1. Masuda, A., Nature, 203, 1062 (1964).
2. Masuda, A., and Matsui, Y., INSJ-53, Inst. Nucl. Study, Univ. Tokyo (1963).
3. Masuda, A., and Matsui, Y., Geochim. Cosmochim. Acta (in the press).
4. Masuda, A., Chigaku-zasshi, 73, 139 (1964).
5. Masuda, A., INSJ-65, Inst. Nucl. Study, Univ. Tokyo (1964).