ATOMIC ABCs

Behind the low-rolling smoke of battle in Korea looms the most terrifying of all war clouds: the topless mushroom of the atomic bomb. Will the Russians make an atom-bomb attack on the U.S.? If it comes, what is the defense? Is there any defense? Last week the Atomic Energy Commission and the Department of Defense issued a 456-page volume, The Effects of Atomic Weapons* which gives the first official answers to some of these questions. In it are the ABCs of atomic disaster which every civil-defense planner—and every dweller in a target area—should know: what an atomic attack would mean, and what to do about it.

WHAT THE BOMB DOES

Although an atomic bomb† is thousands of times more powerful than an ordinary bomb, there are limits to its power and destructiveness. Those limits depend not only on the size of the bomb, but also on how and where the bomb is exploded — and how well the defense is organized to meet it.

What happens when the bomb goes off?

Atomic bombs might be exploded in the air over U.S. cities, under water, or at ground level. Though the effects are different in each case, the principle is the same. At the instant a bomb explodes overhead, fission turns it into a rapidly growing "ball of fire," which dims for an imperceptible instant, then grows to a diameter of 900 feet at a temperature of 7,000° C. (see diagram). Around the fire ball forms a shock wave — a shell of air compressed so tightly that it glows white-hot.

The shock wave rushes out like a solid steel wall. At some points it is joined by a reflected wave. The two combine to apply redoubled pressure (called the "Mach front"). Behind the shock wave comes a great wind, at a speed of 800 m.p.h. A mile from "ground zero" (the point directly under the burst), the speed of the wind drops to 200 m.p.h.; 1½ miles away, to 100 m.p.h. Behind the wind comes a partial vacuum, which acts like another wind coming from the opposite direction. Three miles away, the shock wave, wind and vacuum begin to peter out.

Much of the bomb's energy is released as radiation— heat and light, which shoot out from the fire ball a fraction of a second after the explosion. Five miles away, the light glares as brightly as 100 suns; up to half a mile the heat waves sear everything directly in their path. Then, too, comes the flood of gamma rays (nuclear X rays). Trapped at first within the fire ball, these deadly rays burst forth a fraction of a second after the bomb explodes.

What will the bomb do?

A bomb exploded 2,000 feet above the ground would do the greatest damage. Virtually everything within a radius of half a mile by ground zero will be destroyed or irreparably damaged by the blast, the heat, or by fires started by the heat. Within the next mile, countless fires will be started by the heat radiation. As many fires will be started by broken gas lines, electrical short circuits. Broken water lines will make fire-fighting almost impossible.

Up to the half-mile radius, the gamma rays will be powerful enough, even after penetrating brick or concrete walls two feet thick, to kill or gravely injure people well protected from heat and blast. Beyond the half-mile radius, the rays' deadly power will decrease, gradually at first, then sharply; two miles from the explosion they will be virtually harmless.