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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
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NASA NTRS1977

Solar particle propagation from 1 to 5 AU

The radial variation of the interplanetary propagation of solar cosmic rays is investigated on a grand scale by performing a statistical analysis of charged-particle data obtained by Pioneers 10 and 11 from launch to Jovian encounter (i.e., at distances of 1 to 5 AU). A numerical propagation model is adopted which includes diffusion, convection, and adiabatic deceleration, as well as a variable power-law diffusion coefficient. The study of solar particle events is carried out by analyzing individually each of five key parameters that are uniquely defined in each solar particle event: the time to maximum flux starting from the initial release at the sun, the anisotropy at the time to maximum flux, the flux at that time, the time width of the event at half the flux at the time to maximum, and the decay time. Combined results for the proton energy ranges from 3.4 to 5.2 MeV and 24 to 30 MeV are presented, the average radial diffusion coefficients between 1 and 5 AU are determined for each energy range, and it is found that the combination of a near-impusive injection with a temporally constant spectral index produces a reasonably good fit to the high-energy data but not as good a fit to the low-energy data. Implications of the results obtained are discussed for cosmic-ray propagation theory, solar modulation studies, and interplanetary acceleration of solar particles.

Zwickl, R. D.↗
NASA NTRS1981

Monte-Carlo model of pitch-angle scattering in solar cosmic ray events

Monte Carlo simulations of the propagation of solar cosmic-rays in interplanetary space are reported, including the effects of pitch-angle scattering and adiabatic focusing. Time intensity profiles agree well with the corresponding spatial diffusion approximation for models close to those used by Gombosi and Owens (1980). Monte Carlo simulations of the same model problem yield results that disagree with those of Gombosi and Owens, and the most likely possible source of error in the Monte Carlo simulation is considered to be in the region near the 90 deg pitch angle where the finite step size introduces certain inconsistencies.

Palmer, I. D.↗
NASA NTRS1993

Are cosmic rays effective for ionization of the solar nebula?

In this paper, we argue that the effectiveness of cosmic rays to ionize the bulk of the nebular gas may be further impaired by the influence of the magnetic field on the propagation of cosmic rays. When cosmic rays enter the nebular disk they ionize the gas and make the dynamo generation of magnetic fields possible. However, once magnetic fields are embedded in the nebular gas, the upcoming cosmic rays can no longer penetrate directly into the nebular disk because they start to interact with the magnetic field and lose their energy before propagating significantly toward the midplane. That, in turn, undercuts the ionization source within the bulk of the gas stopping the dynamo action. Nebular dynamo models ignored this back reaction of magnetic fields on cosmic rays. We calculate this back reaction effect, but for the sake of mathematical simplicity, we ignore the effect of magnetic field weakening due to diminishing ionization by cosmic rays.

Dolginov, A. Z.↗
NASA NTRS1985

The role of cosmic rays in magnetic hydrodynamics of interstellar medium

Cosmic ray (CR) propagation in the Galaxy and generally in the cosmic plasma is usually considered in the diffusion approximation. The diffusion is regarded to result from CR scattering due to their interaction with a magnetic and an electric field. In most cases the fields are assumed to be given. Meanwhile, in the Galaxy the CR energy density w sub cr is similar to I eV/cm, i.e., it is comparable with the energy densities of the magnetic field and turbulent motions in the interstellar gas. Therefore, for the Galaxy it becomes necessary to take into account the influence of CR on the gas dynamics and on the magnetic fields in this gas. The simplest way to this is to use the hydrodynamic approximation, but this is possible only on scales greatly exceeding the CR free path lambda before scattering and only for times larger than lambda/v approx. equals lambda/c. One should thus obtain corresponding MHD equations and establish the limits of their applicability.

Ginzburg, V. L.↗
NASA NTRS1985

An experiment to measure the energy spectrum of cosmic ray antiprotons from 100 to 1000 MeV

Production models were developed and the confirmation of each one had significant astrophysical impact. These include radical modifications of propagation models, cosmic ray antiprotons injection from neighboring domains of antimatter, p production by evaporating primordial black holes, and cosmic ray p's as annihilation products of supersymmetry particles that might make up the dark dynamical mass of the Galaxy. It is that p's originating from supersymmetric parents might have distinct spectral features that would survive solar modulation; in one model, higgsino annihilation proceeds through the bb quark-antiquark channel, producing a spectral bump at approx. 0.3 GeV in the p spectrum.

Salamon, M. H.↗
NASA NTRS1994

Are cosmic rays effective for ionization of protoplanetary disks?

The principal uncertainty in studying the magnetic properties of protoplanetary disks concerns the ionization levels of the disk's gas. The low gas temperature precludes thermal ionization, leaving cosmic rays as the dominant source of ionization. It has been shown that the resulting electrical conductivity is just high enough for a MHD dynamo to produce contemporaneously a magnetic field in most of the extended parts of a turbulent protoplanetary disk. Here we argue that the effectiveness of cosmic rays to ionize the bulk of the gas is impaired by the influence of the generated magnetic field on the propagation of cosmic rays within a disk. Cosmic rays scatter on magnetic inhomogeneities, and, as a result, their penetration depth decreases to only a fraction of the disk half-thickness, resulting in a severe depletion of free charge from the midplane regions of a disk. That, in turn, undercuts the dynamo mechanism, so extended parts of the disk are free from a dynamically significant magnetic field. We also point out that any additional, even small, in situ source of ionization, such as radioactive Al-26, may again make a dynamo a viable regeneration process capable of producing a dynamically important magnetic field.

Dolginov, Arkady Z.↗
NASA NTRS1975

Neutron-rich isotopes of cosmic rays with Z between 9 and 16

Data are reported on the isotopic composition of cosmic rays with charges between 9 and 16 at a temperature of 450 MeV per amu. The data show the presence of a considerable neutron-rich component of Mg and Ne, the measured mean masses being 24.3 plus or minus 0.1 and 20.8 plus or minus 0.1, respectively. Coupled with a calculation of the evolution of cosmic-ray isotopic abundances during propagation, these masses indicate that there is probably some neutron-rich material in this charge range at the cosmic-ray source. To explain the Ne mass requires more neutron-rich Ne at the source than is observed in solar-system material. This result is discussed in light of recent theories of nucleosynthesis and cosmic-ray propagation.

Maehl, R. C.↗
NASA NTRS1972

Extragalactic cosmic rays.

A detailed analysis is given of the possibility that a large part of the primary cosmic-ray flux is of extragalactic origin. The problems encountered in theories of galactic cosmic rays are first critically discussed. The objections that have previously been raised to extragalactic theories, particularly on energetic grounds, are then examined. The general problem of the propagation of cosmic rays which are ejected from galactic nuclei or in galactic winds to fill clusters and superclusters is dealt with next. Attention is also given to the limits which are set on the presence of extragalactic cosmic rays by observations of high-energy electrons and background X-rays and gamma rays, or the heating of a hypothetical intergalactic gas. Observable effects of cosmic rays between galaxies are studied, and the possible sources of the local cosmic-ray protons in the extragalactic model are considered.

Brecher, K.↗
NASA NTRS1990

Relative abundances of secondary and primary cosmic rays at high energies

New results on the energy spectra of the cosmic-ray nuclei boron, carbon, nitrogen, and oxygen up to energies around 1 TeV per amu are described. The measurements were performed on the Spacelab 2 mission of the Space Shuttle in 1985. Carbon and oxygen are essentially primary cosmic rays, while boron is purely secondary, and nitrogen has secondary as well as primary contributions. Therefore, the relative abundances of these nuclei provide sensitive information on the propagation of cosmic rays through the Galaxy. It is found that the flux of the secondary cosmic rays continues to decrease relative to that of the primaries over the energy range covered with this observation, and that the mean escape length near 1 TeV per amu is about 1 g/sq cm.

Swordy, Simon P.↗
NASA NTRS1985

Propagation and nucleosynthesis of ultraheavy cosmic rays

The observed fluxes of cosmic ray (C.R.) ultraheavy elements depend on their charge and mass spectrum at the sources and on the propagation effects, on the distribution of path lengths traversed by the particles on their way from the sources to the observation point. The effect of different path length distributions (p.l.d.) on the infered source abunances is analyzed. It seems that it is rather difficult to fit a reasonable p.l.d. so that the obtained source spectrum coincides with the Solar System (SS) abundances in more detail. It suggests that the nucleosynthesis conditions for c.r. nuclei may differ from that for SS matter. The nucleosynthesis of ultraheavy elements fitting its parameters to get the c.r. source abundances is calculated. It is shown that it is possible to get a very good agreement between the predicted and the observed source abundance.

Giler, M.↗
NASA NTRS1982

Data processing for a cosmic ray experiment onboard the solar probes Helios 1 and 2: Experiment 6

The data processing system for the Helios experiment 6, measuring energetic charged particles of solar, planetary and galactic origin in the inner solar system, is described. The aim of this experiment is to extend knowledge on origin and propagation of cosmic rays. The different programs for data reduction, analysis, presentation, and scientific evaluation are described as well as hardware and software of the data processing equipment. A chronological presentation of the data processing operation is given. Procedures and methods for data analysis which were developed can be used with minor modifications for analysis of other space research experiments.

Mueller-Mellin, R.↗
NASA NTRS1992

Post-launch analysis of data from the High Energy Astrophysical Observatory Heavy Nuclei Experiment (HEAO-C3)

The Final Report on the continuing analysis of data from the Heavy Nuclei Experiment (HNE), flown on the HEAO-3 mission, is presented. The HNE was designed to measure the elemental abundances of relativistic cosmic ray nuclei covering the charge range 17 is less than or equal to Z is less than or equal to 130. The result of these measurements is significant to the study of nucleosynthesis, the origin, acceleration, and propagation of cosmic ray nuclei, and the properties of the interstellar medium.

Stone, E. C.↗
NASA NTRS1974

Cosmic ray scintillations. II - General theory of interplanetary scintillations

The motion of charged particles in a stochastic magnetic field with nonzero mean is considered via a generalized quasi-linear expansion of Liouville's equation. The general result is an equation relating cosmic ray scintillations to magnetic fluctuations and to cosmic ray gradients. The resonant interaction between particles and the random magnetic field is considered in detail, and the effect of nonlinear terms in the equations is considered. The nonlinear terms are important in damping out initial conditions and in determining conditions near cyclotron resonances. The application of the theory to the propagation of cosmic rays during quiet times in interplanetary space is considered. It is concluded that cosmic ray scintillations in interplanetary space may provide useful information about interplanetary particles and fields and also about nonlinear plasma interactions.

Owens, A. J.↗
NASA NTRS1978

Cosmic ray electrons - A discussion of recent observations

A recent measurement of the spectrum of cosmic-ray electrons has provided statistically significant evidence for a spectral shape that is much steeper than that of protons. The electron spectrum does not fit well to a single power law, and the abundance of electrons relative to that of protons decreases from approximately 1% at 10 GeV to approximately 0.1% at 300 GeV. This result is consistent with a galactic escape lifetime for electrons exceeding 10 million years. The data are discussed in light of current models for the propagation of cosmic rays in the Galaxy, and conclusions are drawn concerning the consistency of various models with the observations.

Mueller, D.↗
NASA NTRS1983

Research in space physics at the University of Iowa, 1982

The energetic particles and the electric, magnetic, and electromagnetic fields associated with the Earth, the Sun, the Moon, the planets, comets, and the interplanetary medium are examined. Matters under current investigation are following: energetic particles trapped in the Earth's magnetic field, origin and propagation of very low frequency radio waves and electrostatic, the magnetospheres of Jupiter, Saturn and prospectively Uranus and Neptune, diffusion of energetic particles in Saturn's magnetosphere, radio emissions from Jupiter and Saturn, solar modulation and the heliocentric radial dependence of the intensity of galactic cosmic rays, interplanetary propagation and acceleration of energetic particles, the theory of wave phenomena in turbulent plasmas, and basic wave-particle-chemical processes in the ionospheric plasma.

Vanallen, J. A.↗
NASA NTRS1990

Spallation processes and nuclear interaction products of cosmic rays

Most cosmic-ray nuclei heavier than helium have suffered nuclear collisions in the interstellar gas, with transformation of nuclear composition. The isotopic and elemental composition at the sources has to be inferred from the observed composition near the Earth. The source composition permits tests of current ideas on sites of origin, nucleosynthesis in stars, evolution of stars, the mixing and composition of the interstellar medium and injection processes prior to acceleration. The effects of nuclear spallation, production of radioactive nuclides and the time dependence of their decay provide valuable information on the acceleration and propagation of cosmic rays, their nuclear transformations, and their confinement time in the Galaxy. The formation of spallation products that only decay by electron capture and are relatively long-lived permits an investigation of the nature and density fluctuations (like clouds) of the interstellar medium. Since nuclear collisions yield positrons, antiprotons, gamma rays and neutrinos, we shall discuss these topics briefly.

Non-NASA Center↗