Ernest Rutherford proposes the concept of the nucleus as a positively charged mass at the centre of an atom

Albert Einstein formulates the law of photochemical equivalence, a fundamental principle of chemical reactions induced by light

Lawrence Bragg and his father, William, together develop X-ray crystallography, based on the diffraction patterns of crystals

The Danish physicist Niels Bohr uses quantum theory as a key to understanding the structure of the atom

English physicist Henry Moseley proposes that the atomic number of an element is a physical reality, thus laying the basis for the modern periodic table

Einstein submits a paper, The field equations of gravitation, containing the sums required to explain the general theory of relativity

23-year-old German physicist Werner Heisenberg publishes his ground-breaking theory of quantum mechanics

Austrian physicist Wolfgang Pauli formulates his exclusion principle, stating that no two electrons in an atom can have the same four quantum numbers

Werner Heisenberg publishes his Uncertainty Principle, declaring that it is impossible to define precisely the position and momentum of a sub-atomic particle

Wolfgang Pauli announces his mathematical proof of the existence of the particle subsequently known as the neutrino

British theoretical physicist Paul Dirac predicts the existence of an anti-particle of the electron, first observed two years later and named the positron

John Cockcroft and Ernest Walton are the first to split an atom, by bombarding it with accelerated protons

British physicist James Chadwick shows that the behaviour of subatomic particles can be explained by the existence of neutrons, or particles with no electrical charge

Frédéric and Irène Joliot-Curie discover artificial radioactivity

German physicists, led by Otto Hahn, announce their discovery of nuclear fission

German-born US physicist Albert Einstein writes to President Roosevelt, warning of the potential of an atomic bomb

Radar masts along the coasts of Britain give early warning of German air attacks

US physicist J. Robert Oppenheimer is appointed director of the Manhattan Project to develop a nuclear weapon

Enrico Fermi and his team in Chicago achieve the first nuclear chain reaction

US scientists succeed in exploding an atom bomb at Alamogordo, a test site in the New Mexican desert

An atom bomb is dropped on Hiroshima, destroying four square miles of the city and killing 80,000 people

The first of about 20 US tests of atomic and hydrogen bombs is carried out on Bikini Atoll, in the Pacific

Hungarian-born British engineer Dennis Gabor creates the first three-dimensional image from reflected light, subsequently known as a hologram

The first transistor is produced in the Bell Laboratories in Murray Hill, New Jersey

The first Soviet atomic bomb, called by the Americans Joe One, is successfully tested in Kazakhstan