1. Laboratory of Nuclear Science, Tohoku University, Mikamine, Sendai 982
2. National Institute of Radiological Sciences, Anagawa, Inage-ku, Chiba 263
3. Toshiba Co. Ltd., Tokyo 105
4. Department of Physics, Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo 152
5. Department of Energy Science, Tokyo Institute of Technology, Nagatsuta, Yokohama 227