One of the most interesting news stories of last year was the Alexander Litvinenko poisoning - the apparent assassination of a vocal critic of the Russian Federal Security Service (FSB), and the first known human poisoning using the radioactive isotope, Polonium-210. So what is this Polonium, anyway?

History

Polonium itself was first discovered in 1898, by the legendary Marie and Pierre Curie. She named it after her native Poland. Fun fact: Poland wasn’t actually an independent country at the time; this may be the first time in history a chemical has been named specifically to draw attention to a political struggle.

There are 25 different radioactive isotopes of Polonium; the one we’re interested in is Polonium-210. A sample of Po-210 has a half-life of 138 days; that is, 138 days from now it’ll be half as radioactive as it is at the moment. In 276 days, it’ll be one-quarter as radioactive as it is now.

What does it do?

Polonium-210 is an alpha particle emitter; it fires helium-4 nuclei (two protons, two electrons) at roughly 53,962,642 kilometres per hour. Luckily these are fairly light; the layer of dead skin on the outside of the human body can absorb them without letting them cause any harm to the living tissue beneath. The trouble begins when Polonium gets inside the body, either through inhalation, or ingestion.

Once inside the body, the alpha particles that Po-210 launches strike nearby cells, often punching through several before coming to rest. The particles cause ionisation of surrounding tissue; in which atoms gain or lose an electron. This in turn can cause unwanted chemical reactions and interfere with DNA, causing normal cell replication to fail, or even cancer. While cells can repair some damage to DNA, there are limits on this; and if a cell cannot repair the damage and cannot replicate, it will die (”Apoptosis“).

As the polonium spreads throughout the body, it causes damage to a progressively wider range of cells. Some of these cells are less radiation-tolerant than others; these tend to die first. This includes red blood cells, used to transfer oxygen around the body; and white blood cells, which fight infection. Since the Po-210 will keep emitting radiation for months (potentially years) the damage is ongoing.