The trouble in Panama has repercussions that echo all the way to the Livermore, Calif., laboratories of Project Ploughshare, where the AEC is investigating the peaceful uses of atomic energy. Ploughshare scientists are bringing their calculations to a high polish, for if a new Isthmian canal is to be dug, nuclear explosives may be used. And Ploughshare men are sure that they can blast a wide sea-level canal in a couple of years at a fraction of the cost of conventional digging.
Ploughshare optimism is based on studies of a long series of craters blasted by both chemical and nuclear explosives in the Nevada desert. The first, called Buster Jangle-U. (1951), used a crude atom bomb with a yield of 1.2 kilotons. It dug a circular hole 53 ft. deep and 258 ft. in diameter. The next shot, Teapot-Ess, had the same yield, but it was placed deeper and it dug a deeper and wider crater. With these and other shots, Ploughshare scientists built up a body of theory and experience in which they have great confidence. Latest and largest cratering shots, Sedan (100 kilotons) and Danny Boy (400 kilotons), were fired in 1962 and proved that the Ploughshare rules for nuclear explosives work just as well in hard, heavy rock as in loose soil.
Best Depth. The rules are remarkably precise. If a shot is placed at too shallow a depth, as Buster Jangle-U. was, it wastes most of its energy on the air. If it is too deep, it lifts a great amount of soil and broken rock, but lets most of the stuff fall back into the crater.
When placed just right, it throws most of the rubble over the lip of a steep-sided hole. A 100-kiloton shot should be placed 600 ft. below the surface, while a one-megaton shot calls for a depth of 1,300 ft.
Ploughshare has yet to dig any canal-like ditches with long lines of nuclear explosions, but it has experimented elaborately with chemical shots and believes it knows the basic laws that govern both kinds of blasts. If nuclear explosives are placed in "strings" with the distance between them equal to half the diameter of the crater that a single shot would dig, and if they are exploded simultaneously, they will excavate a smooth-bottomed ditch, throwing the rock to the sides. One hundred shots, for instance, of 100 kilotons each, will dig a ditch 1,600 ft. wide, 350 ft. deep and 16 miles long. If its bottom is 60-odd ft. below sea level, it can serve as a spacious ship canal.
Clean Clouds. When a crater-making shot is fired, a mushroom of earth grows out of the ground above the explosion. A jet of hot gas raises a dust cloud high in the air. Most of the dust and debris settle immediately, and hardly any dust falls more than 21 miles from the crater. This dust is not very radioactive. Nearly all of the shot's radioactivity is buried deep under the rubble that falls back into the hole. Ploughshare men are sure that if modern, "clean" explosives are used, the radioactivity that escapes will be of little significance. Permanent population may have to keep away from the neighborhood of the new-dug canal for at least six months, but men under medical supervision may start working there in two weeks.