Marie Curie theory of "radioactivity" (a term that she coined), techniques for isolating radioactive isotopes, and the discovery of two elements, polonium and radium. Under her direction, the world's first studies into the treatment of neoplasms were conducted using radioactive isotopes. She founded the Curie Institutes in Paris and in Warsaw, which remain major centres of medical research today. During World War I, she developed mobile radiography units to provide X-ray services to field hospitals. While a French citizen, Marie Skłodowska Curie, who used both surnames, never lost her sense of Polish identity. She taught her daughters the Polish language and took
Marie Curie and agreed to furnish a new laboratory, but it would not be ready until 1906. In December 1904, Curie gave birth to their second daughter, Ève. She hired Polish governesses to teach her daughters her native language, and sent or took them on visits to Poland. On 19 April 1906, Pierre Curie was killed in a road accident. Walking across the Rue Dauphine in heavy rain, he was struck by a horse-drawn vehicle and fell under its wheels, causing his skull to fracture. Curie was devastated by her husband's death. On 13 May 1906 the physics department of the University