Introduction: Basic concepts regarding the Fukushima accident and radiation and radioactivity

Teruyuki Nakajima, Toshimasa Ohara, Mitsuo Uematsu, Yuichi Onda, Mitsuru Ebihara, Atsushi Shinohara, Yasunori Hamajima, Yasuhito Igarashi, Tatsuo Aono, Michio Aoyama, Masayuki Takigawa, Kimiaki Saito