|Fig. 1: Memorial plaque honoring Lise Meitner and Otto Hahn. The plaque is located on Hessische Straße 1, Berlin-Mitte, Germany and marks the site where Meitner and Hahn conducted research between 1907 and 1912. (Source: Wikimedia Commons)|
Austrian physicist Lise Meitner and German chemist Otto Hahn were longtime friends, collaborators and pioneers in the field of nuclear fission.  The two scientists formed a strong interdisciplinary team with Hahn as the experimentalist and Meitner as the theorist. For over 30 years, they worked together on radioactivity and nuclear physics, discovering several new isotopes and exploring neutron bombardment of uranium.
Hahn and Meitner's greatest scientific contribution came in 1939, with the discovery of nuclear fission of heavy elements.  In a historic breakthrough, Hahn published experimental evidence demonstrating the splitting of the uranium nucleus into lighter elements and Meitner subsequently developed a theoretical interpretation of his data. Five years later, Hahn became the sole recipient of the 1944 Nobel Prize in Chemistry.  The exclusion of Meitner generated controversy and continuous to draw criticism due to claims of gender and religious discrimination in the Nobel Prize decision. 
Otto Hahn (1879-1968) was born in Frankfurt-am-Main to a prosperous family and showed an early tendency for scientific inquiry. [2,4] In 1897, Hahn began graduate studies in Marburg and Munich and, four years later, received his degree in chemistry from the University of Marburg. He subsequently traveled to England and Canada to pursue research in radiochemistry, working with prominent scientists such as Ernest Rutherford. In 1905, Hahn had his first major scientific success when he discovered the element thorium.
Lise Meitner (1878-1968) was born into a Jewish middle class family in Vienna, Austria. [1,5,6] Her parents were highly supportive of her academic ambitions, hiring private teachers for her and enabling her to purse a passion in physics. Overcoming gender restrictions in higher education, Meitner became the 2nd woman to earn a PhD in physics from the University of Vienna in 1905. At university, Meitner was introduced to the growing concept of radioactivity and began to study subatomic particles and atomic structure.
In 1907, Otto Hahn and Lise Meitner met at the University of Berlin, initiating a life-long collaboration between the experimental chemist and the theoretical physicist.  Meitner came to Berlin to work with Max Planck but was severely discriminated against due to her gender. As a women, she required special permission to attend Professor Planck's lectures and was not allowed to work in, or even enter, the chemistry institute in Berlin. With the support of Hahn, Meitner was eventually given a space to conduct research in an abandoned carpenter's shop in the university basement. Meitner collaborated with, ran experiments with and published with Hahn from the makeshift basement laboratory for 5 years (Fig. 1).
In 1912, Hahn and Meitner moved together to the Kaiser-Wilhelm-Institute (KWI) for Chemistry. [1,7] Hahn was hired as Professor of Radiochemistry and Meitner initially worked as an unpaid guest in the department before becoming the first female assistant in Berlin. For twenty-six years, Hahn and Meitner stayed at KWI, pursuing both independent work and continuous collaborations.
In its first few years, the Meitner-Hahn team focused its research on beta emission, the use of radioactive recoil and the decay of radioelements.  Their shared work was scientifically fruitful. They quickly discovered several new isotopes and published three major articles in 1908 and six articles in 1909. A few years later, in 1917, they isolated the long-lived isotope of the element protactinium. Later in their collaboration, the duo transitioned and began investigating a set of scientific questions related to transuranium elements and neutron bombardment of nuclei.
Their significant impact on the fields of radiochemistry and radiophysics was repeatedly recognized by the scientific community. Between 1924 and 1938, Hahn and Meitner were jointly nominated for the Nobel Prize nineteen times, seventeen times in chemistry and twice in physics.  Meitner won the Leibniz Medal from the Berlin Academy of Sciences and the Leibniz Prize from the Austrian Academy of Sciences while Hahn was awarded the Emil Fischer Medal from the German Association of Chemists. [1,8] In 1959, fifty-two years after Hahn and Meitner began their collaboration in Berlin, the Hahn-Meitner-Institut fuer Kernforschung was set up in Berlin. 
Hahn and Meitner's scientific direction shifted in the 1930s due to three major events in nuclear chemistry. [10,11] In 1932, James Chadwick discovered the neutron and, two years later, the Joliot-Curie husband wife team discovered artificial radioactivity. Building on these scientific advancements, Enrico Fermi began bombarding uranium with neutrons, thereby generating new radioactive materials.
Inspired by the work of Fermi, Hahn and Meitner started an interdisciplinary project in 1934 to pursue transuranium research and neutron irradiation of uranium. [3,12] Over the course of the following four years, the team published over a dozen manuscripts together and identified the new beta-emitting isotope 239U. However, in 1938, Meitner and Hahn were forced to separate, prematurely terminating their joint research program, when Jewish-born Meitner emigrated to Stockholm and Hahn remained in Berlin. Only five months after Meitner's escape from Germany, the key experiments discovering the nuclear fission process were successfully conducted by Otto Hahn.
|Fig. 2: Experimental setup used for neutron bombardment experiments which demonstrated nuclear fission. (Source: Wikimedia Commons)|
Following Meitner's departure, the two friends and collaborators remained in close contact, communicating almost daily via letters.  In Germany, Hahn continued his experimental studies of neutron bombardment of uranium with German chemist Fritz Straussmann (Fig. 2), but was puzzled by his findings. Seeking insight from Meitner, Hahn wrote to the exiled physicist in December of 1938 detailing neutron bombardment experiments in which he had surprisingly detected barium among the decay products. He described the process as the 'bursting' of the uranium atom.  In Sweden, Meitner discussed these results with her physicist nephew Otto Frisch. Over the Christmas holiday, the two theoretical physicists laid the foundation for the theory of nuclear fission by interpreting Hahn's experiments. They described how the uranium nucleus could split into multiple smaller nuclei based on the existing liquid-drop model of an atomic nucleus.  Under bombardment from neutrons, the uranium nucleus could elongate and split into smaller drops, generating lighter atoms and releasing energy in the process. Additionally, the two scientists postulated that Einstein's famous equation E = mc2 could be applied to nuclear fission and that mass lost during the splitting of a nucleus was the source of tremendous energy. Meitner and Frisch's final interpretation elegantly integrated the pre-existing liquid-drop nucleus theory, settled misconceptions about transuranic elements as neutron bombardment products and provided quantitative energy predictions.
On January 6th, 1939, Hahn and Staussmann published their uranium splitting results in Die Naturwissenschaft, becoming the first to experimentally describe nuclear fission.  On February 10th, 1939, the two German chemists confirmed their results and published similar findings for thorium in Die Naturwissenschaft.  Meitner and Frisch's theoretical explanation, in which they coined the term nuclear fission, was published a single day later in the journal Nature. 
The discovery of nuclear fission was awarded the Nobel Prize in Chemistry in 1944, but only Otto Hahn was honored.  Other critical scientists, such as Lise Meitner, Fritz Straussmann and Otto Frisch, did not share the award. Lise Meitner's exclusion from the 1944 Chemistry Nobel Prize and subsequent failure to receive a Physics Nobel Prize has remained particularly controversial, especially given the fact that Meitner was nominated for a Nobel Prize a grand total of 48 times. [3,17] For the remainder of their scientific careers, the Hahn-Meitner relationship remain amicable though became somewhat strained. On her side, Meitner publically supported Hahn's Nobel Prize achievement, emphasizing the significance of his experimental work and his deservingness of the prize. Yet, she was bruised by the lack of recognition and stated in private letters that she and Otto Frisch deserved credit as well.  On his side, Hahn cited Meitner's theoretical interpretation in his Nobel Prize lecture but he never used his status as Nobel laureate to nominate Meitner for a Nobel Prize. [2,3] Additionally, he never mentioned her critical role in the discovery process in his memoirs or autobiographies, going so far as to claim that physics impeded the discovery of fission. 
In the 1990s, the Royal Swedish Academy of Sciences released the deliberations of the Nobel Prize decision of 1944.  Analysis of the records suggested that the Nobel Prize committee was ill-equipped to evaluate interdisciplinary work, lacked expertise, underappreciated the political and social circumstances of the times and was biased and ignorant in their assessment. More nefarious, Meitner's personal conflict with committee member Manne Siegbahn and negative personal sentiments of other members may have cost her the 1946 Nobel Prize in Physics.
For her extraordinary life work, Meitner did receive a number of awards, including the Max Planck Medal and the Enrico Fermi Prize, and the element Meitnerium was named in her honor.  However, the controversy surround the Nobel Prize has dominated her scientific legacy.
© Isabel Goronzy. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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