Editing Manhattan Project (section)

== After the war ==
[[File:Army-Navy E Award Ceremony 68997.jpg|thumb|Presentation of the [[Army–Navy "E" Award]] at Los Alamos on 16 October 1945. Standing, left to right: [[J. Robert Oppenheimer]], unidentified, unidentified, [[Kenneth Nichols]], [[Leslie Groves]], [[Robert Gordon Sproul]], [[William Sterling Parsons]].|alt=Men in suits and uniforms stand on a dais decorated with bunting and salute.]]

The Manhattan Project became instantly famous after the bombing of Hiroshima and the partial lifting of its secrecy. It was widely credited with ending the war, and Groves worked to credit its contractors, whose work had hitherto been secret. Groves and Nichols presented them with [[Army–Navy "E" Award]]s, and over 20 [[Presidential Medal for Merit|Presidential Medals for Merit]] were awarded to key contractors and scientists, including Bush and Oppenheimer. Military personnel received the [[Legion of Merit]].<ref>{{harvnb|Nichols|1987|p=226}}.</ref>

The Manhattan Project persisted until 31 December 1946, and the Manhattan District to 15 August 1947.<ref>{{harvnb|Jones|1985|p=600}}.</ref> During this time, it suffered from numerous difficulties caused by technical problems, the effects of rapid demobilization, and a lack of clarity on its long-term mission.

At Hanford, plutonium production declined as Reactors B, D and F wore out, poisoned by fission products and swelling of the graphite moderator known as the [[Wigner effect]]. The swelling damaged the charging tubes where the uranium was irradiated to produce plutonium, rendering them unusable. Production was curtailed and the oldest unit, B pile, was closed down so at least one reactor would remain available. Research continued, with DuPont and the Metallurgical Laboratory developing a [[redox]] solvent extraction process as an alternative [[nuclear reprocessing|plutonium extraction]] technique to the bismuth phosphate process, which left unspent uranium in a state from which it could not easily be recovered.<ref name="Jones, pp. 592-593">{{harvnb|Jones|1985|pp=592–593}}.</ref>

Bomb engineering was carried out by the Z Division,{{sfn|Sandia|1967|p=11}} initially located at Wendover Field but moved to [[Oxnard Field]], New Mexico, in September 1945 to be closer to Los Alamos. This marked the beginning of the [[Sandia Base]]. Nearby Kirtland Field was used as a B-29 base for aircraft compatibility and drop tests.<ref>{{harvnb|Hansen|1995b|p=V-152}}.</ref> As reservist officers were demobilized, they were replaced by about fifty hand-picked regular officers.<ref>{{harvnb|Nichols|1987|pp=225–226}}.</ref>

Nichols recommended that S-50 and the Alpha tracks at Y-12 be closed down. This was done in September.<ref>{{harvnb|Nichols|1987|pp=216–217}}.</ref> Although performing better than ever,<ref>{{harvnb|Hewlett|Anderson|1962|p=624}}.</ref> the Alpha tracks could not compete with K-25 and the new K-27, which had commenced operation in January 1946. In December, the Y-12 plant was closed, cutting the Tennessee Eastman payroll from 8,600 to 1,500 and saving $2&nbsp;million a month.<ref>{{harvnb|Hewlett|Anderson|1962|pp=630, 646}}</ref>

[[File:Atomic Energy Act of 1946 signing.jpg|thumb|left|President [[Harry S. Truman]] signs the [[Atomic Energy Act of 1946]], establishing the [[United States Atomic Energy Commission]].|alt=A man in a suit is seated at a desk, signing a document. Seven men in suits gather around him.]]
Nowhere was demobilization more of a problem than at Los Alamos, where there was an exodus of talent. Much remained to be done. The bombs used on Hiroshima and Nagasaki needed work to make them simpler, safer and more reliable. Implosion methods needed to be developed for uranium in place of the wasteful gun method, and composite uranium-plutonium cores were needed now that plutonium was in short supply. However, uncertainty about the future of the laboratory made it hard to induce people to stay. Oppenheimer returned to his job at the University of California and Groves appointed Norris Bradbury as an interim replacement; Bradbury remained in the post for the next 25 years.<ref name="Hewlett 1962 625">{{harvnb|Hewlett|Anderson|1962|p=625}}.</ref> Groves attempted to combat the dissatisfaction caused by the lack of amenities with a construction program that included an improved water supply, three hundred houses, and recreation facilities.<ref name="Jones, pp. 592-593" />

Manhattan Project personnel participated in the first postwar nuclear tests, [[Operation Crossroads]], conducted at [[Bikini Atoll]] in July 1946. Two Fat Man-type bombs were detonated —&nbsp;one as an airburst, one as an underwater burst —&nbsp;to investigate the effect of nuclear weapons on warships.<ref>{{harvnb|Nichols|1987|p=234}}.</ref><ref>{{harvnb|Jones|1985|p=594}}.</ref> Press and international observers were allowed to attend, making the tests an international spectacle.<ref>{{citation
| last = Weisgall
| first = Jonathan
| year = 1994
| title = Operation Crossroads: The Atomic Tests at Bikini Atoll
| location = Annapolis, Maryland
| publisher = Naval Institute Press
| isbn = 978-1-55750-919-2
| url-access = registration
| url = https://archive.org/details/operationcrossro0000weis
}}</ref>

Following a domestic debate over the peacetime management of the nuclear program, the [[Atomic Energy Act of 1946]] created the [[United States Atomic Energy Commission]] to take over the project's functions and assets. It established civilian control over atomic development. Military aspects were taken over by the [[Armed Forces Special Weapons Project]] (AFSWP).<ref>{{harvnb|Groves|1962|pp=394–398}}.</ref>

After the bombings at Hiroshima and Nagasaki, a number of Manhattan Project physicists founded the ''[[Bulletin of the Atomic Scientists]]'' (1945) and [[Emergency Committee of Atomic Scientists]] (1946), which began as an emergency action undertaken by scientists who saw urgent need for an educational program about atomic weapons.<ref>{{harvnb|Grodzins|Rabinowitch|1963|p=vii}}.</ref> In the face of the destructiveness of the bombs and in anticipation of the [[nuclear arms race]] several project members including Bohr, Bush and Conant expressed the view that it was necessary to reach agreement on [[International control of atomic energy|international control of nuclear research and atomic weapons]]. The [[Baruch Plan]], unveiled in a speech to the newly formed [[United Nations Atomic Energy Commission]] (UNAEC) in June 1946, proposed the establishment of an international atomic development authority, but was not adopted.<ref>{{harvnb|Gosling|1994|pp=55–57}}.</ref>