Abundances in terrestrial and meteoritic matter indicate that the synthesis of D2, Li6, Li7, Be9, B10 and B11 and possibly C13 and N15 occurred during an intermediate stage in the early history of the solar system. In this intermediate stage, the planetary material had become largely separated, but not completely, from the hydrogen which was the main constituent of primitive solar material. Appropriate physical conditions were satisfied by solid planetesimals of dimensions from 1 to 50 metres consisting of silicates and oxides of the metals embedded in an icy matrix. The synthesis occurred through spallation and neutron reactions simultaneously induced in the outer layers of the planetesimals by the bombardment of high energy charged particles, mostly protons, accelerated in magnetic flares at the surface of the condensing Sun. The total particle energy was approximately 1045 ergs while the average energy was close to 500 MeV per nucleon. Recent studies of the abundance of lithium in young T Tauri stars serve as the primary astronomical evidence for this point of view. The observed abundances of lithium and beryllium in the surface of the Sun are discussed in terms of the astronomical and nuclear considerations brought forward. The isotope ratios D2/H1 = 1.5 × 10?4, Li6/Li7 = 0.08, and B10/B11 = 0.23 are the basic data leading to the requirement that 10 per cent of terrestrial-meteoritic material was irradiated with a thermal neutron flux of 107 n/cm2s for an interval of 107 years. The importance of the (n, ?) reactions on Li6 and B10 is indicated by the relatively low abundances of these two nuclei. It is shown that the neutron flux was sufficient to produce the radioactive Pd107 and I129 necessary to account for the radiogenic Ag107 and Xe129 anomalies recently observed in meteorites. The short time interval, ? 6 × 107 years, required for the radioactive decays to be effective applies to the interval between the end of nucleosynthesis in the solar system and the termination of fractionation processes in the parent bodies of the meteorites. It is not necessary to postulate a short time interval between the last event of galactic nucleosynthesis and the formation of large, solid bodies in the solar nebula.
- 1 - natural sciences ; 2 - earth & environmental sciences ; 3 - geochemistry & geophysics
- 1 - sciences appliquees, technologies et medecines ; 2 - sciences biologiques et medicales ; 3 - sciences biologiques fondamentales et appliquees. psychologie ; 4 - biophysique des tissus, organes et organismes
- 1 - Physical Sciences ; 2 - Earth and Planetary Sciences ; 3 - Geochemistry and Petrology
- 1 - Physical Sciences ; 2 - Earth and Planetary Sciences ; 3 - Geophysics