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Poisoning Of Ex-Agent Sets Off Alarm Bells

"When they do these runs, they produce a large amount because it's got a 138-day half-life and they don't want to be making it all the time. It's not possible to maintain complete control by measurement at the source," Priest said.

Other theories suggest that the polonium that killed Litvinenko might have been obtained from an officially tracked commercial supply after it reached its final customer.

Polonium is commonly used in static eliminators in printing plants, photography labs and textile mills. In these applications, it is bound in extremely small quantities with other metals.

Extracting the substance from the molds in which these mixtures are made would be difficult because "polonium science is quite complicated," Priest said.

But with qualified scientists and the right lab conditions, it is possible. "I can see how they could be used to brew up a dose to kill one person," said Peter D. Zimmerman, a nuclear physicist and professor of science and security at King's College London. "It would require very delicate lab work."

In its pure form, polonium-210 is a soft, silvery metal. One microgram, or millionth of a gram, can be fatal, and the body of the poisoned Russian contained multiple times the lethal dose. One gram, about 0.035 of an ounce, could theoretically kill tens of millions of people.

The substance is self-heating and highly radioactive, but as long as it is housed in a sealed capsule of glass or metal, it can be safely transported in, for example, one drop of solution. It eludes radiation detectors in place at airports, border crossings and ports because it emits alpha rays, not the gamma rays the devices look for.

Polonium-210 can be dried into a substance such as chalk and turned into powder. Or it can be mixed with an aerosol solution, allowing it to be sprayed. But many scientists believe the probable method of transporting and dispensing it in the London killing was putting the isotope in a solution that could be tipped at arm's length into a drink or onto food.

"The ideal volume would be a couple of teaspoons of solution; it can sometimes be difficult to transfer a drop or something smaller," Priest said. "Once it's in the body, it irradiates the whole body."

Yet scientists in London did not discover the presence of polonium-210 until Litvinenko's urine was tested with an alpha ray detector at the Atomic Weapons Establishment, the British agency that maintains nuclear warheads. "It's so obscure that it will be among the last things people will look for," Priest said. "And except by extreme luck, there's no chance to work out in a short time what's happened, so it gives the people who did it a long time to get away."

The substance's great giveaway is that once discovered, its telltale traces are easily tracked. Out of its box, polonium smears everything. After Litvinenko's death, it was discovered in planes, cars, hotels and offices -- all places that the victim and people he met had visited around the time of the poisoning.

If it enters the body in tiny amounts, death is certain. The devastating effects were studied in the 1960s at a Moscow institute where the isotope was administered to dogs, rabbits and rats, according to Zhuikov. He said Soviet scientists wanted to understand polonium's potential in case humans were exposed to it, because the isotope was used in various applications in the country's nuclear and space programs.

The painful progression from severe vomiting and diarrhea to hair loss, internal bleeding and organ failure was clear in a photograph of a stricken Litvinenko lying in a London hospital. "If someone hates, really hates, then it's a good material [to use to] to kill," Zhuikov said. "This is real suffering."

The former agent's death has caused anti-terrorism officials to worry that an explosive or airborne dispersal of polonium, particularly in a crowded, enclosed space, could cause numerous fatalities and sow widespread panic, scientists said. Compromise a food or water supply, they said, and the consequences could be even more dire.

"You need a lot of the material," Zimmerman said. "But not more than it is reasonable to think could be diverted from the commercial stream."

The International Atomic Energy Agency is considering tighter controls on polonium.

An IAEA diplomat, who was not authorized to speak for quotation, said that in the wake of the Litvinenko case, concerns have risen at the agency about a mass poisoning through the introduction of polonium into the food chain or drinking water.

Ultimately, scientists such as Zimmerman would like to phase out polonium's commercial use and see the development of anti-static technology using other material.

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