The Dirty Bomb Distraction

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But even a dirty bomb without casualties could spread nuclear panic, based on the danger of long-term cancer. For doses in the 100-rem range, results from historical exposures suggest the increased risk of cancer is about 0.04 percent per rem. Thats a 6 percent increase in your chance of dying from cancer for each year you spend in the square kilometer. If the radioactivity were spread over a larger area, e.g., a 10- by 10-kilometer square, then the dose would be lower (12.6 rems per year) and so would the added risk of cancer: 0.06 percent per year of exposure. (I am assuming, conservatively, that risk is proportional to dose, even at low doses.

With such contamination, would I evacuate my home? Not if I were allowed to stay. To me, the increased riskfrom the pre-existing average risk of cancer of about 20 percent per year to, say, 20.06 percentis not significant.

But I wouldnt be given the choice. The exposure of 12.6 rems per year is 126 times more than the yearly limit allowed to the public. In fact, the Environmental Protection Agency decontamination standard is 0.025 rems per year, meaning that 98 percent of the radioactivity would have to be removed before I would be allowed to return to my home.

In the September 11 attacks, the terrorists took advantage of U.S. policy and prejudices. They knew they didnt need guns to take control because pilots had been instructed to cooperate with hijackers; nobody expected hijackers to turn planes into weapons. Similarly, a terrorist today might use a radiological weapon, not because of its actual damage, but in anticipation the out-of-scale panic and ensuing economic disruption that the weapon could trigger.

Could other radiological attacks be more potent than our hypothesized cesium-137 example? Electrical generators powered by the decay of radioisotopes, found in abandoned lighthouses in Russia, held 400,000 curies of strontium-90. But strontium-90 emits virtually no gamma rays; it is harmful only if you breathe it or ingest it. A cloud of aerosolized Sr-90 can killbut it does not stay in the air for long. For the same reason, even a radiological bomb made using plutonium is unlikely to be dangerous. Anthrax would be deadlier, and much easier to obtain and transport. Nuclear waste storage facilities and nuclear reactors contain vastly more radioactivity, and the danger from them is substantial, if their radioactivity can be released.

If small dirty bombs threaten so little harm, why are they lumped in with true weapons of mass destruction?  The reason is: its the law, as written in the 1997 National Defense Authorization Act (Public Law 104-201) and other places, including California penal code 11417.  Defining them this way was a mistake that could lead to misallocation of resources and a general overreaction if such weapons were used. I hope, and expect, that most of the $450 million to be spent on the anti-nuclear initiative announced last month will be used to protect us from nuclear explosives and attacks on nuclear storage areas, and not specifically from radiological weapons. 

If terrorists do attack this summer using a dirty bomb, the resulting death might come from automobile accidents as people flee. Dirty bombs are not weapons of mass destruction, but weapons of mass disruption. Their success depends on public and government overreaction. Beware not radioactivity but nuclear panic. The main thing we have to fear from a dirty bomb is fear itself.