Niels Bohr was the son of a physiology professor 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. Bohr’s 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 Rutherford’s nuclear model of the atom, in which the atom is seen as a compact nucleus surrounded by a swarm of much lighter electrons. Bohr’s 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. In 1920, he was made director of the university’s 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. Bohr’s work helped lead to the concept that electrons exist in shells, and that the electrons in the outermost shell determine an atom’s chemical properties. In 1939, Bohr convinced physicists at a scientific conference in the United States of the importance of Otto Hahn’s and Fritz Strassman’s 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, Bohr traveled to England and eventually to the United States, where he joined in the effort to develop the first atomic bomb, working at Los Alamos, New Mexico, until the first bomb’s detonation in 1945.
He opposed complete secrecy of the project 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 in 1955 and received the first Atoms for Peace Award two years later.
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.