When nuclear weapons were still in a theoretical phase, scientists and military strategists wondered about their destructive capabilities. Confirmation of the terrifying power of these devices came during World War II, in August 1945, with the detonation of two atomic bombs, one over Hiroshima and the other over Nagasaki, Japan. The United States military's use of these bombs resulted in the surrender of the Japanese and the end of the war in the Pacific.
The tensions and conflict between the United States and the Soviet Union, known as the Cold War, began soon after the end of World War II. During the period between 1945 and 1992, the U.S. conducted more than 1,000 nuclear weapons tests, and the Soviet Union conducted more than 700 such tests. These tests, as well as studies conducted in Hiroshima and Nagasaki following the atomic bomb blasts that occurred there, clearly demonstrated the power nuclear weapons have to devastate huge areas.
Researchers have developed two main types of nuclear weapons. The fission bomb, like those dropped on Japan, is fueled by the energy released when atomic nuclei are split. The hydrogen bomb is fueled by nuclear fusion, or the joining of two atomic nuclei. Both of these nuclear reactions release huge amounts of energy in a very short amount of time.
The energy released in these nuclear explosions affects surrounding areas in a number of ways. First, light and invisible forms of radiation, such as gamma rays and X-rays, emanate from the blast site. Very quickly, this radiation causes combustible materials, such as wood, to heat up and ignite.
Like conventional weapons, nuclear bombs also cause extensive pressure damage to surrounding areas. The blast of pressure arrives after the radiation because it travels at the speed of sound, which is much slower than the speed of light. Depending on the size and power of a nuclear weapon, a single blast may produce a crater hundreds of feet wide and level every building for miles around. For example, a one megaton atomic bomb, equal in power to one million tons of TNT, produces pressures up to 12 pounds per square inch on structures up to several miles away. This is equal to more than 1,700 pounds of pressure per square foot, a force that no building is designed to withstand.