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At least 1,027 records · Page 57

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NASA NTRS1978

Low energy gamma ray observations with the MPI-Compton telescope

Although the evaluation of data from the first balloon-flight of a large area Compton telescope is incomplete, two preliminary results are discussed. From the measured background spectrum at float altitude, the sensitivity of the telescope for the detection of cosmic gamma ray lines is estimated. The energy spectra is determined for an enhanced gamma ray flux observed from the direction of the Seyfert galaxy NGC 4151. A schematic drawing of the telescope is presented and discussed.

Graml, F.↗

NASA NTRS1978

Energetic ionized helium in the quiet time radiation belts - Theory and comparison with observation

Theoretical calculations of helium ion distributions in the inner magnetosphere are compared to observations made by ATS-6 and Explorer-45. Coupled transport equations for equatorially mirroring singly and doubly ionized helium ions in the steady state limit with an outer boundary of L = 7 are solved. Radial profiles and energy spectra are computed at all lower L values. Theoretical quiet time predictions are compared to satellite observations of energetic helium ions in the lower MeV range. It is found that the theory adequately represents the principal characteristics of the radiation belt helium ion population.

Spjeldvik, W. N.↗

NASA NTRS1978

Theory for charge states of energetic oxygen ions in the earth's radiation belts

Fluxes of geomagnetically trapped energetic oxygen ions have been studied in detail. Ion distributions in radial locations below the geostationary orbit, energy spectra between 1 keV and 100 MeV, and the distribution over charge states have been computed for equatorially mirroring ions. Both ionospheric and solar wind oxygen ion sources have been considered, and it is found that the charge state distributions in the interior of the radiation belts are largely independent of the charge state characteristics of the sources. In the MeV range, oxygen ions prove to be a more sensitive probe for radiation belt dynamics than helium ions and protons.

Spjeldvik, W. N.↗

NASA NTRS1977

Reevaluation of the Apollo orbital X-ray fluorescence data

A combination of Al/Mg ratios and Al/Si ratios has provided high-quality geochemical and geological information from the Apollo orbital X-ray fluorescence data. The high sensitivity of the characteristic Si X-rays to alterations in the energy spectra of the solar X-ray flux limits the analytical usefulness of the ratios involving Si. A photometric study indicates that the Si concentration in lunar materials varies by less than about + or - 15% of the Si present. In addition, particle size and surface roughness are shown to have small effects on the characteristic fluorescent X-ray radiation of Si.

Hubbard, N. J.↗

NASA NTRS1978

Simultaneous multispacecraft observations of energetic proton bursts inside and outside the magnetosphere

Energetic proton bursts were observed simultaneously on Imp 6, 7, and 8 both inside and outside the earth's magnetosphere during the period October 1972 through August 1974. It is found that proton bursts are present nearly simultaneously in the vicinity of the outer belt trapping boundary, in the low-latitude magnetotail, in the magnetosheath, and upstream from the bow shock. Large intensity differences, time delays, and differences in energy spectra recorded by the three spacecraft are described. It is suggested that energetic protons and electrons are probably accelerated inside the plasma sheet and propagate to various regions both inside and outside the magnetosphere.

Sarris, E. T.↗

NASA NTRS1978

The magnetopause energetic electron layer. I - Observations along the distant magnetotail

Instrumentation aboard Imp 8 was used to study the magnetopause energetic electron layer along the distant magnetotail, and the observations are discussed. The inner edge of the layer corresponds to the magnetopause boundary, and energetic electrons within the layer persistently stream tailward along local magnetosheath field lines. Pitch angles of electrons along the dusk magnetopause are often restricted to values less than approximately 40 deg, while along the dawnside of the tail somewhat larger pitch angles are normally seen. The differential energy spectra of electrons in the layer, the intensity enhancements, and the average directional intensities are characterized.

Baker, D. N.↗

NASA NTRS1979

Preliminary results of a gamma-ray burst study in the Konus experiment on the Venera-11 and Venera-12 space probes

Twenty-one gamma-ray bursts and 68 solar flares in the hard X-ray range were detected on Venera-11 and Venera-12 space probes during the initial 50-day observation period. Major characteristics of the equipment used and preliminary data on the temporal structure and energy spectra of the gamma-ray bursts are considered. The pattern of gamma-ray burst frequency distribution vs. intensity, N(S), is established.

Mazets, Y. P.↗

NASA NTRS1978

The structure of the temperature minimum region in solar flares and its significance for flare heating mechanisms

The paper analyzes Ca II K-line profiles of one flare and EUV continuum observations of two other flares in an effort to obtain values for temperature enhancements over active region values produced in the upper photosphere around and above the temperature minimum region. Results show that the flare temperature minimum is depressed some two scale heights below its preflare level and that substantial temperature enhancements are produced even at this depth. Consideration is also given to possible heating mechanisms which might be responsible for the observed enhancements, including (1) heating by EUV radiation, (2) heating by proton beams with low dispersion energy spectra centered at 10-20 MeV, and (3) localized heating at temperature minimum levels.

Machado, M. E.↗

NASA NTRS1979

Association of low-frequency waves with suprathermal ions in the upstream solar wind

Observations obtained upstream of the earth's bowshock with the LASL/MPI plasma instruments and the UCLA magnetometers on ISEE-1 and 2 have revealed a striking relationship between the presence of low-frequency fluctuations in solar wind density and field strength and the different types of distribution functions of upstream ions. Waves are absent when the ions have the beamlike distribution of the 'reflected' ions. Large-amplitude waves are present only in conjunction with the 'diffuse' ions, which are characterized by flat energy spectra and broad angular distributions. The waves are largely compressive, showing very good correlation between oscillations in magnetic field strength and plasma density.

Paschmann, G.↗

NASA NTRS1978

A review of the near-earth radiation environment

The spatial volume surrounding the earth out to 30 earth radii has been divided into the five regions known as the interplanetary medium, magnetosheath, plasma sheet, high-latitude magnetotail, and inner magnetosphere. In each region, the primary attributes of the particle populations and available models are described, and integral energy spectra covering the range from 10 to 10 billion eV are shown. The effects of the solar cycle on future projections are discussed.

Sawyer, D. M.↗

NASA NTRS1979

Evidence for the deficiency of short cosmic ray pathlengths and a physically realistic explanation - The no-near-sources model

Recent observations of the charge and energy spectra of cosmic-ray nuclei are used to construct secondary-to-primary charge ratios at the two ends of the charge spectrum. These ratios are found to be inconsistent with the ad hoc leaky-box model of cosmic-ray propagation which leads to an exponential pathlength distribution. Models for which the pathlength distribution function is deficient in short pathlengths provide a more consistent picture. Several of these models, both ad hoc and physical, are investigated. The physical model considered is one for which detailed galactic propagation parameters and boundary conditions are used and for which there exist no near sources of cosmic rays over a time interval corresponding to a few times the cosmic-ray age.

Lezniak, J. A.↗

NASA NTRS1979

Evaluation of flow quality in two NASA transonic wind tunnels

Tests have been conducted in the Langley Research Center 8-foot Transonic Pressure Tunnel and the Ames Research Center 12-foot pressure wind tunnel in order to measure characteristic disturbance levels and energy spectra in their respective settling chambers, test sections, and diffusers and to determine the sources of these disturbances. Results are presented and discussed along with some specific recommendations.

Owen, F. K.↗

NASA NTRS1979

Particle boundary structures at the magnetopause and the plasma sheet

There are three classes of particle events in the vicinity of the magnetopause: a layer of particles right at the magnetopause which we identify with the boundary layer particles; spikes of particles just ahead of the magnetopause; and, sometimes, magnetosheath-like ions appearing inside the magnetosphere, the inclusion events. The energy spectra of these three classes of events are very similar, indicating a common particle source. The presence of a particle layer at the outer boundary of the plasma sheet is shown. This layer has typical dimensions of a few thousand km at 20 Earth radii. A typical velocity is a few tens of km/sec. These velocities and dimensions projected to ionospheric heights resemble those of visual auroras and suggest that aurorally associated particle phenomena are being detected.

Parks, G. K.↗

NASA NTRS1979

Impulsive penetration and viscous interaction

How the magnetosheath plasma enters the entry layer and low latitude boundary layers, with the particle energy spectra almost unchanged is investigated. It was proposed by Lemaire that this is accomplished by impulsive penetration of plasma clouds of plasmoids. Once inside the magnetosphere, a plasmoid with its own momentum will polarize, to create its own electric field for continued motion. This voltage generator charges up the sides of the boundary layers, in the process creating the internal magnetospheric electric field. The entry layer particles will gradient and curvature drift, constituting still another generator, a current generator, to power magnetospheric plasma processes. This may be the explanation for the viscous interaction first proposed by Axford and Hines.

Heikkila, W. J.↗

NASA NTRS1980

Cosmic ray studies with a gas Cherenkov counter in association with an ionization spectrometer

The results from a balloon-borne gas Cherenkov counter (threshold 16.5 GeV/nucleon) and an ionization spectrometer are presented. The gas Cherenkov counter provides an absolute energy distribution for the response of the calorimeter for 5 or = Z 26 nuclei of cosmic rays. The contribution of scintillation to the gas Cherenkov pulse height was obtained by independently selecting particles below the gas Cherenkov threshold using the ionization spectrometer. Energy spectra were derived by minimizing the chi squared between Monte Carlo simulted data and flight data. Best fit power laws, dN/dE = AE-gamma, were determined for C, N, O, Ne, Mg, and Si. The power laws, all consistent with E (-2.7) are not good fits to the data. A better fit is obtained using the spectrum derived from the spectrometer. The data from the ionization calorimeter and the gas Cherenkov are thus completely self-consistent.

Balasubrahmanyan, V. K.↗

NASA NTRS1979

On the inference of properties of Saturn's Ring E from energetic charged particle observations

The paper demonstrates that information about Saturn's Ring E particle size is potentially obtainable from observations of Saturnian trapped radiation. It is shown that observations of the radial dependence of the intensities, energy spectra, electron-to-proton intensity ratio, and pitch angle distributions of energetic charged particles trapped outside of Ring A can potentially provide information (1) on the existence of Ring E, (2) on the effective size of the particulate matter therein, and (3) on the magnitude of the radial diffusion coefficient for energetic particles. A parametric study of these possibilities is specialized to the characteristics of the University of Iowa detectors on Pioneer 11 which was scheduled to make a close encounter with Saturn in 1979.

Thomsen, M. F.↗

NASA NTRS1980

Energetic particle penetrations into the inner magnetosphere

The nose structures observed on 90-deg pitch angle ion spectrograms characteristic of energetic particle injection into the ring current region of the inner magnetosphere in the afternoon to midnight sector are examined in detail on the basis of Explorer 45 data. A statistical analysis of the time dependence of nose structures yields a highest probability of occurrence at around 2000 MLT, and most events are found to occur on successive passes. The appearance of nose events is also related to an enhancement or change in configuration of the geoelectric field which alters magnetospheric convection patterns to drive an ion front close to the earth, where it can be observed by Explorer 45. The observed characteristics of nose structures are interpreted in terms of adiabatic charged particle motions in the magnetosphere in a Volland-Stern convection electric field model, which is also applied to explain the energy spectra and dispersion in penetration distances of electrons and ions observed in the postmidnight to morning sectors.

Ejiri, M.↗

NASA NTRS1980

Impulsive 2-10 keV solar electron events not associated with flares

Data from the ISEE 3 satellite reveal a class of impulsive solar electron events with no measurable increase in flux above 10-20 keV. The flux histories and angular distributions indicate that the electrons propagate through interplanetary space with little or no scattering. The smooth extension of the power-law energy spectra down to the limit of the observations at 2 keV indicates that the electrons are accelerated at altitudes greater than 0.5 solar radii in the solar corona. Although these events occur more frequently than any other type of impulsive solar particle event observed, no correlation is found with flares or flare-related activity. However, there is a close correlation with low-frequency type III radio bursts.

Potter, D. W.↗