The Day the Atomic Age Was Born

The events that have changed man’s destiny—the invention of the stone ax, the discovery of fire, the drift into the Industrial Revolution—few can be pinpointed in time. But one, possibly the greatest of all, can be timed to the minute. At 3:36 p.m. on 2 December 1942, the world entered the Atomic Age. And I was one of 40-­odd witnesses.

The setting was hardly auspicious: a bleak, drafty, dimly lighted squash court under the abandoned and crumbling stadium at the University of Chicago’s Stagg Field. There, within a pile of uranium and graphite bricks the size of a small house, neutrons were being born by the billion each second and hurled out at velocities of 29,000 kilometres a second. Every one that hit the heart of another uranium atom shattered that atom to produce two neutrons.

Thus, every few minutes, the silent, violent storm was doubling itself in history’s first nuclear chain reaction. We were too awed to speak. The silence was broken only by the staccato rattle of counters keeping track of neutron production.

All our advance reasoning indicated that we were safe. Yet we were pushing into territory never before explored. There was at least a chance that the pile would get out of control; that we would be destroyed and a large, thickly settled portion of Chicago would be converted into a radioactive wasteland. Would this, in fact, be doomsday?

To Tickle a Mosquito

Science sometimes moves at a plodding pace. But, with atomic fission, events had moved at breakneck speed. Only four years before, at Kaiser Wilhelm Institute for Chemistry in Berlin, nuclear chemist Otto Hahn and his young assistant, Fritz Strassmann, had bombarded uranium with neutrons from an external source.

Afterward, chemical analysis showed that something extraordinary had happened. Barium and other substances not there before, had appeared as from nowhere and were mixed with the uranium! But if the two experimenters thought that they had split the heavy uranium into barium and other lighter elements, they weren’t prepared to say so.

Interpretation fell to a former Hahn colleague, Lise Meitner, who because of her Jewish blood, had fled from Hitler’s Germany to Sweden. There, during the Christmas holidays of 1938, she and her nephew, Otto Frisch, discussed Hahn’s data. Possibly, their two brilliant minds concluded, these findings weren’t so mysterious after all. Their friend Niels Bohr, the great Danish physicist, had visualized the nucleus of an atom as a liquid drop. If bombardment added an extra neutron to the nucleus, it might become unstable, elongate and divide. The electric repulsion between the two new droplets would be enormous. Within days, Frisch was putting these ideas to experimental test and finding them to be accurate.

When each heavy uranium atom split into lighter atoms, there was a fantastic release of power—200 million electron volts! By itself this was not enough to tickle a mosquito, but if multiplied by trillions it meant a power yield in quantities undreamed of before. The world might no longer have to depend on the fossil fuels alone—coal, oil, natural gas—and face an energy famine when they were gone.

Nuclear chemist Otto Hahn and physicist Lise Meitner

Still, big questions remained if power was to be coaxed from the atom. Could you smash an atom with one neutron and get a yield of two neutrons that would go along to smash again and produce four, eight, and so on? That would be a chain reaction. Moving slowly, such a reaction would produce heat which could be converted into power. If the reaction proceeded fast enough, you would have a behemoth of a bomb.

The Pure Stuff

A fear was with all of us. The German pioneers in the field had almost certainly foreseen the possibilities of such a bomb. If the Nazis got it first, other countries would be at their mercy. This was therefore a race we in the United States had to win.

We had to find out if a chain reaction was possible. Most of the work on ‘The Metallurgical Project’ (our code name) would be concentrated at the University of Chicago. Arthur Holly Compton, of that institution, would head it, and refugee scientist Enrico Fermi would be charged with building CP­1—Chicago Pile No. 1. Fermi had arrived in the United States from Italy in January 1939. (He and his wife and children had gone from Rome to Stockholm to receive a Nobel Prize, and kept right on going.)

As we started work on CP­1, we had no blueprint, only question marks. We knew that natural uranium spontaneously emits a few neutrons. But they travel too fast to cause fission—like a fast­-moving golf ball that skims over a cup, whereas a slow­moving one would drop in. We had somehow to slow down these neutrons. Graphite seemed to offer the best available means of putting a brake on them. Perhaps some sort of lattice could be arranged—bits of uranium surrounded by graphite? Then neutrons from one bit of uranium would pass through the graphite, slow down, strike into atoms in another bit of uranium and cause fission?

There were catches in the process. Any impurities in the graphite would act as neutron sponges and put out any atomic fire. And there was no graphite as pure as we needed, anywhere—and we’d ant it in 100-­ton lots. The problem with uranium—which we’d want by the ton—was much the same.

Industry and universities threw themselves with admirable energy into making the absolutely pure stuff, although we couldn’t tell them why it was so urgent. By the spring of 1942, driblets of uranium metal, uranium oxide and graphite began to arrive. Pile building began (we were to build 30 experimental piles to provide basic data preliminary to the big one).

The work crews—mainly graduate students—had one of the world’s dirtier jobs. Hands and faces became smeared with greasy graphite. Heavy graphite bricks were slippery, and our fingers were inevitably caught between them when we turned bricklayers.

‘Suicide Squad’

On 7 November, Fermi indicated that we were ready for the big challenge. Enough graphite, uranium metal and uranium oxide had been accumulated for the big pile. Work was blocked out. Walter Zinn bossed the day shift. They would plane and shape the 40,000 graphite blocks—some of these drilled to contain slugs of uranium metal or uranium oxide.

I headed the night shift. We would lay the slippery bricks in exact patterns just as fast as they could be produced. Preliminary calculations indicated that the most effective shape for our pile would be a sphere 24 feet in diameter. The most active uranium we had—the metal—would be in the center, with the less active oxide farther out.

The great sphere began to grow: a layer of graphite, then a layer of graphite bricks containing uranium, and so on. For safety controls, we relied principally on three wooden rods, each with strips of cadmium metal tacked on it, running through the pile. Cadmium, the best of neutron sponges, would dampen any atomic conflagration. One rod would be controlled electrically. A second, the ‘zip’ rod, had to be pulled out of the pile by rope; release the rope and it would zip in. The third was for fine control, and would be hand­operated to achieve the level of neutron activity wanted. Any one of the three rods would quench the atomic fire—unless something unforeseen happened.

As a final precaution, three men would be stationed atop the wooden scaffolding surrounding the pile—a ‘suicide squad’. They would have great flasks of cadmium solution to quench a runaway reaction. “If things get away from us,” Fermi told them, “break the flasks. But watch me, and don’t do it until I drop dead. If you do it before, I’ll use a sledge hammer on you!”

By the time my shift took over on 1 December, we were at the 48th layer, and Fermi had calculated that layer would complete the job. He read what was on my mind. There would be the greatest temptation to pull out the control rods and be the first in the world to observe a chain reaction.

“When you have finished layer 51,” he directed, “lock those rods in place. Everyone be here at eight tomorrow morning.” A few hours later, we completed the final layer. Somewhat reluctantly I followed directions, padlocked our 550-­ton monster for the night, and went home.

Inch by Inch

Morning dawned chill and gray, with a dust of snow on the ground. General Eisenhower ad launched his North African campaign. The battle for Guadalcanal was in its final victorious phases. Work was already under way on super­secret atomic­ bomb plants, on the faith that a chain reaction was possible. If our reactor worked, then, it had the potential not only for death, but for ending a nightmarish war and saving millions of lives.

By eight, we had all filed in and taken our places. I was at a control panel to record instrument readings. Zinn was to pull out the zip rod. George Weil manned the all­important hand rod. The suicide squad was at the ready. Observers stood on a small balcony where spectators had formerly watched squash games. The great show was about to begin.

At 9:45, Fermi, speaking in his quiet voice, ordered the electrically controlled rod out. There was a slight whirring of motors, and the clicking of counters could be heard. Neutron activity was rising. Fermi’s mild gray eyes were on the pen as it moved upward on a piece of graph paper before leveling off. Hardly aware of the presence of others, he manipulated a slide rule. Everything was going according to plan.

Chicago Pile One scientists at the University of Chicago on 2 December 1946, the fourth anniversary of their success. Standing in the front row, on the far left is Enrico Fermi, and on the far right, the author Herbert L. Anderson.

At 10, he ordered Zinn to pull out the zip rod. There was another increase in neutron production—but again nothing massive. At 10:37, Fermi directed Weil: “Pull the hand rod out to 13 feet.” The counter began to roar. Anxious faces looked at the pen sweeping upward. Fermi indicated that it would level off at a certain point, and it did. From time to time he ordered Weil to pull the rod out another few inches. Each time there was an upsurge of neutron activity, and our tension rose proportionately—to a point almost unbearable.

Then the spell was broken. “Let’s go to lunch,” said Fermi. It was like Wellington suggesting a lunch break at the Battle of Waterloo. All rods went back in, and counters fell silent, except for an occasional feeble click. Even at rest the pile produced 1,00,000 neutrons a second.

Atomic Storm

At two, we began again, moving more rapidly this time. At three, the counters had to be recalibrated—slowed down to dampen the rattle and give meaning to their sounds. Further, the pen was going off the graph paper.

At 3:19, Fermi ordered the hand rod withdrawn another foot. He glanced at the graph, consulted his slide rule, then turned to Compton, standing beside him. “The next foot should do it,” he said. At 3:36, the hand rod was withdrawn a final foot. And, minutes later, he spoke again: “This time it won’t level off. The curve is exponential”—meaning that the activity would go on doubling and redoubling.

For 17 agonizing minutes the atomic storm raged, growing increasingly violent. The pile was heating up. The first chain reaction was under way. In ominous silence mankind was entering a new age. Fission, we knew, would create new radioactive elements—and with the greatest rapidity. Our pile could be safe one moment and deadly shortly afterward. Understandably, worry was written on many faces. Eyes were on radiation meters, which showed that we were rapidly approaching danger levels.

At 3:53 Fermi turned to Zinn. “Zip in,” he said. As the rod slipped into the pile, activity diminished rapidly. The great drama was coming to an end. We had made a safe journey into the unknown.

If the world is depressed by the fact that two atomic bombs were dropped 32 months later, it might take heart from the enormous benefits that have accrued from fission. Much of medical science has been revolutionized, and the pace of other research quickened. Britain is already deriving ten percent of its electric power from the atom, and today the US Atomic Energy Commission is spending more on peaceful atomic pursuits than on weaponry.

On that bitter, blustery winter afternoon a quarter of a century ago, history was changed. Possibly it was for the worse. Hopefully, time will prove it was for the better.

Editor’s Note:

Since the success of the Metallurgical Project, nuclear power has significantly shaped society through both benefits and challenges. Countries have leveraged nuclear energy for low-carbon electricity production, bolstering energy security and combating climate change and allowed for medical advancements in fields such as cancer treatment. Conversely, catastrophic nuclear disasters in Chernobyl (1986) and Fukushima (2011), as well as its use in the creation of weapons of mass destruction, underscore the potential for widespread environmental and human harm by this transformative technology.

About the author:

Herbert L. Anderson earned his doctorate in physics when, at 28, he was selected by the late Enrico Fermi to help construct the first chain­-reacting atomic pile. From 1958 to 1963 he was director of the Enrico Fermi Institute at the University of Chicago, where he was professor of physics.

First published in Reader's Digest March 1969