1 Health Research Foundation, 103-5 Tanaka-Monzen-cho, Sakyo-ku, Kyoto 606-8225, Japan.
2 National Cancer Center Research Institute, Tsukiji, Chuo-ku, Tokyo 104, Japan Radiation Effects Association, 1-9-16 Kaji-cho, Chiyoda-ku, Tokyo, Japan tanooka-h@wind.ocn.ne.jp.