Editing Nuclear weapon (section)

=== Fusion weapons ===
{{Main|Thermonuclear weapon}}
[[File:Teller-Ulam device 3D.svg|thumb|The basics of the [[Teller–Ulam design]] for a hydrogen bomb: a fission bomb uses radiation to compress and heat a separate section of fusion fuel.]]

The other basic type of nuclear weapon produces a large proportion of its energy in nuclear fusion reactions. Such fusion weapons are generally referred to as '''[[thermonuclear weapon]]s''' or more colloquially as '''hydrogen bombs''' (abbreviated as '''H-bombs'''), as they rely on fusion reactions between isotopes of [[hydrogen]] ([[deuterium]] and [[tritium]]). All such weapons derive a significant portion of their energy from fission reactions used to "trigger" fusion reactions, and fusion reactions can themselves trigger additional fission reactions.<ref>Carey Sublette, [http://nuclearweaponarchive.org/Nwfaq/Nfaq4-5.html#Nfaq4.5.2 Nuclear Weapons Frequently Asked Questions: 4.5.2 "Dirty" and "Clean" Weapons] {{webarchive |url=https://web.archive.org/web/20160303170957/http://nuclearweaponarchive.org/Nwfaq/Nfaq4-5.html |date=March 3, 2016}}, accessed May 10, 2011.</ref>

Only six countries—the [[United States]], [[Russia]], the [[United Kingdom]], [[China]], [[France]], and [[India]]—have conducted thermonuclear weapon tests. Whether India has detonated a "true" multi-staged [[thermonuclear weapon]] is controversial.<ref>On India's alleged hydrogen bomb test, see Carey Sublette, [http://nuclearweaponarchive.org/India/IndiaRealYields.html What Are the Real Yields of India's Test?] {{webarchive |url=https://web.archive.org/web/20110927013551/http://nuclearweaponarchive.org/India/IndiaRealYields.html |date=September 27, 2011}}.</ref> [[North Korea]] claims to have tested a fusion weapon {{as of|2016|January|lc=y}}, though this claim is disputed.<ref>{{cite web|last1=McKirdy|first1=Euan|title=North Korea announces it conducted nuclear test |url=http://www.cnn.com/2016/01/05/asia/north-korea-seismic-event/|website=CNN|date=January 6, 2016|access-date=January 7, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160107193043/http://www.cnn.com/2016/01/05/asia/north-korea-seismic-event/|archive-date=January 7, 2016}}</ref> Thermonuclear weapons are considered much more difficult to successfully design and execute than primitive fission weapons. Almost all of the nuclear weapons deployed today use the thermonuclear design because it results in an explosion hundreds of times stronger than that of a fission bomb of similar weight.<ref>{{Cite web |url=https://www.armscontrol.org/factsheets/Nuclear-Testing-and-Comprehensive-Test-Ban-Treaty-CTBT-Timeline|title=Nuclear Testing and Comprehensive Test Ban Treaty (CTBT) Timeline |website=Arms control association |url-status=dead |archive-url=https://web.archive.org/web/20200421174531/https://www.armscontrol.org/factsheets/Nuclear-Testing-and-Comprehensive-Test-Ban-Treaty-CTBT-Timeline|archive-date=April 21, 2020}}</ref>

Thermonuclear bombs work by using the energy of a fission bomb to compress and heat fusion fuel. In the [[Teller-Ulam design]], which accounts for all multi-megaton yield hydrogen bombs, this is accomplished by placing a fission bomb and fusion fuel ([[tritium]], [[deuterium]], or [[lithium deuteride]]) in proximity within a special, radiation-reflecting container. When the fission bomb is detonated, [[gamma ray]]s and [[X-ray]]s emitted first compress the fusion fuel, then heat it to thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high-speed [[neutron]]s, which can then induce fission in materials not normally prone to it, such as [[depleted uranium]]. Each of these components is known as a "stage", with the fission bomb as the "primary" and the fusion capsule as the "secondary". In large, megaton-range hydrogen bombs, about half of the yield comes from the final fissioning of depleted uranium.<ref name="Hansen" />

Virtually all thermonuclear weapons deployed today use the "two-stage" design described to the right, but it is possible to add additional fusion stages—each stage igniting a larger amount of fusion fuel in the next stage. This technique can be used to construct thermonuclear weapons of arbitrarily large yield. This is in contrast to fission bombs, which are limited in their explosive power due to [[Nuclear criticality safety|criticality]] danger (premature nuclear chain reaction caused by too-large amounts of pre-assembled fissile fuel). The largest nuclear weapon ever detonated, the [[Tsar Bomba]] of the USSR, which released an energy equivalent of over {{convert|50|MtonTNT}}, was a three-stage weapon. Most thermonuclear weapons are considerably smaller than this, due to practical constraints from missile warhead space and weight requirements.<ref name="Sublette">{{cite web |url=http://nuclearweaponarchive.org/ |last=Sublette |first=Carey |title=The Nuclear Weapon Archive |access-date=March 7, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070301105632/http://nuclearweaponarchive.org/ |archive-date=March 1, 2007}}</ref> In the early 1950s the [[Lawrence Livermore National Laboratory|Livermore Laboratory]] in the United States had plans for the testing of two massive bombs, Gnomon and [[Sundial (weapon)|Sundial]], 1 gigaton of TNT and 10 gigatons of TNT respectively.<ref>{{Cite web |last=Simha |first=Rakesh Krishnan |date=2016-01-05 |title=Nuclear overkill: The quest for the 10 gigaton bomb |url=https://www.rbth.com/opinion/2016/01/05/nuclear-overkill-the-quest-for-the-10-gigaton-bomb_556351 |access-date=2023-10-08 |website=Russia Beyond |language=en-US |archive-date=November 29, 2023 |archive-url=https://web.archive.org/web/20231129191303/https://www.rbth.com/opinion/2016/01/05/nuclear-overkill-the-quest-for-the-10-gigaton-bomb_556351 |url-status=live }}</ref><ref>{{Cite web |last=Wellerstein |first=Alex |author-link=Alex Wellerstein |date=2021-10-29 |title=The untold story of the world's biggest nuclear bomb |url=https://thebulletin.org/2021/11/the-untold-story-of-the-worlds-biggest-nuclear-bomb/ |access-date=2023-10-08 |website=Bulletin of the Atomic Scientists |language=en-US |archive-date=August 27, 2023 |archive-url=https://web.archive.org/web/20230827130626/https://thebulletin.org/2021/11/the-untold-story-of-the-worlds-biggest-nuclear-bomb/ |url-status=live }}</ref>
[[File:Edward Teller (1958)-LLNL.jpg|thumb|upright|[[Edward Teller]], often referred to as the "father of the hydrogen bomb"]]

Fusion reactions do not create fission products, and thus contribute far less to the creation of [[nuclear fallout]] than fission reactions, but because all [[thermonuclear weapon]]s contain at least one [[Fission barrier|fission]] stage, and many high-yield thermonuclear devices have a final fission stage, thermonuclear weapons can generate at least as much nuclear fallout as fission-only weapons. Furthermore, high yield thermonuclear explosions (most dangerously ground bursts) have the force to lift radioactive debris upwards past the [[tropopause]] into the [[stratosphere]], where the calm non-turbulent winds permit the debris to travel great distances from the burst, eventually settling and unpredictably contaminating areas far removed from the target of the explosion.