BACKGROUND What is polonium-210 and how lethal is it?

London (dpa) - Polonium is a rare, silver-coloured metal discovered in miniscule quantities in uranium ores by French scientists Marie and Pierre Curie in 1897.Polonium-210 is one of 25 radioactive isotopes of the chemical element."Although it exists naturally, to generate useful quantities polonium-210 needs to be made in a nuclear reactor by bombarding a stable product with neutrons," the US Health Physics Society says.The isotope has several industrial uses, including tiny amounts in devices to eliminate static and dust during high-technology manufacturing processes.It decays over a half-life of 138 days, so the polonium-210 ingested by Russian exile Alexander Litvinenko in London "must have been made relatively recently" before his death in November 2006, according to the London-based Royal Society of Chemistry.The ingestion of just one microgram of the isotope, similar in size to a small speck of dust, "would certainly deliver a fatal dose of radiation," it said.Radiation from polonium-210 (Po-120) provided vital clues after it was found on several people and in several places linked to Litvinenko and the two Russian men accused by a British government inquiry of poisoning him, Dmitry Kovtun and Andrei Lugovoi.From the day he was poisoned, "Litvinenko would have excreted Po-210 in his urine, sweat and tears," the chemistry society said.Police found traces of polonium-210 at several places in London and in the German city of Hamburg, where Kovtun had lived.Kovtun told German investigators in late 2006 that he had received treatment for radiation poisoning at a clinic in Moscow.