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Fat Man

"Fat Man" was the codename of the atomic bomb Nuclear weapon

A nuclear weapon derives its destructive force from nuclear reaction [i]s of fission [i] ... 

 that was detonated over Nagasaki Nagasaki

listen, literally "long peninsula [i]", is the capital [i] and the largest city [i] o ... 

, Japan Japan

is an island country [i] in East Asia [i]. ... 

, by the United States United States

The United States of America, also known as the United States, the U.S., the U.S.A., a... 

 on August 9, 1945. It was the second of the two nuclear weapons to be used in warfare War

War is a conflict involving the organized use of weapon [i]s and physical force by state [i]s or other l ... 

. The name also refers more generically to the early nuclear weapon design Nuclear weapon design

Nuclear weapon designs are physical, chemical, and engineering arrangements which allow for the detonati... 

s of U.S. weapons based on the "Fat Man" model. It was an implosion-type Nuclear weapon design

Nuclear weapon designs are physical, chemical, and engineering arrangements which allow for the detonati... 

 weapon with a plutonium Plutonium

Plutonium is a radioactive [i], metal [i]lic chemical element [i]. ... 

 core. It was detonated at an altitude of about 1,800 feet over the city. It was dropped from the B-29 B-29 Superfortress

The Boeing B-29 Superfortress was a four-engine heavy bomber [i] propeller aircraft [i] ... 

 bomber Bockscar Bockscar

Bockscar, sometimes called Bock's Car or Bocks Car, is the name of a U.S. Army Air Force [i] ... 

, piloted by Major Charles Sweeney.

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Timeline

1945   World War II World War II

World War II, or the Second World War, was a worldwide [i] conflict [i] fought betwe ... 

: The United States United States

The United States of America, also known as the United States, the U.S., the U.S.A., a... 

 detonates an atomic bomb Nuclear weapon

A nuclear weapon derives its destructive force from nuclear reaction [i]s of fission [i] ... 

 nicknamed "Fat Man" over the city of Nagasaki Nagasaki

listen, literally "long peninsula [i]", is the capital [i] and the largest city [i] o ... 

, Japan Japan

is an island country [i] in East Asia [i]. ... 

 at 11:02 AM (local time).



Encyclopedia



"Fat Man" was the codename of the atomic bomb Nuclear weapon

A nuclear weapon derives its destructive force from nuclear reaction [i]s of fission [i] ... 

 that was detonated over Nagasaki Nagasaki

listen, literally "long peninsula [i]", is the capital [i] and the largest city [i] o ... 

, Japan Japan

is an island country [i] in East Asia [i]. ... 

, by the United States United States

The United States of America, also known as the United States, the U.S., the U.S.A., a... 

 on August 9, 1945. It was the second of the two nuclear weapons to be used in warfare War

War is a conflict involving the organized use of weapon [i]s and physical force by state [i]s or other l ... 

. The name also refers more generically to the early nuclear weapon design Nuclear weapon design

Nuclear weapon designs are physical, chemical, and engineering arrangements which allow for the detonati... 

s of U.S. weapons based on the "Fat Man" model. It was an implosion-type Nuclear weapon design

Nuclear weapon designs are physical, chemical, and engineering arrangements which allow for the detonati... 

 weapon with a plutonium Plutonium

Plutonium is a radioactive [i], metal [i]lic chemical element [i].... 

 core.

It was detonated at an altitude of about 1,800 feet over the city. It was dropped from the B-29 B-29 Superfortress

The Boeing B-29 Superfortress was a four-engine heavy bomber [i] propeller aircraft [i] ... 

 bomber Bockscar Bockscar

Bockscar, sometimes called Bock's Car or Bocks Car, is the name of a U.S. Army Air Force [i]... 

, piloted by Major Charles Sweeney. The bomb had a yield of about 21 kilotons of TNT Trinitrotoluene

Trinitrotoluene is an explosive [i].... 

, or 8.78×1013 joules = 88 TJ . Because of Nagasaki's hilly terrain, the damage was somewhat less extensive than that in relatively flat Hiroshima. An estimated 40,000 people were killed outright by the bombing at Nagasaki, and about 25,000 were injured. Many thousands more would die later from related injuries, and radiation sickness Radiation poisoning

Radiation poisoning, also called "radiation sickness", is a form of damage to organic tissue due to exce... 

 from nuclear fallout Nuclear fallout

Fallout is the residual radiation hazard from a nuclear explosion [i], so named because it "falls out" o ... 

.

Technology



The weapon was 7 feet 8 inches long, five feet in diameter, and weighed 10,200 pounds . In accordance with the name, it was more than twice as wide as Little Boy Little Boy

Little Boy was the codename [i] of the atomic bomb [i] which was dropped on Hiroshima [i] ... 

, which was dropped on Hiroshima Hiroshima

The Japanese city of is the capital of Hiroshima Prefecture [i], and the largest city in the Chugoku region [i]... 

 three days earlier; however, the mass was only 10% more.

"Fat Man" was an implosion Implosion

Implosion is a process in which objects are destroyed by collapsing in on themselves.... 

-type weapon using plutonium Plutonium

Plutonium is a radioactive [i], metal [i]lic chemical element [i].... 

. A subcritical sphere of plutonium was placed in the center of a hollow sphere of high explosive Explosive material

Any explosive material has the following characteristics:
... 

. Numerous detonators Exploding-bridgewire detonator

The exploding-bridgewire detonator was invented by Luis Alvarez [i] and Lawrence Johnson [i] ... 

 located on the surface of the high explosive were fired simultaneously to produce a powerful inward pressure Pressure

Pressure is the force [i] per unit area [i] applied on a surface in a direction perpendicular [i] ... 

 on the core, squeezing it and increasing its density, resulting in a supercritical condition and a nuclear explosion.

The difficulty in the design lay primarily in properly compressing the plutonium core into a near-perfect sphere; if the compression was not symmetrical it would cause the plutonium to be simply ejected from the weapon, making it an unefficient and un-impressive "dirty bomb". In order to accomplish the compression, the high-explosive system had to be carefully designed as a series of explosive lens Explosive lens

An explosive lens, as used for example in nuclear weapon [i]s, is a highly specialised explosive charge.... 

es which used alternating fast- and slow-burning explosives to shape the explosive shockwave into the desired spherical shape. An early idea of this sort had been raised by physicist Richard Tolman during early discussions of possible bomb designed, though Seth Neddermeyer Seth Neddermeyer

Seth Neddermeyer was a physicist who worked in the Manhattan Project [i]. ... 

 is credited for developing the idea further. The idea of using shaped charge Shaped charge

A shaped charge is an explosive [i] charge shaped to focus the effect of the explosive's energy. ... 

s came from mathematician John von Neumann John von Neumann

John von Neumann was an Austro-Hungarian [i] mathematician [i] and polymath [i] who ma ... 

, and both he and George Kistiakowsky George Kistiakowsky

George Bogdan Kistiakowsky was a chemistry professor at Harvard [i] who participated in the Manhattan Project [i] ... 

 eventually ended up being the principle architects behind the lens system.



At first it was thought that two pieces of subcritical plutonium could simply be shot into one another to create a nuclear explosion, and a plutonium gun-type design of this sort was worked on for some time during the Manhattan Project. However in April 1944 it was discovered that plutonium created for the bomb in the nuclear reactor Nuclear reactor

A nuclear reactor is a device in which nuclear chain reaction [i]s are initiated, controlled, and sustai ... 

s at Hanford, Washington Hanford Site

The Hanford Site occupies 1,517 km2 in Benton County [i], south-central Washington [i] ... 

—even though it was supergrade weapon plutonium containing only about 0.9% Pu-240—was not as pure as the initial samples of plutonium developed at the cyclotron Cyclotron

A cyclotron is a type of particle accelerator [i]. ... 

s at Ernest O. Lawrence Ernest Lawrence

Ernest Orlando Lawrence was an American [i] physicist and Nobel Laureate best known for h ... 

's Radiation Laboratory Lawrence Berkeley National Laboratory

The Ernest Orlando Lawrence Berkeley National Laboratory , formerly the Berkeley Radiation Laboratory... 

 in Berkeley, California Berkeley, California

Berkeley is a city on the east shore of San Francisco Bay [i] in northern [i] California [i] ... 

. Because of the presence of the isotope Pu-240, reactor-bred plutonium had a much higher rate of spontaneous neutron emission than was previously thought, and if a gun-type device was used it would most likely pre-detonate and result in a messy and costly "fizzle." The spontaneous fission rate of Pu-240 is 415,000 fissions/, and the amount was 0.9% of 6.2 kg, is 56 g. Thus there were 23,000 spontaneous fissions per second. This means that the last few centimeters would have to be travelled in preferably much less than 40 microseconds.

It is theoretically possible to build a plutonium gun-type device, but it would need to be 19 feet long in order to allow the subcritical masses to be fused into a critical mass before a fizzle occurs. The mass of a plutonium gun-type device would have been beyond the payload of the B-29.

After this problem was realized, the entire Los Alamos Los Alamos National Laboratory

Los Alamos National Laboratory is a United States Department of Energy [i] national laboratory [i] ... 

 laboratory re-organized around the problem of the implosion bomb, the "Fat Man" starting in June 1944.

The gun-type method could still be used for highly enriched uranium Uranium

Uranium is a chemical element [i] in the periodic table [i] that has the symbol U and atomic number [i] ... 

, though, and was employed in the "Little Boy Little Boy

Little Boy was the codename [i] of the atomic bomb [i] which was dropped on Hiroshima [i] ... 

" weapon, which was used against Hiroshima Hiroshima

The Japanese city of is the capital of Hiroshima Prefecture [i], and the largest city in the Chugoku region [i]... 

, Japan Japan

is an island country [i] in East Asia [i]. ... 

. For a variety of reasons, the implosion method is both more efficient than the gun-type method, and also far safer, as a perfect synchronization of the explosion lenses is required for the core to properly detonate, greatly reducing the chances of an accidental nuclear detonation.



Because of its complicated firing mechanism, and the need for previously untested synchronization of explosives and precision design, it was felt that a full test of the concept was needed before the scientists and military representatives could be confident it would perform correctly under combat conditions. On July 16, 1945, a device utilizing a similar mechanism detonated in a test explosion Nuclear testing

Nuclear testing is experimentation with nuclear weapon [i]s.... 

 at a remote site in New Mexico New Mexico

New Mexico is a southwestern [i] state in the United States of America [i]. ... 

, known as the "Trinity Trinity test

The "Trinity" test was the first test of a nuclear weapon [i], conducted by the United States [i] ... 

" test. In the end, it gave somewhere around 20 kt , 2 to 4 times the expected yield.

The Soviet Union's first nuclear weapon Soviet atomic bomb project

The Soviet project to develop an atomic bomb began during World War II [i] in the Soviet Union [i]. ... 

 detonated at Operation First Lightning was more or less a purposeful copy of the "Fat Man" device, on which they had obtained detailed information from the spy Klaus Fuchs Klaus Fuchs

Emil Julius Klaus Fuchs was a German [i]-born theoretical physicist [i] and... 

.

The names for all three projects were created by Robert Serber Robert Serber

Robert Serber was a physicist who participated in the Manhattan Project [i].
... 

, a former student of Los Alamos director Robert Oppenheimer Robert Oppenheimer

J. Robert Oppenheimer was an American [i] theoretical physicist [i], ... 

's who worked on the project. According to his later memoirs, he chose them based on their design shapes; the "Thin Man" would be a very long device, and the name came from the Dashiell Hammett Dashiell Hammett

Samuel Dashiell Hammett was an American author of "hard-boiled [i]" detective novels and short stories [i] ... 

 detective novel The Thin Man

The Thin Man is a 1933 mystery novel by Dashiell Hammett [i]. ... 

 and series of movies The Thin Man

The Thin Man is a 1933 mystery novel by Dashiell Hammett [i]. ... 

 by the same name; the "Fat Man" bomb would be round and fat and was named after Sidney Greenstreet Sydney Greenstreet

Sydney Hughes Greenstreet was an actor [i].
... 

's character in The Maltese Falcon The Maltese Falcon

The Maltese Falcon is a detective novel by Dashiell Hammett [i] that has been adapted several times ... 

. "Little Boy" would come last and be named only to contrast to the "Thin Man" bomb.

The bombing of Nagasaki

Main Article: Atomic bombings of Hiroshima and Nagasaki Atomic bombings of Hiroshima and Nagasaki

On the Sunday morning of August 6 [i], 1945 [i] at 8:15AM [i] the United States Army Air Forces [i] dropped th ... 





By August 1, two nuclear weapons had been produced and a third nearly completed. The U.S. Army Air Forces United States Army Air Forces

The United States Army Air Forces was a part of the U.S. Army [i] during World War II [i] ... 

 had trained and deployed to Tinian Tinian

Tinian is one of the three principal islands of the Commonwealth of the Northern Marianas Islands [i]. ... 

 a unit to drop the bombs. Components of the uranium bomb "Little Boy" were delivered by the USS Indianapolis along with its U-235 projectile, and the target rings for "Little Boy" and all components of the "Fat Man" bomb were delivered by air. On August 6, 1945, "Little Boy" was dropped on Hiroshima Hiroshima

The Japanese city of is the capital of Hiroshima Prefecture [i], and the largest city in the Chugoku region [i]... 

.

On the morning of August 9 1945, the U.S. B-29 Superfortress B-29 Superfortress

The Boeing B-29 Superfortress was a four-engine heavy bomber [i] propeller aircraft [i] ... 

 Bockscar Bockscar

Bockscar, sometimes called Bock's Car or Bocks Car, is the name of a U.S. Army Air Force [i]... 

, flown by the crew of 393rd Squadron commander Major Charles W. Sweeney, carried the "Fat Man" bomb, with Kokura Kokura

Kokura is an ancient castle town [i] in Fukuoka Prefecture [i], Japan [i], guarding, via its suburb Moji [i] ... 

 as the primary target and Nagasaki Nagasaki

listen, literally "long peninsula [i]", is the capital [i] and the largest city [i] o ... 

 the secondary target. The mission plan for the second attack was nearly identical to that of the Hiroshima mission, with two B-29's flying an hour ahead as weather scouts and two additional B-29's in Sweeney's flight for instrumentation and photographic support of the mission. Sweeney also took off with his weapon already armed but with the electrical safety plugs still engaged.

Observers aboard the weather planes reported both targets clear. When Sweeny's aircraft arrived at the assembly point for his flight off the coast of Japan, the third plane failed to make the rendezvous. Bockscar and the instrumentation plane circled for forty minutes without locating Hopkins. Already thirty minutes behind schedule, Sweeney decided to fly on without Hopkins. The resulting explosion had a blast yield equivalent to 21 kilotons of TNT.

According to most estimates, about 70,000 of Nagasaki's 240,000 residents were killed instantly, and up to 60,000 were injured. The radius of total destruction was about 1.6 km , followed by fires across the northern portion of the city to 3.2 km south of the bomb. The total number of residents killed is believed to be as many as 80,000, including those who died from radiation poisoning in the following months.

Immediately after the bombings of Japan, the United States produced a technical history of the Manhattan Project, known as the Smyth Report Smyth Report

The Smyth Report was the common name given to an administrative history written by physicist [i] ... 

, that did not disclose the information that the "Fat Man" device was different from the "Little Boy" device, and did not imply that a different method was required for plutonium weapons. The "implosion" design was considered top-secret in the United States until it was declassified and released during the testimony of David Greenglass David Greenglass

David Greenglass was an Atomic Spy [i] for the Soviet Union [i].... 

 against Ethel and Julius Rosenberg Julius and Ethel Rosenberg

Julius Rosenberg and Ethel Greenglass Rosenberg were American [i] Communists [i] ... 

 in 1951. Photographs of the casings of "Little Boy" and "Fat Man" were not released publicly until the 1960s.

The United States produced a small stockpile of "Fat Man" bombs after the war, but they were highly idiosyncratic and extremely delicate. It was eventually reworked in the MK 4 Fat Man bomb, which was similar in principle but was appropriate for long-term stockpiling and use by nonexperts, and used a more efficient implosion system .

Interior of bomb

The original blueprints of the interior of both Fat Man and Little Boy are still classified. However, there is some information about the main parts in the public domain available. Below is a diagram of the main parts of the "Fat Man" bomb itself, followed by a more detailed look at the different materials used in the physics package Physics package

The physics package is the portion of a nuclear weapon [i] that includes the actual explosive portion of ... 

 of the bomb .



  1. AN 219 contact fuse
  2. Archie radar antenna
  3. Plate with batteries
  4. X-Unit, a firing set placed near the charge
  5. Hinge fixing the two ellipsoidal parts of the bomb
  6. High explosive pentagonal lens , together with the next item forming the pattern of a truncated icosahedron Truncated icosahedron

    The truncated icosahedron is an Archimedean solid [i]. ... 

  7. High explosive hexagonal lens
  8. California Parachute tail assembly
  9. Dural casing, ~140 cm inner diameter
  10. Cones that contained the whole sphere
  11. Explosive lenses
  12. Nuclear material
  13. Plate with instruments
  14. Barotube collector


Physics package

Schematic cross-section of the "gadget" used in the Trinity test Trinity test

The "Trinity" test was the first test of a nuclear weapon [i], conducted by the United States [i] ... 

 on which the "Fat Man" design was based; some boundaries are approximate. From left to right :
*****

See also

  • Atomic bombings of Hiroshima and Nagasaki Atomic bombings of Hiroshima and Nagasaki

    On the Sunday morning of August 6 [i], 1945 [i] at 8:15AM [i] the United States Army Air Forces [i] dropped th ... 

  • Fat Man and Little Boy, a 1989 film that reenacts the Manhattan Project
  • List of nuclear weapons
  • Little Boy Little Boy

    Little Boy was the codename [i] of the atomic bomb [i] which was dropped on Hiroshima [i] ... 

  • Manhattan Project Manhattan Project

    The Manhattan Project refers to the effort to develop the first nuclear weapon [i]s during World War II [i] ... 

  • The gadget The gadget

    "The gadget" was the code-name given to the first nuclear explosive [i] developed under t ... 

  • Trinity test Trinity test

    The "Trinity" test was the first test of a nuclear weapon [i], conducted by the United States [i] ... 

  • Bockscar Bockscar

    Bockscar, sometimes called Bock's Car or Bocks Car, is the name of a U.S. Army Air Force [i]... 



Notes


External links

  • and at Nuclear Weapons Archive
  • in QuickTime VR format