Polonium 210 and the Russian spy

Former KGB agent Alexander Litvinenko died in hospital in London last night after suffering the effects of alleged poisoning. Mr Litvinenko fell ill after leaving a sushi bar in Piccadilly, central London and was admitted to hospital with progressive multi-organ failure. In a letter, drafted before his death, Mr Litvinenko accuses Russia's president Vladimir Putin of being behind his poisoning.

Mr Litvinenko was a former KGB-agent who fled to the UK and became a British citizen earlier this year. Initially, he was thought to have been poisoned with the heavy metal thallium, but it was now revealed that polonium, a radio-active element, was found in his system. Three other locations in London have been shown to also be contaminated with this substance.

The isotope polonium-210 (chemically referred to as 210-Po) is only harmful if ingested. The particles it emits on degrading are so-called alpha particles (basically helium atoms minus electrons) which cannot penetrate the skin. It is extremely harmful once ingested. A report today states that those behind the murder of Mr Litvinenko balanced the dose of 210-Po quite carefully. A huge overdose would cause him to collapse and die, but a lesser dose would see him dead, but leave the culprits time to cover their tracks.

During Mr Litvinenko's illness, fingers were pointed at Mr Putin, who used to be head of the KGB in the Soviet era. He has categorically denied any involvement, and reports on news-feeds quote him as saying that Mr Litvinenko's death was not unnatural and that his unfortunate demise is used as a pretext for stirring up trouble for Russia. His remarks were made before the discovery of 210-Po was made.