Science: Nuclear Detection System

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If the diplomats of the great powers back up their scientists, the earth in a few years will be thinly dotted with observation stations, internationally controlled, packed with sensitive instruments, and each manned by 30-odd scientists and technicians. Most of the stations will be on level terrain, and as far as possible from cities, railroads and heavily traveled highways. Their purpose: to detect clandestine tests of nuclear explosives.

After seven weeks of scholarly consultation at Geneva, U.S., British, Russian, Polish and other scientists issued definite recommendations for a nearly trickproof control system (TIME, Aug. 25). There were no minority reports, no signs of maneuvering for political advantage. Both sides agreed that a proper system of fewer than 200 stations would detect with high accuracy even small explosions anywhere on earth.

Air Waves. The experts considered all major means of detecting nuclear tests. If the explosion takes place in air, it starts a powerful acoustic wave that can be detected at great distances as a slight variation of air pressure. A feeble one-kiloton explosion sends a detectable wave as much as 2,000 miles downwind, 300 miles upwind, or an average of 800 miles under conditions of light and varying winds. When exploded under the surface of the ocean, a one-kiloton explosion sends sound waves 6,000 miles through the water.

A deep underground explosion sends no air waves, but such explosions, and surface explosions too, send seismic waves through the earth. A station in a quiet place can detect the waves from a one-kiloton explosion as much as 2,200 miles away. The detecting apparatus is accurate enough to pinpoint the explosion within an area of 40-80 sq. mi., less than one-quarter the area of New York City.

Radio Giveaway. Another detecting method is by means of radio waves caused by the gamma rays from a nuclear explosion above the surface of the earth or sea. Radio waves from a one-kiloton test can be detected 4,000 miles away under favorable Circumstances, and can locate within 20 miles an explosion 600 miles away.

All these detecting methods work very quickly. Another method, collecting radioactive debris from an explosion, takes more time, but is nonetheless useful. The experts recommended that rainfall all over the earth be checked for radioactivity. In dry countries a special collecting surface should be washed down periodically and the water checked. Weather airplanes flying their regular routes can carry observers and collecting equipment.

Each of these methods, the East-West experts pointed out, has its faults. Acoustic waves from a volcanic eruption, for instance, can be mistaken for waves from a nuclear test. Seismic waves from earthquakes can be misinterpreted, too. Nuclear tests deep under the earth or ocean yield no radioactive fallout, send out no air waves or radio waves. But they do send waves through the ocean, the earth, or both. Each type of test is detectable by one or more methods.