Editing John von Neumann (section)

=== Manhattan Project ===
Beginning in the late 1930s, von Neumann developed an expertise in explosions—phenomena that are difficult to model mathematically. During this period, he was the leading authority of the mathematics of [[shaped charge]]s, leading him to a large number of military consultancies and consequently his involvement in the [[Manhattan Project]]. The involvement included frequent trips to the project's secret research facilities at the [[Los Alamos Laboratory]] in New Mexico.<ref name="NYT"/>

Von Neumann made his principal contribution to the [[Nuclear weapon|atomic bomb]] in the concept and design of the [[nuclear weapon design|explosive lenses]] that were needed to compress the [[plutonium]] core of the [[Fat Man]] weapon that was later dropped on [[Nagasaki]].{{sfn|Jacobsen|2015|loc=Ch. 3}} While von Neumann did not originate the "[[Nuclear weapon design#Implosion-type weapon|implosion]]" concept, he was one of its most persistent proponents, encouraging its continued development against the instincts of many of his colleagues, who felt such a design to be unworkable. He also eventually came up with the idea of using more powerful shaped charges and less fissionable material to greatly increase the speed of "assembly".{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=130–133, 157–159}}

When it turned out that there would not be enough [[uranium-235]] to make more than one bomb, the implosive lens project was greatly expanded and von Neumann's idea was implemented. Implosion was the only method that could be used with the [[plutonium-239]] that was available from the [[Hanford Site]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=239–245}} He established the design of the [[explosive lens]]es required, but there remained concerns about "edge effects" and imperfections in the explosives.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=295}} His calculations showed that implosion would work if it did not depart by more than 5% from spherical symmetry.<ref>{{cite web |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html |title=Section 8.0 The First Nuclear Weapons |publisher=Nuclear Weapons Frequently Asked Questions  |first=Carey |last=Sublette |access-date=January 8, 2016}}</ref> After a series of failed attempts with models, this was achieved by [[George Kistiakowsky]], and the construction of the Trinity bomb was completed in July 1945.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=320–327}}

In a visit to Los Alamos in September 1944, von Neumann showed that the pressure increase from explosion shock wave reflection from solid objects was greater than previously believed if the angle of incidence of the shock wave was between 90° and some limiting angle. As a result, it was determined that the effectiveness of an atomic bomb would be enhanced with detonation some kilometers above the target, rather than at ground level.{{sfn|Macrae|1992|p=209}}{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=184}}

[[File:Implosion bomb animated.gif|thumb|left|Implosion mechanism]]
Von Neumann was included in the target selection committee that was responsible for choosing the Japanese cities of [[Hiroshima]] and Nagasaki as the [[Atomic bombings of Hiroshima and Nagasaki|first targets of the atomic bomb]]. Von Neumann oversaw computations related to the expected size of the bomb blasts, estimated death tolls, and the distance above the ground at which the bombs should be detonated for optimum shock wave propagation. The cultural capital [[Kyoto]] was von Neumann's first choice,{{sfn|Macrae|1992|pp=242–245}} a selection seconded by Manhattan Project leader General [[Leslie Groves]]. However, this target was dismissed by [[United States Secretary of War|Secretary of War]] [[Henry L. Stimson]].<ref>{{cite book |last=Groves|first=Leslie |author-link=Leslie Groves |title=Now it Can be Told: The Story of the Manhattan Project |url=https://archive.org/details/nowitcanbetolds00grov|url-access=registration|location=New York |publisher=Harper & Row | year=1983|orig-year=1962 |isbn=978-0-306-70738-4|oclc=537684 |pages=268–276 }}</ref>

On July 16, 1945, von Neumann and numerous other Manhattan Project personnel were eyewitnesses to the first test of an atomic bomb detonation, which was code-named [[Trinity (nuclear test)|Trinity]]. The event was conducted as a test of the implosion method device, at the [[Alamogordo Bombing Range]] in New Mexico. Based on his observation alone, von Neumann estimated the test had resulted in a blast equivalent to {{convert|5|ktonTNT|lk=on}} but [[Enrico Fermi]] produced a more accurate estimate of 10 kilotons by dropping scraps of torn-up paper as the shock wave passed his location and watching how far they scattered. The actual power of the explosion had been between 20 and 22 kilotons.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=371–372}} It was in von Neumann's 1944 papers that the expression "kilotons" appeared for the first time.{{sfn|Macrae|1992|p=205}}

Von Neumann continued unperturbed in his work and became, along with Edward Teller, one of those who sustained the [[Thermonuclear weapon|hydrogen bomb project]]. He collaborated with [[Klaus Fuchs]] on further development of the bomb, and in 1946 the two filed a secret patent outlining a scheme for using a fission bomb to compress fusion fuel to initiate [[nuclear fusion]].<ref>{{cite book | last=Herken |first=Gregg |author-link=Gregg Herken | title=Brotherhood of the Bomb: The Tangled Lives and Loyalties of Robert Oppenheimer, Ernest Lawrence, and Edward Teller |publisher=Holt | location=New York |year=2002 | isbn=978-0-8050-6589-3| oclc=48941348 |pages=171, 374}}</ref> The Fuchs–von Neumann patent used [[radiation implosion]], but not in the same way as is used in what became the final hydrogen bomb design, the [[History of the Teller–Ulam design|Teller–Ulam design]]. Their work was, however, incorporated into the "George" shot of [[Operation Greenhouse]], which was instructive in testing out concepts that went into the final design.<ref name="Bernstein2010">{{cite journal|last1=Bernstein|first1=Jeremy|title=John von Neumann and Klaus Fuchs: an Unlikely Collaboration|journal=Physics in Perspective|volume=12|issue=1|pages=36–50|year=2010|doi=10.1007/s00016-009-0001-1|bibcode = 2010PhP....12...36B|s2cid=121790196}}</ref> The Fuchs–von Neumann work was passed on to the Soviet Union by Fuchs as part of his [[nuclear espionage]], but it was not used in the Soviets' own, independent development of the Teller–Ulam design. The historian [[Jeremy Bernstein]] has pointed out that ironically, "John von Neumann and Klaus Fuchs, produced a brilliant invention in 1946 that could have changed the whole course of the development of the hydrogen bomb, but was not fully understood until after the bomb had been successfully made."<ref name="Bernstein2010"/>

For his wartime services, von Neumann was awarded the [[Navy Distinguished Civilian Service Award]] in July 1946, and the [[Medal for Merit]] in October 1946.{{sfn|Macrae|1992|p=208}}