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第二次世界大戰期間研發出人類首枚核武器的一項軍事計劃
- 曼哈頓計劃（英語：）是第二次世界大戰期間研發出人類首枚核武器的一項軍事計劃，由美國主導，英國和加拿大協助進行。 1942年至1946年間，曼哈頓計劃由美國陸軍工程兵團少將萊斯利·格羅夫斯領導，設計製造原子彈的洛斯阿拉莫斯實驗室則由核物理學家羅伯特·奧本海默負責。
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2024年5月1日 · 曼哈頓計畫 （英語： Manhattan Project ）是 第二次世界大戰 期間 研發 出人類首枚 核子武器 的一項軍事計畫，由美國主導，英國和加拿大協助進行。 1942年至1946年間，曼哈頓計畫由 美國陸軍工程兵團 少將 萊斯利·格羅夫斯 領導，設計製造原子彈的 洛斯阿拉莫斯實驗室 則由核物理學家 羅伯特·奧本海默 負責。 陸軍對軍事行動的慣例是用總部所在地命名，因而計畫中陸軍負責的部分稱 曼哈頓區 。 不過後來「曼哈頓」一名逐漸取代了原有的官方計畫代號 代用材料項目發展 （ Development of Substitute Materials ），成為對整個計畫的稱呼。 該計畫在發展過程中逐漸吸取融合了英國在 合金管工程 中的發現。
The Manhattan Project was a program of research and development undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers.
- 1942–1946
- Oak Ridge, Tennessee, U.S.
曼哈頓計畫 （英語： Manhattan Project ）是 第二次世界大戰 期間 研發 出人類首枚 核子武器 的一項軍事計畫，由美國主導，英國和加拿大協助進行。 1942年至1946年間，曼哈頓計畫由 美國陸軍工程兵團 少將 萊斯利·格羅夫斯 領導，設計製造原子彈的 洛斯阿拉莫斯實驗室 則由核物理學家 羅伯特·歐本海默 負責。 陸軍對軍事行動的慣例是用總部所在地命名，因而計畫中陸軍負責的部分稱 曼哈頓區 。 不過後來「曼哈頓」一名逐漸取代了原有的官方計畫代號 代用材料項目發展 （ Development of Substitute Materials ），成為對整個計畫的稱呼。 該計畫在發展過程中逐漸吸取融合了英國在 合金管工程 中的發現。
- Overview
- Creation of the U.S. atomic weapons program
- Manhattan Project expansion under Groves and Oppenheimer
- The first atomic bombs: Trinity, Hiroshima, and Nagasaki
- Operation Crossroads and the end of the Manhattan Project
In 1939, American scientists, many of whom had fled from fascist regimes in Europe, were aware of advances in nuclear fission and were concerned that Nazi Germany might develop a nuclear weapon. The physicists Leo Szilard and Eugene Wigner persuaded Albert Einstein to send a letter to U.S. President Franklin D. Roosevelt warning him of that danger and advising him to establish an American nuclear research program. The Advisory Committee on Uranium was set up in response. The beginning of the Manhattan Project can be dated to December 6, 1941, with the creation of the Office of Scientific Research and Development, headed by Vannevar Bush.
Who were the most important scientists associated with the Manhattan Project?
American physicist J. Robert Oppenheimer headed the Manhattan Project, with the goal of developing the atomic bomb, and Edward Teller was among the first recruited for the project. Leo Szilard and Enrico Fermi built the first nuclear reactor. Ernest Orlando Lawrence was program chief in charge of the development of the electromagnetic process of separating uranium-235.
Other notable researchers included Otto Frisch, Niels Bohr, Felix Bloch, James Franck, Emilio Segrè, Klaus Fuchs, Hans Bethe, and John von Neumann. The person who oversaw the Manhattan Project, however, was not a scientist. He was Leslie Groves, a brigadier general in the U.S. Army.
What did the Manhattan Project do?
The Manhattan Project produced the first atomic bomb. Several lines of research were pursued simultaneously. Both electromagnetic and fusion methods of separating the fissionable uranium-235 from uranium-238 were explored at Oak Ridge in Tennessee. The production of plutonium-239, first achieved at the University of Chicago, was further pursued at the Hanford Engineer Works in Washington state. In the meantime, at Los Alamos, New Mexico, scientists found a way to bring the fissionable material to supercritical mass (and thus explosion) and to control the timing and devised a weapon to house it. The first test, on July 16, 1945, at Alamogordo air force base in New Mexico, produced a massive nuclear explosion.
American scientists, many of them refugees from fascist regimes in Europe, took steps in 1939 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 to 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 project was put under the direction of the Office of Scientific Research and Development, headed by Vannevar Bush.
After the U.S. entered World War II, the War Department was given joint responsibility for the project, because 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 for the assembled scientists to 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 R. 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.
It was known in 1940 that German scientists were working on a similar project and that the British were also exploring the problem. In the fall of 1941 Manhattan Project chemist Harold C. Urey accompanied Pegram to England to attempt to set up a cooperative effort, and by 1943 a combined policy committee was established with Great Britain and Canada. In that year a number of British and Canadian scientists moved to the United States to join the project.
If the project were to achieve timely success, several lines of research and development had to be carried on simultaneously before it was certain whether any might succeed. The explosive materials then had to be produced and be made suitable for use in an actual weapon.
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Uranium-235, the essential fissionable component of the postulated bomb, cannot be separated from its natural companion, the much more abundant uranium-238, by chemical means; the atoms of these respective isotopes must rather be separated from each other by physical means. Several physical methods to do this were intensively explored, and two were chosen—the electromagnetic process developed at the University of California, Berkeley, under Ernest Orlando Lawrence and the diffusion process developed under Urey at Columbia University. Both of these processes, particularly the diffusion method, required large, complex facilities and huge amounts of electric power to produce even small amounts of separated uranium-235. Philip Hauge Abelson developed a third method called thermal diffusion, which was also used for a time to effect a preliminary separation. These methods were put into production at a 70-square-mile (180-square-km) tract near Knoxville, Tennessee, originally known as the Clinton Engineer Works, later as Oak Ridge.
Only one method was available for the production of the fissionable material plutonium-239. It was developed at the metallurgical laboratory of the University of Chicago under the direction of Arthur Holly Compton and involved the transmutation in a reactor pile of uranium-238. In December 1942 Fermi finally succeeded in producing and controlling a fission chain reaction in this reactor pile at Chicago.
The first atomic bomb was exploded at 5:30 am on July 16, 1945, at the Alamogordo air base 120 miles (193 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-metre) 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 centre 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 explosion came as an intense light flash, a sudden wave of heat, and later a tremendous roar 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 metres). The bomb generated an explosive power equivalent to 15,000 to 20,000 tons of trinitrotoluene (TNT); the tower was completely vaporized and the surrounding desert surface fused to glass for a radius of 800 yards (730 metres).
The following month, two other atomic bombs produced by the project, the first using uranium-235 and the second using plutonium, were dropped on the Japanese cities of Hiroshima and Nagasaki. Neither city had been attacked during the U.S. strategic bombing campaign until that point, and planners wished to demonstrate the destructive power of the bombs. Hiroshima was selected as the primary target because of its military value; the city served as the headquarters of the Japanese Second Army. On August 6, 1945, at about 8:15 am local time, a U.S. B-29 bomber released a gun assembly fission bomb—dubbed Little Boy—above Hiroshima. The weapon detonated at an altitude of 1,900 feet (580 metres), and the explosive yield was estimated to be the equivalent of 15,000 tons of TNT. Some 70,000 people were killed instantly, and by the end of the year the death toll had surpassed 100,000. Two-thirds of the city area was destroyed.
By the morning of August 9, 1945, the Soviet Union had declared war on Japan, but the Japanese government had not yet communicated its intent to surrender to the Allies. A B-29 carrying Fat Man—a plutonium implosion bomb similar to the one used in the Trinity test—was initially dispatched to Kokura (now part of Kitakyūshū, Japan). Thick clouds and haze over Kokura prevented the bombardier from sighting the designated aimpoint, however, and the bomber proceeded to its secondary target, the port city of Nagasaki. At 11:02 am Fat Man exploded at an altitude of 1,650 feet (500 metres) northwest of the city centre. The bomb detonated with the explosive force of 21,000 tons of TNT. An estimated 40,000 people were killed instantly, and at least 30,000 more would die from their injuries and radiation poisoning by the end of the year. About 40 percent of the city’s buildings were completely destroyed or severely damaged. Due to the area’s uneven terrain, a significant part of Nagasaki—particularly in the southeastern industrial and government district—was relatively unscathed. The Japanese initiated surrender negotiations the next day. By this point, Groves had notified U.S. Pres. Harry S. Truman that another bomb would be ready for delivery within a week.
On September 2, 1945, a Japanese delegation signed formal surrender documents on the deck of the USS Missouri. Shortly after the conclusion of hostilities, Manhattan Project physicist Philip Morrison traveled to Hiroshima at the request of the War Department to study the effects of the atomic bomb. Characterizing the bomb as “preeminently a weapon of saturation,” he said, “It destroys so quickly and so completely such a large area that defense is hopeless.” Horrified by what he had witnessed, Morrison would spend the rest of his life campaigning against nuclear weapons and a potential “third bomb.”
After the war, the Manhattan Project oversaw Operation Crossroads, a military-scientific experiment conducted at Bikini atoll in the South Pacific in 1946. “Able,” the first peacetime atomic weapons test, was carried out on July 1, 1946. In attendance were some 42,000 U.S. military personnel, as well as more than 100 journalists and representatives from a dozen foreign countries. A 20-kiloton atomic bomb was dropped from a B-29 and exploded at an altitude of about 520 feet (158 metres) over a fleet of about 80 decommissioned World War II naval vessels. Only five ships were sunk by the blast, and, although several more were damaged, the majority survived the explosion relatively unscathed. Within a day, radiation levels had subsided enough for the ships to be boarded and inspected. Press and foreign military observers seemed underwhelmed that the blast had not vaporized the assembled ships, but such an appraisal discounted the debilitating effect that radiation would have had on a ship’s crew. Many test animals placed throughout the fleet quickly succumbed to radiation sickness, confirming a prediction in the Bulletin of the Atomic Scientists that “a large ship, about a mile away from the explosion, would escape sinking, but the crew would be killed by the deadly burst of radiations from the bomb, and only a ghost ship would remain, floating unattended on the vast waters of the ocean.”
The second test, “Baker,” took place on July 25, 1946. A 23-kiloton device was suspended at a depth of 90 feet (27 metres) from a decommissioned landing craft in the Bikini lagoon. At the moment of the explosion, a luminous dome rose on the surface of the lagoon, followed by an opaque cloud that enveloped about half the target area. The cloud dissipated within seconds, revealing a column of ascending water that lifted the 26,000-ton battleship USS Arkansas into the air for a brief moment. The column of water, some 2,200 feet (670 metres) in diameter, rose to a height of 1 mile (1.6 km), sending spray still higher. The expanding column of spray engulfed about half the ships in the target fleet with radioactive water. Waves traveling outward from the explosion were up to 100 feet (30 metres) tall, even at a distance of 1,000 feet (some 300 metres) from the epicentre. The evaluation board of the Joint Chiefs of Staff reported that the explosion had produced intense radioactivity in the waters of the lagoon. The target ships were saturated with radioactive water so lethal that four days after the test, it was still unsafe for inspection parties to spend “any useful length of time” in the centre of the target area or on any of the ships anchored there. Persistent radiation and the difficulty of decontamination led to the cancellation of “Charlie,” a planned third test that would have involved a bomb being detonated at the bottom of the Bikini lagoon.
- The Editors of Encyclopaedia Britannica
曼哈頓計劃 （英語： Manhattan Project ）是 第二次世界大戰 期間 研發 出人類首枚 核武器 的一項軍事計劃，由美國主導，英國和加拿大協助進行。 1942年至1946年間，曼哈頓計劃由 美國陸軍工程兵團 少將 萊斯利·格羅夫斯 領導，設計製造原子彈的 洛斯阿拉莫斯實驗室 則由核物理學家 羅伯特·奧本海默 負責。 陸軍對軍事行動的慣例是用總部所在地命名，因而計劃中陸軍負責的部分稱 曼哈頓區 。 不過後來「曼哈頓」一名逐漸取代了原有的官方計劃代號 代用材料項目發展 （ Development of Substitute Materials ），成為對整個計劃的稱呼。 該計劃在發展過程中逐漸吸取融合了英國在 合金管工程 中的發現。
2021年11月20日 · 羅斯福總統批准研發原子彈，曼哈頓計劃成立，由奧本海默負責秘密武器試驗室，在他的領導下開始研究核裂變從天然鈾中分離出鈾-235的方法。 Getty Images. 愛因斯坦和奧本海默. 核武器歷史學家維勒斯坦（Alex Wellerstein）表示，「奧本海默在原子彈的研製方面有重大的影響，涉及原子彈設計的許多重大決定，他負有責任。...
2022年8月2日 · 什麼是曼哈頓計劃？ 「曼哈頓計劃 Manhattan Project」於 1941 年 10 月由當時美國總統「小羅斯福」批准啟動，以研發原子彈的為主，領導人為美國陸軍工程兵團少將萊斯利格羅夫斯 Leslie Groves，而因為陸軍對軍事行動的慣例是用總部所在地命名，所以後來「曼哈頓」一名逐漸取代了原有的官方計劃代號「代用材料計畫發展 Development of Substitute Materials」成為對整個計劃的稱呼。
