The Threshold Test Ban Treaty (TTBT) between the United States and the Soviet Union establishes a nuclear threshold through the prohibition of nuclear tests that exceed 150 kilotons. The threshold prevents the testing of new or existing nuclear weapons that exceed the fractional-megaton range. The United States and Soviet Union are subject to verification provisions. These are conducted through hydrodynamic yield measurements, seismic monitoring, and on-site inspections.
Opened for Signature: 3 July 1974
Entry into force: 11 December 1990
Official Text: http://www.state.gov/t/isn/5204.htm#treaty
Status and Signatories: http://www.state.gov/t/isn/5204.htm#narrative