“I’ll bet you a thousand dollars you won’t.”
“I’ll take you on that,” Compton says he answered, “and these men here are the witnesses.”
“I’ll cut the stakes to a five-cent cigar,” Lawrence hedged.
“Agreed,” said Compton, who never smoked a cigar in his life.
After the crowd left, Compton shuffled wearily to his study and called Fermi. “He agreed at once to make the move to Chicago,” Compton writes. Fermi may have agreed, but he found the decision burdensome. He was preparing further experiments. His group was exactly the right size. He owned a pleasant house in a pleasant suburb. He and Laura had buried a cache of Nobel Prize money in a lead pipe under the concrete floor of their basement coal bin against the possibility that as enemy aliens their assets would be frozen. Laura Fermi “had come to consider Leonia as our permanent home,” she writes, “and loathed the idea of moving again.” She says her husband “was unhappy to move. They (I did not know who they were) had decided to concentrate all that work (I did not know what it was) in Chicago and to enlarge it greatly, Enrico grumbled. It was the work he had started at Columbia with a small group of physicists. There is much to be said for a small group. It can work quite efficiently.” But the country was at war. Fermi traveled back and forth by train until the end of April, then camped in Chicago. Laura dug up their buried treasure and followed at the end of June.
To Szilard, the day after the sickbed meeting—he had returned promptly to New York—Compton sent a respectful telegram: THANK YOU FOR COMING TO PRESENT ABLY COLUMBIA’S SITUATION. NOW WE NEED YOUR HELP IN ORGANIZING THE METALLURGICAL LABORATORY OF O.S.R.D. IN CHICAGO. CAN YOU ARRIVE HERE WEDNESDAY MORNING WITH FERMI AND WIGNER… TO DISCUSS DETAILS OF MOVING AND ORGANIZATION. Unlike the Radiation Laboratory at MIT, the new Metallurgical Laboratory hardly disguised its purpose in its name. Who would imagine its goal was the transmutation of the elements to make baseball-sized explosive spheres of unearthly metal?
Before Fermi and his team moved to Illinois they built one more exponential pile, this one loaded with cylindrical lumps of pressed uranium oxide three inches long and three inches in diameter that weighed four pounds each, some two thousand in all, set in blind holes drilled directly into graphite. A new recruit, a handsome, dark-haired young experimentalist named John Marshall, located a suitable press for the work in a junkyard in Jersey City and set it up on the seventh floor of Pupin; Walter Zinn designed stainless steel dies; the powdered oxide bound together under pressure as medicinal tablets pressed from powder—aspirin, for example—do.
Fermi was concerned to free the pile as completely as possible of moisture to reduce neutron absorption. He had canned the oxide before; now he decided to can the entire nine-foot graphite cube. “There are no ready-made cans of the needed size,” Laura Fermi says dryly, “so Enrico ordered one.” That, writes Albert Wattenberg, who joined the group in January, “required soldering together many strips of sheet metal. We were very fortunate in getting a sheet metal worker who made excellent solder joints. It was, however, quite a challenge to deal with him, since he could neither read nor speak English. We communicated with pictures, and somehow he did the job.” Laura Fermi picks up the story: “To insure proper assembly, they marked each section with a little figure of a man: if the can were put together as it should be, all men would stand on their feet, otherwise on their heads.” The Columbia men preheated the oxide lumps to 480°F before loading. They heated the contents of the room-sized can to the boiling point of water and pumped down a partial vacuum. Their heroic efforts reduced the pile’s moisture to 0.03 percent. With the same relatively impure uranium and graphite they had used before but with these improved conditions and arrangements they measured k at the end of April at an encouraging 0.918.
In Chicago in the meantime Samuel Allison had built a smaller seven-foot exponential pile and measured k for his arrangement at 0.94. The University of Chicago had long ago sacrificed football to scholarship; Compton took over the warren of disused rooms under the west stands of Stagg Field, which was conveniently located immediately north of the main campus, and made space available there to Allison. Below solid masonry façades set with Gothic windows and crenellated towers the stands concealed ball courts as well as locker areas. The unheated room Allison had used for his experiment, sixty feet long, thirty feet wide, twenty-six feet high and sunk half below street level was a doubles squash court.
MEASUREMENT OF K
For [his] first exponential experiment and the many similar experiments to come, Fermi defined a single fundamental magnitude for assessing the chain reaction, “the reproduction factor k.” k was the average number of secondary neutrons produced by one original neutron in a lattice of infinite size—in other words, if the original neutron had all the room in the world in which to drift on its way to encountering a uranium nucleus. One neutron in the zero generation would produce k neutrons in the first generation, k2 neutrons in the second generation, k3 neutrons in the third generation and so on. If k was greater than 1.0, the series would diverge, the chain reaction would go, “in which case the production of neutrons is infinite.” If k was less than 1.0, the series would eventually converge to zero: the chain reaction would die out. k would depend on the quantity and quality of materials used in the pile and the efficiency of their arrangement.
—FROM RICHARD RHODES,
THE MAKING OF THE ATOMIC BOMB, P. 397
U.S. Department of Energy
December 2, 1946 reunion of the Chicago Met Lab scientists. Front row, left to right: Enrico Fermi, Walter Zinn, Albert Wattenberg, and Herbert Anderson. Middle row: Harold Agnew, William Sturm, Harold Lichtenberger, Leona Woods Marshall, and Leo Szilard. Back row: Norman Hilberry, Samuel Allison, Thomas Brill, Robert Nobles, Warren Nyer, and Marvin Wilkening.
The Chicago Pile-1: The First Chain Reaction
The first demonstration that an atomic chain-reaction could be self-sustaining took place in a squash court underneath the football stadium at the University of Chicago. This experiment, directed by the Italian physicist Enrico Fermi, was called CP-1, or Chicago Pile-1. The reactor or “pile” was a lattice of graphite blocks interlaced with uranium rods. When the reaction became self-sustaining, Fermi commented: “The event was not spectacular, no fuses burned, no lights flashed. But to us it meant that release of atomic energy on a large scale would be only a matter of time.”
From “Fermi’s Own Story”
BY ENRICO FERMI
The year was 1939. A world war was about to start. The new possibilities appeared likely to be important, not only for peace but also for war.
A group of physicists in the United States—including Leo Szilard, Walter Zinn, now director of Argonne National Laboratory, Herbert Anderson, and myself—agreed privately to delay further publications of findings in this field.
We were afraid these findings might help the Nazis. Our action, of course, represented a break with scientific tradition and was not taken lightly. Subsequently, when the government became interested in the atom bomb project, secrecy became compulsory.
Here it may be well to define what is meant by the “chain reaction” which was to constitute our next objective in the search for a method of utilizing atomic energy.
An atomic chain reaction may be compared to the burning of a rubbish pile from spontaneous combustion. In such a fire, minute parts of the pile start to burn and in turn ignite other tiny fragments. When sufficient numbers of these fractional parts are heated to the kindling points, the entire heap bursts into flames.
A similar process takes place in an atomic pile such as was constructed under the West Stands of Stagg Field at the University of Chicago in 1942.
The pile itself was constructed of uranium, a material that is embedded in a matrix of graphite. With sufficient uranium in the pile, the few neutrons emitted in a single fission that may accidentally occur strike neighboring atoms, which in turn undergo fission and produce more neutrons.
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p; These bombard other atoms and so on at an increasing rate until the atomic “fire” is going full blast.
The atomic pile is controlled and prevented from burning itself to complete destruction by cadmium rods which absorb neutrons and stop the bombardment process. The same effect might be achieved by running a pipe of cold water through a rubbish heap; by keeping the temperature low the pipe would prevent the spontaneous burning.
The first atomic chain reaction experiment was designed to proceed at a slow rate. In this sense it differed from the atomic bomb, which was designed to proceed at as fast a rate as was possible. Otherwise, the basic process is similar to that of the atomic bomb.
The atomic chain reaction was the result of hard work by many hands and many heads. Arthur H. Compton, Walter Zinn, Herbert Anderson, Leo Szilard, Eugene Wigner, and many others worked directly on the problems at the University of Chicago. Very many experiments and calculations had to be performed. Finally a plan was decided upon.
Thirty “piles” of less than the size necessary to establish a chain reaction were built and tested. Then the plans were made for the final test of a full-sized pile.
The scene of this test at the University of Chicago would have been confusing to an outsider—if he could have eluded the security guards and gained admittance.
He would have seen only what appeared to be a crude pile of black bricks and wooden timbers. All but one side of the pile was obscured by a balloon cloth envelope.
As the pile grew toward its final shape during the days of preparation, the measurement performed many times a day indicated everything was going, if anything, a little bit better than predicted by calculations.
Finally, the day came when we were ready to run the experiment. We gathered on a balcony about 10 feet above the floor of the large room in which the structure had been erected.
Beneath us was a young scientist, George Weil, whose duty it was to handle the last control rod that was holding the reaction in check.
Every precaution had been taken against an accident. There were three sets of control rods in the pile. One set was automatic. Another consisted of a heavily weighted emergency safety held by a rope. Walter Zinn was holding the rope ready to release it at the least sign of trouble.
The last rod left in the pile, which acted as starter, accelerator, and brake for the reaction, was the one handled by Weil.
Since the experiment had never been tried before, a “liquid control squad” stood ready to flood the pile with cadmium salt solution in case the control rods failed. Before we began, we rehearsed the safety precautions carefully.
Finally, it was time to remove the control rods. Slowly, Weil started to withdraw the main control rod. On the balcony, we watched the indicators which measured the neutron count and told us how rapidly the disintegration of the uranium atoms under their neutron bombardment was proceeding.
At 11:35 a.m., the counters were clicking rapidly. Then, with a loud clap, the automatic control rods slammed home. The safety point had been set too low.
It seemed a good time to eat lunch.
During lunch everyone was thinking about the experiment but nobody talked much about it.
At 2:30, Weil pulled out the control rod in a series of measured adjustments.
Shortly after, the intensity shown by the indicators began to rise at a slow but ever-increasing rate. At this moment we knew that the self-sustaining reaction was under way.
The event was not spectacular, no fuses burned, no lights flashed. But to us it meant that release of atomic energy on a large scale would be only a matter of time.
The further development of atomic energy during the next three years of the war was, of course, focused on the main objective of producing an effective weapon.
At the same time we all hoped that with the end of the war emphasis would be shifted decidedly from the weapon to the peaceful aspects of atomic energy.
We hoped that perhaps the building of power plants, production of radioactive elements for science and medicine would become the paramount objectives.
Unfortunately, the end of the war did not bring brotherly love among nations. The fabrication of weapons still is and must be the primary concern of the Atomic Energy Commission.
Secrecy that we thought was an unwelcome necessity of the war still appears to be an unwelcome necessity. The peaceful objectives must come second, although very considerable progress has been made also along those lines.
The problems posed by this world situation are not for the scientist alone but for all people to resolve. Perhaps a time will come when all scientific and technical progress will be hailed for the advantages that it may bring to man, and never feared on account of its destructive possibilities.
U.S. Department of Energy
This painting of Chicago Pile-1 shows scientists witnessing the world’s first nuclear chain reaction on December 2, 1942.
ATOMIC REACTIONS AND BURNING RUBBISH PILES
An atomic chain reaction may be compared to the burning of a rubbish pile from spontaneous combustion. In such a fire, minute parts of the pile start to burn and in turn ignite other tiny fragments. When sufficient numbers of these fractional parts are heated to the kindling points, the entire heap bursts into flames.
—ENRICO FERMI
THE NEW WORLD
The success of the first controlled atomic chain reaction that took place at the University of Chicago on December 2, 1942 was discussed in a short phone conversation between Arthur Holly Compton and Dr. James B. Conant. The “Italian navigator” is Enrico Fermi.
ARTHUR H. COMPTON: “Jim, you’ll be interested to know the Italian navigator has just landed in the new world… The earth was not as large as he had estimated, and he arrived at the new world sooner than he had expected.”
JAMES B. CONANT: “Is that so? Were the natives friendly?”
COMPTON: “Everyone landed safe and happy.”
“Fermi was cool as a cucumber”
During the Manhattan Project, Crawford Greenewalt managed the plutonium production operations in Hanford, Washington, for the DuPont Company. As a witness to the first critical nuclear reaction at the Chicago Pile-1, or CP-1, Greenewalt kept a diary in which he recorded these eyewitness notes.
BY CRAWFORD GREENEWALT
On Wednesday afternoon 12/2/42 Compton took me over to West Stands to see the crucial experiment on Pile #1. When we got there the control rod had been pulled out to within 3 inches of the point where K would be 1.0. The rod had been pulled out about 12 inch to reach this point. The resultant effects were being observed 1) by counting the neutrons as recorded on an indium strip inside the pile (see previous notes) and 2) on a recorder connected to an ionization chamber placed about 24 inches from the pile wall. The pile itself was encased in a balloon cloth envelope. The neutron counter was not a good index of what was going on since the number striking the indium strip was near and above the number which could be counted with accuracy. Hence the best index was the recorder attached to the ionization chamber. This had two ranges, one about twenty times as sensitive as the other. Fermi was cool as a cucumber—much more so than his associates who were excited or a bit scared.
Courtesy of the Hagley Museum and Library
Crawford Greenewalt observed that Enrico Fermi was “cool as a cucumber” when the nuclear reaction went critical.
“Proceeding in the dark”
In this account, General Leslie R. Groves relays the challenges of planning amid great uncertainty. In meetings at the University of Chicago in 1942, Groves was taken aback when leading scientists hedged their estimate of how much plutonium was needed for an atomic bomb by a “factor of ten.”
From Now It Can Be Told
BY GENERAL LESLIE R. GROVES
It is essential for the reader to keep in mind the truly pioneering nature of the plutonium development as well as the short time available for research, to appreciate the gigantic steps taken by both scientists and engineers in moving as rapidly as t
hey did from the idea stage to an operating plant of commercial size. It was a phenomenal achievement; an even greater venture into the unknown than the first voyage of Columbus.
The laboratory investigations had to be conducted in the face of incredible handicaps. At the laboratory in Chicago, we were seeking to split atoms, and in the process to transmute one element into another—that is, to change uranium into plutonium. The transmutation of an element involves the conversion of its atoms—the smallest known submicroscopic particles capable of existing alone which are not susceptible to further subdivision by chemical means—into atoms of another element possessing different chemical and physical properties. In effect, the scientists were reviving the classical, but always unsuccessful, search of the ancient alchemists for ways to convert base metals, such as lead, into gold; and the continuing, but theretofore unsuccessful, attempts of more modern chemists to change the character of elements. The precedents of history were surely all against us.
BETWEEN TEN AND A THOUSAND
My position could well be compared with that of a caterer who is told he must be prepared to serve anywhere between ten and a thousand guests.
—GENERAL LESLIE R. GROVES
To carry out the transmutation process, even on a laboratory scale, and at an almost infinitesimal rate of production, a reactor, or as we often referred to it, a pile, of considerable size is necessary; for full scale production, obviously, a much bigger pile is needed. The laboratory unit, it was estimated, would require, among other items, some forty-five tons of uranium or uranium oxide. Such amounts were not available in sufficient purity until late in 1942. Even then, the laboratory unit would not be able to produce enough plutonium to permit normal laboratory research on its recovery—that is, on ways to separate it chemically from the basic uranium and the other radioactive materials that would also be produced.
The Manhattan Project Page 9