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.
Uranium–thorium dating Uranium–thorium dating Uranium–thorium dating, also called thorium-230 dating, uranium-series disequilibrium dating or uranium-series dating, is a radiometric dating technique established in the 1960s which has been used since the 1970s to determine the age of calcium carbonate materials such as speleothem or coral. Unlike other commonly used radiometric dating techniques such as rubidium–strontium or uranium–lead dating, the uranium-thorium technique does not measure accumulation of a stable end-member decay product. Instead, it calculates an age from the degree to which secular equilibrium has been restored between the radioactive isotope thorium-230 and its radioactive parent uranium-234 within a sample. Thorium is not