Trinity test
What was the Trinity test?
What was the purpose of the Manhattan Project?
Where was the first atomic bomb detonated?
Who was in charge of the Manhattan Project?
What is the significance of the Trinity Site today?
Trinity test, detonation of the first atomic bomb at 5:29:45 am on July 16, 1945. The bomb, a plutonium implosion device called Gadget, was exploded at the Alamogordo air base 120 miles (190 km) south of Albuquerque, New Mexico.
The Manhattan Project and the pursuit of the atomic bomb
In 1939 American scientists, many of them refugees from the fascist regimes in Europe, took steps to organize a project to exploit the newly recognized fission process for military purposes. The first contact with the government was made by G.B. Pegram of Columbia University, who arranged a conference between Enrico Fermi and the Navy Department in March 1939. In the summer of 1939 Albert Einstein was persuaded by his fellow scientists to use his influence and present the military potential of an uncontrolled fission chain reaction to Pres. Franklin D. Roosevelt. In February 1940, $6,000 was made available to start research under the supervision of a committee headed by L.J. Briggs, director of the National Bureau of Standards (later National Institute of Standards and Technology). On December 6, 1941—the day before the Japanese attack on Pearl Harbor—the project was put under the direction of the Office of Scientific Research and Development, headed by Vannevar Bush.
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After the United States’ entry into World War II, the War Department was given joint responsibility for the project. By mid-1942 it was obvious that a vast array of pilot plants, laboratories, and manufacturing facilities would have to be constructed by the U.S. Army Corps of Engineers so that the assembled scientists could carry out their mission. In June 1942 the Corps of Engineers’ Manhattan District was initially assigned management of the construction work (because much of the early research had been performed at Columbia University, in Manhattan), and in September 1942 Brig. Gen. Leslie Richard Groves was placed in charge of all army activities (chiefly engineering activities) relating to the project. “Manhattan Project” became the code name for research work that would extend across the country.
Since several different processes offered promise of producing fissionable material and since speed seemed vital, the directors of the Manhattan Project established several large research and development facilities. One was at Oak Ridge, Tennessee, where scientists would pursue uranium enrichment, and another at Hanford, Washington, which would focus on plutonium production. Research laboratories at the University of Chicago and the University of California at Berkeley were also heavily involved. It was at the Chicago laboratory on December 2, 1942, that Manhattan Project scientists first achieved a self-sustaining nuclear chain reaction.
The Trinity test
With Oak Ridge and Hanford producing fuel for the proposed devices, Groves sought a secure site for the bomb laboratory. The location needed to be safe from enemy attack, isolated because of the project’s top secret status, and sparsely populated in the event of a nuclear accident. Several sites in the interior western United States were considered, but it was not until J. Robert Oppenheimer, the scientific director of the bomb laboratory, suggested Los Alamos that the site was chosen. It fulfilled the selection criteria, and Oppenheimer was keen to locate the bomb-production facility at Los Alamos because of its natural beauty. He had enjoyed summers there as a youth and believed that the scenery would help the weapons team endure the arduous challenge ahead. In April 1943 the scientists and engineers began arriving at the Los Alamos Laboratory, as it was then called. At its peak in 1945 more than 5,000 scientists, engineers, technicians, and their families lived at Los Alamos.
The Los Alamos Laboratory was tasked with developing methods to reduce the fissionable products of the production plants to pure metal and fabricate the metal to required shapes. Methods of rapidly bringing together amounts of fissionable material to achieve a supercritical mass (and thus a nuclear explosion) had to be devised, along with the actual construction of a deliverable weapon that would be dropped from a plane and fused to detonate at the proper moment in the air above the target. Most of these problems had to be solved before any appreciable amount of fissionable material could be produced, so that the first adequate amounts could be used at the fighting front with minimum delay.
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By the summer of 1945, Manhattan Project scientists were confident about the gun-assembly design of the uranium-fueled device, and they only had enough uranium-235 for one weapon. Questions remained about the design of the plutonium implosion bomb, however, and Hanford Engineer Works had delivered amounts of plutonium-239 sufficient to produce a nuclear explosion. Weapon development and design were sufficiently advanced so that an actual field test of a nuclear explosive could be scheduled. Such a test was no simple affair. Elaborate and complex equipment had to be assembled to provide a complete diagnosis of success or failure. By this time the original $6,000 authorized for the Manhattan Project had grown to $2 billion.
The first atomic bomb was exploded at 5:29:45 am on July 16, 1945, at the Alamogordo air base 120 miles (190 km) south of Albuquerque, New Mexico. Oppenheimer had called the site “Trinity” in reference to one of John Donne’s Holy Sonnets. The bomb—a plutonium implosion device called Gadget—was raised to the top of a 100-foot (30-meter) steel tower that was designated “Zero.” The area at the base of the tower was marked as “Ground Zero,” a term that would pass into common parlance to describe the center of an (often catastrophic) event. The tower was surrounded by scientific equipment, with remote monitoring taking place in bunkers occupied by scientists and a few dignitaries 10,000 yards (9 km) away. The observers had been instructed to lie down with their feet toward the tower and to protect their eyes from the blinding light of the explosion.
The explosion came as an intense flash that lit up the mountain peaks 10 miles (16 km) away. Then came a sudden wave of heat and, later, a tremendous, sustained roar accompanied by a tornado-like burst of wind as the shock wave passed and echoed in the valley. A ball of fire rose rapidly, followed by a mushroom cloud extending to 40,000 feet (12,200 meters). The bomb generated an explosive power equivalent to 15,000 to 20,000 tons of TNT; the tower was completely vaporized and the surrounding desert surface fused to glass (a material that was subsequently dubbed trinitite) for a radius of 800 yards (730 meters).
The Trinity Site today
Shortly after the detonation of Gadget, the Trinity Site was enclosed in fencing, and signs warning of radioactivity were posted around the perimeter. For several years the site remained off-limits, but by 1953 much of the radioactivity had subsided. In September of that year, members of the general public were allowed to visit the site for the first time. In 1965 an obelisk made of black volcanic rock was erected at Ground Zero, with a plaque commemorating the detonation of the world’s first nuclear device. In 1975 the Trinity Site was designated as a national historic landmark by the National Park Service. The landmark covers 80 square miles (about 210 square km) and includes the camp where Manhattan Project scientists and staff lived; the McDonald Ranch House, where the plutonium core of the bomb was assembled; and Ground Zero.
The Trinity Site is located on the grounds of White Sands Missile Range, a 3,200-square-mile (8,290-square-km) U.S. Army test site. Access to the area is heavily restricted, although public tours have historically been offered twice a year (on the first Saturday in April and the third Saturday in October). Beginning in 2024, the schedule was scaled back, and only the October tour is currently offered.
Radiation levels at the site remain elevated, but short visits are considered safe. A person who spends an hour at Ground Zero is exposed to approximately one-half millirem of radiation; in comparison, a person on a coast-to-coast airline flight would receive a dose of about one millirem. Much of the trinitite created in the explosion was removed or buried by the Atomic Energy Commission in 1952, but some small samples can be found. These specimens are measurably—although not dangerously—radioactive, and removing them from the site is prohibited.