Sen. Mark Dayton (D-Minn.) packed his bags and headed for the hills this month, leaving behind only a note attached to his door in the Russell Senate Office Building explaining that because of a "top-secret intelligence report," his office would be closed until after Nov. 2.

The reaction on Capitol Hill to Dayton's strange behavior seems to have been ridicule. A Republican senator thought it would be funny to inquire about taking over his vacant office space. D.C. Mayor Anthony Williams told a reporter, "I'm literally scratching my head trying to figure out what frequency he's on."

I don't know what Dayton saw in that top-secret report, but whatever horrifying October surprise he's worried about apparently didn't frighten anyone else. So I suspect that Dayton may be suffering from a case of prime-target-fixation syndrome. As a recovering low-level sufferer myself, I feel qualified to make the diagnosis. You won't find PTF syndrome in the Diagnostic and Statistical Manual of Mental Disorders. That's because the malady was first described in 1964 not by a psychologist but by Herman Kahn, the great theorist of mutual assured destruction. Kahn described PTF syndrome as "an expression of apathy or fatalism often found among those who believe that their city or location would constitute a prime target in the event of nuclear attack." Fear of chemical and biological attack can also trigger the syndrome.

PTF syndrome has a characteristic suite of diagnostics. If you keep cellophane-wrapped iodine pills in your wallet, maintain an extensive mental playbook of escape plans or harbor fantasies of a bomb shelter in your basement, you may be a fellow sufferer. Those of us with the syndrome tend to have trouble pushing depressing facts to the periphery of our thoughts -- such as the fact that in 1997 Russian general Alexander Lebed told "60 Minutes" that more than 100 Soviet suitcase nukes are missing, or the fact that the CIA once intercepted al Qaeda chatter about an American "Hiroshima."

In his recent book "Nuclear Terrorism," Graham Allison writes, "In my own considered judgment, on the current path, a nuclear terrorist attack on America in the decade ahead is more likely than not." Former secretary of defense William Perry reportedly puts even odds on an attack in the next six years.

Those kinds of educated predictions can keep a PTF sufferer up at night wondering whether we're all nuts to live in Washington. Even assuming that Allison and Perry have overestimated the risk by an order of magnitude, wouldn't it be rational for us all to follow Dayton's lead and leave town? Humans are notoriously risk-averse creatures. A 50 percent chance of rain is usually all it takes to make us cancel a tee time.

And yet we Washingtonians (like our counterparts in New York) seem to be in chronic denial of the fact that we're living on the side of a volcano. The D.C. real estate market is one of the hottest in the world. People are moving back downtown in droves.

It's impossible, of course, to say whether there's a greater risk of a nuclear attack on Washington today than at the height of the Cold War, but this much is certain: Depending on where you live, you have a much better chance of surviving an Osama bin Laden bomb than you did of surviving one heaven-sent from Nikita Khrushchev. You could run but you couldn't hide from multi-megaton thermonuclear war. The suburbs were no safer than the cities. In contrast, today you can hide from nuclear terrorism. Most experts believe that terrorists would have a tough time getting their hands on a bomb any bigger than 10 kilotons -- smaller than the primitive nuke that was dropped on Hiroshima.

The damage from such an attack would be utterly catastrophic, to be sure, but not inescapable for those of us who don't live and work in center city. PTF sufferers such as Dayton shouldn't have to flee Washington to feel safe; all they've got to do is keep their distance from downtown.

I visited the promotional Web site for Allison's book on nuclear terrorism, where you can interactively map the effects of a 10-kiloton nuclear explosion at your ground zero of choice. Plug in 20500, the Zip code for the White House, and a bull's-eye appears on the screen. The Post's offices, several blocks north of the White House, sit squarely inside the red "1/3 Mile 100 percent fatality" inner ring. Three-quarters of a mile out, at Dupont Circle, people who happened to be outside would suffer fatal radiation doses and most buildings would be reduced to rubble. Farther afield in Georgetown, there'd be fires and radiation exposure. Keep pushing out and you eventually get to my own home and place of work, about 6 miles away in upper Northwest. I'm reassured to learn that even though things would be highly unpleasant for me, I'd almost certainly survive unharmed. As a sufferer of prime-target-fixation syndrome, that ought to make me at least marginally less anxious. Maybe I should invite Dayton to reopen his offices in my basement.

Joshua Foer is a Washington writer.