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1936-01-01
Contributions to nuclear physics
In the early 1930s Bohr was soon to realize that the most exciting questions in theoretical physics were in the process of moving from the outer part of the atom to its nucleus. Not only did he promptly change priorities for his institute, but his personal research and publications changed as well.
In 1936 Bohr proposed the ‘compound nucleus' model, according to which the nucleus during a reaction transfers to a temporary and unstable ‘compound' state before reverting to a stable state after the reaction is completed.
In 1937, seeking to decipher the nuclear energy spectrum, Bohr and his young Danish collaborator Fritz Kalckar proposed the liquid drop model of the nucleus, thus underlining further the difference between the nuclear and the atomic systems.
Incidentally, Bohr's early research as a university student, for which he received the Gold Medal of the Royal Danish Academy of Sciences and Letters in 1907 and which concerned the experimental and theoretical study of water jets, may have helped inspire Bohr to propose the nuclear drop model some thirty years later.
In December 1938 Lise Meitner and her nephew Otto Robert Frisch interpreted, on the basis of Bohr's insights, experiments by Otto Hahn and Fritz Strassmann in Berlin to imply that the nucleus had been split into two parts of nearly equal size - a very radical proposition at the time soon to be termed ‘fission'.
This started a frantic research effort on both sides on the Atlantic, as part of which Bohr at an extended visit to Princeton contributed substantially to the theoretical understanding of fission together with his younger colleague and previous visitor to Bohr's institut, John Wheeler.
(Written by Finn Aaserud, director, Niels Bohr Archive)