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{{Short description|2-stage nuclear weapon}}
{{Use dmy dates|date=December 2019}}
[[File:Teller-ulam-multilang.svg|right|thumb|
A basic diagram of a thermonuclear weapon.<br />
Some designs use spherical secondaries.{{ordered list
 | list_style=margin-left:0; list-style-position:inside;
 | list-style-type=upper-alpha
 | fission primary stage
 | fusion secondary stage
}} {{br}}
{{ordered list
 | list_style=margin-left:0; list-style-position:inside;
 | [[High explosive|High-explosive]] lenses
 | [[Uranium-238]] ("tamper") lined with beryllium reflector
 | [[Vacuum]] ("levitated core")
 | [[Tritium]] "boost" gas (blue) within [[plutonium]] or [[uranium]] hollow core
 | Radiation channel filled with [[polystyrene]] foam
 | Uranium ("pusher/tamper")
 | [[Lithium deuteride|Lithium-6 deuteride]] (fusion fuel)
 | Plutonium ("[[spark plug]]")
 | Radiation case (confines thermal [[X-ray]]s by reflection)
}}]]

A '''thermonuclear weapon''', '''fusion weapon''' or '''hydrogen bomb''' ('''H&nbsp;bomb''') is a second-generation [[nuclear weapon design]]. Its greater sophistication affords it vastly greater destructive power than first-generation [[nuclear bomb]]s, a more compact size, a lower mass, or a combination of these benefits. Characteristics of [[nuclear fusion]] reactions make possible the use of non-fissile [[depleted uranium]] as the weapon's main fuel, thus allowing more efficient use of scarce [[fissile material]] such as [[uranium-235]] ({{SimpleNuclide|uranium|235}}) or [[plutonium-239]] ({{SimpleNuclide|plutonium|239}}). The first full-scale thermonuclear test ([[Ivy Mike]]) was carried out by the United States in 1952, and the concept has since been employed by most of the world's [[List of states with nuclear weapons|nuclear powers]] in the design of their weapons.<ref name="NPR_TOTN" />

Modern fusion weapons essentially consist of two main components: a [[nuclear fission]] primary stage (fueled by {{SimpleNuclide|uranium|235}} or {{SimpleNuclide|plutonium|239}}) and a separate nuclear fusion secondary stage containing thermonuclear fuel: heavy [[isotope]]s of hydrogen ([[deuterium]] and [[tritium]]) as the pure element or in modern weapons [[Lithium hydride#Lithium deuteride|lithium deuteride]]. For this reason, thermonuclear weapons are often colloquially called '''hydrogen bombs''' or '''H-bombs'''.<ref group="note">The misleading term ''hydrogen bomb'' was already in wide public use before fission product [[fallout]] from the [[Castle Bravo]] test in 1954 revealed the extent to which the design relies on fission as well.</ref>

A fusion explosion begins with the [[detonation]] of the fission primary stage. Its temperature soars past 100 million [[kelvin]], causing it to glow intensely with thermal ("soft") [[X-ray|X-rays]]. These X-rays flood the void (the "radiation channel" often filled with [[Polystyrene#Foams|polystyrene foam]]) between the primary and secondary assemblies placed within an enclosure called a radiation case, which confines the X-ray energy and resists its outward pressure. The distance separating the two assemblies ensures that debris fragments from the fission primary (which move much more slowly than X-ray [[Photon|photons]]) cannot disassemble the secondary before the fusion explosion runs to completion.

The secondary fusion stage—consisting of outer pusher/[[Tamper (nuclear weapon)|tamper]], fusion fuel filler and central [[plutonium]] spark plug—is imploded by the X-ray energy impinging on its pusher/ tamper. This compresses the entire secondary stage and drives up the density of the plutonium spark plug. The density of the plutonium fuel rises to such an extent that the spark plug is driven into a [[Criticality (status)|supercritical]] state, and it begins a [[Nuclear chain reaction|nuclear fission chain reaction]]. The [[Nuclear fission product|fission products]] of this chain reaction heat the highly compressed (and thus super dense) thermonuclear fuel surrounding the spark plug to around 300 million kelvin, igniting fusion reactions between fusion fuel nuclei. In modern weapons fueled by lithium deuteride, the fissioning plutonium spark plug also emits free neutrons that collide with lithium nuclei and supply the tritium component of the thermonuclear fuel.

The secondary's relatively massive tamper (which resists outward expansion as the explosion proceeds) also serves as a thermal barrier to keep the fusion fuel filler from becoming too hot, which would spoil the compression. If made of [[uranium]], [[enriched uranium]] or plutonium, the tamper captures [[Neutron temperature|fast fusion neutrons]] and undergoes fission itself, increasing the overall [[Nuclear weapon yield|explosive yield]]. Additionally, in most designs the radiation case is also constructed of a material that undergoes fission driven by fast thermonuclear neutrons. Such bombs are classified as two stage weapons. Fast fission of the tamper and radiation case is the main contribution to the total yield and is the dominant process that produces [[Radioactivity|radioactive]] fission product [[Nuclear fallout|fallout]].<ref>{{Cite book |arxiv = physics/0510071 |last1 = Gsponer |first1 = Andre |title = Fourth Generation Nuclear Weapons: Military effectiveness and collateral effects |publisher=Independent Scientific Research Institute |id=ISRI-05-03 |year = 2005}}</ref><ref>{{cite book |title=The B61-based "Robust Nuclear Earth Penetrator:" Clever retrofit or headway towards fourth-generation nuclear weapons? |first=Andre |last=Gsponer |arxiv=physics/0510052 |publisher=Independent Scientific Research Institute |id=ISRI-03-08 |year=2005}}</ref>

Before Ivy Mike, [[Operation Greenhouse]] in 1951 was the first American nuclear test series to test principles that led to the development of thermonuclear weapons. Sufficient fission was achieved to boost the associated fusion device, and enough was learned to achieve a full-scale device within a year. The design of all modern thermonuclear weapons in the United States is known as the [[history of the Teller–Ulam design|''Teller–Ulam configuration'']] for its two chief contributors, [[Edward Teller]] and [[Stanisław Ulam]], who developed it in 1951<ref name="Teller" /> for the United States, with certain concepts developed with the contribution of physicist [[John von Neumann]]. Similar devices were developed by the Soviet Union, United Kingdom, France, China and India.<ref name=":8" /> The thermonuclear [[Tsar Bomba]] was the most powerful bomb ever detonated.<ref>{{Cite web|url=https://www.smithsonianmag.com/smart-news/russia-declassifies-video-1961-largest-hydrogen-bomb-ever-detonated-180975669/|title=Russia Declassifies Video From 1961 of Largest Hydrogen Bomb Ever Detonated|first1=Smithsonian|last1=Magazine|first2=Theresa|last2=Machemer|website=Smithsonian Magazine}}</ref> As thermonuclear weapons represent the most efficient design for weapon energy yield in weapons with yields above {{convert|50|ktonTNT|lk=in}}, virtually all the nuclear weapons of this size deployed by the [[List of states with nuclear weapons#Recognized nuclear-weapon states|five nuclear-weapon states under the Non-Proliferation Treaty]] today are thermonuclear weapons using the Teller–Ulam design.<ref>{{cite web |url= http://www.nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html#Nfaq4.4 |title= Nuclear Weapons FAQ Section 4.4.1.4 The Teller–Ulam Design|first= Carey |last=Sublette |date= 3 July 2007 |work= Nuclear Weapons FAQ |access-date=17 July 2011}} "So far as is known all high yield nuclear weapons today (>50 kt or so) use this design."</ref>{{nuclear weapons}}

== Public knowledge concerning nuclear weapon design ==
{{more citations needed section|date=December 2015}}
[[File:Edward Teller (1958)-LLNL.jpg|thumb|upright|[[Edward Teller]] in 1958]]

Detailed knowledge of fission and fusion weapons is [[classified information|classified]] to some degree in virtually every [[Developed country|industrialized country]]. In the United States, such knowledge can by default be classified as "[[Restricted Data]]", even if it is created by persons who are not government employees or associated with weapons programs, in a legal doctrine known as "[[born secret]]" (though the constitutional standing of the doctrine has been at times called into question; see ''[[United States v. Progressive, Inc.]]''). ''Born secret'' is rarely invoked for cases of private speculation. The official policy of the [[United States Department of Energy]] has been not to acknowledge the leaking of design information, as such acknowledgment would potentially validate the information as accurate. In a small number of prior cases, the U.S. government has attempted to [[prior restraint|censor weapons information in the public press]], with limited success.<ref>{{cite news|url=https://www.nytimes.com/2015/03/24/science/hydrogen-bomb-physicists-book-runs-afoul-of-energy-department.html?_r=1|title=Hydrogen Bomb Physicist's Book Runs Afoul of Energy Department|work=[[The New York Times]]|first=William J.|last=Broad|date=23 March 2015|access-date=20 November 2015}}</ref> According to the ''New York Times'', physicist [[Kenneth W. Ford]] defied government orders to remove classified information from his book ''Building the H Bomb: A Personal History''. Ford claims he used only pre-existing information and even submitted a manuscript to the government, which wanted to remove entire sections of the book for concern that foreign states could use the information.<ref>{{cite news|url=http://www.businessinsider.com/manhattan-project-secrets-in-new-book-2015-3|title=A physicist might be in trouble for what he revealed in his new book about the H bomb|first=Jes|last=Greene|work=Business Insider|date=25 March 2015|access-date=20 November 2015}}</ref>

Though large quantities of vague data have been officially released—and larger quantities of vague data have been unofficially leaked by former bomb designers—most public descriptions of nuclear weapon design details rely to some degree on speculation, [[reverse engineering]] from known information, or comparison with similar fields of [[physics]] ([[inertial confinement fusion]] is the primary example). Such processes have resulted in a body of unclassified knowledge about nuclear bombs that is generally consistent with official unclassified information releases and related physics and is thought to be internally consistent, though there are some points of interpretation that are still considered open. The state of public knowledge about the Teller–Ulam design has been mostly shaped from a few specific incidents outlined in a section below.

== Basic principle ==
{{Main|Nuclear weapon design}}

=== Primary and secondary stages ===
The basic principle of the [[History of the Teller–Ulam design|Teller–Ulam configuration]] is the idea that different parts of a thermonuclear weapon can be chained together in stages, with the [[detonation]] of each stage providing the energy to ignite the next stage. At a minimum, this implies a ''primary'' section that consists of an implosion-type [[nuclear fission|fission]] bomb (a "trigger"), and a ''secondary'' section that consists of [[Nuclear fuel|fusion fuel]]. The energy released by the ''primary'' compresses the ''secondary'' through the process of [[radiation implosion]], at which point it is heated and undergoes [[nuclear fusion]]. This process could be continued, with energy from the secondary igniting a third fusion stage; the Soviet Union's AN602 "[[Tsar Bomba]]" is thought to have been a three-stage fission-fusion-fusion device. Theoretically by continuing this process thermonuclear weapons with arbitrarily high [[Nuclear weapon yield|yield]] could be constructed.{{citation needed|date=October 2017}} This contrasts with fission weapons, which are limited in yield because only so much fission fuel can be amassed in one place before the danger of its accidentally becoming [[Critical mass|supercritical]] becomes too great.

[[File:Teller-Ulam device.png|right|upright=1.5|thumb|One possible version of the Teller–Ulam configuration]]

Surrounding the other components is a [[hohlraum]] or ''radiation case'', a container that traps the first stage or primary's energy inside temporarily. The outside of this radiation case, which is also normally the outside casing of the bomb, is the only direct visual evidence publicly available of any thermonuclear bomb component's configuration. Numerous photographs of various thermonuclear bomb exteriors have been declassified.<ref name="Allbombs">{{cite web| url=http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html| title=Complete List of All U.S. Nuclear Weapons| date=1 October 1997 | access-date=2006-03-13}}</ref>

The primary is thought{{by who|date=October 2023}} to be a standard implosion method fission bomb, though likely with a [[Pit (nuclear weapon)|core]] [[boosted fission weapon|boosted]] by small amounts of fusion fuel (usually 1:1 [[deuterium]]:[[tritium]] gas) for extra efficiency; the fusion fuel releases excess [[neutron]]s when heated and compressed, inducing additional fission. When fired, the {{SimpleNuclide|link=yes|plutonium|239}} or {{SimpleNuclide|link=yes|uranium|235}} core would be compressed to a smaller sphere by special layers of conventional [[high explosive]]s arranged around it in an [[explosive lens]] pattern, initiating the [[nuclear chain reaction]] that powers the conventional "atomic bomb".

The secondary is usually shown as a column of fusion fuel and other components wrapped in many layers. Around the column is first a "pusher-[[Tamper (nuclear weapon)|tamper]]", a heavy layer of [[uranium-238]] ({{SimpleNuclide|link=yes|uranium|238}}) or [[lead]] that helps compress the fusion fuel (and, in the case of uranium, may eventually undergo fission itself). Inside this is the fusion fuel, usually a form of [[lithium deuteride]], which is used because it is easier to weaponize than liquefied tritium/deuterium gas. This dry fuel, when bombarded by neutrons, produces tritium, a heavy [[isotope]] of [[hydrogen]] that can undergo nuclear fusion, along with the deuterium present in the mixture. (See the article on [[nuclear fusion]] for a more detailed technical discussion of fusion reactions.) Inside the layer of fuel is the "[[spark plug]]", a hollow column of fissile material ({{SimpleNuclide|link=yes|plutonium|239}} or {{SimpleNuclide|link=yes|uranium|235}}) often boosted by deuterium gas. The spark plug, when compressed, can undergo nuclear fission (because of the shape, it is not a critical mass without compression). The tertiary, if one is present, would be set below the secondary and probably be made of the same materials.<ref name="Hansen1988" /><ref name="hansen-swords" />

=== Interstage ===
Separating the secondary from the primary is the [[Nuclear weapon design#Interstage|interstage]]. The fissioning primary produces four types of energy: 1) expanding hot gases from high explosive charges that implode the primary; 2) superheated [[plasma (physics)|plasma]] that was originally the bomb's fissile material and its tamper; 3) the [[electromagnetic radiation]]; and 4) the neutrons from the primary's nuclear detonation. The interstage is responsible for accurately [[Neutron moderator|modulating]] the transfer of energy from the primary to the secondary. It must direct the hot gases, plasma, electromagnetic radiation and neutrons toward the right place at the right time. Less than optimal interstage designs have resulted in the secondary failing to work entirely on multiple shots, known as a "[[Fizzle (nuclear explosion)|fissile fizzle]]". The [[Castle Koon]] shot of [[Operation Castle]] is a good example; a small flaw allowed the [[neutron flux]] from the primary to prematurely begin heating the secondary, weakening the compression enough to prevent any fusion.

{{multiple image
| align = right
| direction = horizontal
| header =
| image1 = Edward Teller & Stanislaw Ulam 1951 On Heterocatalytic Detonations - Secret of hydrogen bomb - p 1.png
| width1 = 160
| image2 = Edward Teller & Stanislaw Ulam 1951 On Heterocatalytic Detonations - Secret of hydrogen bomb - p 3.png
| width2 = 160
| footer = Classified paper by Teller and Ulam on 9 March 1951: ''On Heterocatalytic Detonations I: Hydrodynamic Lenses and Radiation Mirrors'', in which they proposed their revolutionary staged implosion idea. This declassified version is extensively redacted.
}}

There is very little detailed information in the open literature about the mechanism of the interstage. One of the best sources is a simplified diagram of a British thermonuclear weapon similar to the American [[W80 (nuclear warhead)|W80]] warhead. It was released by [[Greenpeace]] in a report titled ''"Dual Use Nuclear Technology"''.<ref>{{cite web|url=http://archive.greenpeace.org/comms/nukes/fig05.gif |title=Figure 5 – Thermonuclear Warhead Components |access-date=27 August 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100712211509/http://archive.greenpeace.org/comms/nukes/fig05.gif |archive-date=12 July 2010 }} A cleaned up version: {{cite web |url=https://fas.org/sgp/eprint/morland_image037.gif |title=British H-bomb posted on the Internet by Greenpeace |publisher=Federation of American Scientists |access-date=27 August 2010}}</ref> The major components and their arrangement are in the diagram, though details are almost absent; what scattered details it does include likely have intentional omissions or inaccuracies. They are labeled "End-cap and Neutron Focus Lens" and "Reflector Wrap"; the former channels neutrons to the {{SimpleNuclide|link=yes|uranium|235}}/{{SimpleNuclide|link=yes|plutonium|239}} Spark Plug while the latter refers to an [[X-ray]] reflector; typically a cylinder made of an X-ray opaque material such as uranium with the primary and secondary at either end. It does not reflect like a mirror; instead, it gets heated to a high temperature by the X-ray flux from the primary, then it [[black-body radiation|emits]] more evenly spread X-rays that travel to the secondary, causing what is known as [[radiation implosion]]. In [[Ivy Mike]], gold was used as a coating over the uranium to enhance the blackbody effect.<ref name="Rhodes 1995" /> 

Next comes the "Reflector/Neutron Gun Carriage". The reflector seals the gap between the Neutron Focus Lens (in the center) and the outer casing near the primary. It separates the primary from the secondary and performs the same function as the previous reflector. There are about six neutron guns (seen here from [[Sandia National Laboratories]]<ref name="W76" />) each protruding through the outer edge of the reflector with one end in each section; all are clamped to the carriage and arranged more or less evenly around the casing's circumference. The neutron guns are tilted so the neutron emitting end of each gun end is pointed towards the central axis of the bomb. Neutrons from each neutron gun pass through and are focused by the neutron focus lens towards the centre of primary in order to boost the initial fissioning of the plutonium. A "[[polystyrene]] Polarizer/Plasma Source" is also shown (see below).

The first U.S. government document to mention the interstage was only recently released to the public promoting the 2004 initiation of the [[Reliable Replacement Warhead]] (RRW) Program. A graphic includes blurbs describing the potential advantage of a RRW on a part-by-part level, with the interstage blurb saying a new design would replace "toxic, brittle material" and "expensive 'special' material... [that require] unique facilities".<ref>[http://nnsa.energy.gov/defense_programs/documents/Graphic_Improved_Security_Safety_Manufacturability_of_RRW.pdf "Improved Security, Safety & Manufacturability of the Reliable Replacement Warhead"] {{webarchive|url=https://web.archive.org/web/20081217082741/http://nnsa.energy.gov/defense_programs/documents/Graphic_Improved_Security_Safety_Manufacturability_of_RRW.pdf |date=2008-12-17 }}, NNSA March 2007.</ref> The "toxic, brittle material" is widely assumed to be [[beryllium]], which fits that description and would also moderate the neutron flux from the primary. Some material to absorb and re-radiate the X-rays in a particular manner may also be used.<ref>[https://fas.org/sgp/eprint/morland_image026.gif A 1976 drawing] that depicts an interstage that absorbs and re-radiates X-rays. From Howard Morland, [https://fas.org/sgp/eprint/cardozo.html "The Article"], ''Cardozo Law Review'', March 2005, p 1374.</ref>

Candidates for the "special material" are polystyrene and a substance called "[[Fogbank]]", an unclassified codename. Fogbank's composition is classified, though [[aerogel]] has been suggested as a possibility. It was first used in thermonuclear weapons with the [[W76]] thermonuclear warhead and produced at a plant in the [[Y-12 National Security Complex|Y-12 Complex]] at [[Oak Ridge, Tennessee]], for use in the W76. Production of Fogbank lapsed after the W76 production run ended. The W76 Life Extension Program required more Fogbank to be made. This was complicated by the fact that the original Fogbank's properties were not fully documented, so a massive effort was mounted to re-invent the process. An impurity crucial to the properties of the old Fogbank was omitted during the new process. Only close analysis of new and old batches revealed the nature of that impurity. The manufacturing process used [[acetonitrile]] as a [[solvent]], which led to at least three evacuations of the Fogbank plant in 2006. Widely used in the petroleum and pharmaceutical industries, acetonitrile is flammable and toxic. Y-12 is the sole producer of Fogbank.<ref>[http://www.armscontrolwonk.com/1814/fogbank Speculation on Fogbank], ''Arms Control Wonk''</ref>

=== Summary ===
A simplified summary of the above explanation is:

# A (relatively) small fission bomb known as the "primary" explodes.
# Energy released in the primary is transferred to the "secondary" (or fusion) stage. This energy compresses the fusion fuel and sparkplug; the compressed sparkplug becomes supercritical and undergoes a fission chain reaction, further heating the compressed fusion fuel to a high enough temperature to induce fusion.
# Energy released by the fusion events continues heating the fuel, keeping the reaction going.
# The fusion fuel of the secondary stage may be surrounded by a layer of additional fuel that undergoes fission when hit by the neutrons from the reactions within. These fission events account for about half of the total energy released in typical designs.

== Compression of the secondary ==
How exactly the energy is "transported" from the ''primary'' to the ''secondary'' has been the subject of some disagreement in the open press but is thought to be transmitted through the X-rays and [[gamma ray]]s that are emitted from the fissioning ''primary''. This energy is then used to compress the ''secondary''. The crucial detail of ''how'' the X-rays create the pressure is the main remaining disputed point in the unclassified press. There are three proposed theories:
* [[Radiation pressure]] exerted by the X-rays. This was the first idea put forth by [[Howard Morland]] in an article in ''[[The Progressive]]''.
* X-rays creating a plasma in the radiation channel's filler (a polystyrene or "Fogbank" plastic foam). This was a second idea put forward by [[Chuck Hansen]] and later by Howard Morland.
* Tamper/pusher [[ablation]]. This is the concept best supported by physical analysis.

=== Radiation pressure ===
The radiation pressure exerted by the large quantity of X-ray [[photon]]s inside the closed casing might be enough to compress the secondary. Electromagnetic radiation such as X-rays or light carries [[momentum]] and exerts a force on any surface it strikes. The pressure of radiation at the intensities seen in everyday life, such as sunlight striking a surface, is usually imperceptible, but at the extreme intensities found in a thermonuclear bomb the pressure is enormous.

For two thermonuclear bombs for which the general size and primary characteristics are well understood, the Ivy Mike test bomb and the modern W-80 cruise missile warhead variant of the W-61 design, the radiation pressure was calculated to be {{convert|73|e6bar|TPa|abbr=on|lk=on}} for the Ivy Mike design and {{convert|1400|e6bar|TPa|abbr=on|lk=on}} for the W-80.<ref name="Nfaq4.4.3.3">{{cite web| url=http://nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html#Nfaq4.4.3.3| title=Nuclear Weapons Frequently Asked Questions 4.4.3.3 The Ablation Process |version=2.04 |date=20 February 1999 |access-date=2006-03-13}}</ref>

=== Foam plasma pressure ===
{{unreferenced section|date=October 2022}}
[[Foam]] plasma pressure is the concept that Chuck Hansen introduced during the ''Progressive'' case, based on research that located declassified documents listing special foams as liner components within the radiation case of thermonuclear weapons.

The sequence of firing the weapon (with the foam) would be as follows:
# The high explosives surrounding the core of the primary fire, compressing the fissile material into a [[critical mass|supercritical]] state and beginning the fission [[chain reaction]].
# The fissioning primary emits thermal [[X-ray]]s, which "reflect" along the inside of the casing, irradiating the polystyrene foam.
# The irradiated foam becomes a hot [[Plasma (physics)|plasma]], pushing against the tamper of the secondary, compressing it tightly, and beginning the fission chain reaction in the spark plug.
# Pushed from both sides (from the primary and the spark plug), the lithium deuteride fuel is highly compressed and heated to thermonuclear temperatures. Also, by being bombarded with neutrons, each [[Isotopes of lithium#Lithium-6|lithium-6]] (<sup>6</sup>Li) atom splits into one tritium atom and one [[alpha particle]]. Then begins a fusion reaction between the tritium and the deuterium, releasing even more neutrons, and a huge amount of energy.
# The fuel undergoing the fusion reaction emits a large [[neutron flux|flux]] of high energy neutrons ({{convert|17.6|MeV|disp=sqbr|abbr=on|lk=on}}), which irradiates the {{SimpleNuclide|uranium|238}} tamper (or the {{SimpleNuclide|uranium|238}} bomb casing), causing it to undergo a fast fission reaction, providing about half of the total energy.
This would complete the fission-fusion-fission sequence. Fusion, unlike fission, is relatively "clean"—it releases energy but no harmful [[Nuclear fission product|radioactive products]] or large amounts of [[nuclear fallout]]. The fission reactions though, especially the last fission reactions, release a tremendous amount of fission products and fallout. If the last fission stage is omitted, by replacing the uranium tamper with one made of [[lead]], for example, the overall explosive force is reduced by approximately half but the amount of fallout is relatively low. The [[neutron bomb]] is a hydrogen bomb with an intentionally thin tamper, allowing as many of the fast fusion neutrons as possible to escape.

[[File:BombH explosion.svg|center|frame|Foam plasma mechanism firing sequence.

{{ordered list
 |list_style=margin-left:0; list-style-position:inside;
 |list-style-type=upper-alpha
 |Warhead before firing; primary (fission bomb) at top, secondary (fusion fuel) at bottom, all suspended in polystyrene foam.
 |High-explosive fires in primary, compressing plutonium core into supercriticality and beginning a fission reaction.
 |Fission primary emits X-rays that are scattered along the inside of the casing, irradiating the polystyrene foam.
 |Polystyrene foam becomes plasma, compressing secondary, and plutonium sparkplug begins to fission.
 |Compressed and heated, [[lithium hydride#Lithium deuteride|lithium-6 deuteride]] fuel produces [[tritium]] ({{SimpleNuclide|hydrogen|3}}) and begins the fusion reaction. The neutron flux produced causes the {{SimpleNuclide|uranium|238}} tamper to fission. A fireball starts to form.
}}]]

Current technical criticisms of the idea of "foam plasma pressure" focus on unclassified analysis from similar high energy physics fields that indicate that the pressure produced by such a plasma would only be a ''small multiplier'' of the basic photon pressure within the radiation case, and also that the known foam materials intrinsically have a very low absorption efficiency of the [[gamma ray]] and [[X-ray]] radiation from the primary. Most of the energy produced would be absorbed by either the walls of the radiation case or the tamper around the secondary. Analyzing the effects of that absorbed energy led to the third mechanism: [[ablation]].

=== Tamper-pusher ablation ===
The outer casing of the secondary assembly is called the "tamper-pusher". The purpose of a tamper in an implosion bomb is to delay the expansion of the reacting fuel supply (which is very hot dense plasma) until the fuel is fully consumed and the explosion runs to completion. The same tamper material serves also as a pusher in that it is the medium by which the outside pressure (force acting on the surface area of the secondary) is transferred to the mass of fusion fuel.

The proposed tamper-pusher ablation mechanism posits that the outer layers of the thermonuclear secondary's tamper-pusher are heated so extremely by the primary's X-ray flux that they expand violently and ablate away (fly off). Because total momentum is conserved, this mass of high velocity ejecta impels the rest of the tamper-pusher to recoil inwards with tremendous force, crushing the fusion fuel and the spark plug. The tamper-pusher is built robustly enough to insulate the fusion fuel from the extreme heat outside; otherwise, the compression would be spoiled.

[[File:TellerUlamAblation.png|center|thumb|700px|Ablation mechanism firing sequence. {{ordered list
 | list_style=margin-left:0; list-style-position:inside;
 | Warhead before firing. The nested spheres at the top are the fission primary; the cylinders below are the fusion secondary device.
 | Fission primary's explosives have detonated and collapsed the primary's [[plutonium pit|fissile pit]].
 | The primary's fission reaction has run to completion, and the primary is now at several million degrees and radiating gamma and hard X-rays, heating up the inside of the [[hohlraum]] and the shield and secondary's tamper.
 | The primary's reaction is over and it has expanded. The surface of the pusher for the secondary is now so hot that it is also ablating or expanding away, pushing the rest of the secondary (tamper, fusion fuel, and fissile spark plug) inwards. The spark plug starts to fission. Not depicted: the radiation case is also ablating and expanding outwards (omitted for clarity of diagram).
 | The secondary's fuel has started the fusion reaction and shortly will burn up. A fireball starts to form.
}}]]

Rough calculations for the basic ablation effect are relatively simple: the energy from the primary is distributed evenly onto all of the surfaces within the outer radiation case, with the components coming to a [[thermal equilibrium]], and the effects of that thermal energy are then analyzed. The energy is mostly deposited within about one X-ray [[Optical depth|optical thickness]] of the tamper/pusher outer surface, and the temperature of that layer can then be calculated. The velocity at which the surface then expands outwards is calculated and, from a basic Newtonian [[momentum]] balance, the velocity at which the rest of the tamper implodes inwards.

Applying the more detailed form of those calculations to the Ivy Mike device yields vaporized pusher gas expansion velocity of {{convert|290|km/s|cm/us}} and an implosion velocity of perhaps {{convert|400|km/s|cm/μs|abbr=on}} if {{frac||3|4}} of the total tamper/pusher mass is ablated off, the most energy efficient proportion. For the [[W80 (nuclear warhead)|W-80]] the gas expansion velocity is roughly {{convert|410|km/s|cm/μs|abbr=on}} and the implosion velocity {{convert|570|km/s|cm/μs|abbr=on}}. The pressure due to the ablating material is calculated to be {{convert|5.3|e9bar|e12Pa|abbr=off|lk=on}} in the Ivy Mike device and {{convert|64|e9bar|e15Pa|abbr=off}} in the W-80 device.<ref name="Nfaq4.4.3.3" />

=== Comparing implosion mechanisms ===
Comparing the three mechanisms proposed, it can be seen that:

{| class="wikitable"
|-
! rowspan="2"|Mechanism !! colspan="2"|Pressure ([[Pascal (unit)|TPa]])
|-
! [[Ivy Mike]]
! [[W80 (nuclear warhead)|W80]]
|-
| Radiation pressure ||align=right| 7.3 ||align=right| 140
|-
| Plasma pressure ||align=right| 35 ||align=right| 750
|-
| Ablation pressure ||align=right| 530 ||align=right| 6400
|}

The calculated ablation pressure is one order of magnitude greater than the higher proposed plasma pressures and nearly two orders of magnitude greater than calculated radiation pressure. No mechanism to avoid the absorption of energy into the radiation case wall and the secondary tamper has been suggested, making ablation apparently unavoidable. The other mechanisms appear to be unneeded.

[[United States Department of Defense]] official declassification reports indicate that foamed plastic materials are or may be used in radiation case liners, and despite the low direct plasma pressure they may be of use in delaying the [[ablation]] until energy has distributed evenly and a sufficient fraction has reached the secondary's tamper/pusher.<ref name="Nfaq4.4.">{{cite web| url=http://nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html#Nfaq4.4.4| title=Nuclear Weapons Frequently Asked Questions 4.4.4 Implosion Systems |version=2.04 |date=20 February 1999 |access-date=2006-03-13}}</ref>

[[Richard Rhodes]]' book ''Dark Sun'' stated that a {{convert|1|in|mm|adj=mid|-thick}} layer of plastic foam was fixed to the lead liner of the inside of the Ivy Mike steel casing using copper nails. Rhodes quotes several designers of that bomb explaining that the plastic foam layer inside the outer case is to delay ablation and thus recoil of the outer case: if the foam were not there, metal would ablate from the inside of the outer case with a large impulse, causing the casing to recoil outwards rapidly. The purpose of the casing is to contain the explosion for as long as possible, allowing as much X-ray ablation of the metallic surface of the secondary stage as possible, so it compresses the secondary efficiently, maximizing the fusion yield. Plastic foam has a low density, so causes a smaller impulse when it ablates than metal does.<ref name="Nfaq4.4." />

== Design variations ==
Possible variations to the weapon design have been proposed:
* Either the tamper or the casing have been proposed to be made of {{SimpleNuclide|link=yes|uranium|235}} (highly enriched uranium) in the final fission jacket. The far more expensive {{SimpleNuclide|link=yes|uranium|235}} is also fissionable with fast neutrons like the {{SimpleNuclide|link=yes|uranium|238}} in depleted or natural uranium, but its fission-efficiency is higher. This is because {{SimpleNuclide|link=yes|uranium|235}} nuclei also undergo fission by slow neutrons ({{SimpleNuclide|link=yes|uranium|238}} nuclei require a minimum energy of about {{convert|1|MeV}}) and because these slower neutrons are produced by other fissioning {{SimpleNuclide|link=yes|uranium|235}} nuclei in the jacket (in other words, {{SimpleNuclide|link=yes|uranium|235}} supports the nuclear chain reaction whereas {{SimpleNuclide|link=yes|uranium|238}} does not). Furthermore, a {{SimpleNuclide|link=yes|uranium|235}} jacket fosters neutron multiplication, whereas {{SimpleNuclide|link=yes|uranium|238}} nuclei consume fusion neutrons in the fast-fission process. Using a final fissionable/fissile jacket of {{SimpleNuclide|link=yes|uranium|235}} would thus increase the yield of a Teller–Ulam bomb above a depleted uranium or natural uranium jacket. This has been proposed specifically for the [[W87]] warheads retrofitted to currently deployed [[LGM-30 Minuteman]] III ICBMs.
* In some descriptions, additional internal structures exist to protect the secondary from receiving excessive neutrons from the primary.
* The inside of the casing may or may not be specially machined to "reflect" the X-rays. X-ray "reflection" is not like light reflecting off a [[mirror]], but rather the reflector material is heated by the X-rays, causing the material to [[black-body radiation|emit X-rays]], which then travel to the secondary.

Most bombs do not apparently have tertiary "stages"—that is, third compression stage(s), which are additional fusion stages compressed by a previous fusion stage. The fissioning of the last blanket of uranium, which provides about half the yield in large bombs, does not count as a "stage" in this terminology.{{fact|date=May 2022}}

The U.S. tested three-stage bombs in several explosions during [[Operation Redwing]] but is thought to have fielded only one such tertiary model, i.e., a bomb in which a fission stage, followed by a fusion stage, finally compresses yet another fusion stage. This U.S. design was the heavy but highly efficient (i.e., [[nuclear weapon yield]] per unit bomb weight) {{convert|25|MtonTNT|abbr=on}} [[B41 nuclear bomb]].<ref>{{cite web |url=http://nuclearweaponarchive.org/Usa/Weapons/B41.html |title=The B-41 (Mk-41) Bomb – High yield strategic thermonuclear bomb |date=21 October 1997 |access-date=2006-03-13}}</ref> The Soviet Union is thought to have used multiple stages (including more than one tertiary fusion stage) in their {{convert|50|MtonTNT|abbr=on}} ({{convert|100|MtonTNT|abbr=on}} in intended use) Tsar Bomba. The fissionable jacket could be replaced with lead, as was done with the Tsar Bomba. If any hydrogen bombs have been made from configurations other than those based on the Teller–Ulam design, the fact of it is not publicly known. A possible exception to this is the Soviet early ''[[Sloika]]'' design.{{fact|date=May 2022}}

In essence, the Teller–Ulam configuration relies on at least two instances of implosion occurring: first, the conventional (chemical) explosives in the primary would compress the fissile core, resulting in a fission explosion many times more powerful than that which chemical explosives could achieve alone (first stage). Second, the radiation from the fissioning of the primary would be used to compress and ignite the secondary fusion stage, resulting in a fusion explosion many times more powerful than the fission explosion alone. This chain of compression could conceivably be continued with an arbitrary number of tertiary fusion stages, each igniting more fusion fuel in the next stage<ref name="Winterberg" />{{rp|pages=192–193}}<ref name="Croddy" />{{better source needed|date=October 2014}} although this is debated. Finally, efficient bombs (but not so-called [[neutron bomb]]s) end with the fissioning of the final natural uranium tamper, something that could not normally be achieved without the [[neutron flux]] provided by the fusion reactions in secondary or tertiary stages. Such designs are suggested to be capable of being scaled up to an [[Nuclear weapon design#Arbitrarily large multi-staged devices|arbitrary large yield]] (with apparently as many fusion stages as desired),<ref name="Winterberg" />{{rp|pages=192–193}}<ref name="Croddy" />{{better source needed|date=October 2014}} potentially to the level of a "[[doomsday device]]." However, usually such weapons were not more than a dozen megatons, which was generally considered enough to destroy even the most hardened practical targets (for example, a control facility such as the [[Cheyenne Mountain Complex]]). Even such large bombs have been replaced by smaller yield [[nuclear bunker buster]] bombs.{{fact|date=May 2022}}

For destruction of cities and non-hardened targets, breaking the mass of a single missile payload down into smaller MIRV bombs in order to spread the energy of the explosions into a "pancake" area is far more efficient in terms of area-destruction per unit of bomb energy. This also applies to single bombs deliverable by cruise missile or other system, such as a bomber, resulting in most operational warheads in the U.S. program having yields of less than {{convert|500|ktonTNT|abbr=on}}.{{fact|date=May 2022}}

=== Ivy Mike ===
In his 1995 book ''Dark Sun: The Making of the Hydrogen Bomb'', author [[Richard Rhodes]] describes in detail the internal components of the "Ivy Mike" ''Sausage'' device, based on information obtained from extensive interviews with the scientists and engineers who assembled it. According to Rhodes, the actual mechanism for the compression of the secondary was a combination of the radiation pressure, foam plasma pressure, and tamper-pusher ablation theories; the radiation from the primary heated the polyethylene foam lining of the casing to a plasma, which then re-radiated radiation into the secondary's pusher, causing its surface to ablate and driving it inwards, compressing the secondary, igniting the sparkplug, and causing the fusion reaction. The general applicability of this principle is unclear.<ref name="Rhodes 1995" />

=== W88 ===
In 1999 a reporter for the ''[[San Jose Mercury News]]'' reported that the U.S. W88 nuclear warhead, a small MIRVed warhead used on the [[Trident (missile)|Trident II]] SLBM, had a [[prolate]] ''primary'' (code-named ''Komodo'') and a spherical ''secondary'' (code-named ''Cursa'') inside a specially shaped radiation case (known as the "peanut" for its shape). The value of an [[egg-shaped]] primary lies apparently in the fact that a MIRV warhead is limited by the diameter of the primary: if an egg-shaped primary can be made to work properly, then the MIRV warhead can be made considerably smaller yet still deliver a high-yield explosion. A W88 warhead manages to yield up to {{convert|475|ktTNT}} with a [[physics package]] {{convert|68.9|inch|mm}} long, with a maximum diameter of {{convert|21.8|inch|mm|}}, and by different estimates weighing in a range from {{convert|175|to|360|kg|lb}}.<ref name="W88/W76 weight">{{cite journal |last1=Harvey |first1=John R. |last2=Michalowski |first2=Stefan |date=21 December 2007 |title=Nuclear weapons safety: The case of trident |journal=Science & Global Security |volume=4 |issue=1 |pages=288 |doi=10.1080/08929889408426405}}</ref> The smaller warhead allows more of them to fit onto a single missile and improves basic flight properties such as speed and range.<ref name="StroberHoffman" />

== History ==
{{Main|History of the Teller–Ulam design}}

=== United States ===
The idea of a thermonuclear fusion bomb ignited by a smaller fission bomb was first proposed by [[Enrico Fermi]] to his colleague [[Edward Teller]] when they were talking at [[Columbia University]] in September 1941,<ref name="Rhodes 1995" />{{rp|page=207}} at the start of what would become the [[Manhattan Project]].<ref name="Teller" /> Teller spent much of the Manhattan Project attempting to figure out how to make the design work, preferring it over work on the atomic bomb, and over the last year of the project he was assigned exclusively to the task.<ref name="Rhodes 1995" />{{rp|pages=117,248}} However once World War II ended, there was little impetus to devote many resources to the ''Super'', as it was then known.<ref name="Bundy" />{{rp|page=202}}<ref>{{cite book | vauthors=Rhodes R | year=1995 | title=Dark Sun: The Making of the Hydrogen Bomb | publisher=Simon & Schuster | isbn=978-0-684-80400-2}}</ref>

The [[RDS-1|first atomic bomb test by the Soviet Union]] in August 1949 came earlier than expected by Americans, and over the next several months there was an intense debate within the U.S. government, military, and scientific communities regarding whether to proceed with development of the far more powerful Super.<ref name="YoungSchilling" />{{rp|pages=1–2}} The debate covered matters that were alternatively strategic, pragmatic, and moral.<ref name="YoungSchilling" />{{rp|page=16}} In their ''Report of the General Advisory Committee,'' [[J. Robert Oppenheimer|Robert Oppenheimer]] and colleagues concluded that "[t]he extreme danger to mankind inherent in the proposal [to develop thermonuclear weapons] wholly outweighs any military advantage." Despite the objections raised, on 31 January 1950, President [[Harry S. Truman]] made the decision to go forward with the development of the new weapon.<ref name="Bundy" />{{rp|pages=212–214}}

[[File:Operation Castle - Romeo 001.jpg|thumb|right|upright|''[[Operation Castle]]'' thermonuclear test, ''[[Castle Romeo]]'' shot]]
Teller and other U.S. physicists struggled to find a workable design.<ref name="YoungSchilling" />{{rp|pages=91–92}} [[Stanislaw Ulam]], a co-worker of Teller, made the first key conceptual leaps towards a workable fusion design. Ulam's two innovations that rendered the fusion bomb practical were that compression of the thermonuclear fuel before extreme heating was a practical path towards the conditions needed for fusion, and the idea of staging or placing a separate thermonuclear component outside a fission primary component, and somehow using the primary to compress the secondary. Teller then realized that the gamma and X-ray radiation produced in the primary could transfer enough energy into the secondary to create a successful implosion and fusion burn, if the whole assembly was wrapped in a ''[[hohlraum]]'' or radiation case.<ref name="Teller" /> 

The "George" shot of [[Operation Greenhouse]] of 9 May 1951 tested the basic concept for the first time on a very small scale. As the first successful (uncontrolled) release of nuclear fusion energy, which made up a small fraction of the {{convert|225|ktonTNT|abbr=on|lk=on}} total yield,<ref>{{Cite web|url=http://www.ctbto.org/specials/infamous-anniversaries/9-may-1951-george/|title=The 'George' shot, Comprehensive Test Ban Treaty Organisation website}}</ref> it raised expectations to a near certainty that the concept would work. On 1 November 1952, the Teller–Ulam configuration was tested at full scale in the "Ivy Mike" shot at an island in the [[Enewetak Atoll]], with a yield of {{convert|10.4|MtonTNT|abbr=on|lk=on}} (over 450 times more powerful than the bomb dropped on Nagasaki during [[World War II]]). The device, dubbed the ''Sausage'', used an extra-large fission bomb as a "trigger" and liquid deuterium—kept in its liquid state by {{convert|20|ST|tonne|lk=on}} of [[Cryogenics|cryogenic]] equipment—as its fusion fuel,{{citation needed|date=January 2016}} and weighed around {{convert|80|ST|tonne|lk=on}} altogether.[[File:Castle-bravo-detonation.ogg|thumb|Castle Bravo detonation, 1st Mar 1954]]
The liquid deuterium fuel of Ivy Mike was impractical for a deployable weapon, and the next advance was to use a solid [[lithium hydride|lithium deuteride]] fusion fuel instead. In 1954 this was tested in the "[[Castle Bravo]]" shot (the device was code-named ''Shrimp''), which had a yield of {{convert|15|MtonTNT|abbr=on|lk=on}} (2.5 times expected) and is the largest U.S. bomb ever tested. Efforts shifted towards developing miniaturized Teller–Ulam weapons that could fit into [[intercontinental ballistic missile]]s and [[submarine-launched ballistic missile]]s. By 1960, with the [[W47]] warhead<ref>{{cite web| url=http://nuclearweaponarchive.org/Usa/Weapons/W47.jpg| title=Photograph of a W47 warhead| format=JPG| access-date=2006-03-13}}</ref> deployed on [[UGM-27 Polaris|Polaris]] [[ballistic missile submarine]]s, megaton-class warheads were as small as {{convert|18|in|m}} in diameter and {{convert|720|lb}} in weight. Further innovation in miniaturizing warheads was accomplished by the mid-1970s, when versions of the Teller–Ulam design were created that could fit ten or more warheads on the end of a small MIRVed missile.<ref name="Allbombs" />

=== Soviet Union ===
{{unreferenced section|date=October 2022}}
{{See also|Soviet atomic bomb project}}

The first Soviet fusion design, developed by [[Andrei Sakharov]] and [[Vitaly Ginzburg]] in 1949 (before the Soviets had a working fission bomb), was dubbed the ''Sloika'', after a Russian [[layer cake]], and was not of the Teller–Ulam configuration. It used alternating layers of fissile material and lithium deuteride fusion fuel spiked with tritium (this was later dubbed Sakharov's "First Idea"). Though nuclear fusion might have been technically achievable, it did not have the scaling property of a "staged" weapon. Thus, such a design could not produce thermonuclear weapons whose explosive yields could be made arbitrarily large (unlike U.S. designs at that time). The fusion layer wrapped around the fission core could only moderately multiply the fission energy (modern Teller–Ulam designs can multiply it 30-fold). Additionally, the whole fusion stage had to be imploded by conventional explosives, along with the fission core, substantially increasing the amount of chemical explosives needed.

The first Sloika design test, [[Joe 4|RDS-6s]], was detonated in 1953 with a yield equivalent to {{convert|400|ktonTNT|abbr=on}} ({{percentage|15|100}}{{hyphen}}{{percentage|20|100}} from fusion). Attempts to use a ''Sloika'' design to achieve megaton-range results proved unfeasible. After the United States tested the "Ivy Mike" thermonuclear device in November 1952, proving that a multimegaton bomb could be created, the Soviets searched for an alternative design. The "Second Idea", as Sakharov referred to it in his memoirs, was a previous proposal by Ginzburg in November 1948 to use lithium deuteride in the bomb, which would, in the course of being bombarded by neutrons, produce tritium and free deuterium.<ref name="Holloway" />{{rp|page=299}} In late 1953 physicist [[Viktor Davidenko]] achieved the first breakthrough of staging the reactions. The next breakthrough of radiation implosion was discovered and developed by Sakharov and [[Yakov Borisovich Zel'dovich|Yakov Zel'dovich]] in early 1954. Sakharov's "Third Idea", as the Teller–Ulam design was known in the USSR, was tested in the shot "[[RDS-37]]" in November 1955 with a yield of {{convert|1.6|MtonTNT|abbr=on}}. The Soviets demonstrated the power of the staging concept in October 1961, when they detonated the massive and unwieldy Tsar Bomba. It was the largest nuclear weapon developed and tested by any country.

=== United Kingdom ===
[[File:OperationGrappleXmasIslandHbomb.jpg|thumb|right|upright|[[Operation Grapple]] on [[Kiritimati|Christmas Island]] was the first British hydrogen bomb test.]]
In 1954 work began at [[Atomic Weapons Establishment|Aldermaston]] to develop the British fusion bomb, with [[William Penney, Baron Penney|Sir William Penney]] in charge of the project. British knowledge on how to make a thermonuclear fusion bomb was rudimentary, and at the time the United States was not exchanging any nuclear knowledge because of the [[Atomic Energy Act of 1946]]. The United Kingdom had worked closely with the Americans on the Manhattan Project. British access to nuclear weapons information was cut off by the United States at one point due to concerns about Soviet espionage. Full cooperation was not reestablished until an agreement governing the handling of secret information and other issues was signed.<ref name="BombBook" />{{Unreliable source?|date=December 2016}} However, the British were allowed to observe the U.S. [[Operation Castle|Castle tests]] and used sampling aircraft in the [[mushroom cloud]]s, providing them with clear, direct evidence of the compression produced in the secondary stages by radiation implosion.<ref name="BombBook" /> Because of these difficulties, in 1955 Prime Minister [[Anthony Eden]] agreed to a secret plan, whereby if the Aldermaston scientists failed or were greatly delayed in developing the fusion bomb, it would be replaced by an extremely large fission bomb.<ref name="BombBook" />

In 1957 the [[Operation Grapple]] tests were carried out. The first test, Green Granite, was a prototype fusion bomb that failed to produce equivalent yields compared to the U.S. and Soviets, achieving only approximately {{convert|300|ktonTNT|abbr=on}}. The second test [[Orange Herald]] was the modified fission bomb and produced {{convert|720|ktonTNT|abbr=on}}—making it the largest fission explosion ever. At the time almost everyone (including the pilots of the plane that dropped it) thought that this was a fusion bomb. This bomb was put into service in 1958. A second prototype fusion bomb, [[Purple Granite]], was used in the third test, but only produced approximately {{convert|150|ktonTNT|abbr=on}}.<ref name="BombBook" />

A second set of tests was scheduled, with testing recommencing in September 1957. The first test was based on a "… new simpler design. A two-stage thermonuclear bomb that had a much more powerful trigger". This test Grapple X Round C was exploded on 8 November and yielded approximately {{convert|1.8|MtonTNT|abbr=on}}. On 28 April 1958 a bomb was dropped that yielded {{convert|3|MtonTNT|abbr=on}}—Britain's most powerful test. Two final air burst tests on 2 and 11 September 1958, dropped smaller bombs that yielded around {{convert|1|MtonTNT|abbr=on}} each.<ref name="BombBook" />

American observers had been invited to these kinds of tests. After Britain's successful detonation of a megaton-range device (and thus demonstrating a practical understanding of the Teller–Ulam design "secret"), the United States agreed to exchange some of its nuclear designs with the United Kingdom, leading to the [[1958 US–UK Mutual Defence Agreement]]. Instead of continuing with its own design, the British were given access to the design of the smaller American [[B28 nuclear bomb|Mk 28 warhead]] and were able to manufacture copies.<ref name="BombBook" />

=== China ===
{{Main|Test No. 6}}

[[Mao Zedong]] decided to begin a Chinese nuclear-weapons program during the [[First Taiwan Strait Crisis]] of 1954–1955. The People's Republic of China detonated its first thermonuclear bomb on 17 June 1967, 32 months after detonating its first fission weapon, with a yield of 3.31 Mt. It took place in the [[Lop Nur#Nuclear Weapons Test Base|Lop Nor Test Site]] in northwest China.<ref>{{Cite web|url=https://www.ctbto.org/specials/testing-times/17-june-1967-chinas-first-thermonuclear-test|title=17 June 1967 – China's first thermonuclear test: CTBTO Preparatory Commission|website=www.ctbto.org|access-date=2016-10-03}}</ref> China had received extensive technical help from the Soviet Union to jump-start their nuclear program, but by 1960 the [[Sino-Soviet split|rift between the Soviet Union and China]] had become so great that the Soviet Union ceased all assistance to China.<ref name="NTI-China">{{cite web |title=China's Nuclear Weapon Development, Modernization and Testing |url=http://www.nuclearthreatinitiative.org/db/china/wnwmdat.htm |publisher=[[Nuclear Threat Initiative]] |date=26 September 2003 |access-date=4 November 2011 |url-status=dead |archive-url=https://web.archive.org/web/20111008195804/http://www.nuclearthreatinitiative.org/db/china/wnwmdat.htm |archive-date=8 October 2011 }}</ref>

A story in ''[[The New York Times]]'' by [[William Broad]]<ref>{{cite news| url=https://www.nytimes.com/1999/09/07/us/spies-vs-sweat-the-debate-over-china-s-nuclear-advance.html| title=Spies versus sweat, the debate over China's nuclear advance| journal=The New York Times| date=7 September 1999| access-date=2011-04-18}}</ref> reported that in 1995, a supposed Chinese [[double agent]] delivered information indicating that China knew secret details of the U.S. W88 warhead, supposedly through espionage.<ref>{{cite book| author=Christopher Cox, chairman| title=Report of the United States House of Representatives Select Committee on U.S. National Security and Military/Commercial Concerns with the People's Republic of China| year=1999| url=http://www.house.gov/coxreport/| url-status=dead| archive-url=https://web.archive.org/web/20050804234332/http://www.house.gov/coxreport/| archive-date=2005-08-04}}, esp. Ch. 2, "PRC Theft of U.S. Thermonuclear Warhead Design Information".</ref> (This line of investigation eventually resulted in the abortive trial of [[Wen Ho Lee]].)

=== France ===
The [[Canopus (nuclear test)|"Canopus" test]] in the [[Fangataufa]] atoll in [[French Polynesia]] on 24 August 1968 was the country's first multistage thermonuclear weapon test. The bomb was detonated from a balloon at a height of {{convert|520|m|ft}}. The result of this test was significant atmospheric contamination.<ref name=":2">{{Cite web|url=https://www.ctbto.org/specials/testing-times/24-august-1968-french-canopus-test/|title=24 August 1968 – French 'Canopus' test: CTBTO Preparatory Commission|website=www.ctbto.org|language=en|access-date=2017-04-15}}</ref> Very little is known about France's development of the Teller–Ulam design, beyond the fact that France detonated a {{convert|2.6|MtonTNT|abbr=on}} device in the "Canopus" test. France reportedly had great difficulty with its initial development of the Teller-Ulam design, but it later overcame these and is believed to have nuclear weapons equal in sophistication to the other major nuclear powers.<ref name="BombBook" />

France and China did not sign or ratify the [[Partial Nuclear Test Ban Treaty]] of 1963, which banned nuclear test explosions in the atmosphere, underwater, or in [[outer space]]. Between 1966 and 1996 France carried out more than 190 nuclear tests.<ref name=":2" /> France's final nuclear test took place on 27 January 1996, and then the country dismantled its Polynesian test sites. France signed the [[Comprehensive Nuclear-Test-Ban Treaty]] that same year, and then ratified the Treaty within two years.

[[File:Temeraire1048.jpg|thumb|One of France's [[Triomphant-class submarine|Triomphant-class nuclear-armed submarines]], [[French submarine Téméraire (S617)|''Le Téméraire'' (S617)]]]]
In 2015 France confirmed that its nuclear arsenal contains about 300 warheads, carried by [[submarine-launched ballistic missile]]s and [[fighter-bombers]]. France has four [[Triomphant-class submarine|Triomphant-class]] ballistic missile submarines. One ballistic missile submarine is deployed in the deep ocean, but a total of three must be in operational use at all times. The three older submarines are armed with 16 [[M45 (missile)|M45 missiles]]. The newest submarine, [[French submarine Terrible (S619)|"Le Terrible"]], was commissioned in 2010, and it has [[M51 (missile)|M51]] missiles capable of carrying [[TN 75]] thermonuclear warheads. The air fleet is four squadrons at four different bases. In total, there are 23 [[Dassault Mirage 2000N/2000D|Mirage 2000N]] aircraft and 20 [[Dassault Rafale|Rafales]] capable of carrying nuclear warheads.<ref name=":3" /> The M51.1 missiles are intended to be replaced with the new M51.2 warhead beginning in 2016, which has a {{convert|3000|km}} greater range than the M51.1.<ref name=":3">{{Cite news|url=http://www.nti.org/learn/countries/france/nuclear/|title=France {{!}} Countries {{!}} NTI|newspaper=The Nuclear Threat Initiative|access-date=2017-04-15}}</ref>

France has about 60 air-launched missiles tipped with [[TN 80]]/[[TN 81]] warheads with a yield of about {{convert|300|ktonTNT|abbr=on}} each. France's nuclear program has been carefully designed to ensure that these weapons remain usable decades into the future.<ref name="BombBook" />{{Unreliable source?|date=December 2016}} Currently, France is no longer deliberately producing critical mass materials such as plutonium and enriched uranium, but it still relies on nuclear energy for electricity, with {{SimpleNuclide|link=yes|plutonium|239}} as a byproduct.<ref name=":4">{{Cite web|url=https://www.ctbto.org/verification-regime/background/overview-of-the-verification-regime/|title=Overview of the verification regime: CTBTO Preparatory Commission|website=www.ctbto.org|language=en|access-date=2017-04-15}}</ref>

=== India ===
{{See also|India and weapons of mass destruction}}
[[File:ShaktiBomb.jpg|thumb|right|upright|Shakti-1]]
On 11 May 1998, India announced that it had detonated a thermonuclear bomb in its [[Pokhran-II|Operation Shakti]] tests ("Shakti-I", specifically, in Hindi the word 'Shakti' means power).<ref>{{Cite news|url=https://www.nytimes.com/1998/05/12/world/india-sets-3-nuclear-blasts-defying-a-worldwide-ban-tests-bring-a-sharp-outcry.html|title=India Sets 3 Nuclear Blasts, Defying a Worldwide Ban; Tests Bring a Sharp Outcry|last=Burns|first=John F.|date=1998-05-12|work=The New York Times|access-date=2019-12-24|language=en-US|issn=0362-4331}}</ref><ref name=":7" /> [[Samar Mubarakmand]], a Pakistani nuclear physicist, asserted that if Shakti-I had been a thermonuclear test, the device had failed to fire.<ref name="The News International">{{cite news|last=Sublette |first=Carey |title=Pakistan's Nuclear Weapons Program - 1998: The Year of Testing |url=http://nuclearweaponarchive.org/Pakistan/PakTests.html|access-date=10 August 2011 |date=10 September 2001 |website=The Nuclear Weapon Archive |quote="[[A. Q. Khan]]...said..."none of these explosions were thermonuclear, we are doing research and can do a fusion test if asked..." ""These boosted devices are like a half way stage towards a thermonuclear bomb. They use elements of the thermonuclear process, and are effectively stronger Atom bombs," Munir Ahmad Khan" |url-status=live |archive-url=https://web.archive.org/web/20110810153614/http://nuclearweaponarchive.org/Pakistan/PakTests.html |archive-date= Aug 10, 2011 }}</ref> However, [[Harold M. Agnew]], former director of the [[Los Alamos National Laboratory]], said that India's assertion of having detonated a staged thermonuclear bomb was believable.<ref name=":8" /> India says that their thermonuclear device was tested at a controlled yield of {{convert|45|ktonTNT|abbr=on}} because of the close proximity of the Khetolai village at about {{convert|5|km}}, to ensure that the houses in that village do not suffer significant damage.<ref name=":6" /> Another cited reason was that radioactivity released from yields significantly more than 45 kt might not have been contained fully.<ref name=":6" /> After the [[Pokhran-II]] tests, [[Rajagopala Chidambaram]], former chairman of the [[Atomic Energy Commission of India]], said that India has the capability to build thermonuclear bombs of any yield at will.<ref name=":8" /> India officially maintains that it can build thermonuclear weapons of various yields up to around {{convert|200|ktonTNT|abbr=on}} on the basis of the [[Pokhran-II|Shakti-1]] thermonuclear test.<ref name=":6" /><ref>{{Cite journal |date=25 September 2009 |title=Nukes of 200kt yield possible: Architect of Pokhran-II |url=https://timesofindia.indiatimes.com/india/Nukes-of-200kt-yield-possible-Architect-of-Pokhran-II/articleshow/5053406.cms |journal=The Times of India}}</ref>

The yield of India's hydrogen bomb test remains highly debatable among the Indian science community and the international scholars.<ref name="The Hindu, 2009">{{cite news|last=PTI|first=Press Trust of India|title=AEC ex-chief backs Santhanam on Pokhran-II|url=http://www.thehindu.com/sci-tech/science/aec-exchief-backs-santhanam-on-pokhranii/article24861.ece|access-date=18 January 2013|newspaper=The Hindu, 2009|date=25 September 2009}}</ref> The question of politicisation and disputes between Indian scientists further complicated the matter.<ref name="What Are the Real Yields of India's Test?">{{cite web|first=Carey |last=Sublette |display-authors=etal |title=What are the real yield of India's Test?|url=http://nuclearweaponarchive.org/India/IndiaRealYields.html|publisher=What Are the Real Yields of India's Test?|access-date=18 January 2013}}</ref> In an interview in August 2009, the director for the 1998 test site preparations, K. Santhanam claimed that the yield of the thermonuclear explosion was lower than expected and that India should therefore not rush into signing the [[Comprehensive Nuclear-Test-Ban Treaty]]. Other Indian scientists involved in the test have disputed Santhanam's claim,<ref>{{cite news|url=http://timesofindia.indiatimes.com/news/india/New-Article/articleshow/4941081.cms|title=Former NSA disagrees with scientist, says Pokhran II successful|work=The Times of India|date=27 August 2009|access-date=20 November 2015|archive-url=https://web.archive.org/web/20090830173039/http://timesofindia.indiatimes.com/news/india/New-Article/articleshow/4941081.cms|archive-date=30 August 2009}}</ref> arguing that his claims are unscientific.<ref name=":7">{{Cite web|url=http://pib.nic.in/newsite/PrintRelease.aspx?relid=52813|title=Pokhran – II tests were fully successful; given India capability to build nuclear deterrence: Dr. Kakodkar and Dr. Chidambaram|website=pib.nic.in|access-date=2019-07-26}}</ref> British seismologist Roger Clarke argued that the magnitudes suggested a combined yield of up to {{convert|60|ktTNT|abbr=on}}, consistent with the Indian announced total yield of {{convert|56|ktTNT|abbr=on}}.<ref>{{Cite journal|date=2 January 1999|title=We have an adequate scientific database for designing ... a credible nuclear deterrent|url=https://frontline.thehindu.com/static/html/fl1601/16010840.htm|journal=Frontline}}</ref> U.S. seismologist Jack Evernden has argued that for correct estimation of yields, one should 'account properly for geological and seismological differences between test sites'.<ref name=":6">{{Cite web|date=24 September 2009|title=Press Statement by Dr. Anil Kakodkar and Dr. R. Chidambaram on Pokhran-II tests|url=http://pib.nic.in/newsite/PrintRelease.aspx?relid=52814|publisher=Press Information Bureau |url-status=dead |archive-url=https://web.archive.org/web/20171024045228/http://pib.nic.in:80/newsite/PrintRelease.aspx?relid=52814 |archive-date= Oct 24, 2017 }}</ref>

=== Israel ===
{{Main|Nuclear weapons and Israel}}

Israel is alleged to possess thermonuclear weapons of the Teller–Ulam design,<ref name="Dawn News Interviews">{{cite news|last=Samdani|first=Zafar|title=India, Pakistan can build hydrogen bomb: Scientist|url=http://www.lib.virginia.edu/area-studies/SouthAsia/SAserials/Dawn/2000/mar25.html#indi|access-date=23 December 2012|newspaper=Dawn News Interviews|date=25 March 2000}}</ref> but it is not known to have tested any nuclear devices, although it is widely speculated that the [[Vela incident]] of 1979 may have been a joint Israeli–South African nuclear test.<ref>{{Citation | url = https://fas.org/nuke/guide/israel/doctrine/ | publisher = FAS | title = Israel | contribution = Doctrine}}.</ref><ref>{{Cite book | title = The Samson Option: Israel's Nuclear Arsenal & American Foreign Policy | ol = 1567229M | url = https://archive.org/details/Sampson_Option | lccn = 91052678 | isbn = 978-0394570068 | oclc = 1159416022 | publisher = Random House | publication-place = New York | last1 = Hersh | first1= Seymour M. | year = 1991 | author-link1 = Seymour Hersh | via = [[Internet Archive]] | df = dmy-all}}</ref>{{rp|page=271}}<ref name="Columbia University Press" />{{rp|pages=297–300}}

It is well established that Edward Teller advised and guided the Israeli establishment on general nuclear matters for some 20 years.<ref name="basement" />{{rp|pages=289–293}} Between 1964 and 1967, Teller made six visits to Israel where he lectured at the [[Tel Aviv University]] on general topics in theoretical physics.<ref>{{cite web|last=Gábor Palló|title=The Hungarian Phenomenon in Israeli Science|publisher=Hungarian Academy of Science|year=2000|volume=25|issue=1|url=https://docs.google.com/viewer?a=v&q=cache:Kihw-fEuORsJ:www.scs.illinois.edu/~mainzv/HIST/bulletin_open_access/v25-1/v25-1%2520p35-42.pdf+edward+teller+israel&hl=en&gl=us&pid=bl&srcid=ADGEESiD0rk9r4olo6gaghkjMmUyrHXccqLZ8L7BFk3NJ08OgyaIQNumKy1gVimWh17r-h52svcP1STekLdeglCpgWtrYDGFHFmOnS42uLzyxIIUehv5_FeLPCObb5TzqHb5wQ3-MCSe&sig=AHIEtbSIoqK_5BW4y6tCHGK-4UFRbJP9Vg|access-date=11 December 2012}}</ref> It took him a year to convince the [[Central Intelligence Agency|CIA]] about Israel's capability and finally in 1976, [[Carl E. Duckett|Carl Duckett]] of the CIA testified to the [[US Congress|U.S. Congress]], after receiving credible information from an "American scientist" (Teller), on Israel's nuclear capability.<ref name="Columbia University Press" />{{rp|pages=297–300}} During the 1990s, Teller eventually confirmed speculations in the media that it was during his visits in the 1960s that he concluded that Israel was in possession of nuclear weapons.<ref name="Columbia University Press">{{Cite book | last1 = Cohen | first1 = Avner | author-link1 = Avner Cohen | title = Israel and the Bomb | publication-date = 1999 | chapter = Chapter 16: The Battle over the NPT | year = 1998 | ol = 344440M | url = https://archive.org/details/israelbomb00cohe | lccn = 98003402 | isbn =978-0585041506 | publisher = [[Columbia University Press]] |oclc=42330721| via = [[Internet Archive]] | df = dmy-all}}</ref>{{rp|pages=297–300}} After he conveyed the matter to the higher level of the U.S. government, Teller reportedly said: "They [Israel] have it, and they were clever enough to trust their research and not to test, they know that to test would get them into trouble."<ref name="Columbia University Press" />{{rp|pages=297–300}}

=== North Korea ===
{{Main|North Korea and weapons of mass destruction}}

North Korea claimed to have tested its miniaturised thermonuclear bomb on 6 January 2016. North Korea's first three nuclear tests (2006, 2009 and 2013) were relatively low yield and do not appear to have been of a thermonuclear weapon design. In 2013, the [[Ministry of National Defense (Republic of Korea)|South Korean Defense Ministry]] speculated that North Korea may be trying to develop a "hydrogen bomb" and such a device may be North Korea's next weapons test.<ref>{{cite news|url=http://english.hani.co.kr/arti/english_edition/e_northkorea/573302.html|title=North Korea could be developing a hydrogen bomb|author=Kim Kyu-won|newspaper=The Hankyoreh|date=7 February 2013|access-date=8 February 2013}}</ref><ref>{{cite news|url=https://www.koreatimes.co.kr/www/news/nation/2013/02/116_130000.html|title=North Korea may detonate H-bomb|author1=Kang Seung-woo |author2=Chung Min-uck |newspaper=Korea Times|date=4 February 2013|access-date=8 February 2013}}</ref> In January 2016, North Korea claimed to have successfully tested a hydrogen bomb,<ref>{{cite web|url=https://www.bbc.com/news/world-asia-35240012|title=North Korea nuclear: State claims first hydrogen bomb test|work=BBC News|date=6 January 2016}}</ref> although only a magnitude 5.1 seismic event was detected at the time of the test,<ref>{{cite report|url=https://earthquake.usgs.gov/earthquakes/eventpage/us10004bnm|title=M5.1 – 21&nbsp;km ENE of Sungjibaegam, North Korea|publisher=USGS|date=6 January 2016|access-date=6 January 2016}}</ref> a similar magnitude to the 2013 test of a {{convert|6|-|9|ktonTNT|abbr=on}} atomic bomb. These seismic recordings cast doubt upon North Korea's claim that a hydrogen bomb was tested and suggest it was a non-fusion nuclear test.<ref>{{cite news|url=https://www.bbc.com/news/world-asia-35241686|title=North Korea nuclear H-bomb claims met by scepticism|work=BBC News|date=2016-01-06}}</ref>

On 3 September 2017, the country's state media reported that a [[2017 North Korean nuclear test|hydrogen bomb test]] was conducted that resulted in "perfect success". According to the [[U.S. Geological Survey]] (USGS), the blast released energy equivalent to an earthquake with a seismic magnitude of 6.3, 10 times more powerful than previous nuclear tests conducted by North Korea.<ref>{{Cite news|url=https://www.reuters.com/article/uk-northkorea-nuclear/north-korea-says-conducts-perfect-hydrogen-bomb-test-idUSKCN1BD0VY|title=North Korea says conducts 'perfect' hydrogen bomb test|date= 3 September 2017 |work=Reuters|access-date=2023-09-10}}</ref> U.S. Intelligence released an early assessment that the yield estimate was {{convert|140|ktonTNT|abbr=on}},<ref name="diplomat-20170906">{{cite magazine |url=https://thediplomat.com/2017/09/us-intelligence-north-koreas-sixth-test-was-a-140-kiloton-advanced-nuclear-device/ |title=US Intelligence: North Korea's Sixth Test Was a 140 Kiloton 'Advanced Nuclear' Device |last=Panda |first=Ankit |magazine=The Diplomat |date=6 September 2017 |access-date=6 September 2017}}</ref> with an uncertainty range of {{convert|70|to|280|ktonTNT|abbr=on}}.<ref name="wp-20170913">{{cite news |url=https://www.washingtonpost.com/world/north-korea-nuclear-test-maybe-have-been-twice-as-strong-as-first-thought/2017/09/13/19b026d8-985b-11e7-a527-3573bd073e02_story.html |title=North Korea nuclear test may have been twice as strong as first thought |author=Michelle Ye Hee Lee |newspaper=Washington Post |date=13 September 2017 |access-date=28 September 2017}}</ref> On 12 September, [[NORSAR]] revised its estimate of the explosion magnitude upward to 6.1, matching that of the [[Comprehensive Nuclear-Test-Ban Treaty Organization|CTBTO]] but less powerful than the [[United States Geological Survey|USGS]] estimate of 6.3. Its yield estimate was revised to {{convert|250|ktonTNT|abbr=on}}, while noting the estimate had some uncertainty and an undisclosed margin of error.<ref>{{Cite web | url=https://www.norsar.no/press/latest-press-release/archive/the-nuclear-explosion-in-north-korea-on-3-september-2017-a-revised-magnitude-assessment-article1548-984.html | title=The nuclear explosion in North Korea on 3 September 2017: A revised magnitude assessment – NORSAR | access-date=18 November 2017 | archive-date=13 September 2017 | archive-url=https://archive.today/20170913180851/https://www.norsar.no/press/latest-press-release/archive/the-nuclear-explosion-in-north-korea-on-3-september-2017-a-revised-magnitude-assessment-article1548-984.html | url-status=dead }}</ref><ref>{{Cite web | url=http://www.38north.org/2017/09/punggye091217/ | title=North Korea's Punggye-ri Nuclear Test Site: Satellite Imagery Shows Post-Test Effects and New Activity in Alternate Tunnel Portal Areas &#124; 38 North: Informed Analysis of North Korea| date=2017-09-12}}</ref> On 13 September, an analysis of before and after [[synthetic-aperture radar]] satellite imagery of the test site was published suggesting the test occurred under {{convert|900|m}} of rock, and the yield "could have been in excess of 300 kilotons".<ref>{{Cite web |website = Arms Control Wonk| url= http://www.armscontrolwonk.com/archive/1203852/sar-image-of-punggye-ri/ |title = SAR Image of Punggye-ri|first = Jeffrey|last = Lewis|date= 13 September 2017}}</ref>

== Public knowledge ==
The Teller–Ulam design was for many years considered one of the top nuclear secrets, and even today it is not discussed in any detail by official publications with origins "behind the fence" of [[Classified information|classification]]. [[United States Department of Energy]] (DOE) policy has been, and continues to be, that they do not acknowledge when "leaks" occur, because doing so would acknowledge the accuracy of the supposed leaked information. Aside from images of the warhead casing, most information in the public domain about this design is relegated to a few terse statements by the DOE and the work of a few individual investigators.

=== U.S. Department of Energy statements ===
[[File:W80 nuclear warhead.jpg|right|thumb|Photographs of warhead casings, such as this one of the [[W80 (nuclear warhead)|W80]] nuclear warhead, allow for some speculation as to the relative size and shapes of the ''primaries'' and ''secondaries'' in U.S. thermonuclear weapons.]]
In 1972 the United States government declassified a document stating "[I]n thermonuclear (TN) weapons, a fission 'primary' is used to trigger a TN reaction in thermonuclear fuel referred to as a 'secondary{{'"}}, and in 1979 added, "[I]n thermonuclear weapons, radiation from a fission explosive can be contained and used to transfer energy to compress and ignite a physically separate component containing thermonuclear fuel." To this latter sentence the US government specified that "''Any elaboration of this statement will be classified''."<ref group="note">emphasis in original</ref> The only information that may pertain to the ''spark plug'' was declassified in 1991: "Fact that fissile or fissionable materials are present in some secondaries, material unidentified, location unspecified, use unspecified, and weapons undesignated." In 1998 the DOE declassified the statement that "The fact that materials may be present in channels and the term 'channel filler', with no elaboration", which may refer to the polystyrene foam (or an analogous substance).<ref>{{cite book| publisher=United States Department of Energy| title=Restricted Data Declassification Decisions, 1946 to the present |volume=7|date=January 2001| url=https://fas.org/sgp/othergov/doe/rdd-7.html}}</ref>

Whether these statements vindicate some or all of the models presented above is up for interpretation, and official U.S. government releases about the technical details of nuclear weapons have been purposely equivocating in the past (e.g., [[Smyth Report]]). Other information, such as the types of fuel used in some of the early weapons, has been declassified, though precise technical information has not been.

=== ''United States v. The Progressive'' ===
{{Main|United States v. The Progressive}}

Most of the current ideas on the workings of the Teller–Ulam design came into public awareness after the DOE attempted to [[prior restraint|censor]] a magazine article by U.S. anti-weapons activist [[Howard Morland]] in 1979 on the "secret of the hydrogen bomb". In 1978, Morland had decided that discovering and exposing this "last remaining secret" would focus attention onto the [[arms race]] and allow citizens to feel empowered to question official statements on the importance of nuclear weapons and nuclear secrecy.{{citation needed|date=January 2016}} Most of Morland's ideas about how the weapon worked were compiled from accessible sources: the drawings that most inspired his approach came from the ''[[Encyclopedia Americana]]''.{{citation needed|date=January 2016}} Morland also interviewed (often informally) many former Los Alamos scientists (including Teller and Ulam, though neither gave him any useful information), and he used a variety of [[Social engineering (security)|interpersonal strategies]] to encourage informative responses from them (i.e., asking questions such as "Do they still use spark plugs?" even if he was not aware what the latter term specifically referred to).<ref name="Morland 1981">{{Cite book | last1 = Morland | first1 = Howard | author-link1 = Howard Morland | title = The secret that exploded | date = 1981 | ol = 4094494M | lccn = 80006032 | isbn = 978-0394512976 | oclc = 7196781 | publisher = [[Random House]] | df = dmy-all}}</ref>

Morland eventually concluded that the "secret" was that the ''primary'' and ''secondary'' were kept separate and that [[radiation pressure]] from the ''primary'' compressed the ''secondary'' before igniting it. When an early draft of the article, to be published in ''[[The Progressive]]'' magazine, was sent to the DOE after falling into the hands of a professor who was opposed to Morland's goal, the DOE requested that the article not be published and pressed for a temporary [[injunction]]. The DOE argued that Morland's information was (1) likely derived from classified sources, (2) if not derived from classified sources, itself counted as "secret" information under the "[[born secret]]" clause of the 1954 [[Atomic Energy Act of 1954|Atomic Energy Act]], and (3) was dangerous and would encourage [[nuclear proliferation]]. Morland and his lawyers disagreed on all points, but the injunction was granted, as the judge in the case felt that it was safer to grant the injunction and allow Morland, et al., to appeal.

Through a variety of more complicated circumstances, the DOE case began to wane as it became clear that some of the data they were attempting to claim as "secret" had been published in a students' encyclopedia a few years earlier. After another H-bomb speculator, [[Chuck Hansen]], had his own ideas about the "secret" (quite different from Morland's) published in a Wisconsin newspaper, the DOE claimed that ''The Progressive'' case was moot, dropped its suit, and allowed the magazine to publish its article, which it did in November 1979. Morland had by then, however, changed his opinion of how the bomb worked, suggesting that a foam medium (the polystyrene) rather than radiation pressure was used to compress the ''secondary'', and that in the ''secondary'' there was a ''spark plug'' of fissile material as well. He published these changes, based in part on the proceedings of the appeals trial, as a short erratum in ''The Progressive'' a month later.<ref>{{cite journal| url=http://progressive.org/?q=node/2252|date=November 1979| volume=43| issue= 11| title=The H-Bomb Secret: How we got it and why we're telling it| journal=The Progressive}}</ref> In 1981, Morland published a book about his experience, describing in detail the train of thought that led him to his conclusions about the "secret".<ref name="Morland 1981" /><ref>{{Cite book | last1 = De Volpi | first1 = Alexander | last2 = Marsh | first2 = Gerald E. | author-link2 = Gerald E. Marsh | last3 = Postol | first3 = Ted | author-link3 = Theodore Postol | last4 = Stanford | first4 = George | title = Born Secret: The H-Bomb, the Progressive Case and National Security | url = https://archive.org/details/bornsecrethbombp0000unse | date = 1981| ol = 7311029M | oclc = 558172005 | isbn = 978-0080259956 | publisher = [[Pergamon Press]] | via = [[Internet Archive]] | df = dmy-all }}</ref>

Morland's work is interpreted as being at least partially correct because the DOE [[Streisand effect|had sought to censor it]], one of the few times they violated their usual approach of not acknowledging "secret" material that had been released; however, to what degree it lacks information, or has incorrect information, is not known with any confidence. The difficulty that other countries had in developing the Teller–Ulam design (even when they apparently understood the design, such as with the United Kingdom) makes it somewhat unlikely that this simple information alone is what provides the ability to manufacture thermonuclear weapons. Nevertheless, the ideas put forward by Morland in 1979 have been the basis for all the current speculation on the Teller–Ulam design.

== Notable accidents ==
{{See also|List of military nuclear accidents}}
On 5 February 1958, during a training mission flown by a [[Boeing B-47 Stratojet|B-47]], a [[Mark 15 nuclear bomb]], also known as the [[Tybee Bomb]], was lost off the coast of [[Tybee Island, Georgia|Tybee Island]] near [[Savannah, Georgia]]. The US Air Force maintains that the bomb was unarmed and did not contain the live plutonium core necessary to initiate a nuclear explosion.<ref>{{cite news |date=2001 |title=Air Force Search & Recovery Assessment of the 1958 Savannah, GA B-47 Accident |publisher=AF Nuclear Weapons and Counterproliferation Agency. U.S. Air Force}}</ref> The bomb was thought by the Department of Energy to lie buried under several feet of silt at the bottom of [[Wassaw Sound]].<ref>{{cite news |title=For 50 Years, Nuclear Bomb Lost in Watery Grave |url=https://www.npr.org/templates/story/story.php?storyId=18587608&t=1566568815867 |work=NPR |date=3 February 2008}}</ref>

On 17 January 1966, [[1966 Palomares B-52 crash|a fatal collision]] occurred between a B-52G and a KC-135 Stratotanker over [[Palomares, Almería|Palomares]], Spain. The conventional explosives in two of the [[B28 nuclear bomb|Mk28]]-type [[Teller–Ulam design|hydrogen bombs]] detonated upon impact with the ground, dispersing plutonium over nearby farms. A third bomb landed intact near Palomares while the fourth fell 12 miles (19&nbsp;km) off the coast into the Mediterranean sea and was recovered a few months later.<ref>{{cite news |title=US to clean up Spanish radioactive site 49 years after plane crash |url=https://www.theguardian.com/world/2015/oct/19/us-to-clean-up-spanish-radioactive-site-49-years-after-palomares-plane-crash |work=The Guardian |date=19 October 2015}}</ref>

On 21 January 1968, a B-52G, with four [[B28 nuclear bomb|B28FI thermonuclear bombs]] aboard as part of [[Operation Chrome Dome]], [[1968 Thule Air Base B-52 crash|crashed on the ice]] of the [[North Star Bay]] while attempting an emergency landing at [[Thule Air Base]] in Greenland.<ref>{{cite news |title=The Cold War's Missing Atom Bombs |url=https://www.spiegel.de/international/world/a-nuclear-needle-in-a-haystack-the-cold-war-s-missing-atom-bombs-a-590513.html |work=Der Spiegel |date=14 November 2008}}</ref> The resulting fire caused extensive radioactive contamination.<ref>{{cite news |title=US B-52 nuclear bomber crash in Greenland 51 years ago has ill Danes seeking compensation |url=https://www.foxnews.com/us/us-b-52-nuclear-bomber-crash-in-greenland-51-years-ago-has-ill-danes-seeking-compensation |work=Fox News |date=3 June 2019}}</ref> Personnel involved in the cleanup failed to recover all the debris from three of the bombs, and one bomb was not recovered.<ref name="Greenland_Telegraph" />

== See also ==
* [[COLEX process (isotopic separation)]]
* [[NUKEMAP]]
* [[Pure fusion weapon]]

== Notes ==
{{Reflist|group="note"|refs=
}}

== References ==
{{reflist|30em|refs=

<ref name=":8">{{cite news |last=Burns |first=John F. |date=1998-05-18 |title=Nuclear Anxiety: The Overview; India Detonated a Hydrogen Bomb, Experts Confirm |language=en-US |work=The New York Times |url=https://www.nytimes.com/1998/05/18/world/nuclear-anxiety-the-overview-india-detonated-a-hydrogen-bomb-experts-confirm.html |access-date=2019-07-26 |issn=0362-4331}}</ref>

<ref name="NPR_TOTN">{{cite podcast | url = https://www.npr.org/transcripts/4994161 | title = Sixty Years of Trying to Control the Bomb (Transcripts) | website = [[Talk of the Nation]] | publisher = NPR | last1 = Conan | first1 = Neal| author-link1 = Neal Conan | date = 2005-11-08 | access-date = 2021-02-10 | quote = But, yes, the hydrogen bomb—that is, a two-stage thermonuclear device, as we refer to it—is indeed the principal part of the US arsenal, as it is of the Russian arsenal..}}</ref>

<ref name="Teller">{{cite tech report | last1 = Teller | first1 = Edward | author-link1 = Edward Teller | last2 = Ulam | first2 = Stanislaw | author-link2 = Stanislaw Ulam | date = 1951-03-09 | title = On Heterocatalytic Detonations I. Hydrodynamic Lenses and Radiation Mirrors | url = http://www.nuclearnonproliferation.org/LAMS1225.pdf | url-status = live | format = pdf | series = A | language = en | publisher = Los Alamos Scientific Laboratory | archive-url = https://web.archive.org/web/20201128023326/http://www.nuclearnonproliferation.org/LAMS1225.pdf | archive-date = 2020-11-28 | access-date = 2021-02-10 | via = Nuclear Non-Proliferation Institute | df = dmy-all}}</ref>

<ref name="Bundy">{{cite book |last1 = Bundy |first1 = McGeorge |author-link1 = McGeorge Bundy |year=1988 |title = Danger and Survival: Choices About the Bomb in the First Fifty Years | language = en | publisher = Random House |isbn = 978-0394522784 | lccn = 89040089 |oclc = 610771749 |ol = OL24963545M | df = dmy-all }}</ref>

<ref name="YoungSchilling">{{cite book |last1 = Young |first1 = Ken |author-link1 = Ken Young |last2 = Schilling |first2 = Warner R. |author-link2 = Warner R. Schilling |year=2020 |title = Super Bomb: Organizational Conflict and the Development of the Hydrogen Bomb | language = en | publisher = Cornell University Press |isbn = 978-1501745164 |oclc = 1164620354 |ol = OL28729278M | df = dmy-all }}</ref>

<ref name="Rhodes 1995">{{Cite Q | Q105755363 | last1 = Rhodes | first1 = Richard | author-link1 = Richard Rhodes | df = dmy-all | via = Internet Archive }}</ref>

<ref name="BombBook">{{cite book| first = Stephen M. | last = Younger | title = The Bomb: A New History | language = en | publisher = HarperCollins | year = 2009 | isbn = 978-0061537196 | url=https://archive.org/details/bombnewhistory00youn | url-access = registration | oclc = 310470696 |ol = OL24318509M | df = dmy-all | via = Internet Archive] }}</ref>

<ref name="Croddy">{{cite book |year=2004 | editor1-last = Croddy | editor1-first = Eric A. |editor2-last = Wirtz | editor2-first = James J. | editor3-last = Larsen ear| editor3-first = Jeffrey A. | title = Weapons of Mass Destruction: An Encyclopedia of Worldwide Policy, Technology, and History | url = https://books.google.com/books?id=ZzlNgS70OHAC&q=almost+unlimited+yield&pg=RA1-PA376 | language = en | publisher = ABC-Clio | isbn = 978-1851094905 | oclc = 941444356 | ol = OL8969957M | access-date = 2021-02-08 | df = dmy-all | via = Google Books }}</ref>

<ref name="Winterberg">{{cite book | last1 = Winterberg | first1 = Friedwardt | author-link1 = Friedwardt Winterberg | title = The Release of Thermonuclear Energy by Inertial Confinement: Ways Towards Ignition | language = en | publisher = World Scientific Publishing Company | date=2010 | isbn = 978-9814295901 | url=https://archive.org/details/releasethermonuc00wint | url-access = registration | oclc = 496957934 |ol = OL26140529M | df = dmy-all | via = Internet Archive }}</ref>

<ref name=basement>{{cite book | last1=Karpin | first1=Michael I. | author-link1 = Michael Karpin | title = The Bomb in the Basement: How Israel Went Nuclear and What That Means for the World | isbn = 978-0743265942 | date = 2006 | publisher = Simon & Schuster | url = https://archive.org/details/bombinbasementho00karp | url-access = registration | oclc = 892937053 |ol = OL3427490M | df = dmy-all | lccn = 2005051689 | via = Internet Archive }}</ref>

<ref name="W76">{{cite web | url = http://nuclearweaponarchive.org/Usa/Weapons/W76.html | title = The W76 Warhead: Intermediate Yield Strategic SLBM MIRV Warhead | last = Sublette | first = Carey | date = 2007-01-09 | website = Nuclear Weapon Archive | language = en | access-date=2021-02-08 | archive-url = https://web.archive.org/web/20210126024256/http://nuclearweaponarchive.org/Usa/Weapons/W76.html | archive-date = 2021-01-26 | df = dmy-all }}</ref>

<ref name="StroberHoffman">{{Cite book |title = A Convenient Spy: Wen Ho Lee and the Politics of Nuclear Espionage |ol = 7927314M |url = https://archive.org/details/convenientspywen00stob |lccn = 2001054945 |isbn = 978-0743223782 |publisher = Simon & Schuster |first1 = Dan | last1= Stober |first2 = Ian | last2= Hoffman |year = 2001 | via = Internet Archive | df = dmy-all}}</ref>

<ref name="Greenland_Telegraph">{{cite news | last1 = Swaine | first1 = Jon | date = 2008-11-11 | title = US left nuclear weapon under ice in Greenland | url = https://www.telegraph.co.uk/news/worldnews/europe/greenland/3439318/US-left-nuclear-weapon-under-ice-in-Greenland.html | url-status = live | work = The Daily Telegraph | language = en | issn = 0307-1235 |oclc = 49632006 | archive-url = https://web.archive.org/web/20090601160800/https://www.telegraph.co.uk/news/worldnews/europe/greenland/3439318/US-left-nuclear-weapon-under-ice-in-Greenland.html | archive-date = 2009-06-01 | access-date = 2021-02-10 | url-access = subscription | quote = Following the crash, and a painstaking clear-up mission to recover thousands of pieces of material from 500 million gallons of ice, the Pentagon stated that all four weapons onboard had been "destroyed". However, documents obtained by the BBC under the US Freedom of Information act have disclosed that while this is technically true—none of the bombs remained complete—one of the weapons was not recovered. | df = dmy-all }}</ref>

<ref name="Holloway">{{cite book| last1 = Holloway | first1 = David | title = Stalin and the Bomb: The Soviet Union and Atomic Energy, 1939–1956 | language = en | publisher = Yale University Press| year = 1994| isbn = 978-0300060560 | oclc = 470165274 |ol = OL1084400M | df = dmy-all }}</ref>

<ref name="hansen-swords">{{cite book |first=Chuck |last=Hansen |title=Swords of Armageddon: U.S. Nuclear Weapons Development Since 1945 |year=2007 |location=Sunnyvale, California |publisher=Chukelea Publications |format=PDF |type=CD-ROM & download available |isbn=978-0979191503 |edition=2nd |url=http://www.uscoldwar.com}}</ref>

<ref name="Hansen1988">{{cite book | last1 = Hansen | first1 = Chuck | author-link1 = Chuck Hansen | year = 1988 | title = U.S. Nuclear Weapons: The Secret History | url = https://archive.org/details/usnuclearweapons0000hans | url-access = registration | publisher = [[Crown Publishing Group|Crown]] | isbn = 978-0517567401 | lccn = 87021995 | oclc = 865554459 | ol = OL2392513M | access-date = 2021-11-10 | via = [[Internet Archive]] | df = dmy-all}}</ref>

}}

== Further reading ==
=== Basic principles ===
{{Refbegin|30em}}
* {{cite web | url = http://nuclearweaponarchive.org/Nwfaq/Nfaq4.html | title = Section 4.0 Engineering and Design of Nuclear Weapons | last = Sublette | first = Carey | date = 2019-03-19 | website = Nuclear Weapon Archive | language = en | access-date=2021-02-09 | url-status = live | archive-url = https://web.archive.org/web/20210206233652/http://nuclearweaponarchive.org/Nwfaq/Nfaq4.html | archive-date = 2021-02-06 | df = dmy-all }}
* {{cite book | last1 = Barroso | first1 = Dalton E. G. | year = 2009 |title = A Fisica dos Explosivos Nucleares | trans-title= The Physics of Nuclear Explosives | url = https://books.google.com/books?id=6bE6781f1Q8C | url-access = limited |language= pt | edition = 2nd |publisher= Livraria da Física | isbn = 978-8578610166 | oclc = 733273749 | ol = OL30689359M | access-date = 2020-02-09 |via= [[Google Books]] | df = dmy-all}}
{{Refend}}

=== History ===
{{Refbegin|30em}}
* {{cite book |last1 = Bundy |first1 = McGeorge |author-link1 = McGeorge Bundy |year=1988 |title = Danger and Survival: Choices About the Bomb in the First Fifty Years | language = en | publisher = [[Random House]] |isbn = 978-0394522784 | lccn = 89040089 |oclc = 610771749 |ol = OL24963545M | df = dmy-all }}
* {{cite book |last1 = DeGroot |first1 = Gerard J. |year=2005 |title = The Bomb: A Life | url = https://archive.org/details/bomblife00degr | url-access = registration | language = en | publisher = [[Harvard University Press]] |isbn = 978-0674017245 |oclc = 57750742 |ol = OL7671320M | df = dmy-all | via = [[Internet Archive]] }}
* {{cite journal | last1 = Galison | first1 = Peter | author-link1 = Peter Galison | last2 = Bernstein | first2 = Barton J. | author-link2 = Barton Bernstein | date = 1989-01-01 | title = In Any Light: Scientists and the Decision to Build the Superbomb, 1952–1954 | journal = [[Historical Studies in the Natural Sciences|Historical Studies in the Physical and Biological Sciences]] | language = en | volume = 19 | issue = 2 | pages = 267–347 | doi = 10.2307/27757627 | jstor = 27757627 | eissn = 1939-182X | issn = 1939-1811 | df = dmy-all}}
* {{cite journal | last1 = Goncharov | first1 = German A. | author-link1 = German Goncharov | date = 1996-10-31 | title = American and Soviet H-bomb development programmes: historical background | journal = [[Physics-Uspekhi]] | language = en | volume = 39 | issue = 10 | pages = 1033–1044 | doi = 10.1070/PU1996v039n10ABEH000174 | bibcode = 1996PhyU...39.1033G | s2cid = 250861572 | eissn = 1468-4780 | issn = 1063-7869 | lccn = 93646146 | oclc = 36334507 | df = dmy-all}}
* {{cite book| last1 = Holloway | first1 = David | title = Stalin and the Bomb: The Soviet Union and Atomic Energy, 1939–1956 | language = en | publisher = [[Yale University Press]]| year= 1994| isbn = 978-0300060560 | oclc = 470165274 |ol = OL1084400M | df = dmy-all }}
* {{cite book| first = Richard| last = Rhodes| author-link1 = Richard Rhodes | title = Dark Sun: The Making of the Hydrogen Bomb | url=https://archive.org/details/darksunmakingofh00rhod | url-access = registration | language = en | location = New York | publisher = [[Simon & Schuster]]| year= 1995| isbn = 978-0684804002 | oclc = 717414304 |ol = OL7720934M | df = dmy-all | via = [[Internet Archive]] }}
* {{cite book | last1 = Schweber | first1 = Silvan S. | author-link1 = Silvan S. Schweber | year = 2007 | title = In the Shadow of the Bomb: Oppenheimer, Bethe, and the Moral Responsibility of the Scientist | url = https://archive.org/details/inshadowofbombbe00schw | url-access = limited | series = Princeton Series in Physics | language = en | publisher = [[Princeton University Press]] | isbn = 978-0691127859 | oclc = 868971191 | ol = OL7757230M | via = [[Internet Archive]] }}
* {{cite magazine |last1= Stix |first1= Gary |author-link1= Gary Stix | date = 1999-10-20 |title= Infamy and Honor at the Atomic Café: Father of the hydrogen bomb, "Star Wars" missile defense and Lawrence Livermore National Laboratory, Edward Teller has no regrets about his contentious career |url= https://www.scientificamerican.com/article/infamy-and-honor-at-the-a/ |url-access= subscription |magazine= [[Scientific American]] |language= en |volume= 281 |issue= 4 | pages=42–43 |issn= 0036-8733 | df = dmy-all }}
* {{cite book |last1 = Young |first1 = Ken |author-link1 = Ken Young |last2 = Schilling |first2 = Warner R. |author-link2 = Warner R. Schilling |year=2020|title = Super Bomb: Organizational Conflict and the Development of the Hydrogen Bomb | language = en | publisher = [[Cornell University Press]] |isbn = 978-1501745164 |oclc = 1164620354 |ol = OL28729278M | df = dmy-all }}
* {{cite book| first = Stephen M. | last = Younger | title = The Bomb: A New History | language = en | publisher = [[HarperCollins]] | year = 2009 | isbn = 978-0061537196 | url=https://archive.org/details/bombnewhistory00youn | url-access = registration | oclc = 310470696 |ol = OL24318509M | df = dmy-all | via = [[Internet Archive]] }}
{{Refend}}

=== Analyzing fallout ===
{{Refbegin|30em}}
* {{cite journal | last1 = De Geer | first1 = Lars-Erik | date = 1991 | title = The radioactive signature of the hydrogen bomb | journal = Science & Global Security | language = en | volume = 2 | issue = 4 | pages = 351–363 | doi = 10.1080/08929889108426372 | bibcode = 1991S&GS....2..351D | issn = 0892-9882| oclc = 15307789 | df = dmy-all}}
* {{cite journal | last1 = Khariton | first1 = Yuli | author-link1 = Yulii Khariton | last2 = Smirnov | first2 = Yuri | last3 = Rothstein | first3 = Linda | last4 = Leskov | first4 = Sergei | year= 1993 | title = The Khariton Version | journal = [[Bulletin of the Atomic Scientists]] | language = en | volume = 49 | issue = 4 | pages = 20–31 | doi = 10.1080/00963402.1993.11456341 | bibcode = 1993BuAtS..49d..20K | eissn = 1938-3282 | issn = 0096-3402 | lccn = 48034039 | oclc = 470268256 | df = dmy-all}}
{{Refend}}

== External links ==
{{Commons category|Teller-Ulam design}}

=== Principles ===
* [http://nuclearweaponarchive.org/Library/Teller.html "Basic Principles of Staged Radiation Implosion (Teller–Ulam)"] from Carey Sublette's NuclearWeaponArchive.org.
* [http://nuclearweaponarchive.org/Nwfaq/Nfaq3.html "Matter, Energy, and Radiation Hydrodynamics"] from Carey Sublette's Nuclear Weapons FAQ.
* [http://nuclearweaponarchive.org/Nwfaq/Nfaq4.html "Engineering and Design of Nuclear Weapons"] from Carey Sublette's Nuclear Weapons FAQ.
* [http://nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html "Elements of Thermonuclear Weapon Design"] from Carey Sublette's Nuclear Weapons FAQ.
* [http://alsos.wlu.edu/qsearch.aspx?browse=science/Nuclear+Weapons+Design Annotated bibliography for nuclear weapons design from the Alsos Digital Library for Nuclear Issues]

=== History ===
* [https://www.pbs.org/wgbh/amex/bomb/filmmore/reference/interview/index.html PBS: Race for the Superbomb: Interviews and Transcripts] {{Webarchive|url=https://web.archive.org/web/20170311225702/http://www.pbs.org/wgbh/amex/bomb/filmmore/reference/interview/index.html |date=11 March 2017 }} (with U.S. and USSR bomb designers as well as historians).
* [https://fas.org/sgp/eprint/cardozo.html Howard Morland on how he discovered the "H-bomb secret"] (includes many slides).
* [http://progressive.org/?q=node/2252 ''The Progressive'' November 1979 issue] – "The H-Bomb Secret: How we got it, why we're telling" (entire issue online).
* [http://alsos.wlu.edu/qsearch.aspx?browse=warfare/Hydrogen+Bomb Annotated bibliography on the hydrogen bomb from the Alsos Digital Library]
* [https://web.archive.org/web/20080226213021/https://www.mcis.soton.ac.uk/Site_Files/pdf/nuclear_history/Working_Paper_No_5.pdf University of Southampton, Mountbatten Centre for International Studies, Nuclear History Working Paper No5.]
* [http://www.atomcentral.com/trinity.html Peter Kuran's "Trinity and Beyond"] {{Webarchive|url=https://web.archive.org/web/20181209124851/http://www.atomcentral.com/trinity.html |date=9 December 2018 }} – documentary film on the history of nuclear weapon testing.
* [https://www.youtube.com/watch?v=pWpqGKUG5yY&list=PLvGO_dWo8VfcmG166wKRy5z-GlJ_OQND5&index=1 YouTube Playlist of declassified nuclear explosion tests obtained by converting film scans to digital at Lawrence Livermore Laboratory]

{{Fusion power}}
{{Authority control}}

[[Category:Nuclear weapon design]]
[[Category:Nuclear secrecy]]
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