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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Cosmic dust in the mesosphere.

Study of the nature of cosmic dust particles collected by two recoverable rockets launched at Fort Churchill, Canada, in the spring of 1970, before the noctilucent cloud season in order to avoid the interference of uplifted atmospheric aerosols during the determination of the concentration of background cosmic dust. The study was designed to verify the results of a previous study for which dust particles were collected in the summer of 1968 by a rocket launched through a noctilucent cloud at the same location. The findings support the hypothesis that occasional high concentrations of dust in the mesosphere are due to uplifted aerosols which could be of a terrestrial or cosmic origin.

Farlow, N. H.↗
NASA NTRS1972

Modulation of low-energy galactic cosmic rays over solar maximum /cycle 20/.

Low-energy (about 60 MeV/nucleon) galactic cosmic rays observed during the recent period of solar maximum are reviewed. For this particular cycle, a significant time lag between intensity changes in the low-energy and high-energy components has been observed. Several possible explanations of this 'hysteresis effect' are discussed. The cosmic-ray intensity gradients provided by Pioneer 10 are soon to be available and are expected to provide a more definite clue to this process of cosmic-ray modulation.

Van Hollebeke, M. A. I.↗
NASA NTRS1972

Modulation of cosmic-ray electrons.

An analytical approach is presented that provides qualitative insight into both observations and numerical calculations of cosmic-ray electron modulation and embodies, as a natural feature of a specific model, two cosmic-ray components whose temporal variations are uncorrelated. In the light of this approach, it is shown that the origin and time variations of the steep spectrum of electrons observed below 20 MeV may be explained by a simple method in which the spectrum of interplanetary cosmic rays is decomposed at low energies into two independently varying components.

Earl, J. A.↗
NASA NTRS1974

The distribution of cosmic rays in the galaxy and their dynamics as deduced from recent gamma-ray observations

Recent data from SAS-2 on the galactic gamma ray line flux as a function of longitude reveal a broad maximum in the gamma ray intensity in the region absolute value of l approximately smaller than 30 deg. These data imply that the low energy galactic cosmic ray flux varies with galactocentric distance and is about an order of magnitude higher than the local value in a toroidal region between 4 and 5 kpc from the galactic center. This enhancement can be plausibly accounted for by first order Fermi acceleration, compression and trapping of cosmic rays consistent with present ideas of galactic dynamics and galactic structure theory. Calculations indicate that cosmic rays in the 4 to 5 kpc region are trapped and accelerated over a mean time of the order of a few million years or about 2 to 4 times the assumed trapping time in the solar region of the galaxy.

Puget, J. L.↗
NASA NTRS1974

Cosmic ray telescope for OGO 2 and 4 spacecraft

The construction and subsequent flight are described of a cosmic ray telescope aboard the OGO-2 and 4 Spacecraft. This instrument was a combination Cerekov-scintillation counter telescope designed to measure the cosmic ray energy spectrum from 1-15 GV and charge composition from Z=1-8. OGO-2 was launched in October 1965; however, attitude control problems caused a rapid loss of control gas, so that after approximately 2 weeks it was no longer possible to point the spacecraft. This mission was officially declared a failure. The cosmic ray instrument appeared to work well during this time. OGO-4 was launched in July 1967, with a similar telescope aboard. It operated successfully approximately one year. The details of the experiment, its operation, and the results are given.

Webber, W. R.↗
NASA NTRS1973

Modulation of solar cosmic rays

Consideration is given to whether the modulation of low energy solar cosmic ray nuclei between the sun and earth can be so extreme that the fluxes observed at 1 AU imply (1) that the cosmic ray energy density in the solar atmosphere is comparable to the thermal energy density, and/or (2) that the cosmic ray intensity is sufficient in the solar atmosphere to produce detectable fluxes of secondary particles such as low energy positrons. It was found that such large modulation is compatible with observations, provided that the modulation occurrence is confined within a solar envelope lying within approximately 0.2 to 0.3 AU of the sun. There is, however, no compelling observational evidence to require that the modulation is this large.

Fisk, L. A.↗
NASA NTRS1974

Mirroring within the Fokker-Planck formulation of cosmic ray pitch angle scattering in homogeneous magnetic turbulence

The Fokker-Planck coefficient for pitch angle scattering, appropriate for cosmic rays in homogeneous, stationary, magnetic turbulence, is computed from first principles. No assumptions are made concerning any special statistical symmetries the random field may have. This result can be used to compute the parallel diffusion coefficient for high energy cosmic rays moving in strong turbulence, or low energy cosmic rays moving in weak turbulence. Becuase of the generality of the magnetic turbulence which is allowed in this calculation, special interplanetary magnetic field features such as discontinuities, or particular wave modes, can be included rigorously. The reduction of this results to previously available expressions for the pitch angle scattering coefficient in random field models with special symmetries is discussed. The general existance of a Dirac delta function in the pitch angle scattering coefficient is demonstrated. It is proved that this delta function is the Fokker-Planck prediction for pitch angle scattering due to mirroring in the magnetic field.

Goldstein, M. L.↗
NASA NTRS1974

Origin of cosmic rays

A model is presented in which cosmic electrons are produced by pulsars, and cosmic protons and alpha particles are accelerated by shock waves in supernova envelopes. It is argued that neither mechanism by itself can produce both the observed protons and electrons at energies above a few hundred MeV. But supernova accelerated electrons could constitute the majority of cosmic electrons with energy below about 10 MeV.

Cohen, J. M.↗
NASA NTRS1973

Extragalactic cosmic rays and the galactic magnetic field

The origin and behavior of cosmic rays in the Galaxy depend crucially upon whether the galactic magnetic field has a closed topology, as does the field of earth, or whether a major fraction of the lines of force connect into extragalactic space. This paper examines the structure of a galactic field that opens initially into intergalactic space and, with the inclusion of turbulent diffusion, finds no possibility for maintaining a significant magnetic connection with an extragalactic field. Unless some mechanism can be found, we are forced to the conclusion that the field is closed, that cosmic rays are of galactic origin, and that cosmic rays escape from the Galaxy only by pushing their way out.

Parker, E. N.↗
NASA NTRS1974

Evidence for primary interstellar cosmic-ray electrons

We have performed a comparative study of the absolute solar modulation of cosmic-ray positrons and electrons. We find that the interstellar electron spectrum, which is described by a power-law slope at higher energies, must flatten below about 100 MeV, that a significant fraction of interstellar cosmic-ray electrons must originate in primary sources, and that the rigidity dependence of the interplanetary cosmic-ray diffusion coefficient, R raised to the power of alpha, changes from alpha greater than zero at higher rigidities to alpha -1 below about 60 MV.

Cummings, A. C.↗
NASA NTRS1974

Cosmic ray charge composition /Z smaller than or equal to 28/

In the light of recent research results, the composition of low-, medium-, and high-energy cosmic ray charges is reviewed, and its energy dependence is examined. Cosmic ray antinuclei research is summarized, and it is shown that no positive identification of primary antimatter has so far been achieved. Special attention is given to the relative abundances of cosmic ray charges at the source, and the difficulties encountered in the extrapolation of experimental abundances back to the source are reviewed, along with some of the attempts made to circumvent these difficulties. Recent discussions and the present status of hypotheses on modification of the source composition by injection and acceleration processes are also reviewed.

Garcia-Munoz, M.↗
NASA NTRS1974

The anomalous abundance of cosmic-ray nitrogen and oxygen nuclei at low energies

Recent measurements using the Goddard-University of New Hampshire cosmic-ray telescope on the Pioneer 10 spacecraft have revealed an anomalous spectrum of nitrogen and oxygen nuclei relative to other nuclei such as He and C, in the energy range 3-30 MeV per nucleon. The intensity of nitrogen and oxygen nuclei is enhanced by a factor of up to 20 relative to their abundance in galactic or solar cosmic rays. It is argued that this is most likely a new extrasolar component of cosmic rays.

Mcdonald, F. B.↗
NASA NTRS1974

The unique cosmic-ray history of the Malakal chondrite

Cosmogenic radionuclides, including Na-22, Al-26, and Mn-54, were measured in a sample of the recently-fallen Malakal hypersthene chondrite. The high Al-26 activity, 79 plus or minus 2 dpm/kg, greatly exceeds the levels expected from elemental production rates, shielding considerations, or comparisons with other ordinary chondrites, and can only be explained by exposure to a uniquely high cosmic-ray flux. Calculations including noble gas, H-3, and Mn-53 data from other laboratories require a two-stage irradiation. Malakal's most probable history is: exposure in excess of 4 m.y. to an effective cosmic-ray flux approximately three times that experienced by other chondrites, an orbit change (very possibly caused by a collision), and a final period of about 2 m.y. during which it was exposed to a normal cosmic-ray flux.

Cressy, P. J., Jr.↗
NASA NTRS1974

The distribution of cosmic rays in the Galaxy and their dynamics as deduced from recent gamma-ray observations

Recent data from SAS-2 on the galactic gamma-ray line flux as a function of longitude reveal a broad maximum in the gamma-ray intensity in the longitude region less than or equal to 30 deg. These data, when unfolded, imply that the low-energy (1 to 10 GeV) galactic cosmic-ray flux varies with galactocentric distance and is about an order of magnitude higher than the local value in a toroidal region between 4 and 5 kpc from the galactic center. It is further shown that this enhancement can be plausibly accounted for by first-order Fermi acceleration, compression, and trapping of cosmic rays consistent with present ideas of galactic dynamics and galactic structure theory. Calculations indicate that cosmic rays in the 4- to 5-kpc region are trapped and accelerated over a mean time of the order of a few million years or about 2 to 4 times the assumed trapping time in the solar region of the Galaxy.

Puget, J. L.↗
NASA NTRS1975

On the origin of cosmic rays

Using Recent surveys of molecular clouds and gamma rays in the galaxy, it is possible to determine the distribution of 1 to 10 GeV cosmic-ray nucleons in the galaxy. This distribution appears to be identical to the supernova remnant distribution to within experimental error and provides strong support for the hypothesis that supernovae produce most of the observed cosmic rays. This distribution resembles that of OB associations of average age approximately 30 million years suggesting that cosmic rays are produced by population objects about 30 million years after their birth.

Stecker, F. W.↗
NASA NTRS1975

K-alpha X-rays from cosmic ray oxygen

Equilibrium charge fractions are calculated for subrelativistic cosmic ray oxygen ions in the interstellar medium. These are used to determine the expected flux of K-alpha rays arising from atomic processes for a number of different postulated interstellar oxygen spectra. Relating these results to the diffuse X-ray background measured at the appropriate energy level suggests an observable line feature. If the flux of low energy cosmic ray oxygen is sufficiently large, K-alpha X-ray line emission from these nuclei will comprise a significant fraction of the total diffuse flux at approximately 0.6 keV. A satellite borne detector with a resolution greater than 30 percent could observe this feature if the subrelativistic interstellar cosmic ray oxygen spectrum is as large as certain theoretical estimates expressed in the text.

Pravdo, S. H.↗
NASA NTRS1975

Photonuclear interactions of ultrahigh energy cosmic rays and their astrophysical consequences

Results of detailed Monte Carlo calculations of the interaction histories of ultrahigh energy cosmic-ray nuclei with intergalactic radiation fields are presented. Estimates of these fields and empirical determinations of photonuclear cross sections are used, including multinuclear disintegrations for nuclei up to 56Fe. Intergalactic and galactic energy loss rates and nucleon loss rates for nuclei up to 56Fe are also given. Astrophysical implications are discussed in terms of expected features in the cosmic-ray spectrum between quintillion and sextillion eV for the universal and supercluster origin hypotheses. The results of these calculations indicate that ultrahigh energy cosmic rays cannot be universal in origin regardless of whether they are protons or nuclei. Both the supercluster and galactic origin hypotheses, however, are possible regardless of nuclear composition.

Puget, J. L.↗
NASA NTRS1975

Significance of medium energy gamma ray astronomy in the study of cosmic rays

Medium energy (about 10 to 30 MeV) gamma ray astronomy provides information on the product of the galactic electron cosmic ray intensity and the galactic matter to which the electrons are dynamically coupled by the magnetic field. Because high energy (greater than 100 MeV) gamma ray astronomy provides analogous information for the nucleonic cosmic rays and the relevant matter, a comparison between high energy and medium energy gamma ray intensities provides a direct ratio of the cosmic ray electrons and nucleons throughout the galaxy. A calculation of gamma ray production by electron bremsstrahlung shows that: bremsstrahlung energy loss is probably not negligible over the lifetime of the electrons in the galaxy; and the approximate bremsstrahlung calculation often used previously overestimates the gamma ray intensity by about a factor of two. As a specific example, expected medium energy gamma ray intensities are calculated for the speral arm model.

Fichtel, C. E.↗