1902

Polonium and Radium

Antoine-Henri Becquerel (1852–1908), Pierre Curie (1859–1906), Marie Salomea Skłodowska Curie (1867–1934)

The 1890s was a period of great tumult in physics and chemistry. The discovery of radio waves and then X-rays prompted new areas of research, among them French physicist Antoine-Henri Becquerel’s attempt to determine whether the luminescence of some minerals could be connected to X-rays. In 1896, he found that uranium salts could expose photographic plates by themselves, without any energy source, which meant that uranium compounds were emitting another undiscovered form of radiation.

Polish-French physicist and chemist Marie Curie, who immigrated to Paris to study physics and mathematics, and her husband, French physicist Pierre Curie, the head of a research laboratory studying magnetism and crystals, were two of the most productive and fearless explorers of these new phenomena. Becquerel’s reports caught Marie’s attention, and she began a systematic search for more such substances. She found that other elements such as thorium gave off the same kind of radiation, and regardless of their chemical form, the amounts of uranium or thorium in a sample determined its radioactivity.

The mineral pitchblende, however, was much more radioactive than could be explained by its uranium content, which led Marie to examine it for unknown radioactive elements. Painstaking work led to the isolation of a new metal, for which the Curies proposed the name polonium (for Marie’s native Poland). Another new element was isolated several months later, which they called radium. Proving the new elements’ existence required isolating them from tons of pitchblende—a massive effort. The Curies worked for the next few years in an unheated (and uncooled) shed, finally isolating useful amounts of both elements in 1902. Marie’s resulting doctoral dissertation, the most famous in chemical history, was the basis for two Nobel Prizes.

It all came at a cost. Both Curies were severely affected by radiation. Their lab notebooks are hazardous material, stored in lead-lined boxes and examined only while wearing protective clothing. They will be dangerous for centuries to come.

Marie and Pierre Curie in the lab. It is safe to assume that everything in this photograph was at least mildly radioactive, including both Curies.