Nuclear weapons tests are experiments that are conducted to assess the performance, effectiveness, and explosive capacity of nuclear weapons. These tests provide valuable information on how weapons work, how detonations are affected by different conditions, and how personnel, structures, and equipment are impacted when exposed to nuclear explosions. Additionally, nuclear tests have often been used as a symbol of scientific and military strength. Tests have been conducted in a variety of locations, including aboard barges, atop towers, suspended from balloons, on the Earth's surface, more than 600 meters underwater, and more than 200 meters underground.
In order to ensure safety during these tests, a salvo is defined as two or more underground nuclear explosions that take place within an area bounded by a circle two kilometers in diameter and occur within a total period of time of 0.1 seconds. In 1996, the international community adopted the Comprehensive Nuclear-Test-Ban Treaty in an effort to end the era of nuclear testing. This treaty not only seeks the total abolition of nuclear weapons but also requires international cooperation to help victims of such tests and remediate contaminated environments. Nuclear tests are also often classified according to their purpose.
For example, some tests are openly political in intention and serve as a public declaration of a nation's nuclear status. Other tests are conducted for research purposes or to assess the effects of radiation on people and the environment. Israel is widely believed to have a sizeable nuclear arsenal but has never tested it unless it participates in Vela. Growing global concern about the consequences of atmospheric tests, including the effects of strontium-90 on nursing mothers and their babies, led to the conclusion of the Partial Test Ban Treaty in 1963 which banned nuclear tests in the atmosphere, underwater, and in space but not underground.
The United States 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) to conduct extensive atomic and nuclear tests by the 1950s. In 1963, three (United Kingdom, United States, Soviet Union) of the four nuclear states at the time and many non-nuclear states signed the Limited Test Ban Treaty which pledged to refrain from testing nuclear weapons in the atmosphere, underwater or in outer space. One of the main ways that rain and nuclear waste are transferred to people through the atmosphere is through dairy products. Logistics would likely lead a terrorist organization to explode a small-scale nuclear fission device at ground level. People within 250 meters of a 0.01 kiloton nuclear detonation would receive doses of 4 Gy of initial whole-body radiation which would cause mortality for almost half of those exposed.