agen. He was the son of a physiologyprofessor, and was educated at the University of Copenhagen, where he earned his doctorate in
1911. That same year he went to Cambridge, England, to study nuclear physics under the British
physicist Sir Joseph John Thomson, but he soon moved to Manchester to work with another
British physicist, Ernest Rutherford.
Bohrs theory of atomic structure won him the Nobel Prize in physics in 1922. It was
published in papers between 1913 and 1915. His work drew on Rutherfords nuclear model of the
atom, in which the atom is seen as a compact nucleus surrounded by a swarm of much lighter
electrons. Bohrs atomic model made use of quantum theory and the Planck constant, which is
the ratio between quantum size and radiation frequency. The model shows that an atom emits
electromagnetic radiation only when an electron in the atom jumps from one quantum level to
another. This model contributed greatly to future developments of theoretical atomic physics.
In 1916 Bohr returned to the University of Copenhagen as a professor of physics, and in
1920 he was made director of the universitys newly formed Institute for Theoretical Physics.
There Bohr developed a theory relating quantum numbers to large systems that follow classical
laws, and made other major contributions to theoretical physics. Bohrs work helped lead to the
concept that electrons exist in shells and that the electrons in the outermost shell determines an
atoms chemical properties.
In 1939 Bohr convinced physicists at a scientific conference in the United States of the
importance of, Otto Hahns and Fritz Strassmans, experiments. He later demonstrated that
uranium-235 is the particular isotope of uranium that undergoes nuclear fission. Bohr then
returned to Denmark, where he was forced to remain after the German occupation of the country
in 1940. Eventually, however, he was persuaded to escape to Sweden. From Sweden the Bohrs
traveled to England and eventually to the United States, where Bohr joined in the effort to
develop the first atomic bomb, working at Los Alamos, New Mexico, until the first bombs
detonation in 1945. He opposed complete secrecy of the project, however, and feared the
consequences of this ominous new development. He desired international control.
In 1945 Bohr returned to the University of Copenhagen, where he immediately began
working to develop peaceful uses for atomic energy. He organized the first Atoms for Peace
Conference in Geneva, held in 1955, and two years later he received the first Atoms for Peace
Award. In 1997 the International Union of Pure and Applied Chemistry announced that the
chemical element with the atomic number 107 would be given the official name bohrium (Bh), in
honor of Niels Bohr.