CHAPTER TEN
CHICAGO
FERMI PLANNED TO TEST his latest prototype reactor in a forest twenty miles southwest of Chicago. His calculations convinced him that a runaway chain reaction spewing deadly radiation was an impossibility. Nevertheless, the distance from the city provided an extra measure of protection. Unfortunately, a labor strike delayed work on the reactor building. Worried about losing more ground to Heisenberg, Fermi was unwilling to wait, so he suggested an alternate location: a squash court inside the abandoned University of Chicago football stadium. Given the chance, albeit remote, of a catastrophic accident, Fermi and his Manhattan Project bosses knew the university president was not likely to approve, so they neglected to inform him of their plans. 81
The day of the test, December 2, 1942, was bitterly cold. Inside the stadium underneath the west stands, Fermi, bundled in his coat and hat, picked up where he left off in New York. The stakes this time could not have been higher.
The United States was at war, and American soldiers were dying on the battlefield. The U.S. State Department had just confirmed rumors of a Nazi extermination campaign against Jews in Nazi-occupied Europe. 82 An estimated two million men, women and children had been killed, and Enrico and Laura were desperately worried about the fate of her brother, sisters and father whom they had left behind in Rome. For Fermi, building a working nuclear reactor was no longer an academic exercise; it was a first step in producing a plutonium bomb and potentially winning the war.
Fermi’s Met Lab associates and some 30 high school dropouts waiting for their draft notices had spent weeks hauling tons of graphite blocks and bricks containing uranium slugs into the stadium and assembling the reactor. 83 As technicians made their final preparations, Fermi and his half-frozen colleagues watched from a balcony overlooking the unheated squash court. Below, George Weil, a young Met Lab scientist, waited for Fermi’s signal to remove the cadmium rods which were soaking up neutrons preventing a chain reaction.
Fermi had built 30 prototypes preparing for this moment. He was confident this one would work. Not quite so certain, his fellow onlookers watched in tense silence. Among them was his Columbia University colleague Leo Szilard.
Several months earlier Szilard had received a vaguely worded telegram from a scientist who knew Heisenberg. The telegram, sent from neutral Switzerland, has been lost, but Szilard had briefed the director of the Chicago Met Lab on its content, and he wrote a memo stating: “that the Germans have succeeded in making the chain reaction work. Our rough guess is that they may have had the reaction working for two or three months.” The memo warned, “there is a real danger of bombardment by the Germans within the next few months using bombs designed to spread radioactive material in lethal quantities.” 84
Fermi and his fellow scientists, no doubt, knew about the memo. An atom bomb in the Nazi arsenal, even a “dirty bomb” that killed by spreading radioactive material, could alter the balance of military power in Europe and throughout the world for generations.
On Fermi’s signal, George Weil removed all but one of the rods from the reactor. After checking his calculations, Fermi signaled Weil to begin inching out the last one. Inside the reactor, split nuclei spewed out thousands, then millions of neutrons. A counter similar to a Geiger counter emitted an arrhythmic clicking noise that rapidly transformed into a steady static. As the spectators held their breath, Fermi remained calm, stopping every few minutes to compare the readings to his estimates.
Over the next hour the clicking intensified as the shivering spectators stomped their feet to keep warm. When the intensity grew too great for the neutron counter, a chart recorder took over, its pen plotting a slowly rising line on a rotating cylinder of graph paper. Then, suddenly, the line angled sharply upward. 85
Fermi held up his hand, confirming what everyone already knew. The reactor had gone critical. One or more neutrons from each split U235 nucleus had managed to find and split another U235 nucleus. The chain reaction was self-perpetuating.
It was 3:49 in the afternoon. Fermi let the reaction run for four minutes before reinserting the rods and shutting it down. The relieved spectators uncorked a bottle of Chianti. Everyone signed the bottle’s straw covering. Those barely decipherable signatures are the only record of who was there that day.
“For some time we had known that we were about to unlock a giant,” Project physicist Eugene Wigner would later write, “still we could not escape an eerie feeling when we knew we had actually done it.” 86
Leo Szilard was frightened. “I shook hands with Fermi, and I said I thought this day would go down as a black day in the history of mankind.” 87
The reactor, a massive structure 20 feet tall, 25 feet wide containing 770,000 pounds of graphite and 93,000 pounds of uranium, generated only half a watt of energy, barely enough to light a flashlight bulb, but enough to keep the Allies within striking distance of Heisenberg in the race for the bomb. 88
As Fermi wrapped up the Chicago experiment, civilian death tolls in Europe mounted. The Germans had systematically targeted civilians in Poland, in bombing raids on British cities during “the London blitz” and in the Nazi death camps. The United States Air Force had initially held back, limiting its targets to German military and industrial facilities. But in 1943 the gloves came off, and it expanded its industrial targets to include worker housing around those facilities.
“We must face the fact that modern warfare as conducted in the Nazi manner is a dirty business,” President Roosevelt told the American people. “We don’t like it . . . but we are going to fight it with everything we’ve got.” As the “dirty business” continued, it prepared the way for even more killing. It made what was once “unthinkable,” a weapon of mass destruction like an atom bomb, “thinkable.” 89
No nation had ever wielded such a powerful weapon. How much energy would it generate? How wide a swath of destruction would it leave? One mile? Two miles? How many lives would it take? No one could be sure. The science of nuclear-fission was still in its infancy. There were no precedents. “Most experience in life can be comprehended by prior experiences,” the physicist Norris Bradbury would later write, “but the atom bomb did not fit any preconceptions possessed by anybody.” 90
The largest explosion ever to hit a populated area came from an accidental blast in Canada during World War I. Oppenheimer used that explosion to estimate the damage from an atom bomb. 91
On December 6, 1917, a French munitions ship, the SS Mount Blanc , sailed into the harbor in Nova Scotia. From there it planned to join a convoy of ships sailing to a port in France. Onboard were 2,300 tons of picric acid, a powerful explosive, 200 tons of TNT, and numerous drums of high-octane fuel. 92
At 9:04 that morning, while negotiating a narrow passage into the harbor, the Mount Blanc collided with a Norwegian ship, setting off a powerful blast that destroyed two square miles of the north end of the city and ignited dozens of fires. The explosion killed more than 1,500 people instantly and injured thousands more.
Hospitals filled to overflowing. Freight cars two miles away were blown off their tracks. Telephone and telegraph facilities were downed for 30 miles around the city. The Toronto Daily Star reported: “Screams of suffering children stabbed the heart.” It appeared “as if some giant scythe had blown down [the] neighborhood and then spat fire on it.” 93
It took more than two thousand tons of high-energy chemical explosives to level those two square miles of Halifax waterfront. How would an atom bomb compare? The volume of chemical explosives onboard the Mount Blanc far exceeded the anticipated volume of U235 or plutonium in an atom bomb. But U235 and plutonium would carry a far greater punch. Chemical explosives release at most five electron volts of energy per atom. The split uranium nuclei in an atomic bomb would yield 200 million electron volts. 94