- 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
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 USA. 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 towards an explanation of
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 behaviour
of electrons within atoms. Bohr's atomic theory was validated 1922
by the discovery of an element he had predicted, which was given the
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 USA. After working on the atomic bomb, he became a passionate
advocate for the control of nuclear weapons.