III.

Research on Radioactivity

From 1896 the Curies worked together on radioactivity, building on the results of German physicist Wilhelm Roentgen, who had discovered X-rays, and French physicist Antoine Henri Becquerel. Becquerel had discovered that uranium salts emit similar, unusual radiation, and Marie Curie turned to investigating whether any other elements emitted these rays. She discovered that the metallic element thorium also emits radiation and found that the mineral pitchblende emitted much stronger radiation than its uranium and thorium content could account for. She coined the term radioactive for the substances that gave off these rays.

The Curies then carried out an exhaustive search for the substance that could be producing the radioactivity. They processed an enormous amount of pitchblende, and performed repeated operations to separate it into its chemical components. Finally, they obtained a few hundredths of a gram containing the source of the radiation. In July 1898 they announced the discovery of a new chemical element, which they named polonium after Marie Curie’s homeland. The discovery of the element radium followed in December 1898. They eventually prepared 1 g (0.04 oz) of pure radium chloride from 8 metric tons of waste pitchblende from Austria. They also established that beta rays (now known to consist of electrons) are negatively charged particles.

In 1903 the Curies and Becquerel were awarded the Nobel Prize in physics for their fundamental research on radioactivity. Marie Curie went on to study the chemistry and medical applications of radium, and in 1911 she was awarded the Nobel Prize in chemistry in recognition of her work in discovering radium and polonium and in isolating radium.

In 1906 Marie took over Pierre Curie’s post at the Sorbonne after he was run over and killed by a horse-drawn carriage. She became the first woman to teach there, and she concentrated all her energies into research and caring for her daughters. The Curies’ older daughter, Irene, later married Frédéric Joliot and became a famous scientist and Nobel laureate herself (see Irene Joliot-Curie; Frédéric Joliot-Curie). In 1910 Marie worked with French chemist André Debierne to isolate pure radium metal. In 1914 the University of Paris built the Institut du Radium (now the Institut Curie) to provide laboratory space for research on radioactive materials.