Energy spectrum of cosmic rays

Figure 6. Compilation of the differential all-particle energy spectrum of cosmic rays over a very wide range of energies.

The suggestion that11B could be enhanced by a low-energy component of cosmic rays over and above the flat spectrum usually assumed (Meneguzzi Reeves 1975) is excluded because it would lead to overproduction of light elements in general. 

The local energy-density spectrum of cosmic rays is related to the observed flux (particles per cm2 per GeV per second per steradian) by... 

To a first approximation, the all-particle spectrum of cosmic rays can be described by a power law on more than 11 decades on particle energy, so that the dependence of cosmic ray intensity on particle energy is close to E 2-7 at energy more than about 10 GeV. Closer examination reveals some structure in the galactic cosmic ray spectrum that includes the knee at 4 x 1015 eV, the second knee at about 1018 eV, and the ankle at 1019 eV. The steady-state spectrum is shaped by two principle processes - the acceleration at the sources and the subsequent propagation in the Galaxy. 

A key region of the spectrum of cosmic rays is its highest energies [1], The flux here is so low that the small event statistics in our observations to date leave us uncertain of the spectral structure above the key energy of 4 x 1019 eV, where a spectral downturn has been predicted [18 19], due to the interaction with 2.7K photons from the cosmic microwave background. 

The origin and cause of acceleration of cosmic rays is somewhat uncertain, but the power-law energy spectrum suggests some kind of electromagnetic process... 

Li, Be, and B are believed to be produced in spallation reactions in which the interstellar 12C and 160 interact with protons in the galactic cosmic rays (GCR). These reactions are high-energy reactions with thresholds of 10-20 MeV. The energy spectrum of the GCR is shown in Figure 12.20. 

Only for the 7Li isotope is cosmic-ray production not the source of most of the nuclei. The cosmic rays produce 7Li/6Li in a ratio near 2, with exact details depending on the energy spectrum assumed for the unseen low-energy cosmic rays but in the solar system that ratio is 12.5. The cosmic rays are the source of 6Li, which means they are the source of only about 1/6 of the 7Li. The remainder is a combination of Big-Bang relic plus production of 7Li in AGB stars. But 6Li, which is produced neither in stars nor Big Bang is entirely the result of cosmic-ray interactions in the interstellar medium. 

The energy spectrum of a nuclear component extends smoothly from about 10 MeV to 10 ° eV (more than 13 decades in energy and 32 decades in intensity). The mean particle energy of the galactic cosmic-ray spectrum is about 1 Gev, and the number density of these particles in interstellar space is about 10" m , almost equal to the... 

B. Wiebel-Sooth, Measurement of the all particle energy spectrum and chemical composition of cosmic rays with the HEGRA detector, PhD thesis, Universitt Wupertal, 1998. 

Abstract Results from direct and indirect measurements of cosmic rays are reviewed. Emphasis is given to the understanding of the knee in the energy spectrum. The data are compared to contemporary models for the knee. Implications on the present understanding of the origin of galactic cosmic rays are discussed. 

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