1. aDepartment of Radiobiology, Institute for Environmental Sciences (IES), 2-121 Hacchazawa, Takahoko, Rokkasho, Kamikita, Aomori 039-3213, Japan
2. bTohoku Nuclear Co., Ltd., 2-41-14 Higashi Okamisawa, Misawa, Aomori 033-0024, Japan
3. cTohoku Research Center, Forestry and Forest Product Research Institute, 92-25 Nabeyashiki, Shimo-Kuriyagawa, Morioka, Iwate 020-0123, Japan