Long-term fluxes of heavy cosmic-ray nuclei based on observations in meteorites and lunar samples

We present here results of observations of fossil tracks due to very heavy (VH) and very very heavy (VVH) cosmic-ray nuclei (Z > 20 and Z > 30, respectively) in a variety of extraterrestrial samples-lunar and meteoritic. These samples represent irradiation by solar as well as galactic cosmic rays during the past years, with effective shielding depths of 10- -10 cm of typical stony material, corresponding to the kinetic-energy interval ( 1 500) MeY per nucleon. Based on these data, we have deduced the average kinetic energy spectrum of VH and VVH nuclei in the ancient cosmic radiation. Our observations indicate that (i) at energies less than 10 MeV per nucleon, the VH and VVH nuclei are entirely of solar origin and (ii) the relative abundance of (Z > 30)/(Z > 20) nuclei is almost constant in the kinetic-energy interval ( ) MeV per nucleon, but that at lower energies, less than 30 MeV per nucleon, the heavier nuclei progressively become more abundant. The ratio of abundance, (Z > 30)/(Z> 20), increases by more than a factor of 5 in going down from 50 to 6 MeY per nucleon. (Effects of shielding geometry and erosion during irradiation have been considered; their effects are found to be unimportant for the conclusions drawn here.) Taking into account typical erosion rates, the exponents in the power-law kinetic-energy spectra of solar VH and VVH nuclei are determined to be -3 and -5, respectively. Subject headings: abundances, cosmic rays - cosmic rays - meteorites and meteors - Moon