Nuclear weapons tests are experiments 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 affected when exposed to nuclear explosions. Additionally, nuclear tests have often been used as a symbol of scientific and military strength. Many tests have been politically motivated; most nuclear-weapon states publicly declared their nuclear status through a nuclear test.
The Nuclear-Test-Ban Treaty was established to prevent such tests. Nuclear medicine procedures or radionuclide imaging are non-invasive and usually painless medical tests that help doctors diagnose conditions. These imaging scans use radioactive materials called radiopharmaceuticals or radiotracers. Studies and evaluations have estimated that cancer deaths due to global radiation doses from nuclear test programs in the atmosphere of the five nuclear-weapon States amount to hundreds of thousands.
South Africa is the only nation to date that voluntarily renounced nuclear weapons under its full control, less than ten years after transitioning to a majority-elected government. In 1946, the United States conducted the first Operation Crossroads underwater nuclear test at its Pacific Proving Grounds in the Marshall Islands to evaluate the effects of nuclear weapons used against naval vessels. France closed and dismantled all of its nuclear test centers in the 1990s, making it the only nuclear-weapon State to date to do so. If data from IMS stations indicate that a nuclear test has been carried out, a Member State may request an on-site inspection to collect evidence and make the final assessment of whether a nuclear explosion actually occurred in violation of the Treaty.
India and Pakistan announced unilateral moratoriums on nuclear testing in 1998 and have not conducted any since then. In 1955, United States Operation Wigwam conducted a single submarine nuclear test at a depth of 600 m to determine the vulnerability of submarines to nuclear energy explosions. The partial nuclear-test-ban treaty makes it illegal to detonate any nuclear explosion anywhere except underground, in order to reduce atmospheric precipitation. Underground nuclear testing was banned by the 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT), which prohibits all nuclear explosions on Earth. At first, neither the United States nor the Soviet Union had many nuclear weapons to spare, so their nuclear tests were relatively limited.
From the first nuclear test in 1945 to the tests in Pakistan in 1998, there was never a period of more than 22 months without nuclear tests. Nuclear accidents occurred during other atmospheric nuclear weapons tests conducted by other countries as well. The Comprehensive Nuclear-Test-Ban Treaty bans all nuclear testing anywhere on Earth's surface, atmosphere, underwater, and underground.