Science: Striking Twelve

After the President’s announcement last week of the U.S.S.R.’s progress in making an atomic bomb (see NATIONAL AFFAIRS), Nobel-Prizewinner Harold C. Urey spoke for U.S. scientists. Said he: “We were never so sorry in our lives that we were so right.” Since June 1947, the Bulletin of the Atomic Scientists had shown on its cover two clock-hands pointing to 11:52. Individual scientists, groups of scientists and scientific associations have solemnly warned, time & again, that the clock would soon strike twelve.

There was no “atomic secret.” The basic fact that uranium atoms can be made to split in two, and release a massive jolt of energy, had been common scientific knowledge since 1939. The famed Smyth Report (A General Account of the Development of Methods of Using Atomic Energy for Military Purposes), which told how to go about making an atomic bomb was published by the U.S. War Department in August 1945. But even without the Smyth Report, U.S. scientists warned it was only a matter of time until some foreign nation, i.e., the U.S.S.R., would build a bomb of its own.

Determined Nations. Some of the early guesses about the timing were remarkably accurate. In One World or None (March 1946), Drs. Frederick Seitz and Hans A, Bethe, who worked on the U.S. bomb, estimated that “any one of several determined foreign nations could duplicate our work in about five years.” The Russians actually did it in a little over four years, counting from Hiroshima. But they may have started sooner than that, and they certainly had some help from German atomic scientists.

What did the Russians need to do? The Smyth Report told them (as their own scientists could have told them anyway) that there are two roads to the release of explosive atomic energy. One is separating explosive uranium 235 from natural uranium. The other is transmuting uranium into explosive plutonium in a chain-reacting pile. The U.S. has used and is still using both methods successfully.

Natural uranium contains two principal “isotopes” (U-235 and nonexplosive U-238) which differ only in atomic weight. Since the isotopes are identical chemically, they cannot be separated by chemical means. They must be separated by some process taking advantage of their slightly different atomic weights. The job is extremely difficult and laborious, but the U.S. developed two processes (gaseous diffusion and electromagnetic separation) that worked efficiently.

Well Enough. Probably the Russians are using one or both of these processes, which have the advantage of working well enough even when they don’t work too well. In the diffusion process, for instance, the U-235 has only to be pure enough to be “fissionable.” If the Russian apparatus is inferior, their U-235 is just as explosive as if it came from the great precision plants at Oak Ridge, Tenn.

Plutonium is trickier. It is made in a pile consisting of natural uranium (mostly U-238) rods imbedded in super-pure graphite. When everything is just right, a chain reaction starts. Plutonium can be separated from _ uranium by comparatively simple chemical refining. But the piles themselves are not simple. If they don’t work just right, they don’t work at all.

If the Russians are producing plutonium, they have really learned the atomic trade, perhaps with the help of German scientists. Once they accumulated enough fissionable material (U-235 or plutonium), it should not have been hard to make an atomic bomb. In quantities below a certain amount (the “critical mass,” sometimes estimated at around 26 lbs.), neither material will explode. But when two such masses are brought together, forming more than a “critical mass,” they explode spontaneously.

Poor Bombs Are Easy. The trick is to bring them together quickly enough. If they approach one another slowly, they begin to react before they are fully in contact. The heat developed drives them apart prematurely, and the reaction stops. In the bomb described in the Smyth Report, the masses were driven together, probably in millionths of a second, by some such “low-order explosive” as TNT. Even if the Russians did not do as well as U.S. scientists, their less efficient bomb would still produce an “atomic explosion.”

No U.S. scientist is inclined to minimize the Russian scientific achievement. It is possible that the Russians have built by persistence and enormous effort a single rather poor bomb. But they have world-renowned physicists, such as Peter Kapitza, and probably many other first-rate men. So it is also quite possible that they have large, fairly efficient plants capable of producing many excellent bombs.

Radioactive Dust. The instruments that recorded the Russian explosion were many and varied. Atom Bombs that explode in the air form mushroom clouds of intensely radioactive dust that billow high in the atmosphere. The dust particles, so small that they fall very slowly, are carried long distances by the wind. The radioactivity of the test explosion at Alamogordo in July 1945 was detected over Maryland, 1,425 miles away.

Since that first year of the Atomic Age, methods of observing such effects have improved enormously. U.S. airplanes, patrolling the perimeter of the U.S.S.R., were equipped to collect enough radioactive dust in air filters or electrostatic precipitators to prove that an atomic cloud had risen somewhere in the interior. Ground observers in some such place as Alaska could have spotted the cloud’s radioactivity by means of instruments.

If the Russians wished to keep their bomb from sending up telltale dust, they could have exploded it deep in some Siberian lake. The second Bikini test bomb (Test Baker), which exploded underwater, did not raise much of a cloud. Most of its dust was carried back into the lagoon by a deluge of radioactive water.*

Earth Waves. But underwater bombs and bombs exploded on a tower above ground smack the earth hard, as high airbursts do not. Seismic (earthquake) waves, shooting off in all directions, can be picked up at tremendous distances. Earth waves from Test Baker were detected by many seismographs on the U.S. Pacific coast, 4,300 miles away. Even the Alamogordo bomb, exploded on a loo-ft. tower, sent out earth waves that were picked up at Tinemaha, Calif., 710 miles away. Specially sensitive seismographs, ringed around the U.S.S.R., could pick up earth waves from a bomb exploded underwater or reasonably near the earth.

Atomic explosions also hit the atmosphere a tremendous wallop. The disturbance shows up at a distance as a wave of slightly increased barometric pressure. Microbarographs (instruments to record slight changes of air pressure) registered the Alamogordo explosion at Haiwee, Calif., 702 miles away. Improved barographs may now have enough range to cover all of the U.S.S.R.

All these instrumental methods are potentially capable of telling more than the mere fact that a bomb has exploded. If the Russian bomb was detected by both its radioactive cloud and its earth-wave effects, U.S. scientists probably know a lot about it. They may know just where it exploded, what it was made of and how efficient it was.

Long Strides. As long ago as 1946, the atomic policymakers decided that strict secrecy alone could not prolong the U S atomic advantage. It was far better, they decided, to release all information that was not strictly military. Then U.S. industry and science, by learning the new techniques, could gain a commanding lead that did not depend upon impermanent ‘ secrets” (TIME, Oct. 28,1946).

This judgment proved good. In four years the knowledge of atomic phenomena has penetrated deeply into U.S. technical life. The radioactive isotopes distributed from Oak Ridge are familiar research tools in most major laboratories. The manufacture of atomic instruments has become a thriving industry. The Russians now have a bomb, perhaps many of them. But the U.S. has taken longer, more powerful steps into the Atomic Age.

* Bikini Atoll, after three years, is still dangerous, it was reported last week. The level of radioactivity in the poisoned lagoon is gradually falling. But radioactive products of the atom bombs have entered the “food-chains” of the atoll’s inhabitants. The humblest forms of life, protozoa and algae, are not damaged much. When they are eaten by larger creatures, the radioactive matter concentrated in them rises link by link through a chain of eaters and eaten. The palms, with their roots in radioactive water, grow radioactive coconuts. It may be years before the food products of Bikini are safe for radiosensitive man.