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At least 361 records · Page 20
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NASA NTRS1981

A cosmic-ray-mediated shock in the solar system

It is pointed out that the flare-induced blast wave of Aug. 4, 1972, the most violent disturbance in the solar wind on record, produced cosmic rays with an efficiency of about 50%. Such a high efficiency is predicted by the self-regulating production model of cosmic-ray origin in shocks. Most interplanetary shocks, according to simple theoretical analysis, are not strong enough to produce cosmic rays efficiently. However, if shock strength is the key parameter governing efficiency, as present interplanetary data suggest, then shocks from supernova blasts, quasar outbursts, and other violent astrophysical phenomena should be extremely efficient sources of cosmic rays.

Eichler, D.↗
NASA NTRS1980

Solar modulation of galactic cosmic rays

The current theory for the solar modulation of galactic cosmic rays is reviewed briefly. The four basic mechanisms which are important for modulation-diffusion, effects associated with the large-scale magnetic field, convection, and energy change - are discussed in simple terms. The equation which describes cosmic-ray behavior in the heliosphere is presented and some sample solutions are considered. It is pointed out that, although the basic mechanisms which describe the cosmic-ray behavior are understood, the actual cause of the variation in the cosmic-ray flux over the solar cycle, or over longer intervals, is beyond current comprehension.

Fisk, L. A.↗
NASA NTRS1981

Confinement of cosmic rays in molecular clouds

The consequences of cosmic ray production by a supernova in a molecular cloud are discussed. Self-trapping problems for a higher flux of cosmic rays in a molecular cloud are focused on. The column density of molecular clouds is probably too high to explain the majority of galactic cosmic ray sources, even allowing for fortuitous asymmetry in the placement of the supernova in the cloud, however, measurements of antiproton flux suggest that some cosmic ray sources do have a high column density. The large predicted gamma-ray luminosity of such a cloud invites comparison with COS-B sources.

Zweibel, E. G.↗
NASA NTRS1981

A measurement of the cosmic-ray antiproton flux and a search for antihelium

Balloon-borne instrument measurements are presented of the cosmic-ray antiproton flux between 130 and 320 MeV, as well as the results of a search for antihelium between 130 and 370 MeV per nuclear. The antiprotons are found to have a spectral shape similar to the protons, down to about 100 MeV. Calculations of the expected flux of these particles under the assumption that they were created by collisions of high-energy cosmic rays with the interstellar gas, using the standard leaky box model for propagation in the Galaxy, predict a flux two orders of magnitude smaller than that observed. The discrepancy between calculation and experiment may be evidence that cosmic-ray protons have passed through more than 5.0 g/sq cm of material during their lifetime. The search for cosmic-ray antihelium sets a 95% confidence level upper limit on the antihelium/helium ratio of 0.000022.

Buffington, A.↗
NASA NTRS1980

Silver isotopic anomalies in iron meteorites - Cosmic-ray production and other possible sources

Sources of excess Ag-107 observed in iron meteorites are investigated with emphasis on reactions of cosmic-ray particles with palladium. Cross sections for the production of the silver isotopes from palladium by energetic cosmic-ray particles are estimated to calculate spallogenic production rates relative to that of Mn-53 from iron. The upper limits for the production rates of Ag-107 and Ag-109 by energetic galactic cosmic-ray particles are 690 and 270 atoms/min/kg(Pd), respectively, and the maximum rate for making excess Ag-107 by spallation reactions is 400 atoms/min/kg(Pd). The excess Ag-107 cannot be produced by a long exposure to cosmic-ray particles, and because it is harder to make the amount of Pd-107 observed in the iron meteorites by an early intense proton irradiation than it is to make the Al-26 observed in other meteorites, it is concluded that the excess Ag-107 is due to the decay of nucleosynthetic Pd-107 in the iron meteorites.

Reedy, R. C.↗
NASA NTRS1981

The charge and isotopic composition of Z equals 7-16 cosmic ray nuclei at their source

Using the combined data from our 1976 and 1977 balloon flights, the charge and isotopic composition of Z equals 7-16 cosmic ray nuclei have been determined. A low abundance of both N and Ne in the cosmic ray source relative to solar cosmic rays is observed. However, the cosmic ray source ratio, Ne-22/Ne is 2.75 plus or minus 0.42 times the solar ratio. A possible enhancement of the Mg-26/Mg ratio, which is 1.29 plus or minus 0.14 times the solar ratio is also observed.

Webber, W. R.↗
NASA NTRS1982

Charge abundance of cosmic rays at their source

The relative charge abundance of galactic cosmic-ray nuclei is measured between 600 and 1000 MeV per nucleon over a range of Z from 2 to 28. The abundances observed at earth are extrapolated to the cosmic-ray source, yielding accurate source abundances for 15 elements. These abundances, together with recently measured isotopic abundance ratios, are compared with the average abundances observed in another sample of accelerated material - solar cosmic rays. Appreciable differences are found in the composition for the elements He, C, N, and Ne. The galactic and solar cosmic-ray abundances are also compared with a variety of compilations of unaccelerated matter.

Webber, W. R.↗
NASA NTRS1983

Cosmic-ray record in solar system matter

The interaction of galactic cosmic rays (GCR) and solar cosmic rays (SCR) with bodies in the solar system is discussed, and what the record of that interaction reveals about the history of the solar system is considered. The influence of the energy, charge, and mass of the particles on the interaction is addressed, showing long-term average fluxes of solar protons, predicted production rates for heavy-nuclei tracks and various radionuclides as a function of depth in lunar rock, and integral fluxes of protons emitted by solar flares. The variation of the earth's magnetic field, the gardening of the lunar surface, and the source of meteorites and cosmic dust are studied using the cosmic ray record. The time variation of GCR, SCR, and VH and VVH nuclei is discussed for both the short and the long term.

Reedy, R. C.↗
NASA NTRS1983

Galactic cosmic rays and N2 dissociation on Titan

The electromagnetic and particle cascade resulting from the absorption of galactic cosmic rays in the atmosphere of Titan is shown to be an important mechanism for driving the photochemistry at pressures of 1 to 50 mbar in the atmosphere. In particular, the cosmic ray cascade dissociates N2, a process necessary for the synthesis of nitrogen organics such as HCN. The important interactions of the cosmic ray cascade with the atmosphere are discussed. The N2 excitation and dissociation rates and the ionization rates of the principal atmospheric consituents are computed for a Titan model atmosphere that is consistent with Voyager 1 observations. It is suggested that HCN may be formed efficiently in the lower atmosphere through the photodissociation of methylamine. It is also argued that models of nitrogen and hydrocarbon photochemistry in the lower atmosphere of Titan should include the absorption of galactic cosmic rays as an important energy source.

Capone, L. A.↗
NASA NTRS1982

Cosmic ray antimatter and baryon symmetric cosmology

The relative merits and difficulties of the primary and secondary origin hypotheses for the observed cosmic-ray antiprotons, including the new low-energy measurement of Buffington, et al. We conclude that the cosmic-ray antiproton data may be evidence for antimatter galaxies and baryon symmetric cosmology. The present bar P data are consistent with a primary extragalactic component having /p=/equiv 1+/- 3.2/0.7x10 = to the -4 independent of energy. We propose that the primary extragalactic cosmic ray antiprotons are most likely from active galaxies and that expected disintegration of bar alpha/alpha ban alpha/alpha. We further predict a value for ban alpha/alpha =/equiv 10 to the -5, within range of future cosmic ray detectors.

Stecker, F. W.↗
NASA NTRS1984

Elemental advances of ultraheavy cosmic rays

The elemental composition of the cosmic-ray source is different from that which has been generally taken as the composition of the solar system. No general enrichment of products of either r-process or s-process nucleosynthesis accounts for the differences over the entire range of ultraheavy (Z 30) elements; specific determination of nucleosynthetic contributions to the differences depends upon an understanding of the nature of any acceleration fractionation. Comparison between the cosmic-ray source abundances and the abundances of C1 and C2 chondritic meteorites suggests that differences between the cosmic-ray source and the standard (C1) solar system may not be due to acceleration fractionation of the cosmic rays, but rather to a fractionation of the C1 abundances with respect to the interstellar abundances.

Source record↗
NASA NTRS1983

Large scale solar modulation of 500 MeV/N galactic cosmic rays seen from 1-30 AU

Using measurements of cosmic rays obtained by Cerenkov counters on Pioneer 10 and Pioneer 11 and neutron monitor data from Earth, the spatial and temperal development of cosmic ray modulation during the last solar maximum were observed. The large-scale features of modulation and recovery are similar at these three sites and thus appear rotationally symmetric near the ecliptic plane. Outward propagating features characterize the radial dependence. The decline of the old cosmic ray cycle is marked by steplike decreases that propagate outward at nearly the solar wind velocity. During the start of the new cosmic ray cycle, recovery occurs first in the inner heliosphere and, after a lag comparable with that of the declining phase, appears later farther out. However, the direction of diffusive propagation is still inward, because the gradient remains positive. Forbush decreases are common at all three sites, and are evidently of great importance in understanding modulation. The largest decrease occurred during a short series of events in the summer of 1982 and had half the amplitude of the eleven year cycle.

Fillius, W.↗
NASA NTRS1983

Solar modulation of galactic cosmic rays. V - Time-dependent modulation

A numerical technique is introduced for the solution of the time-dependent equation for the solar modulation of galactic cosmic rays, in which transport in heliographic latitude is ignored. We illustrate this method with a model for the solar cycle variation in cosmic ray intensity. The variation is assumed to result from changes in the number of enhanced cosmic ray scattering regions, which are produced by flare-generated shock waves in the solar wind. The model can account for the observed solar cycle variation in intensity at different energies as well as the observed spatial gradients. This model also provides a natural explanation for the cosmic ray hysteresis effect.

Perko, J. S.↗
NASA NTRS1984

Integral radial cosmic ray gradients in the solar system from 1972 to 1982

The cosmic-ray telescope data on IMP 8, Voyagers 1 and 2, and Pioneer 10 have been used to determine the integral radial cosmic-ray intensity gradients for energies greater than 60 MeV per nucleon. When the 26 day average counting rates are time-shifted for the effects of the outward propagation speed of the solar modulation, the average integral radial gradients (Gr) are 3.0 + or - 0.35 (percent/AU) from 1975 to 1982. Gr is independent to the first order of the cosmic-ray intensity and radial heliocentric distance out to about 30 AU. After the large transient variations in the cosmic-ray intensity in mid-1982, the integral gradients returned to their original values.

Lockwood, J. A.↗
NASA NTRS1984

Radial gradient of cosmic ray intensity from a comparative study of data from Voyager 1 and 2 and IMP 8

The IMP 8 satellite and Voyager 1 and 2 space probes obtained cosmic ray measurements during the late 1977 to mid-1982 period. Comparisons of 27-day averages of the data show that a positive radial intensity gradient existed on the average during this period, and that the cosmic ray intensity decrease toward solar maximum in 1980-1981 proceeds in a stepwise fashion. The cosmic ray minimum reached in late 1980/early 1981 appears almost simultaneously at 1 AU and at 10 AU, with and without propagation time delay effects, between IMP 8 and the Voyager spacecraft. These data are generally consistent with a heliolatitudinal gradient of 0 + or - 1 percent/deg. Attention is given to the implications of these results in the overall context of cosmic ray modulation theory.

Venkatesan, D.↗
NASA NTRS1985

Long term variability of the cosmic ray intensity

In a previous paper Bhat, et al., assess the evidence for the continuing acceleration of cosmic rays in the Loop I supernova remnant. The enhanced gamma-ray emission is found consistent with the Blandford and Cowie model for particle acceleration at the remnant shock wave. The contributions of other supernovae remnants to the galactic cosmic ray energy density are now considered, paying anisotropy of cosmic rays accelerated by local supernovae ( 100 pc). The results are compared with geophysical data on the fluctuations in the cosmic ray intensity over the previous one billion years.

Bhat, C. L.↗
NASA NTRS1985

A model for the proton spectrum and cosmic ray anisotropy

The problem of the origin of the cosmic rays is still uncertain. As a theory, it should explain the support of particles and energy, the mechanism of acceleration and propagation as well as some important features obtained directly from cosmic ray experiments, such as the power spectrum and the knee. There are two kinds of models for interpreting the knee of the cosmic ray spectrum. One is the leaky box model. Another model suggests that the cut-off rigidity of the main sources causes the knee. The present paper studies the spectrum and the anisotropy of cosmic rays in an isotropic diffuse model with explosive discrete sources in an infinite galaxy.

Xu, C.↗
NASA NTRS1985

Difference between even and odd 11-year cycles in cosmic ray intensity

Cosmic ray data for the period 1946-1984 are used to determine the run of the cosmic ray intensity over three complete solar cycles. The analysis shows a tendency towards a regular alternation of cosmic ray intensity cycles with double and single maxima. Whereas a saddle-like shape is characteristic of even cycles, odd cycles are characterized by a peak-like shape. The importance of this behavior is discussed in terms of different processes influencing cosmic ray transport in the heliosphere.

Otaola, J. A.↗