Yoke. Tests Yuma on Sally and Mohawk on Ruby in 1956 resulted in further soil disturbance on Sally. The Yuma GZ was only a short distance from the earlier Yoke GZ, so one may suppose that some decontamination actions occurred during preparations for Yuma, but available records give no indication as to the disposition of contaminated soil, Following some of the earliest surface tests, it beeame common practice to put down a layer of asphalt in the GZ area for dust suppression so that detonation-time photography would be enhanced. Available documents do not indicate how often, nor where, this practice was followed, but for one test the records are helpful. Preparations for Test Dog on Yvonne included laying 3 inches of asphalt within a 400-foot radius of the GZ, then 1-1/2 inehes to a distance of 1,000 feet. The Dog GZ was about 175 feet from the site of Zebra, condueted 3 years earlier, so the construction area was probably contaminated when preparation began. Records do not indicate the disposition, if any, of contaminated soil. The area may have only been graded prior to placement of asphalt. The asphalt was, for the most part, consumed in the nuclear detonation. Some evidence of the presence of an asphalt layer could be seen in the lip of the Cactus Crater before that area was modified by cleanup actions. Direct Test Effects. A nuclear detonation can aptly be described as awesome as indicated in the accounts presented earlier. Quite apparent are the immediate effects of the intensely hot fireball which ean consume a 300-foot steel tower or plate nearby objects with a thin film of plutonium and fission products; of the giant waves that can wash over everything nearby if the device is detonated under or near a water surface; of the massive cloud of radioactive particles that rise to great heights then slowly drift to earth or wash out in a subsequent rain. Not so apparent are the effects that linger for years after the flash and blast have stilled and ground zero has cooled back to normal. Within a few years after the event, most of the radioactivity has been reduced by natural decay of the nuclides with short half-lives. (Half-life is the time required for the natural decay processes to reduce the initial amount of a radioactive species by one half.) The longer half-life nuclides make up the residue that can create a problem in man's environment. The dominant long-lived radionuclides of concern from nuclear testing are plutonium and americium which are health hazards if inhaled, ingested, or introduced to the body as through a skin wound; and cesium and strontium which are absorbed by plant roots and may be incorporated in the parts of the plant used by man as a source of food. Man's body, in turn, incorporates the cesium and strontium in certain parts where the possibility of deleterious effects is enhanced. The half-life of plutonium-239 is nearly 25,000 years, essentially forever in terms of human time scales. On the brighter side, the half-lives of cesium-137 and strontium-90 are less than 30 years--a short enough period for activity levels to reduce to one-fourth the initial value in one human lifetime. Cesium and strontium generated by the first nuclear tests at Enewetak have already decayed through one half-ife, but for practical purposes the inventory of plutonium-239 is unchanged. If measurement of the level of activity of 2 9pu were accurate to within one percent, it would take 250 years of natural radioactive decay for the change to be measurable. (This degree of accuracy is realistically achievable in the austere conditions of a field laboratory; higher accuracy is attainable in more ideal laboratory environments.) Nuclear detonation effects are not limited to the immediate vicinity of the detonation site. In an extreme case, it was reported following the Mike event that the trees on Leroy, 9 miles distant, were scorched on the side facing the site. All the islands from Alice around to Yvonne were within a 9-mile radius of the Mike GZ; close-in islands received far greater effects than more distant islands. Pre- and post-event photographs taken as part of the Mohawk test on Ruby show healthy vegetation on Ursula reduced to small stubs. The distance was about 8,200 feet. Plants on Belle were burned nearly to the ground by Test Nectar conducted 2.7 miles away. (Palumbo, 1962.) Heat and shock waves transmitted in the air would travel much faster than the following water waves, if any were generated. Radioactive contaminants might initially be uniformly deposited on the soil surface, then swirled around and redeposited in irregular fashion by a series of inundating waves. Later tests, conducted at a distance great enough that no direct blast or wave damage would occur on a given island, might generate a new uniform blanket of fallout on that given island. 14