
A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation
nuclear weapon design
Nuclear weapons design are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types:
# Pure fission weapons are the simplest, least technically de ...
. Its greater sophistication affords it vastly greater destructive power than first-generation
nuclear bomb
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...
s, a more compact size, a lower mass, or a combination of these benefits. Characteristics of
nuclear fusion
Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...
reactions make possible the use of non-fissile
depleted uranium
Depleted uranium (DU), also referred to in the past as Q-metal, depletalloy, or D-38, is uranium with a lower content of the fissile isotope Uranium-235, 235U than natural uranium. The less radioactive and non-fissile Uranium-238, 238U is the m ...
as the weapon's main fuel, thus allowing more efficient use of scarce
fissile material
In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal chain reaction can only be achieved with fissile material. The predominant neutron energy i ...
. Its multi-stage design is distinct from the usage of fusion in simpler
boosted fission weapons. The first full-scale thermonuclear test (
Ivy Mike
Ivy Mike was the code name, codename given to the first full-scale test of a Thermonuclear weapon, thermonuclear device, in which a significant fraction of the explosive nuclear weapon yield, yield comes from nuclear fusion.
Ivy Mike was detona ...
) was carried out by the United States in 1952, and the concept has since been employed by at least the five recognized
nuclear-weapon states and
UNSC
The United Nations Security Council (UNSC) is one of the six principal organs of the United Nations (UN) and is charged with ensuring international peace and security, recommending the admission of new UN members to the General Assembly, an ...
permanent members: the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
,
Russia
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
, the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
,
China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
, and
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
.
The design of all thermonuclear weapons is believed to be the
''Teller–Ulam configuration'', in which a
fission bomb
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear expl ...
primary stage's energy is channelled into implosion of a separate fusion secondary stage containing thermonuclear fuel, usually
lithium-6 deuteride. During detonation, neutrons convert
lithium-6
Naturally occurring lithium (3Li) is composed of two stable isotope ratio, stable isotopes, lithium-6 (6Li) and lithium-7 (7Li), with the latter being far more abundant on Earth. Both of the natural isotopes have an unexpectedly low nuclear bin ...
to
helium-4
Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consi ...
plus
tritium
Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...
. The heavy
isotope
Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...
s of hydrogen,
deuterium
Deuterium (hydrogen-2, symbol H or D, also known as heavy hydrogen) is one of two stable isotopes of hydrogen; the other is protium, or hydrogen-1, H. The deuterium nucleus (deuteron) contains one proton and one neutron, whereas the far more c ...
and tritium, then undergo
an energetic reaction. For this reason, thermonuclear weapons are often colloquially called hydrogen bombs or H-bombs.
[The misleading term ''hydrogen bomb'' was already in wide public use before fission product fallout from the ]Castle Bravo
Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of ''Operation Castle''. Detonated on 1 March 1954, the device remains the most powe ...
test in 1954 revealed the extent to which most designs primarily rely on fast fission
Fast fission is fission that occurs when a heavy atom absorbs a high-energy neutron, called a fast neutron, and splits. Most fissionable materials need thermal neutrons, which move more slowly.
Fast reactors vs. thermal reactors
Fast neutron r ...
.
The weapon firing begins with the
detonation
Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...
of the fission primary. Its temperature soars past 100 million
kelvin
The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By de ...
, emitting
X-rays
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
via
inverse Compton scattering. These flood the radiation case, allowing compression of the separately located secondary. A neutron shield blocks the predetonation of the secondary, which completes detonation before destruction by the primary's fireball.
The secondary stage consists of the outer pusher/
tamper, fusion fuel, and central fissile
sparkplug
A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...
. The primary's X-rays intensely
ionize
Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...
and
ablate the tamper surface, imploding the secondary. This triggers a
fission explosion in the sparkplug. These forces combine to begin
fusion ignition in the fusion fuel, around 300 million kelvin. The
Jetter cycle produces the crucial
tritium
Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...
fuel from neutron-lithium-6 reactions.
Additionally, most weapons use a
natural
Nature is an inherent character or constitution, particularly of the ecosphere or the universe as a whole. In this general sense nature refers to the laws, elements and phenomena of the physical world, including life. Although humans are part ...
or
depleted uranium
Depleted uranium (DU), also referred to in the past as Q-metal, depletalloy, or D-38, is uranium with a lower content of the fissile isotope Uranium-235, 235U than natural uranium. The less radioactive and non-fissile Uranium-238, 238U is the m ...
tamper and case. This undergoes
fast fission
Fast fission is fission that occurs when a heavy atom absorbs a high-energy neutron, called a fast neutron, and splits. Most fissionable materials need thermal neutrons, which move more slowly.
Fast reactors vs. thermal reactors
Fast neutron r ...
from
fast fusion neutrons and is the main contribution to the total yield and
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...
fission product
fallout.
Before Ivy Mike, the US
Operation Greenhouse
Operation Greenhouse was the fifth American nuclear test series, the second conducted in 1951 and the first to test principles that would lead to developing Teller-Ullam, thermonuclear weapons (''hydrogen bombs''). Conducted at the new Pacific ...
in 1951 was the first nuclear test series investigating thermonuclear principles. Shot ''
George'' tested
radiation implosion and the first artificial
thermonuclear fusion
Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutron by-products. The difference in mass between the reactants and products is manifested as either the release or absorption of ener ...
while shot
''Item'' tested the boosted fission principle. The Teller-Ulam configuration was named for its two chief contributors,
Edward Teller
Edward Teller (; January 15, 1908 – September 9, 2003) was a Hungarian and American Theoretical physics, theoretical physicist and chemical engineer who is known colloquially as "the father of the hydrogen bomb" and one of the creators of ...
and
Stanisław Ulam
Stanisław Marcin Ulam ( ; 13 April 1909 – 13 May 1984) was a Polish and American mathematician, nuclear physicist and computer scientist. He participated in the Manhattan Project, originated the History of the Teller–Ulam design, Telle ...
, who developed it in 1951
for the United States, with certain concepts developed with the contribution of physicist
John von Neumann
John von Neumann ( ; ; December 28, 1903 – February 8, 1957) was a Hungarian and American mathematician, physicist, computer scientist and engineer. Von Neumann had perhaps the widest coverage of any mathematician of his time, in ...
.
Multi-stage devices were independently developed and tested by the Soviet Union (
1955), the United Kingdom (
1957
Events January
* January 1 – The Saarland joins West Germany.
* January 3 – Hamilton Watch Company introduces the first electric watch.
* January 5 – South African player Russell Endean becomes the first batsman to be Dismissal (cricke ...
), China (
1966
Events January
* January 1 – In a coup, Colonel Jean-Bédel Bokassa takes over as military ruler of the Central African Republic, ousting President David Dacko.
* January 3 – 1966 Upper Voltan coup d'état: President Maurice Yaméogo i ...
), and France (
1968
Events January–February
* January 1968, January – The I'm Backing Britain, I'm Backing Britain campaign starts spontaneously.
* January 5 – Prague Spring: Alexander Dubček is chosen as leader of the Communist Party of Cze ...
).
There is not enough public information to determine whether
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
,
Israel
Israel, officially the State of Israel, is a country in West Asia. It Borders of Israel, shares borders with Lebanon to the north, Syria to the north-east, Jordan to the east, Egypt to the south-west, and the Mediterranean Sea to the west. Isr ...
,
or
North Korea
North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korea, Korean Peninsula and borders China and Russia to the north at the Yalu River, Yalu (Amnok) an ...
possess multi-stage weapons.
Pakistan
Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...
is not considered to have developed them.
After the 1991
collapse of the Soviet Union
The Soviet Union was formally dissolved as a sovereign state and subject of international law on 26 December 1991 by Declaration No. 142-N of the Soviet of the Republics of the Supreme Soviet of the Soviet Union. Declaration No. 142-Н of ...
, Ukraine, Belarus, and Kazakhstan became the first and only countries to relinquish their thermonuclear weapons, although these had never left the operational control of
Russian forces.
Thermonuclear weapons are the only artificial source of explosions above one
megaton TNT. The
Tsar Bomba
The Tsar Bomba (code name: ''Ivan'' or ''Vanya''), also known by the alphanumerical designation "AN602", was a Thermonuclear weapon, thermonuclear aerial bomb, and by far the most powerful nuclear weapon ever created and tested. The Soviet phy ...
was the most powerful bomb ever detonated at 50 megatons TNT. As they are the most efficient design for yields above , and with decreased relevance of
tactical nuclear weapons
A tactical nuclear weapon (TNW) or non-strategic nuclear weapon (NSNW) is a nuclear weapon that is designed to be used on a battlefield in military situations, mostly with friendly forces in proximity and perhaps even on contested friendly territ ...
, virtually all the nuclear weapons deployed by the five recognized nuclear-weapons states today use the Teller–Ulam design. Their ability to miniaturize high yields, such as in
MIRV warheads, plays an important role in
nuclear deterrence. While some have been developed into
clean bombs, most thermonuclear weapons designed, including all current US and UK nuclear warheads, derive most of their energy from fast fission, causing high fallout.
Terminology
Phrases of the combination "thermonuclear"/"fusion"/"hydrogen" and "weapon"/"bomb"/"device" are applied primarily to multi-stage devices, which allow large fusion yields. These operate on the
radiation implosion principle, and are synonymous with the
Teller-Ulam design
A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lowe ...
, independently developed by at least five countries.
These are in contrast to
boosted fission devices, which employ
thermonuclear fusion
Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutron by-products. The difference in mass between the reactants and products is manifested as either the release or absorption of ener ...
, but detonate a single stage design theoretically limited to around one megaton.
Despite their name, the simplest and most common thermonuclear weapons derive most of their yield (>80% for US weapons) from
fast fission
Fast fission is fission that occurs when a heavy atom absorbs a high-energy neutron, called a fast neutron, and splits. Most fissionable materials need thermal neutrons, which move more slowly.
Fast reactors vs. thermal reactors
Fast neutron r ...
of a
natural
Nature is an inherent character or constitution, particularly of the ecosphere or the universe as a whole. In this general sense nature refers to the laws, elements and phenomena of the physical world, including life. Although humans are part ...
or
depleted uranium
Depleted uranium (DU), also referred to in the past as Q-metal, depletalloy, or D-38, is uranium with a lower content of the fissile isotope Uranium-235, 235U than natural uranium. The less radioactive and non-fissile Uranium-238, 238U is the m ...
tamper. Clean thermonuclear weapons (<10% fission) have also been tested.
Public knowledge concerning nuclear weapon design
Detailed knowledge of fission and fusion weapons is
classified
Classified may refer to:
General
*Classified information, material that a government body deems to be sensitive
*Classified advertising or "classifieds"
Music
*Classified (rapper) (born 1977), Canadian rapper
* The Classified, a 1980s American ro ...
to some degree in virtually every
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
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...
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
censor weapons information in the public press, with limited success. 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.
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
Reverse engineering (also known as backwards engineering or back engineering) is a process or method through which one attempts to understand through deductive reasoning how a previously made device, process, system, or piece of software accompl ...
from known information, or comparison with similar fields of
physics
Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...
(
inertial confinement fusion
Inertial confinement fusion (ICF) is a fusion energy process that initiates nuclear fusion reactions by compressing and heating targets filled with fuel. The targets are small pellets, typically containing deuterium (2H) and tritium (3H).
Typical ...
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
Primary and secondary stages
The basic principle of the
Teller–Ulam configuration is the idea that different parts of a thermonuclear weapon can be chained together in stages, with the
detonation
Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...
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
fission bomb (a "trigger"), and a secondary section that consists of
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
Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...
. This process could be continued, with energy from the secondary igniting a third fusion stage; the Soviet Union's AN602 "
Tsar Bomba
The Tsar Bomba (code name: ''Ivan'' or ''Vanya''), also known by the alphanumerical designation "AN602", was a Thermonuclear weapon, thermonuclear aerial bomb, and by far the most powerful nuclear weapon ever created and tested. The Soviet phy ...
" is thought to have been a three-stage fission-fusion-fusion device. Theoretically by continuing this process thermonuclear weapons with arbitrarily high
yield could be constructed. Fission weapons are limited in yield because only so much fission fuel can be amassed in one place before the danger of its accidentally becoming
supercritical becomes too great.

Surrounding the other components is a
hohlraum
In radiation thermodynamics, a hohlraum (; a non-specific German word for a "hollow space", "empty room", or "cavity") is a cavity whose walls are in radiative equilibrium with the radiant energy within the cavity. First proposed by Gustav Kir ...
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.
The primary is a standard implosion method fission bomb, though likely with a
core boosted by small amounts of fusion fuel (usually 1:1
deuterium
Deuterium (hydrogen-2, symbol H or D, also known as heavy hydrogen) is one of two stable isotopes of hydrogen; the other is protium, or hydrogen-1, H. The deuterium nucleus (deuteron) contains one proton and one neutron, whereas the far more c ...
:
tritium
Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...
gas) for extra efficiency; the fusion fuel releases excess
neutron
The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...
s when heated and compressed, inducing additional fission. When fired, the or core would be compressed to a smaller sphere by special layers of conventional
high explosive
An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An exp ...
s arranged around it in an
explosive lens
An explosive lens—as used, for example, in nuclear weapons—is a highly specialized shaped charge. In general, it is a device composed of several explosive charges. These charges are arranged and formed with the intent to control the sha ...
pattern, initiating the
nuclear chain reaction
In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series or "positive feedback loop" of thes ...
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", a heavy layer of
uranium-238
Uranium-238 ( or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it i ...
() or
lead
Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
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
Lithium hydride is an inorganic compound with the formula Lithium, LiHydride, H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a Hydride#Ionic hydrides, salt-like (ionic) hydride, it has a ...
, 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
Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...
of
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
that can undergo
nuclear fusion
Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...
, along with the deuterium present in the mixture. Inside the layer of fuel is the "
spark plug
A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...
", a hollow column of fissile material ( or ) 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.
Interstage
Separating the secondary from the primary is the
interstage. The fissioning primary produces four types of energy: 1) expanding hot gases from high explosive charges that implode the primary; 2) superheated
plasma that was originally the bomb's fissile material and its tamper; 3) the
electromagnetic radiation
In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength ...
; and 4) the neutrons from the primary's nuclear detonation. The interstage is responsible for accurately
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 "
fissile fizzle". The
Castle Koon shot of
Operation Castle
Operation Castle was a United States series of high-yield (high-energy) nuclear tests by Joint Task Force 7 (JTF-7) at Bikini Atoll beginning in March 1954. It followed ''Operation Upshot–Knothole'' and preceded '' Operation Teapot''.
Con ...
is a good example; a small flaw allowed the
neutron flux
The neutron flux is a scalar quantity used in nuclear physics and nuclear reactor physics. It is the total distance travelled by all free neutrons per unit time and volume. Equivalently, it can be defined as the number of neutrons travelling ...
from the primary to prematurely begin heating the secondary, weakening the compression enough to prevent any fusion.
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 warhead. It was released by
Greenpeace
Greenpeace is an independent global campaigning network, founded in Canada in 1971 by a group of Environmental movement, environmental activists. Greenpeace states its goal is to "ensure the ability of the Earth to nurture life in all its biod ...
in a report titled "Dual Use Nuclear Technology". 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 / spark plug while the latter refers to an
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
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
emits more evenly spread X-rays that travel to the secondary, causing what is known as
radiation implosion. In
Ivy Mike
Ivy Mike was the code name, codename given to the first full-scale test of a Thermonuclear weapon, thermonuclear device, in which a significant fraction of the explosive nuclear weapon yield, yield comes from nuclear fusion.
Ivy Mike was detona ...
, gold was used as a coating over the uranium to enhance the blackbody effect.
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
Sandia National Laboratories (SNL), also known as Sandia, is one of three research and development laboratories of the United States Department of Energy's National Nuclear Security Administration (NNSA). Headquartered in Kirtland Air Force B ...
) 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 center of primary in order to boost the initial fissioning of the plutonium. A "
polystyrene
Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It i ...
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...
hat requireunique facilities". The "toxic, brittle material" is widely assumed to be
beryllium
Beryllium is a chemical element; it has Symbol (chemistry), symbol Be and atomic number 4. It is a steel-gray, hard, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with ...
, 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.
Candidates for the "special material" are polystyrene and a substance called "
Fogbank", an unclassified codename. Fogbank's composition is classified, though
aerogel
Aerogels are a class of manufacturing, synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid wit ...
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 Complex at
Oak Ridge, Tennessee
Oak Ridge is a city in Anderson County, Tennessee, Anderson and Roane County, Tennessee, Roane counties in the East Tennessee, eastern part of the U.S. state of Tennessee, about west of downtown Knoxville, Tennessee, Knoxville. Oak Ridge's po ...
, 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
Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not class ...
as a
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
, 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.
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
A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
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
Radiation pressure (also known as light pressure) is mechanical pressure exerted upon a surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of ...
exerted by the X-rays. This was the first idea put forth by
Howard Morland in an article in ''
The Progressive
''The Progressive'' is a left-leaning American magazine and website covering politics and culture. Founded in 1909 by U.S. senator Robert M. La Follette Sr. and co-edited with his wife Belle Case La Follette, it was originally called ''La Foll ...
''.
* 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
Ablation ( – removal) is the removal or destruction of something from an object by vaporization, chipping, erosion, erosive processes, or by other means. Examples of ablative materials are described below, including spacecraft material for as ...
. This is the concept best supported by physical analysis.
Radiation pressure
The radiation pressure exerted by the large quantity of X-ray
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...
s inside the closed casing might be enough to compress the secondary. Electromagnetic radiation such as X-rays or light carries
momentum
In Newtonian mechanics, momentum (: momenta or momentums; more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. ...
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 for the Ivy Mike design and for the W-80.
Foam plasma pressure
Foam
Foams are two-phase materials science, material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. Note, this source focuses only on liquid ...
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
supercritical state and beginning the fission
chain reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events.
Chain reactions are one way that sys ...
.
# The fissioning primary emits thermal
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
s, which "reflect" along the inside of the casing, irradiating the polystyrene foam.
# The irradiated foam becomes a hot
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
lithium-6
Naturally occurring lithium (3Li) is composed of two stable isotope ratio, stable isotopes, lithium-6 (6Li) and lithium-7 (7Li), with the latter being far more abundant on Earth. Both of the natural isotopes have an unexpectedly low nuclear bin ...
(
6Li) atom splits into one tritium atom and one
alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...
. 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
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications in physics. For transport phe ...
of high energy neutrons (), which irradiates the tamper (or the 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
radioactive products or large amounts of
nuclear fallout
Nuclear fallout is residual radioactive material that is created by the reactions producing a nuclear explosion. It is initially present in the mushroom cloud, radioactive cloud created by the explosion, and "falls out" of the cloud as it is ...
. 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
Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
, for example, the overall explosive force is reduced by approximately half but the amount of fallout is relatively low. The
neutron bomb
A neutron bomb, officially defined as a type of enhanced radiation weapon (ERW), is a low-yield thermonuclear weapon designed to maximize lethal neutron radiation in the immediate vicinity of the blast while minimizing the physical power of the b ...
is a hydrogen bomb with an intentionally thin tamper, allowing as many of the fast fusion neutrons as possible to escape.

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
A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
and
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
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
Ablation ( – removal) is the removal or destruction of something from an object by vaporization, chipping, erosion, erosive processes, or by other means. Examples of ablative materials are described below, including spacecraft material for as ...
.
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.

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
Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be in t ...
, and the effects of that thermal energy are then analyzed. The energy is mostly deposited within about one X-ray
optical thickness
In physics, optical depth or optical thickness is the natural logarithm of the ratio of incident to ''transmitted'' radiant power through a material.
Thus, the larger the optical depth, the smaller the amount of transmitted radiant power throu ...
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
In Newtonian mechanics, momentum (: momenta or momentums; more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. ...
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 and an implosion velocity of perhaps if of the total tamper/pusher mass is ablated off, the most energy efficient proportion. For the
W-80 the gas expansion velocity is roughly and the implosion velocity . The pressure due to the ablating material is calculated to be in the Ivy Mike device and in the W-80 device.
Comparing implosion mechanisms
Comparing the three mechanisms proposed, it can be seen that:
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
The United States Department of Defense (DoD, USDOD, or DOD) is an United States federal executive departments, executive department of the federal government of the United States, U.S. federal government charged with coordinating and superv ...
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
Ablation ( – removal) is the removal or destruction of something from an object by vaporization, chipping, erosion, erosive processes, or by other means. Examples of ablative materials are described below, including spacecraft material for as ...
until energy has distributed evenly and a sufficient fraction has reached the secondary's tamper/pusher.
Richard Rhodes
Richard Lee Rhodes (born July 4, 1937) is an American historian, journalist, and author of both fiction and nonfiction, including the Pulitzer Prize-winning '' The Making of the Atomic Bomb'' (1986), and most recently, ''Energy: A Human History ...
' book ''Dark Sun'' stated that a 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.
Design variations
Possible variations to the weapon design have been proposed:
* Either the tamper or the casing have been proposed to be made of (highly enriched uranium) in the final fission jacket. The far more expensive is also fissionable with fast neutrons like the in depleted or natural uranium, but its fission-efficiency is higher. This is because nuclei also undergo fission by slow neutrons ( nuclei require a minimum energy of about ) and because these slower neutrons are produced by other fissioning nuclei in the jacket (in other words, supports the nuclear chain reaction whereas does not). Furthermore, a jacket fosters neutron multiplication, whereas nuclei consume fusion neutrons in the fast-fission process. Using a final fissionable/fissile jacket of 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
The LGM-30 Minuteman is an American land-based intercontinental ballistic missile (ICBM) in service with the Air Force Global Strike Command. , the LGM-30G (Version 3) is the only land-based ICBM in service in the United States and represents th ...
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
A mirror, also known as a looking glass, is an object that Reflection (physics), reflects an image. Light that bounces off a mirror forms an image of whatever is in front of it, which is then focused through the lens of the eye or a camera ...
, but rather the reflector material is heated by the X-rays, causing the material to
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.
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
The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated. It is usually expressed as a ''TNT equivalent'', the standardized equivalen ...
per unit bomb weight)
B41 nuclear bomb. The Soviet Union is thought to have used multiple stages (including more than one tertiary fusion stage) in their ( 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.
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
although this is debated. Finally, efficient bombs (but not so-called
neutron bomb
A neutron bomb, officially defined as a type of enhanced radiation weapon (ERW), is a low-yield thermonuclear weapon designed to maximize lethal neutron radiation in the immediate vicinity of the blast while minimizing the physical power of the b ...
s) end with the fissioning of the final natural uranium tamper, something that could not normally be achieved without the
neutron flux
The neutron flux is a scalar quantity used in nuclear physics and nuclear reactor physics. It is the total distance travelled by all free neutrons per unit time and volume. Equivalently, it can be defined as the number of neutrons travelling ...
provided by the fusion reactions in secondary or tertiary stages. Such designs are suggested to be capable of being scaled up to an
arbitrary large yield (with apparently as many fusion stages as desired),
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
The Cheyenne Mountain Complex is a United States Space Force installation and defensive bunker located in unincorporated El Paso County, Colorado, next to the city of Colorado Springs, at the Cheyenne Mountain Space Force Station, which host ...
). Even such large bombs have been replaced by smaller yield
nuclear bunker buster
A nuclear bunker buster, also known as an earth-penetrating weapon (EPW), is the nuclear equivalent of the conventional bunker buster. The non-nuclear component of the weapon is designed to penetrate soil, rock, or concrete to deliver a nuclea ...
bombs.
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 .
Ivy Mike
In his 1995 book ''Dark Sun: The Making of the Hydrogen Bomb'', author
Richard Rhodes
Richard Lee Rhodes (born July 4, 1937) is an American historian, journalist, and author of both fiction and nonfiction, including the Pulitzer Prize-winning '' The Making of the Atomic Bomb'' (1986), and most recently, ''Energy: A Human History ...
describes in detail the internal components of the "
Ivy Mike
Ivy Mike was the code name, codename given to the first full-scale test of a Thermonuclear weapon, thermonuclear device, in which a significant fraction of the explosive nuclear weapon yield, yield comes from nuclear fusion.
Ivy Mike was detona ...
" ''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.
Ripple
The Ripple secondary is the cleanest (largest fusion fraction) and highest yield-to-weight ratio device tested. It was tested during the 1962
Operation Dominic series. Unlike previous clean bombs, which were clean simply by replacing the uranium-238 tamper with lead, Ripple was inherently clean. The fission sparkplug was replaced by a large deuterium-tritium gas core, surrounded by a thinner lithium deuteride shell. It is assumed that thin concentric shells of a high-Z material like lead, driven by the small
Kinglet primary allowed propagated sustained shockwaves to the core, sustaining the thermonuclear burn and giving the device its name. The design was influenced by the nascent field of
inertial confinement fusion
Inertial confinement fusion (ICF) is a fusion energy process that initiates nuclear fusion reactions by compressing and heating targets filled with fuel. The targets are small pellets, typically containing deuterium (2H) and tritium (3H).
Typical ...
. Ripple was also extremely efficient; plans were made for a 15 kt/kg. Shot Androscoggin featured a proof-of-concept Ripple design, resulting in a 63-kiloton fizzle (significantly lower than the predicted 15 megatons). It was repeated in shot Housatonic, which featured a 9.96 megaton explosion that was reportedly >99.9% fusion.
While it was extremely lightweight, the large amount of DT gas used made it a low density and thus high volume warhead. Among US ICBMs, only the Titan II was wide enough to deliver it, but the military had already shifted away from it towards the smaller
Minuteman missiles.
W88
In 1999 a reporter for the ''
San Jose Mercury News
''The Mercury News'' (formerly ''San Jose Mercury News'', often locally known as ''The Merc'') is a morning daily newspaper published in San Jose, California, in the San Francisco Bay Area. It is published by the Bay Area News Group, a subsidia ...
'' reported that the U.S.
W88 nuclear warhead, a small MIRVed warhead used on the
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
An oval () is a closed curve in a plane (geometry), plane which resembles the outline of an egg. The term is not very specific, but in some areas of mathematics (projective geometry, technical drawing, etc.), it is given a more precise definitio ...
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 with a
physics package long, with a maximum diameter of , and by different estimates weighing in a range from .
The smaller warhead allows more of them to fit onto a single missile and improves basic flight properties such as speed and range.
History
First tests
United States
The idea of a thermonuclear fusion bomb ignited by a smaller fission bomb was first proposed by
Enrico Fermi
Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian and naturalized American physicist, renowned for being the creator of the world's first artificial nuclear reactor, the Chicago Pile-1, and a member of the Manhattan Project ...
to his colleague
Edward Teller
Edward Teller (; January 15, 1908 – September 9, 2003) was a Hungarian and American Theoretical physics, theoretical physicist and chemical engineer who is known colloquially as "the father of the hydrogen bomb" and one of the creators of ...
when they were talking at
Columbia University
Columbia University in the City of New York, commonly referred to as Columbia University, is a Private university, private Ivy League research university in New York City. Established in 1754 as King's College on the grounds of Trinity Churc ...
in September 1941,
at the start of what would become the
Manhattan Project
The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada.
From 1942 to 1946, the ...
.
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.
However once World War II ended, there was little impetus to devote many resources to the ''Super'', as it was then known.
The
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.
The debate covered matters that were alternatively strategic, pragmatic, and moral.
In their ''Report of the General Advisory Committee,''
Robert Oppenheimer
J. Robert Oppenheimer (born Julius Robert Oppenheimer ; April 22, 1904 – February 18, 1967) was an American theoretical physicist who served as the director of the Manhattan Project's Los Alamos Laboratory during World War II. He is often ...
and colleagues concluded that "
e extreme danger to mankind inherent in the proposal
o develop thermonuclear weaponswholly outweighs any military advantage." Despite the objections raised, on 31 January 1950, President
Harry S. Truman
Harry S. Truman (May 8, 1884December 26, 1972) was the 33rd president of the United States, serving from 1945 to 1953. As the 34th vice president in 1945, he assumed the presidency upon the death of Franklin D. Roosevelt that year. Subsequen ...
made the decision to go forward with the development of the new weapon.

Teller and other U.S. physicists struggled to find a workable design.
Stanislaw Ulam Stanislav and variants may refer to:
People
*Stanislav (given name), a Slavic given name with many spelling variations (Stanislaus, Stanislas, Stanisław, etc.)
Places
* Stanislav, Kherson Oblast, a coastal village in Ukraine
* Stanislaus County, ...
, 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
In radiation thermodynamics, a hohlraum (; a non-specific German word for a "hollow space", "empty room", or "cavity") is a cavity whose walls are in radiative equilibrium with the radiant energy within the cavity. First proposed by Gustav Kir ...
'' or radiation case.
The "George" shot of
Operation Greenhouse
Operation Greenhouse was the fifth American nuclear test series, the second conducted in 1951 and the first to test principles that would lead to developing Teller-Ullam, thermonuclear weapons (''hydrogen bombs''). Conducted at the new Pacific ...
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 total yield, 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
Enewetak Atoll (; also spelled Eniwetok Atoll or sometimes Eniewetok; , , or , ; known to the Japanese as Brown Atoll or Brown Island; ) is a large coral atoll of 40 islands in the Pacific Ocean and with its 296 people (as of 2021) forms a leg ...
, with a yield of (over 450 times more powerful than the bomb dropped on Nagasaki during
World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
). The device, dubbed the ''Sausage'', used an extra-large fission bomb as a "trigger" and liquid deuterium—kept in its liquid state by of
cryogenic
In physics, cryogenics is the production and behaviour of materials at very low temperatures.
The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held in Washington, DC in 1971) endorsed a univers ...
equipment—as its fusion fuel, and weighed around altogether.

The liquid deuterium fuel of Ivy Mike was impractical for a deployable weapon, and the next advance was to use a solid
lithium deuteride
Lithium hydride is an inorganic compound with the formula Lithium, LiHydride, H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a Hydride#Ionic hydrides, salt-like (ionic) hydride, it has a ...
fusion fuel instead. In 1954 this was tested in the "
Castle Bravo
Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of ''Operation Castle''. Detonated on 1 March 1954, the device remains the most powe ...
" shot (the device was code-named ''Shrimp''), which had a yield of (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
An intercontinental ballistic missile (ICBM) is a ballistic missile with a range (aeronautics), range greater than , primarily designed for nuclear weapons delivery (delivering one or more Thermonuclear weapon, thermonuclear warheads). Conven ...
s and
submarine-launched ballistic missile
A submarine-launched ballistic missile (SLBM) is a ballistic missile capable of being launched from Ballistic missile submarine, submarines. Modern variants usually deliver multiple independently targetable reentry vehicles (MIRVs), each of which ...
s. By 1960, with the
W47 warhead deployed on
Polaris
Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris (Latinisation of names, Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an ...
ballistic missile submarine
A ballistic missile submarine is a submarine capable of deploying submarine-launched ballistic missiles (SLBMs) with nuclear warheads. These submarines became a major weapon system in the Cold War because of their nuclear deterrence capabi ...
s, megaton-class warheads were as small as in diameter and 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.
Soviet Union

The first Soviet fusion design, developed by
Andrei Sakharov
Andrei Dmitrievich Sakharov (; 21 May 192114 December 1989) was a Soviet Physics, physicist and a List of Nobel Peace Prize laureates, Nobel Peace Prize laureate, which he was awarded in 1975 for emphasizing human rights around the world.
Alt ...
and
Vitaly Ginzburg in 1949 (before the Soviets had a working fission bomb), was dubbed the ''Sloika'', after a Russian
layer cake
A layer cake (US English) or sandwich cake (UK English) is a cake consisting of multiple stacked sheets of cake, held together by a filling such as frosting, jam, or other preserves. Most cake recipes can be adapted for layer cakes; butte ...
, 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,
RDS-6s, was detonated in 1953 with a yield equivalent to ( 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.
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 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
RDS-37 () was the Soviet Union's first two-stage hydrogen bomb, first tested on 22 November 1955. The weapon had a nominal yield of approximately 3 megatons. It was scaled down to 1.6 megatons for the live test.
Leading to the RDS-37
The R ...
" in November 1955 with a yield of . The Soviets demonstrated the power of the staging concept in October 1961, when they detonated the massive and unwieldy
Tsar Bomba
The Tsar Bomba (code name: ''Ivan'' or ''Vanya''), also known by the alphanumerical designation "AN602", was a Thermonuclear weapon, thermonuclear aerial bomb, and by far the most powerful nuclear weapon ever created and tested. The Soviet phy ...
. It was the largest nuclear weapon developed and tested by any country.
United Kingdom

In 1954 work began at
Aldermaston
Aldermaston ( ) is a village and civil parish in Berkshire, England. In the 2011 census, the parish had a population of 1,015. The village is in the Kennet Valley and bounds Hampshire to the south. It is approximately from Newbury, Basin ...
to develop the British fusion bomb, with
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 Atomic Energy Act of 1946 (McMahon Act) determined how the United States would control and manage the nuclear technology it had jointly developed with its World War II allies, the United Kingdom and Canada. Most significantly, the Act ru ...
. 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.
However, the British were allowed to observe the U.S.
Castle tests and used sampling aircraft in the
mushroom cloud
A mushroom cloud is a distinctive mushroom-shaped flammagenitus cloud of debris, smoke, and usually condensed water vapour resulting from a large explosion. The effect is most commonly associated with a nuclear explosion, but any sufficiently e ...
s, providing them with clear, direct evidence of the compression produced in the secondary stages by radiation implosion.
Because of these difficulties, in 1955 Prime Minister
Anthony Eden
Robert Anthony Eden, 1st Earl of Avon (12 June 1897 – 14 January 1977) was a British politician who served as Prime Minister of the United Kingdom and Leader of the Conservative Party from 1955 until his resignation in 1957.
Achi ...
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.
In 1957 the
Operation Grapple
Operation Grapple was a set of four series of British nuclear weapons tests of early atomic bombs and hydrogen bombs carried out in 1957 and 1958 at Malden Island and Kiritimati (Christmas Island) in the Gilbert and Ellice Islands in the Pa ...
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 . The second test
Orange Herald was the modified fission bomb and produced —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 .
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 . On 28 April 1958 a bomb was dropped that yielded —Britain's most powerful test. Two final air burst tests on 2 and 11 September 1958, dropped smaller bombs that yielded around each.
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
Events
January
* January 1 – The European Economic Community (EEC) comes into being.
* January 3 – The West Indies Federation is formed.
* January 4
** Edmund Hillary's Commonwealth Trans-Antarctic Expedition completes the thir ...
. Instead of continuing with its own design, the British were given access to the design of the smaller American
Mk 28 warhead and were able to manufacture copies.
China
Mao Zedong
Mao Zedong pronounced ; traditionally Romanization of Chinese, romanised as Mao Tse-tung. (26December 18939September 1976) was a Chinese politician, revolutionary, and political theorist who founded the People's Republic of China (PRC) in ...
decided to begin a Chinese nuclear-weapons program during the
First Taiwan Strait Crisis
The First Taiwan Strait Crisis (also known as the Formosa Crisis, the 1954–1955 Taiwan Strait Crisis, the Offshore Islands Crisis, the Quemoy-Matsu Crisis, and the 1955 Taiwan Strait Crisis) was a brief armed conflict between the People's Rep ...
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 Nor Test Site in northwest China. China had received extensive technical help from the Soviet Union to jump-start their nuclear program, but by 1960 the
rift between the Soviet Union and China had become so great that the Soviet Union ceased all assistance to China.
A story in ''
The New York Times
''The New York Times'' (''NYT'') is an American daily newspaper based in New York City. ''The New York Times'' covers domestic, national, and international news, and publishes opinion pieces, investigative reports, and reviews. As one of ...
'' by
William Broad reported that in 1995, a supposed Chinese
double agent
In the field of counterintelligence, a double agent is an employee of a secret intelligence service for one country, whose primary purpose is to spy on a target organization of another country, but who is now spying on their own country's organi ...
delivered information indicating that China knew secret details of the U.S. W88 warhead, supposedly through espionage. (This line of investigation eventually resulted in the abortive trial of
Wen Ho Lee.)
France
The
"Canopus" test in the
Fangataufa atoll in
French Polynesia
French Polynesia ( ; ; ) is an overseas collectivity of France and its sole #Governance, overseas country. It comprises 121 geographically dispersed islands and atolls stretching over more than in the Pacific Ocean, South Pacific Ocean. The t ...
on 24 August 1968 was the country's first multistage thermonuclear weapon test. The bomb was detonated from a balloon at a height of . The result of this test was significant atmospheric contamination.
Very little is known about France's development of the Teller–Ulam design, beyond the fact that France detonated a 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.
France and China did not sign or ratify the
Partial Nuclear Test Ban Treaty
The Partial Test Ban Treaty (PTBT), formally known as the 1963 Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water, prohibited all nuclear weapons testing, test detonations of nuclear weapons except for those co ...
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.
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
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral treaty to ban nuclear weapons test explosions and any other nuclear explosions, for both civilian and military purposes, in all environments. It was adopted by the United Nati ...
that same year, and then ratified the Treaty within two years.

In 2015 France confirmed that its nuclear arsenal contains about 300 warheads, carried by
submarine-launched ballistic missile
A submarine-launched ballistic missile (SLBM) is a ballistic missile capable of being launched from Ballistic missile submarine, submarines. Modern variants usually deliver multiple independently targetable reentry vehicles (MIRVs), each of which ...
s and
fighter-bombers. France has four
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 missiles. The newest submarine,
"Le Terrible", was commissioned in 2010, and it has
M51 missiles capable of carrying
TN 75 thermonuclear warheads. The air fleet is four squadrons at four different bases. In total, there are 23
Mirage 2000N aircraft and 20
Rafales capable of carrying nuclear warheads.
The M51.1 missiles are intended to be replaced with the new M51.2 warhead beginning in 2016, which has a greater range than the M51.1.
France has about 60 air-launched missiles tipped with
TN 80/
TN 81 warheads with a yield of about each. France's nuclear program has been carefully designed to ensure that these weapons remain usable decades into the future.
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 as a byproduct.
India
On 11 May 1998, India announced that it had detonated a thermonuclear bomb in its
Operation Shakti
Pokhran-II (''Operation Shakti'') was a series of five nuclear weapon tests conducted by India in May 1998. The bombs were detonated at the Indian Army's Pokhran Test Range in Rajasthan. It was the second instance of nuclear testing conducted ...
tests ("Shakti-I", specifically, in Hindi the word 'Shakti' means power).
Samar Mubarakmand, a Pakistani nuclear physicist, asserted that if Shakti-I had been a thermonuclear test, the device had failed to fire.
However,
Harold M. Agnew, former director of the
Los Alamos National Laboratory
Los Alamos National Laboratory (often shortened as Los Alamos and LANL) is one of the sixteen research and development Laboratory, laboratories of the United States Department of Energy National Laboratories, United States Department of Energy ...
, said that India's assertion of having detonated a staged thermonuclear bomb was believable.
India says that their thermonuclear device was tested at a controlled yield of because of the close proximity of the Khetolai village at about , to ensure that the houses in that village do not suffer significant damage.
Another cited reason was that radioactivity released from yields significantly more than 45 kt might not have been contained fully.
After the
Pokhran-II
Pokhran-II (''Operation Shakti'') was a series of five nuclear weapon tests conducted by India in May 1998. The bombs were detonated at the Indian Army's Pokhran Test Range in Rajasthan. It was the second instance of nuclear testing conducted ...
tests,
Rajagopala Chidambaram, former chairman of the
Atomic Energy Commission of India
The Atomic Energy Commission of India is the governing body of the Department of Atomic Energy (India), Department of Atomic Energy (DAE), Government of India. The DAE is under the direct charge of the Prime Minister of India, Prime Minister.
...
, said that India has the capability to build thermonuclear bombs of any yield at will.
India officially maintains that it can build thermonuclear weapons of various yields up to around on the basis of the
Shakti-1 thermonuclear test.
The yield of India's hydrogen bomb test remains highly debatable among the Indian science community and the international scholars.
The question of politicisation and disputes between Indian scientists further complicated the matter.
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
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral treaty to ban nuclear weapons test explosions and any other nuclear explosions, for both civilian and military purposes, in all environments. It was adopted by the United Nati ...
. Other Indian scientists involved in the test have disputed Santhanam's claim, arguing that his claims are unscientific.
British seismologist Roger Clarke argued that the magnitudes suggested a combined yield of up to , consistent with the Indian announced total yield of . 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'.
Israel
Israel is alleged to possess thermonuclear weapons of the Teller–Ulam design,
but it is not known to have tested any nuclear devices, although it is widely speculated that the
Vela incident
The Vela incident was an unidentified double flash of light detected by an American Vela Hotel satellite on 22 September 1979 near the South African territory of Prince Edward Islands in the Indian Ocean, roughly midway between Africa and Antar ...
of 1979 may have been a joint Israeli–South African nuclear test.
It is well established that Edward Teller advised and guided the Israeli establishment on general nuclear matters for some 20 years.
Between 1964 and 1967, Teller made six visits to Israel where he lectured at the
Tel Aviv University
Tel Aviv University (TAU) is a Public university, public research university in Tel Aviv, Israel. With over 30,000 students, it is the largest university in the country. Located in northwest Tel Aviv, the university is the center of teaching and ...
on general topics in theoretical physics. It took him a year to convince the
CIA about Israel's capability and finally in 1976,
Carl Duckett of the CIA testified to the
U.S. Congress
The United States Congress is the legislative branch of the federal government of the United States. It is a bicameral legislature, including a lower body, the U.S. House of Representatives, and an upper body, the U.S. Senate. They both ...
, after receiving credible information from an "American scientist" (Teller), on Israel's nuclear capability.
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.
After he conveyed the matter to the higher level of the U.S. government, Teller reportedly said: "They
sraelhave it, and they were clever enough to trust their research and not to test, they know that to test would get them into trouble."
North Korea
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
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. In January 2016, North Korea claimed to have successfully tested a hydrogen bomb, although only a magnitude 5.1 seismic event was detected at the time of the test, a similar magnitude to the 2013 test of a 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.
On 3 September 2017, the country's state media reported that a
hydrogen bomb test was conducted that resulted in "perfect success". According to the
U.S. Geological Survey
The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on March ...
(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. U.S. Intelligence released an early assessment that the yield estimate was ,
with an uncertainty range of .
On 12 September,
NORSAR revised its estimate of the explosion magnitude upward to 6.1, matching that of the
CTBTO but less powerful than the
USGS
The United States Geological Survey (USGS), founded as the Geological Survey, is an government agency, agency of the United States Department of the Interior, U.S. Department of the Interior whose work spans the disciplines of biology, geograp ...
estimate of 6.3. Its yield estimate was revised to , while noting the estimate had some uncertainty and an undisclosed margin of error. 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 of rock, and the yield "could have been in excess of 300 kilotons".
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
classification
Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...
.
United States Department of Energy
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...
(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

In 1972 the United States government declassified a document stating "
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, "
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''."
[emphasis in original] 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).
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''
Most of the current ideas on the workings of the Teller–Ulam design came into public awareness after the DOE attempted to
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
An arms race occurs when two or more groups compete in military superiority. It consists of a competition between two or more State (polity), states to have superior armed forces, concerning production of weapons, the growth of a military, and ...
and allow citizens to feel empowered to question official statements on the importance of nuclear weapons and nuclear secrecy. 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
''Encyclopedia Americana'' is a general encyclopedia written in American English. It was the first general encyclopedia of any magnitude to be published in North America. With '' Collier's Encyclopedia'' and ''Encyclopædia Britannica, Encyclo ...
''. 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
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).
Morland eventually concluded that the "secret" was that the primary and secondary were kept separate and that
radiation pressure
Radiation pressure (also known as light pressure) is mechanical pressure exerted upon a surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of ...
from the primary compressed the secondary before igniting it. When an early draft of the article, to be published in ''
The Progressive
''The Progressive'' is a left-leaning American magazine and website covering politics and culture. Founded in 1909 by U.S. senator Robert M. La Follette Sr. and co-edited with his wife Belle Case La Follette, it was originally called ''La Foll ...
'' 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
An injunction is an equitable remedy in the form of a special court order compelling a party to do or refrain from doing certain acts. It was developed by the English courts of equity but its origins go back to Roman law and the equitable rem ...
. 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, and (3) was dangerous and would encourage
nuclear proliferation
Nuclear proliferation is the spread of nuclear weapons to additional countries, particularly those not recognized as List of states with nuclear weapons, nuclear-weapon states by the Treaty on the Non-Proliferation of Nuclear Weapons, commonl ...
. 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. 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".
Morland's work is interpreted as being at least partially correct because the DOE
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
On 5 February 1958, during a training mission flown by a
B-47, a
Mark 15 nuclear bomb, also known as the
Tybee Bomb, was lost off the coast of
Tybee Island near
Savannah, Georgia
Savannah ( ) is the oldest city in the U.S. state of Georgia (U.S. state), Georgia and the county seat of Chatham County, Georgia, Chatham County. Established in 1733 on the Savannah River, the city of Savannah became the Kingdom of Great Brita ...
. The US Air Force maintains that the bomb was unarmed and did not contain the live fissile core necessary to initiate a nuclear explosion. The bomb was thought by the Department of Energy to lie buried under several feet of silt at the bottom of
Wassaw Sound.
On 17 January 1966,
a fatal collision occurred between a B-52G and a KC-135 Stratotanker over
Palomares, Spain. The conventional explosives in two of the
Mk28-type
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 km) off the coast into the Mediterranean sea and was recovered a few months later.
On 21 January 1968, a B-52G, with four
B28FI thermonuclear bombs aboard as part of
Operation Chrome Dome
Operation Chrome Dome was a United States Air Force Cold War-era mission from 1961 to 1968 in which Boeing B-52 Stratofortress, B-52 strategic bomber aircraft armed with thermonuclear weapons remained on continuous airborne alert, flying routes ...
,
crashed on the ice of the
North Star Bay while attempting an emergency landing at
Thule Air Base
Pituffik Space Base ( ; ; ), formerly Thule Air Base (), is a United States Space Force base located on the northwest coast of Greenland in the Kingdom of Denmark under a defense agreement between Denmark and the United States. 150 United Stat ...
in Greenland. The resulting fire caused extensive radioactive contamination.
Personnel involved in the cleanup failed to recover all the debris from three of the bombs, and one bomb was not recovered.
See also
*
COLEX process (isotopic separation)
*
NUKEMAP
*
Pure fusion weapon
Notes
References
Further reading
Basic principles
*
*
History
*
*
*
*
*
*
*
*
*
*
Analyzing fallout
*
*
External links
Principles
"Basic Principles of Staged Radiation Implosion (Teller–Ulam)"from Carey Sublette's NuclearWeaponArchive.org.
from Carey Sublette's Nuclear Weapons FAQ.
from Carey Sublette's Nuclear Weapons FAQ.
from Carey Sublette's Nuclear Weapons FAQ.
Annotated bibliography for nuclear weapons design from the Alsos Digital Library for Nuclear Issues
History
(with U.S. and USSR bomb designers as well as historians).
(includes many slides).
''The Progressive'' November 1979 issue– "The H-Bomb Secret: How we got it, why we're telling" (entire issue online).
Annotated bibliography on the hydrogen bomb from the Alsos Digital LibraryUniversity of Southampton, Mountbatten Centre for International Studies, Nuclear History Working Paper No5. – documentary film on the history of nuclear weapon testing.
YouTube Playlist of declassified nuclear explosion tests obtained by converting film scans to digital at Lawrence Livermore Laboratory
{{Authority control
Nuclear weapon design
Nuclear secrecy
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