The Woman Who Split the Atom: The Life of Lise Meitner

by Marissa Moss

While nobody in Germany offered help, colleagues abroad reached out. A Swiss physicist invited her to give a lecture in Zurich. James Franck thought he could get her something at the University of Chicago, and Niels Bohr invited her to his institute in Copenhagen.

Thrown out of her home and her work, completely alone, Meitner was finally ready to leave Berlin. She told Bohr she would come to Copenhagen. But Denmark wasn’t willing to take her. How could the Danish consulate give her a visa when her Austrian passport was no longer valid?

Meitner couldn’t earn money. She couldn’t do physics. And now she couldn’t leave Germany. She was trapped.

Once the decision was made to get Meitner out of the Reich, the question was how. The scientists wanted to present her with a path forward in physics so that Meitner would take the risk to flee.

She was a scientist any country should eagerly welcome, having by then been nominated for the Nobel Prize nineteen times.

She knew it was ridiculous to be picky at such a time, but she couldn’t help herself. Having the right place to do her work mattered more to her than food, comfort, even safety. The professor assured her this offer came through Bohr, that he had convinced Siegbahn to open his doors to her. There would be time later for Meitner to go to Copenhagen. The important thing now was to get out of Germany and into a country that would accept her.

As Meitner worried about leaving her lab, news came from Bohr: The visa and position in Sweden were not yet “in order.” The clock was ticking. Each day in Germany seemed full of danger. The borders were still relatively open for those with the right papers, but the political speeches on the radio grew more and more heated, blaming Jews for all of Germany’s problems.

On July 4, 1938, Bosch warned Hahn that Meitner was in danger. He had heard that the new policy prohibiting scientists from leaving Germany would be strictly enforced. Meitner would never get permission to leave. The only way for her to get out was illegally. Risky, yes, but staying was even more dangerous.

Debye went right to Meitner. The Nazis could easily decide to arrest all Jewish scientists to keep them from fleeing. It didn’t matter what kind of position or salary was offered; the crucial thing was for Meitner to leave as soon as possible. Meitner, so stubborn about leaving before, realized she had no choice.

she felt exiled from everything that mattered most to her. She had spent a lifetime working hard to be taken seriously, to earn a place in the world of physics. Now all of that was lost.

Meitner was about to become part of his spy network. She was too valuable a scientist to stay in Germany. Her expertise and her contacts with atomic scientists all over the world were needed.

A whole network of scientists was working to help her, he assured her. She had more support than she knew.

After a lifetime of fighting for a place as a woman, feeling her skirts drag her down, those same skirts now acted as a magical cloak. Traveling with her “husband,” Meitner had become invisible.

.c1

It was the first time, the only time, Meitner felt lucky to be a woman, easily ignored.

.c2

Meitner would have to wait before she could get back to the transuranic research she missed so much. She wrote imploring letters to Hahn: “Perhaps you cannot fully appreciate how unhappy it makes me to realize that you always think that I am unfair and embittered, and that you also say so to other people. If you think it over, it cannot be difficult to understand what it means to me that I have none of my scientific equipment. For me that is much harder than everything else. But I am really not embittered—it is just that I see no real purpose in my life at the moment and I am very lonely.”

To Coster, she wrote, “One dare not look back. One cannot look forward.”

Lost, desperate, depressed.

Hahn showed her the results of his recent work on transuranics. He couldn’t understand them and needed her to explain them to him. Hahn expected to see new, heavier isotopes as a result of the neutron bombardment, as usually happened. Instead, he was seeing lighter elements—including barium.

.c1

Had Hahn been careless, allowing some kind of contamination? Meitner urged him to do the experiments all over again. Hahn thought perhaps he was finding a new kind of lighter radioactive particle instead of the transuranics everyone had been reporting. Meitner knew that wasn’t what was happening. This was something else entirely, if she could only figure out what.

.c2

They may have been in different countries, and Meitner had no lab of her own to check Hahn’s research, but they were working together again through the mail. Hahn ran the experiments, and Meitner interpreted the results. Just long distance, through letters. As they’d done experiments together during the Great War.

Hahn was fine with partnering so long as they didn’t publish the results together. He couldn’t be linked with a Jewish physicist. He’d made that clear to her many times before. It wasn’t the partnering Meitner wanted, but she comforted herself with the thought they were still working together in any fashion.

There was no equipment yet, and her salary was set at the low level of an assistant who had just graduated, rather than at the high level that her experience and reputation deserved.

She wrote, “Scientifically I am completely isolated, for months I speak with no one about physics, sit alone in my room and try to keep myself busy. You cannot call it ‘work.’”

Hahn was worried. He dreaded that all their research on transuranics could be wrong. Uranium was supposed to chip off heavier elements when hit with neutrons. Barium, so much lighter than uranium, made no sense at all as a result of “bursting” the element. This was why Hahn wanted to keep the results secret. Until they understood what was happening and could present a convincing interpretation, simply publishing the data would undercut their last four years of work. They would be presenting a puzzle rather than a discovery. Worse, they would be suggesting that all their earlier discoveries had been wrong.

But after Hahn had repeated the same experiment several times with great care, Meitner took the results seriously. She wrote, “We’ve had so many surprises in nuclear physics that one can’t very well just say it is impossible.” She had to figure out what this impossible thing meant.

Hahn admitted that he and Strassmann, as chemists, had no idea how to explain the results. It was if he, like Galileo, had dropped two objects from a tower, but instead of falling, the objects had floated.

Frisch was just as excited as Meitner. He took off his skis, and the two of them sat down on a snowy log to think it all through. Meitner pulled out paper and pencil and started to do the math. Whatever was happening to the atom, its mass would be conserved since mass can’t simply disappear. If the uranium atom was splitting into lighter elements, the number of protons and neutrons would still remain the same. How could uranium (atomic number 92) split into barium (atomic number 56)? That could happen only if the missing numbers were represented by krypton (atomic number 36). Then the numbers added up. Plus krypton was a gas and would have escaped without Hahn noticing.

The mass of uranium = 238, barium = 139, krypton = 89, which meant barium and krypton only added up to 228. Where were the missing 10 units of mass?

Frisch described the moment in his autobiography: “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.”

After separation, the two drops would be driven apart by their mutual electric repulsion (the way two ends of a magnet with the same poles—negative or positive—are repelled from each other). They would gain speed and release a large amount of energy—about 200 million volts. Where would that energy come from? From the loss of mass! That was wha...

Einstein’s theory of relativity made that clear. Using his formula of E=mc2, one-fifth of a proton mass equaled 200 million electron volts—exactly the energy they had calculated. The math added up: Barium plus krypton plus the energy released equaled the atomic weight of the original uranium nucleus!

So many experiments had been done bombarding atoms—by Bohr, Fermi, and others. Why hadn’t this happened before? The answer, Meitner saw, was that it had. They’d all been splitting atoms. But they hadn’t known it. They didn’t think it was possible, so they hadn’t realized what was happening right in front of them.

“They didn’t think it was possible”—blinded by what they thought they knew to be true.

Meitner admitted that “we had been blinded by ‘the rules.’ The atom could never be split, we believed, so we didn’t have the . . . courage to see the opposite even when it was staring us in the face, even when no other solution would fit.”

Frisch called his aunt, and they agreed he would write a quick draft to send to Nature, the international science journal that could publish most quickly. He sent her his report in a few days, calling the split “fission,” a term he borrowed from a biologist colleague who described cell division that way. Meitner agreed with the coinage and edited the paper, and they submitted it to Nature as “A New Type of Nuclear Reaction.”

While waiting for publication, Frisch replicated Hahn’s experiment and saw with his own eyes the truth of their theory. He sent a brief note to Nature as a follow-up to their report on the new splitting of the atom, “Physical Evidence of the Division of Heavy Nuclei under Neutron Bombardment.”

Meitner explained to Hahn precisely what the experiments meant—not the discovery of new light isotopes, but a rupture of the uranium nucleus. She added, “I have totally retracted my [earlier transuranic] paper as of 14 days ago . . . Since, in fact, I no longer believe in the earlier interpretation of our experiments, and I of course don’t want it published, even in the odd annual publication. The new explanation is also more beautiful and much more clearly comprehensible; it really is a wonderful thing.”

January 26, 1939, Bohr went onstage and announced that Otto Hahn and Fritz Strassmann in Berlin-Dahlem had radiochemical confirmation that bombarding uranium with slow neutrons resulted in barium. Lise Meitner and Otto Robert Frisch had interpreted these results as the splitting of the uranium nucleus, releasing much energy.

.c1

scientists were suddenly rushing out of the hall, eager to test the results for themselves or to call home to their labs and have colleagues duplicate the experiment.

.c2

Meitner and Frisch’s article appeared two weeks later, on February 11, 1939. It concluded: “It seems therefore possible that the uranium nucleus has only small stability of form, and may, after neutron capture, divide itself into two nuclei of roughly equal size.” Just in time for this, Meitner’s lab in Stockholm was ready, and she could, like her nephew, see the evidence with her own eyes. At last, she felt like a physicist again! She submitted a quick follow-up of her own to Nature, “New Products of the Fission of the Thorium Nucleus.”

In 1933, Ernest Rutherford, the British physicist who had discovered the nucleus, wrote, “Anyone who says that with the means at present at our disposal and our present knowledge we can utilize atomic energy is talking moonshine.”

.c1

By 1936, Bohr felt that harvesting atomic energy was less and less likely. “The more our knowledge of nuclear reactions advances the remoter this goal [of harnessing energy] seems to become.” Other scientists saw it as theoretically possible but practically impossible.

.c2

Until Meitner’s discovery.

.c3

Again, no mention was made of Meitner or Frisch. In the flurry of excitement, their role was forgotten. Hahn’s name was still mentioned, but Meitner’s slipped away.

Meitner felt invisible once again. She wrote to Hahn: I don’t feel at all happy. Here I just have a workplace, no position that would entitle me to anything. Try to imagine what it would be like if, instead of your nice private institute, you had a room in an institute which is not your own, without any help, without any rights, and with the attitude of Siegbahn who only loves big machines

.c1

and who is very confident and self-assured—and there am I with my inner shyness and embarrassment! And that I have to do all the petty work which I haven’t done for 20 years. Of course, it’s my fault. I should have prepared my departure much better and much earlier, I should at least have had drawings of the most important apparatus, etc.

.c2

But the essential thing is that I have come here so empty-handed. Now Siegbahn will soon believe—especially after your excellent results—that I didn’t do anything and that you both did all the physics too at Berlin-Dahlem. I am losing all my courage.

.c3

He could not afford to have his name professionally linked to a Jew’s. Over and over again, he thought Meitner should have understood that and not asked so much of him.

Hahn

He wrote a terse letter back, insisting that his discovery “owed nothing to physics!” He conveniently forgot that his own article had left the interpretation to physicists, admitting chemists couldn’t understand the data. He had no idea that Meitner’s thinking was based on quantum physics, on Einstein’s famous formula of the relationship between energy and mass.

Hahn

In late 1939, soon after the start of World War II, she wrote to Hahn that “my work is equivalent to zero.” She felt at the lowest point of her career.

While the United States ended up employing 130,000 people and spending 2 billion dollars on the project, Germany’s Ministry of War set up a small office for nuclear research with nowhere near the personnel, funding, or organization.

As the person who had discovered nuclear fission, Meitner was offered a position alongside her nephew. She was tempted by the thought of a well-equipped lab with an organization solidly supporting her work. But she was horrified by the idea of working on anything that could be used as a weapon.