Under the Cloud: THE DECADES OF NUCLEAR TESTING by Richard L. Miller (The Free Press: $24.95; 530 pp.)

The United States detonated more than 200 nuclear weapons in atmospheric tests between 1945 and 1962. With a combined explosive yield equivalent to several thousand Hiroshima bombs, these tests generated enormous quantities of radioactive material that covered the globe with a fine radioactive dust.

In “Under the Cloud,” Richard L. Miller traces the history of the American and, to a lesser extent, the Soviet nuclear weapons programs, from the early days of the Manhattan Project through the ban on superpower atmospheric tests in 1963 to the continuing controversy over the health effects of those tests.

Much of this history has been recounted many times before. But recent events, including the Chernobyl accident and the American refusal to join the unilateral Soviet moratorium on underground nuclear testing, echo in the reader’s mind and make “Under the Cloud” especially timely.

Radioactive fallout from atmospheric tests, which after 1951 were performed primarily in Nevada, fell most heavily in the regions directly downwind from the Nevada Test Site, including portions of Nevada itself, Utah and northern Arizona. But shifting and often unpredictable meteorological conditions carried some fallout just about everywhere in the continent and beyond. Radiation levels in Los Angeles exceeded recommended limits for two days in October, 1958.

For many years, government scientists assured the American public that atmospheric nuclear-weapons testing would not have any adverse public health consequences. Fallout might be a nuisance, they agreed, but it wasn’t a health hazard. In any case, as Atomic Energy Commission member Willard Libby declared, “People have got to learn to live with the facts of life, and part of the facts of life are fallout (sic).”

But living with fallout became difficult. Thousands of sheep died with radioactive thyroid glands and radiation-induced lesions in Utah in 1953 after grazing on contaminated land. A few years later, clusters of leukemia and other forms of cancer appeared in towns near the test site where cancers had previously been almost unheard of. Though medical journals documented the increased cancer rates among the “downwinders,” federal officials argued--and still maintain--that there is no evidence to conclusively link these cancers to the weapons tests.

By 1980, a Congressional report concluded that “the Government’s program for monitoring the health effects of the tests was inadequate and, more disturbingly, all evidence suggesting that radiation was having harmful effects, be it on the sheep or the people, was not only disregarded but actually suppressed.”

Along with residents downwind from the test site, those most directly exposed to radioactive fallout were soldiers. Nearly 200,000 U.S. servicemen in Nevada and the Pacific participated in simulated combat maneuvers close to “ground zero,” where a real nuclear weapon was detonated. Such exercises were carried out to determine the psychological effects on soldiers of a nearby nuclear explosion.

After one such test, Miller reports, a general told his troops that “for the first time in known history, troops successfully attacked directly toward ground zero immediately following the atomic explosion. You can remember, with a sense of pleasure and accomplishment, that you were one of those troops. . . .” Though the psychological stresses of the test proved not to be debilitating, preliminary epidemiological studies would indicate years later an increased incidence of leukemia in some of these “atomic veterans.”

Miller narrates in exhaustive detail the planning, execution and aftermath of many of the individual explosions. In test after test, we are told the altitude and precise moment at which the bomb was detonated, the exact width of the resulting fireball, the height attained by the cloud, the wind speeds at various altitudes and so on. The “Plumbbob-Boltzmann” test on May 28, 1957, for example, “occurred at 4:55 a.m. Pacific Daylight Time, producing a fireball approximately 900 feet in diameter and lasting 10 seconds. Observers watched the familiar gray-black mushroom form, then rise to 28,765 feet above the desert floor. . . .”

This kind of information, which comprises much of the book, might well be helpful to persons who are concerned with the technicalities of a particular test. But others will probably find it tedious. Rather than being forced into the shape of prose, it should have been left in tabular form in an appendix.

The main thing that distinguishes “Under the Cloud” from so many other similar works is the focus on the meanderings of the clouds of radioactive fallout. Miller reproduces maps of the fallout trajectories for many of the tests, which portray the paths of the clouds across the country, as well as a 40-page appendix which lists the names of the towns over which the clouds passed. But once we know that some fallout settled nearly everywhere, these maps and lists have little more to tell us, since in most cases there is no indication of how much fallout settled as the cloud passed overhead. Even when fallout data is presented, only rates of deposition are given, not population exposures, so that the public health consequences of living under the cloud are obscured.