Untitled Essay Research Paper Nuclear Weapons explosive — страница 4

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of the fission debris from the trigger and from the radioactivity induced by neutrons in coral and seawater. Some of the radioactive debris, however, fell on the Lucky Dragon, a Japanese vessel engaged in tuna fishing about 160 km (about 100 mi) from the test site. This radioactive dust was later analyzed by Japanese scientists. The results demonstrated that the bomb that dusted the Lucky Dragon with fallout was more than just an H-bomb.Fission-Fusion-Fission BombThe thermonuclear bomb exploded in 1954 was a three-stage weapon. The first stage consisted of a big A-bomb, which acted as a trigger. The second stage was the H-bomb phase resulting from the fusion of deuterium and tritium within the bomb. In the process helium and high-energy neutrons were formed. The third stage

resulted from the impact of these high-speed neutrons on the outer jacket of the bomb, which consisted of natural uranium, or uranium-238. No chain reaction was produced, but the fusion neutrons had sufficient energy to cause fission of the uranium nuclei and thus added to the explosive yield and also to the radioactivity of the bomb residues.Effects of Nuclear WeaponsThe effects of nuclear weapons were carefully observed.Blast EffectsAs is the case with explosions caused by conventional weapons, most of the damage to buildings and other structures from a nuclear explosion results, directly or indirectly, from the effects of blast. The very rapid expansion of the bomb materials produces a high-pressure pulse, or shock wave, that moves rapidly outward from the exploding bomb. In

air, this shock wave is called a blast wave because it is equivalent to and is accompanied by powerful winds of much greater than hurricane force. Damage is caused both by the high excess (or overpressure) of air at the front of the blast wave and by the extremely strong winds that persist after the wave front has passed. The degree of blast damage suffered on the ground depends on the TNT equivalent of the explosion; the altitude at which the bomb is exploded, referred to as the height of burst; and the distance of the structure from ground zero, that is, the point directly under the bomb. For the 20-kiloton A-bombs detonated over Japan, the height of burst was about 550 m (about 1800 ft), because it was estimated that this height would produce a maximum area of damage. If the

TNT equivalent had been larger, a greater height of burst would have been chosen.Assuming a height of burst that will maximize the damage area, a 10-kiloton bomb will cause severe damage to wood-frame houses, such as are common in the U.S., to a distance of more than 1.6 km (more than 1 mi) from ground zero, and moderate damage as far as 2.4 km (1.5 mi). (A severely damaged house probably would be beyond repair.) The damage radius increases with the power of the bomb, approximately in proportion to its cube root. If exploded at the optimum height, therefore, a 10-megaton weapon, which is 1000 times as powerful as a 10-kiloton weapon, will increase the distance tenfold, that is, out to 17.7 km (11 mi) for severe damage and 24 km (15 mi) for moderate damage of a frame house.Thermal

EffectsThe very high temperatures attained in a nuclear explosion result in the formation of an extremely hot incandescent mass of gas called a fireball. For a 10-kiloton explosion in the air, the fireball will attain a maximum diameter of about 300 m (about 1000 ft); for a 10-megaton weapon the fireball may be 4.8 km (3 mi) across. A flash of thermal (or heat) radiation is emitted from the fireball and spreads out over a large area, but with steadily decreasing intensity. The amount of heat energy received a certain distance from the nuclear explosion depends on the power of the weapon and the state of the atmosphere. If the visibility is poor or the explosion takes place above clouds, the effectiveness of the heat flash is decreased. The thermal radiation falling on exposed

skin can cause what are called flash burns. A 10-kiloton explosion in the air can produce moderate (second-degree) flash burns, which require some medical attention, as far as 2.4 km (1.5 mi) from ground zero; for a 10-megaton bomb, the corresponding distance would be more than 32 km (more than 20 mi). Milder burns of bare skin would be experienced even farther out. Most ordinary clothing provides protection from the heat radiation, as does almost any opaque object. Flash burns occur only when the bare skin is directly exposed, or if the clothing is too thin to absorb the thermal radiation.The heat radiation can initiate fires in dry, flammable materials, for example, paper and some fabrics, and such fires may spread if conditions are suitable. The evidence from the A-bomb