Thin Man nuclear bomb
Encyclopedia
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...
was a proposed 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...
gun-type
Gun-type fission weapon
Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another...
nuclear bomb which the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
was developing during the Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
. Its development was aborted when it was discovered that the spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
rate of nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
-bred
Breeder reactor
A breeder reactor is a nuclear reactor capable of generating more fissile material than it consumes because its neutron economy is high enough to breed fissile from fertile material like uranium-238 or thorium-232. Breeders were at first considered superior because of their superior fuel economy...
plutonium was too high for use in a gun-type design.
Specifications
The "Thin Man" design was an early nuclear weapon design proposed before plutonium had been successfully bred in a nuclear reactorNuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
from the irradiation of uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
. It was assumed that plutonium, like uranium-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
, would be able to be assembled into a critical mass
Critical mass
A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The...
by simply shooting a sub-critical piece of it into another sub-critical piece. To avoid pre-detonation, a plutonium "bullet" would need to be accelerated to a speed of at least 3000 feet per second (914.4 m/s)—if not, then the plutonium would begin a nuclear 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...
reaction before fully assembling and blow itself apart prematurely.
Estimated dimensions of the Mark 2 were a diameter of 2 foot (0.6096 m) and a length of 18 feet (5.5 m); the long length was necessary in order for the plutonium "bullet" to pick up adequate speed before reaching the "target". Weight was estimated at 7500 pounds (3,401.9 kg) for the final weapon model.
Early decisions
Robert Oppenheimer
Julius Robert Oppenheimer was an American theoretical physicist and professor of physics at the University of California, Berkeley. Along with Enrico Fermi, he is often called the "father of the atomic bomb" for his role in the Manhattan Project, the World War II project that developed the first...
held a conference in Berkeley, California
Berkeley, California
Berkeley is a city on the east shore of the San Francisco Bay in Northern California, United States. Its neighbors to the south are the cities of Oakland and Emeryville. To the north is the city of Albany and the unincorporated community of Kensington...
, at which various engineers and physicists discussed nuclear bomb design issues. Three designs were put forth: a uranium-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
gun-type bomb, a plutonium gun-type bomb, and an early form of a plutonium implosion-type bomb. These later became the "Little Boy
Little Boy
"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...
" (uranium gun), "Thin Man" (plutonium gun), and "Fat Man
Fat Man
"Fat Man" is the codename for the atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9, 1945. It was the second of the only two nuclear weapons to be used in warfare to date , and its detonation caused the third man-made nuclear explosion. The name also refers more...
" (plutonium implosion) code-named design projects.
The names for all three projects were created by Robert Serber
Robert Serber
Robert Serber was an American physicist who participated in the Manhattan Project. He was born in Philadelphia, Pennsylvania; he was the eldest son of David Serber and Rose Frankel. He married Charlotte Leof in 1933. Rose Serber died in 1922; David married Charlotte's cousin Frances Leof in...
, a former student of Oppenheimer'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 detective novels and short stories, and political activist. Among the enduring characters he created are Sam Spade , Nick and Nora Charles , and the Continental Op .In addition to the significant influence his novels and stories had on...
detective novel The Thin Man
The Thin Man
The Thin Man is a detective novel by Dashiell Hammett, originally published in Redbook. Although he never wrote a sequel, the book became the basis for a successful six-part film series which also began in 1934 with The Thin Man and starred William Powell and Myrna Loy...
and series of movies
The Thin Man (film)
The Thin Man is a 1934 American comic detective film starring William Powell and Myrna Loy as Nick and Nora Charles, a flirtatious married couple who banter wittily as they solve crimes with ease. Nick is a hard drinking retired detective and Nora a wealthy heiress...
by the same name; the "Fat Man" bomb would be round and fat and was named after Sidney Greenstreet's character in The Maltese Falcon
The Maltese Falcon (1941 film)
The Maltese Falcon is a 1941 Warner Bros. film based on the novel of the same name by Dashiell Hammett and a remake of the 1931 film of the same name...
. "Little Boy" would come last and be named only to contrast to the "Thin Man" bomb.
At that conference, it was generally agreed that the known physical and nuclear characteristics of uranium-235 and plutonium easily allowed production of gun-type uranium bombs, and with some difficulty plutonium gun-type bombs. Because plutonium had a higher spontaneous fission rate, the plutonium gun bomb would have to have a higher assembly velocity (and a longer, physically much larger gun) than a uranium bomb.
It was estimated that the design of a uranium gun-type bomb, which required a lower velocity, would be much easier than a plutonium gun-type bomb. The early analysis of production methods for plutonium and uranium showed that the Manhattan Project would have problems getting enough uranium for many gun-type bombs before the projected end of the war, but could probably produce enough plutonium.
Implosion-type bombs were determined to be significantly more efficient (in terms of explosive yield per unit mass of fissile material in the bomb), because compressed fissile materials react more rapidly and therefore more completely.
Oppenheimer, reviewing his options in early 1943, determined that two projects should proceed forwards: the "Thin Man" project (plutonium gun) and the "Fat Man" project (plutonium implosion). It was decided that the plutonium gun would receive the bulk of the research effort, since it was the project with the most uncertainty involved. It was assumed that the uranium gun-type bomb could be more easily adapted from it after the fact.
Development
Oppenheimer assembled a team including senior engineer Edwin Rose and senior physicist Charles CritchfieldCharles Critchfield
Charles Louis Critchfield was a mathematical physicist who was chosen by J. Robbert Oppenheimer to help with the Los Alamos National Laboratory in 1943.-External links:* , Charles Babbage Institute, University of Minnesota...
to begin design work on plutonium gun designs. In June 1943, Navy Capt. William Sterling Parsons
William Sterling Parsons
Rear Admiral William Sterling "Deak" Parsons was a naval officer who worked as an ordnance expert on the Manhattan Project during World War II...
took over the Ordnance Division and direct management of the "Thin Man" project.
Design issues
Two major concerns were identified with the "Thin Man" design during its development: first, bomb aerodynamics after being dropped from an aircraft, and second, predetonation.Aerodynamics
The great length of the "Thin Man" bomb led to aerodynamic instabilities. Subscale models of the bomb were dropped from a TBF AvengerTBF Avenger
The Grumman TBF Avenger was a torpedo bomber developed initially for the United States Navy and Marine Corps, and eventually used by several air or naval arms around the world....
at the US Navy test range at Dahlgren, Virginia
Dahlgren, Virginia
Dahlgren is a census-designated place in King George County, Virginia, United States. The population was 997 at the 2000 census. The community is located within the Northern Neck George Washington Birthplace American Viticultural Area winemaking appellation established by the United States...
starting in August, 1943. The bombs would spin sideways after being dropped, and broke up when they hit the ground.
Extensive aerodynamic testing, particularly of the shape of the bomb's nose and tail and the tail fins, proceeded for the next year. The design ended up with a bulging nose, thin body, and wider tail assembly with the plutonium "target" assembly, plus very long tail fins for stability.
Full scale test units were dropped starting on March 6, 1944, at Muroc Army Air Base
Edwards Air Force Base
Edwards Air Force Base is a United States Air Force base located on the border of Kern County, Los Angeles County, and San Bernardino County, California, in the Antelope Valley. It is southwest of the central business district of North Edwards, California and due east of Rosamond.It is named in...
(now Edwards Air Force Base) and were successful.
Predetonation
The feasibility of a plutonium bomb had been questioned in 1942, when James ConantJames Conant
James Conant may refer to:* James Bryant Conant , American chemist and educational administrator* James F. Conant , American philosopher...
heard on 14 November (indirectly via Wallace Akers - then Research Director of ICI
Imperial Chemical Industries
Imperial Chemical Industries was a British chemical company, taken over by AkzoNobel, a Dutch conglomerate, one of the largest chemical producers in the world. In its heyday, ICI was the largest manufacturing company in the British Empire, and commonly regarded as a "bellwether of the British...
) that James Chadwick
James Chadwick
Sir James Chadwick CH FRS was an English Nobel laureate in physics awarded for his discovery of the neutron....
had recently concluded that plutonium might not be a practical fissionable material for weapons because of impurities. He consulted Lawrence and Compton, who acknowledged that scientists at Chicago and Berkeley had known about the problem since October, but could offer no ready solution. He advised Groves, who assembled a special committee of Lawrence, Compton, Oppenheimer and McMillan. They concluded that any problems could be overcome by requiring higher purity. Du Pont (who were considering taking over all the plutonium project, not just the chemical separation process) were advised, but still had strong doubts about the project.
In April 1944, experiments by Emilio G. Segrè
Emilio G. Segrè
Emilio Gino Segrè was an Italian-born, naturalized American, physicist and Nobel laureate in physics, who with Owen Chamberlain, discovered antiprotons, a sub-atomic antiparticle.-Biography:...
on the newly reactor-produced 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...
from Hanford
Hanford Site
The Hanford Site is a mostly decommissioned nuclear production complex on the Columbia River in the U.S. state of Washington, operated by the United States federal government. The site has been known by many names, including Hanford Works, Hanford Engineer Works or HEW, Hanford Nuclear Reservation...
showed that it contained impurities in the form of the isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
plutonium-240
Plutonium-240
Plutonium-240 is an isotope of the metal plutonium formed when plutonium-239 captures a neutron. About 62% to 73% of the time when Pu-239 captures a neutron it undergoes fission; the rest of the time it forms Pu-240. The longer a nuclear fuel element remains in a nuclear reactor the greater the...
. Plutonium-240 has a far higher spontaneous fission rates and radioactivity than the cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
-produced Pu-239 isotopes on which the original measurements had been made, and its inclusion in reactor-bred plutonium appeared unavoidable. This meant that the background fission rate of the plutonium was so high that it would be highly likely the plutonium would predetonate and blow itself apart in the initial forming of a critical mass. The gun barrel required to speed up the plutonium to levels where predetonation would be less likely would require a gun barrel too long for any existing or planned bomber. The only way to use plutonium in a workable bomb was thus implosion — a far more difficult engineering task.
The impracticability of a gun-type bomb using plutonium was agreed a meeting in Los Alamos on July 17, 1944. All gun-type work in the Manhattan Project was directed at the enriched uranium gun design (Little Boy
Little Boy
"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...
), and almost all of the research at Los Alamos
Los 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...
was re-oriented around the problems of implosion for the Fat Man
Fat Man
"Fat Man" is the codename for the atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9, 1945. It was the second of the only two nuclear weapons to be used in warfare to date , and its detonation caused the third man-made nuclear explosion. The name also refers more...
bomb.
History links
- Plutonium Complicates Early Gun Work at the Los Alamos National Laboratory history website
- Little Boy and Fat Man at LANL history website
- Nuclear weapons timeline
- The Enola Gay at US Air Force Association
- Silverplate: Aircraft of the Manhattan Project
- Allbombs.html list of all American nuclear bombs at nuclearweaponarchive.org