Castle Bravo
Encyclopedia
Castle Bravo was the code name
given to the first U.S.
test of a dry fuel thermonuclear
hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll
, Marshall Islands
, as the first test of Operation Castle
. Castle Bravo was the most powerful nuclear device
ever detonated by the United States
(but not the most powerful ever detonated), with a yield of 15 megatons
. That yield, far exceeding the expected yield of 4 to 6 megatons, combined with other factors, led to the most significant accidental radiological contamination
ever caused by the United States. Fallout
from the detonation — intended to be a secret test — poisoned the islanders who had previously inhabited the atoll and returned there afterwards, as well as the crew of Daigo Fukuryū Maru
("Lucky Dragon No. 5"), a Japanese fishing boat, and created international concern about atmospheric thermonuclear testing.
. A sizable array of diagnostic instruments was trained on it, including a number of high-speed cameras which were trained through an arc of mirror towers around the shot cab.
Coordinates for Bravo Crater are 11°41′50"N 165°16′19"E. The coordinates for remains of Castle Bravo causeway are 11°42′6"N 165°17′7"E.
fuel for the fusion
stage, unlike the cryogenic liquid deuterium
–tritium
used as fuel for the fusion stage of the U.S. experimental Ivy Mike
device, which was weaponized as the Mark 16 nuclear bomb
. The bomb tested at Castle Bravo was the first practical deliverable fusion bomb in the U.S. arsenal.
The device detonated for the test was named "Shrimp" and was the same basic configuration as the Ivy Mike
device, except with a different type of fusion fuel. The "Shrimp" device implemented a light case design, using aluminum instead of the heavy steel
case used in Mike.
Inside the cylindrical case was a smaller cylinder of lithium deuteride fusion fuel (the secondary) with a fission
atomic bomb (the primary) at one end, the latter employed to create the conditions needed to start the fusion reaction. Running down the center of the secondary, was a cylindrical rod of plutonium
(the sparkplug), which was used to ignite the fusion reaction. Surrounding this assembly was a natural uranium
tamper. The space between the tamper and the case formed a radiation
channel to conduct X-ray
s from the primary to the secondary. The function of the X-rays was to compress the secondary (see Teller-Ulam design
), increasing the density and temperature of the deuterium to the level needed to sustain a thermonuclear reaction, and compress the sparkplug to supercritical ignition. (See nuclear weapon design.)
It was practically identical to the "Runt" device later detonated in Castle Romeo
, but used partially enriched lithium
in the 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 approximately 40% lithium-6. The primary was a standard RACER IV
fusion-boosted atomic bomb.
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The detonation took place at 06:45 on March 1, 1954 local time (18:45 on February 28 GMT).
When Bravo was detonated, it formed a fireball almost four and a half miles (roughly 7 km) across within a second. This fireball was visible on Kwajalein
atoll over 250 miles (450 km) away. The explosion left a crater of 6,500 feet (2,000 m) in diameter and 250 feet (75 m) in depth. The mushroom cloud
reached a height of 47,000 feet (14 km) and a diameter of 7 miles (11 km) in about a minute; it then reached a height of 130,000 feet (40 km) and 62 miles (100 km) in diameter in less than 10 minutes and was expanding at more than 100 m/s (360 km/h, 224 mph). As a result of the blast, the cloud contaminated more than seven thousand square miles of the surrounding Pacific Ocean including some of the surrounding small islands like Rongerik, Rongelap and Utirik.
In terms of TNT tonnage equivalence
, Castle Bravo was about 1,000 times more powerful than each of the atomic bombs which were dropped
on Hiroshima
and Nagasaki during World War II
. The largest nuclear explosion ever produced was a test conducted by the Soviet Union
seven and a half years later, the ≈50 MT Tsar Bomba
. Castle Bravo is the fifth largest nuclear explosion in history, exceeded by the Soviet tests of Tsar Bomba
at 50.6 MT, Test 219
(24.2 MT), and two other ~20 MT Soviet tests in 1962 at Novaya Zemlya
.
. 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 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 obeyed this assumption.
However, when a lithium-7 isotope is bombarded with energetic neutrons, it captures a neutron then decomposes to form an alpha particle, a tritium nucleus
, and the captured neutron. This means more tritium was produced than expected, and the extra tritium is fused with deuterium. In addition to tritium formation the extra neutron released from lithium-7 decomposition produced a larger neutron flux
. This caused more fissioning of the uranium tamper and increased yield.
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 more lithium-6 been available the usability of the common lithium-7 might not have been discovered.
The fission reactions of the natural uranium tamper were quite dirty, producing a large amount of fallout
. That, combined with the much-larger-than-expected yield and a major wind shift, produced a number of very serious consequences. In the de-classified film "Operation Castle", task force commander General Clarkson points to a diagram indicating that the wind shift was still in the range of "acceptable fallout", although just barely.
The decision to fire the Bravo bomb under the prevailing winds was made by Dr. Alvin C. Graves
(1909–1966), the Scientific Director of Operation Castle. Dr. Graves had total authority over firing the weapon, above that of the military Commander of Operation Castle. Dr. Graves had himself received an exposure of 400 röntgen
s in the 1946 Los Alamos accident in which his personal friend, Dr. Louis Slotin
, died from radiation exposure. Dr. Graves appears in the widely available film of the earlier 1952 test "Ivy Mike", which examines the last-minute fallout decisions. The narrator, 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 the race against the Russians. In Mike the fallout correctly landed north of the inhabited area but, in the 1954 Bravo test, there was a lot of wind shear
, and the wind that was blowing north the day before the test steadily veered towards the east.
Radioactive fallout was spread eastward onto the inhabited Rongelap
and Rongerik
atolls, which were tardily evacuated. Subsequently many Marshall Islands natives suffered from birth defects and received compensation from the U.S. Federal government. A medical study, named Project 4.1
, studied the effects of the fallout on the islanders.
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.
A Japan
ese fishing boat, Daigo Fukuryu Maru
, came in direct contact with the fallout, which caused many of the crew to grow ill; one eventually died. This resulted in an international uproar and reignited Japanese concerns about radiation, especially in regard that Japanese citizens were once more
adversely affected by U.S. nuclear weapons. The official U.S. line had been that the growth in the strength of atomic bombs was not accompanied by an equivalent growth in radiation released. 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 was able to deduce that the bomb had three stages and showed that the fission phase at the end of the explosion increased the amount of radioactivity a thousandfold. 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 U.S. governments quickly reached a political settlement, which gave the fishery a compensation of 2 million dollars with the surviving victims receiving about 2 million each ($5,550 in 1954, US$ in ). It was also agreed that the victims would not be given Hibakusha
status.
Unanticipated fallout and radiation also affected many of the vessels and personnel involved in the test, in some cases trapping them in bunkers. One prominent scientist later recalled that he was on a ship 30 miles (48.3 km) away, and received 10 röntgen of radiation as a result. Sixteen crew members of the aircraft carrier
USS Bairoko
received beta burns and there was an increased cancer rate. Radioactive contamination
also affected many of the testing facilities built on other islands of the Bikini atoll system.
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.
In addition to the radiological accident, 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.
As a result, Nevil Shute
wrote the novel On the Beach, which alarmed the public and sparked public awareness and fear. The novel is about a war that released so much radioactive fallout that all the life in the Northern Hemisphere
disappeared, while the Southern Hemisphere
awaited a similar fate. The American magazine Consumer Reports
warned of the contamination of milk with the radioactive isotope strontium-90
, which also alarmed the public.
The fallout also affected islanders who had previously inhabited the atoll, and who returned there some time after the tests. This was found to be due to the presence of radioactive caesium
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 then had to be evacuated from the atoll a second time.
had previously used lithium deuteride in their Sloika design (known as the "Alarm Clock" 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 limited to 400 kilotons, and 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 outer casing. Consequently this type of bomb is also known as a "fission-fusion-fission"
device. The Soviets, led by Andrei Sakharov
, independently developed and tested
their first Teller-Ulam device in 1955.
The Shrimp device design later evolved into the Mk-21
bomb, of which 275 units were produced, weighing 15,000 pounds (6,800 kg) and measuring 12.5 feet (3.8 m) long and 56 inches (1.4 m) in diameter. This 4 megaton bomb was produced until July 1956. In 1957, it was converted into the Mk-36
and entered into production again.
Code name
A code name or cryptonym is a word or name used clandestinely to refer to another name or word. Code names are often used for military purposes, or in espionage...
given to the first U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
test of a dry fuel thermonuclear
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll
Bikini Atoll
Bikini Atoll is an atoll, listed as a World Heritage Site, in the Micronesian Islands of the Pacific Ocean, part of Republic of the Marshall Islands....
, Marshall Islands
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
, as the first test of Operation Castle
Operation Castle
Operation Castle was a United States series of high-energy nuclear tests by Joint Task Force SEVEN at Bikini Atoll beginning in March 1954...
. Castle Bravo was the most powerful nuclear device
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
ever detonated by the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
(but not the most powerful ever detonated), with a yield of 15 megatons
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
. That yield, far exceeding the expected yield of 4 to 6 megatons, combined with other factors, led to the most significant accidental radiological contamination
Radioactive contamination
Radioactive contamination, also called radiological contamination, is radioactive substances on surfaces, or within solids, liquids or gases , where their presence is unintended or undesirable, or the process giving rise to their presence in such places...
ever caused by the United States. Fallout
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
from the detonation — intended to be a secret test — poisoned the islanders who had previously inhabited the atoll and returned there afterwards, as well as the crew of Daigo Fukuryū Maru
Daigo Fukuryu Maru
was a Japanese tuna fishing boat, which was exposed to and contaminated by nuclear fallout from the United States' Castle Bravo thermonuclear device test on Bikini Atoll, on 1 March 1954....
("Lucky Dragon No. 5"), a Japanese fishing boat, and created international concern about atmospheric thermonuclear testing.
Test location
The device was a very large cylinder weighing 23,500 pounds (10.7 tonnes) and measuring 179.5 inches (4.56 m) in length and 53.9 inches (1.37 m) in width. It was mounted in a "shot cab" on an artificial island built on a reef off Namu Island, in the Bikini AtollBikini Atoll
Bikini Atoll is an atoll, listed as a World Heritage Site, in the Micronesian Islands of the Pacific Ocean, part of Republic of the Marshall Islands....
. A sizable array of diagnostic instruments was trained on it, including a number of high-speed cameras which were trained through an arc of mirror towers around the shot cab.
Coordinates for Bravo Crater are 11°41′50"N 165°16′19"E. The coordinates for remains of Castle Bravo causeway are 11°42′6"N 165°17′7"E.
Bomb design
The bomb used lithium deuterideLithium hydride
Lithium hydride is the inorganic compound with the formula LiH. It is a colorless solid, although commercial samples are gray. Characteristic of a salt-like, or ionic, hydride, it has a high melting point and is not soluble in any solvent with which it does not react...
fuel for the fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
stage, unlike the cryogenic liquid deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
–tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
used as fuel for the fusion stage of the U.S. experimental Ivy Mike
Ivy Mike
Ivy Mike was the codename given to the first United States test of a thermonuclear weapon, in which a major part of the explosive yield came from nuclear fusion. It was detonated on November 1, 1952 by the United States at on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy...
device, which was weaponized as the Mark 16 nuclear bomb
Mark 16 nuclear bomb
The Mark 16 nuclear bomb was a large thermonuclear bomb, based on the design of the Ivy Mike, the first hydrogen bomb test fired. The Mark 16 is more properly designated TX-16/EC-16 as it only existed in Experimental/Emergency Capability versions....
. The bomb tested at Castle Bravo was the first practical deliverable fusion bomb in the U.S. arsenal.
The device detonated for the test was named "Shrimp" and was the same basic configuration as the Ivy Mike
Ivy Mike
Ivy Mike was the codename given to the first United States test of a thermonuclear weapon, in which a major part of the explosive yield came from nuclear fusion. It was detonated on November 1, 1952 by the United States at on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy...
device, except with a different type of fusion fuel. The "Shrimp" device implemented a light case design, using aluminum instead of the heavy steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
case used in Mike.
Inside the cylindrical case was a smaller cylinder of lithium deuteride fusion fuel (the secondary) with a fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
atomic bomb (the primary) at one end, the latter employed to create the conditions needed to start the fusion reaction. Running down the center of the secondary, was a cylindrical rod of plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
(the sparkplug), which was used to ignite the fusion reaction. Surrounding this assembly was a natural uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
tamper. The space between the tamper and the case formed a radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
channel to conduct X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s from the primary to the secondary. The function of the X-rays was to compress the secondary (see Teller-Ulam design
Teller-Ulam design
The Teller–Ulam design is the nuclear weapon design concept used in most of the world's nuclear weapons. It is colloquially referred to as "the secret of the hydrogen bomb" because it employs hydrogen fusion, though in most applications the bulk of its destructive energy comes from uranium fission,...
), increasing the density and temperature of the deuterium to the level needed to sustain a thermonuclear reaction, and compress the sparkplug to supercritical ignition. (See nuclear weapon design.)
It was practically identical to the "Runt" device later detonated in Castle Romeo
Castle Romeo
Castle Romeo was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-17 thermonuclear weapon , the first deployed U.S...
, but used partially enriched lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
in the 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 approximately 40% lithium-6. The primary was a standard RACER IV
RACER IV
RACER IV was a component of several of the first hydrogen bombs made by the United States during the 1950s. It was the first stage for three of the devices tested in four shots of the Castle series...
fusion-boosted atomic bomb.
Detonation
When Bravo was detonated, it formed a fireball almost four and a half miles (roughly 7 km) across within a second. This fireball was visible on Kwajalein
Kwajalein
Kwajalein Atoll , is part of the Republic of the Marshall Islands . The southernmost and largest island in the atoll is named Kwajalein Island. English-speaking residents of the U.S...
atoll over 250 miles (450 km) away. The explosion left a crater of 6,500 feet (2,000 m) in diameter and 250 feet (75 m) in depth. The mushroom cloud
Mushroom cloud
A mushroom cloud is a distinctive pyrocumulus mushroom-shaped cloud of condensed water vapor or debris resulting from a very large explosion. They are most commonly associated with nuclear explosions, but any sufficiently large blast will produce the same sort of effect. They can be caused by...
reached a height of 47,000 feet (14 km) and a diameter of 7 miles (11 km) in about a minute; it then reached a height of 130,000 feet (40 km) and 62 miles (100 km) in diameter in less than 10 minutes and was expanding at more than 100 m/s (360 km/h, 224 mph). As a result of the blast, the cloud contaminated more than seven thousand square miles of the surrounding Pacific Ocean including some of the surrounding small islands like Rongerik, Rongelap and Utirik.
In terms of TNT tonnage equivalence
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
, Castle Bravo was about 1,000 times more powerful than each of the atomic bombs which were dropped
Atomic bombings of Hiroshima and Nagasaki
During the final stages of World War II in 1945, the United States conducted two atomic bombings against the cities of Hiroshima and Nagasaki in Japan, the first on August 6, 1945, and the second on August 9, 1945. These two events are the only use of nuclear weapons in war to date.For six months...
on Hiroshima
Hiroshima
is the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshu, the largest island of Japan. It became best known as the first city in history to be destroyed by a nuclear weapon when the United States Army Air Forces dropped an atomic bomb on it at 8:15 A.M...
and Nagasaki during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. The largest nuclear explosion ever produced was a test conducted by the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
seven and a half years later, the ≈50 MT Tsar Bomba
Tsar Bomba
Tsar Bomba is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated. It was also referred to as Kuz'kina Mat , in this usage meaning "something that has not been seen before"....
. Castle Bravo is the fifth largest nuclear explosion in history, exceeded by the Soviet tests of Tsar Bomba
Tsar Bomba
Tsar Bomba is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated. It was also referred to as Kuz'kina Mat , in this usage meaning "something that has not been seen before"....
at 50.6 MT, Test 219
Test 219
Test 219 was a nuclear test conducted by the Soviet Union in the atmosphere via air drop. The test was performed on December 24, 1962 over at the Novaya Zemlya test range. The yield was 24.2 Mt making it the second largest thermonuclear explosion in history.....
(24.2 MT), and two other ~20 MT Soviet tests in 1962 at Novaya Zemlya
Novaya Zemlya
Novaya Zemlya , also known in Dutch as Nova Zembla and in Norwegian as , is an archipelago in the Arctic Ocean in the north of Russia and the extreme northeast of Europe, the easternmost point of Europe lying at Cape Flissingsky on the northern island...
.
Cause of high yield
The yield of 15 megatons was two and a half times as great as expected. The cause of the high yield was a theoretical error made by designers of the device at Los Alamos National LaboratoryLos Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
. 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 lithium-6 isotope would absorb a neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
from the fissioning plutonium and emit an alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
and tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
in the process, of which the latter would then fuse with the deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
and increase the yield in a predicted manner. Lithium-6 obeyed this assumption.
However, when a lithium-7 isotope is bombarded with energetic neutrons, it captures a neutron then decomposes to form an alpha particle, a tritium nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
, and the captured neutron. This means more tritium was produced than expected, and the extra tritium is fused with deuterium. In addition to tritium formation the extra neutron released from lithium-7 decomposition produced a larger neutron flux
Neutron flux
The neutron flux is a quantity used in reactor physics corresponding to the total length travelled by all neutrons per unit time and volume . The neutron fluence is defined as the neutron flux integrated over a certain time period....
. This caused more fissioning of the uranium tamper and increased yield.
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
Castle Union
Castle Union was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-14 thermonuclear weapon , one of the first deployed U.S...
test used almost pure lithium-6. Had more lithium-6 been available the usability of the common lithium-7 might not have been discovered.
Fallout incident
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
. That, combined with the much-larger-than-expected yield and a major wind shift, produced a number of very serious consequences. In the de-classified film "Operation Castle", task force commander General Clarkson points to a diagram indicating that the wind shift was still in the range of "acceptable fallout", although just barely.
The decision to fire the Bravo bomb under the prevailing winds was made by Dr. Alvin C. Graves
Alvin C. Graves
Alvin C. Graves was an atomic physicist and director of U.S. nuclear weapons testing for many years.Graves was born in 1909 in Washington, DC, the youngest of six children. He graduated at the top of his class from the University of Virginia in 1931 with a bachelors degree in electrical...
(1909–1966), the Scientific Director of Operation Castle. Dr. Graves had total authority over firing the weapon, above that of the military Commander of Operation Castle. Dr. Graves had himself received an exposure of 400 röntgen
Röntgen
The roentgen is a unit of measurement for exposure to ionizing radiation , and is named after the German physicist Wilhelm Röntgen...
s in the 1946 Los Alamos accident in which his personal friend, Dr. Louis Slotin
Louis Slotin
Louis Alexander Slotin was a Canadian physicist and chemist who took part in the Manhattan Project, the secret US program during World War II that developed the atomic bomb....
, died from radiation exposure. Dr. Graves appears in the widely available film of the earlier 1952 test "Ivy Mike", which examines the last-minute fallout decisions. The narrator, Western actor Reed Hadley
Reed Hadley
Reed Hadley was an American movie, television and radio actor.Reed Hadley was born Reed Herring in Petrolia in Clay County near Wichita Falls, Texas, to Bert Herring, an oil well driller, and his wife Minnie. Hadley had one sister, Bess Brenner. He was reared in Buffalo, New York...
, 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 the race against the Russians. In Mike the fallout correctly landed north of the inhabited area but, in the 1954 Bravo test, there was a lot of wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
, and the wind that was blowing north the day before the test steadily veered towards the east.
Radioactive fallout was spread eastward onto the inhabited Rongelap
Rongelap Atoll
Rongelap Atoll or Namorik Atoll is a coral atoll of 61 islands in the Pacific Ocean, and forms a legislative district of the Ralik Chain of the Marshall Islands. Its total land area is only , but it encloses a lagoon with an area of...
and Rongerik
Rongerik Atoll
Rongerik Atoll or Rongdrik Atoll is a coral atoll of 17 islands in the Pacific Ocean, and is located in the Ralik Chain of the Marshall Islands, approximately east of Bikini Atoll. Its total land area is only , but it encloses a lagoon of .-History:Rongerik Atoll was claimed by the Empire of...
atolls, which were tardily evacuated. Subsequently many Marshall Islands natives suffered from birth defects and received compensation from the U.S. Federal government. A medical study, named Project 4.1
Project 4.1
Project 4.1 was the designation for a medical study conducted by the United States of those residents of the Marshall Islands exposed to radioactive fallout from the March 1, 1954 Castle Bravo nuclear test at Bikini Atoll, which had an unexpectedly large yield...
, studied the effects of the fallout on the islanders.
A Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese fishing boat, Daigo Fukuryu Maru
Daigo Fukuryu Maru
was a Japanese tuna fishing boat, which was exposed to and contaminated by nuclear fallout from the United States' Castle Bravo thermonuclear device test on Bikini Atoll, on 1 March 1954....
, came in direct contact with the fallout, which caused many of the crew to grow ill; one eventually died. This resulted in an international uproar and reignited Japanese concerns about radiation, especially in regard that Japanese citizens were once more
Atomic bombings of Hiroshima and Nagasaki
During the final stages of World War II in 1945, the United States conducted two atomic bombings against the cities of Hiroshima and Nagasaki in Japan, the first on August 6, 1945, and the second on August 9, 1945. These two events are the only use of nuclear weapons in war to date.For six months...
adversely affected by U.S. nuclear weapons. The official U.S. line had been that the growth in the strength of atomic bombs was not accompanied by an equivalent growth in radiation released. Japanese scientists who had collected data from the fishing vessel disagreed with this. Sir Joseph Rotblat, working at St Bartholomew's Hospital
St Bartholomew's Hospital
St Bartholomew's Hospital, also known as Barts, is a hospital in Smithfield in the City of London, England.-Early history:It was founded in 1123 by Raherus or Rahere , a favourite courtier of King Henry I...
, London, demonstrated that the contamination caused by the fallout
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
from the test was far greater than that stated officially. Rotblat was able to deduce that the bomb had three stages and showed that the fission phase at the end of the explosion increased the amount of radioactivity a thousandfold. 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 U.S. governments quickly reached a political settlement, which gave the fishery a compensation of 2 million dollars with the surviving victims receiving about 2 million each ($5,550 in 1954, US$ in ). It was also agreed that the victims would not be given Hibakusha
Hibakusha
The surviving victims of the atomic bombings of Hiroshima and Nagasaki are called , a Japanese word that literally translates to "explosion-affected people"...
status.
Unanticipated fallout and radiation also affected many of the vessels and personnel involved in the test, in some cases trapping them in bunkers. One prominent scientist later recalled that he was on a ship 30 miles (48.3 km) away, and received 10 röntgen of radiation as a result. Sixteen crew members of the aircraft carrier
Aircraft carrier
An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...
USS Bairoko
USS Bairoko (CVE-115)
USS Bairoko was a United States Navy . She was named after the Battle of Bairoko, a battle over Bairoko Harbor -- a small inlet on the north coast of New Georgia, Solomon Islands -- which took place on 20 July 1943 between American and Japanese forces...
received beta burns and there was an increased cancer rate. Radioactive contamination
Radioactive contamination
Radioactive contamination, also called radiological contamination, is radioactive substances on surfaces, or within solids, liquids or gases , where their presence is unintended or undesirable, or the process giving rise to their presence in such places...
also affected many of the testing facilities built on other islands of the Bikini atoll system.
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.
In addition to the radiological accident, 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.
As a result, Nevil Shute
Nevil Shute
Nevil Shute Norway was a popular British-Australian novelist and a successful aeronautical engineer. He used his full name in his engineering career, and 'Nevil Shute' as his pen name, in order to protect his engineering career from any potential negative publicity in connection with his novels.-...
wrote the novel On the Beach, which alarmed the public and sparked public awareness and fear. The novel is about a war that released so much radioactive fallout that all the life in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
disappeared, while the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
awaited a similar fate. The American magazine Consumer Reports
Consumer Reports
Consumer Reports is an American magazine published monthly by Consumers Union since 1936. It publishes reviews and comparisons of consumer products and services based on reporting and results from its in-house testing laboratory. It also publishes cleaning and general buying guides...
warned of the contamination of milk with the radioactive isotope strontium-90
Strontium-90
Strontium-90 is a radioactive isotope of strontium, with a half-life of 28.8 years.-Radioactivity:Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard...
, which also alarmed the public.
The fallout also affected islanders who had previously inhabited the atoll, and who returned there some time after the tests. This was found to be due to the presence of radioactive caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...
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
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
, and therefore very similar chemically. Islanders consuming contaminated coconut milk were found to have abnormally high concentrations of caesium in their bodies and then had to be evacuated from the atoll a second time.
Weapon history
The Soviet UnionSoviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
had previously used lithium deuteride in their Sloika design (known as the "Alarm Clock" 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
Boosted fission weapon
A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released in the fission, as well as inducing the fission reactions...
reactions. Its yield was limited to 400 kilotons, and could not be infinitely scaled, as with a true thermonuclear device.
The Teller-Ulam-based Ivy Mike
Ivy Mike
Ivy Mike was the codename given to the first United States test of a thermonuclear weapon, in which a major part of the explosive yield came from nuclear fusion. It was detonated on November 1, 1952 by the United States at on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy...
device had a much greater yield of 10.4 MT
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...
, 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 outer casing. Consequently this type of bomb is also known as a "fission-fusion-fission"
Boosted fission weapon
A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released in the fission, as well as inducing the fission reactions...
device. The Soviets, led by Andrei Sakharov
Andrei Sakharov
Andrei Dmitrievich Sakharov was a Soviet nuclear physicist, dissident and human rights activist. He earned renown as the designer of the Soviet Union's Third Idea, a codename for Soviet development of thermonuclear weapons. Sakharov was an advocate of civil liberties and civil reforms in the...
, independently developed and tested
RDS-37
RDS-37 was the Soviet Union's first "true" hydrogen bomb, first tested on November 22, 1955. The weapon had a nominal yield of approximately 3 megatons. It was scaled down to 1.6 megatons for the live test....
their first Teller-Ulam device in 1955.
The Shrimp device design later evolved into the Mk-21
Mark 21 nuclear bomb
The Mark 21 nuclear bomb was a United States nuclear gravity bomb first produced in 1955. It was based on the TX-21 "Shrimp" prototype that had been detonated during the Castle Bravo test in March 1954...
bomb, of which 275 units were produced, weighing 15,000 pounds (6,800 kg) and measuring 12.5 feet (3.8 m) long and 56 inches (1.4 m) in diameter. This 4 megaton bomb was produced until July 1956. In 1957, it was converted into the Mk-36
Mark 36 nuclear bomb
The Mark 36 was a heavy high-yield United States nuclear bomb designed in the 1950s. It was a thermonuclear bomb, using a multi-stage fusion secondary system to generate yields up to about 10 megatons...
and entered into production again.
External links
- Video of the Castle Bravo shot at sonicbomb.com
- Downloadable/Streamable Declassified Film: Operation Castle Commanders Report, at the Internet Archive
- Downloadable/Streamable Declassified Film: Military Effects Studies Operation Castle, at the Internet Archive
- Operation Castle
- US tests hydrogen bomb in Bikini (BBC NewsBBC NewsBBC News is the department of the British Broadcasting Corporation responsible for the gathering and broadcasting of news and current affairs. The department is the world's largest broadcast news organisation and generates about 120 hours of radio and television output each day, as well as online...
) - First-person article about conducting the test
- Compilation Video of Operation Castle shots on google video