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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Hydrostatic equilibrium of gas, extent of cosmic ray confinement, and radio emission in the Galaxy

A detailed study of the hydrostatic equilibrium of the gas-field system perpendicular to the galactic plane in the neighborhood of the sun, assuming that the magnetic field is parallel to the plane, has been carried out. It is found that the distribution of pressure due to cosmic rays and the magnetic field is different from that due to the gas. The observed radio spectrum in the direction of the galactic pole can be understood if one includes in the hydrostatic equilibrium the distribution of gas in the halo. The results of this analysis show that in the galactic plane, the cosmic-ray density is approximately 2 to 3 eV/cu cm with a magnetic-field strength of about 5 to 6 microgauss. It is inferred that cosmic rays are confined to a more extended volume in the Galaxy (with an equivalent thickness of at least 2 kpc in the solar neighborhood) than the gas disk, and the magnetic-field strength slowly decreases to a value of 1 microgauss only beyond about 5 kpc from the plane. Further, there is no evidence for a quasi-spherical radio halo, although the radio emission extends beyond the gas disk with scale height of at least 1 kpc. A lower limit of about 6 million years for the confinement of cosmic rays in the Galaxy has been set.

Badhwar, G. D.↗
NASA NTRS1977

Primary cosmic rays on the lunar surface

Results are reported for determination of the galactic cosmic ray flux during various time intervals in the 1965-1972 period, on the basis of data from the instruments of a spacecraft that made a soft landing on the lunar surface, and from the radioactivity of samples returned by the spacecraft. During minimum solar activity (the second half of 1965 and the beginning of 1966) I sub 0 (E greater than or equal to 30 percent MeV/nucleon) was determined to be 0.43 (plus or minus 10 percent). These values, within the error limits of the determinations, agree with the corresponding values of galactic cosmic ray intensities determined by stratospheric measurements. The mean flux of galactic cosmic rays over the past million years is equal to I (E greater or equal to 100 MeV/nucleon) + 0.28 (plus or minus 20 percent). This value agrees with the mean flux of modulated cosmic rays during the period of the nineteenth solar cycle. The mean flux of solar protons between 1965 and 1972 was 2.46.

Vernov, S. N.↗
NASA NTRS1977

Apollo-Soyuz pamphlet no. 6: Cosmic ray dosage

The radiation hazard inside spacecraft is discussed with emphasis on its effects on the crew, biological specimens, and spacecraft instruments. The problem of light flash sensations in the eyes of astronauts is addressed and experiment MA-106 is described. In this experiment, light flashes seen by blindfolded astronauts were counted and high energy cosmic ray intensity in the command module cabin were measured. The damage caused by cosmic ray hits on small living organisms was investigated in the Biostack 3 experiment (MA-107). Individual cosmic rays were tracked through layers of bacterial spores, small seeds, and eggs interleaved with layers of AgCl-crystal wafers, special plastic, and special photographic film that registered each cosmic ray particle passed.

Page, L. W.↗
NASA NTRS1978

Diffuse fluxes of cosmic high energy neutrinos

Production spectra of high-energy neutrinos from galactic cosmic ray interactions with interstellar gas and extragalactic ultrahigh energy cosmic-ray interactions with microwave black-body photons are presented and discussed. These production processes involve the decay of charged pions and are thus related to the production of cosmic gamma-rays from the decay of neutral pions. Estimates of the neutrino fluxes from various diffuse cosmic sources are then made and the reasons fro significant differences with previous estimates are discussed. Predicted event rates for a DUMAND type detection system are significantly lower than early estimates indicated.

Stecker, F. W.↗
NASA NTRS1977

Cosmic ray investigation for the Voyager missions: Energetic particle studies in the outer heliosphere - and beyond

The Voyager mission cosmic ray detector system, consisting entirely of solid-state charged-particle detectors, is designed to measure the energy spectrum of electrons in the range 3 to 110 MeV and the energy spectra and elemental composition of cosmic ray nuclei from hydrogen through iron in the range 1 to 500 MeV/nuc; for isotopes of hydrogen through sulfur the range is approximately 2 to 75 MeV/nuc. The cosmic ray investigation deals with the energy content, origin and acceleration process, and dynamics of cosmic rays in the galaxy, with particular attention given to low-energy phenomena in interstellar space and the outer solar system. The precise measurement of three-dimensional stream patterns of nuclei from H to Fe, as well as electrons over a wide energy range, is the data acquisition program emphasized.

Stone, E. C.↗
NASA NTRS1978

The cosmic-ray isotopes

Aspects and implications of isotopic abundance measurements are discussed, taking into account the elemental abundance distribution of the cosmic radiation and the solar system abundances normalized to C. An interesting outcome of observations on cosmic ray isotopes is the determination of the span of time that elapses between nucleosynthesis and acceleration of the particles. This has an immediate bearing on the question whether explosive nucleosynthesis and particle acceleration occur simultaneously, or whether these two phases in the production of cosmic rays are separate. The absence of Co-57, Ti-44, and Ni-59 with K-capture decay rates of approximately 1 yr, 50 yr, and 100,000 yr respectively in the cosmic ray flux would indicate that the time between nucleosynthesis and acceleration would be greater than 1, 50, or 100,000 yr, respectively.

Meyer, P.↗
NASA NTRS1978

The mean mass of the abundant cosmic-ray nuclei from boron to silicon at 1.2 GeV per atomic mass unit

Results are presented for an investigation of cosmic-ray isotopic composition in which a balloon-borne instrument was used to perform an isotopic analysis of the abundant elements from B through Si in the energy range from 1.0 to 1.6 GeV/amu. The technique employed, which depends on the effect of earth's magnetic field on incoming cosmic rays, and reduction of the observational data are described in detail. Mean masses of the elements B, C, N, O, Ne, Mg, and Si are extracted from normalized Cerenkov spectra and evaluated in terms of the 'leaky box' model of galactic propagation and confinement. The implications of the results for cosmic-ray sources are shown to be consistent with the nucleosynthesis of certain isotopes in the cosmic rays in explosive carbon burning under the conditions of peak temperature, density, and neutronization expected in an explosion of a massive highly evolved star. The possibility of alternate interpretations is noted.

Dwyer, R.↗
NASA NTRS1979

Diffuse fluxes of cosmic high-energy neutrinos

Production spectra of high-energy neutrinos from galactic cosmic-ray interactions with interstellar gas and extragalactic ultrahigh-energy cosmic-ray interactions with microwave blackbody photons are presented and discussed. These production processes involve the decay of charged pions and are thus related to the production of cosmic gamma rays from the decay of neutral pions. Estimates of the neutrino fluxes from various diffuse cosmic sources are then made, and the reasons for significant differences with previous estimates are discussed. Small predicted event rates for a DUMAND (deep underwater muon and neutrino detector) type detection system, combined with a possible significant flux of prompt neutrinos from the atmosphere above 50 TeV, may make the study of diffuse extraterrestrial neutrinos more difficult than previously thought.

Stecker, F. W.↗
NASA NTRS1978

The spectrum of cosmic electrons with energies between 6 and 100 GeV

Final results are reported concerning the spectrum of 6-100-GeV cosmic-ray electrons observed during a balloon exposure of approximately 3500 sq m-s-sr at an average depth of 4.8 g/sq cm. The spectral intensity of primary cosmic-ray electrons is found to have a power-law dependence on electron energy with an index of 3.4 + or - 0.1; the ground-level spectrum of secondary cosmic-ray electrons is also shown to be a power-law spectrum, but with an index of 2.9 + or - 0.1. The observed spectrum, which is significantly steeper than the nuclear spectrum, is interpreted as a fully steepened one reflecting an equilibrium between injection and energy loss. It is suggested that the confinement volume for cosmic rays extends beyond the galactic disk and includes a halo of reduced gas density where the Compton-synchrotron mechanism operates but the probability of nuclear interactions is small.

Meegan, C. A.↗
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

The isotopes of neon in the galactic cosmic rays

The paper examines the results obtained by the University of Chicago instrument on board the IMP 7 satellite used to measure the abundances of Ne-20 and Ne-22 in the galactic cosmic rays during 1973-1977, over the general energy range of 60-230 MeV per nucleon. It is reported that the instrument shows a mass resolution of 0.7 amu(sigma) which was confirmed by calibrating a backup instrument at the LBL Bevalac with separated beams of neon isotopes. Through the use of standard solar modulation and cosmic-ray propagation models, the cosmic-ray source ratio inferred is Ne-22/Ne-20 = 0.38 = or -0.07 which is significantly greater than the present solar system ratio. It is concluded that propagation effects or cross-section uncertainties cannot account for such a large abundance of Ne-22, and thus this measurement provides evidence that the cosmic rays come from a source region where the Ne-22 abundance is substantially greater than in solar system material.

Garcia-Munoz, M.↗
NASA NTRS1980

The isotopic composition of galactic cosmic-ray iron nuclei

High-resolution observations made in interplanetary space of 83-284 MeV per nucleon galactic cosmic-ray iron isotopes are reported and it is directly established that Fe-56 is the dominant cosmic-ray Fe isotope. The following percentage abundances for Fe at the cosmic-ray source are found: Fe-54 = 9(+8, -5)%, Fe-55 is less than or equal to 7%, Fe-56 = 91(+5, -11)%, Fe-57 is less than or equal to 8%, and Fe-58 is less than or equal to 6%. When compared to calculated nucleosynthesis yields and other observations, these results place significant constraints on the neutron excess of the environment where cosmic-ray Fe originates.

Mewaldt, R. A.↗
NASA NTRS1980

The isotopic composition of neon and magnesium in the low energy cosmic rays

The ratios Ne-22/Ne-20 and Mg-26/Mg-24 were measured in galactic cosmic rays by the IMP-7 satellite in the 60 to 230 MeV/nucleon range. The neon cosmic ray source ratio Ne-22/Ne-20 is about 0.38, which is much larger than the current solar system relationship; the Mg data agrees with the solar system isotopic ratio of 0.14 at the cosmic ray source. The Ne and Mg source ratios are explained by supernova models, and become a new constraint which should be satisfied by any model of cosmic ray origin.

Garcia-Munoz, M.↗
NASA NTRS1980

Cosmic ray synthesis of organic molecules in Titan's atmosphere

The possible synthesis of organic molecules by the absorption of galactic cosmic rays in an N2-CH4-H2 Titan model atmosphere has been studied. The cosmic-ray-induced ionization results in peak electron densities of 2000/cu cm, with NH(+), C3H9(+), and C4H9(+) being among the important positive ions. Details of the ion and neutral chemistry relevant to the production of organic molecules are discussed. The potential importance of N(2D) reactions with CH4 and H2 is also demonstrated. Although the integrated production rate of organic matter due to the absorption of the cosmic ray cascade is much less than that by solar ultraviolet radiation, the production of nitrogen-bearing organic molecules by cosmic rays may be greater.

Capone, L. A.↗
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.↗