The Bomb Detectives

In the U.S. and Europe, strict secrecy surrounds the methods that are used to detect atomic explosions in another nation's territory. Japan has no atomic weapons and no atomic secrecy, so her scientists can talk. Last week one of them how an unofficial group of Japanese scientists keeps track of both U.S. and Soviet explosions.

According to Dr. Yasuo Miyake, of the Japanese government's Meteorological Research Organization in Tokyo, the detection measures four phenomena: 1) disturbances of atmospheric pressure, 2) variations of tide level (if the explosion is oceanic), 3) variations in atmospheric electricity, 4) radioactivity in rain.

News from the Instruments. The system had a workout last spring, during the tests of U.S. hydrogen bombs. Dr. Miyake had no advance notice except that traffic in certain sea areas had been restricted, but he kept alert. Early in March he learned that a colleague in Kyoto had observed abnormal variations in atmospheric pressure on March 1, so he collected the records of the government's 13 meteorological stations. Instead of the wavy lines of normal pressure changes, the charts showed jagged variations on March 1, March 27, April 26, and May 5. The first and last were the biggest. News also came from the tide gauges. On the same four dates, the water level showed abnormal fluctuations, the tidal impulses arriving about one hour after the atmospheric ones. Nothing was reported by the electrical instruments. They had not been listening at the right times.

Noting carefully the time of arrival of the air waves at different stations, Dr. Miyake drew arcs representing where each wave was at the same instant. The center of the arcs should be the position of the explosion. This turned out, correctly, to be the Bikini region in the central Pacific. Further confirmation: nine days after the May 5 explosion, heavy radioactive rain fell on Japan. After studying the charts of high-altitude winds, Dr. Miyake decided that the radioactive dust had traveled west to the Philippines, then up the China coast to Formosa and Japan, where rain brought it down on May 14. Dust from earlier Bikini tests had made a sharper eastward turn and missed Japan entirely.

Soviet Tests. With their methods checked by this workout, the Japanese scientists waited for more explosions, which came fairly soon. Last Aug. 26, an electrical instrument recorded a sudden rise in atmospheric electricity north-northeast of Japan, presumably in North eastern Siberia. It was not like the rise caused by a thunderstorm, but showed the characteristic profile of an atomic explosion. Four hours later came an air wave. It was only one-sixth as strong as the waves resulting from the U.S. tests, but Dr. Miyake says this does not mean that the Soviet explosion was only one-sixth as powerful. There were no water waves because of the land that lies between Japan and the probable site.

Three days later, another electrical disturbance was detected by Japan's instruments, from the same direction. Although there was no air wave. Dr. Miyake thinks that the Russians exploded two bombs. The radioactive rain, the strongest that has ever fallen on Japan, did not arrive until Sept. 18. The Japanese are not sure why it took so long to travel. They suspect that there may have been a third explosion that did not register otherwise.

Some Japanese newspapers jumped to the conclusion that the Soviet tests were held on Wrangel Island, off the north coast of Siberia, where the Russians have a meteorological station. Dr. Miyake is not as definite. All during the tests, he says, the Russian station kept sending its normal weather bulletins.

The radioactive rain from Siberia caused little resentment in Japan. The disastrous typhoon of Sept. 26 blew it out of the country and off the front pages of the newspapers. But Japanese scientists know now that they are under fire from two directions.

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