Editing Seth Neddermeyer (section)

==Manhattan Project work==
[[File:Implosion bomb animated.gif|thumb|right|Implosion mechanism]]
In early 1941, with [[World War II]] raging in Europe but the United States not yet a belligerent, Neddermeyer joined a team led by [[Charles C. Lauritsen]] and [[William A. Fowler]] at the Department of Terrestrial Magnetism at the [[Carnegie Institution of Washington]], and  then at the [[National Bureau of Standards]] in Washington, D.C., that worked on the photoelectric [[proximity fuze]].<ref name="Physics Today" /><ref name="Oral"/> After this work was completed, Neddermeyer was recruited by Oppenheimer to work at the [[Manhattan Project]]'s [[Los Alamos Laboratory]].<ref name="Physics Today" /> Neddermeyer was an early advocate for the development of an [[Implosion-type nuclear weapon|implosion technique]] for assembling a [[critical mass]] in an atomic bomb.<ref name="Critchfield">{{cite web |url=http://conservancy.umn.edu/bitstream/handle/11299/107233/oh134cc.pdf |title=Oral History Interview with Charles Critchfield |access-date=December 30, 2015 }}</ref> Although implosion was suggested by [[Richard Tolman]] as early as 1942 and discussed in the introductory lectures given to Los Alamos scientists by [[Robert Serber]], Neddermeyer was one of the first to urge its full development.<ref name="Critchfield" />{{sfn|Serber|1942|p=59}} Unable to find much initial enthusiasm for the concept among his fellow Los Alamos scientists, Neddermeyer presented the first substantial technical analysis of implosion in late April 1943. Oppenheimer considered this to be the beginning of implosion research at Los Alamos.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=55–56}}

Though many remained unimpressed, Oppenheimer appointed Neddermeyer the head of a new group to test implosion.{{sfn|Rhodes|1986|pp=466-67}} His group became the E-5 (Implosion) Group, which was part of [[Captain (United States O-6)|Captain]] [[William S. Parsons]]' E Division.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=86–90}} A [[gun-type nuclear weapon]] was the preferred method, but implosion research constituted a backup.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p = 67}} Neddermeyer embarked on an intensive series of experiments testing cylindrical implosions. The result was a series of distorted shapes.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=86–90}} Progress was made; Neddermeyer and a member of his team, [[Hugh Bradner]], along with [[James L. Tuck]] from the [[British contribution to the Manhattan Project|British Mission]], conceived the idea of [[explosive lens]]es, in which shaped charges are used to focus the force of an explosion.<ref name="Critchfield" /> Nevertheless, seemingly unsolvable problems with [[shock wave]] uniformity brought progress on implosion to a crawl.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=86–90}}

By September 1943, Neddermeyer's team had grown from five people to fifty. That month, [[John von Neumann]] came to Los Alamos at Oppenheimer's request. Von Neumann was impressed by the implosion concept and, working with [[Edward Teller]], an old friend, made a series of suggestions. Von Neumann was able to create a sound mathematical model of implosion, enabling Neddermeyer to present a proposal for a greatly expanded research program. [[Edwin McMillan]] and [[Isidor Isaac Rabi]] recommended that [[George Kistiakowsky]], who had a specialized knowledge in the precision use of explosives, be brought in to help the program.{{sfn|Rhodes|1986|pp=541-43}}{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp =129-135}} In February 1944, Kistiakowsky became Parsons' deputy for implosion.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p =139}}

In April 1944, tests on the first sample of [[plutonium]] that had been produced with neutrons in a nuclear reactor revealed that reactor-bred plutonium contained five times more [[plutonium-240]] than that hitherto produced in [[cyclotron]]s. This unwanted isotope that spontaneously decayed and produced neutrons promised to cause a [[predetonation]] without sufficiently quick critical mass assembly. It now became apparent that only implosion would work for practical plutonium bombs; a powerful enough gun could not be constructed small enough to be carried in an aircraft, and plutonium-240 was even more difficult to separate from plutonium-239 than the isotopes of uranium that were giving the rest of the Manhattan Project such difficulties. Plutonium was unusable unless implosion worked, but only plutonium could be produced in quantities that would allow regular production of atomic bombs. Thus, the implosion technique now suddenly stood as the key to production of nuclear weapons.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=240-247}}

In mid-June 1944, a report from Kistiakowsky to Oppenheimer detailing dysfunctionality within the implosion team led to the ousting of Neddermeyer.{{sfn|Rhodes|1986|p=547}} He was replaced as the head of the E-5 Group by Kistiakowsky on June 15, 1944, but remained a technical adviser to the implosion program, with group leader status.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=175}} Neddermeyer was said to have been much embittered by this episode.{{sfn|Rhodes|1986|p=547}} In Oppenheimer's August 1944 reorganization of the Los Alamos Laboratory, Neddermeyer's group was renamed X-1, with [[Norris Bradbury]] as group leader.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=240-247}} The implosion method championed by Neddermeyer was used in the first atom bomb exploded (in the [[Trinity test]]), the [[Fat Man]] bomb dropped on [[Nagasaki, Nagasaki|Nagasaki]], and almost all modern nuclear weapons.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=411-414}} Kistiakowsky later insisted that "the real invention should be given full credit to [Seth] Neddermeyer" (sic).<ref>{{cite web |url=http://manhattanprojectvoices.org/oral-histories/george-kistiakowskys-interview |title=George Kistiakowsky's Interview |work=[[Voices of the Manhattan Project]]|access-date=December 30, 2015 }}</ref>