Cyclotron's Rival

A new electron-hurling machine, weightiest contribution to atomic physics since the cyclotron was invented in 1931, was unveiled before science and the world last week. It can hurl electrons--particles of negative electricity--at nearly the speed of light. It can produce 20,000,000-volt X-rays, some ten times more than the world's biggest X-ray machine. It can out-radiate all the extracted radium supplies on earth--and its further abilities have scarcely been explored. While U.S. scientists speculated upon the discoveries the device might lead to, they welcomed to their front ranks its brilliant young inventor, Donald William Kerst, 30, who calls the machine a "betatron." The cyclotron, whose invention won a Nobel Prize for University of California's Ernest Orlando Lawrence, hurls positively charged particles, the nuclei of atoms. But the betatron hurls the negatively charged particles which spin about the nuclei of atoms. Unlike the cyclotron's positive particles, the betatron's hurtling electrons will not effectively smash atoms--for one reason, they weigh only 1/1 800th as much as the nucleus' proton.

"The heart of the betatron," explains Inventor Kerst, "is a doughnut-shaped glass vacuum tube between the poles of a large electromagnet" (see cut). Inside the tube, a hot filament gives off electrons. Magnetically guided, each electron circles about the tube 400,000 times, accelerated at each rotation by small 70-volt kicks whose cumulative push gives the particle an energy of 20,000,000 volts within a fraction of a second. These fiercely energized electrons are then either: 1) Released continuously from the tube as a beam of beta rays--whence the betatron's name--which are one of the three types of radiation naturally given off by radium; or 2) Directed at a metal target, battering from it X-rays which are much more penetrating than radium's gamma rays. The betatron can produce as much radiation as over 1,000 grams of radium (world's supply: 750 grams).

Hitherto X-rays have been produced by stepping up an ordinary 110-volt current to perhaps 1,000,000 volts in a transformer, then jumping it through a straight vacuum tube at a target from which X-rays are emitted. Now, in effect, the betatron combines transformer and vacuum tube. Instead of circling round & round a magnet in a coil of wire, as in a transformer, the electrons whirl through the empty space inside the doughnut-shaped vacuum while their voltage increases.

Inventor Kerst first learned his physics at the University of Wisconsin, then taught at the University of Illinois, where last year he built his first small betatron -- a 2,300,000-volt table-top model. He saw at once that similar machines capable of imparting energies of 100,000,000 volts, and even higher, could readily be built.

Then General Electric, which long ago learned that such theoretical research means dividends for its stockholders in the not-too-long run, asked him to come to its Schenectady laboratories and help in the construction of the present 20,000,000-volt machine.

This week, while G.E. is starting work on a giant 100,000,000-volt model, Kerst is shipping his betatron to his laboratory in Illinois to see what discoveries he can make with it. Its electron beams have already penetrated inch-thick aluminum, made copper radioactive. Its medical applications, like those of the cyclotron which once struck the bewildered public as a useless device, must be explored. In time the betatron may be able to produce earthborn artificial cosmic rays, whose fantastic energies -- hundreds of millions of volts -- now smite the earth mysteriously from among the stars.

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