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.