The 1938 Discovery of Nuclear Fission by Otto Hahn: A Scientific Revolution That Reshaped Energy and Warfare

Otto Hahn's 1938 Discovery of Nuclear Fission: The Scientific Foundation of Atomic Energy and Weaponry

In late 1938, at the Kaiser Wilhelm Institute for Chemistry in Berlin, an experiment forever altered the trajectory of science and human history. Chemists Otto Hahn and Fritz Strassmann, continuing work disrupted by the persecution of their colleague Lise Meitner, made a startling discovery that shattered a foundational concept of the natural world. By bombarding uranium with neutrons, they produced not heavier "transuranic" elements as anticipated, but the much lighter element barium. This proved the uranium nucleus had split in two, a process Meitner and her nephew Otto Frisch would soon name "nuclear fission". This breakthrough demonstrated the direct conversion of mass into energy, as described by Einstein's equation E=mc², and revealed the potential for a chain reaction that could release energy on an unprecedented scale . The discovery, born in a climate of political terror and scientific perseverance, laid the cornerstone for both the devastating power of nuclear weapons and the transformative potential of nuclear energy.

The Scientific and Historical Path to Fission

The discovery of nuclear fission was not a sudden accident but the culmination of over four decades of international scientific progress in understanding the atom and radioactivity, a journey in which Otto Hahn was a central figure. 

Foundations in Radioactivity (Late 1890s-1900s): The path began with the discovery of X-rays by Wilhelm Röntgen in 1895 and radioactivity by Henri Becquerel in 1896 . Marie and Pierre Curie's subsequent isolation of polonium and radium established the field. Ernest Rutherford, a key mentor to the young Otto Hahn, made critical advances by classifying radiation types (alpha, beta, gamma) and proposing the nuclear model of the atom .

Hahn's Early Career and Collaboration with Meitner: Trained in organic chemistry, Hahn's trajectory shifted during a postdoctoral stint with Sir William Ramsay in London, where he discovered "radiothorium" (thorium-228) . Seeking deeper expertise, he worked under Ernest Rutherford in Montreal before returning to Berlin in 1906. There, he began a legendary, 30-year partnership with Austrian physicist Lise Meitner. Their complementary skills, Hahn's brilliant chemical techniques and Meitner's deep physical insight proved extraordinarily fruitful. Their pre-war collaboration led to the 1917 discovery of the element protactinium .

The Neutron and Fermi's Experiments: A pivotal moment came in 1932 with James Chadwick's discovery of the neutron, a neutral particle ideal for probing atomic nuclei . Inspired by this, Enrico Fermi in Rome began bombarding elements, including uranium, with neutrons in 1934. He believed he had created new, heavier elements beyond uranium (transuranics) and received the 1938 Nobel Prize for this work. However, other scientists, like Ida Noddack, suggested the nucleus might have broken into large fragments, a hypothesis that was largely dismissed at the time .

The Berlin Experiments (1934-1938): Intrigued by Fermi's results, Hahn, Meitner, and later Strassmann embarked on a meticulous, four-year investigation to identify the mysterious products from neutron-irradiated uranium . Their work was conducted under the growing shadow of Nazism. As an Austrian Jew, Meitner was stripped of her position at the University of Berlin and, after the Anschluss in 1938, lost the protection of her Austrian citizenship. In July 1938, with Hahn's active assistance, she was forced to flee Germany, escaping to Sweden via the Netherlands. Despite her exile, Hahn continued to send her detailed letters about their ongoing experiments .

The Critical December 1938 Experiment

With Meitner gone, Hahn and Strassmann continued their painstaking work through late 1938. They employed a methodical, three-room process at their institute: an irradiation room where a uranium sample was bombarded with neutrons slowed by paraffin; a chemistry lab for separating the resulting substances; and a measuring room equipped with Geiger-Müller counters to analyze the radioactive decay of the tiny samples.

By mid-December, they were focused on what they thought was radium (element 88), a plausible product from uranium (element 92). To confirm its identity, they used a classic chemical separation technique: adding barium as a non-radioactive "carrier" to precipitate out the suspected radium. To their profound confusion, they could not separate the radioactive substance from the barium . The evidence became undeniable the radioactive product was barium (element 56), an element less than half the mass of uranium.

Hahn, a conservative chemist who was deeply reluctant to propose a revolutionary physical process, was both astonished and skeptical. In a famous letter to Meitner dated December 19, 1938, he wrote of the barium finding, "Perhaps you can come up with some sort of fantastic explanation" . He and Strassmann submitted their results for publication on December 22, concluding with a remarkable statement of caution: "As chemists... we should substitute the symbols Ba, La, Ce for Ra, Ac, Th. As 'nuclear chemists' fairly close to physics we cannot yet bring ourselves to take this leap, which contradicts all previous experience in nuclear physics" .

Meitner and Frisch: Providing the Theoretical Explanation

Hahn's letter reached Meitner in the Swedish town of Kungälv, where she was spending the Christmas holiday with her nephew, Otto Frisch, a physicist also working in exile . Walking through the snowy woods, they discussed Hahn's baffling results. Using Niels Bohr's recently proposed "liquid drop" model of the nucleus, they conceptualized a breakthrough.

They theorized that when a neutron was captured by a uranium nucleus, it could cause the charged droplet to oscillate violently. If the forces of electrostatic repulsion overcame the strong nuclear force holding the droplet together, it could stretch, narrow in the middle, and finally split into two smaller, lighter nuclei such as barium and krypton releasing a tremendous amount of energy in the process . Meitner performed calculations based on Einstein's mass-energy equivalence formula (E=mc²) and determined the energy released per fission event was approximately 200 million electron volts .

Frisch rushed back to his laboratory in Copenhagen and confirmed this energy release experimentally . He is credited with coining the term "fission," borrowing from the biological process of cell division, in a paper with Meitner published in Nature in February 1939 . This paper provided the crucial physical explanation for Hahn and Strassmann's chemical discovery, completing one of the most significant collaborative scientific achievements of the 20th century.

From Discovery to Chain Reaction and Consequences

The implications of fission became terrifyingly clear almost immediately. Scientists around the world realized that if each fission event released multiple secondary neutrons—as was soon confirmed—those neutrons could induce fissions in neighboring uranium nuclei, creating a self-sustaining chain reaction.

The Path to Weapons and Energy: A controlled, slow chain reaction could produce heat for power generation (a nuclear reactor), while an uncontrolled, fast chain reaction could yield a weapon of unimaginable destructive force (an atomic bomb) . This dual potential defined the future of the discovery. By late 1939, with World War II already begun, this knowledge spurred secret weapons projects: the Manhattan Project in the United States and the smaller Uranverein project in Germany .

Hahn's Wartime Experience and Post-War Anguish: During the war, Otto Hahn focused on basic research, cataloguing the fission products of uranium . He was deeply opposed to the Nazi regime and was not a leading figure in the German bomb effort. In 1945, he and other German scientists were interned at Farm Hall in England. It was there he learned he had been awarded the 1944 Nobel Prize in Chemistry for the discovery of fission, and, more shockingly, heard the news of the atomic bombings of Hiroshima and Nagasaki. Hahn fell into a profound despair, feeling personally responsible for the deaths of hundreds of thousands .

A Legacy of Peaceful Advocacy: This sense of responsibility shaped his post-war life. He became a leading voice against nuclear weapons, using his prestige as the founding president of the Max Planck Society to campaign for the peaceful use of atomic energy . In 1966, he, Meitner, and Strassmann were jointly awarded the Enrico Fermi Award. The full historical recognition of Lise Meitner's indispensable role in the discovery has grown significantly since that time, addressing an earlier imbalance in credit .

Conclusion

The discovery of nuclear fission in December 1938 stands as a profound turning point. It was the product of exemplary international science, a decades-long investigation built upon the work of Curie, Rutherford, Fermi, and others. It was also a human drama, forged in the unique collaboration between Otto Hahn and Lise Meitner and tragically severed by political tyranny. Their work unveiled a fundamental process of nature, proving that the atom could indeed be split and that the energy within its nucleus was accessible. This knowledge bestowed upon humanity a power of cosmic scale, forcing upon it an eternal responsibility a responsibility first shouldered by the discoverers themselves, who understood better than anyone the double-edged nature of their world-altering achievement.

Share this

myearthisone