The Age of Radiance (25 page)

Down the Great Lakes, winter rolled in; university squash courts from the 1930s were unheated. The men casting the uranium, sawing the graphite, and assembling the pile were kept warm by their physical labors, but the military boys outside guarding the world’s biggest secret were freezing to death. A wonderful surprise was discovered in the locker room: the long-gone football team had left behind their outerwear. The key experiment that would be the birth of nuclear power and pave the way for the Atomic Age was thus guarded from enemy attack and Axis spies by men in raccoon coats.

The night before the test, Szilard ate two dinners back-to-back, explaining to his companion that the second was
“just in case an important experiment doesn’t succeed.”

On Wednesday, December 2, 1942, every train, elevated, bus, and trolley was packed and suffocating—wartime gas rationing had begun. The temperature in Chicago rose all the way to 10°F. That day, the US State Department announced that the Nazis had already murdered 2 million Jews and that 5 million more were endangered. German infantryman Willy Peter Reese:
“Marched into Russia. Murdered the Jews. Strangled the women. Killed the children. Everyone knows what we bring.” That night would also be the first night of Hanukkah.

Beginning at 8:30 a.m., Fermi and Szilard’s entire team assembled at Stagg Field to see if history would (or would not) be made. At the squash court’s northern end, a viewing-stand balcony had been converted into a control center, where Fermi, Zinn, Anderson, and Compton monitored the instruments, and everyone else who wanted to watch crowded together.
Before them lay 380 tons of graphite, 40 tons of uranium oxide, 6 tons of uranium metal, 22,000 uranium slugs surrounded by 57 layers of graphite bricks, all at an inflation-adjusted cost of $2.7 million.

Crawford Greenewalt:
“The whole atmosphere there was one of calmly observing an experiment being made. To be sure there was a suicide squad that you could see on the other end of the platform with their cadmium nitrate ready to pour in if it didn’t work. But it became obvious very quickly that it was going to be controlled.”

Within the environs of a reactor, uranium eats itself by throwing pieces of its nuclei against each other, like an organic 3-D pinball machine crowded with a seemingly infinite mass of pinballs. As this happens, the instruments indicating the subatomic activity rise steadily. Then, at fission, the free neutrons are so numerous and their attacks so great that the bombardment turns exponential, into a cascade . . . and a reactor can run away with itself and melt down.

To all who worked with him, Fermi appeared supernaturally confident, but he knew full well how dangerous CP-1 was and had gone step-by-step with his thirty piles preliminary to acquire data and feedback until he knew exactly what he was doing. It was a deliberate, careful, and meticulous process.

For the first reactor, he created a series of three safeguards to make absolutely certain the worst could not happen. Besides the main control rod operated manually on the floor by George Weil, a second, known as ZIP, was attached to a solenoid and an ionization chamber that was set to trigger automatically in the event of high, sustained neutron counts. Untouched by human hands, the solenoid would release ZIP, and gravity would drop it into the pile, stopping the reactor.

Another safeguard ZIP hung over the pile, this one tied by a rope to the balcony, where graduate student Norman Hilberry was standing by with an ax, ready at Fermi’s command to cut the rope and let the rod fall.

Waiting in the wings, meanwhile, was Fermi’s third safety measure, a “suicide squad” of Harold Lichtenberger, W. Nyer, and A. C. Graves. These three stood gravely on a platform over the pile accompanied by buckets of cadmium-salt solution. If the various rod safety devices failed, they would flood the pile.

Today, reactor control panels around the world have the same button for emergency shutdowns, the SCRAM button, and a member of Fermi’s team, Volney Wilson, is credited with coining the term. For decades, insiders believed this referred to Safety Control Rod Ax Man, an homage to Norman
Hilberry. Decades after the fact, Wilson revealed the true story. When an electrician had finished wiring CP-1’s emergency button, he asked Wilson and another physicist, Wilcox Overbeck, what its label should say.

Overbeck:
“Well, what do you do when you push the button?”

Wilson: “You scram out of here as fast as you can.”

And after twenty years of reactors being called the Fermi-Szilard scientific term
piles
, their operators are known as pile drivers.

At 9:45, Fermi announced (for visitors unfamiliar with the mechanism),
“The pile is not performing now because inside it there are rods of cadmium which absorb neutrons. One single rod is sufficient to prevent a chain reaction. So our first step will be to pull out of the pile all control rods, but the one that George Weil will man.”

A recorder’s twitching pen inscribed the permanent data record onto a roll of graph paper, like a lie detector. “This pen will trace a line indicating the intensity of the radiation. When the pile chain-reacts, the pen will trace a line . . . that will not tend to level off. In other words, it’ll be an exponential line. Presently we shall begin our experiment. George will pull out his rod a little at a time. We shall take measurements and verify that the pile will keep on acting as we’ve calculated.”

A little after 10:00, Fermi said, “ZIP out,” and Zinn pulled the rope controlling Hilberry’s manual emergency rod by hand and tied it to the balcony.

Then at 10:37, with all eyes on his instruments, Fermi said,
“Pull it to thirteen feet, George.” Weil threw his switch, a motor buzzed, and the main rod began to withdraw. Marked with a vernier scale to show how much of it remained within the pile, it was now halfway extracted. Everyone in the balcony watched the panel where lights showed the amount of the rod’s penetration, while listening to the staccato tempi of the boron trifluoride counters, barely noticing their clocklike faces. Their click rate increased rapidly, until it stuck a steady beat.

Fermi and his team in the balcony wrote down their findings and computed the results with slide rules. “This is not it,” Fermi said, pointing to the area on the graph paper where the pen would reach when the pile went critical. “The trace will go to this point and level off.”

At 10:42, Fermi ordered the rod pulled to fourteen feet. The counters’ chatter and the pen’s twitch rose once again and settled. The chain had not yet been reached.

At 11:00, he had it extracted to 14.5 feet. The clicks rose and the pen twitched higher, but still the pile had not turned critical.

Norman Hilberry:
“Fermi had, the night before, sat down and computed
what the trace on the recording galvanometer would be for every single position of the control rod. Clearly, if there were any new law of physics, it would begin to show up in an actual deviation of the observed graphs from those he had computed, and each time it hit absolutely right on the nose. I am sure that long before Fermi finally said, ‘George pull it out another ten inches,’ the question had long since been settled in his mind, and it had long since settled in mine, too.”

At 11:15 and 11:25, the rod was inched out again. Each time, Fermi showed his viewers where the instruments would fall, and each time he was correct. The controlled and deliberate experiments he had been known for all his life could not be more apparent than now. Everything was being double-checked. At any moment, the pile would self-sustain.

At 11:35, the automatic, solenoid-controlled ZIP rod was removed. The ratcheting of the counters sounded like a motor come to life. The team watched the graph paper’s spot where Fermi had said critical would be recorded.

Suddenly there was a crash, and the entire team fell into shock. Then, all at once, they realized that the automatic rod had fallen into place. The solenoid’s activation threshold had been set too low. After that problem was fixed, Fermi said, “I’m hungry. Let’s go to lunch.”

While eating, the team and their visitors discussed everything but the experiment.

At 2:00, they reassembled, and at 2:20, Fermi had Weil move the control rod back to its previous spot. The instruments were rechecked.

Thirty minutes later, the control rod was pulled another foot, and the counters ratcheted up into a chatter. The pen was thrown off its chart. But this turned out to be another false alarm; like the automatic rod, the pen’s ratios needed to be reset to accurately indicate fission.

Herb Anderson:
“At first you could hear the sounds of the neutron counter, clickety-clack, clickety-clack. Then the clicks came more and more rapidly, and after a while they began to merge into a roar; the counter couldn’t follow anymore. That was the moment to switch to the chart recorder. But when the switch was made, everyone watched in the sudden silence the mounting deflection of the recorder’s pen. It was an awesome silence. Everyone realized the significance of that switch; we were in the high-intensity region and the counters were unable to cope with the situation anymore. Again and again, the scale of the recorder had to be changed to accommodate the neutron intensity, which was increasing more and more rapidly.”

At 3:20, George Weil at Fermi’s instruction moved the rod another six inches, and five minutes later, Fermi asked for another foot, and it happened: Weil withdrew the rod.

Turning to Compton, his boss, Enrico explained, “This is going to do it. Now it will become self-sustaining. The trace will climb and continue to climb. It will not level off.”

But as he worked his six-inch ivory slide rule, Fermi’s expression seemed to turn grim. He waited a minute, then reran his rule, looking at some numbers he’d jotted earlier on its back side. A few minutes later he looked over the instruments and ran the calculations again. By now, the individual clicks of the counters could not be heard; there was just an insistent buzz, of neutrons attacking nuclei.

Weil:
“I couldn’t see the instruments [so] I had to watch Fermi every second, waiting for orders. His face was motionless. His eyes darted from one dial to another. His expression was so calm it was hard to read. But suddenly, his whole face broke into a broad smile.”

Fermi closed his slide rule and announced with a pleased thrill in his tone, “The reaction is self-sustaining. The curve is exponential.”

For four and a half minutes, the group watched the first nuclear chain reactor producing half a watt of power, their eyes focused on the graph pen, which swept upward and never leveled off. Grad student Leona Woods asked Fermi, in the tone of confirming an instrument’s readout, “When do we become scared?”

Fermi then turned to Zinn: “Okay, ZIP in.” The counters slowed to a fizzle, and the pen stopped its frantic wavering. At 3:53 p.m., it was over. Fermi and Szilard had succeeded in splitting atomic nuclei to produce an immense force. Chicago Pile-1 was the beginning of nuclear medicine, of atomic power and propulsion, and of course the critical start of the Manhattan Project. The Atomic Age was born.

Physicist James Mahaffey: “Fermi’s demonstration of controlled, sustained chain-reacting fission in uranium is the most strangely flawless experiment on record. It was run with 42 witnesses in attendance, dressed in business suits, who watched the world’s 1st operating nuclear reactor do exactly as it was supposed to do. There was no ambiguous evidence, no competing team in another country, no contradictory data, no fudge numbers, and there was no reason to run it a second time to confirm anything. It was simply perfect.”

Eugene Wigner:
“Nothing very spectacular had happened. Nothing had moved and the pile itself had given no sound. Nevertheless, when the rods
were pushed back in and the clicking died down, we suddenly experienced a letdown feeling, for all of us understood the language of the counter. Even though we had anticipated the success of the experiment, its accomplishment had a deep impact on us. For some time we had known that we were about to unlock a giant; still, we could not escape an eerie feeling when we knew we had actually done it. We felt as, I presume, everyone feels who has done something that he knows will have very far-reaching consequences which he cannot foresee.”

Emilio Segrè:
“Probably for Fermi, however, the real victory in the making of a natural uranium reactor had come a few months earlier when he succeeded in building a lattice with
k
> 1, which was tantamount to reaching criticality. In October 1942 while I was in Chicago on a laboratory errand, he locked me up in a room alone to read a few reports on his work. After an hour or two he returned and found me rather speechless and with bulging eyes. Of course I knew of the attempts to obtain a chain reaction with natural uranium, but I had no precise idea of how far the work had proceeded, although my own work was dependent on the production of plutonium and hence on a functioning nuclear reactor. The progress reports I read impressed me as though I had seen a critical pile with my own eyes.”

Eugene Wigner brought out a bottle of Chianti, which he’d been hiding behind his back, to honor the Italian’s success. The bottle was quite a sign of confidence; Wigner had bought it before America entered the war and Italian imports were banned. Enrico popped it open and passed out paper cups for everyone to have a sip. There were no toasts. Later, however, everyone would autograph the bottle’s straw casket.

Arthur Compton called James Conant at Harvard on the phone.
“The Italian navigator has landed in the New World,” he said, in prearranged code, barely able to conceal his excitement.

“How were the natives?” Conant asked.

“Very friendly.”

Arthur Compton:
“One of the things that I shall not forget is the expressions on the faces of some of the men. There was Fermi’s face—one saw in him no sign of elation. The experiment had worked just as he had expected and that was that. But I remember best of all the face of Crawford Greenewalt. His eyes were shining. He had seen a miracle, and a miracle it was indeed. The dawn of a new age. As we walked back across the campus, he talked of his vision: endless supplies of power to turn the wheels of industry, new research techniques that would enrich the life of man, vast new possibilities yet hidden.”