In 1935, Yukawa published his theory of
mesons, which explained the interaction between
protons and
neutrons at Osaka Imperial University, and was a major influence on research into elementary particles. In 1938, Yukawa received a doctorate from Osaka Imperial University for his predictions regarding the existence of mesons and his theoretical work on the nature of
nuclear forces. These research achievements were the reason he was later awarded the
Nobel Prize in Physics. In 1939, Yukawa was appointed Professor of Theoretical Physics at
Kyoto Imperial University. In 1949, he became a visiting professor at
Columbia University, the same year he received the Nobel Prize in Physics—after the discovery by
Cecil Powell,
Giuseppe Occhialini, and
César Lattes of Yukawa's predicted
pi meson in 1947. Yukawa also worked on the theory of
K-capture, in which a low energy electron is absorbed by the nucleus, after its initial prediction by
G. C. Wick. In 1946, Yukawa founded the journal
Progress of Theoretical Physics, and published the books
Introduction to Quantum Mechanics (1946) and
Introduction to the Theory of Elementary Particles (1948). In 1953, Yukawa became the first Director of the Research Institute for Fundamental Physics (now the
Yukawa Institute for Theoretical Physics), a position he held until his retirement in 1970. == Activism ==