Discovery of polonium

In spring 1898 Marie Curie had a puzzle: pitchblende gave off more radiation than its uranium could explain. She guessed that an unknown, intensely active element was hiding inside it in tiny amounts. Pierre set aside his work on crystals to join her.

They ground up pitchblende and put it through the ordinary steps of chemical analysis, measuring the radiation of every fraction with the electrometer. It was a new way of doing chemistry, with the radiation itself as the guide. The activity gathered with bismuth. The new substance behaved almost exactly like bismuth, but was about four hundred times more active than uranium.

On 18 July 1898 their note to the Académie des sciences proposed: "If the existence of this new metal is confirmed, we propose to call it polonium, from the name of the country of origin of one of us." Poland was then divided between Russia, Prussia and Austria, so the name was a quiet political act. The same note is generally cited as the first printed use of the word radio-active.

Polonium proved fiendishly hard to purify. It loses half its activity in 138 days, and Marie Curie never isolated it pure.