I found this in this morning's news @ nature. Just for the curious...
Al.
Unanswered questions after Russian spy poisoning
Despite intense media attention, many aspects of the death of Alexander Litvinenko remain mysterious. News@nature.com looks at what's known about the substance involved.
Jim Giles
Do you need to be an intelligence agent to get hold of polonium-210?
No. Contrary to initial reports, the radioactive substance that last month killed Alexander Litvinenko, a former Russian spy who had been living in London, could probably be obtained by someone without contacts at nuclear reactors, the sites at which polonium-210 is manufactured.
In the United States, tiny amounts can be bought from various supply companies — but one would need to buy thousands in order to amass a dangerous dose. Larger amounts of the substance are found in some commercial products, such as anti-static devices used by the plastics industry. These devices are strictly regulated and are usually only available for lease rather than purchase. Specifications available on manufacturers' websites suggest that they contain enough polonium-210 to kill someone, says Paddy Regan, a physicist at the University of Surrey in Guildford, UK.
How much was used to kill Litvinenko?
No one knows for sure, but the time he took to die — around three weeks after being admitted to hospital — gives a rough clue.
Data from survivors of the Hiroshima and Nagasaki bombs, as well as from nuclear accidents, suggest that a dose of more than 15 sieverts kills within days, as the radiation destroys gut tissue. People exposed to less than 5 Sv usually live for longer than three weeks and may even survive the initial poisoning. A dose within the range of 5-15 Sv is equivalent to the amount of radiation received by someone standing within 800 metres of the Hiroshima bomb.
If ingested, perhaps as little as one ten-millionth of a gram of polonium-210 could deliver this dose. Estimates on the lethal dose vary widely.
Why has polonium-210 been found in hotels and on planes?
Police are still investigating, but it is possible that Litvinenko spread tiny amounts of polonium-210 after being poisoned. The substance could have come out in his sweat or tears, for example.
Theories about the planes that have been grounded after finding hints of radiation on board are even more speculative. Authorities have not said what level of radiation has been detected or even whether the source is polonium-210.
If polonium-210 is found to be the source, further questions need to be answered. The substance decays by emitting alpha particles, which can be stopped by something as flimsy as a sheet of paper. If the polonium-210 was brought from Russia, as many observers have speculated, contamination could easily have been prevented by simply keeping it in a tightly sealed bottle.
Polonium - for the curious
