During a snowy winter day in Sweden, Lise explains nuclear weapons fire | Paul
Professor Lise MeitnerCredit: Jacinta Gonzalez
Imagine that you are a decisive person in the discovery of something in nature of historical proportions. How would you feel to have stepped on ground where no one in the history of mankind has trespassed? What an honor and joy to discover something about nature that is new to our pursuit of knowledge. The obstacles in life seem unimportant during these moments of great discovery. This is exactly what many researchers have experienced in their journey to understanding, among them, Madame Professor Lise Meitner (Lise pronounced “Leeza”) (1878 – 1968), the discoverer of nuclear fission, an Austrian-Swedish physicist of Jewish descent working in Nazi Germany with chemist Otto Hahn (1879 – 1968). Unfortunately, Hahn was the only one to receive the Nobel Prize (in Chemistry) for this momentous discovery of splitting the atom and the German military began investigating it in April 1939, long before the Allies (Overlooked Achievement: The Life of Lise Meitner, lecture by Ruth Lewin Sime). If it were up to me, Lise deserves a posthumous Nobel Prize.
Enrico Fermi had already done experiments in Italy where radioactivity was induced in atoms by bombardment of neutrons (neutral subatomic particles in the atomic nucleus). Fermi expected the neutrons to stick to the nuclei of heavy atoms and produce even heavier atoms, thus missing the chance of almost discover the splitting of the atom. However, Fermi went on to receive a Nobel Prize for his discovery of neutron-induced radioactivity and the importance of slow neutrons in nuclear reactions.
Lise was considered many times to deserve a Nobel and received countless other honors (among them, the naming of element 109 as Meitnerium and in 1966 The Enrico Fermi Prize). She also remained a friend to Hahn throughout their lives. Lise and Otto had worked together years before, and they are both credited with the discovery of a new radioactive element, protactiniumelement 91.
When Hitler was in power, Lise had to flee from Germany to Sweden even though she kept in touch with Otto Hahn via correspondence. Lise explained her experimental results with mathematical proof in collaboration with her nephew Otto Frisch and it was they who coined the scientific term “fission” knowing that it was already used by biologists to describe cell division (Institute for the History of Science). The nucleus of a uranium atom is like a small “liquid drop“, ready to split in two if it gets more neutrons.
The fission of the uranium atom, retrieved from https://www.nuclear-power.com/nuclear-power/fission/liquid-drop-model/Credit: Ida Lee
Hahn and his colleague Fritz Strassmann determined the identity of the atomic fragments with “chemical evidence”, following Lise’s insistence on verifying her experiments more thoroughly. Hahn wrote, “you might be able to come up with a fantastic explanation”. She was still the “intellectual leader of the team” even though she was in Sweden and Hahn in Berlin (Overlooked Achievement: The Life of Lise Meitner, lecture by Ruth Lewin Sime). Some of the fragments were from the element barium, with a mass about half that of uranium. Meitner came up with a “fantastic explanation” and confirmed the results that the atom can split (fission). She calculated that the sum of the parts did not equal the whole. The mass of the fragments (daughter atoms) was thus not exactly the mass of the parent atom the mass defect could only be explained by energy, that is, “the two daughter nuclei would together 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.” (APS Physics).
During a snowy winter day in Sweden, Lise explains nuclear weapons fire
December 1938, over the Christmas holidays, while Lise was in “exile” in Sweden, she received a letter from Otto Hahn. It was a “bright day; snow sparkled on roofs and trees”. Hahn explained that he had bombarded a uranium sample with neutrons and that what remained was barium. Hahn wondered if he and Strassman had made a mistake. Lise’s neurons began to fire, wondering if neutrons had caused the uranium atom to split almost in half. The heavy nucleus of uranium is like a “thin rubber balloon” ready to burst if more neutrons enter its nucleus. “Pinching the letter,” Lise went to her nephew’s hotel. Otto Frisch “wasn’t in the mood” to read a letter. “It is impossible,” Frisch said when he heard his aunt’s possible explanation of Otto Hahn’s results. And so the story continues, after going for a walk with her nephew Frisch and sitting on a “fallen tree trunk”, Lise confirmed that there is “fire” inside the atomic nucleus (Lise Meitner, Atomic Pioneer by Deborah Crawford).
There were two publications on the discovery of nuclear fission: one by chemists Otto Hahn and Fritz Strassmann and another by physicists Lise Meitner and her nephew Otto Frisch. Perhaps out of fear and political repression, Hahn did not mention that he was still in communication with Lise and that she deserved to share the discovery (Overlooked Achievement: The Life of Lise Meitner, lecture by Ruth Lewin Sime). His motives may not be easy to explain. Again, it was Lise who urged Hahn and Strassmann to verify their experimental results (at first they thought the uranium’s daughter atoms were radium, and after verifying their results they were actually from the element barium) and it was Lise who explained the experiment with E = mc2. The discovery of fission belongs to both chemistry and physics.
“A physicist who never lost his humanity”
One of Lise’s favorite authors was Lucretius, an ancient Roman poet: “Atoms move…fixed and eternal; these we call the seeds of things…in them lies the sum of all created things” (Lucretius). It was the concept of atoms already in the 1st century BC. Twenty centuries later, Lise changed Lucretius’ poetic description with paper, pencil and Einstein’s energy formula, sitting on a log with her nephew Frisch in Sweden (Lise Meitner, Atomic Pioneer by Deborah Crawford). Not only are atoms the “sum of all created things,” but Lise went even further and discovered that this “sum” of an atom’s parts did not exactly equal the whole. This could only be explained by energy. In simple terms: Fragment + Energy = Moderatom.
Lise was never recognized with a Nobel, but her name will always be in the Science Hall of Giants (Madame Curie, Albert Einstein, Niels Bohr, Enrico Fermi…). The mother of the atom suffered many obstacles in her life as a human being, as a woman, as a Jew and as a scientist. Her name rose to the pinnacle of physics and her discovery of fission will always be fundamental to our pursuit of knowledge. Eventually, her discovery was weaponized, but she refused to work on the Manhattan Project. Lise resting place is in St James Churchyard, Bramley, Hampshire, England, where she died in 1968. On her tombstone, a epitaph written by Otto Frisch reads: “A physicist who never lost his humanity”.