Today in History – February 11, 1939 – a “one page note” appeared in the magazine Nature by Lise Meitner and her nephew Otto Robert Frisch, entitled “Disintegration of Uranium by Neutrons: A New Type of Nuclear Reaction,” where for the first time a theoretical explanation for the splitting of uranium atoms was published and the term “fission” was coined for that process using the analogy of cell division in biology.

The Royal Swedish Academy of Sciences awarded the 1944 Nobel Prize for Chemistry in 1945 to Otto Hahn, for the discovery of nuclear fission. Lisa Meitner’s work was overlooked by the Nobel Prize Committee, as was the work of the French team Joliot-Curie and Savich. Lise Meitner, a physicist, who collaborated for 30 years with Otto Hahn, a chemist, had to flee Nazi Germany in the summer of 1938, on the brink of discovery of nuclear fission. Otto Hahn never acknowledged Meitner’s or anybody else’s contribution to the discovery of nuclear fission. The dispute about who has priority over this discovery that changed the world remains to this day.

The story began in 1932 with the discovery of the neutron by James Chadwick, who was awarded Nobel Prize in Physics in 1935 for this work. The same year, Nobel Prize in Chemistry was awarded to husband and wife Frederic Joliot and Irene Joilot-Curie for discovery of artificial radioactivity induced by alpha particles. Enrico Fermi, suspecting that neutrons could penetrate the nucleus more easily than positively charged alpha particles, started systematically bombarding all known chemical elements starting from hydrogen and moving through the periodic table of elements. After two years of experiments Fermi was ready to bombard uranium (the heaviest element known at that time with atomic number Z = 92) with neutrons, expecting that an unknown transuranium element with atomic number 93 could be formed by the beta-decay of the uranium isotopes produced by irradiation. Fermi measured new sources of radioactivity, but was not able to chemically identify those”new” transuranium elements. (Fermi was awarded Nobel Prize in Physics in 1938 for “his demonstration of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought by slow neutrons.)

The same happened to the German team of Otto Hahn, Lise Meitner and Fritz Strassmann in 1937: They had the best radiochemistry and nuclear physics expertise at that time but were not able to correctly identify newly formed “transuranium” radioisotopes.

The French team of Irene Joliot-Curie and Pavle Savich then entered the competition, and devised their own experiments. In resulting papers published in 1937 and in October 1938, Joliot-Curie and Savich pointed out a new radioisotope with a relatively large half life of 3.5 hours, that had properties of Lanthanum (in the middle of periodic table, Z = 57). They were within a hair’s breadth of discovering nuclear fission, but did not rule out the possibility that it could be some unknown transuranium isotope, with Z > 92.

The experimental results published in the 1938 Joliot-Curie and Savich paper convinced F. Strassman and O. Hahn to repeat their experiments (by that time L. Meitner had left Nazi Germany and fled to Sweden). Although far apart, Hahn and Meitner exchanged letters almost daily, discussing possible explanations of the experimental results (Ruth Lewis Sime gives details of their correspondence at that time). Hahn also secretly visited Meitner in Copenhagen in November 1938, where she expressed her dissatisfaction with the results and demanded more experiments. O. Hahn and F. Strassmann’s famous paper was published on January 6, 1939 in German scientific journal Naturwissenschaften, where they pointed out: “We must name Barium, Lanthanum and Cerium, what was called previously Radium, Actinium and Thorium. This is a difficult decision, which contradicts all previous nuclear physics experiments.” Although O. Hahn and F. Strassmann confirmed in their paper the presence of radioactive species which behaved as chemical elements in the middle of the periodic table, namely, Barium (Z = 56) and Lanthanum (Z = 57), they failed explain the physics behind the process and did not recognize that the atomic numbers (i.e., the number of protons) of the elements formed after a uranium nucleus is split must add up to 92.

The theory of nuclear fission was recognized and explained for the first time by Lise Meitner and Otto Robert Frisch in their famous paper published in the English journal Nature on February 11, 1939, after Frisch conducted his “recoil” experiment in which he was able to detect large ionization signals due to presence of fission fragments. The new process was named by them and explained using Bohr’s “liquid drop” model of the nucleus. They also calculated that two fission fragments should gain a total kinetic energy of 200 MeV, and pointed out that this was by far the largest energy released in any previously known reactions, and was due to the conversion of mass into energy according to the famous Einstein’s mass-energy relation.

Otto Hahn never acknowledged Meitner’s contribution to the discovery of nuclear fission. Ruth Sime points out: “For the rest of his life, Hahn provided a standard explanation: fission was a discovery that relied on chemistry only and took place after Meitner left Berlin; she and physics had nothing to do with it, except to prevent it from happening sooner. Hahn was believed, he was a Nobel laureate, and a very famous man. Strassmann, very much in his shadow, saw it differently. Lise Maitner had been the intellectual leader of their team, he insisted, and she remained one of them, through her correspondence with Hahn, even after she left. Meitner herself said a little, other than to point out to the essential interdependence of physics and chemistry throughout the long investigation. Privately, she described Hahn’s behavior as “simply suppressing the past (in Nazi Germany).” And, she added, “I am part of his suppressed past.”

The French group also did not receive the recognition for their contribution to the discovery of nuclear fission.

Personal note: I had a chance to meet with Pavle Savich at the Vinca Nuclear Science Institute near Belgrade (former Yugoslavia, now Serbia) where I worked before coming to the US, and to hear from one of the players the first-hand story about the discovery of nuclear fission. He always regretted that Irene Joliot-Curie and he were not confident enough to include a possibility of splitting of uranium in their 1937 and 1938 papers. It was confirmed in Meitner’s letter to Hahn in 1939: “In one of their C[omptes] R[endus] articles they emphasized strongly that their 3.5 h substance had very remarkable chemical properties and emphasized the similarity to lanthanum. The fact that they tried to place it among the transuranes doesn’t change their experimental findings. And these findings led you to begin your experiments. And again you have not stated that quite clearly”.One must not take people’s words so literally. Curie obviously saw that something remarkable was going on, even is she did not think of fission. In November [1938] Hevesy heard her say in a lecture that entire periodic system arises from U + n bombardment.” Irene Joliot-Curie was correct.

An excellent book Lise Meitner: A Life in Physics, that covers in great detail Lise Meitner’s life and career, was written by Ruth Lewin Sime and published by the University of California Press in 1996. Sime notes that the Nobel committee’s failure to recognize Meitner’s contributions were partly due to her physical exile and also institutional sexism. The international community did recognize this Nobel “mistake” and in 1966, Hahn, Meitner, and Strassmann were awarded the U.S. Fermi Prize for “for pioneering research in the naturally occurring radioactivities and extensive experimental studies leading to the discovery of fission”.

See the Engineering Pathway’s educational resources on Lise Meitner, Otto Hahn and nuclear fission. or visit the Nuclear Engineering Education community site for more information. Also our resources on women in science and gender equity today.