Hard Belt

Most of the nation's leading physicists were gathered last week at Manhattan's New Yorker Hotel. The occasion: the annual meeting of the American Physical Society.

Top topic was the discovery by the U.S. moon probe that the world is girdled by two belts of Van Allen*radiation. Many scientists assumed that the belts were of roughly the same character. Dr. Fred Singer of the University of Maryland suggested that they may be quite different, both in nature and origin.

There is wide agreement that the outer radiation belt, whose greatest intensity lies more than 6,000 miles from the earth, is made of protons and electrons shot out of the sun and trapped into spiraling orbits by the earth's magnetic field. These particles are rather feeble, so they should not do much damage to a well-found spaceship or its crew. But Dr. Singer believes the inner radiation belt is made of "hard" particles, which may have several hundred million electron volts of energy.

According to Dr. Singer, the particles in the inner belt are created when cosmic' rays from the depths of space smash into atomic nuclei in the earth's atmosphere. Some of the fragments are high-energy neutrons which bounce back toward space. Since neutrons are uncharged, they are not affected by the earth's magnetic field; most of them escape entirely. But about one in a million splits into a proton and an electron before it covers 100 miles. Since both these particles have electric charges, they are trapped by the earth's magnetic field, which forces them into spiraling orbits in a narrow doughnut around the earth's equator and about 1,500 miles above its surface.

The hard inner belt is not to be fooled with; its particles can easily penetrate several inches of metal. But, says Dr. Singer, if it proves a serious hazard to space navigation, it can be removed. This sweeping of space can be achieved by firing a big satellite of heavy metal into an equatorial orbit that keeps it inside the doughnut-shaped belt. Since the belt's particles are moving on spiral courses at almost the speed of light (186,000 miles per sec., equivalent to five times around the earth per second), they will have many chances to hit the satellite. Those that hit it will be slowed down so much that they will leave the belt. In a few months or years nearly all will be gone. Dr. Singer figures that once the belt is destroyed, it will not build up to its present strength for 100 years.

*Named after Dr. James Van Allen, whose interpretation of data from the Explorer satellites discovered the belts' existence.

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