Kimie Furuuchi recently received a letter encouraging her to come home. Signed by the mayor, it began, "Dear Minamisoma Evacuee. . . ."

"We are trying to create the environment where all evacuees can come back to Minamisoma as soon as possible," the letter stated.

Furuuchi thought it seemed premature. Government authorities and radiation experts kept saying that her old city could become safer, but almost nobody said it was safe. The ambiguity meant that Furuuchi, like tens of thousands of others who fled their homes after the Fukushima No. 1 nuclear disaster in March, had to weigh the comfort of a homecoming against a danger she could not quantify.