Thermal Radiation and Its Effects

GENERAL CHARACTERISTICS OF energy is initially in the form of kinetic THERMAL RADIATION energy of the weapon debris. This kinetic energy is also absorbed by the air 7.01 One of the important difat a slightly later time \(§ 2.109) and ferences between a nuclear and a conserves to further heat the air. The heated ventional high-explosive weapon is the air, which constitutes the fireball, in turn large proportion of the energy of a nuradiates in a spectral region roughly clear explosion which is released in the similar to that of sunlight near the form of thermal (or heat) radiation. Beearth's surface. It is the radiation (ultracause of the enormous amount of energy violet, visible, and infrared) from the liberated per unit mass in a nuclear fireball, traveling with the velocity of weapon, very high temperatures are atlight, which constitutes the thermal ratained. These are estimated to be several diation at distances from the explosion. tens of million degrees, compared with The time elapsing, therefore, between a few thousand degrees in the case of a the emission of this (secondary) thermal conventional explosion. As a conseradiation from the fireball and its arrival quence of these high temperatures, at a target miles away, is quite msignifabout 70 to 80 percent of the total enicant. ergy (excluding the energy of the resid7.02 It is desirable to state specificual radiation) is released in the form of ally what is meant by the term "thermal electromagnetic radiation of short radiation" as it is used in the present wavelength. Initially, the (primary) chapter. Actually, all the energy rethermal radiations are mainly in the soft leased by a nuclear detonation, includX-ray region of the spectrum but, for ing the residual radiation from the nuclear explosions below about 50 weapon debris, is ultimately degraded to miles, the X rays are absorbed in air in thermal energy, i.e., heat. But only part the general vicinity of the burst, thereby of it is regarded as constituting the therheating it to high temperatures. Most of mal radiation of interest which can the remaining 20 to 30 percent of the cause fire damage and personal injury at