Production of Na²²and H³in a thick silicate target and its application to meteorites

Abstract

A number of glass plates chosen from a stack of thick target having the gross chemical composition of stone meteorites, and exposed to 3 Gev protons, were analyzed for Na22 and H3. Na22 was measured by the non-destructive γ-γ coincidence counting, and H3 was measured in gas phase after chemical processing. Complete distributions of these nuclides in the thick target assembly were mapped. Effective cross sections for H3 and Na22 production were calculated on the oxygen and the silicon target basis, respectively. The cross sections show significant buildup factors along the depth followed by an exponential decrease. The distribution of H3, in both the radical as well as the lateral directions, is comparatively steeper. The results are compared with similar published studies on iron targets. The data are used to calculate H3 and Na22 production rates in spherical chondrites exposed to cosmic radiation, assuming that only primary nucleons of energy greater that 1.2 Gev are effective in the nuclide production, and that these can be represented by an average energy of 3 Gev. The calculated production rates of H3 (450–670 atom min−1 kg−1) and Na22 (80–110 atom min−1 kg−1) are comparable to the observed range of concentrations of these nuclides in stone meteorites.