Polonium the Curies while they were investigating the cause of pitchblende radioactivity. Pitchblende, after removal of the radioactive elements uranium and thorium, was more radioactive than the uranium and thorium combined. This spurred the Curies to search for additional radioactive elements. They first separated out polonium from pitchblende in July 1898, and five months later, also isolated radium. German scientist Willy Marckwald successfully isolated 3 milligrams of polonium in 1902, though at the time he believed it was a new element, which he dubbed "radio-tellurium", and it was not until 1905 that it was demonstrated to be the same as polonium.
Isotopes of polonium Isotopes of polonium Polonium (Po) has 33 isotopes, all of which are radioactive, with between 186 and 227 nucleons. Po with a half-life of 138.376 days has the longest half-life of naturally occurring polonium. Po with a half-life of 125 years has the longest half-life of all isotopes of polonium. Po and Po (half-life 2.9 years) can be made through the alpha, proton, or deuteron bombardment of lead or bismuth in a cyclotron. Po is an alpha emitter that has a half-life of 138.376 days; it decays directly to stable Pb. A milligram of Po emits as many alpha particles