Risk and Reality in a Nuclear Attack

Sunday, January 7, 2007

By incorrectly stating that the fallout zone from a nuclear explosion is "often estimated at 50 miles" and supporting the notion that people need to move out as far as Winchester to be safe from such an incident in downtown Washington, The Post spread misinformation in "New Rural Sales Pitch: Work Outside D.C.'s Fallout Zone" [front page, Dec. 26].

While any detonation of a nuclear weapon would be horrific and cause mass casualties in a populated area, it would be likely to exert its terrible effects over a much smaller zone.

There is no typical size for a nuclear fallout zone -- it varies greatly, depending on such factors as the amount of energy that a nuclear weapon produces (its "yield"). Also, bombs do not deposit radioactive fallout in a circular region, as The Post graphic depicted, but in a narrow, oval-shaped region along the direction that the wind blows.

The old headquarters of the Atomic Energy Commission (now used by the Energy Department) were deliberately located in Germantown -- less than 25 miles as the crow flies from downtown -- to be safe from a powerful 20-megaton Soviet-era weapon detonated thousands of feet above the Capitol.

In contrast, the most probable nuclear event today is a terrorist bomb with a yield of about 1 kiloton, many thousands of times less powerful than a Soviet bomb and detonated at or near ground level. For such a burst, the total fallout dose would have significant effects -- defined as 50 percent mortality from radiation -- up to 3.4 miles downwind of the detonation and diminishing to 5 rads (the government's annual dose limit for radiation workers) at about 36 miles downwind.




College Park

The writers are, respectively, a physicist and former science adviser for arms control at the State Department; and a senior science writer at the American Institute of Physics.

© 2007 The Washington Post Company