Lise Meitner and Nuclear Fission
The second in a series of four biographies about overlooked women in science
For a long time it was taught that Otto Hahn invented nuclear fission in 1938 with his breakthrough experiment. However, much of the work was done by his student, Lise Meitner, who was never given the credit she deserved. Her findings in nuclear physics laid the groundwork for the atomic bomb and her story is a complicated tangle of politics, sexism, and anti-Semitism.
Born in Vienna, Austria in 1878, Lise Meitner grew up in a scholarly family. Always curious, she was drawn to mathematics and science at an early age. When she was eight, she studied the colors of an oil slick, thin films, and reflected light.
Meitner completed her final year of middle school in 1892. However, it wasn’t until 1897 that women were permitted to attend public institutions of secondary education in Vienna. The only career available to women at the time was in the classroom, so Meitner trained to become a French teacher.
Once higher education was available to women, Meitner and two other young women started taking private lessons, condensing the eight years they missed into just two.
In 1901, fourteen women sat for a rigorous examination at the Akademisches Gymnasium. Only four women who took the exam passed, including Meitner.
After completing her doctoral research in 1905, Meitner became the first woman from the University of Vienna and only the second in the world to earn a doctoral degree in physics.
Still, the only career available to women in Vienna was teaching. She left for Berlin in 1907, hoping to find opportunities for research.
Meitner was introduced to chemist Otto Hahn after she got a position at the Kaiser Wilhelm Institute for Chemistry (KWIC). Hahn and Meitner had a working relationship for over 30 years.
Meitner served as an X-ray nurse in the Austrian army during World War I. Upon her return to Berlin, she was appointed head of a physics section at KWIC, where she continued her research in nuclear physics.
Meitner’s work changed directions after the discovery of the neutron in 1932. Scientists began using neutrons to probe an atomic nucleus.
In 1934, Enrico Fermi collided neutrons and uranium, recording what he believed were the first elements heavier than uranium. Another lesser known chemist, Ida Noddack, foreshadowed nuclear fission when she suggested the uranium might have broken up in Fermi’s reactions. This would mean the experiment created lighter elements. However, she didn’t put forward any theories or framework as to how it would happen. Her paper was mostly ignored, and no one, including Noddack, pursued her idea.
Following in Fermi’s footsteps, Meitner and Hahn, as well as chemist Fritz Strassmann, began experimenting with collisions of elements (including uranium) and neutrons. They were trying to identify the decay products after these collisions. Meitner specialized in the nuclear physics research, while Hahn was focused on the chemistry involved.
Because of her Jewish heritage, Meitner was only able to work at the KWIC until 1938 when she was forced to leave Berlin and flee from the Nazis. The Nazis annexed Austria in March 1938. As an Austrian Jew, Meitner’s career and life were in serious danger. She escaped in July with only two small suitcases.
After emigrating to the Netherlands, Meitner moved and took a position in Stockholm at the Nobel Institute for Physics. It was difficult to conduct her research alone with few resources and in such a hostile work environment. She never fully escaped anti-Semitism and sexism. Meitner tried to keep in contact with Hahn to continue helping him with their joint research through letters.
In December of 1938, Hahn and Strassmann, who still continued their experiments, noticed what appeared to be barium isotopes in the decay products. They were stumped. At the time, it was believed a neutron couldn’t cause the nucleus to split into two or more parts and produce even lighter elements. Hahn wrote Meitner a letter explaining the strange discovery.
In the letter, Hahn wrote, “It is something with the ‘radium isotopes’, which is so strange that for the time being we only tell you. There could still be a most strange coincidence. But more and more we come to the terrible conclusion: our Ra(dium) isotopes do not behave like Ra(dium), but like Ba(rium). I have arranged with Strassmann that for the time being we only want to tell this to you. Perhaps you can suggest some fantastic explanation. We know for ourselves that it can’t actually burst in Ba(rium).”
During the December holiday break, Meitner was visited by Otto Frisch, her nephew. Frisch was a physicist who worked at Niels Bohr’s institute in Copenhagen. Mietner showed him Hahn’s letter. They both knew that Hahn hadn’t made a mistake, but the results didn’t add up.
Frisch made visual diagrams portraying how, after being hit by a neutron, the uranium nucleus might become elongated like a drop of liquid and could then begin to pinch in the middle. He predicted it could eventually split into two separate ‘drops.’
Frisch and Meitner predicted the two ‘drops’ would be driven apart by their mutual electric repulsion at high energy (they estimated about 200 MeV) after they split.
But where would the energy come from? According to APS Physics, “Meitner determined that the two daughter nuclei together would be less massive than the original uranium nucleus by about one-fifth the mass of a proton, which, when plugged into Einstein’s famous formula, E=mc2, works out to 200 MeV. Everything fit.”
After Frisch left Sweden, he and Meitner collaborated over long-distance telephone calls. Frisch briefly spoke with Bohr, who immediately shared the news of the breakthrough discovery to the United States, where it was met with immense interest.
The scientific community quickly realized that fission reactions emitted massive amounts of energy, especially if a chain reaction could potentially occur. Later, The Manhattan Project was formed to produce an atomic bomb. In 1943, Meitner was asked by the United States to work on the Manhattan Project. However, being a strict pacifist, she denied the offer. Meitner wanted nothing to do with it. She felt that her scientific discoveries shouldn’t be used to create such destructive weapons.
Meitner and Frisch compiled their findings in a paper they sent to Nature (February 11, 1939) right after Hahn and Strassmann published their results in Naturwissenschaften (January 6, 1939). Hahn and Strassmann didn’t acknowledge Meitner’s role in the discovery. It was Meitner and Frisch who named the new nuclear process “fission” after the term “binary fission” used among biologists to explain cell division.
According to the San Diego Super Computer Center, (SCSD), “The proof of fission required Meitner’s and Frisch’s physical insight as much as the chemical findings of Hahn and Strassmann.”
Hahn alone received the 1944 Nobel Prize in chemistry for his contributions to splitting the atom. “Meitner’s colleagues at the time, including physicist Niels Bohr, absolutely felt she was instrumental in the discovery of nuclear fission,” said Ruth Lewin Sime, a biographer of Meitner.
Meitner passed away from a series of strokes in 1968 in Cambridge, England at age 89.
Her accomplishments include, but are not limited to:
- The first woman to become a full professor of physics in Germany
- The first woman from the University of Vienna and only the second in the world to earn a doctoral degree in physics
- Contributed to the construction of Sweden’s first nuclear reactor
- Nominated 48 times for a Nobel Prize
- Awarded the U.S. Fermi Prize.
- Streets, schools, prizes, elements and even asteroids were named after Meitner
“You must not blame us scientists for the use which war technicians have put our discoveries.”