The Ideal Poison for Espionage

The first signs of contamination were the traces of radiation on the laboratory desk of Israeli physicist Dror Sadeh, who was experimenting with an exotic radioisotope called polonium-210.

Sadeh, part of Israel's nuclear program in the 1950s, had taken what he thought were adequate precautions against the hyperactive element. But it wasn't enough: Radiation was discovered "in my private home, and on my hands too and on everything that I touched," he wrote in his diary.

Within a month, one student who worked in Sadeh's lab at the Weizmann Institute of Science was dead from leukemia. When the lab's supervisor died a few years later, Sadeh suspected that he, too, had been contaminated by the leaky polonium-210.

In the century since its discovery by famed French scientists Marie and Pierre Curie, polonium-210 has left a distinctive trail of death. The Curies' daughter, Irene Joliot-Curie, succumbed to leukemia in 1956, 10 years after a sealed capsule of polonium-210 accidentally was broken in her laboratory at the Radium Institute in Paris.

Its latest victim is retired KGB agent Alexander Litvinenko.

For most of polonium's history, death has been a consequence of ignorance. Scientists suspected its radioactivity presented a health risk, but they failed to understand its intricacies.

Engineers have struggled to find a use for the isotope, incorporating it for a time in spark plugs, nuclear warhead triggers and spacecraft power supplies. It plays a small role today as an anti-static agent for printing presses.

Assassins finally may have hit upon its most effective use. "The scientific community is intrigued [by Litvinenko's murder]," said radiation biologist David Dooley, who studied exposure levels in workers who produced polonium for the Manhattan Project to develop the atomic bomb. "It's pretty clever they came up with this."

In many ways, polonium-210 is an ideal poison for espionage -- deadly and undetectable. Pound for pound, polonium-210 is at least 1 million times more toxic than hydrogen cyanide, the poison used to execute prisoners in gas chambers, according to medical toxicology books. Radiation safety experts calculate that a single gram of polonium could sicken 100 million people, killing half. But it is extremely hard to get. Only about 100 grams are produced each year, primarily by Russia. While most radioactive elements emit gamma rays, which register on radiation detectors, polonium-210 instead emits an alpha particle -- composed of two protons and two neutrons -- as it decays.

Unlike other radioactive elements, polonium-210 is relatively safe to transport. Although highly lethal gamma rays pass through most substances, alpha particles can be blocked by a sheet of paper or the thin layer of dead cells on the surface of the skin. To kill, polonium must be inhaled or ingested so that it is in direct contact with healthy tissue. "I could put it in a tiny Ziploc bag, and I would be fine," said Dooley, president and chief executive officer of MJW Corporation in New York.

The first death occurred in 1927. The victim was Nobus Yamada, a Japanese researcher who had joined Marie Curie's lab. In 1924, he worked with Curie's daughter Irene to prepare polonium sources. After returning home the next year, Yamada fell ill. "There was a poisoning from the emanations," he wrote Irene, according to Susan Quinn, author of "Marie Curie: A Life."

Marie and Pierre Curie discovered polonium while they were searching for the cause of excess radiation in a uranium-rich ore called pitchblende.

In 1898, they traced the radiation to a substance that they dubbed radium-F. When Marie Curie determined that it was a unique element, she named it polonium to bring attention to the plight of her homeland, Poland, which had been partitioned among Russia, Prussia and Austria.

There are 25 different isotopes of the element, but polonium-210 is the most stable. After 138 days, half of it decays into a nonradioactive isotope of lead. It takes 10 half-lives -- about three years -- for all of it to be converted into lead.

In the process, it emits a significant amount of heat. A one-gram lump will reach more than 260 degrees Celsius.

As a product, polonium-210 has been mediocre at best.

Its first use was in automobile spark plugs. The alpha particles emitted during its decay supposedly helped produce a stronger spark, according to a 1929 patent issued to J.H. Dillon of Firestone Tire and Rubber. The company began marketing the plugs in 1940, but their benefits were never proved.

Polonium-210 played a key role in World War II. Manhattan Project engineers alloyed the isotope with beryllium and used it to produce the neutrons that triggered the atomic bomb's chain reaction. Because of polonium's short half-life, the nuclear triggers lost their effectiveness in two years and had to be continually replaced. By the 1970s, engineers abandoned it in favor of the hydrogen isotope tritium, with a half-life of 12.3 years.

Polonium was considered as a power source for U.S. satellites, but its short half-life again limited its utility, and plutonium was used instead. The Soviet Union, however, did employ polonium to keep its Lunokhod moon rovers running in the 1970s.

Engineers finally found a viable use for it in printing plants and textile mills, capitalizing on its electron-grabbing ability to neutralize the static electricity generated by moving sheets of paper or fabric. It also is used in photo labs, embedded into the bristles of cleaning brushes to counter the static electricity that causes dust to cling to pictures.

Polonium-210 theoretically could be extracted from the foil or the brushes in a quantity sufficient to poison someone, Emsley said, but it would require a sophisticated knowledge of chemistry and a well-equipped laboratory.