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The gamma‐ray spectrum of the Sun
Author(s) -
Dolan Joseph F.,
Fazio G. G.
Publication year - 1965
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg003i002p00319
Subject(s) - physics , bremsstrahlung , solar flare , gamma ray , proton , electron , flare , spallation , neutron , nuclear physics , radiation , atomic physics , astrophysics
The γ‐ray spectrum ( hν > 10 kev) emitted by the sun is investigated and approximate fluxes at the earth are predicted on the basis of a simple solar‐flare model. The object of this paper is to determine what new information about the sun and, in particular, solar flares we can learn from the detection of this radiation. We also investigate which part of the spectrum is most feasibly detectable and which part yields the most direct information on solar‐flare structure. Our calculations indicate the following sources of γ radiation from the sun. The γ radiation emitted by the quiet sun is negligible compared with emission during a solar flare. The most important emission mechanism in the 10‐kev to 1‐Mev energy region is bremsstrahlung by flare‐accelerated electrons. The photon spectrum is continuous and decreases monotonically with energy. Flare‐accelerated protons will interact with carbon, nitrogen, and oxygen nuclei by inelastic scattering and spallation reactions, producing γ radiation as a result of nuclear de‐excitation. Little effort has been made to detect this line emission. Neutrons resulting from spallation reactions will be partially captured by protons to produce deuterium and 2.23‐Mev γ radiation. The intensity of this line emission is proportional to the neutron density in a flare. Line emission at 0.51 Mev results from positron‐electron annihilation. Positrons are produced by β decay of radioactive nuclei generated by spallation reactions and by the decay of π + mesons produced in proton‐proton reactions. The primary source of photons with energy greater than 50 Mev is the decay of π 0 mesons, which are also produced in proton‐proton reactions. The intensity of these photons is very sensitive to the accelerated proton spectrum in the flare. Flux estimates indicate that the detection of γ radiation resulting from a solar flare is feasible and would yield information on nuclear reactions as well as on the intensity and spectrum of high‐energy protons and electrons.