Polonium and Radium
Curie now expanded her search for other "Becquerel-ray emitting" compounds using pitchblende from Joachimstal, Austria, and found the element thorium to have the same emission characteristics as uranium. She coined the term "radioactivity" to describe this property. Her next hypothesisthat certain complex materials, such as pitchblende, achieved their high radioactivity from the presence of additional as yet unknown elementsmust now be tested by isolating such elements.
Pierre Curie joined Marie in the next stage of the task where various chemical extraction techniques were used to separate the components of pitchblende. His electrometer was again used to measure radioactivity in the resulting fractions. From this work, in 1898, the Curies reported the existence of two new, separate elements that they named polonium and radium.