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At least 613 records · Page 34

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NASA NTRS1976

Observations of magnetospheric bursts of high-energy protons and electrons at approximately 35 earth radii with Imp 7

Proton and electron bursts (above 0.29 MeV and above 0.22 MeV, respectively) in the vicinity of the magnetosphere are studied on the basis of a high-sensitivity experiment. Although the bursts are a permanent feature in the upstream solar wind, the range of observed intensities varies by at least 5 orders of magnitude, depending on magnetic activity. The bursts are typically associated with weak fluctuations in the interplanetary magnetic field, which suggests the presence of hydromagnetic waves. Burst are found in and about the magnetosheath, plasma sheet, and magnetotail boundary layer, and also outside the bow shock; however, they rarely appear at distances greater than 10 earth radii north or south of the neutral sheet. Dawn-dusk asymmetries are present in intensity but not necessarily in frequency of occurrence. Proton bursts are highly anisotropic upstream from the bow shock and in the magnetosheath, while electron bursts are anisotropic only in the upstream solar wind.

Sarris, E. T.↗

NASA NTRS1976

Radiation of whistlers by helical electron and proton beams

The feasibility of generating whistlers by means of an array of helical electron and proton beams is investigated. It is found that quasi-static beam-plasma instabilities will play a vital role in limiting the effective coherent length of the beam. The total radiated power for the whistlers is consequently decreased by 2 orders of magnitude below previously predicted levels (Dowden, 1973). A proton beam is shown to be somewhat less efficient than an electron beam for generating whistlers.

Kuo, Y.-Y.↗

NASA NTRS1976

Electromagnetic instabilities driven by unequal proton beams in the solar wind

The paper sets forth a numerical investigation of the linear dispersion relation for typical solar wind conditions at 1 AU during those times (high-speed streams) when a secondary beam of protons drifting relative to the main proton component is present. Three beam-driven instabilities were found to occur as the beam drift velocity approaches the Alfven speed: (1) a pure, field-aligned magnetosonic wave that is most important at relatively high beta and/or high beam drift speeds; (2) an oblique magnetosonic wave having highest growth rates 15-30 deg from the magnetic field; and (3) an oblique Alfven wave having maximum growth rates at increasing angle to the magnetic field. The linear growth rates for the field-aligned magnetosonic and the Alfven oblique modes are investigated as a function of relative beam density, varying anisotropic pitch angle distributions for the various components, electron temperature, and electron heat flux.

Montgomery, M. D.↗

NASA NTRS1976

Efficiencies for production of atomic nitrogen and oxygen by relativistic proton impact in air

Relativistic electron and proton impact cross sections are obtained and represented by analytic forms which span the energy range from threshold to 1 GeV. For ionization processes, the Massey-Mohr continuum generalized oscillator strength surface is parameterized. Parameters are determined by simultaneous fitting to (1) empirical data, (2) the Bethe sum rule, and (3) doubly differential cross sections for ionization. Branching ratios for dissociation and predissociation from important states of N2 and O2 are determined. The efficiency for the production of atomic nitrogen and oxygen by protons with kinetic energy less than 1 GeV is determined using these branching ratio and cross section assignments.

Porter, H. S.↗

NASA NTRS1976

Proton aurora on Io

The Jovian satellite Io should exhibit substantial auroral activity due to interactions of the satellite's atmosphere with Jovian magnetospheric particles. Plasma sheaths that may form around the satellite will cause substantial proton aurorae on the Jupiter-facing hemisphere and electron aurorae on the outward-facing hemisphere. A sample calculation indicates that Doppler-shifted radiation from high-velocity hydrogen atoms (proton aurora) will be observable from a spacecraft in the vicinity of Jupiter. Emission near Lyman-alpha may be present at a level as much as 100 times that of the solar background reflected from Io's surface.

Pilcher, C. B.↗

NASA NTRS1977

The streaming of 1.3 - 2.3 MeV cosmic-ray protons during periods between prompt solar particle events

The anisotropy of 1.3 to 2.3 MeV protons in interplanetary space was measured using the Caltech electron/isotope spectrometer aboard IMP-7 for 317 6 hour periods from 72/273 to 74/2. Periods dominated by prompt solar particle events are not included. The convective and diffusive anisotropies were determined from the observed anisotropy using concurrent solar wind speed measurements and observed energy spectra. The diffusive flow of particles was found to be typically toward the sun, indicating a positive radial gradient in the particle density. This anisotropy was inconsistent with previously proposed sources of low energy proton increases seen at 1 AU which involve continual solar acceleration. The typical properties of this new component of low-energy cosmic rays were determined for this period which is near solar minimum.

Marshall, F. E.↗

NASA NTRS1977

On the high energy proton spectrum measurements

The steepening of the proton spectrum beyond 1000 GeV and the rise in inelastic cross sections between 20 and 600 GeV observed by the PROTON-1-2-3 satellite experiments were explained by systematic effects of energy dependent albedo (backscatter) from the calorimeter.

Ellsworth, R. W.↗

NASA NTRS1976

Proton aurora on Io

The Jovian satellite Io should exhibit substantial auroral activity due to interactions of the satellite's atmosphere with Jovian magnetospheric particles. Plasma sheaths that may form around the satellite will cause substantial proton aurora on the Jupiter-facing hemisphere and electron aurora on the outward-facing hemisphere. A sample calculation indicates that Doppler-shifted radiation from high-velocity hydrogen atoms (proton aurora) will be observable from a spacecraft in the vicinity of Jupiter. Emission near Lyman-alpha may be present at a level as much as 100 times that of the solar background reflected from Io's surface.

Pilcher, C. B.↗

NASA NTRS1976

Proton-tissue dose buildup factors

When an object is exposed to external radiation, the dose field within the object is a complicated function of the character of the external radiation, the shape of the object (including orientation), and the object's material composition. In this note, the dose conversion factors for protons in tissue are represented using buildup factors. A parametric form for the buildup factors is obtained. The values of the parameters are derived from Monte Carlo calculations of various authors. All the necessary information to estimate nuclear reaction effects in proton irration of convex objects of arbitrary shape is included.

Wilson, J. W.↗

NASA NTRS1977

Approximations for proton excitation of coronal ion fine structure

Explicit approximations that yield proton excitation cross sections and rate coefficients for fine-structure transitions in a wide variety of ions over the low and intermediate energy ranges are obtained in terms of the electric quadrupole transition probability and quadrupole radial integral of a given ion. The range of applicability of these approximations is discussed, and comparisons are made with available cross sections and rate coefficients. Values of quadrupole radial integrals are given for ground configurations of even-Z elements in higher stages of ionization. Proton excitation rate coefficients are computed for coronal transitions involving fine-structure levels in the ions Fe XIII, Fe XV, Fe XVIII, Fe XXI, and Ca XIII.

Kastner, S. O.↗

NASA NTRS1976

Theoretical investigation of protonated carbon dioxide

The equilibrium structure of CO2H(+) has been obtained from self-consistent field and configuration interaction wave functions. Only one stable form has been found, a linear O-C-O chain with the hydrogen bonded to oxygen and slightly off axis, in analogy with known isoelectronic species. A second structure protonated at carbon, which has been inferred from mass spectrometric studies, is found to be unstable with respect to spontaneous rearrangement. The proton affinity of CO2 is calculated to be 136 kcal/mole, in reasonable agreement with the most recent experimental value.

Green, S.↗

NASA NTRS1977

A determination of the L dependence of the radial diffusion coefficient for protons in Jupiter's inner magnetosphere

In a previous paper (Thomsen et al., 1977), a technique was proposed for estimating the radial diffusion coefficient (n) in the inner magnetosphere of Jupiter from the observations of the sweeping effect of the inner Jovian satellites on the fluxes of the energetic charged particles. The present paper extends this technique to permit the unique identification of the parameters D sub O and n, where the diffusion coefficient is assumed to be of the form D = D sub O L to the nth. The derived value of D sub O depends directly on assumptions regarding the nature and efficiency of the loss mechanism operating on the particles, while the value of n depends only on the assumed width of the loss region. The extended technique is applied to the University of Iowa Pioneer 11 proton data, leading to values of n of about O and D(6) of about 3 x 10 to the -8th (R sub J)-squared/sec, when satellite sweepup losses are assumed to be the only loss operating on the protons. The small value of n is strong evidence that the radial diffusion is driven by ionospheric winds.

Thomsen, M. F.↗

NASA NTRS1978

Stochastic acceleration of solar flare protons

The acceleration of solar flare protons is considered by cyclotron damping of intense Alfven wave turbulence in a magnetic trap. The energy diffusion coefficient is computed for a near-isotropic distribution of super-Alfvenic protons and a steady-state solution for the particle spectrum is found for both transit-time and diffusive losses out of the ends of the trap. The acceleration time to a characteristic energy approximately 20 Mev/nucl can be as short as 10 sec. On the basis of phenomenological arguments an omega/2 frequency dependence for the Alfven wave spectrum is inferred. The correlation time of the turbulence lies in the range .0005 less than tau/corr less than .05s.

Barbosa, D. D.↗

NASA NTRS1979

Discrepancy in proton flux extrapolation along field lines in the middle Jovian magnetosphere

An attempt is made to explain the observed modulation of the electron and proton fluxes between 20 and 30 Jupiter radii on the basis of adiabatic theory and assumed symmetry with Jovigraphic longitude. Liouville's theorem is applied with the assumption that particles move conserving their magnetic moments. A magnetic model which matches the intensity and direction of the magnetic field along the Pioneer 10 trajectory is used for determining the positions of the equatorial crossings. Energetic electrons (1.3 MeV) compared in this way appear to be consistently described. Protons, on the other hand, show much weaker fluxes at the off-equatorial points than would be expected by this simple application of Liouville's theorem. Reasons for this discrepancy are offered.

Schardt, A. W.↗

NASA NTRS1979

Tropospheric circulation and interplanetary magnetic sector boundaries followed by MeV proton streams

The MeV proton streams which Svestka et al. (1976) connected with certain sector boundary transits appear to select boundary transits associated with unusually active solar wind conditions. Changes in tropospheric circulation linked to the proton boundary transits were larger than those linked to other boundary transits observed during the same interval. This investigation of sector boundary transits also sheds light on the relationship between changes in solar wind velocity, density and magnetic field and terrestrial changes in the vorticity area index, geomagnetic activity, and cosmic ray flux at earth.

Wilcox, J. M.↗

NASA NTRS1978

The proton and helium rigidity spectra from 10 to 50 GV

A magnet spectrometer flown from Palestine, Texas, (September 15, 1976) has produced measurements on 150,000 protons and 20,000 helium nuclei covering the rigidity range 10-50 GV. In this interval, the proton spectrum has been fitted to a power law with a spectral index of 2.51 + or - 0.03. Similarly, the helium-nuclei rigidity spectrum can be represented as a power law with an index of 2.61 + or - 0.03.

Badhwar, G. D.↗

NASA NTRS1979

Simultaneous quiet time observations of energetic radiation belt protons and helium ions - The equatorial alpha/p ratio near 1 MeV

Simultaneous monitoring of energetic helium ions and protons in the earth's radiation belts has been conducted with Explorer 45 in the immediate vicinity of the equatorial plane. Protons were measured from less than 1 keV to 1.6 MeV and also above 3.3 MeV in a channel responsive up to 22 MeV; helium ions were monitored in three passbands: 910 keV to 3.15 MeV, 590 to 910 keV, and 2.0 to 3.99 MeV. Alpha/proton flux ratios were found to vary significantly with energy and location in the radiation belts. At equal energy per nucleon a range of variability for alpha/p from 0.0001 to well above 0.001 was found, and at equal energy per ion the corresponding variability was from 0.001 to above 10. The latter findings emphasize the relative importance of the very energetic helium ions in the overall radiation belt ion populations.

Fritz, T. A.↗

NASA NTRS1979

Characteristics of the spectra of protons and alpha particles in recurrent events at 1 AU

A study of 31 individual recurrent events from three long-lived corotating particle streams is presented. The spectra of protons and alpha particles during these streams are fit well by an exponential in particle rigidity. Although the spectra show considerable temporal variation, the proton and alpha particle spectra are correlated so that the e-folding rigidities Po(alpha) and Po(p) of the two spectra are in the ratio Po(alpha)/Po(p) = 1.5 plus or minus 0.1. The consistency of this ratio may be a characteristic of the interplanetary acceleration process.

Mewaldt, R. A.↗