1. Masuda, A., Nature, 205, 555 (1965).
2. Masuda, A., Nature, 203, 1161 (1964).
3. Masuda, A., INSJ–65, Inst. Nucl. Study, Univ. Tokyo (1964).
4. Masuda, A., and Matsui, Y., INSJ–53, Inst. Nucl. Study, Univ. Tokyo (1963).
5. Masuda, A., and Matsui, Y., Geochim. Cosmochim. Acta (to be published).