X-ray determination of electron momenta in Li, Be, B, Na, Mg, Al, and LiF.
X ray determination of electron momentum density in various metals using Compton line-shape measurements
Phillips, W. C.↗
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Intensity and galactic absorption of soft background X-rays
Soft X ray background galactic absorption and intensity measurements indicating inverse relation to columnar atomic hydrogen density
Bunner, A. N.↗
Absorption of CO2-laser radiation in a hypocycloidal-pinch plasma
Absorption of a 50-J pulsed CO2 laser beam in the plasma produced in a hypocycloidal-pinch apparatus was studied. The apparatus consists of three disk electrodes with a 5-cm hole on the axis. The current sheets are snow-plowed toward the center of the hole to produce a plasma with a density greater than 10 to the 18th/cu cm and a temperature near 1 keV which emits soft X rays for 5 microsec. IR detectors measured the laser radiation incident onto, transmitted through, and scattered from the plasma as functions of time. For a period up to 70 microsec from the onset of X-ray emission, neither transmitted nor scattered laser radiation was observed above the detector threshold of 0.3% of the incident flux. This indicates effective absorption of the laser beam (greater than 99%) and that the particle confinement time extends far beyond the energy confinement time of 5 microsec. Thus, the plasma in this apparatus appears much more amenable to laser heating than that in a theta pinch.
Lee, J. H.↗
Evolution of the coronal and transition-zone plasma in a compact flare - The event of 1973 August 9
X-ray and extreme ultraviolet observations of a compact flare were analyzed to determine the relative importance of radiation, thermal conduction, and 'evaporation' in the evolution of the temperature and density structure of the plasma. In the event studied (1973 August 9), the electron density was relatively high (5 x 10 to the eleventh to 1 x 10 to the twelfth) and radiation was evidently an important energy-loss and cooling mechanism. The light curves of ultraviolet lines formed at temperatures between 10 to the fifth to 10 to the seventh K indicate a time-varying emission measure gradient, and hence temperature gradient, during the flare. Radiative instability evidently played an important role in determining the steepness of these gradients during the rise and fall phases, and caused strong downward motions of material during the cooling phase. Toward the end of the event, the coronal electron density decreased and the temperature gradient relaxed toward that expected from a conduction-dominated plasma. For this flare, evaporative cooling did not appear to be a significant factor.
Underwood, J. H.↗
A new color correlation method applied to XRF Al/Si ratios and other lunar remote sensing data
Orbital X-ray fluorescence Al/Si intensity ratios, corrected for variations in solar activity, are correlated with normal albedo, elevation measurements from laser altimetry data, and gamma ray data in the 2.75-8.60 MeV range. Each of these data sets is placed into a digital array consisting of 1/4 deg latitude by 1/4 deg longitude pixels. Information relative to the correlation of Al/Si ratios with each of the other data sets is presented in the following forms: (1) histograms are given for each data set to show the frequency distribution within the areas of common coverage; (2) density plots are produced from the plot of a two-dimensional array consisting of the Al/Si ratio vs the other parameter value for each pixel; and (3) color correlation maps are produced by placing the two-dimensional array into a 3 x 3 matrix consisting of nine equal subarrays containing an equal number of data points.
Clark, P. E.↗
The coronal and transition region temperature structure of a solar active region
Using measurements of EUV and X-ray spectral lines, the differential emission measure vs electron temperature from the transition region to the corona of an active region (electron temperature between 100,000 and 5,000,000 K) is derived. The total emission measure and radiative losses are of the order 3 x 10 to the 48th/cu cm and 4 x 10 to the 26th ergs/sec, respectively. The emission measure at electron temperatures greater than approximately 1,000,000 K (i.e. that mainly responsible for the X-ray emission) is about 75% of the total. The use of the Mg x line at 625 A as an indicator of coronal electron density is also examined. A set of theoretical energy balance models of coronal loops in which the loop divergence is a variable parameter is presented and compared with the observations.
Levine, R. H.↗
High resolution X-ray spectra of solar flares. V - Interpretation of inner-shell transitions in Fe XX-Fe XXIII
The paper examines high-resolution solar flare iron line spectra recorded between 1.82 and 1.97 A by a spectrometer flown by the Naval Research Laboratory on an Air Force spacecraft launched on 1979 February 24. The emission line spectrum is due to inner-shell transitions in the ions Fe XX-Fe XXV. Using theoretical spectra and calculations of line intensities obtained by methods discussed by Merts, Cowan, and Magee (1976), electron temperatures as a function of time for two large class X flares are derived. These temperatures are deduced from intensities of lines of Fe XXII, Fe XXIII, and Fe XXIV. The determination of the differential emission measure between about 12-million and 20-million K using these temperatures is considered. The possibility of determining electron densities in flare and tokamak plasmas using the inner-shell spectra of Fe XXI and Fe XX is discussed.
Doschek, G. A.↗
Cosmological constraints on hot plasma in a closed universe
A hot uniform collisionally heated intergalactic medium (IGM) at closure density is reconsidered. Optical depth measurements, plasma cooling and ionic abundances during the recombination epoch are discussed. The data are used to calculate X-radiation at critical energies. The results indicate a present temperature from 160,000 to 4,200,000 K if the reheating of the IGM ceased at the latest possible time. As cessation of heating moves to earlier times, the range of present plasma temperature narrows until at the earliest possible cessation time only about 160,000 K is acceptable. Relevant formulae are provided to modify these numbers as new data become available. This IGM avoids any hard X-ray production and thus assumes that discrete sources alone constitute the entire cosmic X-ray background.
Sherman, R. D.↗
Very long baseline interferometry observations of the RS Canum Venaticorum system HR 5110 at 8.4 GHz
The RS CVn binary system HR 5110 was observed with a well-calibrated four-element VLBI array at a frequency of 8.4 GHz. The total flux density, which was nearly constant at 32 + or - 2 mJy, was monitored throughout the experiment with a 20 km baseline interferometer allowing accurate visibilities to be calculated. The observed visibilities are consistent with a source unresolved on all the baselines. The maximum size of the equivalent Gaussian source is 1.4 milli-arcsec (FWHM), corresponding to a linear size of 1.1 x 10 to the 12th cm at 52 pc. This maximum size is comparable with the overall size of the binary system. The inferred lower limit of the brightness temperature is 4 x 10 to the 8th K, which is higher than the coronal temperature of 10 to the 7th K measured in a soft X-ray survey. This is consistent with a nonthermal mechanism for the radiation process of the moderate radio outburst observed.
Mutel, R. L.↗
Observations of Highly-ionized Interstellar Iron
The spectra of 24 stars, including 5 at distances d 200 pc, have been observed in the regions of the coronal Fe X lambda 6375 and Fe X lambda 5303 lines at detection limits near an equivalent width of 1 mA in the best cases. In general agreement with predictions based on a multi-phase model of the interstellar medium, no absorption which can be attributed to Fe X or Fe X4 ions in hot interstellar gas emitting the soft X-ray background is seen in any of these spectra, except for two. Toward lambda Cephei an absorption line near lambda 6375 is measured with an equivalent width of 8.1 + or - 2 mA, a width corresponding to 20 + or - 5 km/sec or a temperature T or = (0.5 + or - 0.25) x 10 to the 6th power K, and, if it is caused by Fe X ions, a radial velocity of -355 km/sec. On that hypothesis, the interstellar gas constitutes at least 63% of the column density of gas along this light path.
Hobbs, L. M.↗
A dynamic flare with anomalously dense flare loops
The dynamic flare of November 6, 1980 developed a rich system of growing loops which could be followed in H-alpha for 1.5 hours. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of b-values for a hydrogen atom reveal that this requires electron densities in the loops to be close to 10 to the 12th per cu cm. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 10 to the 12th per cu cm if no nonthermal motions were present. It is now general knowledge that flare loops are initially observed in X-rays and become visible in H-alpha only after cooling. For such a high density a loop would cool through radiation from 10 to the 7th K to 10 to the 4th K within a few minutes so that the dense H-alpha loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in H-alpha. Therefore, the density must have been significantly smaller when the loops were formed and the flare loops were apparently both shrinking and becoming denser while cooling.
Svestka, Z.↗
A pulsed electron-photon fluorescence diagnostic technique for temperature and specie concentration measurement at points in relatively dense, unseedded air flows
An analysis is presented on the use of the fluorescence stimulated by combined pulsed electron and photon beams for the study of gas flows up to densities equivalent to an altitude of about 20 km (number density of about 3 x 10 to the 18th/cu cm). The electron beam acts as a pump, requiring no seed gas, to provide a localized concentration of ions or excited state neutrals that can be probed by saturation optical pulses. A short pulse (10ns) electron beam can be used by itself to provide effectively quench-free emission up to number densities of around 10 to the 18th/cm, but is is difficult to maintain satisfactory spatial resolution at this high density. The use of a nearly simultaneous strong optical pulse increases the flexibility of the diagnostic technique, permitting use at densities greater than 10 to the 18th/cu cm with good spatial resolution. The use of flash X-ray sources combined with optical probing also appears promising for densities above 10 to the 19th/cu cm.
Muntz, E. P.↗
Multi-thermal observations of newly formed loops in a dynamic flare
The dynamic flare of November 6, 1980 (max at about 15:26 UT) developed a rich system of growing loops which could be followed in H-alpha for 1.5 hr. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of deviations from LTE populations for a hydrogen atom reveal that this requires electron densities in the loops close to, or in excess of 10 to the 12th/cu cm. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 10 to the 12th/cu cm if no nonthermal motions were present, or 5 x 10 to the 11th/cu cm for a turbulent velocity of about 12 km/s. It is now general knowledge that flare loops are initially observed in X-rays and become visible in H-alpha only after cooling. For such a high density, a loop would cool through radiation from 10 to the 7th to 10 to the 4th K within a few minutes so that the dense H-alpha loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in H-alpha. Therefore, it is suggested that the density must have been significantly lower when the loops were formed, and that the flare loops were apparently both shrinking and increasing in density while cooling.
Svestka, Zdenek F.↗
HEAO 1 A-2 low-energy detector X-ray spectra of the Cygnus Loop
The Cygnus Loop supernova remnant was observed by the A-2 low-energy detector (LED) proportional counters on the HEAO 1 satellite. Recent improvements to the non-X-ray background rejection and detector response simulation have allowed production of the most accurate spectra of the Cygnus Loop to date. Three separate regions of the Cygnus Loop were observed. Single-temperature, Raymond-Smith models are inadequate to describe the spectra, but two component model fits are good. Temperature, column density, and emission measure variations across the Cygnus Loop are found. These results are interpreted and compared with previous work.
Leahy, D. A.↗
On the X-ray emitting boundary layer of the dwarf nova VW Hydri
The temperature and luminosity of the boundary layer of VW Hyi are constrained to kT(BL) of about 10.5 eV, and L(BL) of about 6 x 10 to the 32nd (d/65 pc)squared ergs/sec. This is based on Voyager far- and extreme-ultraviolet spectrophotometry and a measurement of the column density of neutral hydrogen, combined with Exosat LE filter observations. Results are compared with the accretion-disk luminosity found by Polidan et al. (1990) using concurrent optical, IUE, and Voyager spectrophotometric observations. The value of zeta is found to be about 0.04, although theoretical predictions show comparable luminosities at the boundary layer and the accretion disk - zeta is identical to L(BL)/L(disk), which is about 1 - unless the white dwarf rotates very rapidly. Severe contamination of filter observations due to light from the inner accretion disk is also found. This contamination had previously been understood as a result of the luminous ultrasoft boundary layer.
Mauche, Christopher W.↗
Organometallic chemical vapor deposition and characterization of ZnGe(1-x)Si(x)P2-Ge alloys on GaP substrates
The epitaxial growth of ZnGe(1-x)Si(x)P2-Ge alloys on GaP substrates by open tube organometallic chemical vapor deposition (OMCVD) is reported. The chemical composition of the alloys characterized by energy dispersive X-ray spectroscopy shows that alloys with x up to 0.13 can be deposited on (001) GaP. Epitaxial growth with mirror smooth surface morphology was achieved for x less than or equal to 0.05. Transmission electron microscopy (TEM) micrographs of these alloys show specular epitaxy and the absence of microstructural defects indicating a defect density of less than 10(exp 7) cm(sup -2). Selected area electron diffraction pattern of the alloy shows that the epitaxial layer crystallizes in the chalcopyrite structure with relatively weak superlattice reflections indicating certain degree of randomness in the cation sublattice. Hall measurements show that the alloys are p-type, like the unalloyed films; the carrier concentration, however, dropped about 10 times from 2 x 10(exp 18) to 2 x 10(exp 17) cm(sup -3). Absorption measurements indicate that the band tailing in the absorption spectra of the alloy was shifted about 0.04 eV towards shorter wavelength as compared to the unalloyed material. Diodes fabricated from the n(+)-GaP/p-ZnSiP2-ZnGeP2-Ge heterostructure at x = 0.05 have a reverse break-down voltage of -10.8 V and a reverse saturation current density of approximately 6 x 10(exp -8) A/sq cm.
Xing, G. C.↗
The correlation of alkalis and aluminum during high-temperature volatilization of albite and nepheline
Our previous study of high-temperature evaporation of mafic targets has shown a systematic enrichment of newly-formed condensates in silicon and alkalis and depletion in refractory elements (Al, Ca, Ti). This effect, which is consistent with the volatility of the elements, was also tested for several experiments with acidic targets. In one case it was the impact evaporation of granite targets using a light-gas gun facility. Analyses of the condensate which was collected during the impact show that it was enriched in Al and Na so that the composition of the condensate became close to nepheline. In the work of Nagahara, an incongruent evaporation of alkali feldspars under stationary conditions has been also proposed. These discoveries required a more detailed study of high-temperaure evaporation of monomineralic Al-silicate targets. In these experiments, we have used samples of oligoclase and of nepheline. Vaporization of samples was performed in a hermetic cell filled with helium at normal temperature and pressure using a powerful Nd-laser focused on the sample. Laser pulses had the following parameters: luminous energy approximately 600 J, duration approximately 10(exp -3) s, density of luminosity was approximately 5 x 10(exp 6) W/sq cm, the temperature of vaporization is about 3000-4000 K. About 4 cm from the sample, a nickel foil was placed on which the condensate was collected. Films of condensate were analyzed using X-Ray Photo-Electron spectrometer ES-2401. The measurement of internal chemical composition and of the charging state of elements through the whole depth of the condensed films was made layer by layer with argon-ion etching of 200 A of the film per step. Results of this study are given. The bottom layers of condensed film correspond to the front parts of the evaporated cloud or to condensation at the beginning of the evaporative process and surface layers to condensation at the end of the process.
Dikov, Yu. P.↗
FNAS/solar flare energetics
We have performed an extensive study of solar flare energy buildup and release, concentrating in two aspects: (1) relationship with 3D field topology and measured electric currents; and (2) flare onset characteristics as determined from combined x ray and ultraviolet observations. We extended our previous studies on the characteristic topology of flaring regions, by following the evolution of an active region over three consecutive days. From comparison with flare observations in x rays and h alpha, we found further support for the hypothesis that flares were triggered by taking place at the separators (3D generalization of and x-type neutral point). Furthermore, we found that emerging in flux at a site within the active regions where no (or little) activity was previously observed, caused the appearance of a secondary separator and thereon continuous triggering of activity at such site. Our topology arguments were then applied to a study of sympathetic activity between two regions within an active complex. Here again we found that interacting field structures along separators and separatrices, which act as pathways for recurrent flaring to spread between the regions, could be used to understand how activity spread to potentially explosive sites with the complex. We also finished our study of flare onset characteristics as determined from combined x ray and ultraviolet observations. Using a quasi-static modeling approach, we find that this phase is characterized by a relatively low level of energy release, 10 exp 26-27 erg/s, which is sufficient to produce 'gentle' evaporation, a shift in the location of the transition zone as compared to pre-flare conditions, and an increase in the temperature and density of coronal loops. All these changes have profound implications on the observed signatures of impulsive phase phenomena, which had been neglected in the past. As a follow-up of this investigation, we now plan to apply our results to the interpretation of high-sensitivity spectroscopic and hard x-ray data currently being gathered by the Yohkoh and Compton Gamma Ray Observatory satellites.
Machado, M. E.↗