During the second World War, there were two kinds of nuclear bombs that were developed: the fission and the fusion bombs. The fission bomb, known as the atomic bomb, was instrumental in bringing World War II to a rapid close. Two such missiles were dropped in August, 1945—one on Hiroshima, Japan, which destroyed 67 per cent of the city, and the other on Nagasaki, Japan, destroying 40 per cent of the city.
Because of its military importance, little information has been published on the construction of the atomic bomb. Unofficial publications describe the bomb as containing a hollow sphere of high explosives. When detonated, the shaped charges implode (blast inward) and bring together quantities of uranium or plutonium in a specific manner to create a “critical mass.”
A critical mass requires that a certain weight of fissionable material must be assembled to sustain a chain reaction. When the critical mass is attained, the nucleus of the uranium or plutonium atom is bombarded with tremendous amounts of slow-moving neutrons. Some neutrons are successfully absorbed and split the nucleus. The result is the formation of lighter elements, the emission of more neutrons, and a violent release of energy. As more neutrons are multiplied, more nuclei are split—thus accounting for the term “chain reaction.” This entire reaction takes place in a fraction of a second. The size of the explosion depends upon the efficiency of the chain reaction.
The first atomic bomb explosion was performed near Alamogordo, New Mexico, on July16, 1945, atop a steel tower. The blast was so powerful that the tower disintegrated as a result of vaporization and the sand in an 800-yard radius fused to glass.
Explosions of this type are characterized by a blinding flash of light, a heat wave, a tremendous shock wave, and a huge ball of fire rising rapidly in a mushroom-shaped cloud. The destructive force of this device is caused by three distinct actions:
- Blast effect – a violent wind first blowing out from the point of explosion and then reversing its direction, creating a vacuum. Most damage is caused by the side effects, such as flying glass and falling walls.
- Thermal radiation – the “flash” heat caused by absorption of heat energy for a very brief instant. In Japan, persons one and one-half miles from the blast were burned on surfaces facing the blast. Burning is caused by ignition of combustible materials.
- Ionizing radiation – called radioactivity, and causing the least amount of damage. A transfer of energy is affected whereby the human tissues undergo a biophysical and biochemical change.
Because of their vast power, atomic bombs are graded by the equivalent weight of TNT required to release the same amount of energy. The bomb’s power is expressed in kilotons (thousands of tons).
The fusion, or thermonuclear, bomb was first tested in November, 1952. Because the explosion is created by the fusion reaction of hydrogen isotopes, deuterium and tritium, the weapon is calledhydrogen bomb.
A fusion bomb of about 100 kilotons provides the great heat needed to sustain a thermonuclear reaction. The intense heat transforms the deuterium and tritium atoms into atoms of helium—a heavier element than hydrogen. The weight of helium atoms formed is less than the total weight of hydrogen atoms consumed in the fusion reaction. The difference in weight is the mass given off in the form of a violent release of energy. The fusion reaction is not limited like ordinary explosives since heat, not mass, initiates the release of nuclear energy.
Hydrogen and cobalt bombs are many more times as powerful as atomic bombs. Bombs as great as 50 megatons (millions of tons) already have been exploded.
A recent idea is the neutron bomb. It has probably not yet been made. In theory, the N-Bomb will be a fusion explosion like the hydrogen bomb. Unlike the H-bomb, however, the blast will develop into a burst of neutrons instead of a great ball of fire resulting in a radioactive cloud. The neutrons can penetrate solid materials, destroying life but not damaging the buildings.