Fanny Cook Gates (26 April 1872 – 24 February 1931) was an American physicist, an American Physical Society fellow and American Mathematical Society member. She made contributions to the research of radioactive materials, determining that radioactivity could not be destroyed by heat or ionization due to chemical reactions, and that radioactive materials differ from phosphorescent materials both qualitatively and quantitatively.More specifically, Gates showed that the emission of blue light from quinine was temperature dependent, providing evidence that the emitted light is produced from phosphorescence rather than radioactive decay. She also served as head of the Physics department at Goucher, Professor of Physics and Dean of Women at Grinnell College, and the Dean of Women at the Universi