Thermonuclear weapon

Thermonuclear weapons, also known as fusion weapons or hydrogen bombs, are very powerful types of nuclear weapons. They use a process called nuclear fusion to create explosions much bigger than older nuclear weapons. These weapons can be much smaller and lighter but still release far more energy.

The first full test of a thermonuclear weapon was done by the United States in 1952. Since then, several countries have made these kinds of weapons. They work in two stages, with the first stage helping to start the second stage that creates most of the energy.

These weapons are the most powerful ever made, with some able to release energy equal to millions of tons of explosive. Because of their great power, they have played a big role in history, especially during the Cold War, and continue to be important in how countries protect themselves today.

Terminology

Thermonuclear, fusion, and hydrogen weapons are special types of nuclear weapons that use a process called radiation implosion, often linked to the Teller-Ulam design created by scientists in several countries.

These weapons get their power from thermonuclear fusion, where tiny parts called nuclei join together at very high temperatures. This is different from regular nuclear weapons, which rely on neutrons to create an explosion. Some simpler thermonuclear weapons get most of their power from a process called fast fission in materials like natural or depleted uranium.

Basic principle

Main article: Nuclear weapon design

The basic idea of a thermonuclear weapon is that it has different parts that work together in steps. The first part, called the primary, is a smaller bomb that uses fission, or splitting atoms, to explode. This explosion gives off energy that moves to the second part, called the secondary.

The secondary contains fusion fuel, which is special material that can join atoms together to release even more energy. The energy from the primary squeezes the fusion fuel tightly and heats it up, causing it to start a fusion reaction. This process can keep going and can release a lot of energy. Some designs also have a third part that adds even more energy to the explosion.

Compression of the secondary

How the energy moves from the first part of the bomb to the second part has been discussed, but it is believed that X-rays and gamma rays from the first part are responsible. This energy helps squeeze the second part tightly.

There are three ideas about how the X-rays create this squeezing pressure:

• Radiation pressure from the X-rays. This was the first idea suggested.
• Plasma pressure from a special foam inside the bomb. This was a later idea.
• Ablation pressure from the outer layer of the bomb. This idea seems best supported by science.

Each of these ideas explains how the bomb's second part gets compressed to create a powerful explosion. The ablation idea suggests that the outer layer heats up so much that it flies off, pushing the rest of the bomb inward with great force.

Current reviews of the foam plasma pressure idea suggest it may not create as much pressure as thought, because the foam does not absorb much of the X-ray and gamma ray energy. This leads to the third idea: ablation.

Simple calculations show that the ablation effect can create very high pressure. For example, in one bomb design, the outer layer flies off at very high speeds, causing the rest of the bomb to push inward quickly.

The ablation pressure seems much stronger than the other two ideas. Official reports suggest that foam materials might help delay ablation, allowing more energy to reach the second part of the bomb.

In one famous bomb, a thin layer of plastic foam was placed inside the outer casing to delay ablation. Without this foam, the metal would fly off too quickly, reducing the bomb's power. The foam helps keep the bomb together longer, allowing a bigger explosion.

Design variations

Different designs for these special weapons have been suggested. One idea is to use a special kind of material called ²³⁵
U in the outer part of the weapon. This material can help make the explosion even bigger.

Some designs include extra parts inside to shield the main part of the weapon from too many tiny particles called neutrons that come from the first explosion.

Most of these weapons don’t have more than two main parts that explode, but scientists have tested designs with three parts. One example is a very powerful weapon tested by the United States.

The way these weapons usually work involves two steps: first, a small explosion makes a central part split apart, creating a big burst of energy. Then, that energy is used to start a second reaction that creates even more power. This method can be used again and again with more parts, though it’s not always done.

For destroying larger areas like cities, it’s often better to spread the explosion over a wider space instead of making one very big blast. This way, the energy covers more ground. Because of this, many modern weapons are made to have smaller explosions that can be spread out over an area.

Ivy Mike

In a book called Dark Sun: The Making of the Hydrogen Bomb, author Richard Rhodes shares details about a special test named "Ivy Mike." The way this test worked used a mix of heat from the first explosion, foam, and other materials to create the second, bigger explosion.

Ripple

The Ripple design was tested in 1962 and was noted for being very efficient. It used a special mix of gases and materials to create a clean and powerful explosion. However, it was large and not easy to carry on smaller missiles.

W88

In 1999, a report shared details about the W88 weapon used on certain missiles. This weapon has a special shape that allows it to be smaller but still very powerful. Its design lets more of these weapons fit on a single missile, improving how far and how fast the missile can travel.

History

First tests

United States

The idea of a thermonuclear fusion bomb ignited by a smaller fission bomb was first proposed by Enrico Fermi to his colleague Edward Teller when they were talking at Columbia University in September 1941, at the start of what would become the Manhattan Project. 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 US 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, Fermi, and colleagues, warning of the civilian casualties inherent to its use, characterized it as a "weapon of genocide", and concluded that "[t]he extreme danger to mankind inherent in the proposal [to develop thermonuclear weapons] wholly outweighs any military advantage". Despite the objections raised, on 31 January 1950, President Harry S. Truman made the decision to go forward with the development of the new weapon.

Teller and other US physicists struggled to find a workable design. Stanislaw Ulam, a co-worker of Teller, made the first key conceptual leaps towards a workable fusion design. Ulam's two innovations that rendered the fusion bomb practical were that compression of the thermonuclear fuel before extreme heating was a practical path towards the conditions needed for fusion, and the idea of staging or placing a separate thermonuclear component outside a fission primary component, and somehow using the primary to compress the secondary. Teller then realized that the gamma and X-ray radiation produced in the primary could transfer enough energy into the secondary to create a successful implosion and fusion burn, if the whole assembly was wrapped in a hohlraum or radiation case.

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 (940 TJ) 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 Mike shot of Operation Ivy, at an island in the Enewetak Atoll, with a yield of 10.4 Mt (44 PJ) (over 450 times more powerful than the bomb dropped on Nagasaki during World War II). The device, dubbed the Sausage, was created by Richard Garwin, assigned this task by Edward Teller. This was not widely known until 2001, as his involvement was kept secret. It used an extra-large fission bomb as a "trigger" and liquid deuterium—kept in its liquid state by 20 short tons (18 t) of cryogenic equipment—as its fusion fuel, and weighed around 80 short tons (73 t) 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 fusion fuel instead. In 1954 this was tested in the "Castle Bravo" shot (the device was code-named Shrimp), which had a yield of 15 Mt (63 PJ), 2.5 times what was expected, and is the largest US bomb ever tested. Efforts 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 deployed on Polaris ballistic missile submarines, megaton-class warheads were as small as 460 mm (18 in) in diameter and 330 kilograms (720 lb) in weight. Further innovation in miniaturizing warheads was accomplished by the mid-1970s, when versions of the Teller–Ulam design were created that could fit ten or more warheads on the end of a small MIRVed missile.

Soviet Union

The first Soviet fusion design, developed by Andrei Sakharov and Vitaly Ginzburg in 1949 (before the Soviets had a working fission bomb), was dubbed the Sloika, after a Russian layer cake, and was not of the Teller–Ulam configuration. It used alternating layers of fissile material and lithium deuteride fusion fuel spiked with tritium (this was later dubbed Sakharov's "First Idea"). Though nuclear fusion might have been technically achievable, it did not have the scaling property of a "staged" weapon. Thus, such a design could not produce thermonuclear weapons whose explosive yields could be made arbitrarily large (unlike US 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 400 kt (1,700 TJ), 15%-20% of which was 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" in November 1955 with a yield of 1.6 Mt (6.7 PJ). The Soviets demonstrated the power of the staging concept in October 1961, when they detonated the massive and unwieldy Tsar Bomba. It was the largest nuclear weapon developed and tested by any country.

United Kingdom

In 1954 work began at Aldermaston 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 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 US Castle tests and used sampling aircraft in the mushroom clouds, 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 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 tests were carried out. The first test, Green Granite, was a prototype fusion bomb that failed to produce equivalent yields compared to the US and Soviets, achieving only approximately 300 kt (1,300 TJ). The second test Orange Herald was the modified fission bomb and produced 720 kt (3,000 TJ)—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 150 kt (630 TJ).

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 1.8 Mt (7.5 PJ). On 28 April 1958 a bomb was dropped that yielded 3 Mt (13 PJ)—Britain's most powerful test. Two final air burst tests on 2 and 11 September 1958, dropped smaller bombs that yielded around 1 Mt (4.2 PJ) 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. 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

China detonated a full-scale multi-stage thermonuclear bomb, codenamed "639", on 17 June 1967, with a yield of 3.31 Mt (13.8 PJ), becoming the world's fourth thermonuclear power. At only 32 months after detonating its first fission weapon, this remains the fastest success of a national hydrogen bomb program following a nation's first nuclear test. China had previously tested a layer cake design ("596L") boosted fission weapon in May 1966, yielding 220 kt (920 TJ), and a small-scale multi-stage thermonuclear bomb ("629") in December 1966. Testing took place in the Lop Nor Test Site in northwest China.

The Soviet Union assisted the Chinese nuclear program from 1957, but this was abruptly ended by the Sino-Soviet split in 1959. For thermonuclear weapons, China had received a lithium deuteride production plant, and limited knowledge of the Soviet layer cake design. Unlike the US and USSR, at the time of their hydrogen bomb program, China operated no production facilities for plutonium or tritium. Plutonium production reactor in Jiuquan became operational only in 1967, and plutonium separation began in September 1968. During 1963, Chinese scientists led by Peng Huanwu extensively investigated this design, but knew it was too inefficient to be the hydrogen bomb possessed by other countries. Nonetheless, plans were made to test a small layer cake designs in 1966 and "658", a three-staged layer cake design capable of reaching one megaton (similar to the British backup design Orange Herald Large), in October 1967. In September and October 1965, a theoretical research crash project ran in Shanghai led by Yu Min, using digital computers and manual calculation. Yu held a lecture series on the layer cake bomb, and in doing so realized its flaw was its slow production of tritium from lithium deuteride i.e. the Jetter cycle. This resulted in a Teller-Ulam analogue design for compression of a thermonuclear secondary by a fission primary. In December 1965, this design was selected as the focus of thermonuclear development. Yu later stated this rapid development prevented the hydrogen bomb research program from crumbling during the ten-year Cultural Revolution beginning in May 1966 (such as occurred to China's first crewed space program).

The 1966 small layer cake test was still carried out in May 1966 as "596L" (for Project 596 first atomic bomb but with the addition of lithium deuteride). The true two-stage thermonuclear design first tested at a small scale as the "629" device, in December 1966, yielding 120 kt (500 TJ). Following this success it was decided to cannibalize the materials from the backup "658" layer cake project. In the fervor of the Cultural Revolution, the Ninth Academy eagerly competed against Peng Huanwu's prediction that France would test its first hydrogen bomb in 1967, and moved the speculative 639 test date from October to July. The two-stage design was then tested at full scale as the "639" device aka Test No. 6 in June 1967, yielding 3.31 Mt (13.8 PJ).

In China the two-stage design has become known as the Yu Min configuration [zh] (于敏构型, Yú Mǐn gòu xíng). The Chinese government claims that although it is a multi-stage thermonuclear weapon design, it is distinct from the Teller-Ulam design assumed to be used by the other four thermonuclear nations, allowing further miniaturization, and that together these two comprise the only feasible thermonuclear weapon designs. The differences are unclear, as the Chinese design also channels energy from a nuclear fission primary to compress a thermonuclear secondary. Like the initial Soviet and British hydrogen bombs, the secondary is spherical, unlike the first cylindrical secondaries used in the US.

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

France

Following their first nuclear test in 1960, France prioritized fission weapon development and deliverability by Mirage IV bombers. In 1966, de Gaulle felt pressure that China would become the fourth thermonuclear country, and set a deadline of 1968 for the first hydrogen bomb test. A participating scientist, Pierre Billaud, wrote of French thermonuclear knowledge in 1965:

Compared to our American colleagues in 1948, French scientists had many advantages: we knew that hydrogen bombs existed and worked and that they used Li6D [lithium deuteride], and we understood the reactions at work. We also had powerful computers, of US origin, which were not available in the late 1940s. And we knew, more or less, the dimensions and weights of the nuclear weapons deployed at NATO bases in Europe and their yields. This information was obtained from tips we had managed to get, as well as from articles in the open literature from such publications as Aviation Week or the Bulletin of the Atomic Scientists.

Early tests "closely fitted Li6D [lithium deuteride] to the fissile core", implying a layer cake design. France began testing thermonuclear principles in the 1966–70 French nuclear tests, beginning with the 125 kt Rigel boosted fission shot in September 1966. In April 1967, physicist Michel Carayol [fr] outlined the radiation implosion idea central to the Teller-Ulam design, but the weapons scientists were not immediately convinced it was the solution. In June, France lost the hydrogen bomb race to China's three-megaton Project 639 test. By mid-1967, like their Chinese counterparts, French scientists had identified an extremely high, almost twenty-fold density increase of the lithium deuteride fuel, to be crucial to megaton success, but planned a test of Carayol's correct Teller-Ulam analogue as only one of three designs for summer of 1968.

France's hydrogen bomb development path was crucially influenced by the British scientist William Richard Joseph Cook, who led the successful British hydrogen bomb programme a decade prior. Unlike France, the UK, as well as the US and USSR, had aerial reconnaissance capabilities to collect nuclear fallout from testing and make deductions, including France's lack of progress in thermonuclear weapons. In September 1967, Cook provided limited thermonuclear development information to the military attache at the French Embassy in London, specifically that their current designs would not succeed and that the solution was more simple. This allowed the French scientists to identify and proceed with only Carayol's proposal for the ultimately successful 1968 thermonuclear tests. It is believed this was done on the instruction of Prime Minister Harold Wilson, aimed as an overture to de Gaulle, who was currently blocking the accession of the United Kingdom to the European Communities due to its closer relationship to the United States. However, de Gaulle again vetoed UK accession in November 1967, and was very shocked when made aware of the British contribution.

The first DT-boosted warhead, the MR 41, was tested in the Castor and Pollux shots of July and August 1968, successfully yielding 450 kt (1,900 TJ) in the former.

The "Canopus" test in the Fangataufa atoll in French Polynesia on 24 August 1968 was the country's first multistage thermonuclear weapon test. The bomb was detonated from a balloon at a height of 520 metres (1,710 ft). The result of this test was significant atmospheric contamination. France is currently 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 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 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 missiles 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 3,000-kilometre (1,900 mi) 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 300 kt (1,300 TJ) each. France's nuclear program has been carefully designed to ensure that these weapons remain usable decades into the future.^{[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 ²³⁹
Pu as a byproduct.

India

See also: India and weapons of mass destruction

On 11 May 1998, India announced that it had detonated a thermonuclear bomb in its Operation Shakti 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, 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 45 kt (190 TJ) because of the close proximity of the Khetolai village at about 5 kilometres (3 mi), 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 tests, Rajagopala Chidambaram, former chairman of the Atomic Energy Commission of India, said that India has the capability to build thermonuclear bombs of any yield at will. India officially maintains that it can build thermonuclear weapons of various yields up to around 200 kt (840 TJ) 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. 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 60 kilotonnes of TNT (250 TJ), consistent with the Indian announced total yield of 56 kilotonnes of TNT (230 TJ). US seismologist Jack Evernden has argued that for correct estimation of yields, one should 'account properly for geological and seismological differences between test sites'.

Israel

Main article: Nuclear weapons and 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 of 1979 may have been a joint Israeli–South African nuclear test.^{: 271  : 297–300} 

It is well established that Edward Teller advised and guided the Israeli establishment on general nuclear matters for some 20 years.^{: 289–293}  Between 1964 and 1967, Teller made six visits to Israel where he lectured at the Tel Aviv University on general topics in theoretical physics. 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 US Congress, after receiving credible information from an "American scientist" (Teller), on Israel's nuclear capability.^{: 297–300}  During the 1990s, Teller eventually confirmed speculations in the media that it was during his visits in the 1960s that he concluded that Israel was in possession of nuclear weapons.^{: 297–300}  After he conveyed the matter to the higher level of the US 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."^{: 297–300} 

North Korea

Main article: North Korea and weapons of mass destruction

North Korea claimed to have tested its miniaturised thermonuclear bomb on 6 January 2016. North Korea's first three nuclear tests (2006, 2009 and 2013) were relatively low yield and do not appear to have been of a thermonuclear weapon design. In 2013, the 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 6–9 kt (25–38 TJ) 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 US Geological Survey (USGS), the blast released energy equivalent to an earthquake with a seismic magnitude of 6.3, 10 times more powerful than previous nuclear tests conducted by North Korea. US Intelligence released an early assessment that the yield estimate was 140 kt (590 TJ), with an uncertainty range of 70 to 280 kt (290 to 1,170 TJ). 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 estimate of 6.3. Its yield estimate was revised to 250 kt (1,000 TJ), 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 900 metres (3,000 ft) of rock, and the yield "could have been in excess of 300 kilotons".

Public knowledge

Classification

Information about how nuclear weapons work is kept secret in most countries. In the United States, this knowledge is called "Restricted Data" and can be classified even if made by people not working for the government. Some details are considered "born secret" as soon as they are created, though this rule has been debated.

The United States Department of Energy usually does not admit when secret weapon information is leaked, because acknowledging it might confirm its accuracy. In the past, the government has tried to stop news reports about these secrets, but with limited success.

Unclassified knowledge

While some general facts about nuclear weapons have been shared, many details remain unclear. Most of what the public knows comes from guessing based on known science, comparisons with related fields, and a few official statements.

US Department of Energy statements

In 1972, the United States government shared that thermonuclear weapons use a fission "primary" to start a fusion reaction in a "secondary" part. In 1979, they added that radiation from the fission part can be used to compress and ignite the fusion fuel. However, they said any more details would remain secret.

In 1991, they admitted that some parts of the weapon may contain special materials, but did not say where or how they are used.

United States v. The Progressive

Main article: United States v. The Progressive

Much of what is known today about how hydrogen bombs work became public after a magazine article in 1979. An activist named Howard Morland tried to explain the "secret" of these weapons. He used information from books, interviews with scientists, and his own thinking.

The government tried to stop the article from being published, claiming it was too secret. However, the case became weaker when it turned out some of the information had been published before. Eventually, the government let the article be published. Morland later changed some of his ideas about how the bomb worked.

Morland’s work is seen as partly correct because the government tried to stop it, which is rare. However, it is unclear how much of his explanation was fully accurate. Other countries found it difficult to build these weapons, suggesting that understanding the basic idea is not enough to make them.

Notable accidents

Unfortunately, there have been some accidents involving nuclear weapons in the past.

In 1958, a training plane lost a nuclear bomb off the coast of Tybee Island near Savannah, Georgia. The U.S. Air Force says the bomb was not ready to explode.

In 1966, two planes crashed over Palomares in Spain. The explosion scattered material from the bombs, but the danger was contained.

In 1968, another plane crashed in Greenland while trying to land. This caused radioactive contamination, and not all parts of the bombs were found.