Editing Van de Graaff generator (section)

=== Higher energy machines ===

In 1937, the [[Westinghouse Electric (1886)|Westinghouse Electric]] company built a {{convert|65|ft|m|abbr=on}} machine, the [[Westinghouse Atom Smasher]] capable of generating 5&nbsp;MeV in [[Forest Hills, Pennsylvania]]. It marked the beginning of nuclear research for civilian applications.<ref>{{cite book |first=Franklin |last=Toker |title=Pittsburgh: A New Portrait |year=2009 |page=470 |publisher=University of Pittsburgh Press |url=https://books.google.com/books?id=nJM6AQAAIAAJ |isbn=9780822943716}}</ref><ref>{{cite web |title=Van de Graaff particle accelerator, Westinghouse Electric and Manufacturing Co., Pittsburgh, PA, August 7, 1945 |website=Explore PA History |publisher=[[WITF-TV]] |url=http://explorepahistory.com/displayimage.php?imgId=1-2-151C |access-date=February 19, 2015}}</ref> It was decommissioned in 1958 and was partially demolished in 2015.<ref name="bo">{{cite news|last=O'Neill|first=Brian|date=January 25, 2015|title=Brian O'Neill: With Forest Hills atom smasher's fall, part of history tumbles|newspaper=[[Pittsburgh Post-Gazette]]|url=https://www.post-gazette.com/opinion/brian-oneill/2015/01/25/Brian-O-Neill-With-Forest-Hills-atom-smasher-s-fall-part-of-history-tumbles/stories/201501250109}}</ref> (The enclosure was laid on its side for safety reasons.)<ref>{{Cite web|title=Atom smasher in Forest Hills torn down; restoration promised|url=https://www.post-gazette.com/news/science/2015/01/21/Forrest-Hill-nuclear-relic-waits-in-limbo/stories/201501200209|access-date=2022-01-17|website=Pittsburgh Post-Gazette|language=en}}</ref>

A more recent development is the tandem Van de Graaff accelerator, containing one or more Van de Graaff generators, in which negatively charged [[ion]]s are accelerated through one [[potential difference]] before being stripped of two or more electrons, inside a high-voltage terminal, and accelerated again. An example of a three-stage operation has been built in Oxford Nuclear Laboratory in 1964 of a 10&nbsp;MV single-ended "injector" and a 6&nbsp;MV EN tandem.<ref>J. Takacs, ''Energy Stabilization of Electrostatic Accelerators'', John Wiley and Sons, Chichester, 1996</ref>{{page needed|date=April 2016}}

By the 1970s, as much as 14 MV could be achieved at the terminal of a tandem that used a tank of high-pressure [[SF6|sulfur hexafluoride]] (SF<sub>6</sub>) gas to prevent sparking by trapping electrons. This allowed the generation of heavy ion beams of several tens of MeV, sufficient to study light-ion direct nuclear reactions. The greatest potential sustained by a Van de Graaff accelerator is 25.5&nbsp;MV, achieved by the tandem in the Holifield Radioactive Ion Beam Facility in [[Oak Ridge National Laboratory]].<ref>{{cite web |url=https://www.ornl.gov/news/american-physical-society-names-ornls-holifield-facility-historic-physics-site |title=American Physical Society names ORNL's Holifield Facility historic physics site |date=25 July 2016 |publisher=Oak Ridge National Laboratory}}</ref>

A further development is the [[pelletron]], where the rubber or fabric belt is replaced by a chain of short conductive rods connected by insulating links, and the air-ionizing electrodes are replaced by a grounded roller and inductive charging electrode. The chain can be operated at a much greater velocity than a belt, and both the voltage and currents attainable are much greater than with a conventional Van de Graaff generator. The 14&nbsp;UD Heavy Ion Accelerator at [[the Australian National University]] houses a 15&nbsp;MV pelletron. Its chains are more than 20&nbsp;m long and can travel faster than {{convert|50|km/h|mph|abbr=on}}.<ref>{{cite web |title=Particle Accelerator |url=http://www.anu.edu.au/CSEM/machines/Accelerator.htm |date=November 2002 |url-status=dead |archive-url=https://web.archive.org/web/20190608111732/http://www.anu.edu.au/CSEM/machines/Accelerator.htm |archive-date=2019-06-08}}</ref>

The Nuclear Structure Facility (NSF) at [[Daresbury Laboratory]] was proposed in the 1970s, commissioned in 1981, and opened for experiments in 1983. It consisted of a tandem Van de Graaff generator operating routinely at 20 MV, housed in a distinctive building 70&nbsp;m high. During its lifetime, it accelerated 80 different ion beams for experimental use, ranging from protons to uranium. A particular feature was the ability to accelerate rare isotopic and radioactive beams. Perhaps the most important discovery made using the NSF was that of super-deformed nuclei. These nuclei, when formed from the fusion of lighter elements, rotate very rapidly. The pattern of gamma rays emitted as they slow down provided detailed information about the inner structure of the nucleus.<ref>J S Lilley 1982 Phys. Scr. 25 435-442 {{doi|10.1088/0031-8949/25/3/001}})</ref> Following financial cutbacks, the NSF closed in 1993.<ref>{{cite journal |author1=David Dickson |title=Curtain falls on Britain's nuclear structure facility |journal=Nature |date=March 1993 |volume=362 |issue=6418 |pages=278 |url=https://www.nature.com/articles/362278b0.pdf |publisher=Nature Publishing Group |doi=10.1038/362278b0 |access-date=6 February 2024}}</ref>