Seize the Cesium

By Peter D. Zimmerman, a professor of science and security, James M. Acton, a lecturer and M. Brooke Rogers, a researcher at King’s College London (THE NEW YORK TIMES, 01/08/07):

The death of Alexander Litvinenko, the former K.G.B. officer who drank polonium-210 in a cup of tea, underscored the damage that radiological terrorists could do. The most familiar possible situations involve the detonation of a dirty bomb, a modest amount of high explosive mated to a container of radioactive material. But radioactive material inside the human body is far more dangerous than a dirty bomb.

Most analysts believe that about 10 people would die from radiation poisoning after a dirty bomb attack. Others believe that the only people likely to receive a lethal dose of radiation from a dirty bomb would already be dead from the blast. A perfectly feasible terrorist attack using the ingestion, inhalation or immersion of radioactive material, on the other hand, would be almost certain to kill hundreds. We call attacks of these kinds I-cubed attacks (for ingestion, inhalation and immersion). Such attacks can be sneaky, unaccompanied by a flash and bang.

Nothing we write in any way supplies terrorists with information that they don’t already have. We have consulted with American government experts to be certain. Americans need to understand the risks posed by I-cubed attacks, and how to react when one occurs. The unfamiliarity of such attacks compared with dirty bombs may lead to an even greater panic when one is discovered — probably only after large numbers of people get very sick.

The analysts’ favored isotope for a radiological terrorist attack has been cesium-137, which emits very energetic gamma radiation capable of traveling many yards in the air or penetrating lead shielding. Cesium is a nasty chemical. Even its non-radioactive form is highly poisonous.

Fortunately, it’s hard to kill a lot of people with an ingestion attack. Contaminating a reservoir, or even a water main, is ineffective because the radioactivity is quickly diluted, and most water is not used for drinking or cooking. Contaminating agricultural products is similarly difficult. But there are ways, if the terrorist group has enough material and access to the right kinds of facilities, to contaminate food directly.

An inhalation attack, sometimes called a smoky bomb, would use radioisotopes that can be burned, vaporized or aerosolized, and in a confined space could contaminate the air and be inhaled. Isotopes like polonium-210 that emit alpha particles are particularly effective because they can kill either quickly by radiation poisoning or slowly by causing lung cancer. Terrorists could also use something like an insecticide sprayer mounted on a truck to disperse, for example, a polonium compound dissolved in water.

An immersion attack, which would drench victims with a radioactive solution, could kill with only a small fraction of a teaspoon. Just a few drops of contaminated water on the mouth are enough to cause radiation poisoning. The first instinct of somebody soaked with water is to wipe his face, which transfers the isotope from hand to mouth. Even if the victims avoided getting any water inside their bodies, the solution would cause severe radiation burns.

I-cubed attacks are enabled by the easy availability of comparatively large alpha-emitting sources (sources 10 percent the size of a lethal dose can be bought with a specific license) and by the fact that cesium-137 is normally supplied for use in cancer therapy machines, hospital blood sterilizers and elsewhere in industry as a water-soluble powder, the most dangerous possible form.

Water-soluble cesium chloride should be taken off the market immediately. Cesium-137 can instead be supplied embedded in glass. In addition, very large cesium sources are used in places like hospitals. They should be replaced by powerful X-ray machines, which can deliver the same energy radiation in substantially the same quantities.

Cesium-137 is not the only isotope that radiological terrorists might use. The federal Nuclear Regulatory Commission believes that alpha-emitting isotopes like polonium-210 and americium are adequately regulated, but we believe that the quantities supplied without a specific license should be reduced by about a factor of 10. In all cases they should be supplied in hard-to-weaponize forms. The regulatory commission has not been diligent in checking the bona fides of applicants for licenses for large sources of any kind, but thankfully this is being changed.

In the United States, commercial users lose about one radioactive source a day — many large enough for I-cubed attacks — through theft, accidents or poor paperwork. One of these is recovered perhaps every two days, either because the radioactive materials are voluntarily returned or because of good detective work. Many of the losses occur because license holders are negligent. Criminal penalties should be enacted, as they are for some other hazardous materials, to allow prosecution of license holders in the most serious cases.

The government and people need to have a conversation about radiation terrorism before the next attack. The easiest way for such a conversation to take place is through solid reporting and discussion by the news media — discussion focused on the science instead of hype and scary language.

Britons were well served by the reporting on Mr. Litvinenko’s death, and there was little panic. Americans in London on a brief visit at the time were not well informed, as they demonstrated by sending us frantic e-mail messages asking, “Am I going to die?” Our friends weren’t going to die from the attack on Mr. Litvinenko, but one day Americans could be the victims of a larger scale radiation attack, and many could die.