-
- In 1907, German physicist Otto Hahn teamed up with Lise Meitner, one of the first women to earn a physics doctorate in Vienna.
- Later on, Fritz Strassman joined the team and the three of them worked together to study how uranium changes when bombarded by neutrons and their decay patterns.
- Meitner eventually fled Nazi Germany due to her Jewish ancestry, and began work with her nephew, Otto Frisch, at Niels Bohr's Institute in Copenhagen.
-
- Physicist, Arthur Jeffrey Dempster, discovers Uranium-235.
- Unlike the predominant uranium-238, uranium-235 can sustain a nuclear chain reaction.
- The fission of one atom of uranium-235 releases 202.5 MeV inside the reactor.
- U-235 atom has 92 protons and 143 neutrons in its nucleus, and a half-life of approx. 700 million years.
-
- Hahn and Strassmann discovered their uranium experiments had produced barium, a much lighter element, and shared this with Meitner.
- Meitner and Frisch used Bohr’s “droplet” model to explain that uranium had undergone nuclear fission. They showed that the splitting of uranium atoms produced barium, confirming that neutron bombardment could break apart uranium atoms.
- Niels Bohr shared the discovery in the U.S., leading to the start of the Manhattan Project.
-
- Physicist Albert Einstein sends a letter to President Roosevelt warning that Nazi Germany may be attempting to build an atomic bomb.
- September 1939 - Germany invades Poland; Britain and France declare war on Germany, officially starting WWII.
- October 1939 - The Advisory Committee on Uranium is formed to assess the feasibility of nuclear chain reactions and their use for national defense. This committee eventually evolved into The Manhattan Project.
-
February 24, 1941
Physicist Glenn Seaborg, along with his colleagues at the University of California Berkeley, discover plutonium:- Uranium-238 was bombarded with neutrons in the cyclotron (a particle accelerator).
- This produced U-239, which is unstable.
- U-239 decayed (half-life ~23 minutes) into Neptunium-239.
- Neptunium-239 then decayed (half-life ~2.3 days) into Plutonium-239.
-
- Japan launched a surprise air attack on the U.S. Pacific Fleet at Pearl Harbor, Hawaii.
- 2,390 Americans, including both service members and civilians, lost their lives.
- The United States declared war on Japan and officially entered WWII.
-
June 18, 1942: The Army Corps of Engineers Manhattan District is formally established - aka The Manhattan Project.
* The first offices were in New York City
* Their purpose was to organize and oversee the massive secret effort to design and build an atomic bomb before the Nazis could do the same.
* Led by Colonel James Marshall, and later General Leslie Groves.
* Key scientist: J. Robert Oppenheimer -
- Enrico Fermi, an Italian-American physicist, created the world's first artificial nuclear reactor, Chicago Pile-1.
- On December 2, 1942, at the The University of Chicago, the first human-made self-sustaining nuclear chain reaction was initiated in CP-1 during an experiment that Fermi led.
- The reactor used natural uranium and graphite as a neutron moderator- a medium that reduces the speed of neutrons making a nuclear chain reaction more efficient and controllable.
-
- Los Alamos, NM (Project Y): Secret Manhattan Project lab for atomic bomb development.
- Management: Overseen by the University of California and the U.S. Army.
- Leadership: Directed by J. Robert Oppenheimer (1943–1945), succeeded by Norris Bradbury.
- Scientific Work: Scientists conducted research on nuclear fission, developed bomb designs, and refined methods for producing and purifying uranium and plutonium for use in the weapons.
-
- Trinity was the first detonation of a nuclear weapon and was conducted by the U.S. as part of the Manhattan Project.
- Test site: Jornada del Muerto desert in New Mexico.
- The test was of an implosion-design plutonium bomb, "gadget", which was the same design as the "Fat Man" bomb that was later used on Nagasaki, Japan.
- The Trinity bomb released the explosive energy of 25 kilotons of TNT (100 TJ) ± 2 kilotons of TNT (8.4 TJ), and a large cloud of fallout.
-
- The Little Boy atomic bomb detonates over Hiroshima, Japan, killing and wounding tens of thousands.
- The Little Boy was a uranium-based, gun-type weapon that used a simple mechanism to fire one uranium component into another to initiate fission.
- Fissile Material: Uranium-235.
- Design: A long, narrow, rifle-like shape.
- Yield: Approximately 15 kilotons.
- Efficiency: Relatively poor; less than 2% of the uranium underwent fission.
-
- After Japan failed to surrender, the U.S. dropped another atomic bomb, "The Fat Man", over Nagasaki, Japan.
- Mechanism: An "implosion-type" mechanism, compressing a plutonium core from all sides with a layer of conventional explosives.
- Fissile Material: Plutonium-239.
- Design: A plump, spherical shape
- Yield: ~21 kilotons.
- Efficiency: More efficient than Little Boy due to the effective compression of the plutonium core.
-
- On September 2, 1945, Japan formally signed the Instrument of Surrender, marking the official end of the most deadly and destructive war in human history.
- The massive devastation caused by the atomic bombs played a crucial role in persuading Japan’s leaders that continuing the war was hopeless and could result in the “total extinction of the Japanese nation,” as the Emperor stated in his speech.
-
- After the Atomic Energy Commission took over earlier that year, the Manhattan Engineer District was officially dissolved on August 25, 1947, ending the Manhattan Project.
- The Manhattan Project ended because its wartime goal had been achieved, and a new government agency was created to oversee the continued development and management of nuclear technology and weapons.