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NASA NTRS1986

The relative fluorescent efficiency of sodium salicylate between 90 and 800 eV

The relative fluorescent quantum efficiency of sodium salicylate was measured between 90 and 800 eV (138 -15 A) by the use of synchrotron radiation. A general increase in efficiency was observed in this spectral range except for abrupt decreases in efficiency at the carbon and oxygen K-edges. Beyond the oxygen K-edge (532 eV) the efficiency increased linearly with the incident photon energy to the limit of the present observations.

Angel, G. C.↗

NASA NTRS1986

Ultrasonic nondestructive materials characterization

A brief review of ultrasonic wave propagation in solid materials is presented with consideration of the altered behavior in anisotropic and nonlinear elastic materials in comparison with isotropic and linear elastic materials. Some experimental results are described in which ultrasonic velocity and attenuation measurements give insight into materials microstructure and associated mechanical properties. Recent developments with laser beam non-contact generation and detection of ultrasound are presented. The results of several years of experimental measurements using high-power ultrasound are discussed, which provide substantial evidence of the inability of presently accepted theories to fully explain the interaction of ultrasound with solid materials. Finally, a special synchrotron X-ray topographic system is described which affords the possibility of observing direct interaction of ultrasonic waves with the microstructural features of real crystalline solid materials for the first time.

Green, R. E., Jr.↗

NASA NTRS1986

Calculations on the production and use of superfine holographic X-ray gratings for astrophysical observations

Superfine holograhic X-ray gratings may be produced by transferring onto metal an interference pattern generated by two branches of a sufficiently coherent X-ray beam, emitted in the form of synchrotron radiation from high energy electron storage rings. Generation of the coherent beam requires restrictions on the beam size. A calculation is presented which allows an exact evaluation of this restriction. The effect of defocusing optics on the expected resolution is also studied.

Csonka, P. L.↗

NASA NTRS1985

Coordinated observations of X-ray bright BL lacertae objects

Simultaneous multifrequency observations of the BL Lac object Mkn421 covering radio through X-ray wavelengths were performed. Composite multifrequency spectra of the central nonthermal component were obtained at the two epochs after subtracting the optical and infrared light of the underlying galaxy. Physical parameters of Mkn421 are discussed in terms of the synchrotron self-Compton model. Taking the spectral turnover between infrared and radio for synchrotrom self absorption, the radio emmision originates in a more extended region than the infrared to X-ray emission, the source size of which should be less than .01 milliarcseconds. Relativistic beaming is required if the angular size is smaller than a few times .001 milliarcseconds. A possible explanation of the spectral change during the two epochs is also discussed.

Urry, C. M.↗

NASA NTRS1986

Diffusive electron acceleration at SNR shock fronts and the observed SNR radio spectral indices

The radio synchrotron emission from relativistic electrons in shell supernova remnants (SNRs) provides a unique opportunity to probe the energy distribution of energetic electrons at their acceleration site (SNR shock fronts). This information provides insight into the acceleration mechanism(s). The implications of these observations for the diffusive (first-order Fermi) acceleration of electrons at the SNR shock fronts are discussed.

Bogdan, T. J.↗

NASA NTRS1985

Kinetic energies of fragment ions produced by dissociative photoionization of NO

The kinetic energies of ions produced by dissociative photoionization of NO have been measured at the discrete resonance lines of He (584A) and Ne (736A), and with undispersed synchrotron radiation. O sup + ions were identified with energies from 0 to approximately 0.5 eV and two groups of N sup + ions one with energy of 0.36 eV and another with energies between 0.9 and 1.5 eV, apparently produced by predissociation of the C sup 3 P 1 and B'1 sigma states respectively.

Samson, J. A. R.↗

NASA NTRS1985

Solar absolute spectral irradiance 118-300 nm - July 25, 1983

The full-disk solar absolute spectral irradiance in the spectral range 118-300 nm was obtained from a rocket observation above White Sands Missile Range, NM, on July 25, 1983, halfway in time between solar maximum and solar minimum. Comparison with measurements made in May 1982 shows no changes within the absolute errors of the experiment. Comparison with measurements made during solar maximum in 1979 and 1980 indicates a large decrease in the absolute solar irradiance at wavelengths below 190 nm. The absolute calibration of the instruments for this flight was accomplished at the National Bureau of Standards Synchrotron Radiation Facility.

Mount, G. H.↗

NASA NTRS1985

Photoabsorption cross section of CH3CN - Photodissociation rates by solar flux and interstellar radiation

The photoabsorption cross section of CH2CN vapor was measured in the 106-180 nm region using synchrotron radiation as a light source. The cross section and the quantum yield for the production of CN (A, B-X) fluorescence were measured and were used to infer the photodissociation cross section of CH3CN. The cross sections were used to calculate the photodissociation rates of CH3CN by the solar flux and by the interstellar radiation. In both the stratosphere and the troposphere, the solar photodissociation of CH3CN is negligible in comparison with chemical degradation.

Suto, M.↗

NASA NTRS1985

Einstein observations of Vela X and the Vela pulsar

The imaging detectors of the Einstein X-ray observatory have been used to study the Vela pulsar and its surrounding region. Although the pulsar is a relatively strong source of X-rays, there are not detectable pulsations at the pulsar period; the pulsed X-ray luminosity is less than approximately 10 to the 31st ergs/s in the 0.1-4.5 keV band. Nor is there evidence for other types of variability in the pulsar's X-ray emission. The images reveal structure on four spatial scales: (1) a pointlike object coincident with the pulsar; (2) a relatively bright, approximately 4-arcmin nebula of diffuse emission about the pulsar; (3) an approximately 1-degree nebula of hard emission that lies between the pulsar and the radio feature Vela X; and (4) thermal emission from the entire approximately 5-degree Vela supernova remnant. Spectral data from the small nebula are well fitted by a synchrotron model. Under the assumption that emission from the pulsar itself is thermal blackbody radiation, the surface temperature of the neutron star is calculated to be 1 million K.

Harnden, F. R., Jr.↗

NASA NTRS1986

Current issues in the X-ray properties of active galactic nuclei

Some issues raised by soft X-ray spectra and hours variability observations of active galactic nuclei (AGN), made possible by improved energy calibration of the Einstein IPC and the launch of Exosat into a unique 72-hour highly elliptical orbit, are presented. Explanations for steep soft excesses in quasars include the emission from the hot tail of an accretion disk spectrum, and from optically thin bremsstrahlung at 1-2 x 10 to the 6th K from a large volume. Mechanisms for the approximately 1.0 slope in the 0.2-4 keV soft IPC X-ray band quasars include direct synchrotron emission, unsaturated Comptonization of an arbitrary seed spectrum, and synchro-Compton scattering from the infrared. The Exosat observation of NGC 4051 revealed six 1-hour cycles with spectral changes during the variations. AGN time variations may now be able to limit emission models through studying, for example, the lag times between soft and hard variations.

Elvis, M.↗

NASA NTRS1986

Monte Carlo spectra from pair-equilibrium, weakly magnetized thermal plasmas

The results of Monte Carlo simulations of weakly magnetized, relativistic thermal plasmas are reported, including such physical processes as thermal synchrotron emission and absorption, bremsstrahlung, and Compton scattering, as well as pair-annihilation and pair-production. The rates of the latter two processes are kept approximately equal to each other, i.e., the plasmas are in pair equilibrium. The resulting spectra are of power-law form, and can be well described by a set of simple analytical formulae. Neither a pair annihilation feature nor a Wien hump is seen in the spectra. The possible relevance of the results to active galactic nuclei and gamma-bursts is discussed.

Zdziarski, A. A.↗

NASA NTRS1985

Radio polarization characteristics of two RS CVn binaries

The results of multifrequency epoch VLA observations of polarized radio emission from the nearby active RS CVn binaries UX Arietis and HR 1099 are reported. For both systems, there is an excellent correlation between handedness of circular polarization and frequency. Helicity reversal is almost always seen between 1.4 and 5.0 GHz, possibly due to optical depth effects. There may also be an anticorrelation between total intensity and fractional circular polarization, especially at 5 GHz. This is consistent with models in which intense flares are associated with compact selfabsorbed synchrotron sources, while the quiescent emission arises from larger gyrosynchrotron-emitting plasma.

Mutel, R. L.↗

NASA NTRS1986

A flare-induced cascade model of gamma-ray bursts

An analytical model is developed for the source of gamma ray bursts as a stellar flare in the magnetosphere of a neutron star. It is suggested that the loss of energy through synchrotron radiation experienced by electrons moving through a sufficiently strong magnetic field at a large pitch angle may not be regained. Instead, pulsar theory is applied to show that the acceleration of electrons in an electric field parallel to the magnetic field will rapidly be inhibited by curvature radiation as the loop experiences a reconnection. It is shown that electrons passing through a curvature with a radius of one million with an electric field strength of 10 billion e.s.u. will emit photons with energies of up to 10 to the 12.6 eV by curvature radiation. The photons, gamma rays, would annihilate in the magnetosphere, which they cannot escape. The resulting cascade of electron-positron particles would eventually produce photons of sufficiently low energy to escape. Upper and low bounds are estimated for the resulting emission spectrum, which would vary according to the magnetic field geometry. The model explains the observed 511 keV annihilation line and the optical radiation which at times accompanies gamma-ray bursts.

Sturrock, P. A.↗

NASA NTRS1986

Quantitative VUV spectroscopy of Cl2

The photoabsorption and fluorescence cross sections of Cl2 were measured in the 105-145 nm region using synchrotron radiation as a light source. The oscillator strengths for the major absorption bands were calculated from the measured absorption cross sections. The measured oscillator strengths for the 2 3Pi u and 2 1Pi u - X 1Sigma(+)g transitions agree quite well with the theoretical values. The absorption spectrum was analyzed in accord with the excited electronic states calculated by Peyerimhoff and Buenker (1981). The Rydberg series converging to the first and second ionization potentials were classified. The vibrational levels of the 2 1Sigma(+)u ionic state were determined up to v prime = 15 from the fluorescence excitation spectrum. It was observed that a band with peak at 108.3 nm produces VUV fluorescence, but it produces UV fluorescence only by a collisional excitation process.

Lee, L. C.↗

NASA NTRS1986

The clumpy circumstellar medium around young supernova remnants

Each of the youngest supernova remnants known in the Milky Way, Cas A, Kepler's SNR, and Tycho's SNR, shows a different morphological structure caused by different conditions in the progenitor stars and their surroundings. In all three cases, however, the observed shells have a thickness of about 1/4 the radius, a sharp outer edge, and significant brightness irregularities. These features require that the circumstellar medium be highly clumped. To investigate the phenomenon, models of the expansion have been constructed using a one-dimensional spherical hydrodynamic code. As a supernova shock moves down the external density gradient of the star, material behind the shock begins to go into free expansion. Then as surrounding material is encountered a reverse shock moving back into the ejectum will be formed. Until the expansion has swept up about eight times the ejected mass when the situation can be considered as a point explosion in its surroundings, the dynamics are controlled by conditions between the shocks. The region is also where the synchrotron radio emission from relativistic electrons trapped in magnetic fields arises. Initial particles and fields are accelerated and amplified by eddy motion at the interface between the ejected and swept-up material and at the boundaries of clumps. Polarimetry shows that these SNR have a net radial orientation of their magnetic fields apparently from stretching by Rayleigh-Taylor instabilities at the contact surfaces. Without clumps the observed shell is much too narrow and steep on the inside.

Dickel, J. R.↗

NASA NTRS1986

CF2 and CFCl fluorescence from VUV excitation of C2F3Cl

The photoexcitation process of C2F3Cl molecule was investigated in the 106 to 230 nm region using synchrotron radiation as a light source. Photoabsorption and fluorescence cross sections were measured and used to determine the fluorescence quantum yield. Fluorescence yield starts to appear at 170 nm and increases to about 2% at 155 nm. The fluorescence spectra were dispersed to identify the emitting species. At the excitation wavelength of 155 nm, the emission system is CFCl (Hermitian conjugate of A - Hermitian conjugate of X), and at 123.9 nm, both the CF2 (Hermitian conjugate of A - Hermitian conjugate of X) and CFCl (Hermitian conjugate of A - Hermitian conjugate of X) systems are observed. The dissociation processes that produced these excited species are discussed.

Nee, J. B.↗

NASA NTRS1986

VLA observations of Jupiter at 1.3 - 20 cm wavelengths

In order to study the vertical distribution of ammonia as a function of Jovian latitude, high resolution images were obtained with the VLA at 1.3, 2, 6 and 20 cm wavelengths. Although the interpretation of the data is quite complicated due to Jupiter's synchrotron radiation, which in fact is the dominant source of radiation at 29 cm, the belt-zone structure is clearly present at 2 and 6 cm wavelengths. At 1.3 cm near the center of the ammonia band, the structure is less pronounced, and at 20 cm it is absent. The data is currently being fitted with model atmosphere calculations. Since one probes in and through the visible cloud layers at these wavelengths (temperatures of 135 to 400 K), and the opacity is likely all provided by ammonia gas, a detailed vertical distribution of this gas can be obtained as a function of Jovian latitude. This ought to give insight in the formation processes of the white cloud layers in the zones and their absence above the belts.

Depater, Imke↗

NASA NTRS1986

Physics through the 1990s: Scientific interfaces and technological applications

The volume examines the scientific interfaces and technological applications of physics. Twelve areas are dealt with: biological physics-biophysics, the brain, and theoretical biology; the physics-chemistry interface-instrumentation, surfaces, neutron and synchrotron radiation, polymers, organic electronic materials; materials science; geophysics-tectonics, the atmosphere and oceans, planets, drilling and seismic exploration, and remote sensing; computational physics-complex systems and applications in basic research; mathematics-field theory and chaos; microelectronics-integrated circuits, miniaturization, future trends; optical information technologies-fiber optics and photonics; instrumentation; physics applications to energy needs and the environment; national security-devices, weapons, and arms control; medical physics-radiology, ultrasonics, MNR, and photonics. An executive summary and many chapters contain recommendations regarding funding, education, industry participation, small-group university research and large facility programs, government agency programs, and computer database needs.

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