PARTICLE ACCELERATOR

any of various devices that increase the speed and kinetic energy of electrically charged atomic and subatomic particles. Particle accelerators serve as important research tools in nuclear and high-energy physics, providing investigators with a means of studying the structure and properties of the atomic nucleus and the interactions of subatomic particles. They also are employed for industrial radiography, cancer therapy, radioactive isotope production, and various other purposes. In 1932 the British physicists John Douglas Cockcroft and E.T.S. Walton first observed the disintegration of a nucleus by artificially accelerated particles. Thereafter, the importance of accelerators in basic research became comparable to that of microscopes and telescopes. The particles accelerated are most commonly electrons and protons (the nuclei of hydrogen) and their antiparticlespositrons and antiprotons. Heavier nuclei may also be used. The energy of an accelerated particle is expressed in units of electron volts (eV). Frequently employed multiple units are kiloelectron volts (keV; 1,000 eV), megaelectron volts (MeV; 1,000,000 eV), gigaelectron volts (GeV; 1,000,000,000 eV), and teraelectron volts (TeV; 1,000,000,000,000 eV). Accelerators are generally differentiated according to the arrangement of their accelerating electric fields. Though some accelerators, such as the Van de Graaff generator, use constant voltages to provide the electric field, most modern accelerators employ alternating voltages. Accelerators are classified into two basic types: linear and cyclic. any device that produces a beam of fast-moving, electrically charged atomic or subatomic particles. Physicists use accelerators in fundamental research on the structure of nuclei, the nature of nuclear forces, and the properties of nuclei not found in nature, such as the transuranic (heavier than uranium) elements and other unstable elements. Accelerators are also used for radioisotope production, industrial radiography, cancer therapy, sterilization of biological materials, polymerization of plastics, and a certain form of radiocarbon dating. The largest accelerators are used in research on the fundamental interactions of the elementary subatomic particles. This article reviews the development of accelerators and delineates the various types and their distinguishing features. For specific information about the particles accelerated by these devices, see atom and subatomic particle. Additional reading The physics background is dealt with in Frank Close, Michael Marten, and Christine Sutton, The Particle Explosion (1987), at the general level; and at a deeper level by W.S.C. Williams, Nuclear and Particle Physics (1991); and Emilio Segr, Nuclei and Particles: An Introduction to Nuclear and Subnuclear Physics, 2nd ed., completely rev. and enlarged (1977). An extensive survey for nonspecialists is available in the article Particle Accelerator, in McGraw-Hill Encyclopedia of Science & Technology, 7th ed., vol. 13, pp. 114153 (1992). Early research papers of historical interest include J.D. Cockcroft and E.T.S. Walton, Experiments with High Velocity Positive Ions, Proceedings of the Royal Society of London, Series A, vol. 137, pp. 229242 (1932), on the cascade generator; and a selection of articles in Physical Review: Robert J. Van De Graaff, A 1,500,000 Volt Electrostatic Generator, 38:191920 (1931); D.W. Kerst, Acceleration of Electrons by Magnetic Induction, 60:4753 (1941), on the betatron; Ernest O. Lawrence and M. Stanley Livingston, The Production of High Speed Light Ions Without the Use of High Voltages, 40:1935 (1932), on the classical cyclotron; David H. Sloan and Ernest O. Lawrence, The Production of Heavy High Speed Ions Without the Use of High Voltages, 38:202132 (1931), on the development of the resonance linear accelerator idea; Edwin M. McMillan, The Synchrotron: A Proposed High Energy Particle Accelerator, 68:143144 (1945); and D.W. Kerst et al., Attainment of Very High Energy by Means of Intersecting Beams of Particles, 102:590591 (1956). Discussions of some modern accelerators include Maurice Goldsmith and Edwin Shaw, Europe's Giant Accelerator (1977), a nontechnical history of the CERN 450-GeV proton synchrotron; Robert R. Wilson, The Next Generation of Particle Accelerators, Scientific American, 242(1):4257 (January 1980); M.C. Crowley-Milling, High-Energy Particle Accelerators, Reports on Progress in Physics, 46(1):5195 (January 1983); three articles from Scientific American: John R. Rees, The Stanford Linear Collider, 261(4):5865 (October 1989); Stephen Myers and Emilio Picasso, The LEP Collider, 263(1):5461 (July 1990); and Leon M. Lederman, The Tevatron, 264(3):4855 (March 1991); and Christine Sutton, Particle Accelerators, a special 4-page insert in New Scientist, vol. 134, no. 1825 (June 13, 1992). More technical works include M. Stanley Livingston and John P. Blewett, Particle Accelerators (1962); John J. Livingood, Principles of Cyclic Particle Accelerators (1961); A.A. Kolomensky and A.N. Lebedev, Theory of Cyclic Accelerators (1966; originally published in Russian, 1962); Philip J. Bryant and Kjell Johnsen, The Principles of Circular Accelerators and Storage Rings (1993); D.A. Edwards and M.J. Syphers, An Introduction to the Physics of High Energy Accelerators (1993); AIP Conference Proceedings, papers from seminars and courses published by the American Institute of Physics; and IEEE Transactions on Nuclear Science (bimonthly), for new developments in accelerator technology. Yuri M. Ado Frank C. Shoemaker Christine Sutton