By Priya Binwal
Physicist Lise Meitner, lecturing at Catholic University, Washington, D.C., 1946. Credit: Wikimedia Commons
In the summer of 1938, a petite woman aged 59 arrived at the German-Dutch border, with 10 Deutsche Marks in her purse, a few summer clothes in her suitcase, and a diamond ring she had acquired only a few hours ago. Her name — Lise Meitner.
Meitner’s heart pounded nervously throughout the journey across the border — her escape from Berlin was not permitted by German law. But she had to take her chances, for it was now or never. Nazi Germany had just annexed Austria which meant Meitner, a Viennese by birth, had lost her Austrian citizenship and could also no longer hold a post as a physicist at the Kaiser Wilhelm Institute(KWI) because of her Jewish ancestry.
Fleeing the country illegally was the only alternative, and thankfully enough, members of the international physics community helped her escape. Dutch physicist Dirk Coster escorted Meitner on the train, which allowed her to first reach the Netherlands and then go on to Sweden. Her escape from Berlin had been a secret, with no time wasted on goodbyes. Before leaving, Meitner just met one close friend and long-time collaborator, Otto Hahn, who gave her the diamond ring that belonged to his mother, urging her to use it in case of an emergency. And so with 10 marks in her purse and a diamond ring on her finger she fled Germany, never to return.
It might be far-fetched to call Meitner’s life in Sweden a fresh start — she had no possessions, no close friends, and no sense of belonging in this completely new country. Perhaps the only thing that kept her going was something that had also driven her during her girlhood days — her love of physics.
The only woman
Meitner was born in Vienna, in 1878, to a Jewish, upper-middle-class family, and even as a young girl she demonstrated great scientific curiosity. But getting into science was never going to be easy for her because at the time, women in Vienna weren’t allowed to attend public institutions of higher education. Even when things did change in 1897, Meitner was one of only four women out of fourteen to pass the requirement for enrolling in a university program in Austria.
At the University of Vienna, Meitner took a course taught by Ludwig Boltzmann, the famed physicist whose lectures Meitner would later describe as, “the most beautiful and stimulating that I have ever heard.” Boltzmann was also one of the few scientists who accepted female students in his courses. Inspired by his contagious love for physics, Meitner persevered, finally earning her doctorate in Physics in 1906 and becoming the second woman in Vienna to do so.
Even for a talented, young woman like her, the prospects of landing a paid job in academia were rather bleak due to pervasive socio-religious and gender inequalities — Austria hadn’t even had a female assistant by then. But Meitner was able to negotiate an unpaid postdoctoral position in Berlin, where she moved to study and found herself, once again, to be one of the very few women treating the university corridors.
Nuclear physics in Meitner’s time
It was in Berlin where Meitner met Otto Hahn, a radiochemist, with whom she would spark a life-long friendship and collaboration that would eventually result in the discovery of nuclear fission. In 1912, she and Hahn joined the newly opened KWI in Dahlem, Berlin, and Meitner would continue to work there until she was forced to flee Germany almost 30 years later.
Otto Hahn and Lise Meitner working in the laboratory at KWI in 1912. Credit: Wikimedia Commons
By the 1930s, scientists had figured out that the atom consists of negatively charged electrons going around a positively charged nucleus made of protons and neutrons. Scientists also knew that while atoms of the same element have the same number of protons, they could still differ in mass due to a difference in the number of neutrons (isotopes). Research by Henri Becquerel, Marie Curie, Pierre Curie, and others had shown that some of these isotopes could be radioactive, which means that they might have excess nuclear energy that makes them unstable. Unstable isotopes decay by emitting the excess energy as radiation, such as the carbon isotope 14C present in organic matter (this decay process enabled paleontologists to determine the age of dinosaurs from their fossils).
Afterward, scientists realized that bombarding the nuclei of different atoms with subatomic particles could reveal a great deal about atomic structure. However, a tremendous amount of energy was required to accomplish this because early experiments involved bombarding positively charged nuclei with positively charged particles, which led to electrostatic repulsion. Realizing this challenge, the Italian physicist Enrico Fermi began using neutrons to bombard atomic nuclei instead. Fermi expected better results from this method as neutrons carry no electric charge. Soon other researchers, including Meitner and Hahn, began to carry out similar bombarding experiments.
Splitting the atom
Even after Meitner fled from Germany to Sweden, she was able to maintain a close collaboration with Hahn through correspondence. It was through one such letter that Meitner learned about something peculiar that Hahn and another colleague, Strassmann, had just discovered.
Hahn informed her that they had obtained an element chemically similar to barium (Ba), by bombarding uranium (U) nuclei with neutrons. Meitner found this bizarre because it meant that a heavier element, uranium (atomic mass= 235), was somehow giving rise to a lighter one, barium (atomic mass= 141) — and barium was barely half the original mass of uranium.
Meitner was aware that a heavy element could occasionally change into a lighter one by kicking out a proton or alpha particle, but the end result would be a mass not much different from the original value. In this case, though, it seemed like the uranium in their experiments was somehow splitting in half! However, knocking out a large number of particles from the uranium nucleus, especially with insufficient energy, was considered impossible. What was going on?
The Periodic Table, with the elements involved in Meitner's work highlighted in red. Credit: modified from LeVanHan via Wikimedia Commons
In December that year, Meitner was visited by her nephew and physicist, Otto Frisch, and she described to him Hahn’s peculiar findings. Together, they discussed the observations and came to the conclusion that upon being bombarded by a neutron, the nucleus would first become elongated (much like a drop of water) and then start to pinch in the middle, finally splitting into two. They worked out the mechanism behind this using Einstein’s famous mass-energy equivalence (E= mc^2) to show that after the split, the two atoms would be driven apart by about 200 MeV (equal to the loss of 1/5 of a proton mass) of energy. They had done it — finally, they had worked out the mechanics behind splitting the atom, a process known otherwise as nuclear fission!
The equation for uranium fission
A blatant exclusion
While publishing their work on fission, however, Hahn and Strassmann blatantly avoided any mention of Meitner and their collaboration with her. Meitner, after all, was a Jewish refugee in exile, and they couldn’t afford to hurt their reputation in Nazi Germany by openly admitting to collaborating with her. They claimed that the credit for the discovery of fission belonged to chemistry and not to physics. In a letter to Meitner, they wrote, “In all our work we [Hahn and Strassmann] absolutely never touched on physics, instead we only did chemical separations over and over again.”
Meitner wrote to the editor of Nature explaining the mechanism that led to splitting the atom, which Hahn had failed to explain in his paper. However, ultimately the Nobel Prize in Chemistry was awarded to Hahn alone in 1944 for “his discovery of the fission of heavy nuclei.”
Meitner’s exclusion from the Nobel prize may be seen as an outcome of deeply rooted religious and gender bias and the Nobel committee’s inability to fully understand the nature of her interdisciplinary work. One may question this bias: would a non-Jewish man with Meitner’s accomplishments still have suffered a similar fate, still be pushed to the margins with such apparent ease?
Meitner’s accomplishments warrant a second mention as she, along with Hahn, also discovered protactinium-231, a radioactive isotope of protactinium (Pa), in 1917. A later generation of nuclear chemists went on to name an element (Meitnerium, Mt) in her honor.
Meitner was one of the first women scientists to leave her mark in the world of physics, and in doing so she paved the way for generations of other women to come. In Meitner’s own words, “life need not be easy, provided only that it is not empty,” and so it might be said she lived her own life accordingly as a woman in the world of science.
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