Radioactive metal that killed Litvinenko

Polonium-210 is one of the many radioactive isotopes of polonium, an element that occurs naturally in very low concentrations in the Earth's crust. It emits high-energy alpha particles which can damage and destroy living cells once the substance is ingested. Outside the body it is not a significant health hazard and particles can be blocked by the outer surface of the skin.

The isotope emits so many alpha particles that a capsule containing just half a gram of it would reach a temperature of about 500C. Amounts no bigger than a pinch of salt would be enough to cause acute radiation poisoning if ingested.

It takes 138 days for polonium-210 to decay to half of its activity levels. Once in the body, however, the biological half-life of polonium-210 is about 50 days. This suggests that the body of Alexander Litvinenko should still contain some amounts of the element. However, the bulk of the dose will have been excreted. Once ingested, polonium-210 is widely distributed in the soft tissues of the body, including the bone marrow.

It is mainly used industrially to eliminate static electricity generated in manufacturing processes such as rolling paper. The normal method of making polonium-210 in sufficient quantities so as to be useful is to produce it artificially in a nuclear reactor.

Polonium was the first element discovered by Marie Curie in 1898 while searching for the cause of radioactivity of pitchblende ore, which contained uranium.