When was radium discovered by Marie Curie and Pierre Curie?

Marie Curie, Pierre Curie, and their assistant G. Bémont announced the discovery of radium in December 1898.12

The discovery occurred after Marie Curie observed that the radioactivity of pitchblende was significantly higher than could be explained by its uranium content alone. By using a new method of chemical analysis controlled by quantitative measurements of radioactivity, the team successfully identified the presence of the new element. While its existence was confirmed in 1898, it was not until 1902 that Marie Curie succeeded in preparing the first decigram of pure radium salt, and she later isolated the metal itself in 1910 with André-Louis Debierne.12