Otto Hahn (1879 – 1968)- The Father of Nuclear Chemistry

One of the greatest pioneers in radioactivity and radiochemistry, German chemist Otto Emil Hahn was awarded the 1944 Nobel Prize in Chemistry for his phenomenal discovery of nuclear fission. He was an experimental chemist of such eminence that before he actually became a Nobel Laureate, he had been nominated for the Nobel Prize in Chemistry for a record 22 times, and 16 times for the Nobel Prize in Physics!

Hahn’s historic discovery that the nucleus of atoms could be split, followed by a number of other important discoveries made a few years earlier. In 1932, James Chadwick discovered the neutron, offering researchers a powerful new tool for investigating atoms. In 1934, Irène Joliot-Curie and her husband Frédéric Joliot-Curie discovered artificial radioactivity. Soon afterwards, Enrico Fermi successfully bombarded over 60 elements with neutrons including the nuclei of the heaviest natural element Uranium. Keenly interested in Fermi’s work, Hahn, along with his long-time collaborator in research Prof. Lise Meitner, and his student Fritz Strassmann began to further research the bombardment of uranium nuclei, leading to the discovery of what came to be called nuclear fission.

Earlier, Hahn had also discovered a number of radioactive elements, but significant among these, especially from the oncology point of view, was his discovery of mesothorium-1 (Radium-228), a radioactive element that cost half as much to manufacture as Radium-226 that had been discovered by Pierre and Marie Curie, but was equally effective for use in radiation therapy for cancer patients. This discovery won Otto Hahn his first nomination for the Nobel Prize in Chemistry in 1914. He didn’t win it that year, but mesothorium began to be widely used for treating all types of cancer.

One of the many greats emerging from Sir Ernest Rutherford’s group, Hahn’s claim to fame came even before he joined the famed physicist in 1906. During a short stint with another celebrated chemist Sir William Ramsay, he discovered what he thought was a new radioactive element. He called it radiothorium. This was in fact a new isotope of thorium, though the concept of isotopes had not yet been introduced then, being first suggested by Frederick Soddy in 1913. But, Hahn’s discovery set the stage for the discovery and study of radio isotopes.

Early Life

Otto Emil Hahn was born in Frankfurt-on-Main, Germany, on 8 March, 1879. His father Heinrich was a successful glazier. His mother Charlotte came from a family of merchants. Having developed an interest in chemistry while in high school, Hahn pursued further studies in this subject at the German Universities of Marburg and Munich.

In his autobiography, Hahn wrote that during his college days he often spent more time in the beer halls than in studying, regretting that he didn’t pay more attention to physics and mathematics then. But, obviously, he did give enough time to studying chemistry for he got his doctorate in organic chemistry in 1901 from Marburg with Theodor Zincke as his doctoral supervisor.

After completing his one year of military service, Hahn returned to Marburg to serve as assistant to Professor Zincke. Being interested in becoming an industrial chemist, he knew that a recommendation from Zincke would make it easier for him to get a job in a major chemicals company. After two years, in 1904, when Hahn wanted to go to England to improve his grasp on English, Zincke helped him get a job as an assistant in Ramsay’s laboratory at University College, London. Working under Ramsay for a year, Hahn discovered the thorium isotope, and also developed an interest in radiochemistry, an underexploited field at that time. Encouraged by Ramsay, he changed his mind about a career in industry, deciding to persist with research on radioactivity instead.

In 1905, on Ramsay’s recommendation, Rutherford asked Hahn to join him at McGill University in Montreal, Canada. Here, Hahn discovered other new radioactive isotopes before returning to Germany and joining Emil Fischer’s institute at the University of Berlin in 1906, rising quickly through the faculty ranks to become a Professor of Chemistry.

In search of a collaborator for pursuing research on radioactivity, Hahn met and teamed up with the Austrian-born physicist Lise Meitner soon after returning to Germany, commencing a collaboration and friendship that would last for over three decades. Within five years Hahn’s research group moved to the new Kaiser Wilhelm Institute for Chemistry at Berlin-Dahlen where Hahn was made the head of the department of radiochemistry. Soon afterwards, World War I broke out. Hahn served in the German gas warfare service as a chemical warfare specialist, while Meitner volunteered as an X-ray nurse for the Austrian army.

When the war ended, Hahn and Meitner resumed their research work and in 1917 discovered protactinium (meaning ‘mother of actinium’), the till then missing element between thorium and uranium whose existence Mendeleev had predicted in 1871. The protactinium-231 that they discovered was a much longer-lived isotope (half-life 32,670 years) of protactinium than the one discovered in 1913 by Fajans and Göhring (protactinium-234 having half-life of just 1.17 minutes). During the 1920s, Hahn and Meitner were unsuccessfully nominated many times by several scientists for their discovery of protactinium.

In 1929, the brilliant young chemist Strassmann, just 27 years old then, joined the Kaiser Wilhelm Institute. And when Hahn decided to focus his attention on Fermi’s work, Strassmann joined him and Meitner in studying the decay patterns of the products created by the neutron bombardment of uranium nuclei.

Discovery of nuclear fission

In 1938, with the Nazis beginning to persecute all people of Jewish ancestry, Meitner fled from Germany with Hahn’s help and moved to Sweden. Hahn and Strassmann continued with their radioactivity experiments on uranium, but their work threw up perplexing results. The general belief then was in accordance with what Fermi had concluded—that following neutron bombardment of uranium, the products would be elements with atomic weights close to or greater than that of uranium. And so, Hahn had thought the radioactive transmutation products resulting from their experiments could be radium isotopes. But, he and Strassmann found that one of the products they got, seemed to be a radioactive form of the much lighter element barium. Hahn wondered how uranium could have transmuted into a much lighter element. The heavy nucleus of uranium would have to be split to produce something like that. Despite his long years of experience in research work, being a chemist, Hahn was hesitant about announcing something revolutionary related to physics.

So, he sent a detailed letter to Meitner in December 1938. He wrote: “… we are more and more coming to the awful conclusion that our Ra isotopes behave not like Ra, but like Ba. … Perhaps you can suggest some fantastic explanation. We ourselves realise that it can’t really burst into Ba.” He referred to the possible splitting of the uranium atom as “bursting”. Meitner replied that such a “bursting of the uranium nucleus” was hard to accept, but was possible.
A month later, further evidence related to barium, made Hahn almost certain his experiments had produced lighter elements. He published an article in the peer-reviewed monthly scientific journal Naturwissenschaften (The Science of Nature) asserting the same.

In the meanwhile, Meitner and her nephew, the young physicist Otto Frisch, used physics calculations to theoretically understand the baffling results of Hahn’s work and correctly interpreted that the uranium nucleus had indeed been split into lighter atoms, naming the phenomenon “fission”.

Scientists the world over realised the tremendous implications of Hahn’s discovery. Before World War II broke out, the German authorities set up a group to study the possible military applications of nuclear fission. Hahn was relieved that he was excluded from this group and allowed to continue with his own research work.

But, despite not being involved with Germany’s Nuclear Energy Project, Hahn was taken into custody by the Allied forces along with some other leading German scientists and interned in England at Farm Hall, Godmanchester, from July 1945 until January 1946. During his forced stay in England, Hahn kept himself fit by going on a daily run. It was here that he and the other German scientists learned about the atom bombs dropped on Hiroshima and Nagasaki in August 1945. Hahn was completely devastated that his discovery of fission had made it possible to construct the atom bomb and felt he was responsible for the loss of thousands of innocent lives. According to those who held him captive, “With the help of considerable alcoholic stimulant, he was calmed down.”

Hahn was still at Farm Hill when in November 1945 he learned from the Daily Telegraph newspaper that he had been awarded the Nobel Prize in Chemistry for 1944. Being refused permission by his captors to attend the prize ceremony, he attended the one held the following year in December 1946 after returning to his homeland earlier that same year.

Honours and acclaim

In 1948 Otto Hahn was elected President of the former Kaiser Wilhelm Society, newly renamed as the Max Planck Society. Honours and awards continued to be bestowed on him from all parts of the world. Just a list of such recognitions would run into pages. Across Europe and elsewhere, streets, squares, schools, institutes, and bridges were named after him and many medals and prizes declared in his name. As for the 1944 Nobel Prize, when it was announced, some scientists felt that injustice had been done to Meitner and that she too should have got it along with Hahn. But, Meitner said Hahn “fully deserved the Nobel prize in Chemistry”, and later, in a TV interview in 1959, commented on his discovery of fission saying, “Hahn and Strassmann were able to do this by exceptionally good chemistry, fantastically good chemistry, which was way ahead of what anyone else was capable of at that time.”

In 1966 however, Hahn, Meitner, and Strassmann were honoured with the prestigious Enrico Fermi Award. In 1959, the Otto Hahn Institute in Mainz and the Hahn-Meitner-Institute for Nuclear Research (HMI) were thrown open in Berlin. In 1964, the only nuclear-powered civilian ship in Europe was named the NS Otto Hahn. To honour Hahn for his special contribution to German-Israeli relations, in 1974, a wing of the Weizmann Institute of Science in Rehovot, Israel, was named after him.

Unfortunately, tragedy struck Hahn’s family in 1960 when his only son, Hanno—a reputed art historian, and his daughter-in-law Ilse, were killed in an automobile accident. Hahn and his wife never really recovered from this terrible shock. Otto Hahn died on 28 July, 1968 after a fall. His wife passed away just two weeks later.

Advocate of world peace and social responsibility

Convinced that it was a crime to use nuclear energy for developing weapons of war, Otto Hahn began campaigning against further development and testing of nuclear weapons after the war ended. He also initiated the Mainau Declaration of 1955 to highlight the dangers of atomic weapons and in 1959 co-founded the Federation of German Scientists, a non-governmental organisation committed to upholding the ideal of responsible science.
Hahn underscored the inherent dangers of a nuclear arms race and the radioactive contamination of planet Earth through light verse writer Ethel Jacobson’s rhyme:

  • To smash the simple atom
  • All mankind was intent
  • Now any day
  • The atom may
  • Return the compliment.

References

1. NobelPrize.org: Otto Hahn – Biographical – Nobel Media AB 2014, https://www.nobelprize.org/prizes/chemistry/1944/hahn/biographical/
2. Robert Spence: Otto Hahn – Encyclopaedia Britannica, 16 March, 2018, https://www.britannica.com/biography/Otto-Hahn#ref5260
3. The New York Times: Not Forgotten – nytimes.com, 28 July, 2016, https://www.nytimes.com/interactive/projects/cp/obituaries/archives/otto-hahn
4. Atomic Heritage Foundation: Otto Hahn – atomicheritage.org, https://www.atomicheritage.org/profile/otto-hahn
5. Science History Institute: Otto Hahn, Lise Meitner, and Fritz Strassmann – Sciencehistory.org, 7 December 2017, https://www.sciencehistory.org/historical-profile/otto-hahn-lise-meitner-and-fritz-strassmann
6. M. Sgantzos, G. Kyrgias, et al: Otto Hahn (1879-1968): Pioneer in radiochemistry and discoverer of radiotherapeutic mesothorium – Journal of Balkan Union of Oncology, 19(3): 866-869, July 2014
7. Complete Dictionary of Scientific Biography: Hahn, Otto – Encyclopedia.com, 11 Sep. 2018, https://www.encyclopedia.com/people/science-and-technology/chemistry-biographies/otto-hahn
8. ChemViews Magazine: 50th Anniversary: Death of Otto Hahn – chemistryviews.org, 28 July 2018, https://www.chemistryviews.org/details/ezine/11077587/50th_Anniversary_Death_of_Otto_Hahn.html.

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