Search for Extra-Solar Materials as Carriers of Anomalous Noble Gas Isotopes in Meteorites

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1. Nucleosynthetic origin of meteoritic noble gas isotopes of anomalous isotopic compositions were further examined in light of a stellar model prediction by Heymann et al. Our three-isotope analysis has revealed the s- and r-process isotopes more distinctively than previous ones, and shown that the nucleosynthetic model is very promissing in explanation of the observed anomalies in the noble gas abundance. Stellar condition for photodisintegration was found to be the same as deduced earlier by us, i.e. the duration of the silicon burning at peak temperature of T_9=2.05 is (6.5 0.5) x 10^4 sec to yield (^<124>Xe. ^<126>Xe)_p=2.1 0.2 and the observed heavy Xe ratios to constrain the condition of the explosive phase to have a neutron dose of 3.8 x 10^<-7> [mole/cm^3.sec] yielding (^<134>Xe/^<136>Xe)_r=0.675. The carrier phase(s) for s- and r-(＆ p-) isotopes have recently been assigned to very minute SiC and diamond, respectively, but still under debate (see 3. below).2. Energetic photons … More , together with high flux of neutrons, seem to be responsible for reprocessing of chemical elements at supernova explosion. To explore this possibility, photospallation, photofragmentation, photofission and photopion reaction were studied systematically for 13 target nuclei ranging from ^<12>C to ^<209>Bi at bremsstrahlung end point energies of 30-1000 MeV. New characteristic features of their yields and excitation functions were found and examined in light of nuclear theory.3. A sophisticated mass spectrometer of high sensitivity has been constructed and under operation for noble gas isotope study. Meteorite samples were the Allende and Murchison, 10-20 g pieces of which were separately disaggregated by freeze-thaw method and separated into 70 fractions, in case of a 20 g Allende, based on size and density. These fractions were then analyzed for major and trace elements and mineral compositions and for their characteristic features of occurence. Some new types of mineral occurences found in the present work, together with further analysis of noble gas isotopes in the separated fractions, are expected to give observational clues to the origin and formation history of the chemical elements in the solar system. Less