Round-the-World Tracer

The Japanese public does not like radioactive fallout, whether it comes from U.S. or Russian nuclear tests, but Japanese scientists have learned to put it to work. While visiting New York last week, Dr. Yasuo Miyake of Tokyo's Meteorological Research Institute told how radioactive air masses created by the tests are timed, measured and analyzed. Then they are used as tracers to plot the circulation of high altitude winds.

Usually an air mass labeled with radioactivity shows up in Japan a short time after vibrations in the earth, sea or air have disclosed a Russian test in Siberia or a U.S. test in mid-Pacific. But on one occasion last year, a mass crossed Japan that had seemingly got lost. It arrived from the west, dropping radioactive rain on much of Japan and radioactive dust on the northern island of Hokkaido. A sample sent to Tokyo proved to be ordinary dust from the Gobi Desert, which often falls on Japan. It must have got its radioactivity from a "hot" air mass that passed near the Gobi.

1,000 Miles a Day. All this made the radioactivity look at first glance like the product of a Russian test. But Japanese scientists were certain that no Russian test could be blamed for it, and the only other recent tests had been in Nevada, two weeks before and 5,500 miles away in the wrong direction. Since air is not known to cross the North Pacific from east to west, the labeled cloud could not have come direct from Nevada. The only other possibility was that it had traveled three quarters of the way around the earth to reach Japan.

To test this theory, Dr. Miyake and his colleagues studied the world's weather maps. The wind pattern looked encouraging for the theory. On the day the radioactive material rose above the Nevada desert, there was a powerful wind waiting aloft to carry it eastward. The most probable route would take the atmospheric tracer across the U.S., the Atlantic, Europe, Central Asia and China. It should travel about 1,000 miles a day and should reach Japan in about the right time: two weeks (see map).

Rain & Fogged Film. To find out whether the air mass actually traveled around the earth, the Japanese wrote to scientists along its theoretical route asking if they had seen any signs of it. Confirmation came from Paris, where radioactive rain had fallen. The fission products from faraway Nevada had also fogged photographic film as they drifted over Europe. Dr. Miyake is sure that the rest of the trajectory mapped out for the "tracer" is also accurate. The north-and-south waviness of the route is characteristic of the high altitude winds that blow around the earth in north temperate latitudes.

Now Japanese scientists are waiting for the U.S. nuclear tests scheduled for April in mid-Pacific. Any labeled air masses that they send to Japan will be welcomed (meteorologically at least), whether they travel direct or by circumnavigation.

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