Polonium — deadly, hard to make and rare poison

Polonium 210, the highly toxic radioactive isotope found in the body of poisoned former Russian spy Alexander Litvinenko is a very rare, exotic material that is difficult to obtain, scientists said on Friday.

Britain's Health Protection Agency (HPA) said Litvinenko, who died on Thursday in a London hospital, had a significant amount of the radioactive isotope in his body.

But how it got there and where it came from is a mystery.

Although the by-product of uranium that was discovered by Polish chemist Marie Sklodowska Curie in 1898 is found in small amounts in the environment, most of it is made synthetically.

Radiation and chemistry experts say large-scale equipment, such as a nuclear reactor, would be needed to produce sufficient amounts to cause death.

"It is not as simple as the idea that somebody might have broken into a radioactivity cabinet at some local hospital and walked off with some polonium," Dr Andrea Sella, a lecturer in chemistry at University College London, told Reuters.

"You can't make this at home. This is in a different league," he added.

Although scientists would not speculate on the source of the polonium, Sella said Litvinenko's death was not the work of amateurs.

"This is not some random killing. This is not a tool chosen by a group of amateurs. These people had some serious resources behind them," he said.

Polonium-210 is a solid that can be dissolved in a solution. It is not a radiation hazard unless it is absorbed by the body by inhaling, eating or drinking it or if it gets in a wound, according to the HPA.

"It decays mainly by emitting alpha particles, which are unable to penetrate a sheet of paper and so it is not a hazard unless ingested, said Professor William Gelletly of the University of Surrey.

If radiation is going to be dangerous it has to be absorbed by the body. Long-term exposure to radiation can cause mutations and cancer. But exposure to a short, intense burst of radiation causes major damage to key control centres in cells.

Alpha particles emitted by polonium are absorbed very quickly by the body.

"An alpha particle strikes a strand of DNA. It snips it in two, which is bad news, or glues two strands together. Either way normal cell repair mechanisms may be unable to sort that out," said Sella.

"The result is that essentially the cellular command and control network (in the body) falls apart. That is what radiation sickness is all about," he added.

Professor David Ray, of the University of Nottingham, Queens Medical Centre, said even if a high dose of radiation could not be detected externally after Litvinenko was admitted to hospital, it is still possible that a fatal dose could have concentrated in deep tissues such as bone marrow.

"The limited information that has been released about Mr. Litvinenko's condition and the timing of his death is consistent with either radiation poisoning or chemicals that stop cell division," he said.

Polonium-210 also has a very short half-life. The longer the half life the less radioactivity is emitted from the material.

"Polonium 210 has a half-life of 138 days. That is long enough so you can handle it and deliver it to your target and it will pack punch. A smallish amount of material will pack a significant punch," Sella said.