Quote Originally Posted by zxc View Post
Which means its radioactive life is 280 days. Given that he died in under 25 days after allegedly ingesting polonium, and that the alleged killer arrived from Russia to London only two days prior to the alleged poisoning, why exactly is it not possible for it to have killed him if it was in fact polonium?
Actually, given a half-life of 140 days, after 280 days approximately 3/4 (75%) will have decayed, leaving 25% still active and emitting radiation. After 420 days (i.e., 3 half-lives), about 7/8 (87.5%) will have decayed, leaving 12.5% active. (Radioactive decay is exponential; after each half-life period, about half of the remainder decays.)

Anyway, so if we assume that someone slipped some Po-210 into his food about 30 days before he died, then 30/140 means that approximately 1/5 (.2) of a half-life had expired. So using this formula:

100% / 2^(.2) = percent of polonium left after 30 days = about 87%

Meaning that about 13% of the Po-210 would have decayed in that time. Given a sufficiently large starting mass of the polonium, 13% translates to a sh*tload of alpha particles irradiating you from the inside out.

So the real question to ask is, how much Po-210 in grams would they have had to dose Litvinenko with in order for him to die of acute radiation poisoning in just 30 days (rather than dying of leukemia 5 years later, for example)?

And that's actually a question that no one knows the exact answer to -- basically because there are so few known human cases. (Besides Litvinenko's alleged poisoning, Marie Curie's daughter Irène died from accidentally inhaling polonium -- but from leukemia, a full 10 years after the laboratory accident.)

So we can only make crude estimates based on tests done with rats, and then scale up to the body weight of a typical adult man. Also the quantity needed would depend in part on the chemical form of the polonium that was given -- for example, an oxide of polonium might be absorbed by the body differently than a polonium chloride salt. But the amount, for sure, would be a tiny fraction of a milligram; perhaps a few dozen micrograms.

But again, that "10-50 micrograms" estimate is assuming that you're trying to cause extremely acute radiation poisoning that will kill someone within the course of several weeks -- you'd need much less than a microgram of Po-210 if you simply wanted to increase someone's odds of developing leukemia.