Powell, Cecil Frank (1903-1969)

English physicist who was awarded the Nobel Prize for Physics in 1950 for his study of the charged subatomic particles in cosmic radiation by using photographic emulsions carried in weather balloons, and for his discovery of the pion (π meson) in 1947, a particle whose existence had been predicted by Japanese physicist Hideki Yukawa in 1935.

Powell was born in Tonbridge, Kent, and studied at Cambridge, where he carried out research at the Cavendish Laboratory under Ernest Rutherford and C T R Wilson, taking photographs of particle tracks in a cloud chamber. From 1928 Powell worked at the Wills Physics Laboratory at Bristol University, becoming professor in 1948.

In 1938, instead of photographing the cloud-chamber tracks, Powell made the ionizing particles trace paths in the emulsions of a stack of photographic plates. The technique received a boost with the development of more sensitive emulsions during World War II and Powell used it in his discovery of the pion. He collaborated with Italian physicist Giuseppe Occhialini (1907- ), and together they published Nuclear Physics in Photographs (1947), which became a standard text on the subject.