The letter reached Kungälv on Thursday; by return mail that day Meitner responded that the radium-barium finding was “very exciting. Otto R[obert] and I have already puzzled over it.”996 But she let slip no answer to the puzzle and she asked about the lanthanum result.
Friday she sent Hahn a postcard: “Today the manuscript arrived.” An important page was missing but it was all “very amazing.”997 Nothing more; Hahn must have bitten his lip.
In Dahlem Rosbaud passed along the galley proofs. Hahn was more certain now of his findings. The manuscript had set the barium results “against all previous laws of nuclear physics.” He moderated the phrase in proof to “against all previous experience.”998
But even with the carbon copy, the missing page and the December 21 letter finally at hand in Kungälv, Meitner hesitated to leap. On January 1, after conveying New Year’s greetings to Hahn, she wrote: “We have read your work very thoroughly and consider it perhaps possible energetically after all that such a heavy nucleus bursts.” She veered off to worry about their misbegotten transuranics, “not a good reference for my new start.”999 Frisch added a New Year’s wish of his own and a more genial reservation: “If your new findings are really true, it would certainly be of the greatest interest and I am very curious about further results.”1000
Meitner returned to Stockholm later that day and Frisch to Copenhagen. He was “keen to submit our speculations—it wasn’t really more at that time—to Bohr.”1001 The note of hesitancy in their letter to Hahn suggests they sought the authority of Bohr’s blessing. Frisch saw him on January 3: “I had hardly begun to tell him, when he struck his forehead with his hand and exclaimed, ‘Oh what idiots we have all been! Oh but this is wonderful! This is just as it must be!’ ” Their conversation lasted only a few minutes, Frisch wrote his aunt that day, “since Bohr immediately and in every respect was in agreement with us. . . .1002, 1003 [He] still wants to consider this quantitatively this evening and to talk with me again about it tomorrow.”1004
In Stockholm that day Meitner had received Hahn’s revised proofs. Independently they quieted her doubt. She wrote Hahn emphatically: “I am fairly certain now that you really have a splitting towards barium and I consider it a wonderful result for which I congratulate you and Strassmann very warmly. . . . You now have a wide, beautiful field of work ahead of you. And believe me, even though I stand here very empty-handed at the moment, I am still happy about the marvelousness of these findings.”1005
Now those findings needed interpretation. Aunt and nephew outlined a theoretical paper by long-distance telephone. Frisch drafted it Friday, January 6, and that evening took the trolley to the House of Honor to discuss it with Bohr, who was leaving for the United States the next morning for a term of work at the Institute for Advanced Study.1006 There was time the next morning to type only part of the draft; Frisch delivered two pages to Bohr at the train station from which he and his nineteen-year-old son Erik were departing for Göteborg harbor. On the assumption that Frisch would immediately send the paper along to Nature Bohr promised not to mention it to their American colleagues until he heard from Frisch that it had been received and was in press. Among the notes he brought to that final discussion Frisch mentioned an experiment to confirm by physical means the Dahlem chemistry.1007
Hahn’s and Strassmann’s article had been published in Berlin on January 6. When it arrived in Copenhagen the next day Frisch thought to go over the whole business with George Placzek.1008 Placzek was characteristically skeptical and characteristically witty about it. Uranium already suffered from alpha decay, Frisch remembers him scoffing; to think that it could be made to burst as well “was like dissecting a man killed by a falling brick and finding that he would have died of cancer.”1009 Placzek suggested that Frisch use a cloud chamber to look for energetic fragments that would prove the nucleus had split. The institute’s radium-based neutron sources would fog a cloud-chamber photograph with gamma radiation, Frisch realized. But a simple ionization chamber would do. “One would expect fastmoving nuclei, of atomic number about 40–50 and atomic weight 100–150, and up to 100 MeV energy to emerge from a layer of uranium bombarded with neutrons,” he explained his experiment in a subsequent report. “In spite of their high energy, these nuclei should have a range, in air, of a few millimetres only, on account of their high effective charge . . . which implies very dense ionization.”1010 In the course of their short passage his highly charged nuclear fragments would strip about 3 million electrons from the nuclei of air gases. They should be easy to find.
His chamber consisted of “two metal plates separated by a glass ring about 1 cm. high.” The charged plates, which would collect the air ions, connected to a simple amplifier, which connected to an oscilloscope. To the bottom plate he attached a piece of uranium-coated foil. He set up the experiment in the basement of the institute and retrieved three of the neutron sources from the covered well. He placed the sources close to the foil and looked for the expected nuclei to emerge. Since they were highly energetic and strongly ionizing they would create quick, sharp, vertical pulses of the sweeping green beam of the oscilloscope.
Frisch started measurements on the afternoon of Friday, January 13, and “pulses at about the predicted amplitude and frequency (one or two per minute) were seen within a few hours.”1011, 1012 He ran checks with either the neutron sources or the uranium lining removed. He wrapped the sources with paraffin to slow the neutrons and “enhanced the effect by a factor of two.” He continued measurements “until six in the morning to verify that the apparatus was working consistently.” As had Werner Heisenberg before him, he lived upstairs at the institute; exhausted, he climbed the stairs to bed. He remembers thinking that 13 had proved once again to be his lucky number.
Even luckier than that: “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 concentration camp.”1013 His parents would move to Stockholm and share an apartment with his aunt, whose possessions, thanks to Hahn, were eventually shipped.
In “a state of slight confusion” Frisch spent the next day repeating the experiment for anyone who cared to see.1014 One who came down in the morning to the basement laboratory was a black-haired, blue-eyed American biologist of Irish heritage named William A. Arnold who was studying on a Rockefeller Fellowship with George de Hevesy.1015 Arnold was thirtyfour, Frisch’s age, on leave from the Hopkins Marine Station at Pacific Grove, California. He had made his way to Europe from San Francisco the previous September by freighter with his wife and young daughter. He could have gone to Berkeley to pick up radioisotope technique, but would have missed living in Copenhagen, learning from de Hevesy—would have missed contributing a coinage to the gamble that is history. Frisch showed the American the experiment and pointed out the pulses on the oscilloscope. “From the size of the spikes,” Arnold recalls, “it was clear that they must represent 100–200 MeV, very much larger than the spikes from [uranium’s natural background of] alpha particles.”
Later that day Frisch looked me up and said, “You work in a microbiology lab. What do you call the process in which one bacterium divides into two?” And I answered, “binary fission.” He wanted to know if you could call it “fission” alone, and I said you could.
Frisch the sketch artist, good at visualizing as his aunt was not, had metamorphosed his liquid drop into a dividing living cell.1016 Thereby the name for a multiplication of life became the name for a violent process of destruction. “I wrote home to my mother,” says Frisch, “that I felt like someone who has caught an elephant by the tail.”1017
Aunt and nephew conferred by telephone further over the weekend to prepare not one but two papers for Nature: a joint explanation of the reaction and Frisch’s report of the confirming evidence of his experiment.1018 Both reports—“Disintegration of uranium by neutrons: a new type of nuclear reaction” and “Physical evidence for the division of heavy nuclei under neutron bombardment”—used th
e new term “fission.” Frisch finished the two papers on Monday evening, January 16, and posted them airmail to London the next morning.1019 Since he and Bohr had already discussed the theoretical paper and since the experiment only confirmed the HahnStrassmann discovery, he did not hurry to let Bohr know.
* * *
Bohr sailed on the Swedish-American liner Drottningholm with his son Erik and the Belgian theoretician Léon Rosenfeld. “As we were boarding the ship,” Rosenfeld recalls, “Bohr told me he had just been handed a note by Frisch, containing his and Lise Meitner’s conclusions; we should ‘try to understand it.’ ” That meant a working voyage; a blackboard was duly installed in Bohr’s stateroom. The North Atlantic was stormy in that season; it made him “rather miserable, all the time on the verge of seasickness” but hardly stopped the work.1020 The first question he wanted to answer was why, if the nucleus oscillated more or less randomly when it was bombarded, it seemed to prefer splitting into two parts rather than some other number. He was satisfied when he saw that the heaviest nuclei, because of their instability, require no more energy to split than they do to emit a single particle. It was a question of probabilities and two fragments were greatly more probable than a crowd.
The Fermis had arrived in New York on January 2, Laura feeling distinctly alien, Enrico announcing with his usual mock solemnity, “We have founded the American branch of the Fermi family.”1021 They put up temporarily at the King’s Crown Hotel, opposite Columbia University, where Szilard was also living. George Pegram, the tall, soft-spoken Virginian who was chairman of the physics department and dean of graduate studies at Columbia, had met the Fermis as they debarked the Franconia; now in turn they waited at dockside to meet Bohr. The American theoretician John Archibald Wheeler, then twenty-nine years old, who had worked with Bohr in Copenhagen in the mid-1930s and would be working with him again at Princeton, joined them on the crowded West 57th Street pier. He had taught his regular Monday morning class, then caught a midday train.
As the Drottningholm berthed, at 1 P.M. on January 16, Laura Fermi saw Bohr on an upper deck leaning on the railing searching the crowd. She thought him worn when they met: “During the short time that had elapsed since our visit to his home, Professor Bohr seemed to have aged. For the last few months he had been extremely preoccupied about the political situation in Europe, and his worries showed on him. He stooped like a man carrying a heavy burden. His gaze, troubled and insecure, shifted from the one to the other of us, but stopped on none.”1022 No doubt Bohr was worried about Europe. He had also been seasick.
He had business in New York; he and Erik went off with the Fermis. Wheeler took Léon Rosenfeld along to Princeton.1023 Keeping his promise to Frisch, Bohr had not mentioned the Hahn-Strassmann discovery and the Frisch-Meitner interpretation to either Fermi or Wheeler, but he had neglected to tell Rosenfeld of his pledge. Rosenfeld thought Frisch and Meitner had already sent off the paper that would give their work of interpretation priority. He passed on to Wheeler what Bohr had passed on to him. “In those days,” Wheeler remembers, “I was in charge of the Monday evening journal club”—a weekly gathering of Princeton physicists to discuss the latest studies they found in physics journals, a way of keeping up.1024 “It was the custom to get three things reported then, and here was something hot, as I had learned from Rosenfeld on the train.” America first heard the news of the splitting of uranium—the term “fission” had not yet crossed the Atlantic—at the Princeton physics department journal club on the chill Monday evening of January 16, 1939. “The effect of my talk on the American physicists,” says Rosenfeld ruefully, “was more spectacular than the fission phenomenon itself. They rushed about spreading the news in all directions.”1025, 1026
Bohr arrived in Princeton the next day to take up residence and Rosenfeld casually mentioned the journal club talk.1027 “I was immediately frightened,” Bohr wrote his wife that night, “as I had promised Frisch I would wait until Hahn’s note appeared and his own was sent off.” It was more than a point of honor, though that would have been sufficient in itself to trigger the Bohr conscience. It was also that Meitner and Frisch were refugees who could use so spectacular a coup to establish themselves securely in exile. Bohr had at hand the work he and Rosenfeld had accomplished aboard the Drottningholm; for the next three days he labored to convert it into a letter to Nature that would give credit pointedly at the outset to Meitner and Frisch. Three days to produce a seven-hundred-word paper was for Niels Bohr great haste.
“Can you guess where I found out about [Bohr’s news]?” asks Eugene Wigner. “In . . . the [Princeton] infirmary. Because I contracted jaundice and was in the infirmary for six weeks.”1028 Wigner and Princeton had not immediately got along; in 1936 “they said I should look for another job.”1029 Princeton then, he thought, was “an ivory tower; people did not have any normal thinking about the facts of life and so forth and they looked down upon me.” He sought another job and found one at the University of Wisconsin at Madison. “From the second day on I felt at home there. Somebody suggested we go to the track and we ran around the track and we were friends. We talked not only about the most difficult problems but about the daily events. We got down to earth almost.” He met a young American woman in Wisconsin; they were quickly married. She became ill:
I tried to conceal it from her that she had cancer and that there was no hope for her surviving. She was in a hospital in Madison and then she went to see her parents and I went with her but I didn’t want to stay with her parents, of course, because I was, after all, a stranger to her parents. I went for a little while away to Michigan, Ann Arbor, and then I came back and saw her in her bed at her parents’. And then she told me essentially that she knows that she is close to death. She said, “Should I tell you where our suitcases are?” So she knew when she talked to me. I tried to conceal it from her because I felt that it would be better if a reasonably young person does not realize that she is doomed. Of course, we are all doomed.
He returned to Princeton in 1938, the university by then having more sensibly assessed his worth (a sophisticated and highly respected theoretician, Wigner shared the Nobel Prize in Physics in 1963 for his work on the structure of the nucleus).
After Bohr’s arrival Szilard traveled down from New York to visit his sick friend and won a long-overdue surprise:
Wigner told me of Hahn’s discovery.1030 Hahn found that uranium breaks into two parts when it absorbs a neutron. . . . When I heard this I immediately saw that these fragments, being heavier than corresponds to their charge, must emit neutrons, and if enough neutrons are emitted . . . then it should be, of course, possible to sustain a chain reaction. All the things which H. G. Wells predicted appeared suddenly real to me.
At Wigner’s bedside in the Princeton infirmary the two Hungarians debated what to do.
In the meantime Bohr had sent his letter for Nature to Frisch in Copenhagen, asking him to forward it on “if, as I hope, Hahn’s article has already been published and your and your aunt’s note has already been submitted.” He asked for the “latest news” on that front and wondered “how the experiments are proceeding.”1031 In a postscript he added that he had just seen the Hahn-Strassmann paper in Naturwissenschaften.
Ideas infect like viruses. The point of origin of the fission infection was Dahlem. From there it spread to Stockholm, to Kungälv, to Copenhagen. It crossed the Atlantic with Bohr and Rosenfeld. I. I. Rabi and the young California-born theoretician Willis Eugene Lamb, Jr., two Columbia men working at Princeton that week, both heard the news, Lamb perhaps from Wheeler, Rabi from Bohr himself.1032 They returned to New York—“probably Friday night,” Lamb thinks.1033 Rabi says he told Fermi.1034 In 1954 Fermi credited Lamb: “I remember one afternoon Willis Lamb came back very excited and said that Bohr had leaked out great news.”1035 Lamb recalls “spreading it around” but does not recall specifically telling Fermi.1036 Possibly both men talked to the Italian laureate within a space of hours; it was information he of all physic
ists would most need to hear, since the Nobel lecture he had delivered only a month earlier, not yet printed, was now partly obsolete and an embarrassment. (Fermi confined revision to a footnote: “The discovery by Hahn and Strassmann . . . makes it necessary to reexamine all the problems of the transuranic elements, as many of them might be found to be products of a splitting of uranium.”1037 The many other radioactivities he and his group identified and his slow-neutron discovery still secured his Nobel Prize.)
Szilard also hoped to talk to Fermi: “I thought that if neutrons are in fact emitted in fission, this fact should be kept secret from the Germans. So I was very eager to contact Joliot and to contact Fermi, the two men who were most likely to think of this possibility.”1038 He had borrowed Wigner’s apartment and had not yet left Princeton. “I got up one morning and wanted to go out. It was raining cats and dogs. I said, ‘My God, I am going to catch cold!’ Because at that time, the first years I was in America, each time I got wet I invariably caught a bad cold.” He had to go out anyway. “I got wet and came home with a high fever, so I was not able to contact Fermi.”
Fever or not, by January 25—Wednesday—Szilard had returned to New York, had seen the Hahn-Strassmann paper and was writing Lewis Strauss, whose patronage might now be more important than ever:
I feel I ought to let you know of a very sensational new development in nuclear physics.1039 In a paper . . . Hahn reports that he finds when bombarding uranium with neutrons the uranium breaking up. . . . This is entirely unexpected and exciting news for the average physicist. The Department of Physics at Princeton, where I spent the last few days, was like a stirred-up ant heap.
Making of the Atomic Bomb Page 37
