Nuclear weapons tests are experiments carried out to determine the effectiveness, yield, and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that developed nuclear weapons tested them.
Testing nuclear weapons can yield information about how the weapons work, as well as how the weapons behave under various conditions and how personnel, structures, and equipment behave when subjected to nuclear explosions. Nuclear testing has often been used as an indicator of scientific and military strength, and many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status by means of a nuclear test.
The first nuclear device was detonated as a test by the United States at the Trinity site on July 16,with a yield approximately equivalent to 20 kilotons of TNT. The first thermonuclear weapon technology test of engineer device, codenamed " Ivy Mike ", was tested at the Enewetak Atoll in the Marshall Islands on November 1, local datealso by the United States.
The largest nuclear weapon ever tested was the " Tsar Bomba " of the Soviet Union at Novaya Zemlya on October 30,with the largest yield ever seen, an estimated 50—58 megatons. Inthree UK, US, Soviet Union of the four nuclear states and many non-nuclear states signed the Limited Test Ban Treatypledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space.
The treaty permitted underground nuclear testing. France continued atmospheric testing untiland China continued until Neither has signed the treaty. Underground tests in the United States continued until its last nuclear testthe Soviet Union untilthe United Kingdom untiland both China and France until In signing the Comprehensive Nuclear-Test-Ban Treaty inthese states have pledged to discontinue all nuclear testing; the treaty has not yet entered into force because of failure to be ratified by eight countries.
Non-signatories India and Pakistan last tested nuclear weapons in North Korea conducted nuclear tests in, and The most recent confirmed nuclear test occurred [update] in September in North Korea.
Nuclear weapons tests have historically been divided into four categories reflecting the medium or location of the test. Another way to classify nuclear tests are by the number of explosions that constitute the test. The treaty definition of a salvo test is:. In conformity with treaties between the United States and the Soviet Union, a salvo is defined, for multiple explosions for peaceful purposes, as two or more separate explosions where a period of time between successive individual explosions does not exceed 5 seconds and where the burial points of all explosive devices can be connected by segments of straight lines, each of them connecting two burial points, and the total length does not exceed 40 kilometers.
For nuclear weapon tests, a salvo is defined as two or more underground nuclear explosions conducted at a test site within an area delineated by a circle having a diameter of two kilometers and conducted within a total period of time of 0. The USSR has exploded up to eight devices in a Nuclear weapons effects test evaluation and simulation dating salvo test; Pakistan's second and last official test exploded four different devices.
Almost all lists in the literature are lists of tests; in the lists Nuclear weapons effects test evaluation and simulation dating Wikipedia for example, Operation Cresset has separate items for Cremino and Caerphillywhich together constitute a single testthe lists are of explosions.
Separately from these designations, nuclear tests are also often categorized by the purpose of the test itself. Aside from these technical considerations, tests have been conducted for political and training purposes, and can often serve multiple purposes.
Hydronuclear tests study nuclear materials under the conditions of explosive shock compression. They can create sub-critical conditions, or supercritical conditions with yields ranging from negligible all the way up to a substantial fraction of full weapon yield.
Critical mass experiments determine the quantity of fissile material required for criticality with a variety of fissile material compositions, densities, shapes, and reflectors.
They can be sub-critical or super-critical, in which case significant radiation fluxes can be produced. This type of test resulted in several criticality accidents. Sub-critical or cold tests are any type of tests involving nuclear materials and possibly high-explosives like those mentioned above that purposely result in no yield.
The name refers to the lack of creation of a critical mass of fissile material. They are the only type of tests allowed under the interpretation of the Comprehensive Nuclear-Test-Ban Treaty tacitly agreed to by the major atomic powers.
Subcritical test executed by the United States "Nuclear weapons effects test evaluation and simulation dating" There have also been simulations of the effects of nuclear detonations using conventional explosives such as the Minor Scale U. The explosives might be spiked with radioactive materials to simulate fallout dispersal. The first atomic weapons test was conducted near Alamogordo, New Mexico, on July 16,during the Manhattan Projectand given the codename " Trinity ".
The test was originally to confirm that the implosion-type nuclear weapon design was feasible, and to give an idea of what the actual size and effects of a nuclear explosion would be before they were used in combat against Japan. While the test gave a good approximation of many of the explosion's effects, it did not give an appreciable understanding of nuclear falloutwhich was not well understood by the project scientists until well after the atomic bombings of Hiroshima and Nagasaki.
Neither country had very many atomic weapons to spare at first, and so testing was relatively infrequent when the U. However, by the s the United States had established a dedicated test site on its own territory Nevada Test Site and was also using a site in the Marshall Islands Pacific Proving Grounds for extensive atomic and nuclear testing.
The early tests were used primarily to discern the military effects of atomic weapons Crossroads had involved the effect of atomic weapons on a navy, and how they functioned underwater and to test new weapon designs.
During the s, these included new hydrogen bomb designs, which were tested in the Pacific, and also new and improved fission weapon designs. The Soviet Union also began testing on a limited scale, primarily in Kazakhstan.
During the later phases of the Cold Warthough, both countries developed accelerated testing programs, testing many hundreds of bombs over the last half of the 20th century.
Atomic and nuclear tests can involve many hazards. Some these were illustrated in the U. Castle Bravo test in The weapon design tested was a new form of hydrogen bomb, and the scientists underestimated how vigorously some of the weapon materials would react.
As a result, the explosion—with a yield of 15 Mt —was over twice what was predicted. Aside from this problem, the weapon also generated a large amount of radioactive nuclear falloutmore than had been anticipated, and a change in the weather pattern caused the fallout to spread in a direction not cleared in advance.
The fallout plume spread high levels of radiation for over a hundred miles, contaminating a number of populated islands in nearby atoll formations. One crewman died from radiation sickness after returning to port, and it was feared that the radioactive fish they had been carrying had made it into the Japanese food supply. Castle Bravo was the worst U.