Editing Fat Man (section)

==Assembly==
[[File:Fat Man Detonation.png|thumb|Cross section of the Fat Man "physics package". See description and colors in this section for details.|440x440px]]
[[File:Fat Man Assembly Tinian 1945.jpg|thumb|right|Fat Man's "physics package" nuclear device about to be encased]]
[[File:Fat Man Assembled Tinian 1945.jpg|thumb|right|Fat Man on its transport carriage, with liquid asphalt sealant applied over the casing's seams]]
[[File:Atomic Bomb Pits - Tinian - panoramio (3).jpg|thumb|right|Preserved Tinian "bomb pit#2", where Fat Man was loaded aboard ''Bockscar'']]

The [[plutonium pit]]{{sfn|Coster-Mullen|2012|p=52}} was {{convert|3.62|in}} in diameter and contained an "Urchin" [[modulated neutron initiator]] that was {{convert|0.8|in}} in diameter. The [[depleted uranium]] [[Tamper (nuclear weapon)|tamper]] was an {{convert|8.75|in|mm|adj=mid|-diameter}} sphere, surrounded by a {{convert|0.125|in|mm|adj=mid|-thick}} shell of boron-impregnated plastic. The plastic shell had a {{convert|5|in|mm|adj=mid|-diameter}} cylindrical hole running through it, like the hole in a cored apple, in order to allow insertion of the pit as late as possible. The missing tamper cylinder containing the pit could be slipped in through a hole in the surrounding {{convert|18.5|in|mm|adj=mid|-diameter}} aluminum pusher.{{sfn|Coster-Mullen|2012|p=186}} The pit was warm to the touch, emitting 2.4 W/kg-Pu, about 15 W for the {{convert|6.19|kg|adj=on}} core.{{sfn|Coster-Mullen|2012|p=49}}

The explosion symmetrically compressed the plutonium to twice its normal density before the "Urchin" added [[free neutron]]s to initiate a [[nuclear fission|fission]] [[nuclear chain reaction|chain reaction]].{{sfn|Coster-Mullen|2012|p=45}}
* {{legend|#ffff00 |{{resize|98%|An [[exploding-bridgewire detonator]] simultaneously starts a [[detonation wave]] in each of the 32 tapered high-explosive columns (positioned around the explosive material at the face centers of a [[truncated icosahedron]],{{sfn|Coster-Mullen|2012|p=41}} a geometry popularly known from the pattern of common [[soccer ball]]s).}}}}
* {{legend|#cc6633 |{{resize|98%|The detonation wave (arrows) is initially [[wikt:convex|convex]] in the}}...}}
* {{legend|#d79563 |...{{resize|98%|faster explosive ([[Composition B]]: 60% [[RDX]], 40% [[Trinitrotoluene|TNT]]).{{sfn|Coster-Mullen|2012|p=41}} The [[wavefront]]s become [[wikt:Special:Search/concave|concave]] in the}}...}}
* {{legend|#ffcc99 |...{{resize|98%|slower explosive ([[Baratol (explosive)|Baratol]]: 70% [[barium nitrate]], 30% TNT).{{sfn|Coster-Mullen|2012|p=41}} The 32 waves then merge into a single spherical implosive shock-wave which hits the}}...}}
* {{legend|#d79563 |...{{resize|98%|inner charges' faster explosive ([[Composition B]]).{{sfn|Coster-Mullen|2012|p=186}}}}}}
* {{legend|#c6c6c6 |{{resize|98%|The medium-density [[aluminum]] "pusher" transfers the imploding shock-wave from the low-density explosive to the high-density uranium, minimizing undesirable [[turbulence]].{{sfn|Hansen|1995|pp=122–123}} The shock-wave then compresses the inner components, passing through a}}...}}
* {{legend|#0000ff |...{{resize|98%|[[boron]]-plastic shell intended to prevent pre-detonation of the bomb by stray neutrons.{{sfn|Hansen|1995|pp=122–123}} The shock-wave reaches the center of the bomb, where the...}}}}
* {{legend|#008000 |{{resize|98%|...[[beryllium]]–[[Polonium-210|<sup>210</sup>Po]] "Urchin" is crushed,{{sfn|Coster-Mullen|2012|p=48}} pushing the two metals together and thereby releasing a burst of [[neutron]]s into the compressed}}...}}
* {{legend|#ff0000 |{{resize|98%|...[[plutonium pit|pit]] of the [[nickel]]-plated [[plutonium–gallium alloy|delta-phase alloy]] of [[plutonium-239|<sup>239</sup>Pu]]–[[Plutonium-240|<sup>240</sup>Pu]]–[[gallium]] (96%–1%–3% by [[Concentration#Molarity|molarity]]).{{sfn|Coster-Mullen|2012|p=57}}<ref name=nukearchive>{{cite web |first=Carey |last=Sublette |title=Section 8.0 The First Nuclear Weapons |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html|date=3 July 2007 |work=Nuclear Weapons FAQ|access-date=29 August 2013}}</ref> A fission chain reaction then begins. The tendency of the fissioning pit to blow itself apart prematurely is reduced by the inward [[momentum]] of the}}...}}
* {{legend|#808080 |{{resize|98%|...natural-[[uranium]] "tamper" (inertial confinement). The tamper also [[neutron reflector|reflects neutrons]] back into the pit, accelerating the chain reaction. If and when sufficient [[fast neutron]]s are produced, the tamper itself undergoes fission, accounting for up to 30% of the [[nuclear weapon yield|weapon's yield]].<ref name="The Fat Man's Uranium" />}}}}

The result was the fission of about {{convert|1|kg}} of the {{convert|6.19|kg}} of plutonium in the pit, or about 16% of the fissile material present.{{sfn|Coster-Mullen|2012|p=46}}<ref>{{cite web |first=Alex |last=Wellerstein |date=23 December 2013 |title=Kilotons per kilogram |publisher= Restricted Data |url=http://blog.nuclearsecrecy.com/2013/12/23/kilotons-per-kilogram/ |access-date=9 December 2020}}</ref> The detonation released the energy equivalent to the detonation of {{convert|21|ktonTNT|disp=or}}.{{sfn|Malik|1985|p=25}} About 30% of the yield came from fission of the uranium tamper.<ref name="The Fat Man's Uranium">{{cite web |title=The Fat Man's Uranium |first=Alex |last=Wellerstein |date=10 November 2014 |publisher= Restricted Data |url=http://blog.nuclearsecrecy.com/2014/11/10/fat-mans-uranium/ |access-date=9 December 2020}}</ref>