A History Of U.S. Testing

What is a nuclear test? Nuclear physicists find it necessary to make many kinds of tests, most of them quietly in laboratories. But the phrase "nuclear test" has come to mean an experiment that involves a nuclear explosion. Since all such tests are dangerous, the U.S. fires its small ones on the Nevada desert, its big ones on remote Pacific islands. Most of the 169 U.S. tests were exploded on tall towers so that their expanding fireballs would not hit the ground. A few nuclear devices were dropped from airplanes or suspended from captive balloons.

What are the dangers? All near surface tests are classed as "atmospheric" because their radioactive byproducts mix with the atmosphere and may be carried around the earth. Tests exploded under the sea are of much the same nature. Underground shots are considerably safer. The U.S. has fired about half a dozen small tests in tunnels dug into Nevada mountains. Their radioactivity was well confined, and so far there have been no reports of contaminated ground water, but large underground tests could conceivably poison the water supply of an entire state. For relatively small nuclear devices the U.S. is likely to continue underground tests, but the more powerful sod busters of the future will have to be tested in the open because the earth's crust cannot hold them. Former Atomic Energy Commissioner Willard F. Libby estimates that a ten-megaton test would need to be exploded 18 miles below the surface. At this depth the rock is probably so plastic that digging a test hole would be impossible. Another possibility is to fire tests above the earth's atmosphere, as the U.S. did on a small scale in Project Argus (August-September 1958). But a big, rocket-borne test involves intricate problems in technology; countless things could go wrong. A premature explosion on earth, or too early an explosion aloft, could contaminate the atmosphere with radioactive products. All tests in the atmosphere, including last week's Soviet test, will surely raise the level of the earth's radioactivity. The dirtiest tests in the past were fission-fusion-fission bombs, the first of which, exploded by the U.S. in 1954, killed a Japanese fisherman by its fallout and seriously injured many people in the nearby Marshall Islands. When the Russians fol lowed with similar dirty tests, radiation increased all over the world. Especially frightening was the fallout of strontium 90, a deadly fission product that settles in bones and may cause cancer. The new Soviet test series will not necessarily scatter much-dreaded strontium 90, but radioactive products of some sort are sure to, result.

Why are tests needed? Different tests have different purposes. Some are aimed at improving existing nuclear weapons. Designers need to know accurately how much smaller a weapon can be made without loss of punch, how much of a scarce ingredient can be safely omitted, or whether the weapon can be changed in shape to fit another warhead. Most of the answers can be worked out in theory on complex computers, but the history of weapons is full of embarrassing surprises, and scientists can never be sure until the modified weapon has been exploded and its performance has been measured. New and radical kinds of nuclear explosives need testing to see if they will explode at all, or if their performance will justify their cost and weight. Still other tests are merely experiments in nuclear physics. The device tested may be useless as a weapon, but scientists hope that its explosion will yield information about the behavior of atoms and subatomic particles which they cannot obtain in any other way. These far-out tests may be the most important of all because they lead to long-range progress.

What U.S. weapons have already been tested? At the start of the test moratorium in the fall of 1958, the U.S. had a family of well-tested bombs ranging in power from less than one kiloton (1,000 tons of TNT) up to 20 megatons (equivalent to 20 million tons of TNT). The 20-megaton weapons are too heavy for existing U.S. missiles, but more than one of them can be carried by far-ranging B-52 bombers. U.S. authorities, both civilian and military, see little advantage in more powerful bombs, such as the 100-megaton horror mentioned by Khrushchev, because the damage the monsters could do would not increase in proportion to their weight. At any rate, a single 20-megaton bomb is enough to destroy any modern city. In its present H-bomb arsenal, the U.S. has reliable 2-megaton warheads for the Titan I missile, and 500-kiloton warheads for the Navy's Polaris and the Air Force's Minuteman. In an age of megaton H-bombs, mere kilotons sound strangely small, but the Minuteman warhead explodes with 20 times the force of the primitive, 20-kiloton A-bomb that destroyed Hiroshima in 1945. killing 78,-ooo people. Ranging down in power, the U.S. has a large group of small tactical nuclear weapons for use in light rockets, artillery shells, torpedoes, antisubmarine depth charges, air-to-air missiles, etc. The warhead of the air-to-air Genie, which is carried by interceptor planes, yields one-tenth kiloton (100 tons). The state of the stockpile of these weapons is secret, but no U.S. authority can be found who does not believe that the U.S. is far ahead of the Russians in both quantity and quality of nuclear explosives. It is agreed, also, that both countries have more than enough weapons on the shelf to devastate each other--and to kill much of the hu man race as well. A great deal of the destruction would be the result of radio -active fallout.

What remains to be tested? In spite of the stockpiled ability to overkill, testing is still profitable. All experts believe that nuclear explosives can be "improved" --made deadlier and more precise--by slow refinement and by large technical breakthroughs. Explosive efficiencies are still far below the theoretical maximums.

If the efficiency of the Minuteman's warhead, for example, were to be doubled, the missile could be rigged to deliver a bigger bang; a decrease in weight of the current-strength warhead would allow an increase in the missile's range. The same effect would show up all along the line; a B-52 could carry twice as many improved 20-megaton bombs. The U.S. has many new weapons systems with nuclear warheads that have yet to be explosively tested. No ICBM, for instance, has carried a nuclear warhead out of the atmosphere and back again and demonstrated that after its high ride the warhead will still explode. No antimissile nuclear weapon has been tested in space against an incoming missile. U.S. military authorities attach much importance to improved tactical nuclear weapons that are small, light, dependable, and so "clean" that they do not contaminate a battlefield with deadly radioactivity. Such clean weapons are not in hand, and they cannot be developed without many more tests. Even farther away is the much-discussed neutron bomb, which promises to be a small, short-range H-bomb exploded by some other means than the usual "dirty" fission detonator. Its proponents believe that it will kill people by neutrons while its feeble blast and heat will do little damage to property. But before it can be added to the U.S. arsenal, the neutron bomb will require a long and intensive series of tests.

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