Cosmic-ray nuclei up to 10 10 eV/u in the galaxy

1975 ◽  
Vol 277 (1270) ◽  
pp. 319-348 ◽  
Keyword(s):  
Cosmic Rays ◽  
Solar System ◽  
Cross Sections ◽  
Cosmic Ray ◽  
Interstellar Space ◽  
Heavy Nuclei ◽  
Hydrogen Atoms ◽  
Interstellar Gas ◽  
The Galaxy ◽  
Ionization Cross Sections

O f the nuclear cosmic rays arriving in the vicinity of Earth from interstellar space, more than 90% have energies less than 1010 eV /u.f Some effects of their modulation (including deceleration) in the Solar System are briefly discussed. The origin of particles at energies < 107 eV/u is still obscure. They could be due to stellar explosions or to solar emissions, or perhaps to interaction of interstellar gas with the solar wind. Between 108 and 1010 eV/u, the composition appears constant to ca. 30% within the statistics of available data. Cosmic rays traverse a mean path length of 6 g/cm 2 in a medium assumed to contain nine hydrogen atoms for each helium atom. Spallation reactions occurring in this medium result in enhancement of many cosmic-ray elements that are more scarce in the general abundances by several orders of magnitude. Cosmic-ray dwell time in the Galaxy seems to be < 107 years. The source composition of cosmic rays has been derived for elements with atomic numbers 1 ≤ Z ≤ 26. A comparison with abundances in the Solar System implies that the latter is richer in hydrogen and helium by a factor of ca. 20, in N and O by ca. 5, and in C by a factor of ca.2. Possible interpretations invoke (a) nucleosynthesis of cosmic rays in certain sources, e.g. supernovae, or (b) models of selective injection that depend, e.g. on ionization potentials or ionization cross sections. Calculated isotopic abundances of arriving cosmic rays are compared with the observed values now becoming available, and found to be in general agreement. Recent progress in probing the composition and spectrum of ultra-heavy nuclei is outlined.

scholarly journals Composition and Galactic Confinement of Cosmic Rays

1971 ◽  
Vol 2 ◽  
pp. 740-756
Author(s):  
Maurice M. Shapiro
Keyword(s):  
Cosmic Rays ◽  
Cosmic Ray ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Interstellar Space ◽  
Heavy Nuclei ◽  
High Energy Astrophysics ◽  
Transit Times ◽  
The Galaxy ◽  
Path Lengths

The ‘Galactic’ cosmic rays impinging on the Earth come from afar over tortuous paths, traveling for millions of years. These particles are the only known samples of matter that reach us from regions of space beyond the solar system. Their chemical and isotopic composition and their energy spectra provide clues to the nature of cosmic-ray sources, the properties of interstellar space, and the dynamics of the Galaxy. Various processes in high-energy astrophysics could be illuminated by a more complete understanding of the arriving cosmic rays, including the electrons and gamma rays.En route, some of theprimordialcosmic-ray nuclei have been transformed by collision with interstellar matter, and the composition is substantially modified by these collisions. A dramatic consequence of the transformations is the presence in the arriving ‘beam’ of considerable fluxes of purely secondary elements (Li, Be, B), i.e., species that are, in all probability, essentially absent at the sources. We shall here discuss mainly the composition of the arriving ‘heavy’ nuclei -those heavier than helium - and what they teach us about thesourcecomposition, the galactic confinement of the particles, their path lengths, and their transit times.

scholarly journals Cosmic-ray evidence for a halo

1979 ◽  
Vol 84 ◽  
pp. 485-490
Author(s):  
V. L. Ginzburg
Keyword(s):  
Synchrotron Radiation ◽  
Energy Density ◽  
Cosmic Rays ◽  
Solar System ◽  
Thermal Energy ◽  
Cosmic Ray ◽  
Gas Composition ◽  
Electron Component ◽  
Interstellar Gas ◽  
The Galaxy

Cosmic rays were discovered in 1912, but it was only about forty years later that they were found to play an important role in astronomy. Firstly, cosmic rays (including the electron component) are an important source of astronomical information, namely the cosmic synchrotron radiation. Secondly, cosmic rays are essential as energetic and dynamical factors in the galaxy and also as a source of heating and transformation of the interstellar gas composition. Suffice it to remember, for example, that near the solar system the cosmic ray energy density is about the same as the thermal energy of the interstellar gas, and the cosmic ray pressure is likewise about the same as the interstellar gas pressure. Thus, there is every reason to believe that galaxies do not consist of stars and gas only, but of cosmic rays as well.

scholarly journals The composition of galactic cosmic rays

1968 ◽  
Vol 46 (10) ◽  
pp. S544-S547 ◽  
Author(s):  
D. V. Reames ◽  
C. E. Fichtel
Keyword(s):  
Cosmic Rays ◽  
Cross Sections ◽  
Length Distribution ◽  
Cosmic Ray ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Interstellar Space ◽  
Fermi Acceleration ◽  
Fixed Amount ◽  
The Galaxy

Recent measurements of low-energy galactic cosmic rays obtained on sounding rockets and satellites exhibit a composition different from that obtained for intermediate and high-energy radiation obtained at balloon altitudes. In particular the ratio of light to medium nuclei is observed to be 0.2–0.3 in the 50–100 MeV/nucleon interval as compared with values near 0.5 in the 200–500 MeV/nucleon region. Lower values of the ratios C/O, N/O, F/O, and odd-Z/even-Z are also found. In the light of these new measurements and of new measurements on the fragmentation cross sections for cosmic-ray nuclei in interstellar space, an attempt has been made to calculate the composition expected if similar source spectra are assumed. It is found that neither passage through a fixed amount of material nor an equilibrium condition (exponential path-length distribution) is adequate to explain the observed features. The effects of including other mechanisms such as rigidity-dependent escape from the galaxy and Fermi acceleration in interstellar space are evaluated.

Galactic ?-ray Lines Resulting from Interactions Between Low Energy Cosmic Rays and the Interstellar Medium

1979 ◽  
Vol 32 (4) ◽  
pp. 383 ◽  
Author(s):  
Masato Yoshimori
Keyword(s):  
Cosmic Rays ◽  
Supernova Remnants ◽  
Galactic Plane ◽  
Crab Nebula ◽  
Cosmic Ray ◽  
Low Energy ◽  
Longitudinal Distribution ◽  
Galactic Centre ◽  
Interstellar Space ◽  
Interstellar Gas

Calculated spectral profiles and galactic distributions are presented for y-ray lines resulting from interactions between low energy cosmic rays and the interstellar gas and dust. Calculated local intensities are also presented for y-ray lines from discrete sources such as supernova remnants and dense interstellar gas clouds. The y-ray lines from excited dust nuclei (which have long mean lifetimes) are sharp, having widths of the order of a few keV; the lines from excited gas nuclei are relatively narrow, having widths of the order of 100 keV; and the lines from excited cosmic ray nuclei are broad, having widths of the order of 1 MeV. The longitudinal distribution of y-ray lines in the galactic plane shows a significant concentration toward the galactic centre, and a rapid falloff beyond I;. 50�. The most intense y-ray lines arise from positron annihilation (0�511 MeV) and the deexcitation of 12C* (4�439 MeV) and 160* (6�131 MeV). In the direction of the galactic centre, these lines have estimated intensities of the order of 10-5 photons cm-2s-1rad- 1, and so they may be resolved from the diffuse y-ray background there by observing with a high resolution Ge(Li) detector. In the direction of several strong discrete sources, the estimated fluxes are generally lower: ~10-6 photons cm-2s-1 for the Crab Nebula and the Vela pulsar, ~10-8 photons cm-2 s-1 for the interstellar dense cloud pOph, but ~10-5 photons cm-2 s-1 for the ring cloud around the galactic centre. The calculated intensities of various other y-ray lines are compared with available experimental data, and their detectability is considered. The implication of the galactic distribution of low energy cosmic rays for the gas density of the interstellar space through which the cosmic rays propagate is also discussed.

Considerations affecting the estimation of cosmic-ray age

1968 ◽  
Vol 46 (10) ◽  
pp. S561-S568 ◽  
Author(s):  
M. M. Shapiro ◽  
R. Silberberg
Keyword(s):  
Cosmic Rays ◽  
Cross Sections ◽  
Galactic Disk ◽  
Principal Component ◽  
Cosmic Ray ◽  
Light Nuclei ◽  
The Galaxy ◽  
Primary Cosmic Radiation ◽  
Order Of Magnitude ◽  
Medium Nuclei

Previous investigations by Daniel and Durgaprasad on the ratios Be/B and Be/Li in the primary cosmic radiation exploited the decay of 10Be produced in space to deduce a confinement time for cosmic rays in the galaxy. They concluded that this "age" T is at least 50 million years, and thence inferred that the cosmic-ray nuclei are trapped in a volume much larger than that of the galactic disk. These conclusions depended upon the values of fragmentation cross sections available in 1962 to Badhwar, Daniel, and Vijayalakshmi. Recent values of the Orsay group, however, reduce the calculated rates of 10Be and 9Be production by an order of magnitude; and an analysis based upon the latest cross sections leads to the following conclusions: (1) The possibility that cosmic rays are mainly confined to the disk of the galaxy and that T ≈ 106 years is not excluded. (2) The fragmentation parameter for medium nuclei [Formula: see text] into light nuclei [Formula: see text] is revised from 0.48 (the value of Badhwar et al.) to 0.34. (3) The mean path-length of 2.5 ± 0.5 g/cm2 of Badhwar et al. is revised to 4 ± 1 g/cm2. (4) 7Be now appears to be the principal component of cosmic-ray beryllium (about 70 or 80%, depending upon the cosmic-ray lifetime).

scholarly journals Propagation Studies Related to the Origin of Cosmic Rays

1981 ◽  
Vol 94 ◽  
pp. 93-106
Author(s):  
R. Cowsik
Keyword(s):  
Solar Wind ◽  
Cosmic Rays ◽  
Solar System ◽  
Relative Abundance ◽  
Galactic Plane ◽  
Cosmic Ray ◽  
Accurate Method ◽  
Galactic Cosmic Rays ◽  
High Energies ◽  
The Galaxy

Propagation of cosmic rays is discussed with the intent of deriving results relevent to the origin of cosmic rays. Starting from a brief description of the methods for demodulating the effects of the solar wind on the spectra of particles, we describe an accurate method for correcting for spallation effects on the cosmic-ray nuclei during their transport from the sources subsequent to their acceleration. We present the composition of cosmic rays at the sources and discuss its implications to their origin. We discuss briefly the effects of stochastic acceleration in the interstellar medium on the relative spectra of primaries and secondaries in cosmic rays and show that the observation of decreasing relative abundance of secondaries with increasing energy rules out such phenomena for galactic cosmic rays. The spectrum of cosmic-ray electrons is discussed in terms of contributions from a discrete set of sources situated at various distances from the solar system on the galactic plane. We show that unless there are at least 3.104 sources actively accelerating cosmis rays in the Galaxy the spectrum of electrons would have a premature cut-off at high energies. Finally we point out some important questions that need to be clearly resolved for making further progress in the field.

scholarly journals Optical and Radio Information

1968 ◽  
Vol 1 ◽  
pp. 206-209
Author(s):  
Hugh M. Johnson
Keyword(s):  
Cross Sections ◽  
Supernova Remnants ◽  
Galactic Plane ◽  
Optical Data ◽  
X Rays ◽  
Interstellar Gas ◽  
X Ray ◽  
The Galaxy ◽  
Ionization Cross Sections ◽  
Optical Astronomy

The six or eight optically identified X-ray sources comprise starlike objects and extended supernova remnants in the Galaxy, well as as a radio galaxy and a quasar. Both X-ray and radiofrequency radiation penetrate the entire galactic plane, but only two or three galactic radio sources have been identified with X-ray sources. This has led Hayakawa et al. to postulate that detectable X-ray sources are not farther than 1 kpc. However, other studies suggest that there is a cluster of a few intrinsically bright sources actually near the galactic nucleus and a scattering of weaker sources near the sun.The distances of X-ray sources can be estimated from extinction by interstellar gas or intergalactic gas on spectra above 10 Å, but the method ultimately depends on the radio and optical data of the gas. Conversely, interstellar densities of certain elements with large photo-ionization cross-sections may be determined from the absorption of X-rays, after calibration of source distances by the methods of optical astronomy.

ISOTOPIC COMPOSITION OF COSMIC RAYS: RESULTS FROM THE COSMIC RAY ISOTOPE SPECTROMETER ON THE ACE SPACECRAFT

2005 ◽  
Vol 20 (29) ◽  
pp. 6633-6633
Author(s):  
M. H. ISRAEL
Keyword(s):  
Cosmic Rays ◽  
Solar System ◽  
Isotopic Composition ◽  
Nuclear Physics ◽  
Direct Evidence ◽  
Cosmic Ray ◽  
System Composition ◽  
The Galaxy ◽  
Science News ◽  
The Mean

Over the past seven years the Cosmic Ray Isotope Spectrometer (CRIS) on the ACE spacecraft has returned data with an unprecedented combination of excellent mass resolution and high statistics, describing the isotopic composition of elements from lithium through nickel in the energy interval ~ 50 to 500 MeV/nucleon. These data have demonstrated: * The time between nucleosynthesis and acceleration of the cosmic-ray nuclei is at least 105 years. The supernova in which nucleosynthesis takes place is thus not the same supernova that accelerates a heavy nucleus to cosmic-ray energy. * The mean confinement time of cosmic rays in the Galaxy is 15 Myr. * The isotopic composition of the cosmic-ray source is remarkably similar to that of solar system. The deviations that are observed, particularly at 22 Ne and 58 Fe , are consistent with a model in which the cosmic-ray source is OB associations in which the interstellar medium has solar-system composition enriched by roughly 20% admixture of ejecta from Wolf-Rayet stars and supernovae. * Cosmic-ray secondaries that decay only by electron capture provide direct evidence for energy loss of cosmic rays as they penetrate the solar system. This invited overview paper at ECRS 19 was largely the same as an invited paper presented a month earlier at the 8th Nuclei in the Cosmos Conference in Vancouver. The proceedings of that conference will be published shortly by Elsevier as a special edition of Nuclear Physics A. For further summary of results from CRIS, the reader is referred to URL 〈〉 and links on that page to CRIS and to Science News.

Primary γ-rays

1975 ◽  
Vol 277 (1270) ◽  
pp. 365-379 ◽  
Keyword(s):  
Cosmic Rays ◽  
Cosmic Ray ◽  
High Energy ◽  
Structural Features ◽  
Galactic Cosmic Rays ◽  
Interstellar Space ◽  
Characteristic Energy ◽  
The Galaxy ◽  
Ray Density ◽  
Γ Rays

Within our Galaxy, cosmic rays can reveal their presence in interstellar space and probably in source regions by their interactions with interstellar matter which lead to γ-rays with a very characteristic energy spectrum. From the study of the intensity of the high energy γ radiation as a function of galactic longitude, it is already clear that cosmic rays are almost certainly not uniformly distributed in the Galaxy and are not concentrated in the centre of the Galaxy. The galactic cosmic rays appear to be tied to galactic structural features, presumably by the galactic magnetic fields which are in turn held by the matter in the arm segments and the clouds. On the extra-galactic scale, it is now possible to say that cosmic rays are probably not at the density seen near the Earth. The diffuse celestial γ-ray spectrum that is observed presents the interesting possibility of cosmological studies and possible evidence for a residual universal cosmic ray density, which is much lower than the present galactic cosmic-ray density.

scholarly journals The Origin and Dynamical Effects of the Magnetic Fields and Cosmic Rays in the Disk of the Galaxy

1970 ◽  
Vol 39 ◽  
pp. 168-183
Author(s):  
E. N. Parker
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Magnetic Fields ◽  
Dynamical Behavior ◽  
Cosmic Ray ◽  
Interested Reader ◽  
Written Text ◽  
The Galaxy ◽  
Basic Ideas ◽  
The Magnetic Field

The topic of this presentation is the origin and dynamical behavior of the magnetic field and cosmic-ray gas in the disk of the Galaxy. In the space available I can do no more than mention the ideas that have been developed, with but little explanation and discussion. To make up for this inadequacy I have tried to give a complete list of references in the written text, so that the interested reader can pursue the points in depth (in particular see the review articles Parker, 1968a, 1969a, 1970). My purpose here is twofold, to outline for you the calculations and ideas that have developed thus far, and to indicate the uncertainties that remain. The basic ideas are sound, I think, but, when we come to the details, there are so many theoretical alternatives that need yet to be explored and so much that is not yet made clear by observations.

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