Understanding Radiation: General Principles of Nuclear Explosions
An explosion, in general, results from the very rapid release of a large amount of energy within a limited space. This is true for a conventional “high explosive,” such as TNT, as well as for a nuclear (or atomic) explosion,1 although the energy is produced in quite different ways. The sudden liberation of energy causes a considerable increase of temperature and pressure, so that all the materials present are converted into hot, compressed gases.
Since these gases are at very high temperatures and pressures, they expand rapidly and thus initiate a pressure wave, called a “shock wave,” in the surrounding medium air, water, or earth. The characteristic of a shock wave is that there is (ideally) a sudden increase of pressure at the front, with a gradual decrease behind it. A shock wave in air is generally referred to as a “blast wave” because it resembles and is accompanied by a very strong wind. In water or in the ground, however, the term “shock” is used, because the effect is like that of a sudden impact.
Nuclear weapons are similar to those of more conventional types insofar as their destructive action is due mainly to blast or shock. On the other hand, there are several basic differences between nuclear and high-explosive weapons.
In the first place, nuclear explosions can be many thousands (or millions) of times more powerful than the largest conventional detonations.
Second, for the release of a given amount of energy, the mass of a nuclear explosive would be much less than that of a conventional high explosive. Consequently, in the former case, there is a much smaller amount of material available in the weapon itself that is converted into the hot, compressed gases mentioned above. This results in somewhat different mechanisms for the initiation of the blast wave.
Third, the temperatures reached in a nuclear explosion are very much higher than in a conventional explosion, and a fairly large proportion of the energy in a nuclear explosion is emitted in the form of light and heat, generally referred to as “thermal radiation.” This is capable of causing skin burns and of starting fires at considerable distances.
Fourth, the nuclear explosion is accompanied by highly-penetrating and harmful invisible rays, called the “initial nuclear radiation.”
Finally the substances remaining after a nuclear explosion are radioactive, emitting similar radiations over an extended period of time. This is known as the “residual nuclear radiation” or “residual radioactivity” (Figure 6-2).
It is because of these fundamental differences between a nuclear and a conventional explosion, including the tremendously greater power of the former, that the effects of nuclear weapons require special consideration. In this connection, a knowledge and understanding of the mechanical and the various radiation phenomena associated with a nuclear explosion are of vital importance.
The purpose here is to describe the different forms in which the energy of a nuclear explosion are released, to explain how they are propagated, and to show how they may affect people (and other living organisms) and materials. Where numerical values are given for specific observed effects, it should be kept in mind that there are inevitable uncertainties associated with the data, for at least two reasons.
In the first place, there are inherent difficulties in making exact measurements of weapons effects. The results are often dependent on circumstances which are difficult, if not impossible, to control, even in a test and certainly cannot be predicted in the event of an attack.
Furthermore, two weapons producing the same amount of explosive energy may have different quantitative effects because of differences in composition and design.
It is hoped, nevertheless, that the information contained in this volume, which is the best available, may be of assistance to those responsible for defense planning and in making preparations to deal with the emergencies that may arise from nuclear warfare. In addition, architects and engineers may be able to utilize the data in the design of structures having increased resistance to damage by blast, shock, and fire, and which provide shielding against nuclear radiations.