Cecil PowellProfessor

Charged particles moving through photographic emulsions leave tracks that can be examined in the images developed afterward. Cecil Powell made improvements to this technique in order to study radiation and nuclear reactions. In 1947 he discovered that incident cosmic ray particles could react with atomic nuclei in the emulsion, creating other, short-lived particles. These particles turned out to be pi-mesons, the particles proposed by Hideki Yukawa as mediating the strong force binding protons and neutrons in nuclei.