July 2, 1876 - Birth of Harriet Brooks, known for her research on nuclear transmutations and radioactivity

She was the first graduate student of Ernest Rutherford who directed her work on "Damping of oscillations in the discharge of a Leyden jar" and the first woman at McGill University to receive a master's degree, in 1901.

After receiving her degree, and under Rutherford's guidance, she conducted a series of experiments to determine the nature of radioactive emissions from thorium, which served as the basis for the development of nuclear science. She was one of the first to determine the atomic mass of radon, which had been discovered in 1900 by Friedrich Ernst Dorn.

Harriet Brooks, Robert Bowie Owens, and Ernest Rutherford, had observed variations when trying to measure the radiation from thorium oxide. Rutherford realised that thorium compounds continuously emit a radioactive gas that retains radioactive powers for several minutes. He first called this gas emanation (from the Latin "Emanare"), and then thorium emanation (Th Em).

Brooks focused on the case of thorium (a solid radioactive metal), analysing the emanations of this element. At the time, different theories postulated that this material was a gas, a vapour, or a very fine powder. Brooks showed that it was a gas with a molecular weight significantly lower than that of thorium, so it could not simply be a gaseous form of the same element. Her discovery led Rutherford and other scientists to conclude that with radioactivity, one element had become another. She was the first to characterise the gas we now call radon.

If you want to know more about this scientist, please click on the following link: Harriet Brooks