Lise’s options were limited. Only the Netherlands and Sweden were likely to accept her with an Austrian passport, and a paid position as a physicist was hard to come by since so many scientists had left Germany. Her friends abroad worked tirelessly on her behalf, and Bohr finally found her a position in Stockholm. All she had to do was get out quietly and quickly before the Nazis officially sealed the border against her. She almost decided not to leave, afraid that she’d be arrested, but on July 13, 1938, she boarded a train and, accompanied by a Dutch friend, crossed into the Netherlands without incident. Lise was safe.
In a laboratory in Rome that July, Enrico Fermi was concerned. He was the most prominent physicist in Italy, with his laboratory full of the best minds in the country. He had brought fame and honor to his beloved country with his research on radiation and the effects of slow neutrons. But for the past two years, Italy’s fascist government had been Germany’s ally, and now it had finally embraced Hitler’s racist ideology. Fermi’s wife, Laura, was Jewish. If similar race laws were passed, Laura would fall prey to them, and so would their children. It did not matter how famous he was or what he could provide to their country: Italy would have no mercy. He would have to leave as well. He had to come up with a plan.
Lise Meitner had not been happy about the idea of leaving Berlin. At that time, she was not sure she wanted to go to Stockholm. She would have preferred England, where she had friends and the development of atomic physics was already under way. However, thanks to a friend, the offer to work at Manne Siegbahn’s new Nobel Institute for Experimental Physics was her only secure option. From the Netherlands, she flew to Copenhagen, where she was met by the friendly and familiar face of her nephew, Otto Robert Frisch. She spent a few days there with Niels Bohr and his wife before heading on to Sweden.
Naively, she had believed things would work out as they had in Berlin. Unfortunately, unlike Hahn, Siegbahn was not happy to have a woman in his institute, and the spirit of collegiality that had permeated the Kaiser Wilhelm Institute in Berlin was nowhere to be found in Sweden.
The new laboratory held no appeal for her. It was sterile, plain and white, and it still lacked all the necessary equipment for conducting experiments. But what she missed most were her companions; she longed for the friendships she had built during the years alongside Hahn and Strassmann and hovered over the experiments that had yielded so much to her.
Then one day she had a visitor—two, actually. A small, slightly balding man, accompanied by an attractive woman, entered her laboratory, shouting her name. Confusion turned to shock when she realized who had come to visit. Fermi and his wife, Laura, were in the country to pick up the Nobel Prize he had been awarded for his work with neutrons. Lise was flattered by the visit. As he introduced the two women to each other, Enrico noticed that Lise looked tired and worried and wore the tense expression that all refugees had in common. Laura also sympathized with Lise’s dilemma of being in a country that was not her own.
The Nobel Prize had given Fermi’s family the excuse they had been looking for, not only with a financial reward but also the ability to travel. They had been able to go abroad as a family, and now that they were out of Italy, they were not going back. In about ten days, they would be sailing to the friendlier shores of the United States. He hoped one day to meet Lise again under better circumstances.
Unlike the work Lise was now performing in Stockholm on her own, much of the work she had done at the Kaiser Wilhelm Institute in Berlin had been a joint effort between three scientists: herself, Hahn, and Strassmann.
One winter morning when her nephew Otto Robert Frisch joined her for breakfast, she handed him Hahn’s latest letter. On December 19, 1938, Hahn wrote, he and Strassmann had bombarded uranium with a radium-beryllium neutron gun. The result was a small sample that performed like barium, something that could not possibly be. Could Lise make any sense of that? Uranium, atomic number 92, could not suddenly change into barium, atomic number 56, could it? It was a loss of thirty-six units on the element scale. Frisch thought it must be a mistake, but Lise assured him that Hahn was too good a chemist for that.
It was a curious letter, providing a puzzle for Lise to solve. And she had always loved a good puzzle. The idea was almost unimaginable. When neutron experimentation had started, everyone found results that did not fit the expected pattern. Fermi in Rome could not come up with a solution that he deemed convincing. Irène Joliot-Curie and Pavle Savić, and even Hahn and she herself had all thought that the nuclei had captured the neutrons and created new elements heavier than uranium. But now, after a second and third look, Hahn and Strassmann had found something lighter. Maybe, Lise thought, it was not that the neutrons were behaving inappropriately; it was that the scientists who were thinking about the issue were doing so with a closed mind. Perhaps a new rule had to be developed, one adapted to this problem that, if one really thought about it, was not really a problem at all but simply a new surprise, something to force scientists to think more critically about an issue.
She could not recall anyone saying that an atom could not be split in two. Going back to the seminar she had attended with Einstein, she remembered his words precisely: “There is not the slightest indication that energy [in the nucleus] will ever be obtainable,” he had told his audience. “It would mean that the atom would have to be shattered.” But really, what had he said? Lise wondered. It all depended on how one interpreted his statement. It didn’t mean that it could not be done. What Einstein had suggested was that to do so, to get to the nucleus, one really had to split it in two portions. And so far, no one had done it.
Lise and Frisch went off for a walk as they tried to sort out the puzzle. Clearly, the lighter barium had to be a fragment of the uranium nucleus, but how had it happened? Neutrons never broke anything other than a proton or alpha particle away from the nucleus, or so they thought. And a nucleus wasn’t a brittle solid that could be chipped or cracked or broken. They remembered the physicist George Gamow’s theory that a nucleus was more like a liquid drop. What if they could split into smaller drops, gradually stretching, constricting, and finally turning into two drops? It would look something like a dumbbell. The physicists knew that the surface tension of ordinary drops resisted such division, but nuclei were no ordinary drops. They were electrically charged, and that diminished the effects of surface tension.
Lise calculated that the electrical charge of uranium was indeed strong enough to overcome the surface tension, so the nucleus could possibly be unstable enough to divide when a neutron struck it. But the electrical charge of the two new drops would repel, driving them apart at a high speed. Where would that energy come from? Lise remembered Einstein’s equation from that conference so many years ago, E = mc2. She worked out the masses of the new nuclei, and Frisch calculated the energy needed for the repulsion. It all fit.
It was the breakthrough that explained everything, and it had come on a snowy day in Sweden.
Frisch returned to Copenhagen and promptly told his boss, Niels Bohr, of their speculation. Bohr agreed with their theory immediately and urged them to publish a paper. Lise and Frisch decided to write a one-page note about their theory, backed up by physical evidence of the nuclear fragments. They consulted repeatedly over the telephone, the line between Copenhagen and Stockholm as crackly as the ice outside.
Frisch designed a physics experiment to detect the fragments by measuring the bursts of ions they produced. It worked perfectly. Proof in hand, he wrapped up the final paper. Now ready to let the world know of this nuclear fission, he sent their note to the British journal Nature.
Frisch’s note to the journal read in part: “It seems therefore possible that the uranium nucleus has only a small stability of form, and may, after neutron capture, divide itself into two nuclei of roughly equal size (the precise ratio of sizes depending on finer structural features and perhaps partly on chance). These two nuclei will repel each other and should gain a total kinetic energy of c. 200 MeV, (mega-electron v
olt) as calculated from nuclear radius and charge. This amount of energy may actually be expected to be available from the difference in packing fraction between uranium and the elements in the middle of the periodic system. The whole ‘fission’ process can thus be described in an essentially classical way.”
It was a startling note, one that would have profound repercussions across the world. In time, some would point to this moment in history as the start of the atomic age, and to Lise Meitner as the originator of the atomic bomb.
chapter six
A Secret Project
1938–1939
It was not surprising that Niels Bohr was the first to learn of nuclear fission from Otto Robert Frisch. By then Bohr was fifty-four years old, a Nobel laureate, and considered the foremost physicist in the world. He was very excited about this discovery by his longtime friend Lise Meitner and her nephew.
In December 1938, during a lecture in Copenhagen, which was later printed in Niels Bohr’s Times: In Physics, Philosophy, and Polity, he said, “With present technical means it is, however, impossible to purify the rare uranium isotope in sufficient quantity to realize the chain reaction.” As it happened, not far from him, in Stockholm, Lise Meitner was also making a discovery that December that would lead to what he had until then believed to be impossible.
Bohr was preparing to attend the fifth Washington Conference on Theoretical Physics, to be held the following month. His mind had been churning since hearing the news and continued to do so throughout the nine-day transatlantic journey to the United States. He arrived in New York on January 16, 1939, nearly two weeks after the Fermis had docked there. In fact, it was Enrico Fermi who met him at the pier.
By the time he took to the conference podium to share his news, Bohr was positively bubbling over with enthusiasm. He had prepared his remarks on a stack of papers that he held in front of him, but then, looking out at his audience, he swept his notes aside and began to speak freely, as if in front of one of his classes. Fission, he told the audience, referred to the moment when the nucleus of an atom split into two fragments.
As Bohr relayed the information to his colleagues, all of them could feel the electricity running through the auditorium. Although some of the information had been leaked prior to Bohr’s talk, hearing the news from Bohr’s own lips allowed the news to be received with enthusiasm and not even the smallest amount of skepticism. Still, they wanted Bohr to end his speech as soon as possible. It was impolite to get up and leave in the middle of a talk, but they wanted to rush to their own laboratories and check the experiments themselves. Once they did, the theory of nuclear fission would become widely accepted.
A few of these scientists wondered why they had not observed the phenomenon before. Others boasted of having come close to the solution themselves; whether or not that was true, they agreed that they should have stayed with the experiments a little longer.
It was a startling moment, not only for Lise Meitner’s breakthrough but also for nuclear science in general. Many of the scientists in attendance, much like Lise Meitner, would come to the realization that nuclear fission could form a self-sustaining chain reaction—which in turn, if properly utilized, could form a bomb.
Enrico Fermi was in attendance at the Washington conference. Colleges and universities across the United States were hiring professors who were fleeing the racial persecution in Europe, and Fermi, having received the Nobel Prize in Physics in 1938, had been quickly offered jobs at five different universities; he accepted a teaching post at Columbia University in New York City. The university felt it was a real coup to land a man like Fermi, and he did not disappoint.
Soon after the conference ended, Fermi urged his supervisors at Columbia University to repeat the tests that had been conducted in Europe. If they were successful, he told them, they should begin to study the possibilities of a long-range chain reaction. The Columbia laboratory was led by Fermi along with Leo Szilard, a Hungarian émigré. Both of them had fled Europe because of the Nazis, and now it was their job to determine whether or not a chain reaction was possible, and how that could be used against the enemies.
Fermi succeeded in performing a small experiment related to nuclear fission by showing that uranium bombarded by neutrons emitted more neutrons than it absorbed. The Columbia group released a statement saying, “This new process gives the largest conversion of mass into energy that has yet been obtained by terrestrial methods.” The words were a little outlandish and pompous, given that in Europe Fritz Strassmann and Otto Hahn had been conducting those same experiments for months. But then, Fermi was an extravagant man.
From this point on, scientists pursued studies and experiments on fission with abandon, and hundreds of papers were written and published, outlining the methods for fission without regard for who would be at the receiving end of that knowledge. Countries around the world began thinking that fission might be used for military purposes.
Although Americans’ larger aim was to create a nuclear bomb, they had to tackle the questions that came first: They needed to understand how the finer details of nuclear fission worked and whether or not they could control it. Once they got a handle on those things, they could move forward.
Scientists studied these concepts and continued to publish their results. Publication was the natural outcome of years of research, hours of hard and dedicated work, sometimes tedious, at other times exciting. These articles could be read by anyone. Soon, a voluntary ban against publishing research was instituted by the British as well as by those working in the United States. However, the French team, led by the Joliot-Curies, refused to adhere to any ban. They had difficulty accepting the fact that the Nazis might be considering the possibility of constructing a bomb and might be looking to their work for inspiration. And so they continued publishing.
In 1935, Frédéric Joliot-Curie, while delivering a lecture, included the following paragraph: “If, turning towards the past, we cast a glance at the progress achieved by science at an ever-increasing pace, we are entitled to think that scientists, building up or shattering elements at will, will be able to bring about transmutations of an explosive type, true chemical-chain reactions. If such transmutations do succeed in spreading in matter, the enormous liberation of usable energy can be imagined. But unfortunately, if the contagion spreads to all the elements of our planet, the consequences of unleashing such a cataclysm can only be viewed with apprehension.”
Not surprisingly, while listening to Niels Bohr at the Washington conference, some in the audience immediately began to speculate about what kind of weaponry such a discovery could offer. For the military, this could be quite a coup. Up until that point, the notion of a bomb based on the principle of a chain reaction was still an abstract concept in the minds of a few who believed it could never come to fruition—at least not during their lifetimes.
But the discovery of nuclear fission discussed at the Washington conference, and the possibility of it being used for weapons, came at the right moment. There were already hints of war, and it was widely believed that Hitler and his regime would be using methods of warfare previously unheard of. One had to fight fire with fire, but there were questions to contend with: If a chain reaction could be achieved, could it also be sustained, or would the reaction speed up and release energy without assistance, basically uncontrolled? Would it shut itself off whenever it wanted to? Could scientists basically control it?
By the summer of 1939, the Americans believed that Germany had already started its own research program, wanting to be the first to develop an atomic weapon, with the British following close behind. Work was also under way in the Soviet Union, where the possibility of an atomic bomb had been discussed and a proposal appeared in 1940. (The Soviet scientific community had discussed the possibility of an atomic bomb throughout the 1930s, going so far as to make a concrete proposal in 1940, but they initiated their program only during World War II, in 1942.)
Although American scientists believed that a fission c
hain reaction was possible, they were also aware that many obstacles stood in their way. For starters, not every atom could be split in two, though uranium could, especially rare-form uranium-235, which accounted for only 0.72 percent of the naturally occurring element. It was already difficult to separate a large enough amount of identical uranium isotopes for a laboratory reaction; to do it on an industrial scale seemed almost impossible.
Szilard had listened carefully to all that was said at the conference, and he left with two things on his mind: the realization that there was military potential for a nuclear weapon; and the knowledge that the Germans were already very much aware of that potential and were likely working on a bomb.
Szilard realized that the United States and its laboratories had become the beneficiaries of much of the knowledge brought forth by the exiled European scientists. But he was also aware that many other scientists had stayed behind, and they were still working in Germany—for Adolf Hitler. They might have already come up with plans to hand over to Hitler a weapon the likes of which the world had never seen.
Szilard didn’t know whether people would listen to him or his ideas. Small in stature and rather round, he liked to sit in a wide chair when deep in thought and cross his hands over his protruding belly. Some thought he had a flair for the dramatic, a reputation he didn’t particularly like. But in this case, he was correct in thinking that this was an important matter that needed to be studied with special attention. He was sure that many of the new discoveries had to be kept secret, for fear that they would land in the wrong hands. In fact, he was the one who spearheaded the voluntary publication ban.
Atomic Women Page 6
