Tsar Bomba

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Tsar_Bomba 

 

Tsar Bomba
Ground-level view of detonation (source: Rosatom State Corporation Communications Department: Rosatom: 20-08-2020 public release)
Type	Thermonuclear
Place of origin	Soviet Union
Production history
Designer	Yulii Khariton, Andrei Sakharov, Viktor Adamsky, Yuri Babayev and Yuri Smirnov [ru], Yuri Trutnev, and Yakov Zeldovich
Manufacturer	Soviet Union
No. built	1 operational (2 "prototypes")
Specifications
Mass	27,000 kg (60,000 lb)
Length	8 m (26 ft)
Diameter	2.1 m (6 ft 11 in)
Detonation mechanism	Barometric sensor
Blast yield	50–58 megatons of TNT (210–240 PJ)

Coordinates: 73°48′26″N 54°58′54″E

The Tsar Bomba (Russian: Царь-бо́мба) (code name: Ivan or Vanya), also known by the alphanumerical designation "AN602", was a thermonuclear aerial bomb, and the most powerful nuclear weapon ever created and tested. The Soviet physicist Andrei Sakharov oversaw the project at Arzamas-16, while the main work of design was by Sakharov, Viktor Adamsky, Yuri Babayev, Yuri Smirnov [ru], and Yuri Trutnev. The project was ordered by Nikita Khrushchev in July 1961 as part of the Soviet resumption of nuclear testing after the Test Ban Moratorium, with the detonation timed to coincide with the 22nd Congress of the Communist Party of the Soviet Union.

Tested on 30 October 1961, the test verified new design principles for high-yield thermonuclear charges, allowing, as its final report put it, the design of a nuclear device "of practically unlimited power". The bomb was dropped by parachute from a Tu-95V aircraft, and detonated autonomously 4,000 metres (13,000 ft) above the cape Sukhoy Nos of Severny Island, Novaya Zemlya, 15 km (9.3 mi) from Mityushikha Bay, north of the Matochkin Strait. The detonation was monitored by United States intelligence agencies, via a KC-135A aircraft (Operation SpeedLight) in the area at the time. A secret U.S. reconnaissance aircraft named "Speed Light Alpha" monitored the blast, coming close enough to have its antiradiation paint scorched.

The bhangmeter results and other data suggested the bomb yielded around 58 Mt (243 PJ), which was the accepted yield in technical literature until 1991, when Soviet scientists revealed that their instruments indicated a yield of 50 Mt (209 PJ). As they had the instrumental data and access to the test site, their yield figure has been accepted as more accurate. In theory, the bomb would have had a yield in excess of 100 Mt (418 PJ) if it had included the uranium-238 fusion tamper which featured in the design but was omitted in the test to reduce radioactive fallout. As only one bomb was built to completion, that capability has never been demonstrated. The remaining bomb casings are located at the Russian Atomic Weapon Museum in Sarov and the Museum of Nuclear Weapons, All-Russian Scientific Research Institute Of Technical Physics, in Snezhinsk.

Tsar Bomba was a modification of an earlier project, RN202, which used a ballistic case of the same size but a very different internal mechanism. A number of published books, even some authored by those involved in product development 602, contain inaccuracies that are replicated elsewhere, including wrongly identifying Tsar Bomba as RDS-202 or RN202.

Project goals

In the mid-1950s, the United States had an unconditional superiority over the USSR in nuclear weapons, although thermonuclear charges had already been created in the USSR at this time. Also, there were no effective means of delivering nuclear warheads to the US, both in the 1950s and in 1961. The USSR was not therefore able to muster a possible realistic retaliatory nuclear strike against the US.

Given the Soviet Union's actual strategic disadvantage in relation to America's nuclear weapons possessions, foreign policy and propaganda considerations during the leaderships of Georgy Malenkov and Nikita Khrushchev made a response to the perceived US nuclear blackmail imperative. The creation of the Tsar Bomba represented a bluff in order to maintain the concept of nuclear deterrence.

Also on June 23, 1960, the Resolution of the Council of Ministers of the USSR was issued on the creation of a super-heavy ballistic missile N-1 (GRAU index – 11A52) with a warhead weighing 75 tonnes (83 short tons). For a comparative assessment, the weight of the warhead tested in 1964 by the UR-500 ICBM was 14 tonnes (15 short tons).

The development of new designs of nuclear and thermonuclear ammunition requires testing. The operability of the device, its safety in emergency situations, and the calculated energy release during an explosion must be confirmed.

Name

The bomb was officially known as "product 602" (изделие 602) or "AN602", and codenamed "Ivan". The usage of different names can be a source of confusion. The Tsar Bomba, being a modification of the RN202, is sometimes mistakenly labelled as RDS-37, RDS-202 or PH202 (product 202). It has also been referred to as RDS-220 in a number of relatively recent western publications.

Unofficially, the bomb would later become known as "Tsar Bomba" and "Kuzka's mother" (Кузькина мать, Kuz'kina mat'). The name Tsar Bomba (loosely translated as Emperor of Bombs) comes from an allusion to two other Russian historical artifacts, the Tsar Cannon and the Tsar Bell, both of which were created as showpieces but whose large size made them impractical for actual use. The name "Tsar Bomba" does not seem to have been used for the weapon prior to the 1990s. The name "Kuzka's Mother" was inspired by the statement of Khrushchev to then US Vice President Richard Nixon: "We have funds at our disposal that will have dire consequences for you. We will show you Kuzka's mother!"

The Central Intelligence Agency (CIA) designated the test as "JOE 111", using their "JOE" counting scheme begun with RDS-1 in 1949.

Development

A Tsar Bomba-type casing on display at the Sarov atomic bomb museum, Sarov

The development of a super-powerful bomb began in 1956 and was carried out in two stages. At the first stage, from 1956 to 1958, it was "product 202", which was developed in the recently created NII-1011. The modern name of NII-1011 is the "Russian Federal Nuclear Center or the All-Russian Scientific Research Institute of Technical Physics" (RFNC-VNIITF). According to the official history of the institute, the order on the creation of a research institute in the system of the Ministry of Medium Machine Building was signed on April 5, 1955; work at the NII-1011 began a little later.

At the second stage of development, from 1960 to a successful test in 1961, the bomb was called "item 602" and was developed at KB-11 (VNIIEF), V. B. Adamsky was developing, and besides him, the physical scheme was developed by Andrei Sakharov, Yu. N. Babaev, Yu. N. Smirnov, Yu. A. Trutnev.

Product 202

After the successful test of the RDS-37, KB-11 employees (Sakharov, Zeldovich, and Dovidenko) performed a preliminary calculation and, on February 2, 1956, they handed over to N. I. Pavlov, a note with the parameters for charges of 150 Mt (628 PJ) and the possibility of increasing the power to 1 gigaton of TNT (4.2 EJ).

After the creation in 1955 of the second nuclear center – NII-1011, in 1956, by a resolution of the Council of Ministers, the center was assigned the task of developing an ultra-high-power charge, which was called "Project 202".

On March 12, 1956, a draft Joint Resolution of the Central Committee of the Communist Party of the Soviet Union (CPSU Central Committee) and the Council of Ministers of the Soviet Union on the preparation and testing of the 202 product was adopted. The project planned to develop a version of the RDS-37 with a capacity of 30 Mt (126 PJ). RDS-202 was designed with a maximum calculated power release of 50 Mt (209 PJ), with a diameter of 2.1 m (6 ft 11 in), a length of 8 m (26 ft), weighing 26 tonnes (29 short tons) with a parachute system and structurally coordinated with the Tu-95-202 carrier aircraft specially converted for its use. On June 6, 1956, the NII-1011 report described the RDS-202 thermonuclear device with a design power of up to 38 Mt (159 PJ) with the required task of 20–30 Mt (84–126 PJ). In reality, this device was developed with an estimated power of 15 Mt (63 PJ), after testing the products "40GN", "245" and "205" its tests were deemed inappropriate and canceled.

The Tsar Bomba differs from its parent design – the RN202 – in several places. The Tsar Bomba was a three-stage bomb with a Trutnev-Babaev second- and third-stage design, with a yield of 50 Mt. This is equivalent to about 1,570 times the combined energy of the bombs that destroyed Hiroshima and Nagasaki, 10 times the combined energy of all the conventional explosives used in World War II, one quarter of the estimated yield of the 1883 eruption of Krakatoa, and 10% of the combined yield of all other nuclear tests to date. A three-stage hydrogen bomb uses a fission bomb primary to compress a thermonuclear secondary, as in most hydrogen bombs, and then uses energy from the resulting explosion to compress a much larger additional thermonuclear stage. There is evidence that the Tsar Bomba had several third stages rather than a single very large one. RDS-202 was assembled on the principle of radiation implosion, which was previously tested during the creation of RDS-37. Since it used a much-heavier secondary module than in the RDS-37, not one, but two primary modules (charges), located on two opposite sides of the secondary module, were used to compress it. This physical charging scheme was later used in the design of the AN-602, but the AN-602 thermonuclear charge itself (secondary module) was new. The RDS-202 thermonuclear charge was manufactured in 1956, and was planned for testing in 1957, but was not tested and put into storage. Two years after the manufacture of the RDS-202, in July 1958, it was decided to remove it from storage, dismantle and use automation units and charge parts for experimental work (Order No. 277 of the Ministry of Medium Machine Building dated May 23, 1957). The CPSU Central Committee and the Council of Ministers of the USSR adopted a draft Joint Resolution on 12 March, 1956, on the preparation and testing of izdeliye 202, which read:

Adopt a draft resolution of the CPSU Central Committee and the USSR Council of Ministers on the preparation and testing of izdeliye 202.

Paragraphs required for inclusion in the draft resolution:

(a) The Ministry of Medium Engineering (Comrade Avraami Zavenyagin) and the Ministry of Defense of the USSR (Comrade Georgy Zhukov) at the end of the preparatory work for the test of izdeliye 202 to report to the CPSU Central Committee on the situation;

(b) The Ministry of Medium Engineering (Comrade Zavenyagin) to solve the issue of introducing a special stage of protection into the design of izdeliye 202 to ensure disarming of the product in the event of a failure of the parachute system, as well as their proposals reported to the CPSU Central Committee.

Comrades Boris Vannikov and Kurchatov are assigned to edit the final version of this resolution.

Product 602

In 1960, KB-11 began developing a thermonuclear device with a design capacity of one hundred megatons of TNT (four hundred and eighteen petajoules). In February 1961, the leaders of KB-11 sent a letter to the Central Committee of the CPSU with the subject line "Some questions of the development of nuclear weapons and methods of their use", which, among other things, raised the question of the expediency of developing such a 100 Mt device. On July 10, 1961, a discussion took place in the Central Committee of the CPSU, at which First Secretary Nikita Khrushchev supported the development and testing of this super-powerful bomb.

To speed up the work on Tsar Bomba, it was based on the 202 Project, but was a new project, developed by a different group. In particular, in KB-11, six casings for the Project 202 bomb already manufactured at NII-1011 and a set of equipment developed for the 202 Project testing were used.

Tsar Bomba had a "three-stage" design: the first stage is the necessary fission trigger. The second stage was two relatively small thermonuclear charges with a calculated contribution to the explosion of 1.5 Mt (6 PJ), which were used for radiation implosion of the third stage, the main thermonuclear module located between them, and starting a thermonuclear reaction in it, contributing 50 Mt of explosion energy. As a result of the thermonuclear reaction, huge numbers of high-energy fast neutrons were formed in the main thermonuclear module, which, in turn, initiated the fast fission nuclear reaction in the nuclei of the surrounding uranium-238, which would have added another 50 Mt of energy to the explosion, so that the estimated energy release of Tsar Bomba was around 100 Mt.

The test of such a complete three-stage 100 Mt bomb was rejected due to the extremely high level of radioactive contamination that would be caused by the fission reaction of large quantities of uranium-238 fission. During the test, the bomb was used in a two-stage version. A. D. Sakharov suggested using nuclear passive material instead of the uranium-238 in the secondary bomb module, which reduced the bomb's energy to 50 Mt, and, in addition to reducing the amount of radioactive fission products, avoided the fireball's contact with the Earth's surface, thus eliminating radioactive contamination of the soil and the distribution of large amounts of fallout into the atmosphere.

Many technical innovations were applied in the design of Tsar Bomba. The thermonuclear charge was made according to the "bifilar" scheme – the radiation implosion of the main thermonuclear stage was carried out from two opposite sides. These secondary charges produced X-ray compression of the main thermonuclear charge. For this, the second stage was separated into two fusion charges which were placed in the front and rear parts of the bomb, for which a synchronous detonation was required with a difference in initiation of no more than 100 nanoseconds. To ensure synchronous detonation of charges with the required accuracy, the sequencing unit of the detonation electronics was modified at KB-25 (now "Federal State Unitary Enterprise "NL Dukhov All-Russian Scientific Research Institute of Automation")(VNIIA).

Development of the carrier aircraft

The initial three-stage design of Tsar Bomba was capable of yielding approximately 100 Mt through fast fission (3,000 times the power of the Hiroshima and Nagasaki bombs); however, it was thought that this would have resulted in too much nuclear fallout, and the aircraft delivering the bomb would not have had enough time to escape the explosion. To limit the amount of fallout, the third stage and possibly the second stage had a lead tamper instead of a uranium-238 fusion tamper (which greatly amplifies the fusion reaction by fissioning uranium atoms with fast neutrons from the fusion reaction). This eliminated fast fission by the fusion-stage neutrons so that approximately 97% of the total yield resulted from thermonuclear fusion alone (as such, it was one of the "cleanest" nuclear bombs ever created, generating a very low amount of fallout relative to its yield). There was a strong incentive for this modification, since most of the fallout from a test of the bomb would probably have descended on populated Soviet territory.

The first studies on "Topic 242" began immediately after Igor Kurchatov talked with Andrei Tupolev (then held in late 1954). Tupolev appointed his deputy for weapon systems, Aleksandr Nadashkevich, as the head of the Topic. Subsequent analysis indicated that to carry such a heavy, concentrated load, the Tu-95 bomber carrying the Tsar Bomba needed to have its engines, bomb bay, suspension and release mechanisms extensively redesigned. The Tsar Bomba's dimensional and weight drawings were passed in the first half of 1955, together with its placement layout drawing. The Tsar Bomba's weight accounted for 15% of the weight of its Tu-95 carrier as expected. The carrier, aside from having its fuel tanks and bomb bay doors removed, had its BD-206 bomb-holder replaced by a new, heavier beam-type BD7-95-242 (or BD-242) holder attached directly to the longitudinal weight-bearing beams. The problem of how to release the bomb was also solved; the bomb-holder would release all three of its locks in a synchronous fashion via electro-automatic mechanisms as required by safety protocols.

A Joint Resolution of the CPSU Central Committee and the Council of Ministers (Nr. 357-28ss) was issued on 17 March, 1956, which mandated that OKB-156 begin conversion of a Tu-95 bomber into a high-yield nuclear bomb carrier. These works were carried out in the Gromov Flight Research Institute from May to September 1956. The converted bomber, designated the Tu-95V, was accepted for duty and was handed over for flight tests which, including a release of a mock-up "superbomb", were conducted under the command of Colonel S. M. Kulikov until 1959, and passed without major issues.

Despite the creation of the Tu-95V bomb-carrier aircraft, the test of the Tsar Bomba was postponed for political reasons: namely, Khrushchev's visit to the United States and a pause in the Cold War. The Tu-95V during this period was flown to Uzyn, in today's Ukraine, and was used as a training aircraft; therefore, it was no longer listed as a combat aircraft. With the beginning of a new round of the Cold War in 1961, the test was resumed. The Tu-95V had all connectors in its automatic release mechanism replaced, the bomb bay doors removed and the aircraft itself covered with a special, reflective white paint.

In late 1961, the aircraft was modified for testing Tsar Bomba at the Kuibyshev aircraft plant.

Site of the detonation

Test

Nikita Khrushchev, the first secretary of the Communist Party, announced the upcoming tests of a 50-Mt bomb in his opening report at the 22nd Congress of the Communist Party of the Soviet Union on October 17, 1961. Before the official announcement, in a casual conversation, he told an American politician about the bomb, and this information was published on September 8, 1961, in The New York Times. The Tsar Bomba was tested on October 30, 1961.

The Tupolev Tu-95V aircraft, No. 5800302, with the bomb took off from the Olenya airfield, and was flown to State Test Site No. 6 of the USSR Ministry of Defense located on Novaya Zemlya with a crew of nine:

• Test pilot – Major Andrei Yegorovich Durnovtsev
• Lead navigator of tests – Major Ivan Nikiforovich Kleshch
• Second pilot – Captain Mikhail Konstantinovich Kondratenko
• Navigator-operator of the radar – Lieutenant Anatoly Sergeevich Bobikov
• Radar operator – Captain Alexander Filippovich Prokopenko
• Flight engineer – Captain Grigory Mikhailovich Yevtushenko
• Radio operator – Lieutenant Mikhail Petrovich Mashkin
• Gunner-radio operator – Captain Vyacheslav Mikhailovich Snetkov
• Gunner-radio operator – Corporal Vasily Yakovlevich Bolotov

The test was also attended by the Tupolev Tu-16 laboratory aircraft, no. 3709, equipped for monitoring the tests, and its crew:

• Leading test pilot – Lieutenant Colonel Vladimir Fyodorovich Martynenko
• Second pilot – Senior Lieutenant Vladimir Ivanovich Mukhanov
• Leading navigator – Major Semyon Artemievich Grigoryuk
• Navigator-operator of the radar – Major Vasily Timofeevich Muzlanov
• Gunner-radio operator – Senior Sergeant Mikhail Emelyanovich Shumilov

Both aircraft were painted with special reflective paint to minimize heat damage. Despite this effort, Durnovtsev, and his crew, were given only a 50% chance of surviving the test.

The bomb, weighing 27 tonnes (30 short tons), was so large (8 m (26 ft) long by 2.1 m (6 ft 11 in) in diameter) that the Tu-95V had to have its bomb bay doors and fuselage fuel tanks removed. The bomb was attached to an 800-kilogram (1,800 lb), 1,600-square-metre (17,000 sq ft) parachute, which gave the release and observer planes time to fly about 45 km (28 mi) away from ground zero, giving them a 50 percent chance of survival. The bomb was released two hours after takeoff from a height of 10,500 m (34,449 ft) on a test target within Sukhoy Nos. The Tsar Bomba detonated at 11:32 (or 11:33; USGS earthquake monitors list the event as occurring at 11:33:31 ) Moscow Time on October 30, 1961, over the Mityushikha Bay nuclear testing range (Sukhoy Nos Zone C), at a height of 4,200 m (13,780 ft) ASL (4,000 m (13,123 ft) above the target) (some sources suggest 3,900 m (12,795 ft) ASL and 3,700 m (12,139 ft) above target, or 4,500 m (14,764 ft)). By this time the Tu-95V had already escaped to 39 km (24 mi) away, and the Tu-16 53.5 km (33.2 mi) away. When detonation occurred, the shock wave caught up with the Tu-95V at a distance of 115 km (71 mi) and the Tu-16 at 205 km (127 mi). The Tu-95V dropped 1 kilometre (0.62 mi) in the air because of the shock wave but was able to recover and land safely. According to initial data, the Tsar Bomba had a nuclear yield of 58.6 Mt (245 PJ) (significantly exceeding what the design itself would suggest) and was overestimated at values all the way up to 75 Mt (310 PJ).

The Tsar Bomba's fireball, about 8 km (5.0 mi) wide at its maximum, was prevented from touching the ground by the shock wave, but reached nearly 10.5 km (6.5 mi) in the sky – the altitude of the deploying bomber.

Although simplistic fireball calculations predicted it would be large enough to hit the ground, the bomb's own shock wave bounced back and prevented this. The 8-kilometre-wide (5.0 mi) fireball reached nearly as high as the altitude of the release plane and was visible at almost 1,000 km (620 mi) away. The mushroom cloud was about 67 km (42 mi) high (nearly eight times the height of Mount Everest), which meant that the cloud was above the stratosphere and well inside the mesosphere when it peaked. The cap of the mushroom cloud had a peak width of 95 km (59 mi) and its base was 40 km (25 mi) wide.

A Soviet cameraman said:

The clouds beneath the aircraft and in the distance were lit up by the powerful flash. The sea of light spread under the hatch and even clouds began to glow and became transparent. At that moment, our aircraft emerged from between two cloud layers and down below in the gap a huge bright orange ball was emerging. The ball was powerful and arrogant like Jupiter. Slowly and silently it crept upwards ... Having broken through the thick layer of clouds it kept growing. It seemed to suck the whole Earth into it. The spectacle was fantastic, unreal, supernatural."

Test results

The explosion of Tsar Bomba, according to the classification of nuclear explosions, was an ultra-high-power low-air nuclear explosion.

The mushroom cloud of Tsar Bomba seen from a distance of 161 km (100 mi). The crown of the cloud is 65 km (40 mi) high at the time of the picture. (source: Rosatom State Corporation Communications Department 20-08-2020)

• The flare was visible at a distance of more than 1,000 km (620 mi). It was observed in Norway, Greenland and Alaska.
• The explosion's nuclear mushroom rose to a height of 67 km (42 mi). The shape of the "hat" was two-tiered; the diameter of the upper tier was estimated at 95 km (59 mi), the lower tier at 70 km (43 mi). The cloud was observed 800 km (500 mi) from the explosion site.
• The blast wave circled the globe three times, with the first one taking 36 hours and 27 minutes.
• A seismic wave in the earth's crust, generated by the shock wave of the explosion, circled the globe three times.
• The atmospheric pressure wave resulting from the explosion was recorded three times in New Zealand: the station in Wellington recorded an increase in pressure at 21:57, on October 30, coming from the north-west, at 07:17 on October 31, from the southeast, and at 09:16, on November 1, from the northwest (all GMT time), with amplitudes of 0.6 mbar (0.60 hPa), 0.4 mbar (0.40 hPa), and 0.2 mbar (0.20 hPa). Respectively, the average wave speed is estimated at 303 m/s (990 ft/s), or 9.9 degrees of the great circle per hour.
• Glass shattered in windows 780 km (480 mi) from the explosion in a village on Dikson Island.
• The sound wave generated by the explosion reached Dikson Island, but there are no reports of destruction or damage to structures even in the urban-type settlement of Amderma, which is much closer (280 km (170 mi)) to the landfall.
• Ionization of the atmosphere caused interference to radio communications even hundreds of kilometers from the test site for about 40 minutes.
• Radioactive contamination of the experimental field with a radius of 2–3 km (1.2–1.9 mi) in the epicenter area was no more than 1 milliroentgen / hour. The testers appeared at the explosion site 2 hours later; radioactive contamination posed practically no danger to the test participants.

All buildings in the village of Severny, both wooden and brick, located 55 km (34 mi) from ground zero within the Sukhoy Nos test range, were destroyed. In districts hundreds of kilometres from ground zero, wooden houses were destroyed; stone ones lost their roofs, windows, and doors; and radio communications were interrupted for almost one hour. One participant in the test saw a bright flash through dark goggles and felt the effects of a thermal pulse even at a distance of 270 km (170 mi). The heat from the explosion could have caused third-degree burns 100 km (62 mi) away from ground zero. A shock wave was observed in the air at Dikson settlement 700 km (430 mi) away; windowpanes were partially broken for distances up to 900 kilometres (560 mi). Atmospheric focusing caused blast damage at even greater distances, breaking windows in Norway and Finland. Despite being detonated 4.2 km (3 mi) above ground, its seismic body wave magnitude was estimated at 5.0–5.25.

Reactions

Immediately after the test, several US Senators condemned the Soviet Union. Prime Minister of Sweden Tage Erlander saw the blast as the Soviets' answer to a personal appeal to halt nuclear testing that he had sent the Soviet leader in the week prior to the blast. The British Foreign Office, Prime Minister of Norway Einar Gerhardsen, Prime Minister of Denmark Viggo Kampmann and others also released statements condemning the blast. Soviet and Chinese radio stations mentioned the US underground nuclear test of a much smaller bomb (possibly the Mink test) carried out the day prior, without mentioning the Tsar Bomba test.

Consequences of the test

The creation and testing of a superbomb were of great political importance; the Soviet Union demonstrated its potential in creating a nuclear arsenal of great power (at that time, the most powerful thermonuclear charge tested by the United States was 15 Mt (Castle Bravo)). After the Tsar Bomba test, the United States did not increase the power of its own thermonuclear tests and, in 1963 in Moscow, the Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space and Under Water was signed.

The scientific result of the test was the experimental verification of the principles of calculation and design of multistage thermonuclear charges. It was experimentally proven that there is no fundamental limitation on increasing the power of a thermonuclear charge. However, as early as October 30, 1949, three years before the Ivy Mike test which utilized the Teller-Ulam design, in the Supplement to the official report of the General Advisory Committee of the US Atomic Energy Commission, nuclear physicists Enrico Fermi and Isidor Isaac Rabi observed that thermonuclear weapons have "unlimited destructive power". In the tested specimen of the bomb, to raise the explosion power by another 50 Mt, it was enough to replace the lead sheath with uranium-238, as was normally expected. The replacement of the cladding material and the decrease in the explosion power were motivated by the desire to reduce the amount of radioactive fallout to an acceptable level, and not by the desire to reduce the weight of the bomb, as is sometimes believed. The weight of Tsar Bomba did decrease from this, but insignificantly. The uranium cladding was supposed to weigh about 2,800 kg (6,200 lb), the lead sheath of the same volume – based on the lower density of lead – is about 1,700 kg (3,700 lb). The resulting relief of just over one ton is weakly noticeable with a total mass of Tsar Bomba of at least 24 tons and did not affect the state of affairs with its transportation.

The explosion is one of the cleanest in the history of atmospheric nuclear tests per unit of power. The first stage of the bomb was a uranium charge with a capacity of 1.5 Mt, which in itself provided a large amount of radioactive fallout; nevertheless, it can be assumed that Tsar Bomba was really relatively clean – more than 97% of the explosion power was provided by a thermonuclear fusion reaction, which practically does not create radioactive contamination.

A distant consequence was the increased radioactivity accumulated in the glaciers of Novaya Zemlya. According to the 2015 expedition, due to nuclear tests, the glaciers of Novaya Zemlya are 65–130 times more radioactive than the background in neighboring areas, including contamination from the tests of the Kuzka's Mother.

Sakharov was against nuclear proliferation, and played a key role in signing the 1963 Partial Test Ban Treaty. Sakharov became an advocate of civil liberties and reforms in the Soviet Union. These efforts earned him the Nobel Peace Prize in 1975.

Analysis

Total destructive radius, superimposed on Paris with the red circle indicating the area of total destruction (radius 35 kilometres [22 mi]), and the yellow circle the radius of the fireball (radius 3.5 kilometres [2 mi])

The Tsar Bomba is the single most physically powerful device ever deployed on Earth, the most powerful nuclear bomb tested and the largest man-made explosion in history. For comparison, the largest weapon ever produced by the US, the now-decommissioned B41, had a predicted maximum yield of 25 Mt (100 PJ). The largest nuclear device ever tested by the US (Castle Bravo) yielded 15 Mt (63 PJ) because of an unexpectedly-high involvement of lithium-7 in the fusion reaction; the preliminary prediction for the yield was from 4 to 6 Mt (17 to 25 PJ). The largest weapons deployed by the Soviet Union were also around 25 Mt (100 PJ) (e.g., the SS-18 Mod. 3 warhead).

The weight and size of the Tsar Bomba limited the range and speed of the specially-modified bomber carrying it. Delivery by an intercontinental ballistic missile would have required a much stronger missile (the Proton started its development as that delivery system). It has been estimated that detonating the original 100 Mt (420 PJ) design would have increased the world's total fission fallout since the invention of the atomic bomb by 25%. It was decided that a full 100 Mt detonation would create a nuclear fallout that was unacceptable in terms of pollution from a single test, as well as a near-certainty that the release plane and crew would be destroyed before it could escape the blast radius.

The Tsar Bomba was the culmination of a series of high-yield thermonuclear weapons designed by the Soviet Union and the United States during the 1950s (e.g., the Mark 17 and B41 nuclear bombs).

Practical applications

Tsar Bomba was never a practical weapon; it was a single product, the design of which allowed reaching a power of 100 Mt TE. The test of a 50-Mt bomb was, among other things, a test of the performance of the product design for 100 Mt. The bomb was intended exclusively to exert psychological pressure on the United States.

Experts began to develop military missiles for warheads (150 Mt and more) that have been redirected for space use:

• UR-500 – (warhead mass – 40 tons, virtually implemented as a carrier rocket – "Proton" – GRAU index – 8K82)
• N-1 – (warhead mass – 75–95 t (74–93 long tons; 83–105 short tons), the development was reoriented into a carrier for the lunar program, the project was brought to the stage of flight design tests and closed in 1976, GRAU index – 11A52)
• R-56 – (GRAU index – 8K67)

Films

• Footage from a Soviet documentary about the bomb is featured in Trinity and Beyond: The Atomic Bomb Movie (Visual Concept Entertainment, 1995), where it is referred to as the Russian monster bomb. The video states that the Tsar Bomba project broke the voluntary moratorium on nuclear tests. In fact, the Soviets restarted their tests and broke the unilateral voluntary moratorium 30 days before Tsar Bomba, testing 45 times in that month. Since the moratorium was unilateral there was no multilateral legal obstacle. The US had declared their own one-year unilateral moratorium on nuclear tests and, as that year had expired, the US had already announced that it considered itself free to resume testing without further notice. Later, it was stated that the US had not resumed testing at the time of the Tsar Bomba test. That announcement was in error, as the US had in fact tested five times under Operation Nougat between the USSR's ending of the moratorium on 1 October and the Tsar Bomba test on 30 October.
• "World's Biggest Bomb", a 2011 episode of the PBS documentary series Secrets of the Dead produced by Blink Films & WNET, chronicles the events leading to the detonations of Castle Bravo and the Tsar Bomba.
• In connection with the celebration of 75 years of nuclear industry, Rosatom released a declassified Russian language documentary video of the Tsar Bomba test on YouTube in August 2020.

Castle Bravo

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Castle_Bravo 

 

Castle Bravo
Time-lapse of the Bravo detonation and subsequent mushroom cloud.
Information
Country	United States
Test series	Operation Castle
Test site	Bikini Atoll
Date	March 1, 1954 (69 years ago)
Test type	Atmospheric
Yield	15 megatonnes of TNT (63 PJ)
Test chronology

Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of Operation Castle. Detonated on March 1, 1954, the device was the most powerful nuclear device detonated by the United States and its first lithium deuteride fueled thermonuclear weapon. Castle Bravo's yield was 15 megatonnes of TNT (63 PJ), 2.5 times the predicted 6 megatonnes of TNT (25 PJ), due to unforeseen additional reactions involving lithium-7, which led to the unexpected radioactive contamination of areas to the east of Bikini Atoll. At the time, it was the most powerful artificial explosion in history.

Fallout, the heaviest of which was in the form of pulverized surface coral from the detonation, fell on residents of Rongelap and Utirik atolls, while the more particulate and gaseous fallout spread around the world. The inhabitants of the islands were not evacuated until three days later and suffered radiation sickness. Twenty-three crew members of the Japanese fishing vessel Daigo Fukuryū Maru ("Lucky Dragon No. 5") were also contaminated by the heavy fallout, experiencing acute radiation syndrome. The blast incited a strong international reaction over atmospheric thermonuclear testing.

The Bravo Crater is located at 11°41′50″N 165°16′19″E. The remains of the Castle Bravo causeway are at 11°42′6″N 165°17′7″E.

Bomb design

SHRIMP
The SHRIMP device in its shot cab
Type	Teller-Ulam design thermonuclear weapon
Production history
Designer	Ben Diven-project engineer
Designed	24 February 1953 (GMT)
Manufacturer	Los Alamos National Laboratory
Unit cost	About $2,666,000 (1954 USD)
Produced	October 1953 (GMT)
No. built	1
Variants	TX-21C, TX-26
Specifications
Mass	10,659 kilograms (23,499 lb)
Length	455.93 centimeters (179.50 in)
Diameter	136.90 centimeters (53.90 in)
Filling	Lithium-6 deuteride
Filling weight	400 kilograms (880 lb)
Blast yield	15 megatons of TNT (63 PJ)

Primary system

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.

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. The implosion system was quite lightweight at 410 kg (900 lb), because it eliminated the aluminium pusher shell around the tamper and used the more compact ring lenses, 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). 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. A copper pit liner encased within the weapon-grade plutonium inner capsule prevented DT gas diffusion into the plutonium, a technique first tested in Greenhouse Item. 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 into the secondary.

Deuterium and lithium

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.

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. 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 remainder 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 ⁶Li, 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. 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), corresponding to about 400 kg of lithium deuteride (as LiD has a density of 0.78201 g/cm³). 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. 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.

• 

  The SHRIMP shortly before installation in its shot cab.

• 

  SHRIMP’s parabolic projection.

• 

  SHRIMP's cylindrical end.

• 

  Shot-cab installation of SHRIMP device, with humans for scale.

Jetter's cycle

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.

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).

Possible additional tritium for high-yield

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 ⁶LiT. 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, 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

Bravo SHRIMP device shot-cab.

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. 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/cm², 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 Z_eff 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 (T_r) plateau. The primary emits radiation in a manner similar to a flash bulb, and the secondary needs constant T_r to properly implode. 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), 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. 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. 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, 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, 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" the sputtering effect that would otherwise "choke" radiation from compressing the secondary. 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. (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.

SHRIMP device delivered via truck awaiting installation.

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 ²³⁵U is primarily based on the final fission reaction fragments detected in the radiochemical analysis, which conclusively showed the presence of ²³⁷U, found by the Japanese in the shot debris. The first-generation thermonuclear weapons (MK-14, 16, 17, 21, 22 and 24) all used uranium tampers enriched to 37.5% ²³⁵U. The exception to this was the MK-15 ZOMBIE that used a 93.5% enriched fission jacket.

The secondary assembly

In a similar manner to the earlier pipes filled with a partial pressure of helium, as used in the Ivy Mike test of 1952, the 1954 Castle Bravo test was likewise heavily instrumented with Line-of-Sight (LOS) pipes, to better define and quantify the timing and energies of the x-rays and neutrons produced by these early thermonuclear devices. One of the outcomes of this diagnostic work resulted in this graphic depiction of the transport of energetic x-ray and neutrons through a vacuum line, some 2.3 km long, whereupon it heated solid matter at the "station 1200" blockhouse and thus generated a secondary fireball.

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. 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. 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, and 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.

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 k_eff, 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. The neutrons entered the assembly by a small hole through the ≈28 cm thick ²³⁸U 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

Boron was used at many locations in this dry system; it has a high cross-section for the absorption of slow neutrons, which fission ²³⁵U and ²³⁹Pu, but a low cross-section for the absorption of fast neutrons, which fission ²³⁸U. Because of this characteristic, ¹⁰B deposited onto the surface of the secondary stage would prevent pre-detonation of the spark plug by stray neutrons from the primary without interfering with the subsequent fissioning of the ²³⁸U 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 ¹⁰B, the secondary was compressed more highly, at a cost of some radiated neutrons. (The Castle Koon MORGENSTERN device did not use ¹⁰B 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.) 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.

Detonation

Bravo detonation and fireball.

The device was mounted in a "shot cab" on an artificial island built on a reef off Namu Island, in Bikini Atoll. A sizable array of diagnostic instruments were trained on it, including high-speed cameras trained through an arc of mirror towers around the shot cab.

The detonation took place at 06:45 on March 1, 1954, local time (18:45 on February 28 GMT).

When Bravo was detonated, within one second it formed a fireball almost 4.5 miles (7.2 km) across. This fireball was visible on Kwajalein Atoll over 250 miles (400 km) away. The explosion left a crater 6,500 feet (2,000 m) in diameter and 250 feet (76 m) in depth. The mushroom cloud reached a height of 47,000 feet (14,000 m) and a diameter of 7 miles (11 km) in about a minute, a height of 130,000 feet (40 km) and 62 mi (100 km) in diameter in less than 10 minutes and was expanding at more than 100 meters per second (360 km/h; 220 mph). As a result of the blast, the cloud contaminated more than 7,000 square miles (18,000 km²) of the surrounding Pacific Ocean, including some of the surrounding small islands like Rongerik, Rongelap, and Utirik.

In terms of energy released (usually measured in TNT equivalence), Castle Bravo was about 1,000 times more powerful than each of the atomic bombs that were dropped on Hiroshima and Nagasaki during World War II. Castle Bravo is the sixth largest nuclear explosion in history, exceeded by the Soviet tests of Tsar Bomba at approximately 50 Mt, Test 219 at 24.2 Mt, and three other (Test 147, Test 173 and Test 174) ≈20 Mt Soviet tests in 1962 at Novaya Zemlya.

High yield

Diagram of Tritium bonus provided by Lithium-7 isotope.

The yield of 15 megatons was triple that of the 5 Mt predicted by its designers. The cause of the higher yield was an error made by designers of the device at Los Alamos National Laboratory. They considered only the lithium-6 isotope in the lithium-deuteride secondary to be reactive; the lithium-7 isotope, accounting for 60% of the lithium content, was assumed to be inert. It was expected that the lithium-6 isotope would absorb a neutron from the fissioning plutonium and emit an alpha particle and tritium in the process, of which the latter would then fuse with the deuterium and increase the yield in a predicted manner. Lithium-6 indeed reacted in this manner.

It was assumed that the lithium-7 would absorb one neutron, producing lithium-8, which decays (through beta decay into beryllium-8) to a pair of alpha particles on a timescale of nearly a second, vastly longer than the timescale of nuclear detonation. However, when lithium-7 is bombarded with energetic neutrons with an energy greater than 2.47 MeV, rather than simply absorbing a neutron, it undergoes nuclear fission into an alpha particle, a tritium nucleus, and another neutron. As a result, much more tritium was produced than expected, the extra tritium fusing with deuterium and producing an extra neutron. The extra neutron produced by fusion and the extra neutron released directly by lithium-7 decay produced a much larger neutron flux. The result was greatly increased fissioning of the uranium tamper and increased yield.

Summarizing, the reactions involving lithium-6 result in some combination of the two following net reactions:

¹n + ⁶Li → ³H + ⁴He + 4.783 MeV

⁶Li + ²H → 2 ⁴He + 22.373 MeV

But when lithium-7 is present, one also has some amounts of the following two net reactions:

⁷Li + ¹n → ³H + ⁴He + ¹n

⁷Li + ²H → 2 ⁴He + n + 15.123 MeV

This resultant extra fuel (both lithium-6 and lithium-7) contributed greatly to the fusion reactions and neutron production and in this manner greatly increased the device's explosive output. The test used lithium with a high percentage of lithium-7 only because lithium-6 was then scarce and expensive; the later Castle Union test used almost pure lithium-6. Had sufficient lithium-6 been available, the usability of the common lithium-7 might not have been discovered.

The unexpectedly high yield of the device severely damaged many of the permanent buildings on the control site island on the far side of the atoll. Little of the desired diagnostic data on the shot was collected; many instruments designed to transmit their data back before being destroyed by the blast were instead vaporized instantly, while most of the instruments that were expected to be recovered for data retrieval were destroyed by the blast.

In an additional unexpected event, albeit one of far less consequence, X-rays traveling through line-of-sight (LOS) pipes caused a small second fireball at Station 1200 with a yield of 1 kiloton of TNT (4.2 TJ).

High levels of fallout

The Bravo fallout plume spread dangerous levels of radioactivity over an area over 280 miles (450 km) long, including inhabited islands. The contour lines show the cumulative radiation exposure in roentgens (R) for the first 96 hours after the test. Although widely published, this fallout map is not perfectly correct.

The fission reactions of the natural uranium tamper were quite dirty, producing a large amount of fallout. That, combined with the larger than expected yield and a major wind shift, produced some very serious consequences for those in the fallout range. In the declassified film Operation Castle, the task force commander Major General Percy Clarkson pointed to a diagram indicating that the wind shift was still in the range of "acceptable fallout", although just barely.

The decision to carry out the Bravo test under the prevailing winds was made by Dr. Alvin C. Graves, the Scientific Director of Operation Castle. Graves had total authority over detonating the weapon, above that of the military commander of Operation Castle. Graves appears in the widely available film of the earlier 1952 test "Ivy Mike", which examines the last-minute fallout decisions. The narrator, the western actor Reed Hadley, is filmed aboard the control ship in that film, showing the final conference. Hadley points out that 20,000 people live in the potential area of the fallout. He asks the control panel scientist if the test can be aborted and is told "yes", but it would ruin all their preparations in setting up timed measuring instruments. In Mike, the fallout correctly landed north of the inhabited area but, in the 1954 Bravo test, there was a large amount of wind shear, and the wind that was blowing north the day before the test steadily veered towards the east.

Inhabited islands affected

Radioactive fallout was spread eastward onto the inhabited Rongelap and Rongerik atolls, which were evacuated 48 hours after the detonation. In 1957, the Atomic Energy Commission deemed Rongelap safe to return, and allowed 82 inhabitants to move back to the island. Upon their return, they discovered that their previous staple foods, including arrowroot, makmok, and fish, had either disappeared or gave residents various illnesses, and they were again removed. Ultimately, 15 islands and atolls were contaminated, and by 1963 Marshall Islands natives began to suffer from thyroid tumors, including 20 of 29 Rongelap children at the time of Bravo, and many birth defects were reported. The islanders received compensation from the U.S. government, relative to how much contamination they received, beginning in 1956; by 1995 the Nuclear Claims Tribunal reported that it had awarded $43.2 million, nearly its entire fund, to 1,196 claimants for 1,311 illnesses. A medical study, named Project 4.1, studied the effects of the fallout on the islanders.

Map showing points (X) where contaminated fish were caught or where the sea was found to be excessively radioactive. B=original "danger zone" around Bikini announced by the U.S. government. W="danger zone" extended later. xF=position of the Lucky Dragon fishing boat. NE, EC, and SE are equatorial currents.

Although the atmospheric fallout plume drifted eastward, once fallout landed in the water it was carried in several directions by ocean currents, including northwest and southwest.

Daigo Fukuryū Maru

A Japanese fishing boat, Daigo Fukuryū Maru (Lucky Dragon No.5), came in direct contact with the fallout, which caused many of the crew to grow ill due to radiation sickness. One member died of a secondary infection six months later after acute radiation exposure, and another had a child that was stillborn and deformed. This resulted in an international incident and reignited Japanese concerns about radiation, especially as Japanese citizens were once more adversely affected by US nuclear weapons. The official US position had been that the growth in the strength of atomic bombs was not accompanied by an equivalent growth in radioactivity released, and they denied that the crew was affected by radioactive fallout. Japanese scientists who had collected data from the fishing vessel disagreed with this.

Sir Joseph Rotblat, working at St Bartholomew's Hospital, London, demonstrated that the contamination caused by the fallout from the test was far greater than that stated officially. Rotblat deduced that the bomb had three stages and showed that the fission phase at the end of the explosion increased the amount of radioactivity a thousand-fold. Rotblat's paper was taken up by the media, and the outcry in Japan reached such a level that diplomatic relations became strained and the incident was even dubbed by some as a "second Hiroshima". Nevertheless, the Japanese and US governments quickly reached a political settlement, with the transfer to Japan of $15.3 million as compensation, with the surviving victims receiving about ¥2 million each ($5,550 in 1954, or about $56,000 in 2023). It was also agreed that the victims would not be given Hibakusha status.

The device's firing crew was located on Enyu island, variously spelled as Eneu island, as depicted here

Bomb test personnel take shelter

Unanticipated fallout and the radiation emitted by it also affected many of the vessels and personnel involved in the test, in some cases forcing them into bunkers for several hours. In contrast to the crew of the Lucky Dragon No. 5, who did not anticipate the hazard and therefore did not take shelter in the hold of their ship, or refrain from inhaling the fallout dust, the firing crew that triggered the explosion safely sheltered in their firing station when they noticed the wind was carrying the fallout in the unanticipated direction towards the island of Enyu on the Bikini Atoll where they were located, with the fire crew sheltering in place ("buttoning up") for several hours until outside radiation decayed to safer levels. "25 roentgens per hour" was recorded above the bunker.

US Navy ships affected

The US Navy tanker USS Patapsco was at Enewetak Atoll in late February 1954. Patapsco lacked a decontamination washdown system, and was therefore ordered on 27 February, to return to Pearl Harbor at the highest possible speed. A breakdown in her engine systems, namely a cracked cylinder liner, slowed Patapsco to one-third of her full speed, and when the Castle Bravo detonation took place, she was still about 180 to 195 nautical miles east of Bikini. Patapsco was in the range of nuclear fallout, which began landing on the ship in the mid-afternoon of 2 March. By this time Patapsco was 565 to 586 nautical miles from ground zero. The fallout was at first thought to be harmless and there were no radiation detectors aboard, so no decontamination measures were taken. Measurements taken after Patapsco had returned to Pearl Harbor suggested an exposure range of 0.18 to 0.62 R/hr. Total exposure estimates range from 3.3 R to 18 R of whole-body radiation, taking into account the effects of natural washdown from rain, and variations between above- and below-deck exposure.

International incident

The fallout spread traces of radioactive material as far as Australia, India and Japan, and even the United States and parts of Europe. Though organized as a secret test, Castle Bravo quickly became an international incident, prompting calls for a ban on the atmospheric testing of thermonuclear devices.

A worldwide network of gummed film stations was established to monitor fallout following Operation Castle. Although meteorological data was poor, a general connection of tropospheric flow patterns with observed fallout was evident. There was a tendency for fallout/debris to remain in tropical latitudes, with incursions into the temperate regions associated with meteorological disturbances of the predominantly zonal flow. Outside of the tropics, the Southwestern United States received the greatest total fallout, about five times that received in Japan.

Stratospheric fallout particles of strontium-90 from the test were later captured with balloon-borne air filters used to sample the air at stratospheric altitudes, the research (Project Ashcan) was conducted to better understand the stratosphere and fallout times, and arrive at more accurate meteorological models after hindcasting.

The fallout from Castle Bravo and other testing on the atoll also affected islanders who had previously inhabited the atoll, and who returned there some time after the tests. This was due to the presence of radioactive caesium-137 in locally grown coconut milk. Plants and trees absorb potassium as part of the normal biological process, but will also readily absorb caesium if present, being of the same group on the periodic table, and therefore very similar chemically. Islanders consuming contaminated coconut milk were found to have abnormally high concentrations of caesium in their bodies and so had to be evacuated from the atoll a second time.

The American magazine Consumer Reports warned of the contamination of milk with strontium-90.

Weapon history

The Soviet Union had previously used lithium deuteride in its Sloika design (known as the "Joe-4" in the U.S.), in 1953. It was not a true hydrogen bomb; fusion provided only 15–20% of its yield, most coming from boosted fission reactions. Its yield was 400 kilotons, and it could not be infinitely scaled, as with a true thermonuclear device.

The Teller–Ulam-based "Ivy Mike" device had a much greater yield of 10.4 Mt, but most of this also came from fission: 77% of the total came from fast fission of its natural-uranium tamper.

Castle Bravo had the greatest yield of any U.S. nuclear test, 15 Mt, though again, a substantial fraction came from fission. In the Teller–Ulam design, the fission and fusion stages were kept physically separate in a reflective cavity. The radiation from the exploding fission primary brought the fuel in the fusion secondary to critical density and pressure, setting off thermonuclear (fusion) chain reactions, which in turn set off a tertiary fissioning of the bomb's ²³⁸U fusion tamper and casing. Consequently, this type of bomb is also known as a "fission-fusion-fission" device. The Soviet researchers, led by Andrei Sakharov, developed and tested their first Teller–Ulam device in 1955.

The publication of the Bravo fallout analysis was a militarily sensitive issue, with Joseph Rotblat possibly deducing the staging nature of the Castle Bravo device by studying the ratio and presence of tell-tale isotopes, namely uranium-237, present in the fallout. This information could potentially reveal the means by which megaton-yield nuclear devices achieve their yield. Soviet scientist Andrei Sakharov hit upon what the Soviet Union regarded as "Sakharov's third idea" during the month after the Castle Bravo test, the final piece of the puzzle being the idea that the compression of the secondary can be accomplished by the primary's X-rays before fusion began.

The Shrimp device design later evolved into the Mark 21 nuclear bomb, of which 275 units were produced, weighing 17,600 pounds (8,000 kg) and measuring 12.5 feet (3.8 m) long and 58 inches (1.5 m) in diameter. This 18-megaton bomb was produced until July 1956. In 1957, it was converted into the Mark 36 nuclear bomb and entered into production again.

Health impacts

Page 36 from the Project 4.1 final report, showing four photographs of exposed Marshallese. Faces blotted out for privacy reasons.

Following the test, the United States Department of Energy estimated that 253 inhabitants of the Marshall Islands were impacted by the radioactive fallout. This single test exposed the surrounding populations to varying levels of radiation. The fallout levels attributed to the Castle Bravo test are the highest in history. Populations neighboring the test site were exposed to high levels of radiation resulting in mild radiation sickness of many (nausea, vomiting, diarrhea). Several weeks later, many people began suffering from alopecia (hair loss) and skin lesions as well.

The exposure to fallout has been linked to increase the likelihood of several types of cancer such as leukemia and thyroid cancer. The relationship between Iodine-131 levels and thyroid cancer is still being researched. There are also correlations between fallout exposure levels and diseases such as thyroid disease like hypothyroidism. Populations of the Marshall Islands that received significant exposure to radionuclides have a much greater risk of developing cancer.

The female population of the Marshall Islands have a sixty times greater mortality rate from cervical cancer than a comparable mainland United States population. The Islands populations also have a five time greater likelihood of breast or gastrointestinal mortality, and lung cancer mortality is three times higher than the mainland population. The mortality rate of the male population on the Marshall Islands from lung cancer is four times greater than the overall United States rates, and the oral cancer rates are ten times greater.

There is a presumed association between radiation levels and functioning of the female reproductive system.

In popular culture

The Castle Bravo detonation and the subsequent poisoning of the crew aboard Daigo Fukuryū Maru led to an increase in antinuclear protests in Japan. It was compared to the bombings of Hiroshima and Nagasaki, and the Castle Bravo test was frequently part of the plots of numerous Japanese media, especially in relation to Japan's most widely recognized media icon, Godzilla. In the 2019 film Godzilla: King of the Monsters, Castle Bravo becomes the call sign for Monarch Outpost 54 located in the Atlantic Ocean, near Bermuda.

The Donald Fagen song "Memorabilia" from his 2012 album Sunken Condos mentions both the Castle Bravo and Ivy King nuclear tests.

In 2013, the Defense Threat Reduction Agency published Castle Bravo: Fifty Years of Legend and Lore. The report is a guide to off-site radiation exposures, a narrative history, and a guide to primary historical references concerning the Castle Bravo test. The report focuses on the circumstances that resulted in radioactive exposure of the uninhabited atolls, and makes no attempt to address in detail the effects on or around Bikini Atoll.