A decontamination worker at the entrance of Futaba, an abandoned town near the Fukushima nuclear plant.Credit...Toru Hanai/Reuters TOKYO — In the chaotic, fearful weeks after the Fukushima nuclear crisis began, in March 2011, researchers struggled to measure the radioactive fallout unleashed on the public. Michio Aoyama’s initial findings were more startling than most. As a senior scientist at the