The Nobel Prize That Nearly Wasn't - Fermi's New Transuranic Elements That Weren't

Fermi's Discovery and the Dawn of Nuclear Fission

In the annals of scientific discovery, few stories illustrate the unpredictable nature of research quite like Enrico Fermi's 1938 Nobel Prize in Physics. What began as groundbreaking work on artificial radioactivity would ultimately reveal something far more momentous—and dangerous—than anyone initially imagined.

The Slow Neutron Revolution

By the mid-1930s, the Italian physicist Enrico Fermi had already established himself as one of the world's leading nuclear researchers. Working at the University of Rome with his talented team, Fermi was systematically bombarding elements across the periodic table with neutrons, seeking to create new radioactive isotopes. The work built upon the pioneering research of Irène and Frédéric Joliot-Curie, who had discovered artificial radioactivity just two years earlier.

Fermi's breakthrough came through an almost accidental observation. While conducting experiments in 1934, he discovered that surrounding his neutron source with paraffin—a hydrogen-rich material—dramatically increased the radioactivity induced in target elements. The paraffin was slowing down the neutrons through collisions with hydrogen nuclei, and these "slow" or "thermal" neutrons proved remarkably more effective at inducing nuclear reactions than their faster counterparts.

The discovery was revolutionary. Slow neutrons could penetrate atomic nuclei with much greater probability, opening new avenues for creating artificial elements and studying nuclear processes. Fermi and his colleagues systematically worked their way up the periodic table, and when they reached uranium—element 92, the heaviest known at the time—they observed something extraordinary.

The "Transuranium" Elements

When Fermi bombarded uranium with slow neutrons, he detected several new radioactive substances with different decay properties. The logical interpretation seemed clear: the neutrons were being absorbed by uranium nuclei, creating heavier elements beyond uranium on the periodic table. These would be the first "transuranium" elements—artificially created atoms heavier than anything found in nature.

The scientific community was electrified. Here was experimental proof that humans could extend the periodic table itself, creating entirely new forms of matter. Fermi's careful measurements showed decay products with half-lives ranging from minutes to days, and chemical analysis suggested these were indeed new elements with atomic numbers 93 and 94.

The Royal Swedish Academy of Sciences was sufficiently impressed to award Fermi the 1938 Nobel Prize in Physics "for his demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons."

Seeds of Doubt

Yet even as Fermi accepted his Nobel Prize in Stockholm in December 1938, troubling questions lingered in laboratories across Europe. The German radiochemist Ida Noddack had raised concerns as early as 1934, suggesting that uranium nuclei might be breaking apart rather than simply absorbing neutrons. Her hypothesis was largely dismissed—the idea that atomic nuclei could split seemed to violate fundamental principles of nuclear physics.

Meanwhile, in Berlin, Otto Hahn and Fritz Strassmann were conducting their own meticulous chemical analysis of uranium bombardment products. Their work focused on precisely identifying the atomic structure of Fermi's mysterious new substances. What they found would shake the foundations of nuclear physics.

The Revelation

In December 1938—the same month Fermi received his Nobel Prize—Hahn and Strassmann made a discovery that defied all expectations. Their chemical analysis revealed that one of the radioactive products from neutron-bombarded uranium was barium, an element with roughly half the atomic mass of uranium. This was impossible under the prevailing model of nuclear reactions, which typically involved the emission of small particles like alpha rays or protons.

Hahn immediately wrote to his former colleague Lise Meitner, who had fled Nazi Germany earlier that year due to her Jewish heritage. Meitner, working in exile in Sweden with her nephew Otto Robert Frisch, quickly grasped the profound implications. Using Einstein's mass-energy equivalence principle, they calculated that a uranium nucleus could indeed split into two roughly equal fragments, releasing enormous amounts of energy in the process.

Meitner and Frisch coined the term "nuclear fission" for this previously unknown phenomenon, borrowing from the biological process of cell division. Their theoretical framework, published in Nature in February 1939, provided the missing piece of the puzzle.

The Paradigm Shift

The revelation transformed our understanding of Fermi's experiments overnight. Those "transuranium elements" were actually the fission fragments of split uranium nuclei—lighter elements like barium, krypton, and others formed when uranium atoms broke apart. The various decay products Fermi had observed were the radioactive isotopes of these fission fragments, each with its characteristic half-life.

Fermi himself quickly embraced the new interpretation. With characteristic intellectual honesty, he acknowledged that his original conclusion had been incorrect while maintaining pride in the experimental work that had made the discovery possible. His slow neutron technique remained crucial—it was precisely these thermal neutrons that most efficiently triggered uranium fission.

The Unintended Consequences

The discovery of nuclear fission unleashed forces that would reshape the 20th century. Within months of Meitner and Frisch's publication, physicists worldwide recognized the potential for both peaceful nuclear energy and devastating weapons. The very slow neutrons that Fermi had discovered for creating artificial elements now pointed toward the possibility of sustained chain reactions and atomic bombs.

Fermi himself would play a crucial role in these developments, leading the team that achieved the first controlled nuclear chain reaction beneath the University of Chicago's football stadium in 1942. His Nobel Prize work, originally aimed at expanding the periodic table, had inadvertently opened the door to the atomic age.

A Legacy Reconsidered

Today, Fermi's 1938 Nobel Prize stands as a fascinating case study in the evolution of scientific understanding. While his interpretation of the experimental results proved incorrect, the underlying discoveries—slow neutron physics and the nuclear processes in uranium—were absolutely fundamental to the development of nuclear science.

The episode illustrates how even mistaken conclusions can lead to profound advances. Fermi's meticulous experimental technique and his discovery of slow neutron reactions provided the tools necessary for others to uncover nuclear fission. In a sense, he received his Nobel Prize for work that was simultaneously wrong and revolutionary—a fitting paradox for one of the most important discoveries in modern physics.

The story also highlights the collaborative nature of scientific progress. Fermi's experiments, Hahn and Strassmann's chemistry, and Meitner and Frisch's theoretical insights combined to reveal a phenomenon that no single researcher could have discovered alone. From the ashes of one scientific interpretation arose our modern understanding of nuclear physics—and with it, both the promise and peril of the atomic age.

Sources and Further Reading

1. Fermi, E. (1934). "Radioattività provocata da bombardamento di neutroni: III." Ricerca Scientifica, 5(2), 330-331.
2. Fermi, E., Amaldi, E., D'Agostino, O., Rasetti, F., & Segrè, E. (1934). "Artificial radioactivity produced by neutron bombardment." Proceedings of the Royal Society of London A, 146(857), 483-500. https://doi.org/10.1098/rspa.1934.0168
3. The Nobel Foundation. (1938). "The Nobel Prize in Physics 1938: Enrico Fermi." https://www.nobelprize.org/prizes/physics/1938/fermi/facts/
4. Hahn, O., & Strassmann, F. (1939). "Über den Nachweis und das Verhalten der bei der Bestrahlung des Urans mittels Neutronen entstehenden Erdalkalimetalle." Die Naturwissenschaften, 27(1), 11-15. https://doi.org/10.1007/BF01488241
5. Meitner, L., & Frisch, O. R. (1939). "Disintegration of uranium by neutrons: A new type of nuclear reaction." Nature, 143(3615), 239-240. https://doi.org/10.1038/143239a0
6. Frisch, O. R. (1939). "Physical evidence for the division of heavy nuclei under neutron bombardment." Nature, 143(3616), 276. https://doi.org/10.1038/143276a0
7. Noddack, I. (1934). "Über das Element 93." Angewandte Chemie, 47(37), 653-655. https://doi.org/10.1002/ange.19340473707
8. Segrè, E. (1970). Enrico Fermi: Physicist. University of Chicago Press.
9. Rhodes, R. (1986). The Making of the Atomic Bomb. Simon & Schuster. ISBN: 978-0684813783
10. Sime, R. L. (1996). Lise Meitner: A Life in Physics. University of California Press. ISBN: 978-0520208605
11. Rife, P. (1999). Lise Meitner and the Dawn of the Nuclear Age. Birkhäuser. ISBN: 978-0817639082
12. American Physical Society. "December 1938: Discovery of Nuclear Fission." APS Physics. https://www.aps.org/publications/apsnews/200712/physicshistory.cfm
13. CERN Courier. (2013). "Fermi's legacy, 75 years on." https://cerncourier.com/a/fermis-legacy-75-years-on/
14. Atomic Heritage Foundation. "The Discovery of Fission." https://www.atomicheritage.org/history/discovery-fission

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