You have been exposed to constant radiation since the day you were born.

5. KINDS OF A-BOMB RADIATION

You are standing on an open, shadowless plain beneath a sun suddenly come close to the earth. From the searing sky, invisible bullets speed at you. Some are small, some large, yet all are so tiny you can neither see nor feel them when they strike. They leave no bullet holes, yet inside your body they are tearing apart the substance of muscle and bone marrow, exploding the individual cells of your blood, leaving a trail of devastation through solid tissue.

There is an igloo near you made of stone. You crawl inside. The terrible heat is gone. But the stone walls are only a foot thick. They cannot stop the invisible bullets. Still they come, and there is no escape. You die a horrible, frightening death.

This is sheer nightmare of the imagination. It is so much bunk. Ever since science unlocked the atom's power, alarmists have been screaming, "The Geigers will get you if you don't watch out!" The public has been bombarded with graphic descriptions of entire cities suddenly left echoing wastelands, of water supplies contaminated with invisible death, of men in gas masks and lead-lined suits moving slowly through an undamaged town waving the mysterious antenna of radiation counters. The nameless, gnawing fear which came to the world with the first atomic bomb is largely based upon this bogey -- Radiation. The bomb brought the greatest explosive blast that man has yet devised. It brought heat which etches shadows into granite. But these were familiar dangers, forces which had been released for centuries by ordinary bombs on a far smaller scale. The unknown, the new hazard to human life, was radiation. And fear walks the pathways of the unknown.

WHAT IS RADIATION?

Actually, you have been exposed to constant radiation since the day you were born. From outer space, particles of energy called cosmic rays are constantly bombarding the atmosphere. Some get through to the earth's surface. They pass through the walls of your home, through the top of your car, and into your body. You can hear these rays with a Geiger counter. The slow, unsteady clicking of the instrument is the sound made by cosmic rays. Atomic parlance calls it background radiation.

You are also barraged to a lesser extent by radioactivity from the earth beneath you. There are metals in the earth's crust, such as uranium or radium or thorium, which occur partly in radioactive form. These "isotopes" are unbalanced in the way they are built. Thus they are constantly changing, shaking themselves down to different forms of the same element, or to completely different elements. Sometimes they go through several transformations, until the end product is a material at balance with nature, a stable element. For example, uranium in the earth changes to radium, then to a gas called radon, and finally, after many thousands of years, to ordinary lead. This process goes on wherever uranium occurs in the earth, locked in rock in minute amounts.

When miners dig this ore from the earth, and engineers laboriously separate the uranium, and physicists carefully bring larger and larger amounts of it together, the decomposition process can be speeded up. When the amount of the unstable type of uranium or plutonium passes what is known as the "critical mass," the coming apart process flashes through the individual atoms in a chain reaction, and there is an atomic explosion. What takes thousands of years in nature is made to happen in a millionth of a second in the bomb.

In whatever way this magic transformation occurs, there are thrown off tiny particles, together with rays of electrical energy, which account for the change in weight of the original unstable atoms. Even on this smallest of all scales, the fundamental law of conservation still works. Nothing is ever lost in this world.

Radioactivity is like a dog shaking itself after being in the water. The dog is wet and doesn't like it. He is "unstable"; so he shakes. The drops of water fly into the air. The dog is drier and thus happier. But that does not mean the extra water has disappeared. It is there on the ground.

Radiation is the rain of particles and energy from an atom shaking itself or being shaken by man. It comes in small drops and in larger drops and in the units of energy called photons. Ordinary light is made up of photon rays. So are X-rays.

Radioactivity is like a dog shaking itself after being in the water.

Each individual particle or ray is indescribably small. Moving out from an atom, they can pass through air, whose molecules are far apart; through water, whose molecules are closer together; through steel or concrete or lead, whose molecules are closely crowded. Some of the particles can travel farther through these various meshes than others. Some can bounce off obstacles and keep going. Some will be stopped almost immediately. Fire a shotgun through a room full of medicine balls hung from the ceiling. Some of the pellets will get through. Throw a basketball through the same room. Chances are it won't go very far. The same happens to atomic particles.

When an atomic bomb explodes, there is a tremendous initial burst of radiation -- that is, nuclear radiation as differentiated from the radiation of pure heat. After the explosion there is residual radiation. This is caused by the fission products of the bomb which fall to earth, and by the materials, dirt or water or steel, which were close enough to the bomb's explosion to be made radioactive by the initial radiation. Whereas the initial blast of radiation is over in a few seconds, the residual radioactivity may linger on for hours or days or hundreds of years.

INITIAL RADIATION

Different types of atomic bullets are sent off in the A-bomb's colossal blast. There are four kinds of radiation which are a hazard to human health if received in large enough amounts.

1. Alpha -- Relatively heavy particles made up of two protons, each having one positive charge, and two neutrons, which have no charge. Alpha particles are so big they are like the basketball thrown into a room full of medicine balls. They are stopped in air in less than two inches. They can go only an infinitesimal distance in water. They are stopped cold by light cotton clothing, and may not even pierce the skin.

Four kinds of radiation, left to right: Alpha, Beta, Gamma, and Neutrons.

If radioactive dust giving off alpha particles is inhaled or eaten with food, however, it may have grave effects within the body. If enough is absorbed in the system, alpha emitters can kill. Materials which give off alpha particles include uranium and plutonium. When an atom bomb explodes, most of the uranium or plutonium atoms do not break apart, but fall to earth. Poisoning by them is possible, but far from likely unless an enemy sows them deliberately.

2. Beta -- Electrons moving at high speed. Because electrons are extremely light in comparison to alpha particles, they bounce off atoms and molecules in their path very easily. They thus have little effective penetrating power, even in the air. Those shot off from an atomic burst are not considered dangerous in themselves. But beta radiation is created by other forms of radiation striking stable atoms. If those atoms are within the body, beta will contribute to the over-all radiation injury.

Neutrons are subject to elastic scattering.

3. Gamma -- Ultra short waves of pure electro-magnetic energy, made up of photons. The atomic bomb emits these rays at great energies. They are extremely penetrating, and travel farthest from the point of burst of any form of radiation. They move in a straight line and can give an unprotected person a lethal dose at 4,200 feet. Protection from them, at 3,000 feet from the burst of a nominal atomic bomb (20,000 tons of TNT), is a matter of four inches of solid steel or 12 inches of concrete. They can go right through the human body, and leave a path of injured cells behind them.

4. Neutrons -- Particles from the atom's center which carry no electrical charge, but which are 1,800 times the size of electrons. A great burst of neutrons accompanies atomic fission. Like gamma rays, they can penetrate air for considerable distances and are a menace to the human body. They are the other major radiation hazard of the atomic bomb.

Unlike gamma radiation (which are rays rather than particles) neutrons bounce off the molecules of the air, water or solid matter through which they pass. Thus they follow a tortuous path through the atmosphere -- what physicists call "elastic scattering" -- and can come at you from any direction. Any sort of shield against radiation within the lethal range of neutrons -- about 2,400 feet for a nominal bomb -- must protect you from the rear as well as in the direction facing the bomb's burst.

Neutrons are released when an atom breaks apart. They are the bullets which produce a chain reaction.

Once set free, when they collide with atoms of stable materials they knock off electrons, producing beta radiation. They also can agitate the atoms so that gamma rays are shot off. Or they may be absorbed completely by atoms they strike. In that event, the atoms become radioactive. This is what is meant by induced radioactivity. It happens to a small extent in an atomic burst in the air, and to a much greater extent when the bomb is set off underwater or near the ground. If the neutrons are moving at high enough energies, they can completely split an atom they hit, causing fission. The unfounded fear that neutrons might split the atoms of the air or the sea was the basis for the dire predictions of some scientists that an atomic chain explosion would blow up the world from a single bomb. This has been shown to be nonsense. Chain fission happens only under artificial, extremely unstable conditions imposed by man.

RESIDUAL RADIATION

If you can dust yourself off and walk away, there is not much chance of your having absorbed a deadly dose of radiation.

It is upon the amount of residual radioactivity that the real radiation danger of an atomic explosion is largely judged. This is not to say that you cannot receive a lethal dose from the first flash of the bomb. But if you are within radiation's death circle, it is almost certain that you will also be injured or killed outright by the blast wave or the heat of the bomb, falling buildings or burning rubble. Another way of putting it: If, after an atomic bomb bursts, you can dust yourself off and walk away, there is not much chance of your having absorbed a deadly dose of radiation.

An A-bomb burst at 2,000 feet in the air is believed to do the greatest physical damage to a target. At this height, blast is free to act over the widest area. But the height also means that there will be relatively little radioactivity induced on the ground, and the "hot" fission products of the bomb will be scattered over a wide area. Atomic Energy Commission scientists and Defense Department officers say there is little to fear from leftover radioactivity following an air burst.

It is in an atomic explosion underwater or under the ground that residual radioactivity might assume serious proportions. Then the water or the earth surrounding the giant burst of neutrons is made intensely radioactive. It is thrown high in the air for the wind to scatter, covering the surrounding area with a thin layer of material which will produce dangerous amounts of radiation for days or even months. Radiation men will have to move in with their black boxes, and entire city populations may have to be evacuated for a time, fleeing an invisible menace which no one can see.