Nuclear testing is the detonation of nuclear weapons to evaluate their effects. Underground nuclear tests are the detonation tests of nuclear weapons that are carried out underground. The device is detonated remotely from a surface control bunker, creating an underground chamber filled with superheated radioactive gas. As it cools, a pool of molten rock builds up at the bottom of the chamber.
When the device being tested is buried deep enough, the nuclear explosion can be contained, without releasing radioactive materials into the atmosphere. The objective of the test-ban treaty was to limit atmospheric precipitation and exposure to radioactive materials. If the bomb is not buried deep enough in the ground, it will not necessarily produce a classic mushroom cloud, but rather a giant cloud of dust and dirt will explode in the sky. Detonation of nuclear weapons above the earth sends radioactive materials up to 50 miles into the atmosphere.
Large particles fall to the ground near the explosion site, but lighter particles and gases move to the upper atmosphere. The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans nuclear testing anywhere on the planet's surface, atmosphere, underwater and underground. The first Operation Crossroads underwater nuclear test was conducted by the United States in 1946 at its Pacific Proving Grounds in the Marshall Islands for the purpose of evaluating the effects of nuclear weapons used against naval vessels. From then until the signing of the CTBT in 1996, most nuclear tests were conducted underground, in order to prevent nuclear fallout from entering the atmosphere.
Some studies and evaluations estimate that cancer deaths due to global radiation doses from nuclear test programs in the atmosphere of five nuclear-weapon States amount to hundreds of thousands. France closed and dismantled all of its nuclear test centers in the 1990s, becoming the only nuclear-weapon State to date that has done so. Monitors were originally designed to detect radionuclides that were released after detonation of a nuclear weapon. Later, in 1955, United States Operation Wigwam conducted a single submarine nuclear test at a depth of 600 m to determine vulnerability of submarines to nuclear explosions.
India and Pakistan immediately moved to announce unilateral moratoriums on nuclear testing and have not conducted nuclear tests since 1998. Underground nuclear testing was banned by the 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT), which bans all nuclear explosions on Earth. If data from IMS stations indicate that a nuclear test has been carried out, a Member State may request that an on-site inspection be carried out to collect evidence to make final assessment of whether a nuclear explosion actually occurred in violation of the Treaty.