Annoyed, Szilard left his hotel for a walk. He was standing at a stop-light in the Bloomsbury neighborhood, waiting to cross the street, when a bizarre and malevolent possibility occurred to him. He had dutifully studied Chadwick’s results the year before, but perhaps more important, he had also just read H. G. Wells’s The World Set Free and its fantastical account of a mineral that could be provoked into a “chain reaction” that would liberate the binding energy of heavy atoms all at once to create an inferno.
The neutron, thought Szilard as he stood in the London damp, was more than a piece of garbage. It would, in fact, be the perfect arrow to slice through the barrier of an atom’s shell and directly engage the heart of the nucleus. This was not a new thought; Rutherford had predicted as much in his Royal Society lecture thirteen years before. But what if lobbing a neutron at the center of an atom resulted in the discharge of two neutrons that would, in turn, find their own nuclei to strike? The effect would be exponential, a riotous blossoming just as Wells had predicted: a recursive firing of component parts approaching the infinite halving of the flight of Zeno’s arrow.
“As the light changed to green and I crossed the street, it . . . suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbs one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction,” said Szilard, years later.
In another account of the same moment, he said he realized: “In certain circumstances it might be possible to set up a nuclear chain reaction, liberate energy on an industrial scale, and construct atomic bombs.”
He was excited and horrified by this insight. The fictional had become suddenly possible, even likely.
“Knowing what this would mean, and I knew it because I had read H. G. Wells, I did not want this patent to become public,” he said. “The only way to keep it from becoming public was to assign it to the government.”
Szilard made his patent in the name of the British Admiralty, where it was received and promptly forgotten, despite his written warning that “information will leak out sooner or later. It is in the very nature of this invention that it cannot be kept secret for a very long time.”
The discovery of the neutron revolutionized physics not only because it helped complete the diagram of the atom but also because it became an excellent tool for poking around the interior of different atoms, in much the same way that a Texas oil driller will sink a pipe into bedrock to see what lies below the surface.
At the University of Rome, the genial workaholic Enrico Fermi began bombarding the entire menu of the elements with neutrons to see what would happen. Lighter elements seemed impervious, but Fermi found that aluminum, once irradiated, transformed itself into an odd substance with a half-life of twelve minutes—an effect duplicated in heavier elements such as titanium, barium, and copper.
The strangest behavior of all was at the very top of the weight scale. When uranium was hit with neutrons, it ejected an electron and left behind a peculiar radioactive salad of unidentified elements with half-lives ranging from one to thirteen minutes. It would take time to sort out what had actually happened to Fermi’s uranium, but it would eventually become clear that within the hash of metallic leftovers in his dish lay the secret of the atomic bomb.
Events began to move rapidly. The last half of the 1930s became a frenetic phase in physics as the study of uranium gripped laboratories on both sides of the Atlantic. The discoveries multiplied, like a chain reaction in itself.
“It was a period of patient work in the laboratory, of crucial experiments and daring action, of many false starts and many untenable conjectures,” wrote the nuclear scientist J. Robert Oppenheimer, years after the fact. “It was a time of earnest correspondence and hurried conferences, of debate, criticism and brilliant mathematical improvisation. For those who participated it was a time of creation. There was terror as well as innovation in their new insight.”
In Copenhagen, the great physicist Niels Bohr envisioned uranium’s nucleus as “a wobbly droplet,” an idea that helped explain why it was casting off pieces of itself. At the University of Chicago, Arthur J. Dempster discovered a rare version2 of uranium with three fewer neutrons—thenceforth known as U-235—scattered through the rock like chips in a cookie. These atoms were more unstable than their neighbors, more likely to shatter if hit with a neutron. In Berlin, the research team of Otto Hahn and Lise Meitner aimed a stream of neutrons at a sample of uranium and found mysterious traces of middle-order elements such as barium and lanthanum inside the residue. In Paris, Frédéric Joliot-Curie found much the same thing.
And finally, at Christmastime in 1938, a major breakthrough arrived when a young Austrian professor named Otto Frisch, the son of a painter and a concert pianist, sat down for breakfast at a country inn with Lise Meitner, who happened to be his aunt.
Frisch had been working in a Hamburg laboratory before the Nazis took power in 1933. He had never cared much for politics, but the new anti-Semitic climate in Germany made it uncomfortable for him to stay, and he emigrated to London to take a teaching position. Frisch enjoyed whistling Bach fugues while at work in the laboratory and compulsively made pencil sketches of his colleagues during lectures; he later said the trick was to exaggerate their most noticeable features. He would have made a fine newspaper cartoonist had he not already been entranced with atomic physics.
Frisch was a shy man, and he found himself fumbling and stuttering when he was introduced briefly to Albert Einstein in the hallway of a university. But Frisch had a rare gift for a theoretical physicist—he was a superb classroom teacher who also spoke in plain language. His gift was not just of personality, it was one of dimensional visualization. Frisch knew how to conceive of invisible phenomena in vivid strokes, perhaps an extension of his knack for capturing the essence of a colleague’s face in pencil by emphasizing a square jaw or bushy eyebrows. This talent was on full display when he joined his aunt for breakfast at the inn in Sweden where Meitner had been puzzling over a letter from Hahn in which he reported the presence of an uninvited mineral—barium—inside the wreckage of bombarded uranium. Hahn would later say that he had contemplated suicide when the true implications of this experiment became clear to him.
None of that guilt was present between Frisch and his aunt as they talked over breakfast and during a midmorning walk in the woods. Frisch suggested a novel idea. What if the nucleus was held together not so much by interior forces as by the electrical tension on the surface? Such a structure might be vulnerable to destruction when hit by a neutral particle, as the skin of a balloon is vulnerable to a needle. On a fallen log, the two stopped to rest, and Meitner pulled out a pencil and some paper she found in her purse. Frisch drew an oval that was grotesquely squashed in the middle to demonstrate the idea to his aunt—instead of funny faces, he was drawing funny atoms—and the two worked out some crude calculations.
This was the final untangling of the riddle of what was happening inside uranium when it admitted a neutron invader. Its center simply cracked into pieces, leaving behind radioactive fragments of its former self. The total mass was less than that of the uranium, meaning that part of it had escaped as pure energy. This explained the bizarre wreckage humming with fleeting half-lives that had so puzzled the Italian researchers in 1934. Frisch realized what Enrico Fermi could not have known at the time: The uranium atom had not transmuted, but actually had been split in his laboratory. This would seem to confirm what Albert Einstein had postulated in 1905: that even a tiny amount of matter could be converted into mammoth amounts of energy, tempered by the unchanging speed of light.
Frisch was at first doubtful of his own theory, reasoning that all the uranium deposits lying in the earth would have gone up in flames a long time ago if such a thing were possible. But now, he realized, after replicating Fermi’s experiment, the reason they had not was because of the dilution of the unstable U-235 atoms. They occurred in quantities of
about 0.7 percent inside natural uranium. All those neutron-spewing atoms were simply too far from one another to create a chain reaction. It would be like a drop of snake venom that loses its ability to kill when dissolved in gallons of water. But what if that venom could be distilled?
Frisch sent his results to the British journal Nature, which scheduled them for publication on February 11, 1939. The split halves of the uranium would be rushing apart at a speed of one-thirtieth the speed of light, he estimated: enough energy to make a grain of sand twitch from the popping of a single atom. This was a stupendous amount of force, perhaps as much as two hundred million electron volts, from such a small package. And if there was a large cluster of uranium atoms that started to pop? Two would create 4 would create 8 would create 64 would create 4,096. After eighty cycles of this, the number of exploding atoms would be a trillion trillion. It would all take place in less than one second.
Frisch borrowed a term from biology to describe the effect. When a single cell elongates and pulls apart into two, it is called fission. The word was appropriated to describe this new horizon of physical chemistry, invoking, as it did, a mysterious protosexual phase of life, majestic in its opacity. The spermlike neutron, unknown until recently, was the only thing that could pass through the armor of the electron shell and meet the heart of the nucleus. Frisch later wrote: “It was like possessing a magic arrow that would fly through the forest for miles until it found its mark.”
In a later memo to the British government, he predicted that a brick of uranium no heavier than a gallon jug of milk would “produce a temperature comparable to that of the interior of the sun. The blast from such an explosion would destroy life in a wide area. The size of this area is difficult to estimate, but it would probably cover the center of a big city.”
The fast-talking Leo Szilard meanwhile got himself hired on Fermi’s team at Columbia University to work on the problem of chain reaction that had first haunted him at a London traffic signal.
He had been trying, fruitlessly, for the last six years to raise money for secret research and to keep the trick of atom splitting away from Nazi Germany. As part of his campaign, he wrote to the founder of the British General Electric Company, enclosing a copy of the prophetic opening chapter of Wells’s The World Set Free.
“It is remarkable that Wells should have written those pages in 1914,” he wrote, continuing with a lace of sarcasm. “Of course all this is moonshine, but I have reason to believe that in so far as the industrial applications of the present discoveries in physics are concerned, the forecast of the writers may prove to be more accurate than the forecasts of the scientists.”
Szilard was impatient with the dithering, not just from the private sector but on the part of the governments in London and Washington, which had shown no interest in this fearsome quirk of nature that might either save the world or incinerate it. The future, as he saw it, was just as grim as H. G. Wells had foreseen. Scientific imagination was drawn immediately to warfare, and the primary use of the awesome power locked inside the atom would be for military ends. Conflicts could soon be waged—even possibly averted—with an otherwise unremarkable element at the top of the periodic table. Control of a peculiar glass dye from Bohemia would soon become a vital matter of national security.
In September 1938, Adolf Hitler had annexed the Sudetenland—a disputed border province of Czechoslovakia full of German speakers—sparking a diplomatic crisis that eventually led the British prime minister, Neville Chamberlain, to make the notorious statement that “peace for our time” had been secured. In the annexation, Hitler had unknowingly absorbed a jewel: the old mining town of St. Joachimsthal, one of the world’s only known supplies of uranium. Should the Nazis also gain control of the diggings at Shinkolobwe, the United States and Britain would have none of the raw material necessary to construct an atomic weapon. The heaviest element in the periodic table was now widely believed to be the key to unleashing the thunderous force of binding energy. Newspapers were amplifying the news, even before Frisch’s data could be published in Nature. Niels Bohr announced the results at a symposium in Washington, D.C., and the New York Times soon reported that “work on the newest ‘fountain of atomic energy’ is going furiously in many laboratories both here and in Europe. . . . It constitutes the biggest ‘big game hunt’ in modern physics.” Luis Alvarez at the University of California at Berkeley read the news in a wire story reprinted in the San Francisco Chronicle while he was getting a haircut. “I got right out of that barber chair and ran as fast as I could to the Radiation Lab,” he said. Uranium was suddenly in the international spotlight. Citing a January 30, 1939, press conference by the dean of the Columbia University physics department, the Times described the element as a “cannonball,” capable of yielding “the greatest amount of atomic energy so far liberated by man on earth.”
Thankfully, it was not that simple. Thousands of tons of uranium ore would have to be crushed, separated, and somehow enriched into a block of pure U-235 to develop the kind of jug-size bomb core necessary to flatten a city. This was a problem that transcended physics—it reached into geology, engineering, economics, and politics. There was no evidence as yet of a German atomic program, but Szilard thought it prudent not to waste time. He didn’t know how to drive a car, so he enlisted a fellow Hungarian physicist, Eugene Wigner, to take him out to Nassau Point on Long Island, where the grand old man of science, Albert Einstein, had a summer cottage and was spending a few days sailing on Peconic Bay.
The pair got lost on a sandy lane and had to stop a small boy for directions to “Professor Einstein’s house.” Once inside the sitting room, teacups on their laps, the Hungarian visitors described the idea that had been spreading with viral speed among physicists since the publication of Frisch’s article: that a slow neutron aimed at the center of uranium isotope 235 could trigger a splitting that would break the binding force and unleash two hundred million electron volts of electricity, as well as knock loose the fugitive neutrons that would instantly crack the neighboring atoms to create a massive, uncontrolled chain reaction.
Einstein’s amiable reply, as recorded by Szilard: “Daran habe ich gar nicht gedacht!” (“I never thought of that!”)
The resulting conversation in the summer cottage had less to do with physics than with politics and, in particular, with the existence of rock piles in Czechoslovakia and at Shinkolobwe. Szilard made a case that Einstein ought to alert his friend Elisabeth, queen dowager of Belgium, that the radioactive ore from her colony in the Congo ought to be transferred to the control of the United States.
Einstein was “very quick to see the implications and perfectly willing to do anything that needed to be done,” recalled Szilard. “He was willing to assume responsibility for sounding the alarm, even though it was quite possible that the alarm might prove to be a false alarm. The one thing most scientists are really afraid of is to make fools of themselves. Einstein was free of such a fear and this above all else is what made his position unique on this occasion.”
Einstein later allowed his signature to be affixed to the bottom of a measured letter written mostly by Szilard. It would ultimately not be addressed to the queen dowager of Belgium, but would be delivered by hand through an intermediary to President Franklin D. Roosevelt in the Oval Office on October 11, 1939. Though it does not mention Shinkolobwe by name, the threat in the Congo looms behind every sentence.
The letter, in full:
Sir:
Some recent work by E. Fermi and L. Szilard, which has been communicated to me in manuscript, leads me to expect that the element uranium may be turned into a new and important source of energy in the immediate future. Certain aspects of the situation which has arisen seem to call for watchfulness and, if necessary, quick action on the part of the administration. I believe therefore that it is my duty to bring to your attention the following facts and recommendations:
In the course of the last four months it has been made probable—through the work o
f Joliot in France as well as Fermi and Szilard in America—that it may become possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium like elements would be generated. Now it appears almost certain that this could be achieved in the immediate future.
This new phenomenon would also lead to the construction of bombs, and it is conceivable—though much less certain—that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory. However, such bombs might very well prove to be too heavy for transportation by air. The United States has only very poor ores of uranium in moderate quantities. There is some good ore in Canada and the former Czechoslovakia, while the most important source of uranium is Belgian Congo. In view of this situation you may think it desirable to have some permanent contact maintained between the administration and the group of physicists working on chain reactions in America. One possible way of achieving this might be for you to entrust with this task a person who has your confidence and who could perhaps serve in an unofficial capacity. His task might comprise the following:a. To approach Government Departments, keep them informed of the further development, and put forward recommendations for Government action, giving particular attention to the problem of uranium ore for the United States;
Tom Zoellner Page 5
