Radiation by Mistake

Foreign critics screamed that the U.S. high-altitude nuclear test of July 9 would destroy the natural radiation belt that girdles the earth. An impressive group of U.S. scientists including Professor James Van Allen, who discovered the belt, brushed aside such fears. The nuclear explosion, they predicted, would have little effect on the natural radiation belt, and any additional radiation that it might cause in space near the earth would dissipate in a few days. Last week the National Aeronautics and Space Administration, the Atomic Energy Commission and the Department of Defense issued a sheepish joint report that proved both critics and defenders were wildly wrong. The new artificial belt is unexpectedly large, strong and long-lasting.

Saved by Sapphire. At its lowest point, over the South Atlantic, the belt reaches to within 200 miles of the earth's surface. Over the Pacific it stays 500 miles above the surface. In latitude, it extends 1,800 miles north and south of the magnetic equator. It is 3,100 miles thick, reaching well into the Van Allen belt of natural radiation. Its spiraling electrons, which originated in the high altitude test explosion, have as much as 1.,00,000 electron-volts of energy. At their strongest, they are about ten times as intense as the natural radiation.

First victims of the new radiation were three U.S. satellites, TRAAC, Ariel and Transit IV-B, that were knocked out of commission, presumably because of damage to the solar cells that supply their power. Fortunately, the communication satellite Telstar has been unharmed; its solar cells are covered by protective windows of sapphire. In the future, says NASA, all its satellites will have sapphire windows; other necessary changes have not yet been determined. Though the problem is serious, NASA's experts think the new radiation will not affect manned U.S. satellite flights.

Considered Permanent. After their notably poor predictions, few scientists, friendly or otherwise, are eager to give firm estimates of how long the new radiation will last. The AEC dodges by predicting that the lowest electrons will be lost in the atmosphere in 150 days, but that some of the highest may stay up much longer. NASA estimates can be interpreted to mean that some of the highest electrons may last for 10,000 years.

For all its unexpected results, the July 9 high-altitude shot yielded so much information of military value that preparations for other high-altitude shots to evaluate the new data are still continuing. The restricted area around Johnston Island will be re-established next week for new tests. Lower in altitude and lower in energy than the big July shot the next tests may not add many more electrons to the earth's multiple belts. But NASA is now playing it safe; it is hastily building a tough new satellite to keep tab on all radiation, both natural and manmade.

This file is automatically generated by a robot program, so reader's discretion is required.