The Nobel Prize in Physics 1950
Cecil Frank Powell
Born: 5 December 1903, Tonbridge, United Kingdom
Died: 9 August 1969, Italy
Affiliation at the time of the award: Bristol University, Bristol, United Kingdom
Prize motivation: "for his development of the photographic method of studying nuclear processes and his discoveries regarding mesons made with this method"
Field: particle physics
Photographic emulsions can be used as particle detectors because tracks of charged particles can be examined after development. Cecil Powell made improvements to the technique in order to study radiation and nuclear interactions. With emulsions at high altitude, he discovered in 1947 that in reactions between incident cosmic ray particles and nuclei in the emulsion, short lived particles were produced. These particles turned out to be pi-mesons, the particles proposed by Yukawa to mediate the strong interaction between protons and neutrons in nuclei.