Science: Atoms at Retail

So long as U-235, the explosive isotope in natural uranium, was hard to get, only the biggest powers could afford nuclear bombs. Now everybody—Mao, Castro, Nasser or whoever—may soon be able to have a bomb of his own. Previously, U-235 was almost impossible to separate from nonexplosive U-238, except with great expense and difficulty. But, said Tennessee’s Democratic Senator Albert Gore, member of the Joint Committee on Atomic Energy, last week: “recent advances in [centrifuge] technology have now brought the capability of producing weapons-grade material within the reach of not just a few but of many nations.”

This was no surprise to nuclear professionals. When the U.S. was developing the first atomic bomb during World War II, one of the several promising ways to purify U-235 was to pass uranium hexafluoride, a uranium-containing gas, through a centrifuge—a sort of souped-up cream separator—that would spin the gas at enormous speed and subject it to high, gravitylike forces. The slightly lighter molecules containing U-235 would tend to stay near the center of the centrifuge, while the heavier molecules containing U-238 would move toward the spinning sides.

Through the Pores. In their haste to develop the atomic bomb, the World War II scientists put aside the centrifuge. Instead, they built at Oak Ridge, Tenn. an enormous diffusion plant that worked by pumping uranium hexafluoride through thousands of porous barriers. The U-235 went through the pores a bit more easily than U-238, and was separated.

But the gas centrifuge was not forgotten. Atomic Energy Commission scientists kept working on it, as did many Europeans, especially in West Germany. Prominent in this work were Professor Wilhelm Groth, of Bonn University, and Gernot Zippe, who built a gas centrifuge for the U.S.S.R. and was hired in 1958 by the AEC. Zippe returned to Germany last July and is now associated with the Degussa Co. of Frankfurt, which is manufacturing the centrifuges experimentally.

A Pound Per Year. The chief trouble with the early centrifuges was their comparatively slow speed. This was serious because their effectiveness in separating U-235 rises with the fourth power of the speed of the rotor, i.e., doubling the speed would multiply the efficiency by 16. Better materials and construction methods have recently increased the speed to at least 40,000 r.p.m. Up-to-date centrifuges spin in a near vacuum, and they have complicated heating devices to make the gas circulate inside them in a way that multiplies their efficiency.

Professor Groth says that existing centrifuges require only one-tenth as much electric power as diffusion apparatus of the same capacity. The present Degussa model can be built for about $1,000. and according to Zippe, it will produce in one year about one pound of U-235. Improvements already in sight will increase this figure. Both Groth and Zippe believe that centrifuges will eventually compete economically with gaseous diffusion in making nuclear fuel, enriched in U-235, for atomic power plants.

If this were all that they may do, there would be little excitement. But U-235 is not an ordinary commodity; only a few-pounds, perhaps less, are now required to make the detonator for a hydrogen bomb that can smash the world’s biggest city. The other nuclear ingredients of such bombs, deuterium and lithium 6, are comparatively easy to come by. High skill and knowledge are needed to assemble these devices, but both can be acquired by any purposeful nation, however small.

U.S. government officials tried to persuade the West German government to clamp secrecy on centrifuge technology. But no expert believes that knowledge of uranium centrifuges, already widely disseminated, can be regulated away.