NUCLEAR BURSTS

When a nuclear device is detonated in space,

in the atmosphere, or at or below the surface of the earth or ocean, many characteristic effects are produced. Some effects, such as nuclear radiations and expanding debris, are common to all of these environments, though varying in degree. Other effects, such as cratering, blast, and water shock, are peculiar to certain environments. Effects such as light and heat are visible or tangible. Others, like nuclear radiations, are not directly apparent and can only be discerned by instruments or secondary effects. Some effects occur in and last _{only microseconds,} whereas others occur in microseconds but linger for days, months, or even years. Meteorological conditions such as atmospheric pressure, temperature, humidity, winds, and precipitation can affect some of the observed phenomena. All nuclear detonations, however, produce effects that can damage equipment and injure personnel.

The energy released from a nuclear detonation below an altitude of approximately 100,000 feet may be divided into three broad categories. Approximately 50 percent of the energy will be used to produce blast and shock, about 35 percent to produce thermal radiation, and about 15 percent to produce nuclear radiation. The nuclear radiation consists of about 10 percent residual nuclear radiation and about 5 percent initial nuclear radiation. Initial radiation is delivered simultaneously with the detonation and cannot be avoided by maneuvering or evasive actions. The initial radiation dose received will occur within 1 minute after the explosion, and most of it will occur within a matter of seconds. Residual radiation, on the other hand, may be emitted over a long period of time, extending to days and years. Therefore, maneuvering out of an area contaminated by residual radiation may be an effective countermeasure.

When the detonation occurs beneath the surface of the earth or water, some of the energy released is captured beneath the surface. For example, little or no thermal or initial radiation energy from an underwater or underground burst can escape to the surface.

The militarily significant effects of nuclear weapons are covered in the following paragraphs to provide a general understanding of each effect. However, you should refer to other publications for complete information.

The energy yield of a nuclear weapon is described in terms of the amount of TNT that would be required to release a similar amount of energy. Thus, a nuclear weapon capable of releasing an amount of energy equal to the energy released by 20,000 tons of TNT is said to be a 20-kiloton (20-kt) weapon. A nuclear weapon capable of releasing an amount of energy equal to the energy released by 1 million tons of TNT is said to be a 1-megaton (1-Mt) weapon.

A weapon's yield may be a fraction of a kiloton or up to several megatons. Although a weapon's total yield is not significantly influenced by the environment about the burst point, the relative effect of the weapon depends a great deal on the location of the detonation. The detonation can be classified as one of the following, according to its location: . Airburst . High-altitude burst . Surface burst . Underwater burst . Underground burst

Often the underwater and the underground bursts are referred to as subsurface bursts. A discussion of each of the five types of bursts and their effects follows.

AIRBURST

An airburst (fig. 8-2) is a burst where the point of detonation is below an altitude of 100,000 feet and the fireball does not touch the surface of the earth. Air blast, thermal radiation (heat and light),

Figure 8-2.-Airburst.

an electromagnetic pulse, and initial nuclear radiation (neutron and gamma rays) are produced around the point of detonation. There will be no significant residual nuclear radiation (gamma and beta radiations from airborne or deposited radioactive material) unless rain or snow falls through the radioactive cloud. The types and effects of radiation will be discussed later in this chapter.