If you asked a bunch of people to write down an equation associated with nuclear physics, those who could write anything at all would most likely write down
Einstein’s most famous equation. You’d get different results if you asked at a university physics department, and I’d probably write down a beta decay reaction But Einstein’s mass-energy equivalence formula has become so closely associated in popular culture with nuclear fission that I like to think of it as a meme. It is repeated because it is compact and can easily be manipulated by anyone with a most basic understanding of algebra. Please notice that I did not say that it was easy to understand. Some may think they understand the formula because of its simplicity, but it is actually very difficult to derive and even harder to grasp on an intuitive level. The equation is repeated so much because it gives the illusion of understanding and because it is connected to the celebrity of Einstein.
But Einstein himself had almost nothing to do with the development of nuclear physics and published only two papers on experimental physics in his lifetime. There is indeed a connection between nuclear reactions and Einstein, but he had nothing to do with its discovery. The connection was quite unexpected and made by Lise Meitner, a scientist exiled from her own lab.
Lise Meitner at the Kaiser Wilhelm Institute:
Lise Meitner was only the second woman in Austria to be awarded a PhD in Physics left Vienna to continue her work in Berlin. When she first arrived she had trouble finding paid positions and survived on family support while being assigned only less important work. She did have some spare time and access to materials to conduct her own experiments, but Meitner was beginning to think she might not have a future in Berlin. Some of her former teachers from Vienna were now in Berlin and one of those teachers, Max Planck, was able get her a low level paid position. She also started her professional relationship with Otto Hahn during this time.
Meitner’s fortunes would change with the foundation of the Kaiser Wilhelm Society and its associated privately funded research institute. The Institute was mostly staffed with younger scientists and was intended to have a very different culture than early 20th century German universities. With strong lobbying from Hahn and a recommendation from Planck, Meitner was made an equal partner in the nuclear chemistry lab founded by Hahn.
Meitner would run the lab by herself when Hahn was drafted into the German army in WWI, though she shut the lab down and enlisted as a nurse in the Austrian army a year into the war. She was put in charge of the operation of x-ray machines in a military hospital. X-ray imaging was new and the machines were very unreliable. Meitner’s expertise was needed.
After the war, both Meitner and Hahn returned to the Institute. Because of its large private endowment, the Institute was largely untouched by the economic problems of Weimer Germany and both Meitner and Hahn were able to continue their work. Meitner was even able to establish her own independent department, and Hahn was placed in charge of an expanded nuclear chemistry department.
Science in Nazi Germany:
In 1933 the new government began placing restrictions on Jewish staff at German universities. The Institute was not publicly funded and thus had some ability to resist complying with these laws, but Meitner did quit teaching classes and focused solely on research. The German government continued to pressure The Institute and some Jewish research staff were dismissed, though Meitner and others were retained with the strong support of the staff and faculty.
Lise Meitner also had the advantage of Austrian citizenship, so she had Austrian passport and freedom to travel. During a trip to Rome to hear Enrico Fermi lecture she would get the idea for one of the most important research programs of all time, one that would unexpectedly lead to the unexpected discovery of nuclear fission.
In Rome Meitner learned of Fermi’s attempt to synthesize elements heavier than uranium by bombarding uranium atoms with slow moving neutrons. His idea was that the uranium nucleus would absorb the neutron and become unstable. He predicted that the unstable atom would undergo beta decay twice and move up two places on the periodic table to become element 94, what we now call plutonium. This actually is possible, and later on Fermi would work on plutonium synthesis as part of the Manhattan Project, but at the time Fermi’s results were confusing and he could not confirm that he synthesized any new elements.
Lisa Meitner was fascinated by the possibility of synthesizing new elements and returned to Berlin to work on this problem. But to succeed where Fermi failed she would need the help of the best analytic chemist working with radioactive materials. And that was Otto Hahn.
Progress was slow and Meitner and Hahn got the same confusing results Fermi did and could not find any evidence of element 94. During this same time Irene Joliot-Curie, daughter of Marie and Pierre, had reported even stranger results in her similar research. At one point she seemed to detect barium as a result of the interaction between uranium and neutrons. Joliot-Curie was unable to replicate this result. This seemed impossible as all nuclear changes up to that time had been small changes. Alpha emission moves an element down two places on the periodic table, and beta decay moves an element up one place. A complete fracturing seemed unlikely. Scientists working in Germany, including Leo Szilard, had discovered what they called Spaltung, using high energy particles to fracture light nuclei. But how could a low energy interaction split a uranium atom into something as light as barium?
Neither Meitner nor Hahn believed this was possible. After the 1938 Anschulss Lisa Meitner’s Austrian travel papers became invalid and the German government asked that she be dismissed from her research position. Nor would Meitner be allowed to leave Germany. Hahn and others were not able to secure travel papers for Meitner and she eventually resorted to crossing the Netherlands border illegally and would later take an academic position in Sweden.
Hahn would continue the uranium project with his assistant, Fritz Strassmann. Otto Hahn began a secret correspondence with Lise Meitner, who still played a guiding role in the research. Hahn would write to Meitner that he thought he also found barium, though the amount was very small and energy output from the interaction was inconsistent. Meitner argued that he should be certain that he had barium as there was no theoretical explanation for this result. She knew Hahn’s analytic skills would be able to distinguish barium from the much heavier, though chemically similar, radium. Late in 1938 Hahn announced that he had confirmed the presence of barium and published a hastily constructed, though correct, description of Uranspaltung the complete fission of a uranium nucleus into barium, krypton, and three free neutrons. Hahn made no mention of Meitner’s contribution to the final stages of the work.
And lots of energy. It had seemed that not enough energy had gone into the reaction, and a bit too much was coming out.
Theories and Honors:
Even before publication Hahn had written a letter to Meitner asking if she had any explanation for his unusual results and this would lead to a discussion between Meitner and her nephew, Otto Frisch, a physicist working with Bohr in Copenhagen. Meitner would first suggest that Hahn’s Uranspaltung might be a case when Einstein’s mass-energy equivalence might be making a measurable difference in the results and would partly account for the unusual energies in the reaction. Meitner performed a few calculations that modeled how this could be possible, and Frisch would make a few measurements that showed these calculations accounted for the energies.
Meitner and Frisch would publish their theoretical description of what they named “fission” and published their results in Nature in 1939. Frisch is sometimes credited with coining the term “fission” but I am fairly sure the term was in use in France and that Frisch simply popularized it in English. English cognates of the German term spaltung were already used in English and I think Meitner and Frisch chose to adapt the French “fission” to emphasize this was a new type of nuclear process.
One obvious conclusion from Meitner’s analysis of fission was that it would be possible for fission reactions to sustain themselves under certain conditions, and that such a self sustaining series of reactions, a chain reaction, could be made into a powerful weapon.
This theoretical description of the fission process was surely worthy of consideration for a Nobel prize, but the sole recognition of fission by the Nobel committee was that Hahn was awarded the Chemistry Medal in 1945. Many physicists, most notably Nils Bohr, saw this as an oversight and recommended that Meitner should be recognized for her description of energy release in fission. Surely fission was so significant that it also merited a separate prize in physics and Meitner should get it. And after all, Meitner had been the one who started Hahn’s project in the first place.
But there was no prize. There are many different reasons for this. One is simply that the Nobel committee was not really set up to understand the interdisciplinary nature of nuclear research. Much of this is because most committee members were simply from ann earlier generation and had for the most part achieved their success before nuclear science had become such a prominent area of research. They saw nuclear research as primarily a form of chemistry, and thus favored chemists like Hahn over physicists.
And obviously general conservatism and sexism played a part, though I think probably only subtly. That doesn’t mean these biases weren’t important. Two women had previously won Nobels for nuclear work, but this sort of thing tends to happen. When a field of scientific study or artistic expression is new, women are there. But after these fields become established, women become less prominent. Without even looking it up I can think of four women doing top level nuclear research in the 1930s. That number is perhaps a little low, but it’s still a pretty good portion of what was a very small community. However, I can’t name a single woman who was doing top level work in the golden age of subatomic physics in the fifties and sixties. This isI am sure not entirely an accident.
Interestingly, shortly after being passed over for the Nobel, Lise Meitner would become a foreign visiting member of the Swedish Academy, and would become a full member after she became a Swedish citizen.
Pop Culture Fame:
Perhaps the Nobel Prize isn’t that important. Community respect and popular recognition matter too. In the late forties and early fifties Meitner was something of a star. She toured the United States and held two guest professorships there. Most of her prestige came from her association with the atomic bomb and she was sometimes called the “mother” of the bomb. She was quite uncomfortable with this, and tried to make clear that she had declined to join the Manhattan Project when she was recruited for it early in 1943.
By the sixties her popular recognition had faded and Meitner became a name hastily read in textbooks. Meanwhile, Einstein’s mass-energy equation became a popular stand in for nuclear power and nuclear weapons. Almost no one who knew the equation and wasn’t a scientist knew that Meitner had been the one to make the connection between Einstein’s equation and nuclear reactions, and thus allow the power of fission to be quickly developed.
But physicists and chemists still remembered her, and in 1982 when the synthesis of element 109 was confirmed, many suggested that it should be named after Meitner. In 1994 when the IUPAC officially recognized element 109, naming an element takes time, this new element was called Meitnerium.
The Nobel is just the Nobel. Meitner’s name will be on classroom periodic table wall charts as long as there’s still chemistry.
If you want to learn more about Meitner and Hahn, this documentary is quite good.