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Uranium Fission Discovered
In their Berlin lab, just before Christmas in 1938, Otto Hahn and Fritz Strassmann discover the process we now know as fission in uranium. Physicists Lise Meitner and Otto Frisch confirm the Hahn-Strassmann discovery, noting that so much energy had been released that a previously undiscovered kind of process was at work; Firsch names it fission. They quickly communicate their findings to Niels Bohr who reports on the Hahn-Strassman results at a meeting on theoretical physics in Washington, D.C. -
Albert Einstein signs the Einstein–Szilárd letter
Hungarian scientist and refugee Leo Szilard believed the nuclear energy released during fission could be harnessed to produce bombs capable of severe destruction. He convinced Albert Einstein to write a letter describing the possible military implications of the German discovery and the urgent need for American research on the subject. Roosevelt forms the Advisory Committee on Uranium and appoints Lyman J. Briggs as head of the committee. -
Attack on Pearl Harbor
The Japanese attacked the U.S. naval base at Pearl Harbor, Hawaii. This forced the immediate entry of the United States into World War II. The attack destroyed nearly 20 American naval vessels, including eight battleships, and almost 200 airplanes. More than 2,000 Americans soldiers and naval officers died in the attack, and another 1,000 were wounded. The day after the assault, President Franklin D. Roosevelt asked Congress to declare war on Japan. -
Roosevelt Authorizes Manhattan Project
Franklin D. Roosevelt officially authorized the Manhattan Project to develop atomic weapons to use against the enemies of the United States. The project would quickly evolve into one of the most sophisticated large-scale scientific efforts in human history. It involved scientists working at labs in a number of leading universities in the United States, Britain, and Canada, as well as the creation of significant new federal facilities. -
First Research Facility Acquired
The U.S. government acquired land in Oak Ridge, TN as the first research site (of many) and Headquarters for the Manhattan Project. Initially called Site X, between 1943 and 1945, Oak Ridge grew from sparsely populated farmland (original residents were evicted) to a city and scientific facility of more than seventy-five thousand people. Oak Ridge was the home of the uranium enrichment plants, the liquid thermal diffusion plant, and the pilot plutonium production reactor. -
Y-12 Calutron Plant at Oak Ridge
Ernest O. Lawrence, working at UC-Berkeley, determined that when an electrically-charged Uranium-238 atom was placed in a magnetic field, Uranium-235 could be isolated. Inspired by this research, ground was broken for the Y-12 plant at Oak Ridge with the purpose of housing 1,152 “calutrons” (CALifornia University cycloTRONs). The calutrons (mostly run by women) were responsible for separating uranium isotopes into Uranium-235 which was ultimately used in the creation of the first atomic bomb. -
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Calutron Girls
Thousands of young women, most only high school graduates, were recruited from all across the Southeast, many for the purpose of monitoring the Y-12’s calutrons which were used to separate uranium-235 from the uranium-238 isotopes. The women weren't told that their work was directly contributing to the development of a nuclear weapon and were sworn to silence about what they did know. -
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Calutron Girls, continued
At Y-12, some men didn’t think women were competent enough to monitor calutrons. So they had a contest: boys vs/ girls. The supervisor ultimately found that the young women were better at monitoring the calutrons than the men. If something went wrong with the calutron, male scientists would try to figure out the cause of the problem, while women simply alerted a supervisor. Also, scientists were guilty of fiddling with the dials too much, while women only adjusted them when necessary. -
Trinity Test
The Trinity Test was the first test conducted by the U.S. of an atomic weapon, called "The Gadget." The site chosen was a remote corner on the Alamagordo Bombing Range known as the "Jornada del Muerto," or "Journey of Death," 210 miles south of Los Alamos. Scientists were trying to determine key aspects of the reaction such as symmetry of the implosion and the amount of energy released. The nuclear age began as they passed around a bottle of whiskey, celebrating their "success". -
Potsdam Declaration
Statement by leaders of the United States, the Republic of China, and Great Britain which called for the unconditional surrender of all Japanese armed forces. The document warned that if they didn't surrender, Japan would face "prompt and utter destruction." Later, American bombers dropped over 3 million leaflets, describing the declaration, over Japan (a bomb was not mentioned). -
Little Boy is Dropped on Hiroshima
At 8:15 a.m. local time, the B-29 Enola Gay dropped a gun-type uranium bomb known as Little Boy on the Japanese city of Hiroshima. Within a matter of minutes, a twenty-thousand-foot mushroom cloud rose over the city. The initial explosion and radiation killed an estimated sixty thousand people, while another sixty thousand are estimated to have died from radiation poisoning and other injuries in the weeks and months that followed. -
Fat Man is Dropped on Nagasaki
At 10:58 a.m. local time, the second atomic bomb named Fat Man (a plutonium implosion bomb) was dropped on the Japanese city of Nagasaki, killing an estimated thirty-five thousand people outright, with another forty thousand dying in the aftermath from severe injuries or the effects of radiation. -
Japan Signs Instrument of Surrender
The document, prepared by the U.S. War Department and approved by President Harry S. Truman, formalized Japan's “unconditional surrender to the Allied Powers,” Allied forces assembled aboard the USS Missouri in Tokyo Bay to sign the Japanese Instrument of Surrender, which effectively ended World War II. -
Manhattan Project Dismantled
The newly created Atomic Energy Commission took over Manhattan Project facilities to manage the peacetime development of atomic science. One important initiative was to begin supplying reactor-produced radioisotopes to universities and hospitals for research, making them far more available than they had been before the war. Much of the work done during the war at facilities such as Oak Ridge contributed significantly to postwar advances in biological research and medicine.