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Their marriage in 1895 marked the start of a partnership that was soon to achieve results of world significance, in particular the discovery of polonium in the summer of 1898, and that of radium a few months later. Following Henri Becquerel's discovery in 1896 of a new phenomenon, which Madame Curie later called "radioactivity", she was looking for a subject for a thesis. She decided to find out if the property discovered in uranium was to be found in other matter. She discovered that this was true for thorium. .
Turning to minerals, her attention was drawn to pitchblende, a mineral whose activity, superior to that of pure uranium, could only be explained by the presence in the ore of small quantities of an unknown substance of very high activity. Her husband then joined her in the work that she had undertaken to resolve this problem and that led to the discovery of the new elements, polonium and radium. While Curie's husband devoted himself chiefly to the physical study of the new radiations, Madame Curie struggled to obtain pure radium in the metallic state. On the results of this research Curie received her doctorate of science in June 1903 and, with her husband, was awarded the Davy Medal of the Royal Society. Also in 1903 they shared with Becquerel the Nobel Prize for Physics for the discovery of radioactivity. .
The birth of her two daughters, Irene and Eve, in 1897 and 1904 did not interrupt Curie's intensive scientific work. She was appointed lecturer in physics at a prestigious academy for girls in 1900 and was there introduced to a method of teaching based on experimental demonstrations. In December 1904 she was appointed chief assistant in the laboratory directed by her husband. .
The sudden death of Curie's husband on April 19, 1906, was a bitter blow to her, but it was also a decisive turning point in her career. Because of this she was able to devote all her energy to completing alone the scientific work that they had undertaken.
