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Cloud chamber used to photograph cosmic rays
Medal displayed with permission of the Frederick Soddy Trust.
Frederick Soddy FRS (1877-1956) won the 1921 Nobel prize in Chemistry 'for his contributions to our knowledge of the chemistry of radioactive substances, and his investigations into the origin and nature of isotopes'. After working on radioactivity with Rutherford at McGill University he joined Sir William Ramsay FRS at University College London. His most important contribution was made in 1913 with the concept of isotopes: that is, that certain elements exist in two or more forms which have different atomic weights but are chemically indistinguishable.
This was Chadwick's first printed announcement of his theory that the radiation emitted when beryllium was bombarded with alpha particles consisted of 'particles of mass 1 and charge 0, or neutrons'. He described his findings to the Royal Society on 28 April 1932, and in June published another article, now simply called 'The Existence of a Neutron', in the Proceedings of the Royal Society, Series A.
(Royal Society Archives PB/2/1)Blackett worked at the Cavendish Laboratory with Rutherford throughout the 1920s. His notebooks record his work with cloud chamber photographs of the tracks of atomic particles. In one of the books another hand (probably Rutherford's) has initially written 'all wrong' under Blackett's calculations: this has been crossed out and replaced by 'quite all right'.
Patrick Blackett FRS, Nobel prize lecture (1948)
(Royal Society Archives PB/2/6/19)
(Royal Society Archives PB/2/3/5)
Blackett won the Nobel prize in physics 'for his development of the Wilson cloud chamber method, and his discoveries therewith in the fields of nuclear physics and cosmic radiation'. He used the cloud chamber to detect the tracks of particles formed during the disintegration of nitrogen nuclei, and also to see cosmic ray particles.
Blackett was able to photograph the particle tracks. The forks are caused by particles colliding with the nucleus of an atom. He took thousands of photographs like these during his research career: the geophysicist E C Bullard FRS claimed Blackett's photographs 'have adorned almost every text book of nuclear physics for the past fifty years'.
(Royal Society Archives MS/850)
Research into the potential use of atomic energy was both exciting and, during wartime, extremely secret. These papers were written by French physicists working at the Cavendish Laboratory in 1941. They deal with nuclear fission in uranium, and it was considered 'inadvisable to publish' them at the time. They were rediscovered in the Royal Society Archives in 2007.
On loan from the Whipple Museum for the History of Science, Cambridge (Wh. 3370).
The cyclotron is a type of particle accelerator, invented by American physicist Ernest Lawrence in 1929. Cyclotrons accelerate charged particles using a high frequency alternating voltage. The D-shaped electrodes, or 'dees', are mounted in a vacuum chamber between the two poles of a large magnet. The particles, injected near the centre of the magnetic field, accelerate only when passing through the gap between the dees. They follow a spiral path increasing in radius until they hit a target at the perimeter of the vacuum chamber. The pipes leading into each dee were part of the original cooling system. Cyclotrons provide a source of high-energy beams for experiments in nuclear physics; these beams can also be used to treat cancer by killing tumours with radiation. The examples displayed here were used by researchers at the Cavendish Laboratory at the University of Cambridge.
The Large Hadron Collider (LHC) is the world's largest particle accelerator, intended to collide opposing beams of protons or lead ions, each travelling at 0.999999991 times the speed of light. Like Lawrence's cyclotron dees, the Large Hadron Collider uses magnets to accelerate and focus the beams of particles. It is hoped that it will allow scientists to study the tiniest particles of matter that were present at the beginning of the universe. These include the Higgs boson, a hypothetical particle predicted but not yet observed.
Find out more about the LHC on the CERN website.
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