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She tells her children, ages 6 to 15, to wear medical masks, long-sleeved shirts and a hat whenever they go out, and not to play outside.

She still avoids drinking tap water and keeps a daily log of her own radiation monitoring around the house, kindergarten and schools her children attend.

“We Fukushima people are exposed to radiation more than anyone else outside the prefecture, but we just have to do our best to cope,” she said. “We cannot stay inside the house forever.”

Japanese officials say mental health problems caused by excessive fear of radiation are prevalent and posing a bigger problem than actual risk of cancer caused by radiation.

But what kind of cancer risks do the Japanese really face?

Information on actual radiation exposures for individuals is scarce, and some experts say they can not draw any conclusions yet about risk to the population.

Michiaki Kai, professor of environmental health at Oita University of Nursing and Health Sciences, said that based on tests he has seen on people and their exposure levels, nobody in Fukushima except for some plant workers has been exposed to harmful levels of radiation.

Radiation generally raises cancer risk in proportion to its amount. At low-dose exposures, many experts and regulators embrace the idea that this still holds true.

But other experts say direct evidence for that is lacking, and that it’s not clear whether such small doses raise cancer risk at all.

“Nobody knows the answer to that question,” says Dr. Mettler, an emeritus professor of radiology at the University of New Mexico and the U.S. representative to the United Nations Scientific Committee on the Effects of Atomic Radiation, or UNSCEAR.

If such low doses do produce cancers, they’d be too few to be detected against the backdrop of normal cancer rates, he said.