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Period: to
German physicist Wilhem Roentgen and French physicist Henri Becquerel
They have been working on radioactivity before Marie and Pierre joined their research. -
Period: to
Marie and Pierre worked together investigating radioactivity.
The Curies joined Roentgen and Becquerel's research -
Announced the discovery of Polonium
The Curies discovered a new chemical element -
Announced the discovery of Radium
The Curies discovered another chemical element