29 November, 2012

Science behind the news: Perfect Poison?

This week the body of former PLO Leader Yasser Arafat was exhumed so that samples could be taken to determine if he was poisoned. The mysterious nature of Arafat's death in 2004 has led to much speculation, particularly among Palestinians, that he was poisoned, presumably by Israel. In July this year an investigation by Aljazeera culminated in a team of Swiss scientists announcing that they had "measured an unexplained, elevated amount of unsupported polonium-210 in the belongings of Mr. Arafat."

Polonium-210 is the same substance that was implicated in the death of former KGB agent Alexander Litvinenko who became a vocal critic of Vladimir Putin.

So what is it about Polonium-210 that makes it the 'go to' poison for modern day assassins?

Polonium-210 is unstable and decays with a half-life of 138 days into the stable daughter isotope Lead-206. As it decays it emits ionising radiation, specifically huge amounts of alpha radiation. Ionising radiation damages cells by knocking electrons off atoms creating chemically reactive and biologically damaging ions.

Ionising radiation comes in several flavours including  alpha, beta, gamma and neutrons. Alpha radiation is more ionising than beta which is more ionising than gamma. The story for neutrons is more complicated.

source: http://www.ansto.gov.au
In order to damage cells, radiation must be able to penetrate the tissue. Gamma radiation is able to penetrate deeply and requires thick barriers of concrete or lead for effective shielding. Beta radiation is stopped by sheets of metal, glass or perspex. Alpha radiation is stopped by a thin sheet of paper, several centimeters of air or the outer layer of the skin (epidermis).

The low penetration of alpha emitters makes them pretty attractive to the budding assassin. You can carry them round in a vial in your pocket without having to worry about frying your gonads, and they are not likely to be detected by airport security. However, despite their low penetration, when alpha emitters are ingested and absorbed into tissues they cause severe damage.

Slip some Polonium-210 into someone's tea and it gets taken up by the liver, kidney and bone marrow and starts to cause havoc. The first your victim knows is some nausea and other symptoms, by which time its probably too late for them to be effectively treated. As a citrate or nitrate, Polonium is also tasteless so your victim will at least enjoy their last cuppa. Even if it wasn't tasteless, they probably wouldn't notice as the lethal dose is less than one microgram.

So how do you get your hands on some of this stuff? There are incredibly small trace amounts in nature from the natural decay of Uranium but you are going to have to process a mountain of ore to get a useful amount. It is much simpler to go down to your local Russian black marketeer ask him to nick some from a nuclear reactor that uses molten lead-bismuth as a coolant.

Spy silhouetteThose of you who have been paying attention may have noticed something. I mentioned that the half of polonium-210 is 138 days, while Arafat died 8 years ago. That's 22 half-lives, so less than 1 part in 4 million of the original Polonium would remain. Detecting an amount of 'bugger all' divided 4 million sounds tricky, but the boffins reckon they are up to the task and who are we to doubt them?

It will be several months before we know the results of the tests of Arafat's body, but in the meantime, if someone in a trench coat and dark glasses offers you a cup of tea, politely decline or at least pull out your pocket Geiger counter.

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