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Trinity (nuclear test)
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===Instrumentation and measurements=== {{See also|Nuclear weapon yield#Calculating yields and controversy}} [[File:Trinity Test - Lead lined Sherman tank.jpg|thumb|Lead-lined Sherman tank used in Trinity test]] The T (Theoretical) Division at Los Alamos had predicted a yield of between {{convert|5|and|10|ktonTNT}}. Immediately after the blast, two lead-lined [[M4 Sherman]] tanks made their way to the crater. [[Nuclear weapon yield|Radiochemical analysis]] of soil samples that they collected indicated that the total yield (or energy release) had been around {{convert|18.6|ktonTNT}}.{{sfn|Widner|2009|pp=10β24}} This method turned out to be the most accurate means of determining the efficiency of a nuclear explosion and was used for many years after.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=376}} The energy of the [[blast wave]] was measured by a large number of sensors using a variety of physical principles. The piezoelectric blast gauges were thrown off scale and no records were obtained. The excess-velocity blast-yield measurement (precise measurement of the velocity of sound at the site of the explosion and then comparing it with the velocity of the blast wave){{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=359}} provided among the most accurate measurements of the blast pressure. Another method was to use the aluminum diaphragm box gauges designed to record the peak pressure of the blast wave. These indicated a blast energy of {{convert|9.9|ktonTNT}} Β± {{convert|1.0|ktonTNT}}. They were supplemented by a large number of other types of mechanical pressure gauges. And only one of them gave a reasonable result of about {{convert|10|ktonTNT}}.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=375-376}} Fermi prepared his own experiment to measure the energy that was released as blast. He later recalled:{{blockquote|About 40 seconds after the explosion the air blast reached me. I tried to estimate its strength by dropping from about six feet small pieces of paper before, during, and after the passage of the blast wave. Since, at the time, there was no wind I could observe very distinctly and actually measure the displacement of the pieces of paper that were in the process of falling while the blast was passing. The shift was about 2 1/2 meters, which, at the time, I estimated to correspond to the blast that would be produced by ten thousand tons of T.N.T.<ref>{{cite web |url=http://www.dannen.com/decision/fermi.html |title=Trinity Test, July 16, 1945, Eyewitness Accounts β Enrico Fermi |publisher=Gene Dannen |access-date=November 4, 2014 |archive-date=November 4, 2014 |archive-url=https://web.archive.org/web/20141104122441/http://www.dannen.com/decision/fermi.html |url-status=live }}</ref>}} {| class="wikitable floatright" width="250px" |+Fission bomb's energy distribution in the "moderate" kiloton range near sea level | colspan=2 |Contemporary fundamental physics, data from the Trinity test, and others, resulted in the following total blast and thermal energy fractionation being observed for fission detonations near sea level<ref name="fas.org">{{cite web |url=https://fas.org/nuke/guide/usa/doctrine/dod/fm8-9/1ch3.htm |title=Chapter 3 Effects of Nuclear Explosions Section I β General |access-date=October 29, 2015 |archive-date=January 11, 2016 |archive-url=https://web.archive.org/web/20160111173824/http://fas.org/nuke/guide/usa/doctrine/dod/fm8-9/1ch3.htm |url-status=live }}</ref><ref>[https://web.archive.org/web/20170125171152/https://ke.army.mil/bordeninstitute/published_volumes/nuclearwarfare/chapter1/chapter1.pdf "Nuclear Events and Their Consequences"]. Borden Institute. "... approximately 82% of the fission energy is released as kinetic energy of the two large fission fragments. These fragments, being massive and highly charged particles, interact readily with matter. They transfer their energy quickly to the surrounding weapon materials, which rapidly become heated"</ref><ref>{{cite web |url=http://www.oektg.at/wp-content/uploads/02-Nuclear-Engineering-Overview1.pdf |archive-url=https://web.archive.org/web/20180515201022/http://www.oektg.at/wp-content/uploads/02-Nuclear-Engineering-Overview1.pdf |title=Nuclear Engineering Overview |archive-date=May 15, 2018 |publisher=Technical University Vienna}} The various energies emitted per fission event p. 4. 167 MeV is emitted by means of the repulsive electrostatic energy between the two daughter nuclei, which takes the form of the kinetic energy of the fission fragments, this kinetic energy results in both later blast and thermal effects. 5 MeV is released in prompt or initial gamma radiation, 5 MeV in prompt neutron radiation (99.36% of total), 7 MeV in delayed neutron energy (0.64%) and 13 MeV in beta decay and gamma decay (residual radiation).</ref> |- |Blast||50% |- |Thermal energy||35% |- |Initial [[ionizing radiation]]||5% |- |Residual [[fallout]] radiation||10% |} There were also several gamma ray and [[neutron detector]]s; few survived the blast, with all the gauges within {{convert|200|ft}} of ground zero being destroyed,{{sfn|Widner|2009|pp=10β25}} but sufficient data were recovered to measure the gamma ray component of the ionizing radiation released.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=375}} Some fifty different cameras had been set up, taking motion and still photographs. Special [[Fastax]] cameras taking 10,000 frames per second would record the minute details of the explosion. [[Spectrograph]] cameras would record the wavelengths of light emitted by the explosion, and [[pinhole camera]]s would record gamma rays. A rotating drum spectrograph at the {{convert|10000|yd|adj=on}} station would obtain the spectrum over the first hundredth of a second. Another, slow recording one would track the fireball. Cameras were placed in bunkers only {{convert|800|yd}} from the tower, protected by steel and lead glass, and mounted on sleds so they could be towed out by the lead-lined tank.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=354β355}} Some observers brought their own cameras despite the security. SegrΓ¨ brought in [[Jack Aeby]] with his 35 mm Perfex 44. He took the only known well-exposed color photograph of the detonation explosion.<ref name="ABQ">{{cite news |url=https://www.abqjournal.com/trinity/trinity1.htm |newspaper=[[Albuquerque Journal]] |date=July 1995 |title=The Nuclear Age's Blinding Dawn |first=Larry |last=Calloway |access-date=February 1, 2019 |archive-date=October 7, 2018 |archive-url=https://web.archive.org/web/20181007173637/https://www.abqjournal.com/trinity/trinity1.htm |url-status=live }}</ref> The official estimate for the total yield of the Trinity bomb, which includes the energy of the blast component together with the contributions from the [[bhangmeter|explosion's light output]] and both forms of [[ionizing radiation]], is {{convert|21|ktonTNT}},<ref>{{cite web |url=http://www.dtra.mil/docs/documents-ntpr-factsheets/trinity---2014.pdf?sfvrsn=0 |archive-url=https://web.archive.org/web/20141125082310/http://www.dtra.mil/docs/documents-ntpr-factsheets/trinity---2014.pdf?sfvrsn=0 |archive-date=November 25, 2014 |publisher=[[Defense Threat Reduction Agency]] |title=Fact Sheet β Operation Trinity |access-date=November 15, 2014 |url-status=dead }}</ref> of which about {{convert|15|ktonTNT}} was contributed by fission of the plutonium core, and about {{convert|6|ktonTNT}} was from fission of the natural uranium tamper.<ref>{{cite web |url=http://blog.nuclearsecrecy.com/2014/11/10/fat-mans-uranium/ |title=The Fat Man's uranium |first=Alex |last=Wellerstein |date=November 10, 2014 |publisher=Restricted Data: The Nuclear Secrecy Blog |access-date=November 15, 2014 |archive-date=November 13, 2014 |archive-url=https://web.archive.org/web/20141113044340/http://blog.nuclearsecrecy.com/2014/11/10/fat-mans-uranium/ |url-status=live }}</ref> A re-analysis of data published in 2021 put the yield at {{convert|24.8|+/-|2|ktonTNT}}.<ref name="Trinity_yield" /> As a result of the data gathered on the size of the blast, the detonation height for the bombing of Hiroshima was set at {{convert|1885|ft}} to take advantage of the [[Mach stem]] blast reinforcing effect.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=374}} The final Nagasaki burst height was {{convert|1650|ft}} so the Mach stem started sooner.<ref>{{citation |url=http://www.rerf.jp/shared/ds02/index.html |title=Reassessment of the Atomic Bomb Radiation Dosimetry for Hiroshima and Nagasaki |publisher=Radiation Effects Research Foundation |access-date=August 25, 2015 |page=47 |archive-date=September 24, 2015 |archive-url=https://web.archive.org/web/20150924090132/http://www.rerf.jp/shared/ds02/index.html |url-status=live }}</ref> The knowledge that implosion worked led Oppenheimer to recommend to Groves that the uranium-235 used in a [[Little Boy]] gun-type weapon could be used more economically in a [[Fat Man]] implosion-type weapon containing a [[pit (nuclear weapon)|composite core]] with plutonium and enriched uranium. It was too late to do this with the first Little Boy, but the composite cores would soon enter production.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=377}}
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