Powerful Invader

At the American Physical Society Convention in Seattle last week, Dr. Marcel Schein of the University of Chicago had news to make even a sensation-jaded physicist draw a sharp breath. Last winter, he reported, he and his assistants tied a pack of photographic plates to a balloon, sent them up to 100,000 ft. over Texas to be exposed to the powerful primary cosmic rays that bombard the top of the atmosphere. Later, studying the plates in the laboratory, Dr. Schein got more and more excited as he followed a peculiar ray track through the pack. The track was a bundle of slim Vs made by pairs of negative and positive electrons and there was no trace of larger charged particles (e.g., protons) usually present. His cautious conclusion: "something" had hit the film pack with the unheard-of energy of 10 million billion electron-volts.

This was energy of a wholly different magnitude from any ever observed in atomic particles--more than 1,500,000 times the energy of the particles shot out by the University of California's powerful bevatron, and 50 million times the energy of a splitting uranium atom in an Abomb. The "something," Physicist Schein thought, was most probably an illusive particle called an antiproton (negative proton), which theoretical physicists have long guessed about, but never observed.

He believes that it hit an ordinary proton in the aluminum wrapping of the film pack and annihilated not only itself but the earthly matter in its target as well, turning all of their mass into energy.

The peculiar track was made by enormously powerful gamma rays that created electron-positron pairs as they streaked away from the site of the collision.

Like most careful physicists, Dr. Schein does not like to speculate about the possible origin of antiprotons. It is quite possible, says he, that remote stars may be made of "reversed matter," whose atoms have negative antiprotons in their nuclei and positrons (positive electrons) revolving around them. There would be no way to tell; the reversed matter would send out the same kind of light as ordinary matter. It would behave itself normally as long as it stayed at home. But if particles from an antiproton star should wander into a region, like the earth's atmosphere, where the other kind of matter abounds, they would not live to tell the tale except in gamma rays.

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