There are conflicting reports on how much radiation has leaked and might still escape from the nuclear power plant in Fukushima Dai-ichi, Japan damaged by Friday's disaster in Japan.
But there's no doubt that any significant exposure to extra radiation poses a health risk.
On "The Early Show" Monday, CBS News Medical Correspondent Dr. Jennifer Ashton observed that, "When you talk about radiation exposure ... you're talking about really three key factors: the time that you're exposed to the radiation, the distance from the source of the radiation, and whether there's any shielding. That could be anything from being inside a building, to a lead-apron, to protective clothing."
Who's most at risk?
"Two big groups of population right now," Ashton told co-anchor Erica Hill. "One is the cleanup workers. The people who are working at these facilities are taking extra precautions. They're limiting their amount of time (of exposure) to the direct radiation, to the highest radiation sources, and, of course, they're wearing protective clothing. But those people are at greatest risk. Then we talk about the general Japanese population -- children up to the age of 18 tend to be most at risk, because they have the most actively-dividing cells in their body. But really, anyone who's within a certain radius could be at risk. Not just short-term, but long-term."
Anyone at risk could take potassium iodide as a protective measure, Ashton says.
"What happens," she explained, "is the thyroid gland uses iodine very actively. So anyone who will be exposed to radiation should be taking ... potassium iodide as soon as possible before exposure, so that their thyroid gland uses that, and not the radioactive iodine.
"We're talking about the radioactive source is I-131 that can be liberated in these types of radiation accidents. So you want to protect the thyroid gland.
"You also want to think about actively-dividing tissue in the gastro-intestinal tract. And you can see short-term consequences like nausea, vomiting, diarrhea, some blood effects short-term, as well as long-term: When you talk about thyroid cancer, that might not show up for two-to-four years. Blood cancers, like leukemias, might not be detected for decades."