The "Fat Man" was round and fat so it was named after Kasper Gutman, a rotund character in Hammett's 1930 novel The Maltese Falcon, played by Sydney Greenstreet in the 1941 film version.
The first shipments of highly enriched uranium were sent to the Los Alamos Laboratory in June 1944. Most of the uranium necessary for the production of the bomb came from the Shinkolobwe mine and was made available thanks to the foresight of the CEO of the High Katanga Mining Union, Edgar Sengier, who had of uranium ore transported to a New York warehouse in 1940.
The "Fat Man" was round and fat so it was named after Kasper Gutman, a rotund character in Hammett's 1930 novel The Maltese Falcon, played by Sydney Greenstreet in the 1941 film version.
Enrichment was performed at Oak Ridge, Tennessee, where the electromagnetic separation plant, known as Y-12, became fully operational in March 1944.
The first shipments of highly enriched uranium were sent to the Los Alamos Laboratory in June 1944. Most of the uranium necessary for the production of the bomb came from the Shinkolobwe mine and was made available thanks to the foresight of the CEO of the High Katanga Mining Union, Edgar Sengier, who had of uranium ore transported to a New York warehouse in 1940.
At least part of the in addition to the uranium ore and uranium oxide captured by the Alsos Mission in 1944 and 1945 went to Oak Ridge for enrichment, as did of uranium oxide captured on the Japan-bound after Germany's surrender in May 1945. Little Boy was a simplification of Thin Man, the previous gun-type fission weapon design.
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. In July 1944, almost all research at Los Alamos was redirected to the implosion-type plutonium weapon.
"Little Boy" was the codename for the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II.
At least part of the in addition to the uranium ore and uranium oxide captured by the Alsos Mission in 1944 and 1945 went to Oak Ridge for enrichment, as did of uranium oxide captured on the Japan-bound after Germany's surrender in May 1945. Little Boy was a simplification of Thin Man, the previous gun-type fission weapon design.
The simplified weapon was short enough to fit into a B-29 bomb bay. The design specifications were completed in February 1945, and contracts were let to build the components.
The bomb, except for the uranium payload, was ready at the beginning of May 1945.
Manhattan District Engineer Kenneth Nichols expected on 1 May 1945 to have uranium-235 "for one weapon before August 1 and a second one sometime in December", assuming the second weapon would be a gun-type; designing an implosion bomb for uranium-235 was considered, and this would increase the production rate.
The only test explosion of a nuclear weapon concept had been of an implosion-type device employing plutonium as its fissile material, and took place on 16 July 1945 at the Trinity nuclear test.
Neutron initiators at the base of the projectile were activated by the impact. ===Counter-intuitive design=== For the first fifty years after 1945, every published description and drawing of the Little Boy mechanism assumed that a small, solid projectile was fired into the center of a larger, stationary target.
The first drop test was conducted with L-1 on 23 July 1945.
Jeppson monitored the bomb's circuits. The bomb was dropped at approximately 08:15 (JST) on 6 August 1945.
According to figures published in 1945, 66,000 people were killed as a direct result of the Hiroshima blast, and 69,000 were injured to varying degrees.
After considering many estimation methods, a 1985 report concluded that the yield was ± 20%. ==Physical effects== After being selected in April 1945, Hiroshima was spared conventional bombing to serve as a pristine target, where the effects of a nuclear bomb on an undamaged city could be observed.
The Navy Bureau of Ordnance built another 25 Little Boy assemblies in 1947 for use by the Lockheed P2V Neptune nuclear strike aircraft which could be launched from the Midway-class aircraft carriers.
By early 1947, the problem caused by the Wigner effect was on its way to solution, and the three officers were reassigned. The Navy Bureau of Ordnance built 25 Little Boy assemblies in 1947 for use by the nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft (which could be launched from but not land on the Midway-class aircraft carriers).
Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six.
All the Little Boy units were withdrawn from service by the end of January 1951. ==Naming== Physicist Robert Serber named the first two atomic bomb designs during World War II based on their shapes: Thin Man and Fat Man.
All the Little Boy units were withdrawn from service by the end of January 1951. The Smithsonian Institution displayed a Little Boy (complete, except for enriched uranium), until 1986.
In 1953, Frederick Reines calculated the yield as .
The picture at right shows the effects of a nuclear-bomb-generated 5 psi pressure wave on a test structure in Nevada in 1953. A major effect of this kind of structural damage was that it created fuel for fires that were started simultaneously throughout the severe destruction region. ===Fire=== The first effect of the explosion was blinding light, accompanied by radiant heat from the fireball.
This figure became the official yield. ===Project Ichiban=== In 1962, scientists at Los Alamos created a mockup of Little Boy known as "Project Ichiban" in order to answer some of the unanswered questions, but it failed to clear up all the issues.
In 1982, Los Alamos created a replica Little Boy from the original drawings and specifications.
After considering many estimation methods, a 1985 report concluded that the yield was ± 20%. ==Physical effects== After being selected in April 1945, Hiroshima was spared conventional bombing to serve as a pristine target, where the effects of a nuclear bomb on an undamaged city could be observed.
All the Little Boy units were withdrawn from service by the end of January 1951. The Smithsonian Institution displayed a Little Boy (complete, except for enriched uranium), until 1986.
The government returned the emptied casing to the Smithsonian in 1993.
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