1. (1) A. Kudo, J. Zheng, R.M. Koerner, D.A. Fisher, D.C. Santry, Y. Mahara, and M. Sugahara, J. Environ. Radioact. 40, 289 (1998).
2. (2) J.H. Harley, J. Radiat. Res. 21, 83 (1980).
3. (3) R.W. Perkins and C.W. Thomas, Transuranic Elements in the Environment, Ed. W.C. Hanson, pp. 53, Tech. Inf. Center US Department of Energy (1980).
4. (4) K. Hirose, Y. Igarashi, M. Aoyama, and T. Miyao, Plutonium in the Environment, Ed. A. Kudo, Elsevier Science, Amsterdam, pp. 251 (2001).
5. (5) UNSCEAR, Report to the General Assembly, United Nations, New York (2000).