1. Reeves, H., Fowler, W. A., and Hoyle, F., Nature, 226, 727 (1970).
2. Urey, H. C., Revs. Geophys., 2, 1 (1964).
3. Cameron, A. G. W., in Origin and Distribution of the Elements (edit. by Ahrens, L. H.) (Pergamon, Oxford, 1968).
4. Baedecker, P. A., in Handbook of Elemental Abundances in Meteorites (edit. by Mason, B.) (Gordon and Breach, New York, 1971).
5. Harder, H., Nachr. Akad. Wiss. Math-Phys. Gottingen, 1, 1 (1961).