Long-term variations in the cosmic-ray flux

Abstract

The present-day information on the temporal and spatial variations in the flux and chemical composition of cosmic-ray protons and multicharged nuclei during certain intervals of time, since the beginning of the Solar System, is discussed. This information has been deduced on the basis of analyses of isotopic changes and alterations in the crystalline matrix of meteoritic and lunar materials. Most of the samples analysed were exposed to cosmic radiation during the recent time period, 0-10 Ma B.P. and some during 100-1000 Ma B.P. Limited data are also available for the time period soon after the formation of solid objects in the Solar System, i.e. ca . 4500 Ma B.P., based on analyses of certain meteorites. The cosmic-ray parameters deduced are for the 1-3 AU space and are average values for time periods of 105-1 0 7 a for protons, a -particles, v.h./v.v.h. nuclei in the kinetic energy interval (1-1500) MeV/nucleon. The archaic cosmic-ray data provide information on the long term average features of acceleration of protons and heavy nuclei by the Sun and on the relative contributions of solar particles to the total cosmic-ray particle population at 1 AU. The implications of absence of any marked time variations in the flux and energy spectra of protons v.h. (Z ^ 20) andv.v.h. (Z ^ 30) nuclei are discussed briefly in relation to cosmic-ray sources and propagation.