It did not help that the government recently had to backtrack on the acceptable exposure levels for schoolchildren after a senior government adviser quit in a tearful news conference, saying he did not want children to be exposed to such levels, and parents protested. The recent discovery that radioactive beef made it into stores raised fresh alarms.

“We need to do strict research to make people feel assured,” said Keiichi Miho, the mayor of Nihonmatsu, a city of 60,000 people west of the Daiichi plant. The mayor is one of a growing number of local officials who have tackled the issue directly, spending millions of dollars on steps like creating a radiation map of his city. “That’s the only way to regain credibility.”

Mrs. Okoshi, a lifelong farmer, lives with her 85-year-old mother, and one of her daughters resisted the lure of the cities that has drawn so many Japanese, choosing instead to live under the same roof as her mother and grandmother.

In uncharted territory, Mrs. Okoshi said she apologized to her neighbor for making trouble.

Still, she felt she had no other choice. Several weeks after the crisis began in March, there were still fewer than 10 monitoring posts in Iwaki, and most of them were in the more populated parts of the city, rather than its outlying villages, like Shidamyo, where Mrs. Okoshi lives.

Plus, her rambling farmhouse was feeling increasingly empty, since her husband died several months ago and her daughter’s family fled, as did many others.

“Our life was so lively when the four boys were running around the mountains in the back of the house,” she said.