Niels Bohr

Niels Henrik David Bohr was a Danish physicist, born October 7, 1885 in Copenhagen and died November 18, 1962 in the same city, whose model of the atom and later work on nuclear fission underpin the physical basis of nuclear energy. After earning his doctorate in 1911, he proposed in 1913 that an atom's electrons occupy discrete energy levels and jump between them rather than spiraling continuously into the nucleus, a model that reshaped atomic physics, and in 1921 he founded the Institute of Theoretical Physics in Copenhagen, later renamed the Niels Bohr Institute. He received the 1922 Nobel Prize in Physics for his investigation of atomic structure and radiation. Working from his own liquid drop model of the nucleus, Bohr correctly identified uranium-235, rather than the far more common uranium-238, as the isotope responsible for fission triggered by slow neutrons, an insight central to understanding how a nuclear chain reaction could be sustained. After fleeing Nazi-occupied Denmark in September 1943, he joined the Manhattan Project's British mission, where he contributed ideas on modulated neutron initiators for the atomic bomb.