The Age of Radiance (19 page)

Lise returned to Stockholm and became even more depressed after learning that her brother-in-law, Otto Robert’s father, Jutz, had been arrested along with thirty thousand other Jewish men and was now interned at Dachau. She tried to arrange for her sister Auguste to emigrate. Then she learned that Otto Hahn had referred to concentration-camp victims as “human undesirables” and begun joking that people assumed he was Jewish because of his name, because he was born in Frankfurt, worked at KWI, and had resigned from the University of Berlin in protest in 1933. The “joke” turned on Otto when he discovered his name included in “The Eternal Jew,” a traveling exhibit of anti-Semitism, and he had to give institute officials affidavits confirming his “Aryan” lineage. Otto Hahn did, though, keep working to get Lise her due during this period and was able to unfreeze her bank account for her sister to use. But he had no luck with her pension. Then after months of delay, her possessions arrived in Stockholm severely vandalized, the Swedish shipper saying he’d never seen anything like it.

On November 20, Meitner wrote von Laue,
“One always thinks life in this world cannot get much harder, but one is mistaken.”

While the Fermis were in Sweden for the Nobel ceremonies, Laura recalled,
“One day, while strolling in the streets of Stockholm we ran into a mousy little woman with a tense expression. She was Lise Meitner, then a refugee from German persecution. . . . Fermi and Meitner did not talk about physics that day in the street. To me the significance of that encounter lay in Meitner’s tense, almost scared look, a look that I was to see time and time again on the face of other refugees.” Who could imagine—least of all Lise Meitner herself—that this woman, in this predicament, would soon be as significant and as revolutionary a figure in the history of physics as Röntgen, Fermi, and both Curies?

I
n December, the Swedish sun rose at noon and set at three, and Lise’s sense of hopelessness ballooned. She decided she couldn’t spend the holiday
brooding and alone and instead arranged to return to stay with Eva. Otto Robert was also invited, and wanting to be with family in the wake of his father’s arrest and his mother’s sorrow, he accepted. Before she left, however, Meitner received a letter from Hahn dated December 19, 1938 . . . perhaps the most important letter in the history of nuclear science:
“Monday evening, in the lab. . . . It is now practically eleven o’clock at night. Strassmann will be coming back at 11:45 so that I can get home at long last. The thing is: there is something so ODD about the ‘radium isotopes’ that for the moment we don’t want to tell anyone but you. . . . We are more and more coming to the awful conclusion that our Ra [radium] isotopes behave not like Ra, but like Ba [barium]. . . . Perhaps you can suggest some fantastic explanation.” On the twenty-first, he then wrote, “How beautiful and exciting it would be just now if we could have worked together as before. We cannot suppress our results, even if they are perhaps physically absurd. You see, you will do a great deed if you can find a way out of this.” Meitner responded on the twenty-first with “Your radium results are very startling. A reaction with slow neutrons that supposedly leads to barium! . . . At the moment the assumption of such a thoroughgoing breakup seems very difficult to me but in nuclear physics we have experienced so many surprises, that one cannot unconditionally say: It is impossible.”

Otto Hahn:
“Miss Meitner—Professor Meitner—had left our laboratory on July 1938 on account of these Hitler regime things and she had to go to Sweden. And Strassmann and myself, we had to work alone again and in the autumn of ’38 we found strange results. . . . We could conclude that the substances could be really only radium because barium was prohibited by the physicists that we didn’t dare to think it barium in those times. We always tried to explain what is wrong in our experiments, not to say we do have barium, but we always thought it can’t be there and therefore we have to say, ‘What is the nonsense we are doing?’ So really, it is so, that we poor chemists—isn’t it the same with you?—we are so afraid of these physics people.”

It was now Christmas Day 1938. Just when she had reached the top of her field and her greatest research had begun, she had been exiled from both her longtime collaborator, her work, and the institute that had been her life’s passion. Alongside Marie and Irène Curie, she had been the most famous and acclaimed woman in global physics. Now, exiled into Siegbahn’s inhospitable refuge, she was essentially homeless, stateless, and impoverished. She felt, suddenly, old, useless, a failure, a woman without hope.

On Christmas Eve in Kungälv, after Lise and Otto Robert both “gagged”
on the traditional dish of lutefisk, all Lise could talk about was Hahn’s barium. It didn’t make sense! Otto Frisch:
“Was it a mistake? No, said Lise Meitner; Hahn was too good a chemist for that. But how could barium be formed from uranium? No larger fragments than protons or helium nuclei (alpha particles) had ever been chipped away from nuclei, and to chip off a large number, not nearly enough energy was available. Nor was it possible that the uranium nucleus could have been cleaved right across. A nucleus was not like a brittle solid that can be cleaved or broken. . . . Bohr had given good arguments that a nucleus was much more like a liquid drop.”

Every time an experiment revealed new elements of the atom, a new model (or new analogy) was proposed. Was the atom’s nucleus equivalent to a magnetic fog? A roiling plum pudding? Or a solid amalgamation of particles that, when bombarded, could be turned into chips? Wilfrid Wefelmeier was inspired to propose heavy nuclei stacked in a lump . . . a “nuclear sausage.” Besides nuclear “mush,” Bohr, in a 1936
Nature
article, had proposed a “liquid droplet model” of the nucleus, amending and supporting his Russian student George Gamow, who’d published something similar in 1934.

The aunt and nephew went out that afternoon for a walk in the snow, Frisch on skis, and Meitner in boots. They sat on the logs of a fallen tree and discussed Bohr’s raindrop model of the atom versus Rutherford’s planetary version. Resting against a branch, Meitner took out paper and pencil and drew a Bohr nucleus. She drew it pulled apart and then split. She wrote the calculations of energy and mass that held the nucleus together, then started recalculating the numbers, assuming that the “surface tension” of the uranium nucleus was weaker than previously believed. Frisch: “Perhaps a drop could divide itself into two smaller drops in a more gradual manner, by first becoming elongated, then constricted, and finally being torn rather than broken in two? We knew that there were strong forces that would resist such a process, just as the surface tension of an ordinary liquid drop tends to resist its division into two smaller ones. But nuclei differed from ordinary drops in one important way: They were electrically charged, and that was known to counteract the surface tension.”

If the nucleus was split, the resulting electric charge would repel the two pieces away from each other in a burst of energy, about 200 million electron volts (an electron volt is the energy of a single electron after being charged with a single volt). Meitner remembered what was called the packing-fraction formula and thought that the two split nuclei should be lighter than the original by one-fifth the mass of a proton. When taking into account Einstein’s E = mc
²
, her calculations produced . . . 200 million electron volts.

Frisch: “The charge of a uranium nucleus, we found, was indeed large enough to overcome the effect of the surface tension almost completely; so the uranium nucleus might indeed resemble a very wobbly unstable drop, ready to divide itself at the slightest provocation, such as the impact of a single neutron. But there was another problem. After separation, the two drops would be driven apart by their mutual electric repulsion and would acquire high speed and hence a very large energy, about 200 MeV in all; where could that energy come from? . . . [Lise] worked out that the two nuclei formed by the division of a uranium nucleus together would be lighter than the original uranium nucleus by about one-fifth the mass of a proton. Now, whenever mass disappears, energy is created, according to Einstein’s formula E = mc
²
, and one-fifth of a proton mass was just equivalent to 200 MeV. So here was the source for that energy; it all fitted!”

Meitner was flabbergasted, and Frisch, amazed. When she finally had a chance to later read their joint paper, she said,
“These results, I realized, had opened up an entirely new scientific path, and I also realized how far we had gone astray in our earlier work!”

On December 28, 1938, Hahn wrote Lise,
“What is the possibility that uranium 239 could split into one Ba and one Ma? One Ba 138 and one Ma 101 gives 239.” On January 3, 1939, she replied,
“Dear Otto! I am now almost certain that the two of you really do have a splitting to Ba [barium] and I find that to be a truly beautiful result, for which I must heartily congratulate you and Strassmann. . . . Both of you now have a beautiful, wide field of work ahead of you. And believe me, even though I stand here with very empty hands, I’m nevertheless happy for these wondrous findings.”

Otto Frisch:
“When I came back to Copenhagen I found Bohr just on the point of parting, of leaving for America, and I just managed to catch him for five minutes and tell him what we had done. And I hadn’t spoken for half a minute when he struck his head with his fist and said, ‘Oh, what idiots we have been that we haven’t seen that before. Of course this is exactly as it must be.’ And he added, ‘This is very beautiful,’ and, had we written a paper? So I said no, we were in the process of writing one.”

On January 3, Otto Robert wrote Lise,
“Dear Tante, I was able to speak with Bohr only today about the splitting of uranium. The conversation lasted only five minutes as Bohr agreed with us immediately about everything. He just couldn’t imagine why he hadn’t thought of this before, it is such a direct consequence of the current concept of nuclear structure. He agreed with us completely that this splitting of a heavy nucleus into two big pieces is practically a classical phenomenon, which does not occur at all below a certain
energy, but goes readily above it.” Frisch then asked American biologist William A. Arnold, working at Bohr’s institute, what biologists call it when cells divide. “Binary fission,” Arnold said. Three days later, Frisch again met with Bohr and gave him a draft of the
Nature
article.

On January 7, Niels Bohr, his nineteen-year-old son, Erik, and University of Liège physicist Léon Rosenfeld set sail from Göteborg, Sweden, for New York. Bohr was so excited by Frisch and Meitner’s theorem that he had a blackboard installed in his cabin for the trip. Rosenfeld:
“When we met on the boat, [Bohr] said, ‘I have in my pocket a paper that Frisch has given me which contains a tremendous new discovery, but I don’t yet understand it. We must look at it.’ Bohr accepted the conclusions because it was an argument directly following from the experiments. But he did not understand why the nucleus would split. And then during the trip that took six days or so, he got hold of the solution, and it turned out to be extremely simple. Meanwhile, back in Denmark, Frisch wanted to check by experiment the idea that uranium can split in two. Several methods could be used to study sub-atomic particles. The easiest was to look at electrical effects in an ionization chamber, using an amplifier and oscilloscope. Invisible particles passing through the chamber would show up as pulses on the screen of the oscilloscope. The hallmark of fission would be the size of the pulses: the two halves of a split atom would have far greater energy than any known particle.”

Otto Frisch: “I rigged up a pulse amplifier for the special purpose, and I also built a small ionization chamber; but the whole thing only took me about two days, and then I worked most of the night through to do the measurements because the counting rates were very low. But by three in the morning I had the evidence of the big pulses. And I went to bed at three in the morning, and then at seven in the morning I was knocked out of bed by the postman, who brought a telegram to say that my father had been released from the concentration camp.” On January 13, Frisch observed uranium pulsing in ionization when hit by neutrons, proving it emitted energy when split. It was the alchemy of transformation, of matter becoming energy, and it was visible.

On the sixteenth, he sent both the article coauthored with his aunt, “Disintegration by Neutrons: A New Type of Nuclear Reaction,” and the solo report on his follow-up experiments, “Physical Evidence for the Division of Heavy Nuclei under Neutron Bombardment,” dating them both the sixteenth, to
Nature
, the same day that Bohr docked in New York at the Swedish American Line’s pier on West Fifty-Seventh Street. Rosenfeld:
“We had bad weather through the whole crossing, and Bohr was rather miserable, on the verge of seasickness all the time. Nevertheless, we persevered for nine days, and before the American coast was in sight, Bohr had a full grasp of the new process and its main implications.”

So many colleagues were on hand to welcome Bohr to America that he and Fermi did not discuss the Meitner breakthrough at that moment, but when John Wheeler sat next to Rosenfeld on the train to Princeton, Rosenfeld, not knowing that Bohr was keeping the material quiet until publication, told Wheeler all about it. (Rosenfeld would have assumed that the Meitner/Frisch paper would be released immediately; instead, not understanding the extraordinary nature of what they had, it took until February 11 for the editors of
Nature
to publish.) Rosenfeld then repeated the news at the Princeton physics students’ weekly Journal Club on Monday. From there, the shocking revelation spread across the American physics community with amazing speed. Isidor Rabi traveled from Princeton back to Columbia, carrying Rosenfeld’s news; Fermi remembered hearing it from Willis Lamb, who had also just been at Princeton.