THERMAL RADIATION

Thermal radiation is the radiant energy (heat and light) that is emitted by the fireball. Thermal radiation travels at the speed of light and persists as long as the fireball is luminous. The duration of thermal radiation emission depends on weapon yield. It will last less than 1 second for a l-kt yield and approximately 8 or 9 seconds for a l-Mt yield. Thermal radiation is effectively shielded by anything that will cast a shadow (opaque materials). Thermal radiation can incapacitate exposed personnel by causing skin burns, flash blindness, or retinal burns.

Overland, thermal radiation will ignite fires in buildings, vehicles, dry vegetation, and other combustible materials.

Thermal radiation is modified by the height of the point of detonation, weapon yield, atmospheric conditions, cloud cover, and terrain features. As the height of the point of detonation is increased, the area of the earth's surface exposed to the thermal radiation increases because line-of-sight area increases and there are less shadows from such things as existing structures, vegetation, and terrain features.

As the weapon yield is increased, the range at which thermal radiation can cause skin burns and eye injuries to exposed personnel increases. It will extend well beyond the range at which blast and initial nuclear radiation are of significance. The emission rate of thermal radiation from a highyield weapon is slower than that from a low-yield weapon. Thus, the high-yield weapon must deliver more thermal energy to do an equivalent amount of damage because a target has more time to dissipate the heat being received.

The ability of the atmosphere to lessen the effect of thermal radiation depends on such factors as absorption by water vapor, carbon dioxide, ozone, and impurities in the air. On days when fog, haze, and clouds are between the point of detonation and the target, thermal radiation will be decreased. On the other hand, when fog, haze, and clouds are above the burst and the target, a significant amount of thermal radiation will reflect downward and increase the severity of burns received at a given location. Such conditions can also increase the number of personnel who are flash blinded or dazzled by a burst. The terrain surface cover, such as snow, can also reflect significant thermal radiation. This adds to both the range and severity of the thermal effect.

NUCLEAR RADIATION

Four basic types of nuclear radiation are given off during a nuclear explosion: alpha particles, beta particles, gamma rays, and neutrons.

Alpha particles travel only a few centimeters in air before they are stopped. They cannot penetrate even a thin sheet of paper.

Beta particles can travel several feet in air, but they cannot penetrate a sheet of aluminum that is more than a few millimeters in thickness. Beta particles cannot penetrate the normal combat uniform.

Gamma rays are a form of electromagnetic radiation, indistinguishable from X rays.

Neutrons are electrically neutral particles. Both gamma rays and neutrons can travel great distances in air. Gamma rays and neutrons have greater penetrating power than the other forms of nuclear radiation. Their injurious effects on personnel are also quite similar.

Nuclear radiation does not affect most materials in any visible manner. Thus ships, vehicles, electronic equipment (except transistors), and other equipment are not damaged by radiation. However, radioactive contamination does pose a danger to operating personnel. The term contamination is used to mean radioactive material that has been deposited where it is not wanted. All radioactive contamination presents a hazard to personnel.