Types of Nuclear Weapons Tests
Nuclear explosions have been detonated in all environments: above ground, underground and underwater. Bombs have been detonated on top of towers, onboard barges, suspended from balloons, on the earth's surface, underwater to depths of 600m, underground to depths of more than 2,400m and in horizontal tunnels. Test bombs have been dropped by aircraft and fired by rockets to altitudes of over 500 kilometres.
Atmospheric testing refers to explosions which take place in the atmosphere.
All told, of the over 2,000 nuclear explosions detonated worldwide between 16 July 1945 (United States) and 29 July 1996 (China), 25 % or over 500 bombs were exploded in the atmosphere: over 200 by the United States, over 200 by the Soviet Union, about 20 by Britain, about 50 by France and over 20 by China.
International concern over radioactive fallout resulting from atmospheric tests escalated in the mid 1950s. In March 1954, the United States tested its hydrogen bomb Castle Bravo in the Pacific’s Marshall Islands. The Bravo test created the worst radiological disaster in the United States’ testing history. By accident, local civilians on the Marshall Islands, U.S. servicemen stationed on Rongerik atoll, and the Japanese fishing trawler Lucky Dragon, were contaminated with the fallout.
Nuclear weapon tests have been carried out in all environments: above ground, underground and underwater.
Atmospheric testing was banned by the 1963 Partial Test Ban Treaty. Negotiations had largely responded to the international community’s grave concern over the radioactive fallout resulting from atmospheric tests. The United States, the Soviet Union and the United Kingdom became Parties to the Treaty; France and China did not. France conducted its last atmospheric test in 1974, China in 1980.
High-altitude nuclear testing
Around 20 nuclear tests were conducted by the United States and the Soviet Union in high altitudes or lower outer space between 1958 and 1962. The main aim of these explosions, detonated at heights between 40 and 540 kilometres, was to determine the feasibility of nuclear weapons as anti-ballistic missile defense or anti-satellite weapons. The largest such test, the 1.4 megaton U.S. Starfish Prime test in 1962, damaged and destroyed several of the satellites in orbit at the time and led to wide-spread power outages on the ground. High-altitude or outer space nuclear testing is equally banned by the 1963 Partial Test Ban Treaty as well as by the 1967 Outer Space Treaty.
Underwater testing refers to explosions which take place underwater or close to the surface of the water. Relatively few underwater tests have been conducted. The first underwater nuclear test - 'Baker' (video) - was conducted by the United States in 1946 at its Pacific Proving Grounds in the Marshall Islands with the purpose of evaluating the effects of nuclear weapons used against naval vessels. Later, in 1955, the United States’ Operation Wigwam conducted a single underwater nuclear test at a depth of 600 m to determine the vulnerability of submarines to nuclear explosions.
Underwater nuclear explosions close to the surface can disperse large amounts of radioactive water and steam, contaminating nearby ships, structures and individuals.
Underwater nuclear testing was banned by the 1963 Partial Test Ban Treaty. The CTBTO's hydroacoustic IMS stations are those best suited to detect nuclear explosions underwater.
Of the over 2,000 nuclear explosions detonated worldwide between 1945 and 1996, 25 % or over 500 bombs were exploded in the atmosphere.
Underground testing means that nuclear explosions are detonated at varying depths under the surface of the earth. These comprised the majority (i.e. about 75%) of all nuclear explosions detonated during the Cold War (1945–1989); that is, over 800 of all tests conducted by the United States and nearly 500 of all tests conducted by the Soviet Union.
When the explosion is fully contained, underground nuclear testing emits negligible fallout compared to atmospheric testing. However, if underground nuclear tests "vent" to the surface, they can produce considerable radioactive debris. Underground testing is usually evident through seismic activity related to the yield of the nuclear device.
Underground nuclear testing was banned by the 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT) that bans all nuclear explosions anywhere, by anyone.
75 % of all nuclear explosions have been conducted underground.
The CTBTO’s seismic IMS stations are used to detect nuclear explosions underground. The seismic data is combined with radionuclide data. Only the radionuclide technology can determine if an explosion is nuclear in origin; its stations and laboratories around the world monitor the presence of particulates and/or noble gases in the atmosphere.
Next chapter: Nuclear Testing 1945-2009