Sunday, November 26, 2006

210Po

Last week, the former Russian spymaster Alexander Litvinenko was killed by radiation poisoning after ingesting a dose of 210Po. I am not qualified to comment on the political ramifications of this radiological attack, I can give the bare-bones information on 210Po.

There are three basic ways to make short-lived radionuclides here on Earth. The first is to collect the short-lived intermediate decay products of Th or U isotopes, which undergo complex decay chains from the relatively stable initial isotopes, through increasingly unstable decay products, to Pb, which is stable. The second is to fission a heavy nuclide into unstable daughter products. The third is to irradiate a stable or long-lived nuclide such as 39K, 238U or 59Co in a reactor or particle accelerator to produce a less stable daughter, like 39Ar, 239Pu, or 60Co.

210Po -> 206Pb is the final decay in the 238U -> 206Pb decay system. As such, it is present in natural uranium ore in concentrations that are inversely proportional to the ratio of the decay constants of 210Po and 238U . This ratio is about 8.6x10-11. So for every kg of U in natural ore, there is 86ng of 210Po. (alternatively, that is 86ug/ton).

There have been reports that the soviets stockpiled 210Po during the cold war. While this may be true, it is unlikely that this is the source for the poison used today. 210Po has a half life of 138 days, and the cold war ended about 5800 days, or 14 210Po half-lives, ago. Thus essentially all of a cold war stockpile would have disappeared by now.

There are several options for 210Po generators, including 210Pb (half-life 22 years), and 226Ra (half-life 1600 years). In fact, polonium was originally discovered by Marie & Pierre Curie, after their isolation of Radium.

210Po can also be formed by neutron irradiation of 209Bi, at least according to Wikipedia. It is not abundant in spent nuclear fuel.

Anyway, the point of all this is that whoever killed the guy must have had access to either a reactor, a supply of the highly radioactive isotopes 226Ra or 210Pb, or an industrial scale U processing facility and a chemistry lab that can deal with serious amounts of radiation. It is way more sophisticated than stealing a spent fuel rod or a medical radiation source, and thus is considerably more worrisome than a mere dirty bomb. This radiological attack was obviously perpetrated by someone who knew what they were doing, and had access to some serious infrastructure.

4 comments:

Anonymous said...

I have a question. Why 210Po? Surely there are lots of other, more readily available radioisotopes with which to poison someone that do not scream out state involvement at some level...

Lab Lemming said...

Why poison people at all? Why not just live together in peace and harmony?

In my lab, I only poison undergrads and OSHA inspectors, so it is hard for me to really understand the mindset.

If I had to go out on a limb, though, I would guess that it relates to the fact that this particular isotope has only an alpha decay to a stable daughter, so there are no betas or gammas to set off airport radiation detectors (safer to carry, too).

Chris said...

210Po is available in commercial products such as fire alarms and antistatic brushes. According to a news story I read at the time, some brushes have 50X lethal dose.

In these products, it's in a form that's difficult to ingest. But I bet it's easier to extract it from those products than to gain access to a reactor etc.

Chris

Lab Lemming said...

Fire alarms contain Americium, not 210Po. Since 210Po has a half life of only half a year or so, any fire alarm that required it would need to be replaced on a regular basis.

The question is not whether or not one can buy what is considered a lethal dose via your news story (were their calculations transparent?); the question is whether or not you could buy an ammount equal to that actually used in the attack. The calcs I've seen online suggest that you would need something like several thousand record cleaners to do that.