Marie had taken to calling uranic rays by the more general term “Becquerel rays” after she detected them in thorium. Now she introduced an altogether original term for the ability of select heavy elements such as uranium and thorium to radiate: “radio-active” appeared for the first time in the title of the report she coauthored with Pierre, “On a New Radio-active Substance Contained in Pitchblende,” which Becquerel read to the assembled Académiciens on July 18, 1898.
