File:Cockcroft-Walton accelerator Clarendon Lab Oxford.jpg

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English: 1.2 megavolt Cockcroft-Walton particle accelerator (background) at the Clarendon Laboratory, Oxford University, UK in 1948. It consists of a 6 stage voltage multiplier stack with a large globe to store charge at the top. The black segments of each column contain capacitors to store the charge, while the diagonal "crossrungs" contain high voltage vacuum tube rectifiers called kenotrons, which only conduct current in one direction. An alternating voltage of several hundred kilovolts is applied between the bottom columns. The columns function as a charge pump, pumping electric charge up the columns until the top terminal is at a potential of 1.2 million volts. The voltage is applied to opposite ends of an evacuated accelerator tube (not shown) which accelerates charged subatomic particles traveling through it to high speeds. All the metal parts of the machine must be covered by smooth curved metal "corona rings" to prevent corona discharge, which can cause charge to leak into the air. The Cockcroft-Walton accelerator was invented by British physicists John Douglas Cockcroft and Ernest Thomas Sinton Walton in 1932.
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Source Retrieved April 13, 2015 from "Britain gets atom smasher" in Popular Science monthly, Popular Science Publishing Co., New York, Vol. 153, No. 5, November 1948, p. 113 on Google Books
Author Unknown authorUnknown author
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This 1948 issue of Popular Science magazine would have the copyright renewed in 1976. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1975, 1976, and 1977 show no renewal entries for Popular Science. Therefore the copyright was not renewed and it is in the public domain.

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This work is in the public domain because it was published in the United States between 1929 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs. Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.

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