Chapter Six
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The Deuton Affair
Ernest’s invitation to the Solvay Conference was more than an acknowledgment of the Rad Lab’s standing in international science; it was the lab’s coming-out party.
The October 1933 conference, which was devoted specifically to “the structure and properties of the atomic nucleus,” was the seventh in the series founded by the Belgian chemist and industrialist Ernest Solvay in 1911. Ernest’s appearance would be only the eighth by a US physicist since the inception. He would be the lone American in attendance this time, rubbing shoulders and debating the fine points of nuclear physics with the most glittering stars of European science. Among the other guests would be Einstein, Heisenberg, Bohr, Erwin Schrödinger, and Marie Curie and her daughter and son-in-law, Irène and Frederic Joliot-Curie, none of whom had anything like the resources at Ernest’s disposal when they did their groundbreaking work. There would be eight delegates from Cambridge alone, including Rutherford, Chadwick, and Cockcroft.
Ernest lost no time spreading the news of his invitation, declaring himself to be “surprised and tremendously pleased” in letters to Swann and other friends, and cadging $300 from the university to help cover travel expenses. In the weeks before the event, he prepared detailed comments on papers submitted by Cockcroft and Chadwick—laying out, in effect, a direct challenge to the work of the revered Cavendish Laboratory. But Lawrence was about to step onto thin ice. When he plunged through, he would almost drag the reputations of the cyclotron and the Rad Lab down with him, sullying the perceived promise of Big Science.
The subject at hand was a particle known then as the “deuton.” (Today the accepted term is “deuteron.”) A nucleus of heavy hydrogen, or deuterium, the deuton and Ernest Lawrence made each other famous.
The neutron and deuterium were both discoveries from that miraculous year of 1932, when nuclear physics gave up some of its greatest secrets. Deuterium had come first. Harold Urey, a Berkeley chemistry PhD working at Columbia, had set out to identify a heavy isotope of hydrogen that had been postulated by Raymond Birge, among others. Urey’s quarry was an atom of mass 2 that by Birge’s reckoning appeared in hydrogen gas at a concentration of 1 for every 4,500 atoms of hydrogen-1. His discovery was a triumph of scientific deduction, for the neutron, which gives deuterium its additional weight, was not discovered until many months after he identified the isotope itself. When James Chadwick found the neutron, that uncharged nuclear particle that Rutherford had been seeking for a decade, the puzzle of deuterium’s atomic structure was complete: while the nucleus of common hydrogen comprises a lone proton, deuterium’s nucleus—the deuteron—comprises both a proton and a neutron.
Urey’s discovery inspired Gilbert Lewis, his former Berkeley mentor and the legendary head of its Chemistry Department, to search for a way to produce large quantities of heavy water—that is, water molecules with deuterium in place of common hydrogen—to function as a medium for experimentation on the new isotope. Living up to his reputation for experimental resourcefulness, Lewis conceived an electrolytic process involving distilled battery acid; soon he was turning out samples with a 50 percent concentration of deuterium, a higher purity at greater volume than anyone else. Lewis was so confident of his process that he was profligate with what was still a rare substance. “He liked to tell how he fed some of his first heavy water to a fly,” recalled one student, “and it rolled over on his back and winked at him.” More plausibly, he told of feeding his initial sample by eyedropper to a mouse, which showed no ill effects after ingesting what was then “the world supply” of heavy water.
Lewis soon was providing heavy water in quantity to Ernest Lawrence, who vaporized it into gas to pump into the cyclotron. Lewis was an avatar of old-school solitary research, but he was delighted to play a role in stretching science’s boundaries. Now he became a fixture in the Rad Lab, wreathed in smoke from his ever-present black cigar, as he perched on a stool and watched Ernest’s assistants bombard every element they could find with this new, startlingly effective projectile.
Lawrence’s excitement about the possibilities of the deuton matched Lewis’s. Any other ion twice as heavy as a simple proton—a proton-proton pair, for example—would have packed an extra wallop when aimed at a target nucleus, but because of its doubled charge also would have been more strongly repelled by the target’s own positive charge. The deuton, however, had twice the heft of the proton but not the additional charge, so it should be better at penetrating a target’s electromagnetic field. But even Ernest was unprepared for how effective the deuton turned out to be. “As soon as we used deuterons,” Livingston recalled, “we got enormous yields of reactions that had never been seen before.” Aimed at lithium, the deuton produced ten times as many disintegrations as did mere protons (measured by the emission of alpha particles); aimed at beryllium, the yield jumped a hundredfold.
“Ernest’s love affair with the deuteron beam was legendary,” Luis Alvarez would observe later. Eventually the Rad Lab was able to manifest the projectile’s power visibly by deflecting deutons out of the vacuum chamber and into the air via a platinum “window”: Lawrence would never tire of displaying for visitors the eerie purple glow produced by the deuton beam as it ionized nitrogen in the air. But there was much more to it than a purple glow. Every element bombarded with deutons yielded copious alpha particles, signifying their disintegration.
The discovery returned Lawrence to a round-the-clock schedule at the Rad Lab, supervising the bombardment of dozens of elements with his magic bullet. For light elements like lithium and beryllium, the high yield was not particularly surprising, but the same thing happened with heavier atoms like gold and platinum. At last, the Rad Lab was humming with excitement over experimental results, not merely from the achievement of building a bigger machine. Finally, the lab was exploiting the advantages that made it unique: in this case, Lewis’s large supply of deuterium combined with the high energies produced by the cyclotron. No lab in the world could match it in either respect. Suddenly the Rad Lab was looking like a respectable rival to the Cavendish, which was still basking in the glow of Chadwick’s discovery of the neutron. That was especially true of the Rad Lab’s work with heavier elements, which required bombardments at energies well beyond the relatively meager powers of the Cavendish’s Cockcroft-Walton apparatus.
“All of a sudden we were flooding the world with papers on nuclear physics,” Stan Livingston recalled, “in a field that no one else could enter because they didn’t have the deuterium and they didn’t have the high energies.” The deuton, Livingston added, “was what made the Berkeley laboratory famous. We were opening up a whole new field of science.” Before the end of May, Ernest authorized Berkeley’s publicity department to issue a release detailing the “transitions” seen in lithium, beryllium, boron, nitrogen, fluorine, aluminum, and sodium, and declaring that “at this rate of progress, one dares not guess what will be achieved in nuclear physics within a few years.”
That was only the beginning. As they prepared for the formal unveiling of their deuton results to the world in the July 1933 issue of Physical Review, the Rad Lab team noticed that every bombardment, no matter the target, emitted protons of identical energy and range—eighteen centimeters, or about seven inches, in air. According to conventional nuclear physics, this was extraordinary, even bizarre: nuclei of different weights would be expected to emit disintegration products of widely variable energies, with the heavy elements producing the more energetic recoils. “I am almost bewildered,” Lawrence wrote Cockcroft.
His perplexity did not last long. Within a few days, he proposed a solution: the protons were disintegration products not of the targets but of the deutons themselves, which were “exploding” upon contact with the atomic nuclei. This conclusion led to another equally astonishing hypothesis: if the shattering of the deuton imparted equal energy to its two constituents, proton and neutron, then simple math yielded a weight for the neutron o
f one atomic mass unit, or “unity.” (The mass unit was then pegged at one-sixteenth the weight of the oxygen atom.) This was a neutron much lighter than any other lab had postulated.
Lawrence’s results bore important implications for nuclear physics. His neutron’s weight directly contradicted the value proposed by the Cavendish, which was in the range of 1.0067 to 1.0072 units. The Cavendish understandably harbored a proprietary interest in the characteristics of the particle it had discovered, not to mention a native pride in its ability to extract precise measurements from its meticulously hand-built equipment. It was not about to take Lawrence’s challenge lying down. A major battle between small science and Big Science was taking shape in the run-up to the Solvay.
Initially, Lawrence’s brash salesmanship held the stage. During a May conference at Caltech honoring the visiting Niels Bohr, he alluded to the lightweight neutron while describing the disintegration of eight heavy targets, up to aluminum, by deuton bombardment. Bohr pronounced the results a “marvelous advancement.” Caltech president Robert Millikan suppressed his institution’s feelings of rivalry with Berkeley to compliment Lawrence on his “altogether extraordinary” discoveries.
Then it was on to the annual meeting of the American Physical Society, held in Chicago in the glare of the 1933 World’s Fair. This was Ernest’s debut on the national stage. He proved to be fully up to the challenge, reigning as the star of two front-page articles in the New York Times and a prominent feature in Time magazine. The Times’s science correspondent, William L. Laurence, labeled Berkeley’s deuton “a new miracle worker of science . . . The most powerful cannon yet found for liberating relatively enormous stores of energy locked up in the inner core of the atom.” Cribbing a metaphor from Francis Aston of the Cavendish, Laurence reported that the energy unleashed from a glass of water could power the ocean liner Mauretania “across the Atlantic and back again.” He introduced Ernest Lawrence to his readers as the leader of a “scouting party” of Berkeley wunderkinder, most of them “still in their early thirties.”
Lawrence’s talent for communicating with a lay audience was the theme of Time’s report. The article began by describing Bohr’s becoming entangled in his microphone cord, drawing a pained high-pitched squeal from the loudspeaker. “It was much easier, and more pleasant, to understand round-faced young Professor Ernest Orlando Lawrence of the University of California tell how he transmuted elements with ‘deuton’ bullets.” Time had detected the transition taking place between the “philosophizing” old guard of small-scale physics represented by “Theorist Bohr,” whom the audience “tried hard to understand,” and the new breed of strapping young experimentalists such as Ernest Lawrence, who skipped blithely over the thickets of theory to fire deutons at atoms of lithium “like a boy with a sling shot.” Lawrence had been talent-spotted by Time; his elevation to the magazine’s cover boy as the symbol of modern American science would soon follow.
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The Cavendish, meanwhile, had not been idle. Ernest Rutherford was as quick as Lawrence and Lewis to divine the virtues of the deuton as a nuclear projectile. Unable to produce deuterium in his own lab, he acquired a tiny supply from the visiting Gilbert Lewis that May—about half a cubic centimeter of pure heavy water, or a tenth of a teaspoon, sealed in three delicate glass ampoules. Mark Oliphant developed a method of converting the water to gas with virtually no loss, allowing the lab to recycle the precious supply over and over again.
Generously, Rutherford sang Lawrence’s praises to Lewis, offering congratulations to “Lawrence and his colleagues for the prompt use they have made of the new club to attack the nuclear enemy . . . These developments make me feel quite young again.” But Rutherford’s colleagues found reason to doubt Lawrence’s results. Knowing that the immense energies available to Lawrence via the cyclotron were hopelessly out of reach of their equipment, they opted for lower energies but a higher proton current—less power but more particles. They had no trouble finding Lawrence’s 18-centimeter protons, but only in the lighter elements lithium and beryllium. At the Cavendish, gold resisted the disintegration effect, except for a modest result the scientists traced to contamination of the heavier targets by light impurities such as boron. Tellingly, Oliphant detected proton emissions even from a clean steel target, which should have been all but inert. Having also determined that the emission rate increased with the length of the bombardment, he concluded that deutons were “sticking to the target,” and therefore that what Lawrence interpreted as the disintegration of the bombarding deuton was, in fact, deutons merely striking other deutons on the targets’ surfaces. In other words, Lawrence’s targets were contaminated—his supposed great discovery the product of poor technique. The difference in experience between the two labs told the tale: to the veteran experimentalists of the Cavendish, contamination was a familiar and well-understood phenomenon, but not so to the brash bombardiers of Berkeley.
As the Solvay drew near, interest in the deuton spread beyond Berkeley and the Cavendish, as did doubts about Lawrence’s disintegration theory and, consequently, his calculation for the neutron’s weight. From Merle Tuve at the Carnegie Institution came a sharply worded warning to his boyhood friend “Ernie” about his tendency to jump to unwarranted conclusions before all the facts were in. Lawrence wrote back, at once chastened and defensive, on the eve of his departure for Brussels. “I quite agree that the production of neutrons from beryllium is no evidence for the disintegration of deutons and a low mass for the neutron,” he wrote. “However, I think we have now pretty conclusive evidence on the point . . . We have observed neutrons from targets other than beryllium in just the amount we expected.” He set sail brimming with confidence. To his friend Henry Barton, director of the American Institute of Physics, he wrote that he was prepared “to convince anybody that the deuton is disintegrated.” The toughest audience he ever faced was waiting for him across the Atlantic.
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Lawrence arrived in Belgium only a few weeks after he engaged in a minor dustup with Rutherford, at long range, over the prospects for useful energy from the atomic nucleus. At a September meeting of the British Association for the Advancement of Science, Rutherford had thrown cold water on the very idea: “Energy produced by the breaking down of the atom is a very poor thing,” he cautioned. “Anyone who says that, with the means at present at our disposal and with our present knowledge we can utilize atomic energy, is talking moonshine.”
The “moonshine” quote raced around the world, heartening skeptics. “Perhaps this will at least partially cool the ardor of irresponsible writers who have . . . told their impressionable readers that . . . the energy now locked up within the atoms contained in a mere thimbleful of matter will drive a liner across the Atlantic and back,” declared Scientific American magazine. When it was brought before Lawrence, however, he took a very different line. He agreed with Rutherford that the energy produced by nuclear reactions was a “poor thing,” but he attributed this to “purely a matter of marksmanship. At the present time it is possible to break up the atom by disintegrating its nucleus only about once in a million ‘shots’ . . . But the fact remains that when a ‘hit’ is made, the atom gives up about twenty times as much energy as was needed to break it . . . Personally, I have no opinion as to whether it can ever be done, but we are going to keep on trying.”
Superficially, the two Ernests seemed to be in direct disagreement, and that was how their statements were taken at the time. In truth, however, their views were not so divergent. Rutherford had carefully specified that he was thinking in terms of “the means at present at our disposal.” He certainly was not ruling out that at some point in the future, the “marksmanship” mentioned by Lawrence would improve to the point that the energy required to split the atom would fall well below the resulting yield. The big difference between them was that for Lawrence, the future might well be now. In this, as in many other scientific debates when foresight would eventually trump nearsightedness
, Lawrence was right.
In any case, discussion at the Solvay would turn not on predictions of the future but on results nearer at hand. Lawrence knew the Cavendish delegates were skeptical not only of his deuton theory but also of the cyclotron itself as a laboratory tool. He had received copies of the participants’ papers in advance and marked up their texts accordingly—angrily crossing out a line in Cockcroft’s paper asserting that “only small currents are possible” from the cyclotron and scribbling the marginal note “Not true!”
At the conference, Cockcroft sugarcoated the Cavendish’s doubts about the exploding deuton by labeling Lawrence’s contention not necessarily erroneous but certainly premature: “It is rather superfluous to discuss further the nature of the transformations . . . until we have more experimental information”—preferably from his own accelerator, its current, if not its energies, so much stronger than that of the cyclotron. “Our present information does not suffice.” Rutherford and Chadwick stated flatly that they had not found Lawrence’s suspiciously light neutrons in any of their bombardments and saw no reason to revise their calculation of the neutron’s weight to conform to Lawrence’s.
Lawrence was more surprised to hear his deuton theory come under sustained attack from other European delegates. Werner Heisenberg argued that the Rad Lab’s experimental results simply could not be reconciled with nuclear theory, and showed his contempt for American science by declaring flatly that it was Lawrence’s results, not established theory, that must yield. Theory dictated that if the supposed disintegration were occurring within the nucleus’s electric field, the production of protons and neutrons would diminish as the targets got heavier. Niels Bohr, who had so fulsomely lauded Lawrence at Caltech, now backed his friend and student Heisenberg, positing that even if the deuton did split after entering a target nucleus, the speed and range of the ejected proton would increase with the weight of the target—not remain constant, as Lawrence had found. Marie Curie and the Joliots proposed a neutron even heavier than Chadwick’s, at a value that solved numerous riddles of nuclear activity in one stroke. They tried to let Lawrence down gently, speculating that perhaps there were different types of neutrons with varied weights; but their posited neutron weight ultimately would prove to come closest of all to the right answer. Lawrence did his best to field all these challenges, but plainly he was overmatched.
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