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NASA NTRS1974

On the irradiation history and origin of gas-rich meteorites

Transmission electron microscope study of the track density gradients and irradiation geometries of track-rich grains and chondrules in sections of Fayetteville and Kapoeta, and in sections of lunar breccias and grains from lunar soil. A substantial fraction (50 to 90%) of the meteoritic track-rich grains and chondrules show evidence of having been irradiated anisotropically in their different faces, as would be expected for irradiation on the surface of a parent body. The observations thus support the hypothesis that the irradiation of these grains and chondrules took place on the regoliths of asteroidal-sized bodies. Measurements of steepest track density gradients indicate that, while there are finite differences between spectra exhibited by individual gas-rich meteorites, the average solar flare spectral shapes have been similar over the last 4 b.y. or so.

Rajan, R. S.↗

NASA NTRS1979

Principal component analysis of solar flares in the soft X-ray flux

The paper considers principal component analysis of solar flares in the soft X-ray flux, a technique for extracting the salient features from a mass of data. The method applies particularly to the analysis of nonstationary ensembles, and its computations require the evaluation of eigenvalues of matrices. The Eispack matrix eigen system routines were used to analyze full-disk proportional-counter data from the X-ray event analyzer which was part of the Skylab experiment. Empirical orthogonal functions were derived for events in the soft X-ray spectrum between 2.5 and 20 A during different time periods, indicating that about 90% of the cumulative power of each analyzed flare is contained in the largest eigenvector. The first two largest eigenvectors are sufficient for an empirical curve fit through the raw data and a characterization of solar flares in the soft X-ray flux, and power spectra of two largest eigenvectors reveal a reported periodicity of about 5 min.

Teuber, D. L.↗

NASA NTRS1980

Densities and mass motions in transition-zone plasmas in solar flares observed from Skylab

The electron densities and bulk motions in the transition-zone plasma of a solar flare are investigated by an analysis of EUV emission line spectra taken on Skylab. Spectra of three flares were obtained with the NRL normal incidence grating slit spectrograph in the ranges 1100-1940 and 1940-3940 A. The line ratios of transition-zone Si III lines and the intensity of the forbidden O IV 1401-A lines during flare maximum indicate electron densities on the order of 10 to the 12th/cu cm, decreasing by a factor of 2 to 3 in the flare decay phase. Line broadening of the transition-zone ions such as Si III, O IV, C IV and N V is noted, and the observed asymmetrical N V line profiles are approximated by a bi-Gaussian model of a stationary and a moving plasma component with a bulk velocity of 12 to 70 km/sec. Turbulent velocities of from 45 to 85 km/sec and from 20 to 40 km/sec are also indicated for the moving and stationary components of the transition-zone plasma, respectively.

Cheng, C.-C.↗

NASA NTRS1983

Solar flare neutron fluxes derived from interplanetary charged particle measurements

The first observation of interplanetary protons produced by the decay of solar neutrons made by Evenson et al. (1983) after a solar flare which occurred on June 3, 1982, is expanded, extending the measurement of the spectrum of the decay protons to higher energy. The spectrum of the decay protons for the June 21, 1980, neutron event observed by Chupp et al. (1982) is also determined. The measurements suggest that neutron emission from solar flares is isotropic and that different flares emit neutrons with similar spectra. The importance of such measurements in the study of interplanetary propagation of charged particles is discussed.

Evenson, P.↗

NASA NTRS1992

MIRACAL: A mission radiation calculation program for analysis of lunar and interplanetary missions

A computational procedure and data base are developed for manned space exploration missions for which estimates are made for the energetic particle fluences encountered and the resulting dose equivalent incurred. The data base includes the following options: statistical or continuum model for ordinary solar proton events, selection of up to six large proton flare spectra, and galactic cosmic ray fluxes for elemental nuclei of charge numbers 1 through 92. The program requires an input trajectory definition information and specifications of optional parameters, which include desired spectral data and nominal shield thickness. The procedure may be implemented as an independent program or as a subroutine in trajectory codes. This code should be most useful in mission optimization and selection studies for which radiation exposure is of special importance.

Nealy, John E.↗

NASA NTRS1987

The collection and analysis of extraterrestrial dust particles

Techniques used for the collection of interplanetary dust particles (IDPs) from the earth's surface, upper atmosphere, and space and for the particles' curation and examination are discussed together with the properties of the collected IDPs and the information available on the interplanetary and interstellar dust from astronomical observations. Consideration is given to the physical and spectral properties of chondritic IDPs as well as of nonchondritic Al- and Ca-rich particles of extraterrestrial origin. Special attention is given to the determination of the sources of the extraterrestrial particles by spectral comparisons with meteorites, asteroids, and comets and by examination of the solar flare track densities within mineral grains in the IDPs. A spectral comparison with interstellar spectra revealed common features supporting the belief that some of the collected IDPs contain 'primitive' components that date back to the origin of the solar system and perhaps beyond.

Sandford, Scott A.↗

NASA NTRS1984

First-order Fermi shock acceleration in solar flares

The first-order Fermi shock acceleration model is compared with specific observations where electron, proton, and alpha particle spectra are available. In all events, it is found that a single shock with a compression ratio as inferred from the low-energy proton spectra can reasonably produce the full proton, electron, and alpha particle spectra. The model predicts that the acceleration time to a given energy will be approximately equal for electrons and protons and, for reasonable solar parameters, can be less than 1 sec to 100 MeV.

Ellison, D. C.↗

NASA NTRS1983

The solar cosmic ray neutron event on June 3, 1982

The observation of solar neutrons from the earth has been reported. The observations were carried out June 3, 1982, following the intense gamma-ray line flare at 1143 UT. The emission spectra of the neutrons was calculated over an energy range from 40 MeV to 1.2 GeV, on the basis of measurements from a gamma-ray/neutron scintillation spectrometer, and the IGY Jungfraujoch neutron monitor at an altitude of 3500 m. Some possible terrestrial effects of the solar neutrons are discussed. It is shown that the calculated spectra conform to the requirement of ion acceleration to GeV energies a few seconds after the start of the impulsive phase of a solar ion flare event.

Debrunner, H.↗

NASA NTRS1984

High resolution hard X-ray spectra of solar and cosmic sources

High resolution hard X-ray observations of a large solar flare and the Crab Nebula were obtained during balloon flights using an array of cooled germanium planar detectors. In addition, high time resolution high sensitivity measurements were obtained with a 300 square cm NaI/CsI phoswich scintillator. The Crab spectrum from both flights was searched without finding evidence of line emission below 200 keV. In particular, for the 73 keV line previously reported a 3 sigma upper limit for a narrow (1 keV FWHM) line .0019 and .0014 ph square cm/sec for the 1979 and 1980 flights, respectively was obtained.

Schwartz, R. A.↗

NASA NTRS1987

On the relationship of flare size and particle anisotropy in solar gamma-ray flares

The effects of radiation directivity on the interpretation of SMM gamma-ray flare observations. If the electron anisotropy is independent of flare size, the size distribution of 300 keV-1 Mev flare is much flatter than that of X-ray flares. This implies that larger flares have, on average, harder electron spectra. Distributions of electrons strongly peaked downward into the solar photosphere are not consistent with the data.

Dermer, Charles D.↗

NASA NTRS1987

Ion and relativistic electron acceleration by Alfven and whistler turbulence in solar flares

A model is proposed in which turbulent Alfven and whistler waves simultaneously produce the proton and electron spectra implied by the gamma-ray observations noted during the impulsive phase of the June 3, 1982 flare. The results demonstrate that protons can be accelerated to several GeV in less than about 10 sec by Alfven turbulence whose energy density is greater than a few erg/cu cm. It is also found that electrons may be accelerated to tens of MeV on similar time scales by whistler and Alfven turbulence. A lower limit on the energy density of the Alfven turbulence is obtained which is small compared to the total magnetic energy density.

Miller, James A.↗

NASA NTRS1986

Secondary antiproton production in relativistic plasmas

Angular and energy spectra of bremsstrahlung have been calculated from anisotropic electron distributions in solar flares. Results have been compared to observations of gamma-ray limb-brightening and the data on the variation of the gamma-ray spectrum with flare position on the sun.

Dermer, C. D.↗

NASA NTRS1975

Low energy particle composition

The energy spectra and composition of the steady or 'quiet-time' particle flux, whose origin is unknown was studied. Particles and photons which are associated with solar flares or active regions on the sun were also studied. Various detection techniques used to measure the composition and energy spectra of low energy particles are discussed. Graphs of elemental abundance and energy spectra are given.

Gloeckler, G.↗

NASA NTRS1972

Analysis of solar X-ray data

Type III solar bursts occurring in the absence of solar flares were observed to be accompanied by weak X-radiation. The energy scale of an OSO-3 soft X-ray ion chamber was assessed using realistic theoretical X-ray spectra. Relationships between soft solar X-rays and solar activity were investigated. These included optical studies, the role of the Type III acceleration mechanism in establishing the soft X-ray source volume, H alpha flare intensity variations, and gross magnetic field structure.

Teske, R. G.↗

NASA NTRS1990

Solar neutron decay proton observations in cycle 21

Measurement of the flux and energy spectrum of the protons resulting from the decay of solar flare neutrons gives unique information on the spectrum of neutrons from 5 to 200 MeV. Neutrons from three flares have been observed in this manner during solar cycle 21. The use of the decay protons to determine neutron energy spectra is reviewed, and new and definitive energy spectra are presented for the two large flares on June 3, 1982 and April 25, 1984.

Evenson, Paul↗

NASA NTRS2011

Deducing Electron Properties from Hard X-Ray Observations

X-radiation from energetic electrons is the prime diagnostic of flare-accelerated electrons. The observed X-ray flux (and polarization state) is fundamentally a convolution of the cross-section for the hard X-ray emission process(es) in question with the electron distribution function, which is in turn a function of energy, direction, spatial location and time. To address the problems of particle propagation and acceleration one needs to infer as much information as possible on this electron distribution function, through a deconvolution of this fundamental relationship. This review presents recent progress toward this goal using spectroscopic, imaging and polarization measurements, primarily from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Previous conclusions regarding the energy, angular (pitch angle) and spatial distributions of energetic electrons in solar flares are critically reviewed. We discuss the role and the observational evidence of several radiation processes: free-free electron-ion, free-free electron-electron, free-bound electron-ion, photoelectric absorption and Compton backscatter (albedo), using both spectroscopic and imaging techniques. This unprecedented quality of data allows for the first time inference of the angular distributions of the X-ray-emitting electrons and improved model-independent inference of electron energy spectra and emission measures of thermal plasma. Moreover, imaging spectroscopy has revealed hitherto unknown details of solar flare morphology and detailed spectroscopy of coronal, footpoint and extended sources in flaring regions. Additional attempts to measure hard X-ray polarization were not sufficient to put constraints on the degree of anisotropy of electrons, but point to the importance of obtaining good quality polarization data in the future.

Kontar, E. P.↗

NASA NTRS1989

Relativistic electron transport and bremsstrahlung production in solar flares

A Monte Carlo simulation of ultrarelativistic electron transport in solar flare magnetic loops has been developed. It includes Coulomb, synchrotron, and bremsstrahlung energy losses; pitch-angle scattering by Alfven and whistler turbulence in the coronal region of the loop; and magnetic mirroring in the converging magnetic flux tubes beneath the transition region. Depth distributions, time profiles, energy spectra, and angular distributions of the resulting bremsstrahlung emission are calculated. It is found that both the preferential detection of solar flares with greater than 10 MeV emission near the limb of the sun and the observation of ultrarelativistic electron bremsstrahlung from flares on the disk are consequences of the loop transport model. The declining portions of the observed time profiles of greater than 10 MeV emission from solar flares can also be accounted for, and it is proposed that these portions are determined by transport and not acceleration.

Miller, James A.↗

NASA NTRS1995

The He-3/He-4 ratios for solar energetic particle events during the Combined Release and Radiation Effects Satellite Mission

Helium data measured by the University of Chicago instrument, ONR-604, are employed to determine the ratio of He-3 to He-4 for solar energetic particle (SEP) events over an energy range 50-110 MeV/nucleon during the 1990/1991 Combined Release and Radiation Effects Satellite mission. The Sun in this period is extremely active. A total of 29 separate SEP events have been identified; among them 16 major events have been analyzed to obtain He-3/He-4 ratios, with a mass resolution of 0.10 amu. Thirteen events have a He-3/He-4 ratio larger than 0.005, one order of magnitude greater than the solar coronal value. The He-3/He-4 ratio at energies of 50-110 MeV/nucleon is independent of the size of the SEP event, for the moderately large flares analyzed here. The helium energy spectra are represented by power laws. During the 1991 June flare period, different large-particle injections associated with different solar flares, but occurring from the same active region, have a similar average spectral index and a similar He-3/He-4 ratio. The spectral index of He-4 varies from event to event, i.e., from as small as 1.5 to as large as 7.5. A correlation is found between the inferred spectral index from gamma-ray measurements and our measured spectral indices for the 1991 June 11 and June 15 events, suggesting that the high-energy SEPs may come from the same acceleration event as the particles that interact at the Sun and produce the gamma rays. The implications of these results for particle acceleration and propagation at the flare site and in the solar corona are discussed.

Chen, Jiasheng↗