Trinity was the first detonation of a nuclear weapon, conducted by the United States Army at 5:29 a.m. Mountain War Time (11:29:21 GMT) on July 16, 1945, as part of the Manhattan Project. The test was of an implosion-design plutonium bomb, or "gadget" – the same design as the Fat Man bomb later detonated over Nagasaki, Japan, on August 9, 1945. Concerns about whether the complex Fat Man design would work led to a decision to conduct the first nuclear test. The code name "Trinity" was assigned by J. Robert Oppenheimer, the director of the Los Alamos Laboratory. The name was possibly inspired by the poetry of John Donne. Planned and directed by Kenneth Bainbridge, the test was conducted in the Jornada del Muerto desert about 35 miles (56 km) southeast of Socorro, New Mexico, on what was the Alamogordo Bombing and Gunnery Range, but was renamed the White Sands Proving Ground just before the test. The only structures originally in the immediate vicinity were the McDonald Ranch House and its ancillary buildings, which scientists used as a laboratory for testing bomb components. Fears of a fizzle prompted construction of "Jumbo", a steel containment vessel that could contain the plutonium, allowing it to be recovered, but Jumbo was not used in the test. On May 7, 1945, a rehearsal was conducted, during which 108 short tons (98 t) of high explosive spiked with radioactive isotopes was detonated. 425 people were present on the weekend of the Trinity test. In addition to Bainbridge and Oppenheimer, observers included Vannevar Bush, James Chadwick, James B. Conant, Thomas Farrell, Enrico Fermi, Hans Bethe, Richard Feynman, Isidor Isaac Rabi, Leslie Groves, Philip Morrison, Frank Oppenheimer, Geoffrey Taylor, Richard Tolman, Edward Teller, and John von Neumann. 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 test was conducted without evacuating nearby residents. Postwar radiation safety guidelines, developed in part from Trinity data, would have required evacuation at those distances. The test site was declared a National Historic Landmark district in 1965 and listed on the National Register of Historic Places the following year.
Background
The creation of nuclear weapons arose from the scientific and political developments of the 1930s. The decade saw many new discoveries about the nature of atoms, including the existence of nuclear fission. The concurrent rise of fascist governments in Europe led to a fear of a German nuclear weapon project, especially among scientists who were refugees from Nazi Germany and other fascist countries. When their calculations showed that nuclear weapons were theoretically feasible, the British and United States governments supported an all-out effort to build them. These efforts were transferred to the authority of the U.S. Army in June 1942 and became the Manhattan Project. Brigadier General Leslie R. Groves, Jr. was appointed its director in September. The weapons development portion of this project was located at the Los Alamos Laboratory in northern New Mexico, under the directorship of physicist J. Robert Oppenheimer. The University of Chicago, Columbia University, and the Radiation Laboratory at the University of California, Berkeley, conducted other development work. Manhattan Project scientists had identified two fissile isotopes for potential use in bombs: uranium-235 and plutonium-239. Uranium-235 became the basis of the Little Boy bomb design, first used (without prior testing) in the bombing of Hiroshima; the design used in the Trinity test, and eventually used in the bombing of Nagasaki (Fat Man), was based on plutonium. The original design considered for a weapon based on plutonium-239 was Thin Man, in which (as in the Little Boy uranium bomb) two subcritical masses of fissile material would be brought rapidly together to form a single critical mass. Plutonium is a synthetic element with complicated properties about which little was known at first, as until 1944 it had been produced only in cyclotrons in very pure microgram amounts, whereas a weapon would require kilogram quantities bred in a reactor. In April 1944, Los Alamos physicist Emilio Segrè discovered that plutonium produced by the X-10 Graphite Reactor at Clinton Engineer Works contained plutonium-240 as an impurity. Plutonium-240 undergoes spontaneous fission at thousands of times the rate of plutonium-239, and the extra neutrons thereby released made it likely that plutonium in a gun-type fission weapon would detonate too soon after a critical mass was formed, producing a "fizzle"—a nuclear explosion many times smaller than a full explosion. The Thin Man design would therefore not work. Project scientists then turned to a more technically difficult implosion design. In September 1943, mathematician John von Neumann had proposed surrounding a fissile "core" by two different high explosives which produced shock waves of different speeds. Alternating the faster- and slower-burning explosives in a carefully calculated configuration would produce a compressive wave upon their simultaneous detonation. This so-called "explosive lens" focused the shock waves inward with sufficient force to rapidly compress the solid plutonium core to several times its original density. The increase in density caused the core – previously subcritical – to become supercritical. At the same time, the shock wave activated a small neutron source at the center of the core, thereby assuring that the chain reaction would begin in earnest immediately at the moment of compression. Such a complicated design required substantial research and experimentation in engineering and hydrodynamics, and in August 1944 the entire Los Alamos Laboratory was reorganized to focus on this work.
Preparation
Decision
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