Atomic Age: Manhattan District

Behind the blackout curtains, physicists got their work orders. A few, horrified by what was planned, refused the summons. But most went to work, knowing that discovery could not be stopped, that the U.S. and its scientific allies must make it first. Many hoped that they would fail and that their failure would prove forever irrevocable.

Last week the War Department told the story of their success. Professor H. D. Smyth, chairman of Princeton’s physics department, who wrote the report, could not tell it all. But what he could tell, even in the prim language of the scientific laboratory, made the most fantastic and meaningful story to come out of the war.

Partnership Formed. The U.S. entered the atom race in the fall of 1939 when Franklin Roosevelt appointed an informal “Advisory Committee on Uranium.” It was a small project until the Nazi panzers roared over France. Then the world was struck by a terrible urgency. On Oct. 11, 1941, nearly two months before Pearl Harbor, President Roosevelt wrote to Winston Churchill, offering British nuclear physicists a plan to work in the U.S. Churchill accepted. The U.S. and Britain were partners.

All through the perilous spring of 1942, the scientists worked. In numerous guarded laboratories, their strange apparatus glowed and hummed. By June they had made progress. The program mushroomed, was transferred to the War Department.

“The Manhattan Engineer District” was the purposely deceptive name given the project. Its centers were full of G-men. Its couriers were Army officers, brief cases chained to their wrists. It rated highest priorities for men and materials. From dozens of universities and industrial plants physicists, chemists and mathematicians vanished into thin air; the Manhattan District had snatched them.

Explosive Calculations. Before the war it was discovered that slow-moving neutrons could split the atoms of the uranium isotope, U-235, giving a mighty gush of energy. Besides energy, their “fission” produced more flying neutrons. If enough of these in turn split uranium atoms, the reaction would maintain itself, gain momentum. It would flash through all the uranium, like the flame of a match through excelsior.

This “chain reaction,” which the Manhattan District now had to develop, did not happen naturally, chiefly because only one part in 140 of ordinary uranium is U-235. Most of the rest is another isotope, U-238—which, instead of splitting like U-235, absorbs the newborn neutrons with the result that the atomic flame goes out like a match in wet excelsior.

Obviously, the remedy was to separate the active U-235 from natural uranium, getting rid of the U-238. It was simple in principle, like drying the water content out of a sodden fuel. But the physicists shuddered when they finished their calculations. No chain reaction, they found, could take place in a small bit of U-235, but a large enough chunk would surely explode.

The problem, once they had the big chunk, might be to keep it from exploding whenever it was struck by any wandering neutron. The explosion, they calculated, would certainly be more violent than anything yet seen on earth.

Two New Elements. There was one more possibility. When natural uranium (one part U-235, 140 parts U-238) is bombarded with slow neutrons, more happens than the cracking of the U-235 particles. Some of the neutrons produced by these fissions are absorbed by the more phlegmatic U-238; This forms a new, unstable element, neptunium, which soon turns into plutonium.*

Plutonium is a fairly stable element. Like the rare U-235, it is also “fissionable” it can be made to explode in a violent chain reaction. Furthermore, it is not an isotope of uranium, but an entirely different chemical element. Therefore it can be separated from uranium comparatively easily by chemical means while U-235 clings to U-238 with tenacious obstinacy.

Graphite Moderator. The atomic reaction producing plutonium did not take place in nature as a chain reaction. Many of the neutrons from the splitting U-235 flashed right out of the material. Others were wasted on impurities. Only a very few changed U-238 into plutonium.

The scientists went to work to change that. One measure: increasing the size of the active material to keep the neutrons from escaping so soon. Another: eliminating impurities. Another: slowing down the neutrons to keep them near the uranium until they could be absorbed.

This last could be done by imbedding small bits of uranium in a “moderator”—a substance which would slow the speed of the neutrons but not absorb them. The Germans may have tried heavy water for this job. The Manhattan District men decided on graphite which was easier to get. If they could produce plutonium at an orderly controlled rate, they would have a charge for the bomb that would change the world.

No Pilot Plants. So far nearly all the work had been on the level of theory. No chain reaction had been achieved; no appreciable quantity of U-235 had been isolated; no plutonium had been produced. But on June 17, 1942, the various committees concerned sent their report to the President: let’s make plutonium as well as U-235.

Full-scale plants, the committees urged, should be built at once. It was not known which processes were the best, so all the more promising ones should be started immediately. There was no time for failures, or even for pilot plants. The Nazis might be ahead in the race for Doomsday.

The President agreed, made money available. Theory had felt out the road to the goal. Now production would bulldoze it wide.

Men & Mountains. Like an ever-growing snowball the Manhattan District rolled around the nation, picking up men (125,000), money ($2,000,000,000), mountains of materials, trainloads of equipment. It enlisted famed corporations — Eastman, Dupont, Stone & Webster, Union Carbide and Carbon, and others.

Professors, including many Nobel Prize winners, deserted their campuses to live in dusty deserts. Workers trekked in their trailers — careful New England craftsmen, burly Southern Negroes, all the races and types of the great U.S. In general terms they were told the shouting urgency of the mighty thing they were doing, but few of them knew its extraordinary character.

Under the cover name of “The Metallurgical Laboratory,” some of the most important discoveries were made at the University of Chicago directed by famed Dr. Arthur Holly Compton. His leading associate: Italian-born Dr. ‘Enrico Fermi, whom many consider the world’s foremost nuclear physicist. But there were also scores of other laboratories where the work went on: Columbia, University of California, Iowa State, industrial research centers.

Processes & Places. There were many possible ways of separating U-235 from natural uranium. Two processes at least were found to work well. In the first (mass spectrograph), uranium particles were electrically charged, fired through a huge electromagnet, sent into a curving course. The lighter U-235 swung more widely on the curve. Traps were set at the end of the turn, and U-235 was caught there, while U-238 was discarded.

In the second, as incredibly delicate as the first, a gaseous uranium compound was pumped through the finest of sub-microscopic filters. The faintly more volatile U-235 passed through more easily. Result: a higher percentage of U-235 beyond the filters.

The experimental work of the electromagnetic method was done at the University of California under blond, boyish Dr. E. O. Lawrence; on diffusion, at Columbia under Dr. H. C. Urey. By 1943, before the experiments were completed, vast plants to carry out both processes were being constructed at Oak Ridge, a sparsely inhabited region near Knoxville, Tenn.

Into that brand-new city (called Dogpatch) flooded weird equipment: thousands of powerful, new-type pumps, gigantic electromagnets, innumerable other machines and instruments. Amid oceans of mud and battlefront confusion, they finally found their places. Both plants were successful, produced effective quantities of precious U-235.

Squash Court Pile. Production of plutonium was probably no more important, but vastly more dramatic. On a squash court under the stands of University of Chicago’s football field, a strange apparatus took form. It was an oblate spheroid (doorknob shape), built up of graphite bricks with lumps of uranium or uranium oxide imbedded in their corners. This was the world’s first chain reaction “pile”—a uranium “lattice” and a graphite “moderator.” If it worked according to Dr. Fermi’s theories, it would produce the first chain reaction ever set up on earth. .

With care, and great trepidation, the physicists laid the bricks. They knew they were deep in unknown territory; anything might happen. Around them hummed southside Chicago. Nearby, students passed on their way to classes.

By theory, the chain reaction should start spontaneously when nearly all the bricks were laid. Then it could be stopped short of a disastrous explosion by inserting strips of cadmium to break the chain.

But far below the “critical size” of the theory, instruments gave the alarm. The reaction was starting to cook. Luckily, the cadmium strips had been inserted at “retard” position. Slowed down by their influence, the reaction was easily stopped. “This,” commented Dr. Smyth dryly, “was fortunate.”

This momentous experiment—the very first chain reaction—marked the beginning of the Atomic Age. The pile was successful. Long before the queasy process had been reduced to an orderly procedure, a gigantic, full-sized plutonium plant had been started at Hanford on the desert near Yakima, Wash. Advantages of the unattractive site: isolation, a good supply of Grand Coulee power and the Columbia River which would carry away the enormous heat generated in the piles.

City of Pluto. The original pile at Chicago had been a ticklish business, but the giant piles at Hanford were studies in unexplored dangers. Theory warned that as soon as they started working, they would generate floods of deadly radiation and produce unknown radioactive elements, most of them fiendishly poisonous: These effects could conceivably be so powerful and so long-lasting that no living thing could approach a pile which had once been in operation.

Accordingly, elaborate devices were developed for operating the piles by remote control from behind thick protective shields. Even so, the deadly unknowns escaped. The cooling water was radioactive. It had to be impounded and exhausted of radioactivity before going back to the river. The wind blowing over the chemical plant picked up another load of peril for the stacks gave off a radioactive gas. The City of Pluto was a place of grim possibilities.

Rigid precautions guarded the health of the workers. They all carried small electroscopes or bits of photographic film for nightly tests to show the amount of radiation to which each had been exposed. A gadget called “Sneezy” measured radioactive dust in the air; “Pluto” watched lab desks and instruments. Clothing was carefully checked. Devices rang an alarm when a radioactive worker came near.

Energy & Poisons. Besides plutonium, the Hanford plant produced two frightening by-product effects. The water which cooled the piles carried off enough energy, derived from the chain reaction, to heat the Columbia River appreciably. No definite figures have been released, but the hints in Dr. Smyth’s report are portentous. Some relative of the uranium pile may still prove a power source great enough to run all the world’s machines.

The second by-product was pure horror. In the ordinary operation of a large-scale pile, calculated Dr. Smyth, enough radioactive poisons could be produced every day to make “large areas uninhabitable.”

Peril in Los Alamos. While the mighty plants were being built and the processes studied to make them run, another team of physicists was colonizing still another desert. In March 1943, a group led by Professor J. R. Oppenheimer of the University of California, gathered at Los Alamos, New Mexico. Their job was to design, assemble and test the atomic bomb itself. The pile constructors had struggled to keep their brain child from blowing up. The bomb men had the more deadly mission of finally blowing up theirs at the time and place that war demanded.

For obvious reasons, Dr. Smyth’s description of the bomb is incomplete. But he gives some hints. U-235 and plutonium do not have to be exploded by a detonator like TNT. They explode automatically whenever gathered together in large quantities. Therefore a main problem in an atomic bomb is to design a mechanism which will bring small masses to the explodable “critical size.” Until the explosion is well started, they should be held together by a heavy-material “tamper.” A possible source of heavy material: the hoarded gold of Fort Knox.

About the Future. Dr. Smyth’s War Department report breaks off at the end of June 1945, shortly before the fearful test on the desert which proved the bomb a smash-hit (TIME, Aug. 13). Dr. Smyth was sure of success before the test was made, but he was not completely happy about it: “Initially, many scientists could and did hope that some principle would emerge which would prove that atomic bombs were inherently impossible. This hope has faded gradually. . . .”

For the future, rapid improvement in the technique of atom fission is foreseeable. For science this will be progress but, says Dr. Smyth: “Should a scheme be devised for converting to energy even as much as a few per cent of the matter of some common material, civilization would have a means to commit suicide at will.”

-Named for the planet Pluto, which is beyond Uranus and Neptune in the solar system. Pluto was also the god of the underworld.