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- Fission weapons
- Boosted fission weapons
- Thermonuclear weapons
Nuclear weapons are explosive devices that rapidly release the energy produced from the fission or fusion of atomic nuclei. Pound for pound, nuclear explosives are thousands of times more powerful than chemical explosives, such as TNT. The explosive power, or "yield," of nuclear weapons is usually expressed in the quantity of TNT that would release an equivalent amount of energy, measured in thousands of tons of TNT or kilotons (kt)—and, for the most powerful weapons, in millions of tons of TNT or megatons (mt). For example, first-generation fission bombs built by nations have had yields in the range of 10 to 20 kt. Considerably larger yields, however, are possible from fission weapons. The three basic types of nuclear weapons are fission, boosted fission, and thermonuclear.
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For an overview of the basic types of nuclear weapons, see the "Bomb Basics" multimedia presentation.
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The atomic cloud over Nagasaki. |
Fission weapons rapidly
assemble somewhat more than a
critical mass of
fissile material
to create an uncontrolled fission chain reaction. The energy of this
reaction is released within a fraction of a second, resulting in a powerful
explosion. Fission weapons were once commonly called "atomic bombs," and are the
only type of nuclear weapon ever used in wartime. The United States used one
fission weapon against the Japanese city of Hiroshima and a second against the
city of Nagasaki at the end of World War II, in 1945. Since then, no nuclear
weapon of any type has been used in combat.
As upcoming sections of this tutorial will discuss, it is
possible that terrorist organizations could build fission weapons if they
are able to acquire enough fissile material. Terrorists could also
obtain fission weapons from states that possess these weapons in their
nuclear arsenals.
A nuclear weapon that relies primarily on fission, but obtains some of its power from fusion, is known as a "boosted fission" weapon. A boosted fission nuclear weapon contains small amounts of two isotopes of hydrogen, deuterium and tritium, that when fused together release enormous amounts of energy. In this type of weapon, the fission chain reaction creates the heat and pressure necessary to induce the nuclei of the hydrogen isotopes to initiate a fusion reaction, creating more energy and neutrons, which cause additional fissioning of the uranium or plutonium, thereby "boosting" the effectiveness of the fission reaction. Many of the nuclear weapons deployed by China, France, Great Britain, Russia, and the United States are boosted fission weapons. India, Israel, and Pakistan may also possess boosted fission weapons.
Even if terrorist organizations obtained fissile material, it is very unlikely that they would be able to build boosted fission weapons because of their technical complexity, though it is possible that terrorists could obtain a boosted fission weapon from the arsenal of a state possessing such weapons.
Thermonuclear weapons use a fission reaction to initiate a fusion reaction, from which they derive most of their power. These weapons are commonly called "hydrogen bombs," since two isotopes of hydrogen, deuterium and tritium, are used in the fusion reaction. The destructive power of thermonuclear weapons can be much greater than that of fission weapons. The largest thermonuclear weapons formerly deployed by the Soviet Union and the United States during the Cold War had yields measured in megatons (millions of tons of TNT equivalent). Currently, Russia and the United States deploy large numbers of thermonuclear weapons, and China, France, and the United Kingdom also possess them. Most aircraft and missile-launched nuclear weapons currently deployed by the five major nuclear powers are thermonuclear weapons with yields from 100 to 750 kt.
Thermonuclear weapons would be beyond the manufacturing capabilities of terrorist organizations, even if they obtained fissile material. However, one cannot exclude the possibility that terrorists might obtain an operational thermonuclear weapon, with a yield well in excess of 100 kt, from the nuclear arsenal of a state possessing thermonuclear or boosted fission weapons.
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