Secular variations in the abundances of heavy nuclei in cosmic rays

Abstract

The ratios of fluxes of heavy cosmic-ray nuclei [(30 ≤ Z ≤ 40)/(20 > Z ≤ 28), where Z is the atomic number ∫, based on studies of meteorites and lunar samples, show little variation with time, distance in the solar system (1 to 3 astronomical units), or kinetic energy (30 to 2000 megaelectron volts per nucleon). Samples exposed for time intervals of 10³ to 10⁸ years show that the variations in the flux of 30 ≤ Z ≤ 40 nuclei relative to that of the iron group nuclei (20 < Z ≤ 28) have remained within the range of (1.3 ± 0.6) × 10^-3 during the last billions of years, thus indicating a remarkable similarity in the elemental composition of sources responsible for these nuclei in the cosmic radiation.