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Published February 1962 | Published
Journal Article Open

Nucleosynthesis during the Early History of the Solar System


Abundances in terrestrial and meteoritic matter indicate that the synthesis of D^2, Li^6, Li^7, Be^9, B^(10) and B^(11) and possibly C^(13) and N^(15) 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 10^(45) 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 D^2/H^1 = 1.5 × 10^(−4), Li^6/L^i7 = 0.08, and B^(10)/B^(11) = 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 10^7 n/cm^2 s for an interval of 10^7 years. The importance of the (n, α) reactions on Li^6 and B^(10) is indicated by the relatively low abundances of these two nuclei. It is shown that the neutron flux was sufficient to produce the radioactive Pd^(107) and I^(129) necessary to account for the radiogenic Ag^(107) and Xe^(129) anomalies recently observed in meteorites. The short time interval, ∼ 6 × 10^7 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.

Additional Information

Copyright © 1962 The Royal Astronomical Society. (Received 1961 April 17) Our indebtedness to Harold C. Urey has already been acknowledged in the introduction. We also wish to acknowledge discussions and/or correspondence on subjects related to this paper with Edward Anders, Stanley Bashkin, Harrison S. Brown, Norman R. Davidson, Samuel Epstein, Gerhart Friedlander, Norman H. Horowitz, Charles C. Lauritsen, V. Rama Murthy, Arthur M. Poskanzer, John H. Reynolds, Oliver A. Schaeffer and Gerry J. Wasserburg. The research which serves as the basis of this paper has been assisted in part by the Joint Programme of the Office of Naval Research and the U.S. Atomic Energy Commission and in part by the Air Force Office of Scientific Research of the Air Research and Development Command.

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Published - Geophys._J._Int.-1962-Fowler-148-220.pdf


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August 19, 2023
October 18, 2023