1. Graduate School of Engineering Science Kyushu University, Fukuoka, 812-8581 Japan.
2. Tokai Establishment, JAERI, Ibaraki 319-1195, Japan
3. Naka Establishment, JAERI, Ibakaki 319-1195, Japan
4. Forschungzentrum Karlsruhe, HVT-TLK, P.O. Box 3640, D-76021 Karlsruhe, Germany