Gone, Fission: How Lise Meitner was Written Out of the Nuclear Age. (Women in Science 75!)
To fully appreciate Lise Meitner, you have to first forget everything you learned about the atom in high school. Forget that the nucleus is made up of neutral particles called neutrons and positive particles called protons. Forget about how electrons live in statistically determined probability clouds outside the nucleus. Forget entirely about how Alpha decay ejects a Helium nucleus from the atom, and Beta decay allows neutrons and protons to change into each other to preserve stability.
All of those powerful commonplaces were entirely unknown to Meitner’s generation until they took up the bafflingly complicated task of discovering them through brilliant manipulations of magnetism, radiochemistry, and theoretical physics. That era, the age of the atom’s unveiling, is littered with scientific immortals: Bohr and Einstein, Heisenberg and Schrödinger, Fermi and Pauli, and the theoretician of nuclear fission, Lise Meitner (1878-1968).
The mythology of Meitner is a complicated yarn basket of truths and obfuscations that historians of science have only started to untangle in the past few decades. In the United States, she was wildly popular based on a story that she stole Hitler’s nuclear bomb plans and smuggled them to the Allies, which was manifestly not true and embarrassed her thoroughly every time it was brought up. Meanwhile, in Europe, her critical role in nuclear fission’s discovery was carefully erased by a dedicated team of German chemists who wanted to keep the credit for themselves as part of Germany’s post-war spiritual reconstruction. Lionized for what she didn’t do, and summarily punted out of what she did do, Meitner only received something like proper acclaim for her many accomplishments towards the end of her long, frustrating, exciting life.
As impressive as her scientific career was to become, it was very nearly smothered at age fourteen. Meitner was an Austrian, and Austria was one of the decided latecomers to the idea of women’s education. Up until the very last years of the nineteenth century, public education for girls simply ended at fourteen. At that age, your choices were either to wait for marriage or to find a private teaching position . School taught girls drawing and singing, but no math beyond what was needed to balance the housekeeping books. Meitner, who dearly loved science and math from a young age, was faced with the prospect of a career as a French tutor as the summit of her hopes.
For seven crucial years, from 1892 when she completed the public education a girl was allowed, to 1899, years when her male contemporaries were learning all the science they could consume, Meitner waited. Finally, in 1897 the government opened the universities to women, if they could pass the Matura. Meitner raced to catch up on the years of education she had been forbidden and, in 1901, took the test that allowed her to finally follow her calling.
She passed, and attended the University of Vienna, where she caught the bug for physics from Ludwig Boltzmann, one of those rare scientific geniuses who was also a tremendous, human, and approachable educator. He had not a stick of gender prejudice about him, and promoted Meitner’s studies with understanding and zeal.
It wasn’t in Austria, however, but in Berlin, under Max Planck (who was considerably more skeptical about women’s ability to do science until Meitner proved him wrong), that Meitner would record the string of discoveries that made her name. She was interested in the mysteries of radioactivity, a field ripe with potential for a physicist wanting to understand the nature of atomic structure and nuclear stability. Those studies, however, called for complicated chemical separations that required the guiding hand of a master chemist. Meitner found hers in a fellow young researcher named Otto Hahn.
For three decades, from 1907 to 1938, Hahn and Meitner were a physico-chemical power team, Hahn handling the tricky chemical manipulations required to isolate radioactive substances while Meitner handled the mathematics and physics of explaining the results. In practice, Meitner handled as much of the chemical experimentation as Hahn did, but in the years of their closest collaboration, the breakdown of duties hardly mattered. They were a team that worked, and success rolled out of their lab at a steady clip.
They started by categorizing different alpha and beta emitting substances with an eye towards locking down the similarities and differences between the two types of radiation. In the process of doing that, they rediscovered an effect that would be crucial to all their future research: radioactive recoil. It’s when a nucleus, after ejecting a particle, flies away from its parent substance, depositing as a film on a nearby surface. Remember that Harriet Brooks had discovered the effect previously, but its significance had gone unremarked until Meitner and Hahn rediscovered it and began using it as a way to separate radioactive substances from each other. Rutherford, ever Brooks’s advocate, wrote to Hahn pointing out that the effect had been noted by Brooks, but Hahn refused to concede her priority.
This touchiness over priority ought to have troubled Meitner, but she and Hahn had other atoms to fry. In particular, with the coming of World War I, and Hahn’s drafting into Germany’s poison gas program, Meitner was left on her own to divide her time between war work (which included volunteering as an x-ray technician at the front, inspired by the example of Marie and Irene Curie) and continuing the team’s research. Without appreciable input from Hahn, she succeeded in the unspeakably fine task of discovering a new element, protoactinium, a major result which was nevertheless published with Hahn’s name first.
Why Meitner released a result she obtained by herself with Hahn’s name is unknown, and why she put his name first is nearly unfathomable, but it was an act of generosity that would come to haunt her later, when Hahn’s apologists tried to characterize her as merely Hahn’s lab assistant, rather than a full scientist in her own right.
The war over, Hahn and Meitner had to struggle under the weight of performing experiments while hindered by incorrect but plausible theories about how the atom is structured. Before 1932, when neutrons were discovered, the best theory for how the nucleus worked was based on the idea of nuclear electrons, i.e. electrons that live in the nucleus. We now know that the reason a U-238 nucleus, for example, has a charge of +92 but a mass of 238 is because it has 92 protons and 238-92 = 146 neutrons. But without the neutrons, you could only assume that the nucleus had 238 protons, whose charge was brought down to 92 by the presence of 146 electrons in the nucleus.
Figuring out how Beta decay works when you have a model of the nucleus like that as your starting point is a daunting task, made even worse by the fact that the electrons emitted during Beta decay seemed to have a continuous distribution of energies, which flew in the face of everything physics knew about the Conservation of Energy. Meitner would spend much of the 1920s trying to nail down precisely the order of events in Beta Decay, and for her rigorous work establishing the Beta sequence, she was made Germany’s first woman professor of physics in 1926.
As if that conundrum weren’t perplexing enough, the Thirties brought a whole new vat of Puzzling to ponder over in the form of neutrons, positrons, and neutron impact events. There is a ton of fascinating science that Meitner did during this period, including experiments with gamma scattering to determine how photons interact with matter, and her work discovering the first positrons from a non-cosmic source, but I have a feeling the reason you’re here is fission, so let’s get to it.
In 1934, Meitner had determined that the energy of a neutron when it collides with a nucleus has a role to play as to whether that neutron is simply captured or whether it punches an alpha particle out of the nucleus. That same year, Enrico Fermi, through neutron bombardment, appeared to have made the world’s first transuranium elements (elements higher than Uranium on the periodic table). The scientific community rushed to confirm the results, but difficulties arose in verifying the chemical status of the products. What was known was that a neutron struck an element, and the result was a different element, the assumption being that it was the next higher element, or element 93. For four years, nobody considered the possibility that the product elements were in fact much smaller fragments of the original uranium atom.
Meitner and Hahn worked on the project of identifying the transuranium elements, doing what they could under the increasingly oppressive shadow of Nazi Germany. Hahn, though not a member of the Nazi party, was of “pure” racial lineage, but Meitner was of Jewish descent, and a woman, two things that the Nazi administration couldn’t long stand in a position of respect and authority. That she lasted in her post as long as she did was largely a measure of the length of time she had been in her position, and her work during the First World War as a nurse and field technician.
But the walls were closing. Meitner hesitated, not wanting to leave behind her work and her routine for untested waters, but by 1938 there was no more hiding the fact that she needed to flee Germany as soon as possible. The government was rounding the turn from encouraging Jews to leave to making it impossible for them to do so. Meitner, as somebody with technical expertise, and somebody with an international reputation, was doubly forbidden to emigrate, lest she pass on vital information to Germany’s competitors and discredit the German state, as Einstein had done with his emigration earlier. She had no choice but to illegally flee the country, leaving her books, her furniture, much of her clothes, and her work behind as she was snuck out of the country by friends and aided by sympathetic border guards. She was bound for Sweden, her greatest discovery, and decades of frustration.
Her new post was in Manne Siegbahn’s recently established nuclear laboratory, where she was given an empty space and left to her own devices, living on a pittance in a small unfurnished room with nothing to wear except the few articles of clothing she could gather up before her flight. Siegbahn considered her an imposition, and was routinely and aggressively unhelpful in securing her the equipment she needed to do the barest of research. Her only solace was in advising Hahn and their assistant, Fritz Strassmann, on their transuranium studies, pushing them to investigations that, as chemists, they were unwilling to do, but that turned out to be crucial to the discovery of nuclear fission.
Their experiments were turning up an element that looked a lot less like element 93 and a lot more like good old barium, but they couldn’t bring themselves to believe it, and repeatedly asked Meitner whether the results made sense from a physics standpoint. Meitner, during a walk with her nephew, Otto Robert Frisch, worked out a model whereby the nucleus split, releasing energy corresponding to the difference in stability of the parent and daughter atoms, and found that the numbers worked out perfectly. Frisch coined the term “fission” for the process of an atom breaking into pieces, and the nuclear age was born.
At first, the priority was relatively clear. Hahn, Meitner, and Strassmann had been working on the project until Meitner was forced to flee. Hahn and Strassmann continued the physical experiments, under Meitner’s remote guidance, which uncovered the fact of fission, and Meitner’s grasp of physics provided the theoretical explanation for the results. To any sane person, fission was an interdisciplinary discovery to be credited to Hahn, Meitner, and Strassmann, with Frisch thrown in if you were feeling generous about it.
But that’s not how Germany would remember it. After the Second World War, the German nuclear physicists were gathered up by the Allies and kept under observation in an electronically bugged house. There, they crafted the myth that the Germans were technically proficient enough to create an atomic bomb, but that they didn’t because they were too moral. It was a complete lie, and one of its sub-stories was that the discovery of fission, which kicked off the whole nuclear age, was the doing of German chemistry alone, and belonged solely to Hahn and Strassmann, and that, come to think of it, Meitner had been impeding the discovery the whole time she was around.
After the war, Meitner was able to finally return to research when, in 1947, she left Siegbahn’s lab to take up a position at the Royal Institute of Technology. There, starting anew at the age of 69, she studied the role that neutrons play in atomic stability, how heavy elements besides uranium capture neutrons, and how energy released during fission relates to the size of the fragments created. It was important work for the development of nuclear reactors and the theoretical understanding of fission, but it was marred by Hahn’s forceful attempts, while maintaining ties of personal friendship with Meitner, to exclude her from co-credit for fission, which he and Strassmann received a Nobel Prize for just after the war.
Hahn was the lion of German science following World War II, a charming and photogenic spokesperson for a Germany trying to forget its past and get on with the business of becoming an economic and scientific superpower again. Research centers and children were named after him. Lise Meitner died in 1968 just shy of her ninetieth birthday, honored bountifully as a person by the country that had done her so much wrong, but not as a scientist. Great as Germany was growing, it was not halfway great enough to think of her intellectually as anything but Hahn’s loyal assistant until quite recently. Some half-lives are longer than others.
FURTHER READING: Otto Hahn’s A Scientific Autobiography (1962) is an interesting read about the chemistry of early radioactivity studies, and a clear example of his unwillingness to give the least credit to Meitner for her part in fission’s discovery. As to biographies, I’ve talked before about how great Ruth Lewin Sime’s Lise Meitner: A Life in Physics (1996) is, particularly in the detail it goes into about the confusing rush of experimentation in the early days of radioactivity research. The concluding chapters get a bit samey-samey, but in the name of publishing a story that had been vigorously suppressed for the better part of four decades, I think we can deal.