Lawrence's 60-inch cyclotron, with magnet poles 60 inches (5 feet, 1.5 meters) in diameter, at the University of California Lawrence Radiation Laboratory, Berkeley, in August, 1939, the most powerful accelerator in the world at the time. Glenn T. Seaborg and Edwin M. McMillan (right) used it to discover plutonium, neptunium, and many other transuranic elements and isotopes, for which they received the 1951 Nobel Prize in chemistry. The cyclotron's huge magnet is at left, with the flat accelerating chamber between its poles in the center. The beamline which analyzed the particles is at right.
A modern cyclotron used for radiation therapy. The magnet is painted yellow.

A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley,[1][2] and patented in 1932.[3][4] A cyclotron accelerates charged particles outwards from the center along a spiral path.[5][6] The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (radio frequency) electric field. Lawrence was awarded the 1939 Nobel prize in physics for this invention.[6][7]

Cyclotrons were the most powerful particle accelerator technology until the 1950s when they were superseded by the synchrotron, and are still used to produce particle beams in physics and nuclear medicine. The largest single-magnet cyclotron was the 4.67 m (184 in) synchrocyclotron built between 1940 and 1946 by Lawrence at the University of California, Berkeley,[1][6] which could accelerate protons to 730 million electron volts (MeV). The largest cyclotron is the 17.1 m (56 ft) multimagnet TRIUMF accelerator at the University of British Columbia in Vancouver, British Columbia which can produce 500 MeV protons.

Over 1200 cyclotrons are used in nuclear medicine worldwide for the production of radionuclides.[8]


The first cyclotron was developed and patented[4] by Ernest Lawrence in 1932 at the University of California, Berkeley.[9] He used large electromagnets recycled from obsolete Poulsen arc radio transmitters provided by the Federal Telegraph Company.[10] A graduate student, M. Stanley Livingston, did much of the work of translating the idea into working hardware.[11] Lawrence read an article about the concept of a drift tube linac by Rolf Widerøe,[12][13] who had also been working along similar lines with the betatron concept. At the Radiation Laboratory of the University of California, Berkeley, Lawrence constructed a series of cyclotrons which were the most powerful accelerators in the world at the time; a 69 cm (27 in) 4.8 MeV machine (1932), a 94 cm (37 in) 8 MeV machine (1937), and a 152 cm (60 in) 16 MeV machine (1939). He also developed a 467 cm (184 in) synchrocyclotron (1945). Lawrence received the 1939 Nobel prize in physics for this work.

The first European cyclotron was constructed in Leningrad in the physics department of the Radium Institute, headed by Vitaly Khlopin [ru]. This Leningrad instrument was first proposed in 1932 by George Gamow and Lev Mysovskii [ru] and was installed and became operative by 1937.[14][15][16] In Nazi Germany a cyclotron was built in Heidelberg under supervision of Walther Bothe and Wolfgang Gentner, with support from the Heereswaffenamt, and became operative in 1943.

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