United States tests first hydrogen bomb

United States tests first hydrogen bomb

The United States detonates the world’s first thermonuclear weapon, the hydrogen bomb, on Eniwetok atoll in the Pacific. The test gave the United States a short-lived advantage in the nuclear arms race with the Soviet Union.

Following the successful Soviet detonation of an atomic device in September 1949, the United States accelerated its program to develop the next stage in atomic weaponry, a thermonuclear bomb. Popularly known as the hydrogen bomb, this new weapon was approximately 1,000 times more powerful than conventional nuclear devices. Opponents of development of the hydrogen bomb included J. Robert Oppenheimer, one of the fathers of the atomic bomb. He and others argued that little would be accomplished except the speeding up of the arms race, since it was assumed that the Soviets would quickly follow suit.The opponents were correct in their assumptions. The Soviet Union exploded a thermonuclear device the following year and by the late 1970s, seven nations had constructed hydrogen bombs. The nuclear arms race had taken a fearful step forward.

WATCH: U.S. Develops Hydrogen Bomb

This Day In History: The US Detonates The World’s First H-Bomb Test (1952)

On this date in history, the US took the lead in the nuclear arms race during the Cold War. The United States detonates the world&rsquos first thermonuclear device or the hydrogen bomb on a tiny atoll in the South Pacific. The test was a sensation at the time and it seemed to give the United States a decisive advantage in the Cold War. The news of the successful test was regarded as something of a triumph in Washington. Many Americans had been shocked by the successful test of an atomic bomb by the Soviet Union in 1949. This persuaded many in the Washington establishment to develop a bigger and a better weapon. The idea of a thermonuclear device had been first mooted in the early days of WWII. The idea of a thermonuclear fusion bomb that was a ignited by a smaller fission bomb was first proposed by the Italian physicist Enrico Fermi to his colleague Edward Teller in 1941. Teller was to be one of the driving forces behind the development of the hydrogen bomb. He took Fermi&rsquos theoretical ideas and tried to turn them into a working nuclear weapon. It took Teller almost ten years to perfect the design and he was assisted by many brilliant scientists. Chief among them was Stanislaw Ulam, who helped to design the all-important mechanism of the weapon. On this day in history, the first thermonuclear weapon was detonated. The device, known as the Sausage, because of its shape, employed an extra-large fission bomb to ignite the explosion. The weapon was huge and it weighed several tons and it took several years to miniaturize it, show that it could be deployed on a missile.

Technicians working on the A-Bomb

The hydrogen bomb, developed by the Americans involved a chain of nuclear detonations and it was up to 46 times more powerful than the A-bomb. The development of the H-bomb was very controversial and many opposed it as it would only lead to the Soviet&rsquos developing their own version of the bomb and this would only heighten the risk of a nuclear war that would annihilate modern civilization. The United States had failed to realize that the Soviets were making real progress on their own H-bomb. The first Soviet H-bomb was designed by Andrei Sakharov and Vitaly Ginzburg in 1949 and was known as the Sloika, after a popular Russian cake and was based on a very different design to the American weapon. Later Sakharov would become a leading Soviet dissident.

In the following year, 1953, the Soviets perfected their own thermonuclear device and detonated it in the Republic of Kazakhstan. The nuclear arms race had entered a new and dangerous phase. By the 1980s several countries had managed to test an H-bomb including China and Israel. The stockpile of H-Bombs held by the US and the Russian Federation is now well below the levels seen in the 1980s.

The First Hydrogen Bomb

The first US airdrop of a thermonuclear bomb happened on May 20th, 1956.

The first hydrogen bomb dropped from the air exploded with a force estimated as equal to a minimum of fifteen million tons of TNT and created a fireball at least four miles wide and brighter than 500 suns.

It was described as ‘by far the most stupendous release of explosive energy on earth so far.’ Dropped from an American B52 jet bomber named the Barbara Grace, flying at around 45,000ft above Namu Island in the Bikini Atoll in the Pacific, it was set off at 5.51 a.m. local time at an altitude of 10,000ft – to minimize the radioactive fallout – in view of some 13,500 people. There were thirty or more observers in reconnaissance aircraft and thousands of civilian observers and journalists in a fleet of ships thirty miles or so from the scene. The bomb missed its target by about four miles. The bomber itself was fifteen miles away by the time the bomb went off and got away safely, though all the aircraft involved were struck by a tremendous shock wave from the explosion.

The correspondent of the London Times, watching through high-density goggles from one of the ships, saw the fireball shoot up into the air, followed almost instantly by a giant pillar of fire and then by an enormous mushroom cloud climbing up and spreading out until ‘it appeared as though it would envelop the entire earth’. It glowed with colours from deep purple to orange and pink at the top and was eventually more than twenty-five miles high and a hundred miles across.

Theoretical physicists in the USA had considered a ‘super’ bomb even before the atomic bomb was developed. Robert Oppenheimer and Edward Teller were already discussing thermonuclear weapons in 1942 and when the Los Alamos laboratory in New Mexico was established under Oppenheimer in 1943, Teller led a ‘Super’ research programme. There were serious theoretical problems and the atomic bomb was given priority, but work on the ‘Super’ was continued after the war by a group which included the Soviet spy Klaus Fuchs. The first successful American test was conducted in the Pacific in 1952, the first Soviet test in the following year. An American crash programme under Teller was ready to drop the first H-bomb ever launched from an aircraft in May 1956. William Lawrence, an American authority who watched the test, described it as ‘an effective substitute for war’.

RDS-6s (Joe-4)

A little less than a year after the United States tested its first thermonuclear device with the Mike Shot on November 1, 1952, the Soviets tested their own thermonuclear bomb. On August 8, 1953, Soviet Premier Georgy Malenkov announced that the United States no longer had a monopoly on the hydrogen bomb. Four days later, on August 12, 1953, the RDS-6s test, the first test of a Soviet thermonuclear device, took place.

The test, which became known as Joe-4 (this had been the fourth Soviet nuclear explosion whose occurrence was announced by the United States), took place at the Semipalatinsk test site and yielded roughly 400 kilotons of TNT. The explosion took place on a tower the purpose of this was to reduce the fallout hazard which would be created as a result of the explosion. The test vaporized the steel tower and left a massive crater in its place. The area surrounding the crater was covered in a "yellow lumpy glass" which became thinner from the epicenter.

Act II: Creating a Monster

Almost three months after the Castle Bravo test, Toho Co. released a groundbreaking film that drew inspiration from the Daigo Fukuryu Maru Incident and called it Gojira. The film captured Japanese fears of nuclear annihilation.

However, Gojira did not initially start out with this premise. Rather, producer Tomoyuki Tanaka originally wanted to a monster movie like the American film The Beast from 20,000 Fathoms. When he was traveling from Indonesia to Japan in 1954, he flew over Bikini Atoll. Seeing the site of the Castle Bravo test inspired him to create a monster that was born from nuclear testing.[ix] This inspiration is evident with the opening scene of the film.

The film starts with an idyllic scene of fishermen relaxing on their boat as they play music. A sudden thunderous boom disrupts them, and they run to the railings of the ship to investigate. The camera follows their gaze to the ocean, and an eerie glow bubbles beneath the surface. The camera pans back to the confused fishermen. Then, a bright flash, resembling pika-don (the “flash-bang” of the atomic bombs that Hiroshima and Nagasaki survivors witnessed), blinds them and the audience. The ship burns from the explosive flash and sinks into the ocean. A radio operator desperately sends a message back to Tokyo as the ship burns and eventually sinks.

Toho Co. hired director and screenwriter Ishiro Honda for the project. Known for his attention to detail, he brought to life a monster whose name comes from the combination of the Japanese words for whale (鯨 kujira) and gorilla (ゴリラ gorira).[x]

Special effects director Eiji Tsuburaya could not rely on stop-motion-capture, because that method of special effects would take at least six months to complete. Instead, he resorted to making a miniature set of Tokyo and putting an actor into a rubber monster suit. He also utilized a technique called “optical compositing” to allow the monster and the characters to exist within the same scene. Additionally, he employed animation techniques to create the famous radioactive breath and glowing dorsal fins. Tsuburaya’s innovative style “us[ing] realistic elements to depict imaginary creatures serves as a catalyst that stimulates the audience’s imagination and creates an unparalleled sense of awe and surprise.”[xi]

Gojira paved the way for today’s Japanese pop culture, movies, and special effects. It single handedly created the kaiju no eiga (monster movie) genre[xii] and started the tokusatsu (special effects) style.[xiii] It was also one of a number of post-Occupation films that dealt with the atomic bombings. Other films included Hiroshima and Children of Hiroshima.

What the First H-Bomb Test Looked Like

O n Nov. 1, 1952&mdash63 years ago this week&mdashthe U.S. detonated the first hydrogen bomb, resulting in the first successful full-scale thermonuclear weapon explosion.

Operation Ivy was conducted on the Eniwetok Atoll in the Marshall Islands. It involved two test bombs, one (“Mike”) a fusion device and the other a &ldquostockpile&rdquo fission device. An experimental hydrogen bomb weighing an immense 82 tons, Mike was not a deliverable weapon&mdashbut it was noteworthy as the first nuclear bomb to get a significant portion of its explosive energy from fusion, or the joining of atoms, instead of only from fission, the splitting of atoms. In order to work, it relied on a fission explosion that would trigger fusion in liquid deuterium, a heavy hydrogen isotope.

At 7:15 a.m. local time on Elugelab Island, Mike was detonated from a control ship 30 m. away. The detonation resulted in a massive explosion, equivalent to 10.4 Megatons of TNT. As a military report on the history of Operation Ivy noted, &ldquoThe Shot, as witnessed aboard the various vessels at sea, is not easily described. Accompanied by a brilliant light, the heat wave was felt immediately at distances of thirty to thirty-five miles. The tremendous fireball, appearing on the horizon like the sun when half-risen, quickly expanded after a momentary hover time.&rdquo

In a cover story after the test was confirmed to the public, TIME described its effects: &ldquothe force and horror of atomic weapons had entered a new dimension&hellipthe first full-dress H-blast (Operation Ivy) had turned the mid-Pacific sandspit named Elugelab into a submarine crater.&rdquo

The fireball reached about 3.25 m. in diameter. Elugelab, the island on which Mike&rsquos detonation took place, was indeed vaporized, leaving a crater 6,300 ft. in diameter and 160 ft. deep. The mushroom cloud was 100 m. wide at its greatest extent. A sailor who witnessed the blast, however, didn’t think that “mushroom” was the foodstuff most applicable: “The cloud itself was kind of rough,” a sailor wrote, “yet it looked smooth &mdash something like a cauliflower.”

At that point in 1952 it was the largest nuclear explosion ever. Today it still ranks fourth largest among all U.S. nuclear tests.

News of the test leaked immediately, but went unconfirmed. A TIME reporter called the Atomic Energy Commission and a LIFE reporter called the Department of Defense, both requesting confirmation of an H-bomb less than three hours after the test&mdashboth reporters gave the correct time of detonation, which was highly secret information&mdashbut nonetheless news of Ivy Mike was not publicly acknowledged until April 1, 1954, when a 28-minute television film was released to the public.

Read more about Operation Ivy Mike, here in the TIME Vault: The Road Beyond Elugelab

Bikini Bombshell: The First H-bomb Test on the Eniwetok Atoll

On November 1 st , 1952 the United States detonated the world’s first hydrogen bomb on a large atoll called Eniwetok in the Marshall Islands in the South Pacific (190 miles west of the more famous Bikini Atoll) as a part of Operation Ivy. Previously in September of 1949, the Soviet Union had detonated its atomic bomb, prompting the United States to increase efforts to develop an even greater thermonuclear weapon to surpass the capacity of the Soviets. The creation and detonation of the first hydrogen bomb on the Eniwetok atoll allowed the United States to temporarily step ahead of the Soviets during the arms race. Overall there were 43 nuclear tests conducted at Enewetak from 1948 to 1958. H-bombs, which get their power from fusion, are about 1000 times more powerful than atomic bombs, which derive their force from fission.

Colonel Anthony J. Perna was Deputy of the 509th Composite Bomb Wing after the end of WWII. He was assigned to organize Operation Crossroads, a program on the island Kwajalein in the Marshall Islands of the Pacific to set up the Bikini bomb test. Prior to his Deputy position he was a Commander of a B-29 school at Denver, Colorado. Perna was present during the bombing on Eniwetok atoll and describes his experiences.

Go here to read about the July 1945 Trinity test at Los Alamos and when the U.S. accidentally dropped four H-bombs over Spain.

“I was convinced when I saw the thing go off that you could never use them”

PERNA: The war ended in August 󈧱 when they dropped the bomb on Hiroshima and Nagasaki. In January 1946, a couple months later, I joined the unit that had dropped the bomb, and I became Deputy of the 509th Composite Bomb Wing. We organized a program to go to an island called Kwajalein in the Pacific in the Marshall Islands where we set up the Bikini bomb test. The Bikini bomb test was called Operations Crossroads. This was a program to detonate a nuclear weapon under scientifically controlled and test conditions. The ones we had detonated heretofore was the test one in White Sands (the first one that went off), and then the second one was the one we dropped on Hiroshima, and the third one was dropped on Nagasaki. There was no test data to speak of, so we set up this test program and dropped one from an airplane onto a target ship, the Nevada. We had a whole fleet of navy vessels, a whole bunch of army buildings, and army materiel, including guns and tanks, etc….

PERNA: Everything to be tested, to see what happened when you dropped a nuclear weapon. We dropped from 30,000 feet. I did not fly the airplane that dropped it. I was flying an airplane around the target site and I had what we call blast gauges in my airplane. When we came down to the point that they were going to release the bomb, I released these blast gauges. Other pilots with other bombers like mine released blast gauges and with telemetering equipment and radio transmission they were able to record the blast and the data scientifically so that they could find out at various altitudes how much intensity you had from the burst of the bomb.

Q: How far away were you from the blast?

PERNA: I was eleven miles slant range. When the bomb went off here and I was eleven miles at 28,000 feet. We wore goggles for fear of retina damage to the eyes. When the shock wave hit us the whole airplane jerked. It felt like someone took a tremendous plank and slammed it against the airplane, and this was at 11 miles. Well, we stayed out there for the second shot which was where we put a weapon on a tower again up at the Bikini lagoon and we set it off on a tower about 200 feet above the ground.

Q: This was how much later?

PERNA: This was just a matter of weeks, a month later. We did a test in April and May, and then we came home in the summer. We had to produce all the scientific data and recording material that we had. We had a tremendous array of instrumentation from Los Alamos and from all the scientific community in America, including some of the scientific colleges. These people were under contract to the War Department and recording the data to see what would happen. We had animals, we had materiel, we had structures, we had medicines, we had everything you can think of that somebody wanted to see what were the effects of a nuclear detonation.

This was a very impressive moment in my life and I was convinced when I saw the thing go off that you could never use these. Then I spent the rest of my life hauling them around as part of the deterrent against the Russians. But I was convinced when I saw that one go off that this was not the answer for mankind. But we used the threat of them as a successful deterrent.

This Kwajalein “Crossroads” duty with the 509th lasted until the summer when we got our data together, then packed up and came back to Roswell, N.M. and Washington and turned in our report. I delivered the Air Force report called “The employment of nuclear weapons by the US Air Force” to the Air Force headquarters. This was Top Secret in those days. A lot of service politics were involved and interesting at the time.

The weapons had large explosive charges put in a casing, they called them “Fatman.” The Fatman was probably 5 or 6 feet high, probably 8 or 10 feet long. In the core of it was where the uranium went. This was the material that caused the fission, but to make it detonate you had to have an implosion of all the high explosives. When it exploded inward, it made the U-235 go critical, and you caused the fission phenomena. The ingredients U-235 capsule that went inside was controlled by the Navy. We had a Navy Admiral on board our Air Force airplane, Admiral Parsons, who was the man who had inserted it on the flight to Hiroshima. So the Air Force did not have control of the whole thing, the Navy had control of the critical ingredients of the bomb, and he had to wait until we took off, and when we got in flight….

Q: It was inserted in flight?

PERNA: It was inserted in flight, when you were at low altitude and didn’t need oxygen to get in the bomb bay to put the thing in. This was a very interesting period. We had everybody in the world out there looking at the test.

The nuclear testing on Eniwetok had major effects on the health of its inhabitants and the environment of the atoll. Marshallese people claim that they have suffered cancers and thyroid problems as a result of this nuclear testing. In 1983 the United States and the Government of the Marshall Islands agreed upon and signed the Compact of Free Association. This agreement seeks compensate for the damage and injury caused by the nuclear testing on the Bikini Islands. Originally the compact required the United States to establish a $150 million trust fund to the Marshallese government. This amount was later revised to $244 million after nuclear soil testing was conducted in 2000 by the Nuclear Claims Tribunal. The attempts toward environmental restoration have been successful in reducing the amount of radiation by filtering and replacing the topsoil of the island. Further efforts are still in progress as of today to continue to improve the quality of life on the islands.


Nuclear weapons tests have historically been divided into four categories reflecting the medium or location of the test.

  • Atmospheric testing designates explosions that take place in the atmosphere. Generally these have occurred as devices detonated on towers, balloons, barges, islands, or dropped from airplanes, and also those only buried far enough to intentionally create a surface-breaking crater. The United States, the Soviet Union, and China have all conducted tests involving explosions of missile-launched bombs (See List of nuclear weapons tests#Tests of live warheads on rockets). Nuclear explosions close enough to the ground to draw dirt and debris into their mushroom cloud can generate large amounts of nuclear fallout due to irradiation of the debris. This definition of atmospheric is used in the Limited Test Ban Treaty, which banned this class of testing along with exoatmospheric and underwater.
  • Underground testing refers to nuclear tests conducted under the surface of the earth, at varying depths. Underground nuclear testing made up the majority of nuclear tests by the United States and the Soviet Union during the Cold War other forms of nuclear testing were banned by the Limited Test Ban Treaty in 1963. True underground tests are intended to be fully contained and emit a negligible amount of fallout. Unfortunately these nuclear tests do occasionally "vent" to the surface, producing from nearly none to considerable amounts of radioactive debris as a consequence. Underground testing, almost by definition, causes seismic activity of a magnitude that depends on the yield of the nuclear device and the composition of the medium in which it is detonated, and generally creates a subsidence crater. [2] In 1976, the United States and the USSR agreed to limit the maximum yield of underground tests to 150 kt with the Threshold Test Ban Treaty.
    Underground testing also falls into two physical categories: tunnel tests in generally horizontal tunnel drifts, and shaft tests in vertically drilled holes.
  • Exoatmospheric testing refers to nuclear tests conducted above the atmosphere. The test devices are lifted on rockets. These high-altitude nuclear explosions can generate a nuclear electromagnetic pulse (NEMP) when they occur in the ionosphere, and charged particles resulting from the blast can cross hemispheres following geomagnetic lines of force to create an auroral display.
  • Underwater testing involves nuclear devices being detonated underwater, usually moored to a ship or a barge (which is subsequently destroyed by the explosion). Tests of this nature have usually been conducted to evaluate the effects of nuclear weapons against naval vessels (such as in Operation Crossroads), or to evaluate potential sea-based nuclear weapons (such as nuclear torpedoes or depth charges). Underwater tests close to the surface can disperse large amounts of radioactive particles in water and steam, contaminating nearby ships or structures, though they generally do not create fallout other than very locally to the explosion.

Salvo tests Edit

Another way to classify nuclear tests are by the number of explosions that constitute the test. The treaty definition of a salvo test is:

In conformity with treaties between the United States and the Soviet Union, a salvo is defined, for multiple explosions for peaceful purposes, as two or more separate explosions where a period of time between successive individual explosions does not exceed 5 seconds and where the burial points of all explosive devices can be connected by segments of straight lines, each of them connecting two burial points, and the total length does not exceed 40 kilometers. For nuclear weapon tests, a salvo is defined as two or more underground nuclear explosions conducted at a test site within an area delineated by a circle having a diameter of two kilometers and conducted within a total period of time of 0.1 second. [3]

The USSR has exploded up to eight devices in a single salvo test Pakistan's second and last official test exploded four different devices. Almost all lists in the literature are lists of tests in the lists in Wikipedia (for example, Operation Cresset has separate items for Cremino and Caerphilly, which together constitute a single test), the lists are of explosions.

Separately from these designations, nuclear tests are also often categorized by the purpose of the test itself.

  • Weapons-related tests are designed to garner information about how (and if) the weapons themselves work. Some serve to develop and validate a specific weapon type. Others test experimental concepts or are physics experiments meant to gain fundamental knowledge of the processes and materials involved in nuclear detonations.
  • Weapons effects tests are designed to gain information about the effects of the weapons on structures, equipment, organisms and the environment. They are mainly used to assess and improve survivability to nuclear explosions in civilian and military contexts, tailor weapons to their targets, and develop the tactics of nuclear warfare.
  • Safety experiments are designed to study the behavior of weapons in simulated accident scenarios. In particular, they are used to verify that a (significant) nuclear detonation cannot happen by accident. They include one-point safety tests and simulations of storage and transportation accidents.
  • Nuclear test detection experiments are designed to improve the capabilities to detect, locate, and identify nuclear detonations, in particular to monitor compliance with test-ban treaties. In the United States these tests are associated with Operation Vela Uniform before the Comprehensive Test Ban Treaty stopped all nuclear testing among signatories.
  • Peaceful nuclear explosions were conducted to investigate non-military applications of nuclear explosives. In the United States these were performed under the umbrella name of Operation Plowshare.

Aside from these technical considerations, tests have been conducted for political and training purposes, and can often serve multiple purposes.

Hydronuclear tests study nuclear materials under the conditions of explosive shock compression. They can create subcritical conditions, or supercritical conditions with yields ranging from negligible all the way up to a substantial fraction of full weapon yield. [4]

Critical mass experiments determine the quantity of fissile material required for criticality with a variety of fissile material compositions, densities, shapes, and reflectors. They can be subcritical or supercritical, in which case significant radiation fluxes can be produced. This type of test has resulted in several criticality accidents.

Subcritical (or cold) tests are any type of tests involving nuclear materials and possibly high-explosives (like those mentioned above) that purposely result in no yield. The name refers to the lack of creation of a critical mass of fissile material. They are the only type of tests allowed under the interpretation of the Comprehensive Nuclear-Test-Ban Treaty tacitly agreed to by the major atomic powers. [5] [6] Subcritical tests continue to be performed by the United States, Russia, and the People's Republic of China, at least. [7] [8]

Subcritical test executed by the United States include: [9] [10] [11]

There have also been simulations of the effects of nuclear detonations using conventional explosives (such as the Minor Scale U.S. test in 1985). The explosives might be spiked with radioactive materials to simulate fallout dispersal.

The first atomic weapons test was conducted near Alamogordo, New Mexico, on July 16, 1945, during the Manhattan Project, and given the codename "Trinity". The test was originally to confirm that the implosion-type nuclear weapon design was feasible, and to give an idea of what the actual size and effects of a nuclear explosion would be before they were used in combat against Japan. While the test gave a good approximation of many of the explosion's effects, it did not give an appreciable understanding of nuclear fallout, which was not well understood by the project scientists until well after the atomic bombings of Hiroshima and Nagasaki.

The United States conducted six atomic tests before the Soviet Union developed their first atomic bomb (RDS-1) and tested it on August 29, 1949. Neither country had very many atomic weapons to spare at first, and so testing was relatively infrequent (when the U.S. used two weapons for Operation Crossroads in 1946, they were detonating over 20% of their current arsenal). However, by the 1950s the United States had established a dedicated test site on its own territory (Nevada Test Site) and was also using a site in the Marshall Islands (Pacific Proving Grounds) for extensive atomic and nuclear testing.

The early tests were used primarily to discern the military effects of atomic weapons (Crossroads had involved the effect of atomic weapons on a navy, and how they functioned underwater) and to test new weapon designs. During the 1950s, these included new hydrogen bomb designs, which were tested in the Pacific, and also new and improved fission weapon designs. The Soviet Union also began testing on a limited scale, primarily in Kazakhstan. During the later phases of the Cold War, though, both countries developed accelerated testing programs, testing many hundreds of bombs over the last half of the 20th century.

Atomic and nuclear tests can involve many hazards. Some of these were illustrated in the U.S. Castle Bravo test in 1954. The weapon design tested was a new form of hydrogen bomb, and the scientists underestimated how vigorously some of the weapon materials would react. As a result, the explosion—with a yield of 15 Mt—was over twice what was predicted. Aside from this problem, the weapon also generated a large amount of radioactive nuclear fallout, more than had been anticipated, and a change in the weather pattern caused the fallout to spread in a direction not cleared in advance. The fallout plume spread high levels of radiation for over 100 miles (160 km), contaminating a number of populated islands in nearby atoll formations. Though they were soon evacuated, many of the islands' inhabitants suffered from radiation burns and later from other effects such as increased cancer rate and birth defects, as did the crew of the Japanese fishing boat Daigo Fukuryū Maru. One crewman died from radiation sickness after returning to port, and it was feared that the radioactive fish they had been carrying had made it into the Japanese food supply.

Castle Bravo was the worst U.S. nuclear accident, but many of its component problems—unpredictably large yields, changing weather patterns, unexpected fallout contamination of populations and the food supply—occurred during other atmospheric nuclear weapons tests by other countries as well. Concerns over worldwide fallout rates eventually led to the Partial Test Ban Treaty in 1963, which limited signatories to underground testing. Not all countries stopped atmospheric testing, but because the United States and the Soviet Union were responsible for roughly 86% of all nuclear tests, their compliance cut the overall level substantially. France continued atmospheric testing until 1974, and China until 1980.

A tacit moratorium on testing was in effect from 1958 to 1961, and ended with a series of Soviet tests in late 1961, including the Tsar Bomba, the largest nuclear weapon ever tested. The United States responded in 1962 with Operation Dominic, involving dozens of tests, including the explosion of a missile launched from a submarine.

Almost all new nuclear powers have announced their possession of nuclear weapons with a nuclear test. The only acknowledged nuclear power that claims never to have conducted a test was South Africa (although see Vela Incident), which has since dismantled all of its weapons. Israel is widely thought to possess a sizable nuclear arsenal, though it has never tested, unless they were involved in Vela. Experts disagree on whether states can have reliable nuclear arsenals—especially ones using advanced warhead designs, such as hydrogen bombs and miniaturized weapons—without testing, though all agree that it is very unlikely to develop significant nuclear innovations without testing. One other approach is to use supercomputers to conduct "virtual" testing, but codes need to be validated against test data.

There have been many attempts to limit the number and size of nuclear tests the most far-reaching is the Comprehensive Test Ban Treaty of 1996, which has not, as of 2013 [update] , been ratified by eight of the "Annex 2 countries" required for it to take effect, including the United States. Nuclear testing has since become a controversial issue in the United States, with a number of politicians saying that future testing might be necessary to maintain the aging warheads from the Cold War. Because nuclear testing is seen as furthering nuclear arms development, many are opposed to future testing as an acceleration of the arms race.

In total nuclear test megatonnage, from 1945 to 1992, 520 atmospheric nuclear explosions (including eight underwater) were conducted with a total yield of 545 megatons, [18] with a peak occurring in 1961–1962, when 340 megatons were detonated in the atmosphere by the United States and Soviet Union, [19] while the estimated number of underground nuclear tests conducted in the period from 1957 to 1992 was 1,352 explosions with a total yield of 90 Mt. [18]

The first atomic test, "Trinity", took place on July 16, 1945.

The Sedan test of 1962 was an experiment by the United States in using nuclear weapons to excavate large amounts of earth.

The nuclear powers have conducted more than 2,000 nuclear test explosions (numbers are approximate, as some test results have been disputed):

  • United States: 1,054 tests by official count (involving at least 1,149 devices). 219 were atmospheric tests as defined by the CTBT. These tests include 904 at the Nevada Test Site, 106 at the Pacific Proving Grounds and other locations in the Pacific, 3 in the South Atlantic Ocean, and 17 other tests taking place in AmchitkaAlaska, Colorado, Mississippi, New Mexico and Nevada outside the NNSS (see Nuclear weapons and the United States for details). 24 tests are classified as British tests held at the NTS. There were 35 Plowshare detonations and 7 Vela Uniform tests 88 tests were safety experiments and 4 were transportation/storage tests. [20] Motion pictures were made of the explosions, later used to validate computer simulation predictions of explosions. [21]United States' table data.
  • Soviet Union: 715 tests (involving 969 devices) by official count, plus 13 unnumbered test failures. [22][23] Most were at their Southern Test Area at Semipalatinsk Test Site and the Northern Test Area at Novaya Zemlya. Others include rocket tests and peaceful-use explosions at various sites in Russia, Kazakhstan, Turkmenistan, Uzbekistan and Ukraine. Soviet Union's table data.
  • United Kingdom: 45 tests (21 in Australian territory, including three at the Montebello Islands, nine in mainland South Australia at Maralinga and Emu Field, some at Christmas Island (Kiritimati) in the Pacific Ocean, plus 24 in the United States at the Nevada Test Site as part of joint test series). [24] 43 safety tests (the Vixen series) are not included in that number, though safety experiments by other countries are. The United Kingdom's summary table.
  • France: 210 tests by official count (50 atmospheric, 160 underground [25] ), four atomic atmospheric tests at C.E.S.M. near Reggane, 13 atomic underground tests at C.E.M.O. near In Ekker in the French AlgerianSahara, and nuclear atmospheric and underground tests at and around Fangataufa and Moruroa Atolls in French Polynesia. Four of the In Ekker tests are counted as peaceful use, as they were reported as part of the CET's APEX (Application pacifique des expérimentations nucléaires), and given alternate names. France's summary table.
  • China: 45 tests (23 atmospheric and 22 underground), at Lop Nur Nuclear Weapons Test Base, in Malan, Xinjiang[26] There are two additional unnumbered failed tests. China's summary table.
  • India: Six underground explosions (including the first one in 1974), at Pokhran. India's summary table.
  • Pakistan: Six underground explosions at Ras Koh Hills and the Chagai District. [27]Pakistan's summary table.
  • North Korea: North Korea is the only country in the world that still tests nuclear weapons, and their tests have caused escalating tensions between them and the United States. Their most recent nuclear test was on September 3, 2017. North Korea's summary table

There may also have been at least three alleged but unacknowledged nuclear explosions (see list of alleged nuclear tests) including the Vela Incident.

From the first nuclear test in 1945 until tests by Pakistan in 1998, there was never a period of more than 22 months with no nuclear testing. June 1998 to October 2006 was the longest period since 1945 with no acknowledged nuclear tests.

A summary table of all the nuclear testing that has happened since 1945 is here: Worldwide nuclear testing counts and summary.

There are many existing anti-nuclear explosion treaties, notably the Partial Nuclear Test Ban Treaty and the Comprehensive Nuclear Test Ban Treaty. These treaties were proposed in response to growing international concerns about environmental damage among other risks. Nuclear testing involving humans also contributed to the formation of these treaties. Examples can be seen in the following articles:

The Partial Nuclear Test Ban treaty makes it illegal to detonate any nuclear explosion anywhere except underground, in order to reduce atmospheric fallout. Most countries have signed and ratified the Partial Nuclear Test Ban, which went into effect in October 1963. Of the nuclear states, France, China, and North Korea have never signed the Partial Nuclear Test Ban Treaty. [28]

The 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions everywhere, including underground. For that purpose, the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization is building an international monitoring system with 337 facilities located all over the globe. 85% of these facilities are already operational. [29] As of May 2012 [update] , the CTBT has been signed by 183 States, of which 157 have also ratified. However, for the Treaty to enter into force it needs to be ratified by 44 specific nuclear technology-holder countries. These "Annex 2 States" participated in the negotiations on the CTBT between 1994 and 1996 and possessed nuclear power or research reactors at that time. The ratification of eight Annex 2 states is still missing: China, Egypt, Iran, Israel and the United States have signed but not ratified the Treaty India, North Korea and Pakistan have not signed it. [30]

The following is a list of the treaties applicable to nuclear testing:

Name Agreement date In force date In effect today? Notes
Unilateral USSR ban March 31, 1958 March 31, 1958 no USSR unilaterally stops testing provided the West does as well.
Bilateral testing ban August 2, 1958 August 2, 1958 no USA agrees ban begins on 31 October 1958, 3 November 1958 for the Soviets, and lasts until abrogated by a USSR test on 1 September 1961.
Antarctic Treaty System December 1, 1959 June 23, 1961 yes Bans testing of all kinds in Antarctica.
Partial Nuclear Test Ban Treaty (PTBT) August 5, 1962 October 10, 1963 yes Ban on all but underground testing.
Outer Space Treaty January 27, 1967 October 10, 1967 yes Bans testing on the moon and other celestial bodies.
Treaty of Tlatelolco February 14, 1967 April 22, 1968 yes Bans testing in South America and the Caribbean Sea Islands.
Nuclear Non-proliferation Treaty January 1, 1968 March 5, 1970 yes Bans the proliferation of nuclear technology to non-nuclear nations.
Seabed Arms Control Treaty February 11, 1971 May 18, 1972 yes Bans emplacement of nuclear weapons on the ocean floor outside territorial waters.
Strategic Arms Limitation Treaty (SALT I) January 1, 1972 no A five-year ban on installing launchers.
Anti-Ballistic Missile Treaty May 26, 1972 August 3, 1972 no Restricts ABM development additional protocol added in 1974 abrogated by the US in 2002.
Agreement on the Prevention of Nuclear War June 22, 1973 June 22, 1973 yes Promises to make all efforts to promote security and peace.
Threshold Test Ban Treaty July 1, 1974 December 11, 1990 yes Prohibits higher than 150 kt for underground testing.
Peaceful Nuclear Explosions Treaty (PNET) January 1, 1976 December 11, 1990 yes Prohibits higher than 150 kt, or 1500kt in aggregate, testing for peaceful purposes.
Moon Treaty January 1, 1979 January 1, 1984 no Bans use and emplacement of nuclear weapons on the moon and other celestial bodies.
Strategic Arms Limitations Treaty (SALT II) June 18, 1979 no Limits strategic arms. Kept but not ratified by the US, abrogated in 1986.
Treaty of Rarotonga August 6, 1985 ? Bans nuclear weapons in South Pacific Ocean and islands. US never ratified.
Intermediate Range Nuclear Forces Treaty (INF) December 8, 1987 June 1, 1988 no Eliminated Intermediate Range Ballistic Missiles (IRBMs). Implemented by 1 June 1991. Both sides alleged the other was in violation of the treaty. Expired following U.S. withdrawal, 2 August 2019.
Treaty on Conventional Armed Forces in Europe November 19, 1990 July 17, 1992 yes Bans categories of weapons, including conventional, from Europe. Russia notified signatories of intent to suspend, 14 July 2007.
Strategic Arms Reduction Treaty I (START I) July 31, 1991 December 5, 1994 no 35-40% reduction in ICBMs with verification. Treaty expired 5 December 2009, renewed (see below).
Treaty on Open Skies March 24, 1992 January 1, 2002 yes Allows for unencumbered surveillance over all signatories.
US unilateral testing moratorium October 2, 1992 October 2, 1992 no George. H. W. Bush declares unilateral ban on nuclear testing. [31] Extended several times, not yet abrogated.
Strategic Arms Reduction Treaty (START II) January 3, 1993 January 1, 2002 no Deep reductions in ICBMs. Abrogated by Russia in 2002 in retaliation of US abrogation of ABM Treaty.
Southeast Asian Nuclear-Weapon-Free Zone Treaty (Treaty of Bangkok) December 15, 1995 March 28, 1997 yes Bans nuclear weapons from southeast Asia.
African Nuclear Weapon Free Zone Treaty (Pelindaba Treaty) January 1, 1996 July 16, 2009 yes Bans nuclear weapons in Africa.
Comprehensive Nuclear Test Ban Treaty (CTBT) September 10, 1996 yes (effectively) Bans all nuclear testing, peaceful and otherwise. Strong detection and verification mechanism (CTBTO). US has signed and adheres to the treaty, though has not ratified it.
Treaty on Strategic Offensive Reductions (SORT, Treaty of Moscow) May 24, 2002 June 1, 2003 no Reduces warheads to 1700–2200 in ten years. Expired, replaced by START II.
START I treaty renewal April 8, 2010 January 26, 2011 yes Same provisions as START I.

Over 500 atmospheric nuclear weapons tests were conducted at various sites around the world from 1945 to 1980. As public awareness and concern mounted over the possible health hazards associated with exposure to the nuclear fallout, various studies were done to assess the extent of the hazard. A Centers for Disease Control and Prevention/ National Cancer Institute study claims that nuclear fallout might have led to approximately 11,000 excess deaths, most caused by thyroid cancer linked to exposure to iodine-131. [32]

  • United States: Prior to March 2009, the U.S. was the only nation to compensate nuclear test victims. Since the Radiation Exposure Compensation Act of 1990, more than $1.38 billion in compensation has been approved. The money is going to people who took part in the tests, notably at the Nevada Test Site, and to others exposed to the radiation. [33][34]
  • France: In March 2009, the French Government offered to compensate victims for the first time and legislation is being drafted which would allow payments to people who suffered health problems related to the tests. The payouts would be available to victims' descendants and would include Algerians, who were exposed to nuclear testing in the Sahara in 1960. However, victims say the eligibility requirements for compensation are too narrow. [33]
  • United Kingdom: There is no formal British government compensation program. However, nearly 1,000 veterans of Christmas Island nuclear tests in the 1950s are engaged in legal action against the Ministry of Defense for negligence. They say they suffered health problems and were not warned of potential dangers before the experiments. [33]
  • Russia: Decades later, Russia offered compensation to veterans who were part of the 1954 Totsk test. However, there was no compensation to civilians sickened by the Totsk test. Anti-nuclear groups say there has been no government compensation for other nuclear tests. [33]
  • China: China has undertaken highly secretive atomic tests in remote deserts in a Central Asian border province. Anti-nuclear activists say there is no known government program for compensating victims. [33]

The following list is of milestone nuclear explosions. In addition to the atomic bombings of Hiroshima and Nagasaki, the first nuclear test of a given weapon type for a country is included, as well as tests that were otherwise notable (such as the largest test ever). All yields (explosive power) are given in their estimated energy equivalents in kilotons of TNT (see TNT equivalent). Putative tests (like Vela Incident) have not been included.


The primary system Edit

The Castle Bravo device was housed in a cylinder that weighed 23,500 pounds (10.7 t) and measured 179.5 inches (456 cm) in length and 53.9 inches (137 cm) in diameter. [3]

The primary device was a COBRA deuterium-tritium gas-boosted atomic bomb made by Los Alamos Scientific Laboratory, a very compact MK 7 device. This boosted fission device was tested in the Upshot Knothole Climax event and yielded 61 kilotonnes of TNT (260 TJ) (out of 50–70 kt expected yield range). It was considered successful enough that the planned operation series Domino, designed to explore the same question about a suitable primary for thermonuclear bombs, could be canceled. [6] : 197 The implosion system was quite lightweight at 410 kg (900 lb), because it eliminated the aluminium pusher shell around the tamper [Note 1] and used the more compact ring lenses, [Note 2] a design feature shared with the Mark 5, 12, 13 and 18 designs. The explosive material of the inner charges in the MK 7 was changed to the more powerful Cyclotol 75/25, instead of the Composition B used in most stockpiled bombs at that time, as Cyclotol 75/25 was denser than Composition B and thus could generate the same amount of explosive force in a smaller volume (it provided 13 percent more compressive energy than Comp B). [7] : 86 : 91 The composite uranium-plutonium COBRA core was levitated in a type-D pit. COBRA was Los Alamos' most recent product of design work on the "new principles" of the hollow core. [6] : 196 A copper pit liner encased within the weapon-grade plutonium inner capsule prevented DT gas diffusion in plutonium, a technique first tested in Greenhouse Item. [6] : 258 The assembled module weighed 830 kg (1,840 lb), measuring 770 mm (30.5 in) across. It was located at the end of the device, which, as seen in the declassified film, shows a small cone projecting from the ballistic case. This cone is the part of the paraboloid that was used to focus the radiation emanating from the primary to the secondary. [8]

Deuterium and lithium Edit

The device was called SHRIMP and had the same basic configuration (radiation implosion) as the Ivy Mike wet device, except with a different type of fusion fuel. SHRIMP used lithium deuteride (LiD), which is solid at room temperature Ivy Mike used cryogenic liquid deuterium (D2), which required elaborate cooling equipment. Castle Bravo was the first test by the United States of a practical deliverable fusion bomb, even though the TX-21 as proof-tested in the Bravo event was not weaponized. The successful test rendered obsolete the cryogenic design used by Ivy Mike and its weaponized derivative, the JUGHEAD, which was slated to be tested as the initial Castle Yankee. It also used a 7075 aluminium ballistic case 9.5 cm thick. Aluminium was used to drastically reduce the bomb's weight and simultaneously provided sufficient radiation confinement time to raise yield, a departure from the heavy stainless steel casing (304L or MIM 316L) employed by contemporary weapon-projects. [6] : 54 : 237 [9]

The SHRIMP was at least in theory and in many critical aspects identical in geometry to the RUNT and RUNT II devices later proof-fired in Castle Romeo and Castle Yankee respectively. On paper it was a scaled-down version of these devices, and its origins can be traced back to the spring and summer of 1953. The United States Air Force indicated the importance of lighter thermonuclear weapons for delivery by the B-47 Stratojet and B-58 Hustler. Los Alamos National Laboratory responded to this indication with a follow-up enriched version of the RUNT scaled down to a 3/4 scale radiation-implosion system called the SHRIMP. The proposed weight reduction (from TX-17's 42,000 pounds (19,000 kg) to TX-21's 25,000 pounds (11,000 kg)) would provide the Air Force with a much more versatile deliverable gravity bomb. [6] : 237 The final version tested in Castle used partially enriched lithium as its fusion fuel. Natural lithium is a mixture of lithium-6 and lithium-7 isotopes (with 7.5% of the former). The enriched lithium used in Bravo was nominally 40% lithium-6 (the balance was the much more common lithium-7, which was incorrectly assumed to be inert). The fuel slugs varied in enrichment from 37 to 40% in 6 Li, and the slugs with lower enrichment were positioned at the end of the fusion-fuel chamber, away from the primary. The lower levels of lithium enrichment in the fuel slugs, compared with the ALARM CLOCK and many later hydrogen weapons, were due to shortages in enriched lithium at that time, as the first of the Alloy Development Plants (ADP) started production by the fall of 1953. [10] : 208 The volume of LiD fuel used was approximately 60% the volume of the fusion fuel filling used in the wet SAUSAGE and dry RUNT I and II devices, or about 500 liters (110 imp gal 130 U.S. gal), [Note 3] corresponding to about 400 kg of lithium deuteride (as LiD has a density of 0.78201 g/cm 3 ). [11] : 281 The mixture cost about 4.54 USD/g at that time. The fusion burn efficiency was close to 25.1%, the highest attained efficiency of the first thermonuclear weapon generation. This efficiency is well within the figures given in a November 1956 statement, when a DOD official disclosed that thermonuclear devices with efficiencies ranging from 15% to up about 40% had been tested. [6] : 39 Hans Bethe reportedly stated independently that the first generation of thermonuclear weapons had (fusion) efficiencies varying from as low as 15% to up about 25%.

The thermonuclear burn would produce (like the fission fuel in the primary) pulsations (generations) of high-energy neutrons with an average temperature of 14 MeV through Jetter's cycle.

Jetter's cycle Edit

The Jetter cycle is a combination of reactions involving lithium, deuterium, and tritium. It consumes Lithium-6 and deuterium, and in two reactions (with energies of 17.6 MeV and 4.8 MeV, mediated by a neutron and tritium) it produces two alpha particles. [12] : 4

The reaction would produce high-energy neutrons with 14 MeV, and its neutronicity was estimated at ≈0.885 (for a Lawson criterion of ≈1.5).

Maybe additional tritium for high-yield Edit

As SHRIMP, along with the RUNT I and ALARM CLOCK, were to be high-yield shots required to assure the thermonuclear “emergency capability”, their fusion fuel may have been spiked with additional tritium, in the form of 6 LiT. [10] : 236 All of the high-energy 14 MeV neutrons would cause fission in the uranium fusion tamper wrapped around the secondary and the spark plug's plutonium rod. The ratio of deuterium (and tritium) atoms burned by 14 MeV neutrons spawned by the burning was expected to vary from 5:1 to 3:1, a standardization derived from Mike, [10] while for these estimations, the ratio of 3:1 was predominantly used in ISRINEX. The neutronicity of the fusion reactions harnessed by the fusion tamper would dramatically increase the yield of the device.

SHRIMP's indirect drive Edit

Attached to the cylindrical ballistic case was a natural-uranium liner, the radiation case, that was about 2.5 cm thick. Its internal surface was lined with a copper liner that was about 240 μm thick, and made from 0.08-μm thick copper foil, to increase the overall albedo of the hohlraum. [17] [18] [ 0.08 μm?? - verification needed ] Copper possesses excellent reflecting properties, and its low cost, compared to other reflecting materials like gold, made it useful for mass-produced hydrogen weapons. Hohlraum albedo is a very important design parameter for any inertial-confinement configuration. A relatively high albedo permits higher interstage coupling due to the more favorable azimuthal and latitudinal angles of reflected radiation. The limiting value of the albedo for high-Z materials is reached when the thickness is 5–10 g/cm 2 , or 0.5–1.0 free paths. Thus, a hohlraum made of uranium much thicker than a free path of uranium would be needlessly heavy and costly. At the same time, the angular anisotropy increases as the atomic number of the scatterer material is reduced. Therefore, hohlraum liners require the use of copper (or, as in other devices, gold or aluminium), as the absorption probability increases with the value of Zeff of the scatterer. There are two sources of X-rays in the hohlraum: the primary's irradiance, which is dominant at the beginning and during the pulse rise and the wall, which is important during the required radiation temperature's (Tr) plateau. The primary emits radiation in a manner similar to a flash bulb, and the secondary needs constant Tr to properly implode. [19] This constant wall temperature is dictated by the ablation pressure requirements to drive compression, which lie on average at about 0.4 keV (out of a range of 0.2 to 2 keV) [Note 4] , corresponding to several million kelvins. Wall temperature depended on the temperature of the primary's core which peaked at about 5.4 keV during boosted-fission. [22] : 1–11 [20] : 9 The final wall-temperature, which corresponds to energy of the wall-reradiated X-rays to the secondary's pusher, also drops due to losses from the hohlraum material itself. [17] [Note 5] Natural uranium nails, lined to the top of their head with copper, attached the radiation case to the ballistic case. The nails were bolted in vertical arrays in a double-shear configuration to better distribute the shear loads. This method of attaching the radiation case to the ballistic case was first used successfully in the Ivy Mike device. The radiation case had a parabolic end, which housed the COBRA primary that was employed to create the conditions needed to start the fusion reaction, and its other end was a cylinder, as also seen in Bravo's declassified film.

The space between the uranium fusion tamper, [Note 6] and the case formed a radiation channel to conduct X-rays from the primary to the secondary assembly the interstage. It is one of the most closely guarded secrets of a multistage thermonuclear weapon. Implosion of the secondary assembly is indirectly driven, and the techniques used in the interstage to smooth the spatial profile (i.e. reduce coherence and nonuniformities) of the primary's irradiance are of utmost importance. This was done with the introduction of the channel filler – an optical element used as a refractive medium, [23] : 279 also encountered as random-phase plate in the ICF laser assemblies. This medium was a polystyrene plastic foam filling, extruded or impregnated with a low-molecular-weight hydrocarbon (possibly methane gas), which turned to a low-Z plasma from the X-rays, and along with channeling radiation it modulated the ablation front on the high-Z surfaces it "tamped" [Note 7] the sputtering effect that would otherwise "choke" radiation from compressing the secondary. [Note 8] The reemitted X-rays from the radiation case must be deposited uniformly on the outer walls of the secondary’s tamper and ablate it externally, driving the thermonuclear fuel capsule (increasing the density and temperature of the fusion fuel) to the point needed to sustain a thermonuclear reaction. [25] ( pp438-454 ) (see Nuclear weapon design). This point is above the threshold where the fusion fuel would turn opaque to its emitting radiation, as determined from its Rosseland opacity, meaning that the generated energy balances the energy lost to fuel's vicinity (as radiation, particle losses). After all, for any hydrogen weapon system to work, this energy equilibrium must be maintained through the compression equilibrium between the fusion tamper and the spark plug (see below), hence their name equilibrium supers. [26] : 185

Since the ablative process takes place on both walls of the radiation channel, a numerical estimate made with ISRINEX (a thermonuclear explosion simulation program) suggested that the uranium tamper also had a thickness of 2.5 cm, so that an equal pressure would be applied to both walls of the hohlraum. The rocket effect on the surface of tamper's wall created by the ablation of its several superficial layers would force an equal mass of uranium that rested in the remainder of the tamper to speed inwards, thus imploding the thermonuclear core. At the same time, the rocket effect on the surface of the hohlraum would force the radiation case to speed outwards. The ballistic case would confine the exploding radiation case for as long as necessary. The fact that the tamper material was uranium enriched in 235 U is primarily based on the final fission reaction fragments detected in the radiochemical analysis, which conclusively showed the presence of 237 U, found by the Japanese in the shot debris. [27] : 282 The first-generation thermonuclear weapons (MK-14, 16, 17, 21, 22 and 24) all used uranium tampers enriched to 37.5% 235 U. [27] : 16 The exception to this was the MK-15 ZOMBIE that used a 93.5% enriched fission jacket.

The secondary assembly Edit

The secondary assembly was the actual SHRIMP component of the weapon. The weapon, like most contemporary thermonuclear weapons at that time, bore the same codename as the secondary component. The secondary was situated in the cylindrical end of the device, where its end was locked to the radiation case by a type of mortise and tenon joint. The hohlraum at its cylindrical end had an internal projection, which nested the secondary and had better structural strength to support the secondary's assembly, which had most of the device's mass. A visualization to this is that the joint looked much like a cap (the secondary) fitted in a cone (the projection of the radiation case). Any other major supporting structure would interfere to radiation transfer from the primary to the secondary and complex vibrational behavior. With this form of joint bearing most of the structural loads of the secondary, the latter and the hohlraum-ballistic case ensemble behaved as a single mass sharing common eigenmodes. To reduce excessive loading of the joint, especially during deployment of the weapon, the forward section of the secondary (i.e. the thermal blast/heat shield) was anchored to the radiation case by a set of thin wires, which also aligned the center line of the secondary with the primary, as they diminished bending and torsional loads on the secondary, another technique adopted from the SAUSAGE. [25] : 438–454 The secondary assembly was an elongated truncated cone. From its front part (excluding the blast-heat shield) to its aft section it was steeply tapered. Tapering was used for two reasons. First, radiation drops by the square of the distance, hence radiation coupling is relatively poor in the aftermost sections of the secondary. This made the use of a higher mass of the then scarce fusion fuel in the rear end of the secondary assembly ineffective and the overall design wasteful. This was also the reason why the lower-enriched slugs of fusion fuel were placed far aft of the fuel capsule. Second, as the primary could not illuminate the whole surface of the hohlraum, in part due to the large axial length of the secondary, relatively small solid angles would be effective to compress the secondary, leading to poor radiation focusing. By tapering the secondary, the hohlraum could be shaped as a cylinder in its aft section obviating the need to machine the radiation case to a parabola at both ends. This optimized radiation focusing and enabled a streamlined production line, as it was cheaper, faster and easier to manufacture a radiation case with only one parabolic end. The tapering in this design was much steeper than its cousins, the RUNT, and the ALARM CLOCK devices. SHRIMP's tapering and its mounting to the hohlraum apparently made the whole secondary assembly resemble the body of a shrimp. The secondary's length is defined by the two pairs of dark-colored diagnostic hot spot pipes attached to the middle and left section of the device. [Note 9] These pipe sections were 8 + 5 ⁄ 8 inches (220 mm) in diameter and 40 feet (12 m) long and were butt-welded end-to-end to the ballistic case leading out to the top of the shot cab. They would carry the initial reaction's light up to the array of 12 mirror towers built in an arc on the artificial 1-acre (0.40 ha) shot island created for the event. From those pipes, mirrors would reflect early bomb light from the bomb casing to a series of remote high-speed cameras, so that Los Alamos could determine both the simultaneity of the design (i.e. the time interval between primary's firing and secondary's ignition) and the thermonuclear burn rate in these two crucial areas of the secondary device. [6] : 63 : 229

This secondary assembly device contained the lithium deuteride fusion fuel in a stainless-steel canister. Running down to the center of the secondary was a 1.3 cm thick hollow cylindrical rod of plutonium, nested in the steel canister. This was the spark plug, a tritium-boosted fission device. It was assembled by plutonium rings and had a hollow volume inside that measured about 0.5 cm in diameter. This central volume was lined with copper, which like the liner in the primary's fissile core prevented DT gas diffusion in plutonium. The spark plug's boosting charge contained about 4 grams of tritium and, imploding together with the secondary's compression, was timed to detonate by the first generations of neutrons that arrived from the primary. Timing was defined by the geometric characteristics of the sparkplug (its uncompressed annular radius), which detonated when its criticality, or keff, transcended 1. Its purpose was to compress the fusion material around it from its inside, equally applying pressure with the tamper. The compression factor of the fusion fuel and its adiabatic compression energy determined the minimal energy required for the spark plug to counteract the compression of the fusion fuel and the tamper's momentum. The spark plug weighed about 18 kg, and its initial firing yielded 0.6 kilotonnes of TNT (2.5 TJ). Then it would be completely fissioned by the fusion neutrons, contributing about 330 kilotonnes of TNT (1,400 TJ) to the total yield. The energy required by the spark plug to counteract the compression of the fusion fuel was lower than the primary's yield because coupling of the primary’s energy in the hohlraum is accompanied by losses due to the difference between the X-ray fireball and the hohlraum temperatures. [20] The neutrons entered the assembly by a small hole [Note 10] through the ≈28 cm thick 238 U blast-heat shield. It was positioned in front of the secondary assembly facing the primary. Similar to the tamper-fusion capsule assembly, the shield was shaped as a circular frustum, with its small diameter facing the primary's side, and with its large diameter locked by a type of mortise and tenon joint to the rest of the secondary assembly. The shield-tamper ensemble can be visualized as a circular bifrustum. All parts of the tamper were similarly locked together to provide structural support and rigidity to the secondary assembly. Surrounding the fusion-fuel–spark-plug assembly was the uranium tamper with a standoff air-gap about 0.9 cm wide that was to increase the tamper's momentum, a levitation technique used as early as Operation Sandstone and described by physicist Ted Taylor as hammer-on-the-nail-impact. Since there were also technical concerns that high-Z tamper material would mix rapidly with the relatively low-density fusion fuel — leading to unacceptably large radiation losses — the stand-off gap also acted as a buffer to mitigate the unavoidable and undesirable Taylor mixing.

Use of boron Edit

Boron was used at many locations in this dry system it has a high cross-section for the absorption of slow neutrons, which fission 235 U and 239 Pu, but a low cross-section for the absorption of fast neutrons, which fission 238 U. Because of this characteristic, 10 B deposited onto the surface of the secondary stage would prevent predetonation of the spark plug by stray neutrons from the primary without interfering with the subsequent fissioning of the 238 U of the fusion tamper wrapping the secondary. Boron also played a role in increasing the compressive plasma pressure around the secondary by blocking the sputtering effect, leading to higher thermonuclear efficiency. Because the structural foam holding the secondary in place within the casing was doped with 10 B, [6] : 179 the secondary was compressed more highly, at a cost of some radiated neutrons. (The Castle Koon MORGENSTERN device did not use 10 B in its design as a result, the intense neutron flux from its RACER IV primary predetonated the spherical fission spark plug, which in turn "cooked" the fusion fuel, leading to an overall poor compression. [6] : 317 ) The plastic's low molecular weight is unable to implode the secondary's mass. Its plasma-pressure is confined in the boiled-off sections of the tamper and the radiation case so that material from neither of these two walls can enter the radiation channel that has to be open for the radiation transit. [10]

Hydrogen Bomb

On August 12, 1953 the Soviet Union detonated a thermonuclear (“hydrogen”) bomb at the Semipalatinsk test site in northern Kazakhstan. Work on the super-bomb had begun in 1946, three years before the Soviet Union exploded its first atomic bomb. The project was organized by the First Chief Directorate under Lavrentii Beria, Minister of State Security (MGB). It was headed by Igor Kurchatov (1903-60), a physicist who had been appointed scientific director of the Soviet Union’s nuclear project in 1943. The design for the bomb was based on the “layer cake” concept developed by the physicist Andrei Sakharov (1921-89), according to which alternate layers of thermonuclear material and uranium-238 were placed in a fission bomb.

Unlike the first Soviet atomic bomb the development of which was hastened by espionage in the United States, the first Soviet hydrogen bomb was of an original design. In the spring of 1954, the United States tested its own two-stage super-bomb in the Pacific. This type of “deliverable” weapon was replicated by Soviet physicists and first tested on November 22, 1955.

A by-product of the Cold War, the Soviet nuclear arms program was given the highest priority by Stalin and was continued apace by his successors. Before Stalin’s death in March 1953, there had been three nuclear tests between August 1953 and the end of 1955 there were sixteen including three thermonuclear explosions. In October 1953 Sakharov was elected to full membership of the Academy of Sciences at the age of thirty-two, and he, Kurchatov, and several other physicists were made Heroes of Socialist Labor. However, there was political fallout from the hydrogen bomb. In a speech of March 1954, Georgii Malenkov, chairman of the Council of Ministers, referred to the danger of “a new world war, which with modern weapons means the end of world civilization.” Raising this specter went beyond what Khrushchev and other party leaders were willing to acknowledge publicly, and even though he subsequently reverted to the standard line that nuclear aggression by the United States would lead to the “collapse of the capitalist social system,” Malenkov could not undo the damage to his own political career.


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. [6] 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. [7]

Though large quantities of vague data have been officially released, and larger quantities of vague data have been unofficially leaked by former bomb designers, most public descriptions of nuclear weapon design details rely to some degree on speculation, reverse engineering from known information, or comparison with similar fields of physics (inertial confinement fusion is the primary example). Such processes have resulted in a body of unclassified knowledge about nuclear bombs that is generally consistent with official unclassified information releases, 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.

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.

Surrounding the other components is a hohlraum or radiation case, a container that traps the first stage or primary's energy inside temporarily. The outside of this radiation case, which is also normally the outside casing of the bomb, is the only direct visual evidence publicly available of any thermonuclear bomb component's configuration. Numerous photographs of various thermonuclear bomb exteriors have been declassified. [8]

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 239
or 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 ( 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 ( 239
or 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. [9] [10]

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 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 is a good example a small flaw allowed the neutron flux from the primary to prematurely begin heating the secondary, weakening the compression enough to prevent any fusion.

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 in a report titled "Dual Use Nuclear Technology". [11] 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 235
/ 239
Spark Plug while the latter refers to an X-ray reflector typically a cylinder made out 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, gold was used as a coating over the uranium to enhance the blackbody effect. [12] 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 [13] ) each protruding through the outer edge of the reflector with one end in each section all are clamped to the carriage and arranged more or less evenly around the casing's circumference. The neutron guns are tilted so the neutron emitting end of each gun end is pointed towards the central axis of the bomb. Neutrons from each neutron gun pass through and are focused by the neutron focus lens towards the centre of primary in order to boost the initial fissioning of the plutonium. A "polystyrene Polarizer/Plasma Source" is also shown (see below).

The first U.S. government document to mention the interstage was only recently released to the public promoting the 2004 initiation of the Reliable Replacement Warhead 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". [14] 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. [15]

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. [16]

Summary Edit

A simplified summary of the above explanation is:

  1. A (relatively) small fission bomb known as the "primary" explodes.
  2. 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.
  3. Energy released by the fusion events continues heating the fuel, keeping the reaction going.
  4. 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.

The basic idea of the Teller–Ulam configuration is that each "stage" would undergo fission or fusion (or both) and release energy, much of which would be transferred to another stage to trigger it. 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 rays 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:

    exerted by the X-rays. This was the first idea put forth by Howard Morland in the article in The Progressive.
  • X-rays creating a plasma in the radiation channel's filler (a polystyrene or "FOGBANK" plastic foam). This was a second idea put forward by Chuck Hansen and later by Howard Morland. /Pusher ablation. This is the concept best supported by physical analysis.

Radiation pressure Edit

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

For two thermonuclear bombs for which the general size and primary characteristics are well understood, the Ivy Mike test bomb and the modern W-80 cruise missile warhead variant of the W-61 design, the radiation pressure was calculated to be 73 million bars (7.3 trillion pascals) for the Ivy Mike design and 1,400 million bars (140 trillion pascals) for the W-80. [17]

Foam plasma pressure Edit

Foam plasma pressure is the concept that Chuck Hansen introduced during the Progressive case, based on research that located declassified documents listing special foams as liner components within the radiation case of thermonuclear weapons.

The sequence of firing the weapon (with the foam) would be as follows:

  1. The high explosives surrounding the core of the primary fire, compressing the fissile material into a supercritical state and beginning the fission chain reaction.
  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.
  4. 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 (Li6) atom splits into one tritium atom and one alpha particle. Then begins a fusion reaction between the tritium and the deuterium, releasing even more neutrons, and a huge amount of energy.
  5. The fuel undergoing the fusion reaction emits a large flux of high energy neutrons (17.6 MeV [2.82 pJ]), which irradiates the 238
    tamper (or the 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.

  1. Warhead before firing primary (fission bomb) at top, secondary (fusion fuel) at bottom, all suspended in polystyrene foam.
  2. High-explosive fires in primary, compressing plutonium core into supercriticality and beginning a fission reaction.
  3. Fission primary emits X-rays that are scattered along the inside of the casing, irradiating the polystyrene foam.
  4. Polystyrene foam becomes plasma, compressing secondary, and plutonium sparkplug begins to fission.
  5. Compressed and heated, lithium-6 deuteride fuel produces tritium ( 3
    ) and begins the fusion reaction. The neutron flux produced causes the 238
    tamper to fission. A fireball starts to form.

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

Tamper-pusher ablation Edit

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.

  1. Warhead before firing. The nested spheres at the top are the fission primary the cylinders below are the fusion secondary device.
  2. Fission primary's explosives have detonated and collapsed the primary's fissile pit.
  3. The primary's fission reaction has run to completion, and the primary is now at several million degrees and radiating gamma and hard X-rays, heating up the inside of the hohlraum and the shield and secondary's tamper.
  4. The primary's reaction is over and it has expanded. The surface of the pusher for the secondary is now so hot that it is also ablating or expanding away, pushing the rest of the secondary (tamper, fusion fuel, and fissile spark plug) inwards. The spark plug starts to fission. Not depicted: the radiation case is also ablating and expanding outwards (omitted for clarity of diagram).
  5. The secondary's fuel has started the fusion reaction and shortly will burn up. A fireball starts to form.

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

Applying the more detailed form of those calculations to the Ivy Mike device yields vaporized pusher gas expansion velocity of 290 kilometres per second (180 mi/s) and an implosion velocity of perhaps 400 km/s (250 mi/s) if + 3 ⁄ 4 of the total tamper/pusher mass is ablated off, the most energy efficient proportion. For the W-80 the gas expansion velocity is roughly 410 km/s (250 mi/s) and the implosion velocity 570 km/s (350 mi/s). The pressure due to the ablating material is calculated to be 5.3 billion bars (530 trillion pascals) in the Ivy Mike device and 64 billion bars (6.4 quadrillion pascals) in the W-80 device. [17]

Comparing implosion mechanisms Edit

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

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

United States Department of Defense official declassification reports indicate that foamed plastic materials are or may be used in radiation case liners, and despite the low direct plasma pressure they may be of use in delaying the ablation until energy has distributed evenly and a sufficient fraction has reached the secondary's tamper/pusher. [18]

Richard Rhodes' book Dark Sun stated that a 1-inch-thick (25 mm) 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. [18]

A number of possible variations to the weapon design have been proposed:

  • Either the tamper or the casing have been proposed to be made of 235
    (highly enriched uranium) in the final fission jacket. The far more expensive 235
    is also fissionable with fast neutrons like the 238
    in depleted or natural uranium, but its fission-efficiency is higher. This is because 235
    nuclei also undergo fission by slow neutrons ( 238
    nuclei require a minimum energy of about 1 megaelectronvolt (0.16 pJ) 1 mega-electron volt), and because these slower neutrons are produced by other fissioning 235
    nuclei in the jacket (in other words, 235
    supports the nuclear chain reaction whereas 238
    does not). Furthermore, a 235
    jacket fosters neutron multiplication, whereas 238
    nuclei consume fusion neutrons in the fast-fission process. Using a final fissionable/fissile jacket of 235
    would thus increase the yield of a Teller–Ulam bomb above a depleted uranium or natural uranium jacket. This has been proposed specifically for the W87 warheads retrofitted to currently deployed LGM-30 Minuteman III ICBMs.
  • In some descriptions, additional internal structures exist to protect the secondary from receiving excessive neutrons from the primary.
  • The inside of the casing may or may not be specially machined to "reflect" the X-rays. X-ray "reflection" is not like light reflecting off of a mirror, but rather the reflector material is heated by the X-rays, causing the material itself to emit X-rays, which then travel to the secondary.

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 (100 PJ) B41 nuclear bomb. [19] The Soviet Union is thought to have used multiple stages (including more than one tertiary fusion stage) in their 50 Mt (210 PJ) (100 Mt (420 PJ) 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).

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 [20] ( pp192–193 ) [21] [ better source needed ] although this is debated (see more: Arbitrarily large yield debate). Finally, efficient bombs (but not so-called neutron bombs) end with the fissioning of the final natural uranium tamper, something that could not normally be achieved without the neutron flux provided by the fusion reactions in secondary or tertiary stages. Such designs are suggested to be capable of being scaled up to an arbitrary large yield (with apparently as many fusion stages as desired), [20] ( pp192–193 ) [21] [ better source needed ] potentially to the level of a "doomsday device." However, usually such weapons were not more than a dozen megatons, which was generally considered enough to destroy even the most hardened practical targets (for example, a control facility such as the Cheyenne Mountain Complex). Even such large bombs have been replaced by smaller-yield bunker buster type nuclear bombs (see more: nuclear bunker buster).

As discussed above, 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 500 kt (2,100 TJ).

United States Edit

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, [12] ( p207 ) at the start of what would become the Manhattan Project. [4] Teller spent much of the Manhattan Project attempting to figure out how to make the design work, preferring it to work on the atomic bomb, and over the last year of the project was assigned exclusively to the task. [12] ( pp117,248 ) However once World War II ended, there was little impetus to devote many resources to the Super, as it was then known. [22] ( p202 )

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. [23] ( pp1–2 ) The debate covered matters that were alternatively strategic, pragmatic, and moral. [23] ( p16 ) In their Report of the General Advisory Committee, Robert Oppenheimer and colleagues concluded that "[t]he extreme danger to mankind inherent in the proposal [to develop thermonuclear weapons] wholly outweighs any military advantage." Despite the objections raised, on January 31, 1950, President Harry S. Truman made the decision to go forward with the development of the new weapon. [22] ( pp212–214 )

But deciding to do it did not make it a reality, and Teller and other U.S. physicists struggled to find a workable design. [23] ( pp91–92 ) Stanislaw Ulam, a co-worker of Teller, made the first key conceptual leaps towards a workable fusion design. Ulam's two innovations that rendered the fusion bomb practical were that compression of the thermonuclear fuel before extreme heating was a practical path towards the conditions needed for fusion, and the idea of staging or placing a separate thermonuclear component outside a fission primary component, and somehow using the primary to compress the secondary. Teller then realized that the gamma and X-ray radiation produced in the primary could transfer enough energy into the secondary to create a successful implosion and fusion burn, if the whole assembly was wrapped in a hohlraum or radiation case. [4] Teller and his various proponents and detractors later disputed the degree to which Ulam had contributed to the theories underlying this mechanism. Indeed, shortly before his death, and in a last-ditch effort to discredit Ulam's contributions, Teller claimed that one of his own "graduate students" had proposed the mechanism. [ citation needed ]

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, [24] it raised expectations to a near certainty that the concept would work.

On November 1, 1952, the Teller–Ulam configuration was tested at full scale in the "Ivy Mike" shot at an island in the Enewetak Atoll, with a yield of 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, 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, [ citation needed ] 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 expected) and is the largest U.S. bomb ever tested.

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 [25] deployed on Polaris ballistic missile submarines, megaton-class warheads were as small as 18 inches (0.46 m) in diameter and 720 pounds (330 kg) 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 (see the section on the W88 below). [8]

Soviet Union Edit

The first Soviet fusion design, developed by Andrei Sakharov and Vitaly Ginzburg in 1949 (before the Soviets had a working fission bomb), was dubbed the Sloika, after a Russian layer cake, and was not of the Teller–Ulam configuration. It used alternating layers of fissile material and lithium deuteride fusion fuel spiked with tritium (this was later dubbed Sakharov's "First Idea"). Though nuclear fusion might have been technically achievable, it did not have the scaling property of a "staged" weapon. Thus, such a design could not produce thermonuclear weapons whose explosive yields could be made arbitrarily large (unlike U.S. designs at that time). The fusion layer wrapped around the fission core could only moderately multiply the fission energy (modern Teller–Ulam designs can multiply it 30-fold). Additionally, the whole fusion stage had to be imploded by conventional explosives, along with the fission core, substantially multiplying 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% 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. [26] ( p299 ) In late 1953 physicist Viktor Davidenko achieved the first breakthrough, that of keeping the primary and secondary parts of the bombs in separate pieces ("staging"). The next breakthrough was discovered and developed by Sakharov and Yakov Zel'dovich, that of using the X-rays from the fission bomb to compress the secondary before fusion ("radiation implosion"), 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, a 50 Mt (210 PJ) hydrogen bomb that derived almost 97% of its energy from fusion. It was the largest nuclear weapon developed and tested by any country.

United Kingdom Edit

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. However, the British were allowed to observe the U.S. 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. [27]

Because of these difficulties, in 1955 British 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. [27]

In 1957 the Operation Grapple tests were carried out. The first test, Green Granite was a prototype fusion bomb, but failed to produce equivalent yields compared to the U.S. 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). [27]

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 November 8 and yielded approximately 1.8 Mt (7.5 PJ). On April 28, 1958 a bomb was dropped that yielded 3 Mt (13 PJ)—Britain's most powerful test. Two final air burst tests on September 2 and September 11, 1958, dropped smaller bombs that yielded around 1 Mt (4.2 PJ) each. [27]

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. [27]

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. [27] [ unreliable source? ]

China Edit

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. [28] 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. [29]

A story in The New York Times by William Broad [30] 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. [31] (This line of investigation eventually resulted in the abortive trial of Wen Ho Lee.)

France Edit

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 metres (1,710 ft). The result of this test was significant atmospheric contamination. [32] Very little is known about France's development of the Teller–Ulam design, beyond the fact that France detonated a 2.6 Mt (11 PJ) 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. [27]

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. [32] 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. [33] The M51.1 missiles are intended to be replaced with the new M51.2 warhead beginning in 2016, which has a 3,000 kilometres (1,900 mi) greater range than the M51.1. [33]

France also 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. [27] [ 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
as a byproduct. [34]

India Edit

On May 11, 1998, India announced that it had detonated a thermonuclear bomb in its Operation Shakti tests ("Shakti-I", specifically). [35] [36] Dr. Samar Mubarakmand, a Pakistani nuclear physicist, asserted that if Shakti-I had been a thermonuclear test, the device had failed to fire. [37] 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. [38] 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 (3.1 mi), to ensure that the houses in that village do not suffer significant damage. [39] Another cited reason was that radioactivity released from yields significantly more than 45 Kilotons might not have been contained fully. [39] 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. [38]

The yield of India's hydrogen bomb test remains highly debatable among the Indian science community and the international scholars. [40] The question of politicisation and disputes between Indian scientists further complicated the matter. [41]

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, [42] arguing that Santhanam's claims are unscientific. [36] 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). [43] 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’. [39]

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. [39] [44]

Israel Edit

Israel is alleged to possess thermonuclear weapons of the Teller–Ulam design, [45] 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. [46] [47] ( p271 ) [48] ( pp297–300 )

It is well established that Edward Teller advised and guided the Israeli establishment on general nuclear matters for some twenty years. [49] ( pp289–293 ) Between 1964 and 1967, Teller made six visits to Israel where he lectured at the Tel Aviv University on general topics in theoretical physics. [50] 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. [48] ( pp297–300 ) 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. [48] ( pp297–300 ) After he conveyed the matter to the higher level of the U.S. government, Teller reportedly said: "They [Israel] have it, and they were clever enough to trust their research and not to test, they know that to test would get them into trouble." [48] ( pp297–300 )

Pakistan Edit

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). [37] None of these boosted fission devices was the thermonuclear weapon design, according to KRL and PAEC. [37]

North Korea Edit

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. [51] [52] In January 2016, North Korea claimed to have successfully tested a hydrogen bomb, [53] although only a magnitude 5.1 seismic event was detected at the time of the test, [54] 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. [55]

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. [56] U.S. Intelligence released an early assessment that the yield estimate was 140 kt (590 TJ), [57] with an uncertainty range of 70 to 280 kt (290 to 1,170 TJ). [58]

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 kt (1,000 TJ), while noting the estimate had some uncertainty and an undisclosed margin of error. [59] [60]

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". [61]

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. United States Department of Energy (DOE) policy has been, and continues to be, that they do not acknowledge when "leaks" occur, because doing so would acknowledge the accuracy of the supposed leaked information. Aside from images of the warhead casing, most information in the public domain about this design is relegated to a few terse statements by the DOE and the work of a few individual investigators.

DOE statements Edit

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." [62] 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). [63]

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 (see, 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.

The Progressive case Edit

Most of the current ideas on the workings of the Teller–Ulam design came into public awareness after the Department of Energy (DOE) attempted to censor a magazine article by U.S. antiweapons activist Howard Morland in 1979 on the "secret of the hydrogen bomb". In 1978, Morland had decided that discovering and exposing this "last remaining secret" would focus attention onto the arms race and allow citizens to feel empowered to question official statements on the importance of nuclear weapons and nuclear secrecy. [ citation needed ] Most of Morland's ideas about how the weapon worked were compiled from highly accessible sources—the drawings that most inspired his approach came from none other than the Encyclopedia Americana. [ citation needed ] Morland also interviewed (often informally) many former Los Alamos scientists (including Teller and Ulam, though neither gave him any useful information), and 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). [64]

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

Morland and his lawyers disagreed on all points, but the injunction was granted, as the judge in the case felt that it was safer to grant the injunction and allow Morland, et al., to appeal, which they did in United States v. The Progressive (1979).

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. [65] 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". [64] [66]

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 a number of nations 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.

In January 1986, Soviet leader Mikhail Gorbachev publicly proposed a three-stage program for abolishing the world's nuclear weapons by the end of the 20th century. [67] 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. [68] 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. [69] 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. [68] 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. [70]

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. [71]

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. [72]

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. [73] The resulting fire caused extensive radioactive contamination. [74] Personnel involved in the cleanup failed to recover all the debris from three of the bombs, and one bomb was not recovered. [75]

Ivy Mike Edit

In his 1995 book Dark Sun: The Making of the Hydrogen Bomb, author Richard Rhodes describes in detail the internal components of the "Ivy Mike" Sausage device, based on information obtained from extensive interviews with the scientists and engineers who assembled it. According to Rhodes, the actual mechanism for the compression of the secondary was a combination of the radiation pressure, foam plasma pressure, and tamper-pusher ablation theories described above the radiation from the primary heated the polyethylene foam lining 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. [12]

Watch the video: Hiroshima: Dropping The Bomb - Hiroshima - BBC (January 2022).