Editing Cyclotron (section)

{{Short description|Type of particle accelerator}}
{{Other uses}}
{{good article}}

[[File:Cyclotron with glowing beam.jpg|300px|thumb|right|Lawrence's {{Convert|60|in|cm|0|adj=on}} cyclotron, {{Circa|1939}}, showing the beam of accelerated [[ion]]s (likely [[proton]]s or [[deuteron]]s) exiting the machine and ionizing the surrounding air causing a blue glow]]

A '''cyclotron''' is a type of [[particle accelerator]] invented by [[Ernest Lawrence]] in 1929–1930 at the [[University of California, Berkeley]],<ref>{{Cite web|url=http://www2.lbl.gov/Science-Articles/Archive/early-years.html|title=Ernest Lawrence's Cyclotron|website=www2.lbl.gov|access-date=2018-04-06}}</ref><ref>{{Cite web| url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1939/lawrence-bio.html|title=Ernest Lawrence – Biographical| website=nobelprize.org|access-date=2018-04-06}}</ref> and patented in 1932.<ref name="Patent1948384">{{US patent|1948384}} Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: January 26, 1932, granted: February 20, 1934</ref><ref name="Lawrence">{{cite journal
 |last1 = Lawrence
 |first1 = Earnest O.
 |last2 = Livingston
 |first2 = M. Stanley
 |title = The Production of High Speed Light Ions Without the Use of High Voltages
 |journal = Physical Review
 |volume = 40
 |issue = 1
 |pages = 19–35
 |publisher = American Physical Society
 |date = April 1, 1932
 |doi = 10.1103/PhysRev.40.19
 | bibcode = 1932PhRv...40...19L
 |doi-access = free
 }}</ref> A cyclotron accelerates [[charged particle]]s outwards from the center of a flat cylindrical vacuum chamber along a spiral path.<ref name="Nave">{{cite web
 |last = Nave
 |first = C. R.
 |title = Cyclotron
 |publisher = Dept. of Physics and Astronomy, Georgia State University
 |date = 2012
 |url = http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/cyclot.html
 |access-date = October 26, 2014}}</ref><ref name="Close">{{cite book
 |last1 = Close
 |first1 = F. E.
 |last2 = Close
 |first2 = Frank
 |last3 = Marten
 |first3 = Michael
 |title = The Particle Odyssey: A Journey to the Heart of Matter
 |publisher = Oxford University Press
 |date = 2004
 |pages = 84–87
 |url = https://books.google.com/books?id=PX87qqj5B2UC&pg=PA86
 |isbn = 978-0-19-860943-8
 |display-authors=etal|bibcode = 2002pojh.book.....C
 }}</ref> The particles are held to a spiral trajectory by a static [[magnetic field]] and accelerated by a rapidly varying [[electric field]]. Lawrence was awarded the 1939 [[Nobel Prize in Physics]] for this invention.<ref name="Close"/><ref>{{Cite web|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1939/lawrence-facts.html|title=Ernest Lawrence – Facts|website=nobelprize.org|access-date=2018-04-06}}</ref>

The cyclotron was the first "cyclical" accelerator.<ref name="Serway" /> The primary accelerators before the development of the cyclotron were [[electrostatic accelerator]]s, such as the [[Cockcroft–Walton generator]] and the [[Van de Graaff generator]].  In these accelerators, particles would cross an accelerating [[electric field]] only once.  Thus, the energy gained by the particles was limited by the maximum [[electrical potential]] that could be achieved across the accelerating region. This potential was in turn limited by [[electrical breakdown|electrostatic breakdown]] to a few million volts. In a cyclotron, by contrast, the particles encounter the accelerating region many times by following a spiral path, so the output energy can be many times the energy gained in a single accelerating step.<ref name="Lawrence"/>

Cyclotrons were the most powerful particle accelerator technology until the 1950s, when they were surpassed by the [[synchrotron]].<ref name="Bryant">{{cite conference |url=https://cds.cern.ch/record/261062/files/p1_2.pdf |title=A Brief History and Review of Accelerators |last1=Bryant|first1=P.J. |date=September 1992 |publisher=[[CERN]] |book-title=Proceedings, Vol. 2  |page=12 |location=  Jyvaskyla, Finland|conference=CAS-CERN Accelerator School: 5th general accelerator physics course}}</ref> Nonetheless, they are still widely used to produce particle beams for [[nuclear medicine]] and basic research. As of 2020, close to 1,500 cyclotrons were in use worldwide for the production of [[radionuclide]]s for nuclear medicine and ultimately, for the production of radiopharmaceuticals.{{r|itnonline}} In addition, cyclotrons can be used for [[particle therapy]], where particle beams are directly applied to patients.<ref name="itnonline">{{cite web| date=March 10, 2020|title=MEDraysintell identifies close to 1,500 medical cyclotrons worldwide| url=https://www.itnonline.com/content/medraysintell-releases-unique-cyclotron-directory#:~:text=March%2010%2C%202020%20%E2%80%94%20MEDraysintell%20released,to%201%2C500%20medical%20cyclotrons%20worldwide.|work=ITN Imaging Technology News}}</ref>