A report on Project Y

Robert Oppenheimer (left), Leslie Groves (center) and Robert Sproul (right) at the ceremony to present the Los Alamos Laboratory with the Army-Navy "E" Award at the Fuller Lodge on 16 October 1945
In nuclear fission, the atomic nucleus of a heavy element splits into two or more light ones when a neutron is captured. If more neutrons are emitted, a nuclear chain reaction becomes possible.
In nuclear fusion, the nuclei of light elements are fused to create a heavier element.
Map of Los Alamos site, New Mexico, 1943–45
Four-family apartment units at Los Alamos
The Technical Area at Los Alamos. There was a perimeter fence around the entire site, but also an inner fence shown here around the Technical Area.
The main gate at Los Alamos
Passage between buildings A and B in the Technical Area
Isidor Isaac Rabi, Dorothy McKibbin, Robert Oppenheimer and Victor Weisskopf at Oppenheimer's home in Los Alamos in 1944
A row of Thin Man casings. Fat Man casings are visible in the background. The tow truck was used by the 216th Army Air Forces Base Unit to move them.
A ring of electrorefined plutonium. It has a purity of 99.96%, weighs 5.3 kg, and is about 11 cm in diameter. It is enough plutonium for one bomb core. The ring shape helps with criticality safety.
Plutonium has six allotropes at ambient pressure: alpha (α), beta (β), gamma (γ), delta (δ), delta prime (δ'), & epsilon (ε)
Explosive lenses are used to compress a fissile core inside an implosion-type nuclear weapon.
An implosion-type nuclear bomb. In the center is the neutron initiator (red). It is surrounded by the plutonium hemispheres. There is a small air gap (white, not in the original Fat Man design) and then the uranium tamper. Around that is the aluminium pusher (purple). This is encased in the explosive lenses (gold). Colors are the same as in the diagram opposite.
Norris Bradbury, group leader for bomb assembly, stands next to the partially assembled Gadget atop the Trinity test tower. Later, he became the director of Los Alamos vice Oppenheimer.
A Little Boy unit on Tinian connected to test equipment, possibly to test or charge components within the device
Water Boiler
The April 1946 colloquium on the Super. In the front row are (left to right) Norris Bradbury, John Manley, Enrico Fermi and J. M. B. Kellogg. Robert Oppenheimer, in dark coat, is behind Manley; to Oppenheimer's left is Richard Feynman. The Army officer on the left is Colonel Oliver Haywood.
Herbert Lehr and Harry Daghlian loading the assembled tamper plug containing the plutonium pit and initiator into a sedan for transport from the McDonald Ranch House to the Trinity shot tower
The explosives of "the gadget" were raised to the top of the tower for the final assembly.
Deak Parsons (right) supervises loading the Little Boy bomb into the B-29 Enola Gay. Norman Ramsey is on his left, with his back to the camera.
Fat Man bomb, with liquid asphalt sealant sprayed on the casing's seams, is readied on Tinian.
Remote handling of a kilocurie source of radiolanthanum for a RaLa Experiment at Los Alamos
Bradbury (left) examines plans for new laboratory sites and permanent housing with Leslie Groves of the Armed Forces Special Weapons Project (center) and Eric Jette (right) in April 1947; Colonel Lyle E. Seeman stands behind Bradbury, second from the left.

Secret laboratory established by the Manhattan Project and operated by the University of California during World War II.

- Project Y
Robert Oppenheimer (left), Leslie Groves (center) and Robert Sproul (right) at the ceremony to present the Los Alamos Laboratory with the Army-Navy "E" Award at the Fuller Lodge on 16 October 1945

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The Trinity test of the Manhattan Project on 16 July 1945 was the first detonation of a nuclear weapon.

Manhattan Project

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Research and development undertaking during World War II that produced the first nuclear weapons.

Research and development undertaking during World War II that produced the first nuclear weapons.

The Trinity test of the Manhattan Project on 16 July 1945 was the first detonation of a nuclear weapon.
Enrico Fermi, John R. Dunning, and Dana P. Mitchell in front of the cyclotron in the basement of Pupin Hall at Columbia University
March 1940 meeting at Berkeley, California: Ernest O. Lawrence, Arthur H. Compton, Vannevar Bush, James B. Conant, Karl T. Compton, and Alfred L. Loomis
Different fission bomb assembly methods explored during the July 1942 conference
Manhattan Project Organization Chart, 1 May 1946
Oppenheimer and Groves at the remains of the Trinity test in September 1945, two months after the test blast and just after the end of World War II. The white overshoes prevented fallout from sticking to the soles of their shoes.
Groves confers with James Chadwick, the head of the British Mission.
Shift change at the Y-12 uranium enrichment facility at the Clinton Engineer Works in Oak Ridge, Tennessee, on 11 August 1945. By May 1945, 82,000 people were employed at the Clinton Engineer Works. Photograph by the Manhattan District photographer Ed Westcott.
Physicists at a Manhattan District-sponsored colloquium at the Los Alamos Laboratory on the Super in April 1946. In the front row are Norris Bradbury, John Manley, Enrico Fermi and J. (Jerome) M. B. Kellogg (1905-1981). Robert Oppenheimer, in dark coat, is behind Manley; to Oppenheimer's left is Richard Feynman. The Army officer on the left is Colonel Oliver Haywood.
Map of Los Alamos site, New Mexico, 1943–45
Hanford workers collect their paychecks at the Western Union office.
The majority of the uranium used in the Manhattan Project came from the Shinkolobwe mine in Belgian Congo.
Oak Ridge hosted several uranium separation technologies. The Y-12 electromagnetic separation plant is in the upper right. The K-25 and K-27 gaseous diffusion plants are in the lower left, near the S-50 thermal diffusion plant. The X-10 was for plutonium production.
Alpha I racetrack at Y-12
Calutron Girls were young women who monitored calutron control panels at Y-12. Gladys Owens, seated in the foreground, was unaware of what she had been involved in.
Oak Ridge K-25 plant
The S-50 plant is the dark building to the upper left behind the Oak Ridge powerhouse (with smoke stacks).
Workers load uranium slugs into the X-10 Graphite Reactor.
Aerial view of Hanford B-Reactor site, June 1944
Map of the Hanford Site. Railroads flank the plants to the north and south. Reactors are the three northernmost red squares, along the Columbia River. The separation plants are the lower two red squares from the grouping south of the reactors. The bottom red square is the 300 area.
A row of Thin Man casings. Fat Man casings are visible in the background.
An implosion-type nuclear bomb
Remote handling of a kilocurie source of radiolanthanum for a RaLa Experiment at Los Alamos
The explosives of "the gadget" were raised to the top of the tower for the final assembly.
The Trinity test of the Manhattan Project was the first detonation of a nuclear weapon.
Major General Leslie R. Groves, Jr., speaks to service personnel Oak Ridge Tennessee in August 1945.
A billboard encouraging secrecy among Oak Ridge workers
Security poster, warning office workers to close drawers and put documents in safes when not being used
Allied soldiers dismantle the German experimental nuclear reactor at Haigerloch.
Silverplate B-29 Straight Flush. The tail code of the 444th Bombardment Group is painted on for security reasons.
Little Boy explodes over Hiroshima, Japan, 6 August 1945 (left);
Fat Man explodes over Nagasaki, Japan, 9 August 1945 (right).
Presentation of the Army–Navy "E" Award at Los Alamos on 16 October 1945. Standing, left to right: J. Robert Oppenheimer, unidentified, unidentified, Kenneth Nichols, Leslie Groves, Robert Gordon Sproul, William Sterling Parsons.
President Harry S. Truman signs the Atomic Energy Act of 1946, establishing the United States Atomic Energy Commission.
The Lake Ontario Ordnance Works (LOOW) near Niagara Falls became a principal repository for Manhattan Project waste for the Eastern United States. All of the radioactive materials stored at the LOOW site—including thorium, uranium, and the world's largest concentration of radium-226—were buried in an "Interim Waste Containment Structure" (in the foreground) in 1991.
A "bomb" (pressure vessel) containing uranium halide and sacrificial metal, probably magnesium, being lowered into a furnace
After the reaction, the interior of a bomb coated with remnant slag
A uranium metal "biscuit" from the reduction reaction

Nuclear physicist Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs.

J. Robert Oppenheimer, c. 1944

J. Robert Oppenheimer

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American theoretical physicist.

American theoretical physicist.

J. Robert Oppenheimer, c. 1944
Heike Kamerlingh Onnes' Laboratory in Leiden, Netherlands, 1926. Oppenheimer is in the middle row, second from the left.
The University of California, Berkeley, where Oppenheimer taught from 1929 to 1943
Physicists Albert Einstein and Oppenheimer conferring circa 1950
Oppenheimer's ID badge from the Los Alamos Laboratory
Presentation of the Army-Navy "E" Award at Los Alamos on October 16, 1945. Oppenheimer (left) gave his farewell speech as director on this occasion. Robert Gordon Sproul right, in suit, accepted the award on behalf of the University of California from Leslie Groves (center).
A group of physicists at the 1946 Los Alamos colloquium on the Super. In the front row are Norris Bradbury, John Manley, Enrico Fermi and J.M.B. Kellogg. Behind Manley is Oppenheimer (wearing jacket and tie), and to his left is Richard Feynman. The army colonel on the far left is Oliver Haywood. In the third row between Haywood and Oppenheimer is Edward Teller.
The Trinity test of the Manhattan Project was the first detonation of a nuclear device.
Oppenheimer's Van Gogh, Enclosed Field with Rising Sun (1889).
Institute for Advanced Study in Princeton, New Jersey
Oppenheimer in 1946 with his trademark cigarette
President Dwight D. Eisenhower receives a report from Lewis L. Strauss, Chairman of the Atomic Energy Commission, on the Operation Castle hydrogen bomb tests in the Pacific, March 30, 1954. Strauss pressed for Oppenheimer's security clearance to be revoked.
Oppenheimer's former colleague, physicist Edward Teller, testified on behalf of the government at Oppenheimer's security hearing in 1954.
Oppenheimer Beach, in Saint John, U.S. Virgin Islands
Award of honorary degrees at Harvard to Oppenheimer (left), George C. Marshall (third from left) and Omar N. Bradley (fifth from left). The President of Harvard University, James B. Conant, sits between Marshall and Bradley. June 5, 1947
Oppenheimer and Leslie Groves in September 1945 at the remains of the Trinity test in New Mexico. The white canvas overshoes prevented fallout from sticking to the soles of their shoes.
J. Robert Oppenheimer giving a speech during a 1966 visit to Israel

A professor of physics at the University of California, Berkeley, Oppenheimer was the wartime head of the Los Alamos Laboratory and is often credited as the "father of the atomic bomb" for his role in the Manhattan Project – the World War II undertaking that developed the first nuclear weapons.

Trinity Site Obelisk

Trinity (nuclear test)

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The code name of the first detonation of a nuclear weapon.

The code name of the first detonation of a nuclear weapon.

Trinity Site Obelisk
Map of the Trinity Site
Trinity Site (red arrow) near Carrizozo Malpais
The Trinity test base camp
Jumbo arrives at the site
The Jumbo container after the test
Men stack crates of high explosives for the 100-ton test
Norris Bradbury, group leader for bomb assembly, stands next to the assembled Gadget atop the test tower. Later, he became the director of Los Alamos, after the departure of Oppenheimer.
Mockup of the Gadget physics package at the Nuclear Weapons Instructional Museum, Kirtland Air Force Base.
Basic nuclear components of the Gadget. The uranium slug containing the plutonium sphere was inserted late in the assembly process.
Louis Slotin and Herbert Lehr with the Gadget prior to insertion of the tamper plug (visible in front of Lehr's left knee)
The 30 m "shot tower" constructed for the test
The Gadget is unloaded at the base of the tower for the final assembly
The Trinity explosion, 16 ms after detonation. The viewed hemisphere's highest point in this image is about 200 m high.
Trinitite
Original color-exposed photograph by Jack Aeby, July 16, 1945.
Lead-lined Sherman tank used in Trinity test
Major General Leslie Groves and Robert Oppenheimer at the Trinity shot tower remains a few weeks later. The white overshoes were to prevent the trinitite fallout from sticking to the soles of their shoes.
Visitors to the Trinity site in 1995 for 50th anniversary
Ground zero after the test
An aerial photograph of the Trinity crater shortly after the test.{{efn|1=The small crater in the southeast corner was from the earlier test explosion of {{convert|108|tonTNT}}.}}
Trinity Site Historical Marker, 2008
Remnants of Jumbo, 2010
Plaque on the obelisk
Closeup of plaque on obelisk, 2018
Trinitite display table, 2018
Sign warning against removal of trinitite, 2018
Crowds gather around Ground Zero, 2018
Post World War II atomic bomb casing

The code name "Trinity" was assigned by J. Robert Oppenheimer, the director of the Los Alamos Laboratory, inspired by the poetry of John Donne.

Replica of the original Fat Man bomb

Fat Man

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Codename for the type of nuclear bomb that was detonated over the Japanese city of Nagasaki by the United States on 9 August 1945.

Codename for the type of nuclear bomb that was detonated over the Japanese city of Nagasaki by the United States on 9 August 1945.

Replica of the original Fat Man bomb
Replica of the original Fat Man bomb
Replica mockup of a Fat Man displayed in the National Museum of the United States Air Force, beside the Bockscar B-29 that dropped the original device – black liquid asphalt sealant was sprayed over the original bomb casing's seams, simulated on the mockup.
Flash X-ray images of the converging shock waves formed during a test of the high-explosive lens system.
A pumpkin bomb (Fat Man test unit) being raised from the pit into the bomb bay of a B-29 for bombing practice during the weeks before the attack on Nagasaki.
Fat Man internal schematic
Fat Man's detonation method
Fat Man's "physics package" nuclear device about to be encased
Fat Man on its transport carriage, with liquid asphalt sealant applied over the casing's seams
Preserved Tinian "bomb pit#2", where Fat Man was loaded aboard Bockscar
Mushroom cloud after Fat Man exploded over Nagasaki on 9 August 1945
Effects of the Fat Man's detonation on Nagasaki
Espionage information procured by Klaus Fuchs, Theodore Hall, and David Greenglass led to the first Soviet device "RDS–1" (above), which closely resembled Fat Man, even in its external shape.

It was built by scientists and engineers at Los Alamos Laboratory using plutonium from the Hanford Site, and it was dropped from the Boeing B-29 Superfortress Bockscar piloted by Major Charles Sweeney.

Fermi in 1943

Enrico Fermi

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Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1.

Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1.

Fermi in 1943
Fermi was born in Rome at Via Gaeta 19.
Plaque at Fermi's birthplace
Enrico Fermi as a student in Pisa
A light cone is a three-dimensional surface of all possible light rays arriving at and departing from a point in spacetime. Here, it is depicted with one spatial dimension suppressed. The timeline is the vertical axis.
Fermi and his research group (the Via Panisperna boys) in the courtyard of Rome University's Physics Institute in Via Panisperna, c. undefined 1934. From left to right: Oscar D'Agostino, Emilio Segrè, Edoardo Amaldi, Franco Rasetti and Fermi
Enrico Fermi between Franco Rasetti (left) and Emilio Segrè in academic dress
Beta decay. A neutron decays into a proton, and an electron is emitted. In order for the total energy in the system to remain the same, Pauli and Fermi postulated that a neutrino (\bar{\nu}_e) was also emitted.
Diagram of Chicago Pile-1, the first nuclear reactor to achieve a self-sustaining chain reaction. Designed by Fermi, it consisted of uranium and uranium oxide in a cubic lattice embedded in graphite.
Fermi's ID photo from Los Alamos
Ernest O. Lawrence, Fermi, and Isidor Isaac Rabi
The FERMIAC, an analog computer invented by Fermi to study neutron transport
Laura and Enrico Fermi at the Institute for Nuclear Studies, Los Alamos, 1954
Fermi's grave in Chicago
The sign at Enrico Fermi Street in Rome
Memorial plaque in the Basilica Santa Croce, Florence. Italy

At Los Alamos, he headed F Division, part of which worked on Edward Teller's thermonuclear "Super" bomb.

Atomic bomb mushroom clouds over Hiroshima (left) and Nagasaki (right)

Atomic bombings of Hiroshima and Nagasaki

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The United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August 1945, respectively.

The United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August 1945, respectively.

Atomic bomb mushroom clouds over Hiroshima (left) and Nagasaki (right)
U.S. Army propaganda poster depicting Uncle Sam preparing the public for the invasion of Japan after ending war on Germany and Italy
A B-29 over Osaka on 1 June 1945
The Operation Meetinghouse firebombing of Tokyo on the night of 9–10 March 1945, was the single deadliest air raid in history; with a greater area of fire damage and loss of life than either of the atomic bombings of Hiroshima or Nagasaki.
Leslie Groves, Manhattan Project director, with a map of Japan
The "Tinian Joint Chiefs": Captain William S. Parsons (left), Rear Admiral William R. Purnell (center), and Brigadier General Thomas F. Farrell (right)
Aircraft of the 509th Composite Group that took part in the Hiroshima bombing. Left to right: Big Stink, The Great Artiste, Enola Gay
The mission runs of 6 and 9 August, with Hiroshima, Nagasaki, and Kokura (the original target for 9 August) displayed
Various leaflets were dropped on Japan, three versions showing the names of 11 or 12 Japanese cities targeted for destruction by firebombing. The other side contained text stating "...we cannot promise that only these cities will be among those attacked ..."
General Thomas Handy's order to General Carl Spaatz ordering the dropping of the atomic bombs
The Enola Gay dropped the "Little Boy" atomic bomb on Hiroshima. Paul Tibbets (center in photograph) can be seen with six of the aircraft's crew.
Strike order for the Hiroshima bombing as posted on 5 August 1945
The Hiroshima atom bomb cloud 2–5 minutes after detonation
For decades this "Hiroshima strike" photo was misidentified as the mushroom cloud of the bomb that formed at c. 08:16. However, due to its much greater height, the scene was identified by a researcher in March 2016 as the firestorm-cloud that engulfed the city, a fire that reached its peak intensity some three hours after the bomb.
Leaflet AB12, with information on the Hiroshima bomb and a warning to civilians to petition the Emperor to surrender was dropped over Japan beginning on 9 August, by the 509th Composite Group. An AB11 is in the possession of the Nagasaki Atomic Bomb Museum.
The Bockscar and its crew, who dropped a Fat Man atomic bomb on Nagasaki
The harbor at Nagasaki in August 1945 before the city was hit with the atomic bomb
Strike order for the Nagasaki bombing as posted 8 August 1945
Nagasaki before and after the bombing, after the fires had burned out.
Urakami Tenshudo (Catholic Church in Nagasaki) destroyed by the bomb, the dome/bell of the church, at right, having toppled off
The Nagasaki Prefecture Report on the bombing characterized Nagasaki as "like a graveyard with not a tombstone standing".
Partially incinerated child in Nagasaki. Photo from Japanese photographer Yōsuke Yamahata, one day after the blast and building fires had subsided. Once the American forces had Japan under their military control, they imposed censorship on all such images including those from the conventional bombing of Tokyo; this prevented the distribution of Yamahata's photographs. These restrictions were lifted in 1952.
Memorandum from Groves to Marshall regarding the third bomb, with Marshall's hand-written caveat that the third bomb not be used without express presidential instruction.
A telegram sent by Fritz Bilfinger, delegate of the International Committee of the Red Cross (ICRC), on 30 August 1945 from Hiroshima
Torii, Nagasaki, Japan. One-legged torii in the background

Groves appointed J. Robert Oppenheimer to organize and head the project's Los Alamos Laboratory in New Mexico, where bomb design work was carried out.

A post-war Little Boy model

Little Boy

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The codename for the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II.

The codename for the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II.

A post-war Little Boy model
As part of Project Alberta, Commander A. Francis Birch (left) assembles the bomb while physicist Norman Ramsey watches. This is one of the rare photos where the inside of the bomb can be seen.
The "gun" assembly method. When the hollow uranium projectile was driven onto the target cylinder, a nuclear explosion resulted.
Two Little Boy type bombs with casings open.
Arming plugs for a Little Boy type atomic bomb on display at the National Air and Space Museum's Steven F. Udvar-Hazy Center.
Little Boy in the bomb pit on Tinian island, before being loaded into Enola Gays bomb bay. A section of the bomb bay door is visible on the top right.
Enola Gay after Hiroshima mission, entering hardstand. It is in its 6th Bombardment Group livery, with victor number 82 visible on fuselage just forward of the tail fin.
The mushroom cloud over Hiroshima after the dropping of Little Boy
Frame house in 1953 nuclear test, 5 psi overpressure
Hiroshima blast and fire damage, U.S. Strategic Bombing Survey map
One of five casings built for the Little Boy bomb used on Hiroshima on display at the Imperial War Museum in London during 2015

Little Boy was developed by Lieutenant Commander Francis Birch's group at the Manhattan Project's Los Alamos Laboratory during World War II, a reworking of their unsuccessful Thin Man nuclear bomb.

James Chadwick

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English physicist who was awarded the 1935 Nobel Prize in Physics for his discovery of the neutron in 1932.

English physicist who was awarded the 1935 Nobel Prize in Physics for his discovery of the neutron in 1932.

The original building of the Cavendish Laboratory was the home of some of the great discoveries in physics. It was founded in 1874 by the Duke of Devonshire (whose family name was Cavendish), and its first professor was James Clerk Maxwell. The Laboratory has since moved to West Cambridge.
Sir Ernest Rutherford's laboratory
"Red brick" Victoria Building at the University of Liverpool
Key British physicists. Left to right: William Penney, Otto Frisch, Rudolf Peierls and John Cockcroft. They are wearing the American Medal of Freedom.
Part of Liverpool devastated by the Blitz
Mackenzie King, Franklin D. Roosevelt and Winston Churchill at the first Quebec Conference in 1943
Chadwick (left) with Major General Leslie R. Groves, Jr., the director of the Manhattan Project

When the Quebec Agreement merged his project with the American Manhattan Project, he became part of the British Mission, and worked at the Los Alamos Laboratory and in Washington, D.C. He surprised everyone by earning the almost-complete trust of project director Leslie R. Groves, Jr. For his efforts, Chadwick received a knighthood in the New Year Honours on 1 January 1945.

"Thin Man" plutonium gun test casings

Thin Man (nuclear bomb)

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The code name for a proposed plutonium gun-type nuclear bomb that the United States was developing during the Manhattan Project.

The code name for a proposed plutonium gun-type nuclear bomb that the United States was developing during the Manhattan Project.

"Thin Man" plutonium gun test casings
"Thin Man" plutonium gun test casings at Wendover Army Air Field, as part of Project Alberta in the Manhattan Project. "Fat Man" casings can be seen behind them.

Oppenheimer reviewed his options in early 1943, and he gave priority to the gun-type weapon, but as a hedge against the threat of predetonation, he created the E-5 Group at the Los Alamos Laboratory under Seth Neddermeyer to investigate implosion.

Aerial view

Los Alamos National Laboratory

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United States Department of Energy national laboratory initially organized during World War II for the design of nuclear weapons as part of the Manhattan Project.

United States Department of Energy national laboratory initially organized during World War II for the design of nuclear weapons as part of the Manhattan Project.

Aerial view
Aerial view
The first stages of the explosion of the Trinity nuclear test.

At the time it was known as Project Y and was the center for weapon design and overall coordination.