Genius in the Shadows

by William Lanouette

  (Egon Weiss Collection)

  PART TWO

  1933–1945

  CHAPTER 10

  “Moonshine”

  1933

  Work for the Academic Assistance Council (AAC) kept Leo Szilard so busy during the spring and summer of 1933 that he had no time to read the physics journals, but when he heard from academics that Lord Ernest Rutherford was to speak at the annual meeting of the British Association for the Advancement of Science, he wanted to attend. Then director of the eminent Cavendish Laboratory at Cambridge, Rutherford was a nuclear physicist renowned for his early work in the structure of the atom. Szilard’s feisty nature kept him from holding anyone in awe, but he deeply respected Rutherford as a nuclear pioneer.

  At the beginning of this century, Rutherford had discovered and named two of the three kinds of radiation: “alpha,” the positively charged radioactive particles, and “beta,” which have a negative charge.1 With chemist Frederick Soddy in 1906, Rutherford had postulated the radioactive “transmutation” of atoms—their disintegration and change when bombarded by radioactive particles. In 1911, Rutherford envisioned the atom as having a small, heavy core, or “nucleus,” of positively charged “protons.” Around the nucleus whirled lighter, negatively charged “electrons.” Two years later, Niels Bohr combined Rutherford’s view with new theories of quantum physics (explaining how energy is emitted and absorbed in discrete and impulsive amounts) to create a description of the atom still popular today. With Bohr’s discovery, “atomic” physics became “nuclear” physics—the study of the atom’s nucleus.

  In 1919, the year he became director at the Cavendish Laboratory, Rutherford published the first evidence that the nuclei of atoms can be charged artificially and that they split off when they are bombarded with alpha radiation. But more had to be understood about the mechanism of atoms before their energy could be released, and two necessary steps in this direction both occurred at the Cavendish in 1932. The young physicists John D. Cockcroft and Ernest T. S. Walton managed to split atoms by a new method; not, as Rutherford had done, with naturally radioactive radium but by using high-voltage electricity to speed up streams of hydrogen protons that bombarded small samples of lithium, a light metal. This was the first nuclear transformation produced by purely artificial means when, as the two reported in Nature, “the lithium isotope of mass seven occasionally captures a proton and the resulting nucleus of mass eight breaks into two alpha particles, each of mass four. . . .”2

  In the same year, physicist James Chadwick identified a third particle in the atom: the “neutron.” His discovery gave a new, more complete description to the atom: a nucleus of both positive protons and neutral neutrons surrounded by orbiting, negative electrons. Having no charge, a neutron could, in theory, enter and leave an atom’s nucleus more easily than a charged proton or electron. At first, Chadwick and others saw the neutron only as a research tool, although it would later provide the means of releasing the atom’s energy. Szilard, too, only wondered briefly about the neutron’s potential uses for research when he first read of it in Nature3 The morning of Rutherford’s lecture, September 11, 1933, Szilard awoke with a bad cold and stayed in bed. But the next morning, curious about the talk he had missed, Szilard paged through The Times and spied this intriguing column of type:

  THE BRITISH ASSOCIATION

  — — — — — —

  BREAKING DOWN

  THE ATOM

  — — — — — —

  TRANSFORMATION OF

  THE ELEMENTS

  Farther down the column, Szilard saw:

  THE NEUTRON

  NOVEL TRANSFORMATIONS

  He read on, about Rutherford’s survey of “the discoveries of the last quarter century in atomic transmutation,” to this summary:

  HOPE OF TRANSFORMING ANY ATOM

  What, Lord Rutherford asked in conclusion, were the prospects 20 or 30 years ahead?

  High voltages of the order of millions of volts would probably be unnecessary as a means of accelerating the bombarding particles. Transformations might be effected with 30,000 or 70,000 volts . . . [and] we should be able to transform all the elements ultimately.

  We might in these processes obtain very much more energy than the proton supplied, but on the average we could not expect to obtain energy in this way. It was a very poor and inefficient way of producing energy, and anyone who looked for a source of power in the transformation of the atoms was talking moonshine.

  “Lord Rutherford was an expert in nuclear physics,” Szilard thought, and “an expert is a man who knows what cannot be done.” Szilard found that last paragraph “rather irritating because how can anyone know what someone else might invent?” Perhaps, thought Szilard, the famous Lord Rutherford is talking “moonshine.”

  In the days that followed, he pondered Rutherford’s declaration in a routine favored for serious thought: long soaks in the bathtub and long walks in the park. There were no large parks near the Imperial Hotel, but its Bloomsbury neighborhood was a patchwork of Georgian terraces and tree-lined squares, so along and through this shaded cityscape Szilard walked and wondered that chilly September, seeking with each quick step a way to disprove the “expert” Rutherford.

  “I was wondering about this while strolling through the streets of London,” Szilard recalled. A week or two passed, and then it happened. Southampton Row, the main street in front of the Imperial, is a busy but narrow thoroughfare lined with banks and shops. “Walking along Southampton Row, I had to stop for a streetlight, and at the very moment when the light turned green, it occurred to me that Rutherford might be wrong. . . .”4 Szilard’s pause in his normally brisk movement would change his life, and ours, and ultimately the history and fate of the twentieth century.

  He recalled:

  As I was waiting for the light to change and 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 absorbed one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction. I didn’t see at the moment just how one would go about finding such an element or what experiments would be needed, but the idea never left me.5

  What he did see at that fateful intersection were two concepts needed to free the energy locked in the atom: the “nuclear chain reaction” and the “critical mass” needed to set off and sustain it.

  Szilard quickly seized the implications: “In certain circumstances it might become possible to set up a nuclear chain reaction, liberate energy on an industrial scale, and construct atomic bombs.” Suddenly the H. G. Wells novel he had read a year before had a grave new meaning. Atomic bombs were science fiction to Wells when he wrote The World Set Free in 1913, and they were frightful to contemplate when Szilard first read about them in 1932. But by the fall of 1933, Rutherford’s challenge and Szilard’s response were moving atomic bombs away from fiction to scientific fact. Atomic bombs, and the chain reaction that would power them, became Szilard’s “obsession,”6 pushing aside his plans for a new career in biology.

  “The thought did not come entirely out of the clear sky,” he said later, but seeing both the mechanism and its fateful implications when he did was Szilard’s special insight. The chain-reaction concept was common in chemistry, studied by Szilard’s friend Michael Polanyi and others, and an atomic bombardment process similar to Szilard’s had appeared in the Nature account of Rutherford’s speech on “transmutation”:

  Beryllium, of mass 9 and charge 4, when bombarded, captures an alpha particle of mass 4 and charge 2, giving rise to a structure of mass 12 and charge 6 and emitting a neutron of mass 1 and charge zero.7

  To enhance this process, Szilard substituted a neutron for the alpha particle that bombarded the beryllium. “I was wondering whether Rutherford was right when it occurred to me that neutrons, in contrast to alpha particles, do not ionize [or electrically charge] the substance through which t
hey pass. Consequently, neutrons need not stop until they hit a nucleus with which they may react.”8 Szilard further assumed that when one neutron entered the nucleus, two might be expelled, creating a chain reaction that seemed awesome. Two calculations fired his imagination, and his fears.

  First, if a neutron could strike an atom’s nucleus with such force that it would emit two neutrons, then with each collision the freed neutrons might double in number. One neutron would release 2, which would each strike an atomic nucleus to release 4. These would each strike a nucleus, releasing 8, then 16, 32, 64, 128, and so on. In millionths of a second, billions of atoms would split, and as they tore apart, the energy that held them together would be released.

  Second, the amount of energy released could be huge. If Einstein’s calculations of 1905 were accurate, then his famous formula E = mc2 assured that Energy equals mass multiplied by the speed of light (whose symbol is c) squared. The number for mass was minute, but the number for light speed in this equation is immense, and at least in theory, the amount of energy latent in matter was also immense.

  What allowed Szilard to put together the stray clues about a nuclear chain reaction, clues that scientists working directly in atomic research had overlooked? No conclusive answer is possible, given the mysteries of Szilard’s creative mind and the scant details he recalled. But this much is clear: While teaching discussion courses at the University of Berlin, Szilard followed developments in nuclear physics by reading scientific journals. He also questioned anyone who knew about a subject, often with the precision of a prosecuting attorney. Unlike his colleagues in nuclear physics, Szilard was no experimentalist. Instead, he was free to speculate haphazardly—intuitively—about the implications of other scholars’ practical works, not bound to move each insight only as far as its next logical step and experiment.

  In fact, Szilard’s restless mind led him to consider studying biology in 1933 because he desired to be a theorist in a field still practical and analytic. Moreover, his early speculations about biology might have included the rapid multiplication of dividing cells. Szilard was both predisposed and eager to pick seemingly unrelated facts from diverse scientific sources, then blend them whimsically. And while living on his savings, Szilard had no other scientific or academic burdens and deadlines. No family. No close friends. No household chores. No pets. No hobbies. When he wanted to think about the chain reaction, he could. And did. For days and nights at a time.

  Beyond his eclectic and intense work habits, Szilard’s thoughts often sprang from his feisty spirit of defiance. Contradiction led him to pose an opposite view to whatever he heard. In novel ways he loved to play the constructive dissident. Rutherford must be wrong, Szilard assumed. But how? Perhaps by overlooking some basic mechanical process in nuclear transmutation, one even simpler than the structural changes that the experts at the Cavendish then studied.

  Perhaps Szilard’s idea for the nuclear chain reaction was even aided by the London traffic light itself—in a sequence that appears to move spheres of light from green to amber to red to amber to green. Viewed from across the street, the change of lights can resemble colliding billiard balls. Not a knocking, one against another, but something subtler; a blur of one into another, through another.

  By whatever means Szilard conceived the nuclear chain reaction, as soon as he had, he turned his mind on himself and tried to prove the idea right or wrong. He retreated to his room at the Imperial. Thinking. Scribbling calculations. Sketching hasty schematic patterns. For a week or more he saw no one, broke his meditation only to eat meals sent up by room service, and each night fell exhausted into bed to sleep.9 Szilard soaked for hours at a time in his bathtub, dozed and daydreamed on his bed, and forced his impulsive vision at the traffic light into twin hypotheses. Not only did he see a chain-reaction mechanism to release the atom’s energy; he also realized why a critical mass of material was necessary: Only with many atoms close together could the neutrons reach other nuclei and not escape.

  Having fled Nazi Germany that spring, Szilard also saw beyond his hypotheses to their political implications. He had feared for months that the Nazis were preparing for war and now worried that in the coming conflict Germany might be the first to build—and use—atomic bombs.

  By mid-October, Szilard moved out of the Imperial Hotel, perhaps to find quieter or cheaper quarters, and rented a flat at 97 Cromwell Road, in a block of Victorian row houses a few doors west of Gloucester Road.10 There he continued his calculations, but apparently found it difficult to concentrate. A glance at the morning papers would have been distraction enough. Germany had quit the foundering League of Nations, and rhetoric at the Nazi party’s rallies in Nuremberg was increasingly anti-Semitic and bellicose. No longer just a political aberration, the Nazi party was now the German state.11

  A few weeks later, Szilard hoisted his two suitcases and moved from Gloucester Road back into central London, to the Strand Palace Hotel, a white marble structure in the busy thoroughfare that links the newspaper and legal world of Fleet Street with the government offices around Trafalgar Square and Whitehall. The Strand Palace appeared more conventional than the eccentric Imperial, but its lower rates appealed to Szilard now that the academic year had begun and he was not working. Although he entertained friends in the hotel’s elegant dining room, among them the AAC’s secretary, Esther Simpson, to save money, Szilard rented a tiny room that had once been a maid’s closet.12 His new room had no private bathtub, but shared one down the hall, and it was there that Szilard continued his brainstorming, usually beginning each day with a soak around nine to “dream about the possibilities” of nuclear physics.13

  “Are you all right, sir?” asked the maid, knocking on the bathroom door at about noon. Yes. Szilard was quite all right, thank you. He had just been thinking; in particular about beryllium, a steel-gray metal that he knew could give off neutrons. What if extra neutrons split off when beryllium was bombarded by neutrons? “The reason that I suspected beryllium of being a potential candidate for sustaining a chain reaction,” Szilard later wrote, “was that the mass of beryllium was such that it could disintegrate into two other particles and a neutron.”14 This Szilard may have known before, but it, too, was suggested in the Nature account of Rutherford’s speech, so he had good reason for his suspicion. The only difference was that the beryllium described in Nature was bombarded by alpha particles, not by neutrons. Yet elsewhere in the same article neutrons had been described as “a very powerful weapon of research.”15

  Other elements might also split and release extra neutrons, Szilard thought, and “this possibility intrigued me so much that I gave up the idea of shifting to biology. . . .” He credits this decision to three people: H. G. Wells, who showed Szilard “what the liberation of atomic energy on a large scale would mean”; and Frédéric and Irène Joliot-Curie, the French nuclear scientists who at about this time demonstrated that radioactivity could be created artificially and need not depend on nature’s elemental design. Working in Paris, the Joliot-Curies had bombarded aluminum foil with alpha particles, then noticed that the foil continued to emit radiation after the stream of particles was shut off. “If elements could be made radioactive by bombarding them with alpha particles,” Szilard reasoned, “then why shouldn’t elements be made radioactive when they are bombarded by neutrons?” And if neutrons could make an element radioactive, then science had “a very simple tool” to study nuclear physics.

  “In science it is not enough to think of an important problem on which to work,” Szilard reflected years later. “It is also necessary to know the means which could be used to investigate this problem.” In short, Rutherford’s challenge to nuclear transmutation had driven Szilard to the chain-reaction concept, and the Joliot-Curies’ discovery of artificial radiation had provided the means that would make the concept work.16

  Cautiously, Szilard mentioned his “nuclear chain reaction” idea to a distinguished professor of physics he had met on his rounds for the AAC, George Page
t Thomson at the Imperial College of Science in London. (Thomson would share the 1937 Nobel Prize in physics for discovering diffraction phenomena in electrons.) When Thomson showed little interest, Szilard called on Prof. Patrick M. S. Blackett in the physics department at the University of London. Blackett then specialized in the use of Wilson cloud chambers, instruments that detect ionizing radiation. (For this research, and for work on cosmic rays, he would receive the 1948 Nobel Prize in physics.) But from him, too, Szilard “couldn’t evoke any enthusiasm.”17 Szilard then believed that while beryllium did not disintegrate spontaneously, it might yet split if “tickled” by a neutron.

  “What one ought to do,” Szilard told Blackett, “would be to get a large mass of beryllium, large enough to be able to notice whether it could sustain a chain reaction.” But beryllium was so expensive that it was almost unobtainable, even in tiny quantities. “Look,” Blackett finally complained to Szilard, “you will have no luck with such fantastic ideas in England. Yes, perhaps in Russia. If a Russian physicist went to the government and said, ‘We must make a chain reaction,’ they would give him all the money and facilities which he would need. But you won’t get it in England.”18

  With this rebuff Szilard turned, in December 1933, to British industry. Szilard may have feared the chain reaction’s use in a bomb, but he also fancied its commercial possibilities as a source of power. Through Michael Polanyi’s contacts at General Electric (U.K.), Szilard approached the director of the company’s research laboratories.19 That same month, Szilard gave his friend Esther Simpson power of attorney to protect his patents and assets. At year’s end those assets stood at 1,594 pounds, 8 shillings, and 9 pence.20 “Who knows?” Szilard may have wondered as he dreamed about a new Industrial Revolution fueled by nuclear power. Someday it may be millions.

  CHAPTER 11