(Henrik David) (1885-1962) Danish physicist. His theoretical work produced a new model of atomic structure, now called the Bohr model, and helped establish the validity of quantum theory. He also explained the process of nuclear fission. Nobel Prize for Physics 1922.
Bohr’s first model of the atom was developed working with Ernest Rutherford at Manchester, UK. He was director of the Institute of Theoretical Physics in Copenhagen from 1920. During World War II he took part in work on the atomic bomb in the US. In 1952 he helped to set up CERN, the European nuclear research organization in Geneva. He proposed the doctrine of complementarity: that a fundamental particle is neither a wave nor a particle, because these are complementary modes of description.
Bohr was born and educated in Copenhagen. In 1911 he went to the UK to study at the Cambridge atomic-research laboratory under J J Thomson, but moved 1912 to Manchester to work with New Zealand physicist Rutherford. Bohr developed models of the atom in which electrons are disposed in rings around the nucleus, a first step toward an explanation of atomic structure.
In 1913 Bohr developed his theory of atomic structure by applying quantum theory to the observations of radiation emitted by atoms. The authorities in Denmark made him a professor 1916 and then built the Institute of Theoretical Physics for him. Leading physicists from all over the world developed Bohr's work there, resulting in the theories of quantum and wave mechanics that more fully explain the behavior of electrons within atoms. Bohr's atomic theory was validated 1922 by the discovery of an element he had predicted, which was given the name hafnium.
In 1939 Bohr proposed his liquid-droplet model for the nucleus, which explained why a heavy nucleus could undergo fission following the capture of a neutron. Working from experimental results, Bohr was able to show that only the isotope uranium-235 would undergo fission with slow neutrons.
When Denmark was invaded by Nazi Germany, Bohr took an active part in the resistance movement. In 1943, he escaped to Sweden and on to the US. After working on the atomic bomb, he became a passionate advocate for the control of nuclear weapons.

(1922-) Danish physicist who produced a new model of the nucleus of the atom 1952, known as the collective model. For this work, he shared the 1975 Nobel Prize for Physics. He was the son of Niels Bohr.
Aage Bohr was born and educated in Copenhagen. During the German occupation of Denmark in World War II, he worked in London 1943–45. From 1946 he worked at his father's Institute of Theoretical Physics in Copenhagen, and became professor of physics at the University of Copenhagen 1956. He was director of the Niels Bohr Institute (formerly the Institute of Theoretical Physics) 1963–70 and director of Nordita (Nordic Institute for Theoretical Atomic Physics) 1975–81.
Aage Bohr, Ben Mottelson, and James Rainwater shared the 1975 Nobel Prize for “the discovery of the connection between the collective motion and the particle motion in atomic nuclei and the development of the theory of the structure of the atomic nucleus, based on this connection”. Rainwater had suggested the theory 1950 and Bohr and Mottelson obtained experimental results that proved it.
The work of these three people paved the way for nuclear fusion.