Hiroshima and Nagasaki apart, there have been very few deaths from acute radiation poisoning. Thirty-one firemen, engineers and others at Chernobyl; two physicists who fumbled when handling a sphere of plutonium at Los Alamos, one in 1946 and one in 1947; and a few others, including some contaminated by contact with illegally dumped radiation sources, are the only people to have been lethally irradiated in a non-medical setting. Alexander Litvinenko joins them. But his death from polonium-210 is unprecedented. This is the first time – to our knowledge – that someone has been deliberately killed by the administration of a radioactive substance.

Marie and Pierre Curie discovered polonium in 1898. They separated tiny amounts from pitchblende, a black mineral dug from the Joachimsthal silver mine in Austria-Hungary. Polonium remained a rarity until the Manhattan Project. The alpha particles it gave off generated neutrons when they struck other elements. Neutrons were needed to detonate a plutonium atom bomb with maximum yield; a device that mixed polonium and beryllium provided them in the right amounts. It was the trigger in the Nagasaki bomb. Codenamed ‘Urchin’, one of its lead designers was Klaus Fuchs, who was later arrested, tried and imprisoned in Britain as a Soviet spy.

The processes used in polonium manufacture in the 1940s have not changed in their fundamentals. In 1943, Robert Oppenheimer assigned its production to Charles Thomas, central research director of the Monsanto chemical company. He set up a laboratory in the indoor tennis court of his mother-in-law’s large and remote estate in Dayton, Ohio. The polonium was made by irradiating slugs of bismuth metal in one of the new nuclear reactors at Hanford in Washington State. After most of the bismuth had been converted to polonium, the slugs were melted and converted into pellets by sieving them into water. They were then dissolved in aqua regia, a mixture of concentrated nitric and hydrochloric acids. After more manipulation, the polonium was plated by electricity onto platinum. It was so radioactive that when concentrated it destroyed some of the chemicals in which it was dissolved. Because of recoil from the alpha particles that shot out from it, it moved and contaminated everything it came into contact with. The best that could be said is that it glowed in the dark with a blue light. So it is absolutely certain that the polonium that killed Alexander Litvinenko was not made in a bed-sit or garage or even in a well-equipped university or chemical company lab.

The British learned about polonium the hard way in their own atom bomb programme in the late 1940s. They had no information about how the Americans purified it, and the McMahon Act passed by Congress in 1946 meant that they couldn’t get any. They made it in the two Windscale Piles, the air-cooled nuclear reactors in Cumbria. The laboratory there suffered serious contamination and some of the staff had to be taken off the work for a time because of polonium ingestion. No doubt the knowledge acquired then is suddenly coming in useful.

In 1957, Windscale spread polonium-210 about again, when Pile No. 1 caught fire on the afternoon of Thursday 10 October and burned for a day. The wind was in the west and polonium was detected in northern Europe very quickly. Its detection there drew little attention, but its omission from some of the lists of radioactive substances that had escaped into the environment later drew accusations of a cover-up. Its use in atom bombs was being phased out at the time and it was said that the British didn’t want to be accused of being old-fashioned by admitting that they were still using it.

Replacement of ‘Urchin’ bomb triggers with other devices means that since the early 1950s the need for countries with mature nuclear weapons technology to make lots of polonium routinely has diminished. In small amounts it has industrial uses: securely sealed it is anti-static; spark plugs that incorporate it are said to be better at cold-starting an engine. But polonium-210 does not keep. Its half-life of 138.4 days means that its radioactivity will have fallen by 99 per cent within two and a half years of its manufacture. So, more likely than not, Alexander Litvinenko’s murder weapon was made to order. You’d need access to a nuclear reactor or a cyclotron to irradiate highly purified bismuth (probably welded into aluminium cans for ease of handling), and a ‘hot lab’ designed for processing radioactive materials. And much thought must have gone into the means of delivery. Polonium-210 is five thousand times more radioactive than radium: a few specks are lethal. But the alpha particle radiation can be stopped by a piece of paper, so it has to be got into the body.

Once ingested, the polonium gets widely distributed. It is now in intimate contact with cells close enough for alpha particles to kill them. Getting the lethal specks into Litvinenko was not a trivial enterprise. They could have been shot into him using an umbrella, Bulgarian-style. We have no evidence of that. The likeliest route was in food or drink. Coating the specks in a soluble capsule and camouflaging them as grains of salt or crystals of brown sugar would do nicely. The coating would protect the assassin from contamination. Transporting the polonium into the UK in such a form would be completely risk-free. These would be easy parts of the plot. The coated specks would have to be designed and doses calculated. Experiments in a hot lab would be needed to get the process right.

It is too early to say whether those responsible for Alexander Litvinenko’s end intended its cause to be discovered. A lingering death caused by a painful poison unknown to science sends out a powerful message. But not as strong as one caused by radioactivity. Nuclear fear is deeply etched into our souls. It is doubtful whether Cobra, the cabinet committee for co-ordinating crisis management, would have met several times if Litvinenko had been shot or stabbed. The head of the Health Protection Agency has never been on television so much.

Polonium has been found at several places in London and in planes that have flown the Moscow run. The levels haven’t been announced; the reassurances given indicate that they are low, but bigger than those occurring naturally. If the poisoning was with a massive dose, which seems pretty certain, enough would come out in Litvinenko’s sweat and saliva to contaminate his hands. Anyone shaking them would go on to contaminate door handles, balustrades, seatbelts and so on. At each step, the polonium would be diluted, but detection methods are sensitive enough to cope. The only really big threat to the public from the polonium that poisoned Litvinenko would come from eating his faeces or drinking his urine.

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