On the variation of cosmic ray composition in the past

Abstract

The fossil-track technique is used to determine the abundance of cosmic-ray nuclei with atomic number of at least 30 (VVH group) relative to the iron group in a number of lunar samples and meteorites. This study was undertaken to obtain information about time variations, energy dependences, and spatial variations in the flux of heavy galactic cosmic rays. It is found that for kinetic energies of at least 0.1 GeV/n, variations of the VVH abundance in galactic cosmic rays have remained within a very narrow range, suggesting that the sources of these particles are very similar in their heavy-element abundances. The VVH abundances in the lunar samples and meteorites are also found to exhibit little variation with time or distance from the sun, indicating that these nuclei are probably produced by the same process of nucleosynthesis.