or atomic weapon or thermonuclear weapon
Bomb or other warhead that derives its force from either nuclear fission , nuclear fusion , or both and is delivered by an aircraft, missile, or other system.
Fission weapons, commonly known as atomic bomb s, release energy by splitting the nuclei of uranium or plutonium atoms; fusion weapons, known as hydrogen bomb s or thermonuclear bombs, fuse nuclei of the hydrogen isotopes tritium or deuterium. Most modern nuclear weapons actually combine both processes. Nuclear weapons are the most potent explosive devices ever invented. Their destructive effects include not only a blast equivalent to thousands of tons of TNT but also blinding light, searing heat, and lethal radioactive fallout . The number of nuclear weapons reached its peak in the 1980s, when the U.S. had some 33,000 and the Soviet Union 38,000. Since the end of the Cold War both countries have decommissioned or dismantled thousands of warheads. Other declared nuclear powers are the United Kingdom, France, China, India, and Pakistan. Israel is widely assumed to possess nuclear weapons, and North Korea, Iran, and Iraq often have been accused of seeking to build them. Some countries, such as South Africa, Brazil, and Argentina, have acknowledged pursuing nuclear weapons in the past but have abandoned their programs. See also Nuclear Nonproliferation Treaty ; Nuclear Test Ban Treaty .