Yesterday news reports on the Japanese nuclear leak all seemed to mention Prime Minister Naoto Kan's advice that people living near the damaged Fukushima Nuclear Power station remain inside to avoid exposure to radioactivity.  The New York Times quoted chief cabinet secretary Yukio Edano directing citizens: "Please do not go outside, please stay indoors, please close windows and make your homes airtight."

This struck us as odd. Does staying inside a wooden house really do anything to protect from something that lingers in the environment as long as nuclear radiation? We were skeptical since it reminded us of the the Department of Homeland Security's infamous advice to ward off bioterrorism with duct tape: not a bad idea, but probably not an adequate solution to the problem.

So we shot off a few emails to scientists with this rather naïve question: does the Japanese government's directive make any sense at all? They say, yes, but only to a point. 

Kent Hansen, professor emeritus of nuclear science and engineering at MIT, said there are "several different kinds of radiation. The most penetrating are called gamma rays." Staying inside a house wouldn't do much against those, unless by house you mean more of a bunker--something with substantial concrete walls. Other forms of radiation, however, like "charged particles" or alpha or beta rays, don't penetrate as far, and staying inside would provide a measure of protection against those. "But I think the more likely reason," he continued, "for people to be inside would not be to shield them from radiation but to protect them from inhaling radioactive material into the lungs." It's the same rationale for the facemasks: "if radioactive material stuck to a piece of dust the facemask would keep that from getting into your lungs," where it would do its nasty work and start killing off lung tissue.

We got roughly the same response from Jasmina Vujic, a professor of nuclear engineering at Berkeley. The primary contamination issue people appear to be worried about here is leak of "fission gases" and radioactive particles from the plant. Staying indoors works for that. In other words: remember those reports from yesterday about winds "dispersing radioactive material" over the Pacific Ocean? If people living in Japan stay inside, they won't be breathing that in before it's dispersed.