Science: Space-Test Eye

Any system to detect clandestine atom bomb tests must consider tests in space. A nuclear burst in a vacuum does not form a bright fireball; it gives off very little visible light and even if it were as near as the moon, its flash might be too feeble to attract unalerted attention. Sponsors of such a test would know where and when to look for it, and they would have instruments ready, to assess the results. A sneak test of this sort would be difficult and expensive, but not impossible.

Detecting such a test is not impossible either, given the right instruments. On a roof at Los Alamos Scientific Laboratory, six wide-angle lenses stare day and night at the sky. Each is linked to a filter that makes it blind to all light except a special kind that comes from the fluorescence of nitrogen or oxygen. If light of this unusual sort comes down from the sky, the rooftop apparatus at Los Alamos will ring an alarm that will sound around the world. It will mean that some nation has attempted a secret bomb test in space—and has been caught in the act.

The U.S. tests above the atmosphere in 1958 taught that when a nuclear bomb explodes in a vacuum, about half of its energy goes into invisible X rays. These hit the atmosphere and make its oxygen and nitrogen fluoresce in characteristic wave lengths that can easily be distinguished from the spectrum of sunlight. When Los Alamos Physicist Donald R. Westervelt learned about this, he designed a detection system based upon it. A few dozen of his detectors spotted around the earth would be an adequate network. Some of them would always be under clear skies. In daylight they would detect a one-megaton burst 2,000,000 miles from the earth, much farther at night. Cost of each station: $100,000.

A problem still remaining is to prove that no natural phenomenon will look like a space test to Westervelt’s detectors. The model at Los Alamos has already passed one test: it is not fooled by lightning. Next month it will be moved to Fairbanks, Alaska to see whether it cries a false bomb scare when a strong aurora shines in the night sky. Only if it can distinguish a nuclear explosion from all natural events will the detector be recommended for international test watching.