Proton-Busters

Physicists will never be happy until they take the atom completely apart. Most of them already consider the atom bomb just a frontier skirmish. Last week they gathered at the University of California to discuss the big topic in nuclear physics: subatomic particles. To the American Physical Society, U.S. atom-busters described carefully laid plans for further busting.

Until recently, atomic physicists thought they knew nearly everything there was to know about the atom. Now, Nuclear Physicist J. Robert Oppenheimer told the meeting, they are "frankly puzzled." The notion that an atom consists only of electrons, protons and neutrons has been knocked into a cocked hat by the discovery of mystifying sub-particles --positrons, mesotrons, and a hypothetical particle called the neutrino.

Nobody knows, said Oppenheimer, how the sub-particles fit together or affect each other. To find out, physicists must somehow duplicate the atom-smashing carried on in nature by cosmic rays.

The human proton-buster's problem: how to make a machine that approaches the power of a cosmic ray bullet. The most powerful machine in existence (General Electric's betatron) develops 100 million electron volts. Physicists now aim at one billion volts. The big news at Berkeley: they are getting warm.

Cyclotron. For high-powered work, the cyclotron has had a basic flaw: at very high speeds it runs head on into relativity. In a cyclotron, nuclear bullets (such as deuterons--the nucleus of the heavy hydrogen atom) are whirled around in a drum divided across the middle, like a halved round cheese. Each time a bullet crosses the gap between the drum halves, it gets an electrical kick, increasing its speed. Because of the bullet's great speed (it circles the drum in millionths of a second), accurate timing of the kick is all-important. But as the bullet approaches the speed of light, it gains in mass, according to Einstein's relativity principle that at high speeds energy is converted into matter. Result: the heavier particle slows down and the timing system is thrown out of kilter.

The relativity effect has limited most cyclotrons to considerably less than 100 million electron volts. But last week California's Physicist Edwin M. McMillan reported that he had found a way to thwart relativity. His device: a frequency modulator (the same principle as in FM radio) which automatically adjusts the frequency of a cyclotron's kicks to the speed of its bullets. It will beef up California's new 184-inch cyclotron (to be completed by autumn) to 200-400 million electron volts.

Straight Shooter. The sensation of the meeting, however, was a brand-new type of machine which promises to outpower the cyclotron. Prosaically named the "linear accelerator," it is a tube which shoots its nuclear bullets straight instead of in a circle. The idea came from two crack young physicists, M.I.T.'s Julius Halpern and California's Luis W. Alvarez, who have developed separate versions of the machine.

Its basic principle: powerful bursts of radio microwaves that speed up atomic bullets as they hurtle through successive sections of a long copper "rifle" barrel. Unlike the cyclotron and its modifications (betatron, synchrotron), the linear accelerator requires no heavy magnets; its power is increased simply by adding sections to the pipe. Alvarez announced plans for an experimental 280-foot model at California which will shoot protons at 280 million electron volts. Halpern calculated that his machine, which uses electrons as bullets, in a 300-foot model could top one billion electron volts.

Said Oppenheimer calmly: "We are going to see what goes on in the nucleus when it is ripped apart."

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