What was the title of Marie Curie's doctoral thesis?

Marie Curie's doctoral thesis was titled Recherches sur les substances radioactives, usually translated as Research on Radioactive Substances. She submitted it to the University of Paris, now the Sorbonne, in 1903.

The thesis grew out of her investigation of the radiation discovered by Henri Becquerel in uranium salts. Curie measured the ionizing effects of different materials and showed that radioactivity was not limited to uranium. Her results supported the revolutionary idea that radiation came from atoms themselves. During this period, she and Pierre Curie also investigated pitchblende and discovered the elements polonium and radium.

Curie was awarded her doctorate in June 1903 under the supervision of Gabriel Lippmann. The thesis was completed before she received the Nobel Prize in Physics later that year, which she shared with Pierre Curie and Becquerel. The title is sometimes shortened informally in English, but alternatives such as “Thesis on Radium” or “On Radioactivity” are not the official title. Her doctoral work helped create the scientific field of radioactivity and became a foundation for later nuclear physics and medical applications of radiation.