Japan's worst nuclear radiation accident took place at a uranium reprocessing facility in Tokaimura, northeast of Tokyo, on 30 September 1999. The direct cause of the accident was cited as the depositing of a uranyl nitrate solution--containing about 16.6 kg of uranium, which exceeded the critical mass--into a precipitation tank. Three workers were exposed to extreme doses of radiation.

Hiroshi Ouchi, one of these workers, was transferred to the University of Tokyo Hospital Emergency Room, three days after the accident. Dr. Maekawa and his staff initially thought that Ouchi looked...