Nuclide production rates in stone meteorites and lunar samples by galactic cosmic radiation

Abstract

The distributions of radionuclides H3 and Na22 have been measured in thick silicate targets exposed to protons of 0.44- and 1.0-Gev energy. The effective production cross sections for these nuclides from glass matrix are given. Measurements of Na22 in Mg foils at 1 Gev are also presented. At 1 Gev both the nuclides show a buildup inside the target that is not seen at 0.44 Gev. The production rates of these nuclides in spherical chondrites exposed to galactic cosmic radiation (E ≥ 0.25 Gev) are calculated and are found to be: Na22, 80 to 110 dpm/kg; H3, 500 to 700 dpm/kg, in good agreement with measured values. The calculations have been extended to He3 and Ne22. The He3 production rate in most meteorites is calculated to be (2 to 3) × 10−8 cc NTP g−1 m.y.−1. Production rates of several radionuclides in lunar rocks by galactic cosmic rays have been calculated. The reported measured concentrations are generally in good agreement with the measured values in shielded samples.