nuclear weapons. Some testing was also done with military personnel in the vicinity to determine military survivability and fighting capacity in a nuclear war. Research was also done on civilians exposed to radiation from nuclear testing to determine the effects of such exposure. Nuclear testing was also done in some cases for political purposes. India and Pakistan, for example, testing in 1998 in order to assert their status as nuclear weapon states.
Partial Test Ban Treaty
In response to growing international awareness of the risks of radiation from nuclear tests, the Soviet Union, US and UK in 1963 negotiated an agreement to prohibit nuclear testing in the atmosphere, outer space and underwater. France and China did not join the treaty and continued atmospheric testing. France stopped atmospheric testing in 1975 following a case in the International Court of Justice and China stopped in 1980.
However, the PTBT did not prevent underground testing, nor the development of new types of nuclear weapons and an increase in stockpiles. In fact the pace of nuclear testing increased after 1963, and nuclear stockpiles doubled between 1963 and 1990.
Threshold Test Ban Treaty
In 1974 the US and Soviet Union concluded the Threshold Test Ban Treaty under which they agreed not to conduct nuclear tests with an explosive yield over 150 kilotons (i.e. about 10 times the force of the Hiroshima bomb). This prevented tests of the high yield hydrogen bombs, but did not slow down the rate of testing either.
Comprehensive Test Ban Treaty
In 1996, the United Nations adopted the Comprehensive Test Ban Treaty which had been negotiated in the Conference on Disarmament. The CTBT prohibits all nuclear test explosions, including explosions for peaceful purposes, but does not prohibit testing by other means (see below).
To enter into force, the CTBT requires the ratification of all states with nuclear reactors. Three such states - India, Pakistan and North Korea - have not signed the CTBT. In addition the US Senate has refused to ratify.
In anticipation that there would be some required states that would be slow in ratifying, the treaty includes a provision calling for conferences to of states parties to be held to consider ways to facilitate entry into force. The first of these conferences in 2001 did not take any significant actions in this regard and it does not seem likely that the treaty will enter into force in the near future.
Comprehensive Test Ban Treaty Organisation (CTBTO)
The CTBT establishes an agency for its implementation including an international monitoring system (IMS) to assist in verification. The IMS comprises facilities owned by the CTBTO, and those owned and operated by States parties. Although the agency itself cannot officially be established until the CTBT enters into force, the IMS is operating and providing useful data for monitoring and interpretation of seismic events to determine whether or not they are nuclear explosions.
For more information on the CTBTO see http://www.ctbto.org/
Nuclear Testing by other means
Although the CTBT has not entered into force, States which have signed are generally obliged to adhere to their commitments under the treaty not to violate the principle provisions. Thus none of the signatories has conducted a nuclear explosion since signing. However, the US, Russia, UK and France have openly conducted other forms of nuclear testing including sub-critical explosions (i.e. where there is no nuclear reaction), fusion experiments, computer simulations and high energy experiments. It is believed that China has also conducted at least one sub-critical test.
One of the reasons for these tests is to upgrade existing weapons designs and test new designs. Following such tests under the "Stockpile Stewardship Program" the US, for example, has introduced a new weapon into its stockpile - the B61-mod11.
The US and France are known to be constructing new facilities capable of conducting nuclear experiments including the National Ignition Facility in California, the Dual-Axis Radiographic Hydrodynamic Testing Facility (DARHT) in Nevada and the Megajoule Facility in ?