Polonium

Category: metalloid Atomic number: 84 Colour: silvery grey Melting point: 254°C (489°F) Boiling point: 962°C (1,764°F) First identified: 1898

Marie Curie didn’t discover radioactivity – X-rays had been identified in 1895 by Wilhelm Röntgen, and uranium radiation in 1896 by Henri Becquerel, who she would go on to work with. However, she did coin the term and did a great deal, together with her husband Pierre, to expand our understanding of this phenomenon.

The extraction of polonium by Marie and Pierre was a tricky undertaking. They were exploring the radioactive ore pitchblende (now known as uranite), which contains uranium but seemed to be more radioactive than it should be on account of that element. They managed to remove the uranium and sieved through tons of the remaining rubble to find a few crumbs of polonium, named after Marie’s native Poland.

Polonium is extremely rare, and it is uneconomical to use Curie’s method to extract it. Instead, bismuth-209 is bombarded with neutrons, which creates bismuth-210, which in turn decays to form polonium. It can be classed as a metal rather than metalloid, as its electrical conductivity falls at high temperatures – a quality that means it can eliminate static electricity in some industrial processes. It has a short half-life, which means it generates a lot of heat. This has been exploited as a way to generate thermoelectric power in satellites and lunar vehicles, such as the Russian ‘Lunokhod’ rovers that explored the moon’s surface.

Murder by Polonium

The murder of the Russian ex-agent Alexander Litvinenko in 2006 was carried out using a small amount of polonium – it emits alpha particles (containing protons and neutrons) that are weakly penetrating, so it is a relatively safe substance to (for instance) carry in a small container. However, if polonium is ingested, the same radiation becomes extremely dangerous as it attacks cells within the body by being absorbed into them, and this was what killed the unfortunate Litvinenko.