 2.2 plus or minus 0.6 x 10 to the -4th, only slightly smaller than the ratio observed by other experiments at higher energies. The measured flux is significantly larger than predicted, and some cosmic-ray models which could explain this result are discussed.
Results associated with exact solution of the Einstein-Boltzmann and Einstein-Maxwell-Boltzmann equations are presented. The generalization of Ehler's killing vector approach for the distribution function to charged particles is considered.
The generation of electromagnetic radiation from the free energy available in electron streams is discussed. The fundamental principles involved in a particular class of coherent plasma radiation sources, i.e., plasma lasers, are reviewed, focusing on three wave coupling, nonlinear parametric instabilities, and negative energy waves. The simplest case of plasma lasers, that of an unmagnetized plasma containing a finite level of density fluctuations and electrons streaming with respect to the ions, is dealt with. A much more complicated application of plasma lasers to the case of auroral kilometric radiation is then examined. The concept of free electron lasers, including the role of relativistic scattering, is elucidated. Important problems involving the escape of the excited radiation from its generation region, effects due to plasma shielding and nonlinear limits, are brought out.
Gamma ray observations of the solar system, the galaxy and extragalactic radiation are reported. Topics include: planets, comets, and asteroids; solar observations; interstellar medium and galactic structure; compact objects; cosmology; and diffuse radiation. The instrumentation used in gamma ray astronomy in covered along with techniques for the analysis of observational spectra.
An analytical model calculation of the ionization structure of matter accreting onto a degenerate dwarf was carried out. Self-consistent values of the various parameters are used. The possibility of nuclear burning of the accreting matter is included. We find the blackbody radiation emitted from the stellar surface keeps hydrogen and helium ionized out to distances much larger than a typical binary separation. Except for low mass stars or high accretion rates, the assumption of complete ionization of the elements heavier than helium is a good first approximation. For low mass stars or high accretion rates the validity of assuming complete ionization depends sensitivity on the distribution of matter in the binary system.
Five instruments (Bragg Spectrometer, Large Area Proportional and Scintillation Counter Detectors, Wide Field X-ray Cameras and a Gamma-Ray Burst Monitor) are discussed and estimates of their performance are given. Their scientific aims are summarized and sample observing programmes are discussed.
The paper presents new calculations of ionization equilibrium fractions of 11 abundant elements (C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni) as functions of temperature. Convenient coefficients for fitting the rates of collisional ionization, radiative recombination, and dielectronic recombination are also tabulated. Many of the ionization rates are based on recent experimental measurements of cross sections for collisional ionization and autoionization following inner-shell excitation. These rates are used elsewhere in computations of nonequilibrium ionization, radiative cooling, radiative shock models, and plasma emission diagnostics.
Nonthermal physical processes in the solar atmosphere are discussed. The solar atmospheric regions are defined, and solar convection and its phenomena are explained. The relationship of the solar dynamo, magnetic field, and flares is explored. The solar atmospheric velocity fields are discussed, and the unresolved problem of the nature of atmospheric heating is detailed. The solar wind heating and acceleration are discussed and the need for global solar atmospheric models is emphasized. The application of these solar nonthermal processes to the stars in general is then taken up, employing the same categories as were applied to the solar atmosphere.
(Previously announced in STAR as N82-20098)
Future satellites should carry instruments having over an order of magnitude greater sensitivity than those flown thus far as well as improved energy and angular resolution. The information to be obtained from these experiments should greatly enhance knowledge of: the very energetic and nuclear processes associated with compact objects; the structure of our galaxy; the origin and dynamic pressure effects of the cosmic rays; the high energy particles and energetic processes in other galaxies; and the degree of matter-antimatter symmetry of the universe. The relevant aspects of extragalactic gamma ray phenomena are emphasized along with the instruments planned. The high energy gamma ray results of forthcoming programs such as GAMMA-1 and the Gamma Ray Observatory should justify even more sophisticated telescopes. These advanced instruments might be placed on the space station currently being considered by NASA.