Science: A Boost for Bevatron

A conservatively dressed man with graying hair strode unflinchingly to the target area of one of the world's most powerful nuclear particle accelerators last week and donned a molded plastic mask. At a signal, the accelerator beam was switched on, and nitrogen nuclei, traveling at almost the speed of light, flashed into his temple through a hole in the mask. At first nothing happened, even though the beam struck his optic nerve, behind the retina. For the next pulse, however, his head was moved so that the beam passed through his retina. "Hey, there's one!" he shouted. "Hey, there's a whole constellation!"

Physicist Edwin McMillan, 63, Nobel laureate and head of the Lawrence Berkeley Laboratory in California, had seen in his own lab the same flashes of light that astronauts see in space when their eyes are closed. Furthermore, he said, the experiment showed that atomic particles were causing the flashes -not through impact with the optic nerve or passage through the eye fluid, but by penetrating the retina itself.

McMillan's excitement went beyond the light experiment. Hundreds of technicians, engineers and scientists had worked since March at modifying the Berkeley Bevatron-which was designed for experiments with high-energy protons-to accelerate even heavier particles: nitrogen ions. As a result, McMillan announced at a press conference last week, nitrogen nuclei had been boosted to 36 billion electron volts, the highest energy level ever attained for such heavy particles in a laboratory.

Bare Nuclei. What the Bevatron apparatus had really done was create a kind of homemade cosmic ray, a big step in bringing the universe down to earth. Like cosmic rays from outer space, the particles shot through the Bevatron are really bare nuclei of atoms-in this case nitrogen-that have been stripped of their electrons and accelerated to tremendous velocities. By shooting these tiny bullets into a plastic target rich in hydrogen atoms, the Berkeley team was able to dissect the laboratory-produced cosmic rays. The collisions fragmented the nitrogen nuclei into every element lighter than nitrogen in the periodic table. By analyzing the results of this and similar experiments, physicists hope to bolster their meager store of knowledge about not only the atomic nucleus but also the pulsars and supernovae in which cosmic rays are thought to be born. "It opens up a whole new way of studying nuclear structure," said Berkeley Physicist Harry Heckman.

Scientists have no lack of chores for a machine with the capabilities of the Bevatron. Biophysicists, for example, are optimistic about using heavy ions, or other particles that can be made from these ions, to combat cancer, acromegaly (a rare disease in which facial features, hands and feet thicken) and Parkinson's disease. Unlike X rays and gamma rays, heavy particles do not damage healthy tissue on their way to a tumor; they do most of their deadly work only after reaching it. (Before the modification of the Bevatron, heavy ions could not be accelerated enough even to penetrate the skin.) In addition, scientists may some day create stable, superheavy elements by bombarding uranium with heavy ions. To bring this goal closer, Berkeley is now developing its one-two punch, connecting the Bevatron with another atom smasher, the Heavy Ion Linear Accelerator, 550 ft. away, to achieve even higher energy levels.