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Portal:Nuclear technology

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This symbol of radioactivity is internationally recognized.
Nuclear technology is technology that involves the nuclear reactions of atomic nuclei. Among the notable nuclear technologies are nuclear reactors, nuclear medicine and nuclear weapons. It is also used, among other things, in smoke detectors and gun sights.
A nuclear weapon (also called an atom bomb, nuke, atomic bomb, nuclear warhead, A-bomb, or nuclear bomb) is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or from a combination of fission and fusion reactions (thermonuclear bomb). Both bomb types release large quantities of energy from relatively small amounts of matter. The first test of a fission ("atomic") bomb released an amount of energy approximately equal to 20,000 tons of TNT (84 TJ). The first thermonuclear ("hydrogen") bomb test released energy approximately equal to 10 million tons of TNT (42 PJ). A thermonuclear weapon weighing little more than 2,400 pounds (1,100 kg) can release energy equal to more than 1.2 million tons of TNT (5.0 PJ). A nuclear device no larger than traditional bombs can devastate an entire city by blast, fire, and radiation. Since they are weapons of mass destruction, the proliferation of nuclear weapons is a focus of international relations policy.

Nuclear weapons have been used twice in war, both times by the United States against Japan near the end of World War II. On August 6, 1945, the U.S. Army Air Forces detonated a uranium gun-type fission bomb nicknamed "Little Boy" over the Japanese city of Hiroshima; three days later, on August 9, the U.S. Army Air Forces detonated a plutonium implosion-type fission bomb nicknamed "Fat Man" over the Japanese city of Nagasaki. These bombings caused injuries that resulted in the deaths of approximately 200,000 civilians and military personnel. The ethics of these bombings and their role in Japan's surrender are subjects of debate.


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Operation Crossroads Baker (wide).jpg
Operation Crossroads was a pair of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. They were the first nuclear weapon tests since Trinity in July 1945, and the first detonations of nuclear devices since the atomic bombing of Nagasaki on August 9, 1945. The purpose of the tests was to investigate the effect of nuclear weapons on warships.

The Crossroads tests were the first of many nuclear tests held in the Marshall Islands, and the first to be publicly announced beforehand and observed by an invited audience, including a large press corps. They were conducted by Joint Army/Navy Task Force One, headed by Vice Admiral William H. P. Blandy rather than by the Manhattan Project, which had developed nuclear weapons during World War II. A fleet of 95 target ships was assembled in Bikini Lagoon and hit with two detonations of Fat Man plutonium implosion-type nuclear weapons of the kind dropped on Nagasaki, each with a yield of 23 kilotons of TNT (96 TJ).

The first test was Able. The bomb was named Gilda after Rita Hayworth's character in the 1946 film Gilda, and was dropped from the B-29 Superfortress Dave's Dream of the 509th Bombardment Group on July 1, 1946. It detonated 520 feet (158 m) above the target fleet and caused less than the expected amount of ship damage because it missed its aim point by 2,130 feet (649 m).

The second test was Baker. The bomb was known as Helen of Bikini and was detonated 90 feet (27 m) underwater on July 25, 1946. Radioactive sea spray caused extensive contamination. A third deep-water test named Charlie was planned for 1947 but was canceled primarily because of the United States Navy's inability to decontaminate the target ships after the Baker test. Ultimately, only nine target ships were able to be scrapped rather than scuttled. Charlie was rescheduled as Operation Wigwam, a deep-water shot conducted in 1955 off the coast of Mexico (Baja California).

Bikini's native residents agreed to evacuate the island, and were evacuated on board the LST-861, with most moving to the Rongerik Atoll. In the 1950s, a series of large thermonuclear tests rendered Bikini unfit for subsistence farming and fishing because of radioactive contamination. Bikini remains uninhabited , though it is occasionally visited by sport divers. Planners attempted to protect participants in the Operation Crossroads tests against radiation sickness, but one study showed that the life expectancy of participants was reduced by an average of three months. The Baker test's radioactive contamination of all the target ships was the first case of immediate, concentrated radioactive fallout from a nuclear explosion. Chemist Glenn T. Seaborg, the longest-serving chairman of the Atomic Energy Commission, called Baker "the world's first nuclear disaster."

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Sparc february 2018.jpg
Credit: Ken Filar

Visualization of the proposed SPARC tokamak experiment. Using high-field magnets built with newly available, high-temperature superconductor, this experiment would be the first controlled fusion plasma to produce net energy output. (Credit: Ken Filar, PSFC Research Affiliate)"

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Hans Bethe won the 1967 Nobel Prize in Physics for his work on the theory of stellar nucleosynthesis.
Hans Albrecht Bethe (German: [ˈhans ˈalbʁɛçt ˈbeːtə]; July 2, 1906 – March 6, 2005) was a German-American nuclear physicist who made important contributions to astrophysics, quantum electrodynamics and solid-state physics, and won the 1967 Nobel Prize in Physics for his work on the theory of stellar nucleosynthesis.

For most of his career, Bethe was a professor at Cornell University. During World War II, he was head of the Theoretical Division at the secret Los Alamos laboratory which developed the first atomic bombs. There he played a key role in calculating the critical mass of the weapons and developing the theory behind the implosion method used in both the Trinity test and the "Fat Man" weapon dropped on Nagasaki in August 1945.

After the war, Bethe also played an important role in the development of the hydrogen bomb, though he had originally joined the project with the hope of proving it could not be made. Bethe later campaigned with Albert Einstein and the Emergency Committee of Atomic Scientists against nuclear testing and the nuclear arms race. He helped persuade the Kennedy and Nixon administrations to sign, respectively, the 1963 Partial Nuclear Test Ban Treaty and 1972 Anti-Ballistic Missile Treaty (SALT I).

His scientific research never ceased and he was publishing papers well into his nineties, making him one of the few scientists to have published at least one major paper in his field during every decade of his career – which, in Bethe's case, spanned nearly seventy years. Freeman Dyson, once one of his students, called him the "supreme problem-solver of the 20th century".

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