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Thermonuclear weapon

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1950s fusion bomb design with cylindrical fusion stage
(modern designs use spherical secondaries)
A) fission primary stage
B) fusion secondary stage
1) High-explosive lenses
2) Uranium-238 ("tamper") lined with beryllium reflector
3) Vacuum ("levitated core")
4) Tritium "boost" gas (blue) within plutonium or uranium hollow core
5) Radiation channel filled with Polystyrene foam
6) Uranium ("pusher/tamper")
7) Lithium-6 deuteride (fusion fuel)
8) Plutonium (spark plug)
9) Radiation case (confines thermal X-rays by reflection)

A thermonuclear weapon, or fusion weapon, is a second-generation nuclear weapon design. Its greater sophistication over pure fission weapons may afford it vastly greater destructive power than first-generation atomic bombs, a more compact size, a lower mass or a combination of these benefits. Characteristics of nuclear fusion reactions make possible the use of non-fissile depleted uranium as the weapon's main fuel, thus allowing more efficient use of scarce fissile material (U-235 and Pu-239).

Modern fusion weapons consist essentially of two main components: a nuclear fission primary stage (fueled by uranium-235 or plutonium-239) and a separate nuclear fusion secondary stage containing thermonuclear fuel: the heavy hydrogen isotopes deuterium and tritium, or in modern weapons lithium deuteride. For this reason, thermonuclear weapons are often colloquially called hydrogen bombs or H-bombs.[1]

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

The secondary fusion stage—consisting of outer pusher/tamper, fusion fuel filler and central plutonium spark plug—is imploded by the X-ray energy impinging on its pusher/tamper. This compresses the entire secondary stage and drives up the density of the plutonium spark plug. The density of the plutonium fuel rises to such an extent that the spark plug is driven into a supercritical state, and it begins a nuclear fission chain reaction. The fission products so produced heat the highly compressed, and thus superdense, thermonuclear fuel surrounding the spark plug to the region of some three hundred million Kelvins, igniting fusion reactions between fusion fuel nuclei. In modern weapons fueled by lithium deuteride, the fissioning plutonium spark plug also emits free neutrons which collide with lithium nuclei and supply the tritium component of the thermonuclear fuel.

The secondary's relatively massive tamper (which resists outward expansion as the explosion proceeds) also serves as a thermal barrier to keep the fusion fuel filler from becoming too hot, which would spoil the compression. If made of uranium, enriched uranium or plutonium, the tamper captures fast fusion neutrons and undergoes fission itself, increasing the overall explosive yield. Additionally, in most designs the radiation case is also constructed of a fissile material that undergoes fission driven by fast thermonuclear neutrons. Such bombs are classified as three stage weapons, and most current Teller–Ulam designs are such fission-fusion-fission weapons. Fast fission of the tamper and radiation case is the main contribution to the total yield and is the dominant process that produces radioactive fission product fallout.[2][3]

The first full-scale thermonuclear test was carried out by the United States in 1952; the concept has since been employed by most of the world's nuclear powers in the design of their weapons.[4] The design of all modern thermonuclear weapons in the United States is known as the Teller–Ulam configuration for its two chief contributors, Edward Teller and Stanislaw Ulam, who developed it in 1951[5] for the United States, with certain concepts developed with the contribution of physicist John von Neumann. Similar devices were developed by the Soviet Union, United Kingdom, France, and China.

As thermonuclear weapons represent the most efficient design for weapon energy yield in weapons with yields above 50 kilotons of TNT (210 TJ), virtually all the nuclear weapons of this size deployed by the five nuclear-weapon states under the Non-Proliferation Treaty today are thermonuclear weapons using the Teller–Ulam design.[6]

Public knowledge concerning nuclear weapon design

Detailed knowledge of fission and fusion weapons is classified to some degree in virtually every industrialized nation. In the United States, such knowledge can by default be classified as "Restricted Data", even if it is created by persons who are not government employees or associated with weapons programs, in a legal doctrine known as "born secret" (though the constitutional standing of the doctrine has been at times called into question; see United States v. Progressive, Inc.). Born secret is rarely invoked for cases of private speculation. The official policy of the United States Department of Energy has been not to acknowledge the leaking of design information, as such acknowledgment would potentially validate the information as accurate. In a small number of prior cases, the U.S. government has attempted to censor weapons information in the public press, with limited success.[7] 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 nations could use the information.[8]


Basic principle

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 of each stage providing the energy to ignite the next stage. At a bare 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 a process called "radiation implosion", at which point it is heated and undergoes nuclear fusion. This process could be continued, with energy from the secondary igniting a third fusion stage; Russia's AN602 "Tsar Bomba" is thought to have been a three-stage fission-fusion-fusion device. Theoretically by continuing this process thermonuclear weapons with arbitrarily high yield could be constructed.[citation needed] This contrasts with fission weapons which are limited in yield because only so much fission fuel can be amassed in one place before the danger of its accidentally becoming supercritical becomes too great.

One possible version of the Teller–Ulam configuration


The primary is thought to be a standard implosion method fission bomb, though likely with a core boosted by small amounts of fusion fuel (usually 50/50% deuterium/tritium gas) for extra efficiency; the fusion fuel releases excess neutrons when heated and compressed, inducing additional fission. When fired, the plutonium-239 (Pu-239) or uranium-235 (U-235) core would be compressed to a smaller sphere by special layers of conventional high explosives arranged around it in an explosive lens pattern, initiating the nuclear chain reaction that powers the conventional "atomic bomb".

The secondary is usually shown as a column of fusion fuel and other components wrapped in many layers. Around the column is first a "pusher-tamper", a heavy layer of uranium-238 (U-238) or lead that helps compress the fusion fuel (and, in the case of uranium, may eventually undergo fission itself). Inside this is the fusion fuel itself, usually a form of lithium deuteride, which is used because it is easier to weaponize than liquefied tritium/deuterium gas. This dry fuel, when bombarded by neutrons, produces tritium, a heavy isotope of hydrogen which can undergo nuclear fusion, along with the deuterium present in the mixture. (See the article on nuclear fusion for a more detailed technical discussion of fusion reactions.) Inside the layer of fuel is the "spark plug", a hollow column of fissile material (plutonium-239 or uranium-235) often boosted by deuterium gas. The spark plug, when compressed, can itself 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 up of the same materials.[10][11]




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 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... [which require] unique facilities".[15] The "toxic, brittle material" is widely assumed to be beryllium which fits that description and would also moderate the neutron flux from the primary. Some material to absorb and re-radiate the X-rays in a particular manner may also be used.[16]

Candidates for the "special material" are polystyrene and a substance called "FOGBANK", an unclassified codename. FOGBANK's composition is classified, though aerogel has been suggested as a possibility. It was first used in thermonuclear weapons with the W-76 thermonuclear warhead, and produced at a plant in the Y-12 Complex at Oak Ridge, Tennessee, for use in the W-76. Production of FOGBANK lapsed after the W-76 production run ended. The W-76 Life Extension Program required more FOGBANK to be made. This was complicated by the fact that the original FOGBANK's properties weren't fully documented, so a massive effort was mounted to re-invent the process. An impurity crucial to the properties of the old FOGBANK was omitted during the new process. Only close analysis of new and old batches revealed the nature of that impurity. The manufacturing process used acetonitrile as a solvent, which led to at least three evacuations of the FOGBANK plant in 2006. Widely used in the petroleum and pharmaceutical industries, acetonitrile is flammable and toxic. Y-12 is the sole producer of FOGBANK.[17]


A simplified summary of the above explanation is:

  2. Energy released in the primary stage is transferred to the secondary (or fusion) stage. The exact mechanism whereby this happens is highly classified. This energy compresses the fusion fuel and sparkplug; the compressed sparkplug becomes critical and undergoes a fission chain reaction, further heating the compressed fusion fuel to a high enough temperature to induce fusion, and also supplying neutrons that react with lithium to create tritium for fusion.
  3. The fusion fuel of the secondary stage may be surrounded by uranium or enriched uranium, or plutonium. Fast neutrons generated by fusion can induce fission even in materials normally not prone to it, such as depleted uranium whose U-238 is not fissile and cannot sustain a chain reaction, but which is fissionable when bombarded by the high-energy neutrons released by fusion in the secondary stage. This process provides considerable energy yield (as much as half of the total yield in large devices). Although it is sometimes considered to be a separate stage, it should not be confused with a true tertiary stage. Tertiary stages are further fusion stages (see below), which have been put in only a handful of bombs, none of them in large-scale production.


Compression of the secondary


Radiation pressure



Foam plasma pressure



  2. The fissioning primary emits thermal X-rays, which "reflect" along the inside of the casing, irradiating the polystyrene foam.
  3. 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.
  5. The fuel undergoing the fusion reaction emits a large flux of high energy (17.6 MeV) neutrons, which irradiates the U-238 tamper (or the U-238 bomb casing), causing it to undergo a fast fission reaction, providing about half of the total energy.

This would complete the fission-fusion-fission sequence. Fusion, unlike fission, is relatively "clean"—it releases energy but no harmful radioactive products or large amounts of nuclear fallout. The fission reactions though, especially the last fission reactions, release a tremendous amount of fission products and fallout. If the last fission stage is omitted, by replacing the uranium tamper with one made of lead, for example, the overall explosive force is reduced by approximately half but the amount of fallout is relatively low. The neutron bomb is a hydrogen bomb with an intentionally thin tamper, allowing most of the fast fusion neutrons as possible to escape.

Foam plasma mechanism firing sequence.


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.

Ablation mechanism firing sequence.



Comparing implosion mechanisms

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

Mechanism Pressure (TPa)
Ivy Mike W80
Radiation pressure 7.3 140
Plasma pressure 35  750
Ablation pressure 530  6400




Design variations


  • Either the tamper or the casing have been proposed to be made of uranium-235 (highly enriched uranium) in the final fission jacket. The far more expensive U-235 is also fissionable with fast neutrons like the U-238 in depleted or natural uranium, but its fission-efficiency is higher. This is because U-235 nuclei also undergo fission by slow neutrons (U-238 nuclei require a minimum energy of about 1 mega-electron volt), and because these slower neutrons are produced by other fissioning U-235 nuclei in the jacket (in other words, U-235 supports the nuclear chain reaction whereas U-238 does not). Furthermore, a U-235 jacket fosters neutron multiplication, whereas U-238 nuclei consume fusion neutrons in the fast-fission process. Using a final fissionable/fissile jacket of U-235 would thus increase the yield of a Teller–Ulam bomb above a depleted uranium or natural uranium jacket. This has been proposed specifically for the W87 warheads retrofitted to currently deployed LGM-30 Minuteman III ICBMs.

Two special variations exist that will be discussed in a subsequent section: the cryogenically cooled liquid deuterium device used for the Ivy Mike test, and the putative design of the W88 nuclear warhead—a small, MIRVed version of the Teller–Ulam configuration with a prolate (egg or watermelon shaped) primary and an elliptical 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 (see Operation Redwing) but is thought to have fielded only one such tertiary model, i.e., a bomb in which a fission stage, followed by a fusion stage, finally compresses yet another fusion stage. This U.S. design was the heavy but highly efficient (i.e., nuclear weapon yield per unit bomb weight) 25 Mt B41 nuclear bomb.[20] The Soviet Union is thought to have used multiple stages (including more than one tertiary fusion stage) in their 50 megaton (100 Mt in intended use) Tsar Bomba (however, as with other bombs, the fissionable jacket could be replaced with lead in such a bomb, and in this one, for demonstration, it was). 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).




United States


Operation Castle thermonuclear test, Castle Romeo shot


The "George" shot of Operation Greenhouse of 9 May 1951 tested the basic concept for the first time on a very small scale. As the first successful (uncontrolled) release of nuclear fusion energy, which made up a small fraction of the 225 kt total yield,[23] it raised expectations to a near certainty that the concept would work.



Efforts in the United States soon shifted towards developing miniaturized Teller–Ulam weapons that could fit into intercontinental ballistic missiles and submarine-launched ballistic missiles. By 1960, with the W47 warhead[24] deployed on Polaris ballistic missile submarines, megaton-class warheads were as small as 18 inches (0.5 m) in diameter and 720 pounds (320 kg) in weight. It was later found in live testing that the Polaris warhead did not work reliably and had to be redesigned.[citation needed] 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 (see the section on the W88 below).[9]

Soviet Union

The Soviet thermonuclear weapons program was aided heavily by Klaus Fuchs. Fuchs’ most valuable contribution to the Soviet weapons program concerned the hydrogen bomb. The idea of a hydrogen bomb arose from discussions between Enrico Fermi and Edward Teller in 1941. From 1943 Teller lectured at Los Alamos on what he called the "super".[25] Following their meeting, Fermi was convinced by Teller to present a series of lectures detailing the current state of research into thermonuclear weapons.[26] In September 1945 Fuchs passed a synopsis of these lectures to the Soviets. This information was important to the Soviets, but not solely for the information about the US bomb project. The importance of this material was in that it confirmed that the United States were working on their own thermonuclear weapon research.[27] Although the information provided by Fuchs regarding the thermonuclear weapons research was not seen as entirely beneficial, it still provided the Soviet Union with knowledge such as the properties of tritium. Tritium is an isotope of hydrogen with two neutrons, which allows for more efficient fusion reactions to occur during the detonation of a nuclear weapon. Discovering the properties of this radioactive material would allow the Soviet Union to develop a more powerful weapon that requires less fuel. Following Fuchs's return, experts from the Soviet Union spent a great deal of time researching his findings for themselves. Even though the Soviets did obtain some original ideas, the findings of this research served to confirm Fuchs's notes from the American lectures on the matter. After his return to England in mid-1946, Fuchs was not again in touch with Soviet intelligence until September 1947, when his controller confirmed the Soviet interest in thermonuclear weapons. In response Fuchs provided details of the "ongoing theoretical superbomb studies in the U.S. under the direction of Teller and Enrico Fermi at the University of Chicago."[28] Fuchs obtained information regardless of the American McMahon Act, which prevented Anglo-American cooperation on nuclear weapons research. Under this act, Fuchs did not have routine access to American collaborators like Fermi and Teller. Fuchs was very close to Teller at Los Alamos, and while there Fuchs had worked on thermonuclear weapons. As Teller later recalled, "he [Fuchs] talked with me and others frequently in depth about our intensive efforts… it was easy and pleasant to discuss my work with him. He also made impressive contributions, and I learned many technical facts from him."[29] The information Fuchs obtained energized the Soviets to direct new intelligence activities against research in Chicago. In February 1948 the Soviet Union formally began its hydrogen bomb program. A month later Fuchs again met with Feklisov, an event which "played an exceptional role in the subsequent course of the Soviet thermonuclear bomb program."[27] A report of June 1953 warned that, although no indication of Soviet development of hydrogen bombs had been found, "Soviet research, development and even field testing of thermonuclear reactions based on the disclosures of Fuchs may take place by mid-1953."[30] U.S. intelligence thus recognized for the first time that Fuchs' material held invaluable information for the Soviet thermonuclear weapons program.




United Kingdom






American observers had been invited to these kinds of tests. After Britain's successful detonation of a megaton-range device (and thus demonstrating a practical understanding of the Teller–Ulam design "secret"), the United States agreed to exchange some of its nuclear designs with the United Kingdom, leading to the 1958 US–UK Mutual Defence Agreement. Instead of continuing with its own design, the British were given access to the design of the smaller American Mk 28 warhead and were able to manufacture copies.[32]



Mao Zedong decided to begin a Chinese nuclear-weapons program during the First Taiwan Strait Crisis of 1954–1955. The People's Republic of China detonated its first hydrogen (thermonuclear) bomb on June 17, 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.[33] 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.[34]

A story in The New York Times by William Broad[35] reported that in 1995, a supposed Chinese double agent delivered information indicating that China knew secret details of the U.S. W88 warhead, supposedly through espionage.[36] (This line of investigation eventually resulted in the abortive trial of Wen Ho Lee.)


France's journey in building nuclear weapons began prior to World War II in 1939. The development of nuclear weapons was slowed during the country's German invasion. The United States did not want France to acquire expert knowledge about nuclear weaponry, which ultimately led to the Alsos Mission. The missions followed closely behind the advancing forward-front to obtain information about how close Germany was to building an atomic weapon. Following the surrender of the Nazis, Germany was divided into "zones of occupation". The "zone" given to the French was suspected to contain several nuclear research facilities. The United States conducted Operation Harborage to seize any and all information about nuclear weaponry from the French. The Operation strategized to have American troops intercede advancing French army, allowing the Americans to seize any German scientists or records as well as destroy the remaining functional facilities.[37][38]

In 1945, the French Atomic Energy Commission (Commissariat à l'Énergie Atomique, CEA) was founded under Charles de Gaulle; the CEA served as the country's atomic energy authority, overseeing commercial, military, and scientific uses of atomic power. However it was not until 1952 that a tangible goal of building plutonium reactors progressed. Two years later, a reactor was being built and a plutonium separating plant began construction shortly after. In 1954 the question about continuing to explore building an atomic bomb was raised.[39] The French cabinet seemed to be favoring less the building of an atomic bomb. Ultimately, the Prime Minister decided to continue efforts developing an atomic bomb in secret. In late 1956, tasks were delegated between the CEA and Defense Ministry to propel atomic development such as finding a test site, providing the necessary uranium, and physical device assembly.

Charles de Gaulle returned to power and was elected France's Fifth Republic's first president in 1958. De Gaulle, a strong believer in the nuclear weapons program, approved the country's first nuclear test to take place in one of the early months of 1960. The country's first nuclear explosion took place on 13 February at Reggane Oasis in the Sahara Desert in French Algeria of the time. It was called "Gerboise Bleue", translating to "Blue jerboa".[39][40] The first explosion was detonated at a tower height of 105 meters. The bomb used a plutonium implosion design with a yield of 70 kilotons.[39] The Reggane Oasis test site was used for three more atmospheric tests before testing activity moved to a second site, Ecker, to carry out a total of 13 underground tests into 1967.[40]

The French nuclear testing site was moved to the unpopulated French atolls in the Pacific Ocean. The first test conducted at these new sites was the "Canopus" test in the Fangataufa atoll in French Polynesia on 24 August 1968, the country's first multistage thermonuclear weapon test. The bomb was detonated from a balloon at a height of 520 meters. The result of this test was significant atmospheric contamination.[41] Very little is known about France's development of the Teller–Ulam design, beyond the fact that France detonated a 2.6 Mt 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.[32]

France and China did not sign or ratify the Partial Nuclear Test Ban Treaty of 1963, which banned nuclear test explosions in the atmosphere, underwater, or in outer space. Between 1966 and 1996 France carried out more than 190 nuclear tests.[41] France's final nuclear test took place on January 27, 1996, and then the country dismantled its Polynesian test sites. France signed the Comprehensive Nuclear-Test-Ban Treaty that same year, and then ratified the Treaty within two years.

France confirmed that its nuclear arsenal contains about 300 warheads, carried by submarine-launched ballistic missiles (SLBMs) and fighter-bombers in 2015. 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.[42] The M51.1 missiles are intended to be replaced with the new M51.2 warhead beginning in 2016, which has a 3,000 km greater range than the M51.1.[42]

President François Hollande announced 180 billion euros would be used from the annual defense budget to improve the country's nuclear deterrence.[42] France contains 13 International Monitoring System facilities that monitor for nuclear explosive activity on Earth through the use of seismic, infrasound, and hydroacoustic monitors.[43]

France also has about 60 air-launched missiles tipped with TN 80/TN 81 warheads with a yield of about 300 kilotons each. France's nuclear program has been carefully designed to ensure that these weapons remain usable decades into the future.[32][unreliable source?] 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 Pu-239 as a byproduct.[43]



On May 11, 1998, India purportedly detonated a thermonuclear bomb in its Operation Shakti tests ("Shakti-I", specifically).[44][45] Dr. Samar Mubarakmand, a Pakistani nuclear physicist, asserted that if Shakti-I had been a thermonuclear test, the device had failed to fire.[45] However, Dr. Harold M. Agnew, former director of the Los Alamos National Laboratory, said that India's assertion of having detonated a staged thermonuclear bomb was believable.[46] India says that their thermonuclear device was tested at a controlled yield of 45 kt because of the close proximity of the Khetolai village at about 5 km, to ensure that the houses in that village do not suffer significant damage.[47] Another cited reason was that radioactivity released from yields significantly more than 45 Kilotons might not have been contained fully.[47] After the Pokhran-II tests, Dr. Rajagopal Chidambaram, former chairman of the Atomic Energy Commission of India said that India has the capability to build thermonuclear bombs of any yield at will.[46]

The yield of India's hydrogen bomb test remains highly debatable among the Indian science community and the international scholars.[48] The question of politicisation and disputes between Indian scientists further complicated the matter.[49]

In an interview in August 2009, the director for the 1998 test site preparations, Dr. K. Santhanam claimed that the yield of the thermonuclear explosion was lower than expected and that India should therefore not rush into signing the CTBT. Other Indian scientists involved in the test have disputed Dr. K. Santhanam's claim,[50] arguing that Santhanam's claims are unscientific.[44] British seismologist Roger Clarke argued that the magnitudes suggested a combined yield of up to 60 kilotonnes, consistent with the Indian announced total yield of 56 kilotonnes.[51] 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’.[47]

India claims that it can build thermonuclear weapons of various yields up to around 200 kilotons on the basis of the Shakti-1 thermonuclear test.[47][52]


Israel is alleged to possess thermonuclear weapons of the Teller–Ulam design,[53] but it is not known to have tested any nuclear devices, although it is widely speculated that the Vela Incident of 1979 may have been a joint Israeli–South African nuclear test.[54][55][56]

It is well established that Edward Teller advised and guided the Israeli establishment on general nuclear matters for some twenty years.[57] Between 1964 and 1967, Teller made six visits to Israel where he lectured at the Tel Aviv University on general topics in theoretical physics.[58] 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, after receiving credible information from an "American scientist" (Teller), on Israel's nuclear capability.[56] 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.[56] After he conveyed the matter to the higher level of the U.S. government, Teller reportedly said: "They [Israel] have it, and they were clever enough to trust their research and not to test, they know that to test would get them into trouble."[56]


According to the scientific data received and published by PAEC, the Corps of Engineers, and Kahuta Research Laboratories (KRL), in May 1998, Pakistan carried out six underground nuclear tests in Chagai Hills and Kharan Desert in Balochistan Province (see the code-names of the tests, Chagai-I and Chagai-II).[45] None of these boosted fission devices was the thermonuclear weapon design, according to KRL and PAEC.[45]

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.[59][60] In January 2016, North Korea claimed to have successfully tested a hydrogen bomb,[61] although only a magnitude 5.1 seismic event was detected at the time of the test,[62] a similar magnitude to the 2013 test of a 6–9 kt 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.[63]

On 3 September 2017, the country's state media reported that a hydrogen bomb test was conducted which resulted in "perfect success". According to the U.S. Geological Survey (USGS), the blast resulted in an earthquake with a magnitude of 6.3, 10 times more powerful than previous nuclear tests conducted by North Korea.[64] U.S. Intelligence released an early assessment that the yield estimate was 140 kilotons,[65] with an uncertainty range of 70 to 280 kilotons.[66]

On 12 September, NORSAR revised its estimate of the earthquake magnitude upward to 6.1, matching that of the CTBTO, but less powerful than the USGS estimate of 6.3. Its yield estimate was revised to 250 kilotons, while noting the estimate had some uncertainty and an undisclosed margin of error.[67][68]

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 900 metres (3,000 ft) of rock and the yield "could have been in excess of 300 kilotons".[69]

Public knowledge



DOE statements

In 1972 the United States government declassified a document stating "[I]n thermonuclear (TN) weapons, a fission 'primary' is used to trigger a TN reaction in thermonuclear fuel referred to as a 'secondary'", and in 1979 added, "[I]n thermonuclear weapons, radiation from a fission explosive can be contained and used to transfer energy to compress and ignite a physically separate component containing thermonuclear fuel." To this latter sentence the US government specified that "Any elaboration of this statement will be classified."[70] 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).[71]


The Progressive case






Nuclear reduction

Two years before his death in 1989, Andrei Sakharov's comments at a scientists’ forum helped begin the process for the elimination of thousands of nuclear ballistic missiles from the US and Soviet arsenals. Sakharov (1921–89) was recruited into the Soviet Union's nuclear weapons program in 1948, a year after he completed his doctorate. In 1949 the US detected the first Soviet test of a fission bomb, and the two countries embarked on a desperate race to design a thermonuclear hydrogen bomb that was a thousand times more powerful. Like his US counterparts, Sakharov justified his H-bomb work by pointing to the danger of the other country's achieving a monopoly. But also like some of the US scientists who had worked on the Manhattan Project, he felt a responsibility to inform his nation's leadership and then the world about the dangers from nuclear weapons.[75] Sakharov's first attempt to influence policy was brought about by his concern about possible genetic damage from long-lived radioactive carbon-14 created in the atmosphere from nitrogen-14 by the enormous fluxes of neutrons released in H-bomb tests.[76] In 1968 a friend suggested that Sakharov write an essay about the role of the intelligentsia in world affairs. Self-publishing was the method at the time for spreading unapproved manuscripts in the Soviet Union. Many readers would create multiple copies by typing with multiple sheets of paper interleaved with carbon paper. One copy of Sakharov's essay, "Reflections on Progress, Peaceful Coexistence, and Intellectual Freedom", was smuggled out of the Soviet Union and published by the New York Times. More than 18 million reprints were produced during 1968–69. After the essay was published, Sakharov was barred from returning to work in the nuclear weapons program and took a research position in Moscow.[75] In 1980, after an interview with the New York Times in which he denounced the Soviet invasion of Afghanistan the government put him beyond the reach of Western media by exiling him and his wife to Gorky. In March 1985 Gorbachev became general secretary of the Soviet Communist Party. More than a year and a half later, he persuaded the Politburo, the party's executive committee, to allow Sakharov and Bonner to return to Moscow. Sakharov was elected as an opposition member to the Soviet Congress of People's Deputies in 1989. Later that year he had a cardiac arrhythmia and died in his apartment. He left behind a draft of a new Soviet constitution that emphasized democracy and human rights.[77]

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. The bomb was thought by the Department of Energy to lie buried under several feet of silt at the bottom of Wassaw Sound.[78]

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..[79]

On 21 January 1968, a B-52G, with four B28FI thermonuclear bombs aboard as part of Operation Chrome Dome, crashed on the ice of the North Star Bay while attempting an emergency landing at Thule Air Base in Greenland.[80] The resulting fire caused extensive radioactive contamination.[81] One of the bombs remains lost.[82]


Ivy Mike






See also


  2. ^ Gsponer, Andre (2005). "Fourth Generation Nuclear Weapons: Military effectiveness and collateral effects". arXiv:physics/0510071.
  3. ^ Andre Gsponer. "The B61-based "Robust Nuclear Earth Penetrator:" Clever retrofit or headway towards fourth-generation nuclear weapons?". CiteSeerX
  10. ^ Hansen, Chuck (1988). U.S. nuclear weapons: The secret history. Arlington, Texas: Aerofax. ISBN 978-0-517-56740-1.
  14. ^
  15. ^ "Improved Security, Safety & Manufacturability of the Reliable Replacement Warhead" Archived 2008-12-17 at the Wayback Machine, NNSA March 2007.
  17. ^ Speculation on Fogbank, Arms Control Wonk
  23. ^ "The "George" shot, Comprehensive Test Ban Treaty Organisation website".
  25. ^ Anne Fitzpatrick, Igniting the light elements: The Los Alamos thermonuclear weapon project, 1942–1952 (PhD Thesis LA-13577-T, Virginia Polytechnic Institute, 1999), 105.
  26. ^ "Summary of Notes on Lectures by E. Fermi", G.P. Thomson Papers, Trinity College, University of Cambridge, J84.
  27. ^ a b German A. Goncharov, "The 50th anniversary of the beginning of research in the USSR on the potential creation of a nuclear fusion reactor," Physics-Uspekhi, 44:8
  28. ^ German A. Goncharov, "Thermonuclear milestones", Physics today (Nov 1996), 51
  29. ^ Cited in Stanley A. Blumberg and Gwinn Owens, Energy and conflict: The life and times of Edward Teller (New York, 1976), 228.
  30. ^ "NIE-65: Soviet Bloc Capabilities Through 1957", June 1953, PRO DEFE 41/155.
  31. ^ Holloway, David (1994). Stalin and the bomb: The Soviet Union and atomic energy, 1939–1956. New Haven, Connecticut: Yale University Press. p. 299. ISBN 978-0-300-06056-0.
  32. ^ a b c d e f g h Younger, Stephen (2009). The Bomb: A New History. New York: Harper Collins. ISBN 978-0-06-173614-8.
  33. ^ "17 June 1967 – China's first thermonuclear test: CTBTO Preparatory Commission". Retrieved 2016-10-03.
  36. ^ Christopher Cox, chairman (1999). Report of the United States House of Representatives Select Committee on U.S. National Security and Military/Commercial Concerns with the People's Republic of China. Archived from the original on 2005-08-04., esp. Ch. 2, "PRC Theft of U.S. Thermonuclear Warhead Design Information".
  37. ^ "Alsos Mission". Atomic Heritage Foundation. Retrieved 2017-04-15.
  38. ^ "U.S. Intelligence and the French Nuclear Weapons Program". Retrieved 2017-04-15.
  39. ^ a b c "nuclear weapon | History, Facts, Types, & Effects". Encyclopædia Britannica. Retrieved 2017-04-15.
  40. ^ a b "13 February 1960 – the first French nuclear test : CTBTO Preparatory Commission". Retrieved 2017-04-15.
  41. ^ a b "24 August 1968 – French 'Canopus' test: CTBTO Preparatory Commission". Retrieved 2017-04-15.
  42. ^ a b c "France | Countries | NTI". Retrieved 2017-04-15.
  43. ^ a b "Overview of the verification regime: CTBTO Preparatory Commission". Retrieved 2017-04-15.
  44. ^ a b "Pokhran – II tests were fully successful; given India capability to build nuclear deterrence: Dr. Kakodkar and Dr. Chidambaram". Retrieved 2019-07-26.
  46. ^ a b Burns, John F. (1998-05-18). "Nuclear Anxiety: The Overview; India Detonated a Hydrogen Bomb, Experts Confirm". The New York Times. ISSN 0362-4331. Retrieved 2019-07-26.
  47. ^ a b c d "Press Statement by Dr. Anil Kakodkar and Dr. R. Chidambaram on Pokhran-II tests". Press Information Bureau. 24 September 2009.
  49. ^ Carey Sublette; et al. "What are the real yield of India's Test?". What Are the Real Yields of India's Test?. Retrieved 18 January 2013.
  51. ^ "'We have an adequate scientific database for designing ... a credible nuclear deterrent'". Frontline. January 2, 1999.
  52. ^ "Nukes of 200kt yield possible: Architect of Pokhran-II". The Times Of India. September 25, 2009.
  54. ^ "Doctrine", Israel, FAS.
  55. ^ Hersh, Seymour (1991), The Samson Option: Israel's Nuclear Arsenal and American Foreign Policy, New York City: Random House, p. 271.
  57. ^ Karpin, Michael (2005). The Bomb in the Basement. New York: Simon & Schuster Paperbacks. pp. 289–293. ISBN 978-0-7432-6595-9.
  58. ^ Gábor Palló (2000). "The Hungarian Phenomenon in Israeli Science". Hungarian Academy of Science. 25 (1). Retrieved 11 December 2012.
  62. ^ M5.1 – 21km ENE of Sungjibaegam, North Korea (Report). USGS. January 6, 2016. Retrieved January 6, 2016.
  63. ^ "North Korea nuclear H-bomb claims met by scepticism".
  64. ^ "North Korea conducts sixth nuclear test, says developed H-bomb". Reuters. 3 September 2017. Retrieved 2017-09-03.
  65. ^ Panda, Ankit (6 September 2017). "US Intelligence: North Korea's Sixth Test Was a 140 Kiloton 'Advanced Nuclear' Device". The Diplomat. Retrieved 6 September 2017.
  66. ^ Michelle Ye Hee Lee (13 September 2017). "North Korea nuclear test may have been twice as strong as first thought". Washington Post. Retrieved 28 September 2017.
  67. ^
  68. ^
  69. ^
  70. ^ emphasis in original
  72. ^ a b Morland, Howard (1981). The secret that exploded. New York: Random House. ISBN 978-0-394-51297-6.
  74. ^ Alexander De Volpi; Jerry Marsh; Ted Postol & George Stanford (1981). Born secret: the H-bomb, the Progressive case and national security. New York: Pergamon Press. ISBN 978-0-08-025995-6.
  75. ^ a b A. Sakharov, Memoirs, R. Lourie, trans., Knopf (1990), and Moscow and Beyond, 1986–1989, A. Bouis, trans., Knopf (1991); for Elena Bonner's account of their time in Gorky, see E. Bonner, Alone Together, A. Cook, trans., Knopf (1986).
  76. ^ A. Sakharov, At. Energy 4, 6 (1958), reprinted in Sci. Global Secur. 1, 175 (1990)
  78. ^ "For 50 Years, Nuclear Bomb Lost in Watery Grave". NPR. February 3, 2008.
  79. ^ "US to clean up Spanish radioactive site 49 years after plane crash". The Guardian. 19 October 2015.
  83. ^ Dan Stober & Ian Hoffman (2001). A convenient spy: Wen Ho Lee and the politics of nuclear espionage. New York: Simon & Schuster. ISBN 978-0-7432-2378-2.


Basic principles
  • David Holloway, Stalin and the bomb: The Soviet Union and atomic energy, 1939–1956 (New Haven, Connecticut: Yale University Press, 1994). ISBN 0-300-06056-4
Analyzing fallout

External links