View source for Nuclear weapon yield

{{Short description|Energy released in nuclear weapons explosions}}
{{Use American English|date=January 2019}}[[Image:US nuclear weapons yield-to-weight comparison.svg|right|thumb|350px|[[Log–log plot]] comparing the yield (in kilotonnes) and mass (in kilograms) of various nuclear weapons developed by the United States.]]<!--The file is supposed to have ALL nuclear weapons developed by the US, but it contains only about 60 whereas the data file on which it is supposedly based gives these data for 83. In total that data file has 113 weapons, but for 30 of them it doesn't give the weight and yield.-->

The explosive '''yield of a nuclear weapon''' is the amount of [[energy]] released such as blast, thermal, and nuclear radiation, when that particular [[nuclear weapon]] [[Effects of nuclear explosions|is detonated]], usually expressed as a [[TNT equivalent]] (the standardized equivalent [[mass]] of [[trinitrotoluene]] which, if detonated, would produce the same energy discharge), either in kilotonnes (kt—thousands of tonnes of TNT), in megatonnes (Mt—millions of tonnes of TNT), or sometimes in [[terajoule]]s (TJ).  An explosive yield of one terajoule is equal to {{Cvt|1|TJ|ktTNT|3|lk=on|abbr=|sp=us|disp=output only}}. Because the accuracy of any [[Bomb calorimetry|measurement]] of the energy released by TNT has always been problematic, the conventional definition is that one kilotonne of TNT is held simply to be equivalent to 10<sup>12</sup> [[calorie]]s.

The yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon. The practical maximum yield-to-weight ratio for fusion weapons ([[thermonuclear weapon]]s) has been estimated to six megatonnes of TNT per tonne of bomb mass (25&nbsp;TJ/kg). Yields of 5.2 megatonnes/tonne and higher have been reported for large weapons constructed for single-warhead use in the early 1960s.<ref>[http://nuclearweaponarchive.org/Usa/Weapons/B41.html The B-41 Bomb]</ref> Since then, the smaller warheads needed to achieve the increased net damage efficiency (bomb damage/bomb mass) of [[Multiple independently targetable reentry vehicle|multiple warhead systems]] have resulted in increases in the yield/mass ratio for single modern warheads.

==Examples of nuclear weapon yields==

In order of increasing yield (most yield figures are approximate):

{|class=wikitable
|-
!rowspan=2|Bomb
!colspan=2|Yield
!rowspan=2|Notes
!rowspan=2|Weight of nuclear material
|-
!kt TNT
!TJ
|-
||[[Davy Crockett (nuclear device)|Davy&nbsp;Crockett]]
|{{convert|0.02|ktTNT|disp=table}}
|[[Variable yield]] tactical nuclear weapon—mass only 23&nbsp;kg (51&nbsp;lb), lightest ever deployed by the United States (same warhead as [[Special Atomic Demolition Munition]] and [[AIM-26 Falcon|GAR-11 Nuclear Falcon missile]]).
|
|-
||[[AIR-2 Genie]]
|{{convert|1.5|ktTNT|disp=table}}
|An unguided [[air-to-air rocket]] armed with a [[W25 (nuclear warhead)|W25]] [[nuclear warhead]] developed to intercept bomber squadrons.
|Total weight of nuclear material and bomb was 98.8 - 100.2&nbsp;kg
|-
|Hiroshima's {{nowrap|"[[Little Boy]]"}} {{nowrap|[[gravity bomb]]}}
|{{convert|13|-|18|ktTNT|disp=table}}
|Gun type [[uranium-235]] fission bomb (the first of the two nuclear weapons that have been used in warfare).
|64&nbsp;kg of Uranium-235, about 1.38% of the uranium fissioned
|-
|Nagasaki's {{nowrap|"[[Fat Man]]"}} gravity&nbsp;bomb
|{{convert|19|-|23|ktTNT|disp=table}}
|Implosion type [[plutonium-239]] fission bomb (the second of the two nuclear weapons used in warfare).
|6.2&nbsp;kg of Plutonium-239, about 1&nbsp;kg fissioned
|-
|[[W76]] warhead
|{{convert|100|ktTNT|disp=table}}
|Twelve of these may be in a [[MIRV]]ed [[Trident missile|Trident II missile]]; treaty limited to eight.
|
|-
|[[W87]] warhead
|{{convert|300|ktTNT|disp=table}}
|Ten of these were in a [[MIRV]]ed [[LGM-118A Peacekeeper]].
|
|-
|[[W88]] warhead
|{{convert|475|ktTNT|disp=table}}
|Eight of these may be in a Trident II missile.
|
|-
|[[Ivy King]] device
|{{convert|500|ktTNT|disp=table}}
|Most powerful US pure fission bomb,<ref name=nwa-bomb-list/> 60&nbsp;kg uranium, implosion type. Never deployed.
|60&nbsp;kg of Highly enriched uranium (HEU)
|-
|[[Orange Herald|Orange Herald Small]]
|{{convert|800|ktTNT|disp=table}}
|Most powerful tested UK [[boosted fission weapon|boosted fission missile warhead]].
|117&nbsp;kg of Uranium-235
|-

|[[B83 nuclear bomb]]
|{{convert|1200|ktTNT|disp=table}}
|Variable yield weapon, most powerful US weapon in active service.
|
|-
|[[B53 nuclear bomb]]
|{{convert|9000|ktTNT|disp=table}}
|Was the most powerful US bomb in active service until 1997. 50 were retained as part of the "Hedge" portion of the [[Enduring Stockpile]] until completely dismantled in 2011.<ref>{{cite magazine |first=Spencer |last=Ackerman |title=Last Nuclear 'Monster Weapon' Gets Dismantled |magazine=[[Wired (magazine)|Wired]] |url=https://www.wired.com/dangerroom/2011/10/b53-dismantled/ |access-date=23 October 2011 |date=October 23, 2011}}</ref> The Mod 11 variant of the [[B61 nuclear bomb|B61]] replaced the B53 in the bunker busting role. The W53 warhead from the weapon was used on the [[LGM-25C Titan II|Titan II Missile]] until the system was decommissioned in 1987.
|
|-
|[[Castle Bravo]] device
|{{convert|15000|ktTNT|disp=table}}
|Most powerful US test.<ref>{{cite web|url=https://www.brookings.edu/blog/up-front/2014/02/27/castle-bravo-the-largest-u-s-nuclear-explosion/|title=Castle Bravo: The Largest U.S. Nuclear Explosion |first=Ariana|last=Rowberry |publisher=Brookings Institution|access-date=23 September 2017}}</ref> Never deployed.
|400&nbsp;kg of Lithium-6 deuteride
|-
|EC17/Mk-17, the EC24/Mk-24, and the [[B41 nuclear bomb|B41]]&nbsp;(Mk-41)
|{{convert|25000|ktTNT|disp=table}}
|Most powerful US weapons ever: {{convert|25|MtTNT}}; the Mk-17 was also the largest by area square footage and mass cubic footage: about {{convert|20|ST|kg}}. The Mk-41 or [[B41 nuclear bomb|B41]] had a mass of 4800&nbsp;kg and yield of 25&nbsp;Mt; this equates to being the highest yield-to-weight weapon ever produced.  All were gravity bombs carried by the [[B-36]] bomber (retired by 1957).
|
|-
|The entire [[Operation Castle]] nuclear test series
|{{convert|48200|ktTNT|disp=table}}
|The highest-yielding test series conducted by the US.
|
|-
|[[Tsar Bomba]] device
|{{convert|50000|ktTNT|disp=table}}
|USSR, most powerful nuclear weapon ever detonated, yield of 50 megatonnes, (50 million tonnes of TNT). In its "final" form (i.e. with a [[depleted uranium]] [[Tamper (nuclear weapon)|tamper]] instead of one made of [[lead]]) it would have been 100 megatonnes.
|
|-
|All [[nuclear testing]] as of 1996
|{{convert|510300|ktTNT|disp=table}}
|Total energy expended during all nuclear testing.<ref>{{cite journal |url={{GBurl|xAwAAAAAMBAJ|page=63}} |page=63 |title=Known Nuclear Tests Worldwide, 1945-1995 |first1=Robert S. |last1=Norris |first2=William M. |last2=Arkin |journal=Bulletin of the Atomic Scientists |date=May 1996 |volume=52 |issue=3|doi=10.1080/00963402.1996.11456628 |bibcode=1996BuAtS..52c..61. |doi-access=free }}</ref>
|}

[[Image:Comparative nuclear fireball sizes.svg|right|thumb|250px|Comparative fireball radii for a selection of nuclear weapons.{{citation needed|date=February 2014}} Contrary to the image, which may depict the initial fireball radius, the maximum average fireball radius of Castle Bravo, a 15-megatonne yield [[surface burst]], is {{convert|3.3|to|3.7|km|abbr=on}},<ref>{{Cite web |last=Walker |first=John |author-link=John Walker (programmer) |title=Nuclear Bomb Effects Computer |publisher=Fourmilab |date=June 2005 |access-date=2009-11-22 |url=http://www.fourmilab.ch/cgi-bin/Bombcalc?yield=15&yunit=1000&range=5&runit=0.62137119&rotate=310&imsize=800}}
</ref><ref name="bombcalc">{{Cite web |last=Walker |first=John |author-link=John Walker (programmer) |title=Nuclear Bomb Effects Computer Revised Edition 1962, Based on Data from The Effects of Nuclear Weapons, Revised Edition |quote=The maximum fireball radius presented on the computer is an average between that for air and surface bursts. Thus, the fireball radius for a surface burst is 13 percent larger than that indicated and for an air burst, 13 percent smaller. |publisher=Fourmilab |date=June 2005 |access-date=2009-11-22 |url=http://www.fourmilab.ch/bombcalc/instructions.html}}</ref> and not the 1.42&nbsp;km displayed in the image. Similarly the maximum average fireball radius of a 21-kilotonne low altitude [[airburst]], which is the modern estimate for the [[Fat Man]],  is {{convert|.21|to|.24|km|abbr=on}},<ref name=bombcalc/><ref>{{cite web |last=Walker |first=John |author-link=John Walker (programmer) |title=Nuclear Bomb Effects Computer |publisher=Fourmilab |date=June 2005 |access-date=2009-11-22 |url=http://www.fourmilab.ch/cgi-bin/Bombcalc?yield=20&yunit=1&range=5&runit=0.62137119&rotate=310&imsize=800}}
</ref> and not the 0.1&nbsp;km of the image.]]
In comparison, the blast yield of the [[GBU-43 Massive Ordnance Air Blast bomb]] is 0.011&nbsp;kt, and that of the [[Oklahoma City bombing]], using a truck-based fertilizer bomb, was 0.002&nbsp;kt. The estimated strength of the [[2020 Beirut explosions|explosion at the Port of Beirut]] is 0.3-0.5 kt.<ref>{{cite web |first=Ryan |last=Pickrell |title=Beirut's Devastating Explosion Equivalent to Several Hundred Tons of TNT, Experts Say |url=https://www.sciencealert.com/beirut-s-devastating-port-explosion-100-times-bigger-than-the-mother-of-all-bombs |access-date=2020-08-06 |website=ScienceAlert |date=6 August 2020 |language=en-gb}}</ref> Most [[List of the largest artificial non-nuclear explosions|artificial non-nuclear explosions]] are considerably smaller than even what are considered to be very small nuclear weapons.

=== Yield limits ===
The yield-to-mass ratio is the amount of weapon yield compared to the mass of the weapon. The highest achieved values are somewhat lower, and the value tends to be lower for smaller, lighter weapons, of the sort that are emphasized in today's arsenals, designed for efficient MIRV use or delivery by cruise missile systems.

* The 25 Mt yield option reported for the [[B41 nuclear bomb|B41]] would give it a yield-to-mass ratio of 5.1&nbsp;megatonnes of TNT per tonne. While this would require a far greater efficiency than any other current U.S. weapon (at least 40% efficiency in a fusion fuel of lithium deuteride), this was apparently attainable, probably by the use of higher than normal [[isotopes of lithium|lithium-6]] enrichment in the [[lithium deuteride]] fusion fuel. This results in the [[B41 nuclear bomb|B41]] still retaining the record for the highest [[Power density|yield-to-mass]] weapon ever designed.<ref name="Cozzani">{{cite book |last=Cozzani |first=Franco |url=http://www.ieri.be/fr/publications/ierinews/2011/juillet/fission-fusion-and-staging |title=Fission, Fusion and Staging: A bird's view at the core concepts of nuclear weapon design and the curious ideas about it |date=July 26, 2011 |publisher=[[IERI]] |access-date=February 3, 2017}}.</ref>
* The [[W56]] demonstrated a yield-to-mass ratio of 4.96&nbsp;kt per kilogram of device mass, and very close to the predicted 5.1&nbsp;kt/kg achievable in the highest yield-to-mass weapon ever built, the 25-megatonne B41. Unlike the B41, which was never proof-tested at full yield, the W56 demonstrated its efficiency in the XW-56X2 Bluestone shot of [[Operation Dominic]] in 1962,<ref>{{cite web |url=http://nuclearweaponarchive.org/Usa/Tests/Dominic.html |title=Operation Dominic |website=The Nuclear Weapon Archive}}</ref> thus, from information available in the public domain, the W56 may hold the distinction of demonstrating the highest efficiency in a nuclear weapon to date.
* In 1963 DOE declassified statements that the U.S. had the technological capability of deploying a 35&nbsp;Mt warhead on the Titan&nbsp;II, or a 50–60&nbsp;Mt gravity bomb on B-52s. Neither weapon was pursued, but either would require yield-to-mass ratios superior to a 25&nbsp;Mt Mk-41. 
* For current smaller US weapons, yield is 600 to 2200&nbsp;kilotonnes of TNT per tonne. By comparison, for the very small tactical devices such as the [[Davy Crockett (nuclear device)|Davy Crockett]] it was 0.4 to 40&nbsp;kilotonnes of TNT per tonne. For historical comparison, for [[Little Boy]] the yield was only 4&nbsp;kilotonnes of TNT per tonne, and for the largest [[Tsar Bomba]], the yield was 2&nbsp;megatonnes of TNT per tonne (deliberately reduced from about twice as much yield for the same weapon, so there is little doubt that this bomb as designed was capable of 4&nbsp;megatonnes per tonne yield).
* The largest ''pure-fission'' bomb ever constructed, [[Ivy King]], had a 500&nbsp;kilotonne yield,<ref name=nwa-bomb-list>{{cite web |title=Complete List of All U.S. Nuclear Weapons |url=http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html#MK-18 |website=The Nuclear Weapon Archive |access-date=August 29, 2014 |date=October 14, 2006}}</ref> which is probably in the range of the upper limit on such designs.{{citation needed|date=July 2017}} Fusion boosting could likely raise the efficiency of such a weapon significantly, but eventually all fission-based weapons have an upper yield limit due to the difficulties of dealing with large critical masses. (The UK's [[Orange Herald]] was a very large boosted fission bomb, with a yield of 800&nbsp;kilotonnes.) However, there is no known upper yield limit for a fusion bomb.

Large single warheads are seldom a part of today's arsenals, since smaller [[MIRV]] warheads, spread out over a pancake-shaped destructive area, are far more destructive for a given total yield, or unit of payload mass. This effect results from the fact that destructive power of a single warhead on land scales approximately only as the cube root of its yield, due to blast "wasted" over a roughly hemispherical blast volume, while the strategic target is distributed over a circular land area with limited height and depth. This effect more than makes up for the lessened yield/mass efficiency encountered if ballistic missile warheads are individually scaled down from the maximal size that could be carried by a single-warhead missile.

=== Yield efficiency ===
The efficiency of an atomic bomb is the ratio of the actual yield to the theoretical maximum yield of the atomic bomb. Not all atomic bombs possess the same yield efficiency as each individual bombs design plays a large role in how efficient it can be. In order to maximize yield efficiency one must make sure to assemble the critical mass correctly, as well as implementing instruments such as tampers or initiators in the design. A tamper is typically made of uranium and it holds the core together using its inertia. It is used to prevent the core from separating too soon to generate maximum fission, so as not to cause a "fizzle". The initiator is a source of neutrons either inside of the core, or on the outside of the bomb, and in this case it shoots neutrons at the core at the moment of detonation. It is essentially kick starting the reaction so the maximum fission reactions can occur to maximize yield. <ref>{{Cite web |title=Nuclear Weapons Primer |url=https://www.wisconsinproject.org/nuclear-weapons/ |access-date=2023-04-28 |website=Wisconsin Project on Nuclear Arms Control |language=en-US}}</ref>

==Milestone nuclear explosions==
The following list is of milestone nuclear explosions. In addition to the [[atomic bombings of Hiroshima and Nagasaki]], the first nuclear test of a given weapon type for a country is included, as well as tests that were otherwise notable (such as the largest test ever). All yields (explosive power) are given in their estimated energy equivalents in kilotons of [[trinitrotoluene|TNT]] (see [[TNT equivalent]]). [[List of nuclear tests#Alleged tests|Putative tests]] (like [[Vela incident]]) have not been included.

{|class="wikitable sortable"
|- style="background-color:#efefef;"
! Date
! Name
! data-sort-type="number" | {{longitem|Yield (kt)}}
! Country
!class="unsortable"| Significance
|-
| {{Birth date|1945|07|16}}
| '''''[[Trinity test|Trinity]]'''''
| {{sort|19|18–20}}
| [[Nuclear weapons and the United States|United States]]
| First fission-device test, first plutonium implosion detonation.
|-
| {{Birth date|1945|08|06}}
| '''''[[Little Boy]]'''''
| {{sort|15|12–18}}
| [[Nuclear weapons and the United States|United States]]
| [[Atomic bombings of Hiroshima and Nagasaki|Bombing]] of [[Hiroshima]], [[Japan]], first detonation of a uranium gun-type device, first use of a nuclear device in combat.
|-
| {{Birth date|1945|08|09}}
| '''''[[Fat Man]]'''''
| {{sort|20.5|18–23}}
| [[Nuclear weapons and the United States|United States]]
| [[Atomic bombings of Hiroshima and Nagasaki|Bombing]] of [[Nagasaki, Nagasaki|Nagasaki]], [[Japan]], second detonation of a plutonium implosion device (the first being the Trinity Test), second and last use of a nuclear device in combat.
|-
| {{Birth date|1949|08|29}}
| '''''[[RDS-1]]'''''
| 22
| [[Soviet atomic bomb project|Soviet Union]]
| First fission-weapon test by the Soviet Union.
|-
| {{Birth date|1951|05|08}}
| '''''[[Operation Greenhouse|George]]'''''
| 225
| [[Nuclear weapons and the United States|United States]]
| First boosted nuclear weapon test, first weapon test to employ fusion in any measure.
|-
| {{Birth date|1952|10|03}}
| '''''[[Operation Hurricane|Hurricane]]'''''
| 25
| {{nowrap|[[Nuclear weapons and the United Kingdom|United Kingdom]]}}
| First fission weapon test by the United Kingdom.
|-
| {{Birth date|1952|11|01}}
| '''''[[Ivy Mike]]'''''
| 10,400
| [[Nuclear weapons and the United States|United States]]
| First "[[Nuclear weapon design#Two-stage thermonuclear weapons|staged]]" thermonuclear weapon, with cryogenic fusion fuel, primarily a test device and not weaponized.
|-
| {{nowrap|{{Birth date|1952|11|16}}}}
| '''''[[Ivy King]]'''''
| 500
| [[Nuclear weapons and the United States|United States]]
| Largest pure-fission weapon ever tested.
|-
| {{Birth date|1953|08|12}}
| '''''[[RDS-6s]]'''''
| 400
| [[Soviet atomic bomb project|Soviet Union]]
| First fusion-weapon test by the Soviet Union (not "staged").
|-
| {{Birth date|1954|03|01}}
| '''''[[Castle Bravo]]'''''
| 15,000
| [[Nuclear weapons and the United States|United States]]
| First "staged" thermonuclear weapon using dry fusion fuel. A serious [[nuclear fallout]] accident occurred. Largest nuclear detonation conducted by United States.
|-
| {{Birth date|1955|11|22}}
| '''''[[RDS-37]]'''''
| 1,600
| [[Soviet atomic bomb project|Soviet Union]]
| First "staged" thermonuclear weapon test by the Soviet Union (deployable).
|-
| {{Birth date|1957|05|31}}
| '''''[[Orange Herald]]'''''
| 720
| [[Nuclear weapons and the United Kingdom|United Kingdom]]
| Largest boosted fission weapon ever tested. Intended as a fallback "in megaton range" in case British thermonuclear development failed.
|-
| {{Birth date|1957|11|08}}
| '''''[[Operation Grapple#Grapple X|Grapple X]]'''''
| 1,800
| [[Nuclear weapons and the United Kingdom|United Kingdom]]
| First (successful) "staged" thermonuclear weapon test by the United Kingdom
|-
| {{Birth date|1960|02|13}}
| {{nowrap|'''''[[Gerboise Bleue]]'''''}}
| 70
| [[France and weapons of mass destruction|France]]
| First fission weapon test by France.
|-
| {{Birth date|1961|10|31}}
| '''''[[Tsar Bomba]]'''''
| 50,000
| [[Soviet atomic bomb project|Soviet Union]]
| Largest thermonuclear weapon ever tested—scaled down from its initial 100&nbsp;Mt design by 50%.
|-
|July 30, 1963
|[[B41 nuclear bomb|B41 / Mk-41]]
|25,000
|[[United States]]
|3-staged, the highest relative effectiveness and is the most efficient thermonuclear weapon in terms of total yield / mass ratio.
|-
| {{Birth date|1964|10|16}}
| '''''[[596 (nuclear test)|596]]'''''
| 22
| [[People's Republic of China and weapons of mass destruction|China]]
| First fission-weapon test by the People's Republic of China.
|-
| {{Birth date|1967|06|17}}
| '''''[[Chinese nuclear test No. 6|Test No. 6]]'''''
| 3,300
| [[People's Republic of China and weapons of mass destruction|China]]
| First "staged" thermonuclear weapon test by the People's Republic of China.
|-
| {{Birth date|1968|08|24}}
| '''''[[Canopus (nuclear test)|Canopus]]'''''
| 2,600
| [[France and weapons of mass destruction|France]]
| First "staged" thermonuclear weapon test by France
|-
| {{Birth date|1974|05|18}}
| {{nowrap|'''''[[Smiling Buddha]]'''''}}
| 12
| [[India and weapons of mass destruction|India]]
| First fission nuclear explosive test by India.
|-
| {{Birth date|1998|05|11}}
| '''''[[Pokhran-II]]'''''
| 45–50
| [[India and weapons of mass destruction|India]]
| First potential fusion-boosted weapon test by India; first deployable fission weapon test by India.
|-
| {{Birth date|1998|05|28}}
| '''''[[Chagai-I]]'''''
| 40
| [[Pakistan and weapons of mass destruction|Pakistan]]
| First fission weapon (boosted) test by Pakistan<ref name=pakfas>{{Cite web |title=Pakistan Nuclear Weapons: A Brief History of Pakistan's Nuclear Program |url=http://www.fas.org/nuke/guide/pakistan/nuke/ |publisher=[[Federation of American Scientists]] |date=11 December 2002 |access-date=30 October 2019}}</ref>
|-
| {{Birth date|2006|10|09}}
| '''''{{nowrap|[[2006 North Korean nuclear test|2006 nuclear test]]}}'''''
| {{sort|0.5|under 1}}
| {{nowrap|[[North Korea and weapons of mass destruction|North Korea]]}}
| First fission-weapon test by North Korea (plutonium-based).
|-
| {{Birth date|2017|09|03}}
| '''''{{nowrap|[[2017 North Korean nuclear test|2017 nuclear test]]}}'''''
| {{sort|110|200–300}}
| {{nowrap|[[North Korea and weapons of mass destruction|North Korea]]}}
| First "staged" thermonuclear weapon test claimed by North Korea.
|}

;Note
* "Staged" refers to whether it was a "true" [[thermonuclear weapon]] of the so-called [[Teller–Ulam]] configuration or simply a form of a [[boosted fission weapon]]. For a more complete list of nuclear test series, see [[List of nuclear tests]]. Some exact yield estimates, such as that of the [[Tsar Bomba]] and the tests by India and Pakistan in 1998, are somewhat contested among specialists.

==Calculating yields and controversy==
{{see also|Fermi problem}}
Yields of [[nuclear explosion]]s can be very hard to calculate, even using numbers as rough as in the kilotonne or megatonne range (much less down to the resolution of individual [[terajoule]]s). Even under very controlled conditions, precise yields can be very hard to determine, and for less controlled conditions the margins of error can be quite large. For fission devices, the most precise yield value is found from "[[radiochemistry|radiochemical]]/Fallout analysis"; that is, measuring the quantity of [[fission product]]s generated, in much the same way as the [[chemical yield]] in chemical reaction products can be measured after a [[chemical reaction]]. The radiochemical analysis method was pioneered by [[Herbert L. Anderson]].

For nuclear explosive devices where the fallout is not attainable or would be [[neutron bomb|misleading]], [[neutron activation]] analysis is often employed as the second most accurate method, with it having been used to determine the yield of both [[Little Boy]]<ref name=Kerr2005>{{cite book |chapter-url=http://www.rerf.or.jp/shared/ds02/pdf/chapter01/cha01-p42-61.pdf |chapter=Bomb Parameters |last1=Kerr |first1=George D. |last2=Young |first2=Robert W. |last3=Cullings |first3=Harry M. |last4=Christy |first4=Robert F. |pages=42–43 |title=Reassessment of the Atomic Bomb Radiation Dosimetry for Hiroshima and Nagasaki – Dosimetry System 2002 |year=2005 |publisher=The Radiation Effects Research Foundation |editor-first1=Robert W. |editor-last1=Young |editor-first2=George D. |editor-last2=Kerr |access-date=2014-11-08 |archive-date=2015-08-10 |archive-url=https://web.archive.org/web/20150810210007/http://www.rerf.or.jp/shared/ds02/pdf/chapter01/cha01-p42-61.pdf |url-status=dead }}</ref><ref name=Malik1985>{{cite web |url=http://www.osti.gov/manhattan-project-history/publications/LANLHiroshimaNagasakiYields.pdf |title=The Yields of the Hiroshima and Nagasaki Explosions |last=Malik |first=John |date=September 1985 |publisher=Los Alamos National Laboratory |access-date=March 9, 2014}}</ref> and [[thermonuclear]] [[Ivy Mike]]'s<ref>{{cite book |title=Operation Ivy Final Report Joint Task Force 132 |year=1952 |url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a995443.pdf |archive-url=https://web.archive.org/web/20140311064141/http://www.dtic.mil/dtic/tr/fulltext/u2/a995443.pdf |url-status=live |archive-date=March 11, 2014 |author=US Army}}</ref> respective yields.

Yields can also be inferred in a number of other [[remote sensing]] ways, including scaling law calculations based on blast size, [[infrasound]], fireball brightness ([[Bhangmeter]]), [[seismograph]]ic data ([[CTBTO]]),<ref>[https://www.princeton.edu/~ota/disk2/1988/8838/883809.PDF Estimating the yields of nuclear explosions. chapter 7. Seismic verification of nuclear testing treaties.]</ref> and the strength of the shock wave.
{| class="wikitable" style="float:right; margin: 1em"
|+ Alongside contemporary fundamental physics, data from nuclear testing 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 – General}}</ref><ref>{{cite web |url=https://ke.army.mil/bordeninstitute/published_volumes/nuclearwarfare/chapter1/chapter1.pdf |archiveurl=https://web.archive.org/web/20170125171152/https://ke.army.mil/bordeninstitute/published_volumes/nuclearwarfare/chapter1/chapter1.pdf |archivedate=2017-01-25 |title=Nuclear Events and their Consequences |publisher=The Borden Institute |quote=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 are listed on p. 4: ''"167 MeV"'' is emitted by means of the repulsive electrostatic energy between the 2 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]] ||style="text-align:right"| 5%
|-
| Residual [[fallout radiation]] || 10%
|}
[[Enrico Fermi]] famously made a (very) rough calculation of the yield of the [[Trinity test]] by dropping small pieces of paper in the air and measuring how far they were moved by the [[blast wave]] of the explosion; that is, he found the [[Overpressure|blast pressure]] at his distance from the detonation in [[pounds per square inch]], using the deviation of the papers' fall away from the vertical as a crude [[barograph|blast gauge/barograph]], and then with pressure ''X'' in psi, at distance ''Y'', in miles figures, he extrapolated backwards to estimate the yield of the Trinity device, which he found was about 10&nbsp;[[kilotonne]]s of blast energy.<ref>[http://www.abqjournal.com/trinity/trinity1.htm Article featuring Jack Aeby talking about his photograph].</ref><ref>{{cite book |last=Rhodes |first=Richard |author-link=Richard Rhodes |title=[[The Making of the Atomic Bomb]] |location=New York |publisher=Simon & Schuster |year=1986 |isbn=0-671-44133-7|oclc=13793436|pp=674–677}}</ref>

Fermi later recalled:
{{blockquote|
I was stationed at the Base Camp at Trinity in a position about ten miles [16&nbsp;km] from the site of the explosion... About 40&nbsp;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&nbsp;1/2&nbsp;meters, which, at the time, I estimated to correspond to the blast that would be produced by ten thousand tonnes of TNT.<ref>E. Fermi. [https://web.archive.org/web/20130302233056/http://www2.vo.lu/homepages/geko/atom/report.htm My Observations During the Explosion at Trinity on July 16, 1945].</ref><ref>{{cite web |url=http://www.dannen.com/decision/fermi.html |title=Trinity Test, July 16, 1945, Eyewitness Accounts – Enrico Fermi |access-date=November 4, 2014 }}</ref><ref name=weapons-2-2005>{{cite web |title=Eyewitnesses to Trinity |url=http://www.lanl.gov/science/weapons_journal/wj_pubs/11nwj2-05.pdf |website=Nuclear Weapons Journal, Issue 2, 2005 |publisher=Los Alamos National Laboratory |access-date=18 February 2014 |page=45 |year=2005 |archive-date=29 December 2018 |archive-url=https://web.archive.org/web/20181229223636/https://www.lanl.gov/science/weapons_journal/wj_pubs/11nwj2-05.pdf |url-status=dead }}</ref>}}

The [[surface area]] (A) and volume (V) of a sphere are <math>A = 4\pi r^2</math> and <math>V = \frac{4}{3} \pi r^3</math> respectively.

The blast wave, however, was likely assumed to grow out as the surface area of the approximately hemispheric near [[surface burst]] blast wave of the Trinity gadget.
The paper is moved 2.5&nbsp;meters by the wave, so the effect of the Trinity device is to displace a hemispherical shell of air of volume 2.5&nbsp;m × 2π(16&nbsp;km)<sup>2</sup>. Multiply by 1&nbsp;atm to get an energy of {{val|4.1|e=14|u=J}} ~ 100&nbsp;kT TNT.{{quantify|date=May 2015}}

<!--[[thumb]]
[https://www.theatlantic.com/photo/2015/07/70-years-since-trinity-when-we-tested-nuclear-bombs/398735/ -->
[[Image:Trinity Test Fireball 25ms.jpg|right|thumb|250px|This photograph of the Trinity blast, captured by [[Berlyn Brixner]], was used by G.&nbsp;I. Taylor to estimate its yield.]]

A good approximation of the yield of the Trinity test device was obtained in 1950 by the British physicist [[Geoffrey Ingram Taylor|G. I. Taylor]] from simple [[dimensional analysis]] and an estimation of the heat capacity for very hot air. Taylor had initially done this highly classified work in mid-1941 and published an article with an analysis of the Trinity data fireball when the Trinity photograph data was declassified in 1950 (after the USSR had exploded its own version of this bomb).

Taylor noted that the [[radius]] ''R'' of the blast should initially depend only on the energy ''E'' of the explosion, the time ''t'' after the detonation, and the density ρ of the air. [[Buckingham π theorem|The only equation]] having compatible dimensions that can be constructed from these quantities is

: <math>R = S\left(\frac{E t^2}{\rho}\right)^{\frac{1}{5}}.</math>

Here ''S'' is a dimensionless constant having a value approximately equal to 1, since it is low-order function of the [[heat capacity ratio]] or adiabatic index

: <math>\gamma = \frac{C_P}{C_V},</math>

which is approximately 1 for all conditions.

Using the picture of the Trinity test shown here (which had been publicly released by the U.S. government and published in ''[[Life (magazine)|Life]]'' magazine), using successive frames of the explosion, Taylor found that ''R''<sup>5</sup>/''t''<sup>2</sup> is a constant in a given nuclear blast (especially between 0.38&nbsp;ms, after the shock wave has formed, and 1.93&nbsp;ms, before significant energy is lost by thermal radiation). Furthermore, he estimated a value for ''S'' numerically at 1.

Thus, with ''t'' = 0.025&nbsp;s and the blast radius being 140&nbsp;metres, and taking ''ρ'' to be 1&nbsp;kg/m<sup>3</sup> (the measured value at Trinity on the day of the test, as opposed to sea-level values of approximately 1.3&nbsp;kg/m<sup>3</sup>) and solving for ''E'', Taylor obtained that the yield was about 22&nbsp;kilotonnes of TNT (90&nbsp;TJ). This does not take into account the fact that the energy should only be about half this value for a hemispherical blast, but this very simple argument did agree to within 10% with the official value of the bomb's yield in 1950, which was {{convert|20|ktonTNT}} (see G.&nbsp;I. Taylor, ''Proc. Roy. Soc. London A'' '''200''', pp.&nbsp;235–247 (1950)).

A good approximation to Taylor's constant ''S'' for <math>\gamma</math> below about 2 is<ref>{{cite web |url=http://glasstone.blogspot.com/2006/03/analytical-mathematics-for-physical.html |title=Analytical mathematics for physical understanding, versus abstract numerical computation |website=The effects of nuclear weapons. Credible nuclear deterrence, debunking "disarm or be annihilated". Realistic effects and credible nuclear weapon capabilities for deterring or stopping aggressive invasions and attacks which could escalate into major conventional or nuclear wars |date=2006-03-29}}</ref>

: <math>S = \left(\frac{75(\gamma - 1)}{8\pi}\right)^{\frac{1}{5}}.</math>

The value of the [[heat capacity ratio]] here is between the 1.67 of fully dissociated air molecules and the lower value for very hot diatomic air (1.2), and under conditions of an atomic fireball is (coincidentally) close to the [[Standard temperature and pressure|STP]] (standard) gamma for room-temperature air, which is 1.4. This gives the value of Taylor's '''S''' constant to be 1.036 for the adiabatic hypershock region where the constant ''R''<sup>5</sup>/''t''<sup>2</sup> condition holds.

As it relates to fundamental dimensional analysis, if one expresses all the variables in terms of mass ''M'', length ''L'', and time ''T'':<ref>Thayer Watkins. [https://web.archive.org/web/20140701221514/http://applet-magic.com/fireball.htm ''The Expansion of the Fireball of an Explosion'']. San José State University.</ref>

: <math>E = [M \cdot L^2 \cdot T^{-2}]</math>

(think of the expression for kinetic energy, <math>E = mv^2/2</math>),

: <math>\rho = [M \cdot L^{-3}],</math>

: <math>t = [T],</math>

: <math>r = [L],</math>

and then derive an expression for, say, ''E'', in terms of the other variables, by finding values of <math>\alpha</math>, <math>\beta</math>, and <math>\gamma</math> in the general relation

: <math>E = \rho^\alpha \cdot t^\beta \cdot r^\gamma</math>

such that the left and right sides are dimensionally balanced in terms of ''M'', ''L'', and ''T'' (i.e., each dimension has the same exponent on both sides).

===Other methods and controversy===
{{original research|date=March 2021}}
Where these data are not available, as in a number of cases, precise yields have been in dispute, especially when they are tied to questions of politics. The weapons used in the [[atomic bombings of Hiroshima and Nagasaki]], for example, were highly individual and very idiosyncratic designs, and gauging their yield retrospectively has been quite difficult. The Hiroshima bomb, "[[Little Boy]]", is estimated to have been between {{convert|12|and|18|ktTNT}} (a 20% margin of error), while the Nagasaki bomb, "[[Fat Man]]", is estimated to be between {{convert|18|and|23|ktTNT}} (a 10% margin of error).

Such apparently small changes in values can be important when trying to use the data from these bombings as reflective of how other bombs would behave in combat, and also result in differing assessments of how many "Hiroshima bombs" other weapons are equivalent to (for example, the [[Ivy Mike]] hydrogen bomb was equivalent to either 867 or 578 Hiroshima weapons — a rhetorically quite substantial difference — depending on whether one uses the high or low figure for the calculation).

Other disputed yields have included the massive [[Tsar Bomba]], whose yield was claimed between being "only" {{convert|50|MtTNT}} or at a maximum of {{convert|57|MtTNT}} by differing political figures, either as a way for hyping the power of the bomb or as an attempt to undercut it.

==See also==
*[[Effects of nuclear explosions]] — goes into detail about different effects at different yields
*[[List of nuclear weapons]]

==References==

<references/>

==External links==
{{Commons category}}
*[http://www.warbirdforum.com/hiroshim.htm "What was the yield of the Hiroshima bomb?"] {{Webarchive|url=https://web.archive.org/web/20170913004426/https://www.warbirdforum.com/hiroshim.htm |date=2017-09-13 }} (excerpt from official report)
*[https://web.archive.org/web/20051201184506/http://www.cddc.vt.edu/host/atomic/nukeffct/enw77a.html "General Principles of Nuclear Explosions"], Chapter 1 in Samuel Glasstone and Phillip Dolan, eds., ''The Effects of Nuclear Weapons'', 3rd edn. (Washington D.C.: U.S. Department of Defense/U.S. Energy Research and Development Administration, 1977); provides information about the relationship of nuclear yields to other effects (radiation, damage, etc.).
*[https://web.archive.org/web/20060405211214/http://www.saag.org/papers5/paper451.html "THE MAY 1998 POKHRAN TESTS: Scientific Aspects"], discusses different methods used to determine the yields of the Indian 1998 tests.
*[https://fas.org/nuke/guide/india/nuke/ Discusses some of the controversy over the Indian test yields]
*[http://nuclearweaponarchive.org/India/IndiaRealYields.html "What are the real yields of India's nuclear tests?"] from Carey Sublette's NuclearWeaponArchive.org
*[http://meyerweb.com/eric/tools/gmap/hydesim.html High-Yield Nuclear Detonation Effects Simulator] {{Webarchive|url=https://web.archive.org/web/20090216184207/http://meyerweb.com/eric/tools/gmap/hydesim.html |date=2009-02-16 }}

{{Nuclear technology}}

[[Category:Nuclear weapon design|Yield]]
[[Category:Energy measurement]]