Genius in the Shadows

by William Lanouette

  Initially, Szilard aimed to bombard his elements with neutrons in order to create new compounds that would be medically useful. He hoped that their temporary radioactivity could help trace liquids and gases within the human body. But a few days’ work convinced Szilard and Chalmers that neutrons made some new compounds so unstable that their constantly changing states were difficult to control or calibrate. This was not the Fermi effect, but something quite different. Faced with this unexpected result, many scientists would have abandoned their idea for some other project. But Szilard, in the words of his later colleague physicist Maurice Goldhaber, “turned this apparent defeat around, and it led him to a brilliantly simple method of isotope separation.”31 They had just devised a way to isolate radioactive and nonradioactive forms of the same element.

  Some basic physics will help to explain their feat. The isotopes of an element have the same number of positively charged protons in their nuclei but differing numbers of uncharged neutrons. As a result, the isotopes’ atomic weights can vary, yet they remain chemically indistinguishable. Beryllium offers a good example. All beryllium found in nature is Be9, a stable element that is not itself radioactive. (In this case, the number 9 denotes a nucleus containing 4 protons and 5 neutrons.) Beryllium’s unstable isotopes, having fewer or more neutrons in their nuclei, are Be7, Be8, and Be10.

  In the empty laboratory that summer, Szilard and Chalmers beamed neutrons from a radon-beryllium source onto iodine and measured their results. To Hopwood, then on holiday, Szilard wondered in a letter “whether we can separate the radioactive Iodine from the bulk of the bombarded Iodine,” admitting that “this sounds ‘blasphemous’ to the chemist, but I hope it can be achieved. . . .”32 Until Szilard and Chalmers began their work, different “isotopes” of the same element could only be separated through tedious and expensive methods. One was “gaseous diffusion” through a series of porous barriers; another was “electromagnetic” isolation involving costly apparatus. In 1934 it was deemed a major achievement when Mark Oliphant and others at the Cavendish Laboratory managed to separate less than one-ten-millionth part of a gram of a lithium isotope by using electromagnetic currents.

  When Szilard and Chalmers tried to isolate iodine128 by bombarding an iodine compound (ethyl iodide) with neutrons, they freed an irradiated isotope from the compound radioactively. Their results were published in the scientific journal Nature that September, giving researchers a simple method for separating isotopes. Known as the Szilard-Chalmers effect, this technique became widely used. With time they also recognized that slight amounts of the irradiated element sometimes do remain in the original compound, so their method had medical uses, after all—as “tracers” in the body.33

  In September 1934, Szilard was praised for his discovery during an international conference on nuclear physics in London.34 Although largely self-taught, “these experiments established me as a nuclear physicist,” Szilard said wryly a quarter century later, “not in the eyes of Cambridge but in the eyes of Oxford.” At Rutherford’s Cavendish Laboratory, Szilard said, he was considered “just an upstart who might make all sorts of observations, but these observations could not be regarded as discoveries until they had been repeated at Cambridge and confirmed.”35

  At St. Bartholomew’s Hospital, Szilard enhanced his “upstart” reputation by arguing with the staff about publishing “prematurely” the results of his experiments—a matter later resolved amiably. And he ignored certain hospital procedures and regulations. One required that the radium needles he and Chalmers used be returned to a safe between 6:00 P.M. and 9:00 A.M. But as they worked late many nights, Szilard found this routine impossible to follow.

  “You must understand my point of view if I suggest to you that you are to pay more attention to the customs of the hospital,” Hopwood scolded Szilard. “It is the point of view of a man who is very much aware of the fact that these walls you see from the window have been standing here for over five hundred years.”

  “I understand that very well,” Szilard replied, “but please keep in mind that these walls may not be standing here ten years from now.” Szilard remembered this tense conversation years later, after the area around St. Paul’s was heavily bombed in World War II and the wall seen from Hopwood’s window was destroyed.36

  While still at St. Bartholomew’s in the summer of 1934, Szilard asked his friend Michael Polanyi for permission to work as his guest in Manchester: another instance of Szilard’s frantic indecision, for as soon as Polanyi obliged, Szilard changed his mind.37 Instead, he searched for private investors to finance his chain-reaction research, and beginning that fall, Szilard made new overtures to Chaim Weizmann, the renowned chemist and Zionist leader. Weizmann was unable to raise the 2,000 pounds (then about $10,000) that Szilard needed to systematically bombard all seventy elements with neutrons. Michael Polanyi and the University of London’s Frederick Donnan brainstormed one fall weekend to find Szilard “a very rich man, who would let you do just as you please, asking only for a dividend at the end,” and on his own Polanyi sought out a possible “silent partner” for Szilard’s research. But that fall Polanyi also reported a complaint against Szilard that would be heard for years to come: “Donnan told me that there is an opposition to you on account of taking patents,” he wrote.38

  By late November 1934, Szilard completed an experiment to test beryllium’s potential for a chain reaction, drawing on research conducted in Berlin and London. This appeared in Nature on December 8, coauthored by Szilard, Arno Brasch, Fritz Lange, A. Waly, T. E. Banks, Chalmers, and Hopwood as “Liberation of Neutrons from Beryllium by X-rays: Radioactivity Induced by Means of Electron Tubes.” Brasch, Lange, and Waly were in Berlin, assisted by Lise Meitner.39 This work proved to be well ahead of its time by its use of X-rays, which Szilard knew about from work in the 1920s with Hermann Mark.

  For this experiment, Szilard had his Berlin colleagues bombard beryllium (Be9) with X-rays. This produced photoneutrons, which they beamed at a sample of bromoform, a colorless, heavy liquid used for chemical synthesis that is analogous to chloroform. Then Szilard had the bromoform flown to London, where he and Chalmers extracted the radioactive beryllium using their new isotope-separation method. This experiment was conducted using an incorrect measurement for the mass of the Be9, which misled Szilard to speculate that beryllium might be “metastable” and release neutrons when it was bombarded.40 Szilard was then alone among scientists in his belief that nuclear chain reactions might liberate the atom’s energy; at the time, his friend and mentor Albert Einstein was touring the United States, where he told newspaper reporters that such efforts would be “fruitless.”41

  In late December, Szilard and Chalmers drafted an article for Nature.42 Somehow rumors about their work reached Rome by the first week in January 1935, prompting Fermi and his colleagues to rush into similar experiments and to publish their results hastily. Although the Rome physicists looked upon Szilard with some amusement, they were also coming to respect his forays into the unknown.43

  By then, Szilard had packed his two suitcases, checked out of the Strand Palace, and caught a train to Oxford, hoping to talk his way into Lindemann’s Clarendon Laboratory and continue chain-reaction experiments. Szilard’s first stop in town—as it was for many central European refugees—was the spacious cottage home of Francis Simon, a physicist who had studied and taught in Berlin and recently emigrated from Breslau (now Wroclaw, Poland). The Simons entertained students constantly in their two large sitting rooms and deep garden; there was always an extra place at dinner, and their Sunday teas were known for a predictable spread of goodies and an unpredictable array of guests. When Szilard decided to stay in Oxford for a few weeks, the Simons referred him to the English physicist James Tuck, who sublet a room with breakfast in his house on Banbury Road. At breakfast after the first night, Tuck said he hoped Szilard had had a comfortable night.

  “Oh, not quite,” Szilard said. “I didn’t like the bed at all.”

  “Well
, you’ll get used to it,” Tuck reassured him. “It takes a little time to get used to a bed.”

  At breakfast the next morning, Szilard reported, “It’s still very bad.” Again Tuck reassured him.

  On the third morning, Szilard appeared pale and haggard. “There can’t be anything wrong,” Mrs. Tuck insisted, and went upstairs to check. There she discovered Szilard’s trouble. The charwoman, when she had remade the bed for this new lodger, had forgotten to put back the mattress. Szilard had been sleeping on the bedsprings.44

  Through Simon’s introduction, Szilard met Lindemann at the Clarendon Laboratory, a neo-Gothic complex on Parks Road near the university cricket ground. Hoping for a fellowship, Szilard described his research project confidently, and when Lindemann could offer no support, Szilard decided to stay on in Oxford anyway. He drafted a fresh round of appeals to rich men, seeking support for a new organization that would combine social and scientific interests—in a way, a practical version of the Bund and a forerunner to his idea for the Salk Institute.45

  Poking around the Oxford colleges, as he had at the research institutes in Dahlem, Szilard quickly sensed that his exuberance was not considered charming but quite odd. Even his friends had their doubts. “Terrible! Terrible!” Szilard announced as he walked in on Simon one day. “There’s a case of cholera in London!”

  “Okay,” Simon said, nodding, not really believing him but already expecting the unusual from Szilard.

  “I’m getting worried,” Szilard said two days later when he stopped in again. “Fifty deaths from cholera! What should we do?”

  “Oh, come, come,” Simon replied. “You exaggerate.”

  But the next day Szilard returned to warn: “It’s getting worse! More cases of cholera. More deaths.”

  “Szilard! Where do you learn these things?” Simon demanded. “I’ve not heard of this.”

  “It’s in The Time’s,” Szilard insisted. And it was. In the column of news from a hundred years ago.46

  This mistake typifies Szilard’s frantic life. Driven by the irrepressible energies and fears of his mind, he yearned to understand everything his senses touched, though seldom for very long. Many scientists are inquisitive as they try to comprehend and explain their universe and their own existence. But for Szilard, knowing and understanding were not enough. His thoughts about his world attained a reality all their own, and his life became an urgent struggle to animate these thoughts and perhaps control them. For many hours a day Szilard kept company with thoughts that drew him, logically and persistently, toward a future that often he alone could see.

  Impatient that there were no openings at Oxford, Szilard packed his two bags again and sailed on the SS Olympic, landing in New York on February 21, 1935. There he hoped to explore the laboratory situation at NYU and tend to the US immigration papers he had filed in 1931. After a visit with Einstein at Princeton, Szilard wrote to Lindemann with an impertinent scheme for chain-reaction research at Oxford. Einstein had been offered a place at Christ Church College, Szilard wrote. Why not apply that money to Szilard’s work at the Clarendon?

  His wandering mind prevented Szilard from conducting any systematic research at NYU; the only work he finished was to build an ionization chamber to study the scattering of slow neutrons. As it turned out, slow neutrons would prove to be the key to a chain reaction, and Szilard may have already suspected this, but he was too impatient to take his suspicions the next logical step to a conclusive experiment. Within a few months, Szilard’s hosts at NYU seemed impatient with him, too. “They emphasize that I could leave here at twenty-four hours’ notice if required,” he wrote Lindemann.47 And by the end of March, when Lindemann offered a research fellowship at the Clarendon, Szilard promptly accepted.

  Typically, Szilard had trouble focusing on any project for long, and in the months spent at NYU’s labs he enjoyed discussing the chairman’s experiments with electric eels and searched restlessly for something else to think about and to do. One research opening seemed possible at His Master’s Voice, the electronics company that became part of RCA.48 In New York, Szilard also visited the Research Corporation, a nonprofit group that reinvested profits from patents on scientific discoveries into new research—later a model for his own finance schemes.49

  Before sailing for England, Szilard walked around the Columbia University campus, dropping in on physicist Isidor I. Rabi, whom he had met before in Berlin and New York, and on chemist Harold Urey, who had recently received the Nobel Prize for isolating the heavy hydrogen isotope deuterium, a discovery that fascinated Szilard.

  “Szilard kept telling me which experiments I should conduct,” Rabi recalled years later. “Finally, I said, ‘Leo, if you really think this is so important, do it yourself.’ Of course, he never did.”50

  Irresistibly, politics engaged Szilard again when Pyotr Kapitza, the Russian physicist who had worked at the Cavendish Laboratory for twelve years, was barred by Stalin in 1934 from returning to England after a visit to Moscow. Kapitza’s detention was on Szilard’s mind when he attended the first Theoretical Physics Conference in Washington during the spring of 1935 with Paul Dirac. A Cambridge physicist who had married Eugene Wigner’s sister, Dirac had shared the 1933 Nobel Prize in physics with Schrödinger for their equations explaining quantum mechanics. He was friendly with Kapitza at Cambridge and a regular member of his weekly discussion “Club.”

  At the Washington meeting, Szilard and Dirac tried to alert their American colleagues to Kapitza’s plight, proposing a scientific boycott of the Soviet Union. But their only ally was Nobel laureate Robert A. Millikan, a physicist (and president of the California Institute of Technology) who was noted for his anti-Soviet views.51 When Szilard at NYU and Dirac at the Institute for Advanced Study in Princeton could muster scant support for Kapitza, Szilard devised a bolder scheme: smuggle Kapitza from Russia in a submarine.52

  The “Washington meeting,” held each spring since 1935 at the Department of Terrestrial Magnetism (DTM) of the Carnegie Institution of Washington, was, despite the awesome title of the locale, an informal and lively event in the physics community, a fair-weather gathering of the great minds in a small but expanding field. The conference was cozy, with no more than three dozen scientists attending, at the DTM’s spacious grounds near the city’s Rock Creek Park and at the National Academy of Sciences (NAS) by the National Mall. Here Szilard could talk with several nuclear innovators: Gregory Breit from Wisconsin, who had helped land his NYU appointment; Hans Bethe, then at Cornell; George Gamow, a Russian émigré to America whom he had met at Cambridge; and Rabi from Columbia. Szilard also met Edward U. Condon, a lively and humorous journalist-turned-physicist from Princeton, and Ernest O. Lawrence, the pioneer with cyclotrons from Berkeley. On the steps of the NAS building on April 27, Szilard urged Lawrence to keep secret his research on neutrons, at one point raising his index finger to his lips in a sign of silence.53

  One sunny afternoon, Szilard and Bethe decided to take a stroll and ambled by the Lincoln Memorial through West Potomac Park. Stopping by the Tidal Basin, they watched as tourists in rented paddle boats glided by the famous cherry trees. And they talked physics. For the first time, Szilard tried to tell Bethe about the nuclear chain reaction but instead carried the idea a step further to describe how neutrons might escape by an entirely different process.

  Until then, Szilard had proposed splitting heavy elements apart to release their neutrons, but that day he told Bethe how neutrons might also be released by forcing light elements together. Szilard suggested compressing Urey’s deuterium by immensely high temperatures. At the Cavendish Laboratory a year earlier, Rutherford and Oliphant had studied deuterium, and they had bombarded it with other deuterium atoms.54 But Bethe realized later that Szilard’s suggestion was the first time he had heard about a thermonuclear reaction that might become self-sustaining. Bethe wondered about how such a process might occur, especially how it might be confined once the reaction began. Years later, the concept of magnetic confineme
nt would make the idea of nuclear “fusion” a possibility. In 1935, by the banks of the Potomac on that sunny spring afternoon, it all seemed intriguing and romantically impractical to Bethe, like so many of Szilard’s ideas.55

  Back at NYU Szilard realized for the first time the significance of his work with Chalmers, and deciding to focus on studying the chain reaction in Oxford, he sailed from New York aboard the SS Majestic on May 23, 1935.56 From London he wrote Lindemann an urgent letter about a matter of “great seriousness” involving nuclear physics. Indium—a soft, silvery metal extracted from zinc—had by now replaced beryllium as Szilard’s candidate for creating a chain reaction, and he was eager to study it.57

  This June 3 letter to Lindemann spelled out Szilard’s strategies for conducting nuclear research while keeping the results secret among a small circle of atomic scientists “in England, America, and perhaps in one or two other countries. . . .” He proposed filing patents on discoveries but assigning control to “some suitable body” that would “ensure their proper use.” Szilard said that “obviously it would be misplaced” to consider his own patents as “private property” or to “pursue them with a view to commercial exploitation for private purposes.” Instead, he recommended that a £1,000 budget be raised from private donors to allow him to hire two laboratory assistants—all, ultimately, in the name of trying to “greatly accelerate the building up of nuclear physics in Oxford. . . .”58

  A week later, Szilard admitted to science historian Charles Singer (an active member of the AAC) that he had abandoned efforts to finance nuclear research, yet urgently predicted that his work approached “the starting point of a new industrial revolution.” He predicted a fifty-fifty chance that the proposed experiments might work out. But, Szilard wrote, “the disaster to which all this may lead is more imminent than the pleasant changes it may bring about, since applications for purposes of war are closer at hand than anything else and go beyond anything one is likely to conceive.”59