Otto Hahn

German chemist

• Born: March 8, 1879; Frankfurt am Main, Germany
• Died: July 28, 1968; Göttingen, West Germany (now in Germany)

A pioneer in radioactivity, Hahn and his colleagues Fritz Strassmann and Lise Meitner are credited with having discovered nuclear fission as well as certain radioactive isotopes and elements. Hahn was awarded the 1944 Nobel Prize in Chemistry and played a major role in reestablishing German science after World War II.

Primary field: Chemistry

Specialties: Radiochemistry; nuclear physics; organic chemistry

Early Life

Otto Hahn was born in Frankfurt am Main, Germany, on March 8, 1879. Hahn was a good student and his interest in chemistry began to develop in childhood. He attended adult-oriented lectures on chemistry, conducted experiments, and began reading about chemistry on his own. Hahn decided to pursue the study of chemistry and entered the University of Marburg in 1897; he also attended the University of Munich for two terms in 1898. There, he attended lectures given by another future chemistry Nobel Prize–winner, Adolf von Baeyer.

Hahn returned to Marburg to complete his work in organic chemistry under the supervision of Theodor Zincke. In 1901 Hahn was awarded the degree of doctor of philosophy magna cum laude. During the summer of that year, he prepared his thesis for publication. It was recognized as an important contribution to the field of organic chemistry for many years after its appearance.

Life’s Work

Following one year of military service after the completion of his degree, Hahn returned to Marburg for two more years as assistant to Zincke. Zincke was able to secure Hahn a place in Scottish chemist William Ramsay’s laboratory at University College, London. While with Ramsay, Hahn discovered the previously unknown radioactive element, radiothorium (thorium, element 90), when he extracted radium from barium using the Curie method.

Ramsay encouraged Hahn to accept a position with the Chemical Institute of the University of Berlin to research radioactivity. In 1905, before going to Berlin, Hahn traveled to McGill University in Canada in to work with Ernest Rutherford, who was at that time the best source of information on radioactivity in the world. Hahn spent a year at McGill, during which time he discovered another new radioactive element, radioactinium (thorium-227), and helped determine the process or chains of radioactive decay.

Hahn eventually arrived in Berlin in 1906. There, he discovered another isotope—mesothorium, an isotope of radium. He was also acquiring a thorough familiarity with methods of separating radioactive substances. In the fall of 1907 physicist Lise Meitner arrived in Berlin to do some postgraduate work in theoretical physics under Max Planck at the Institute of Physics. The Hahn-Meitner association that resulted became a thirty-year collaboration.

In 1912, the new Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry opened its doors, and Hahn was made head of the radiochemistry department. He invited Meitner to join him in continuing their work together examining beta radiation, the decay products of radioactive isotopes, and the measurements of extremely weak radioactive substances (rubidium and potassium). During this period Hahn married Edith Junghans on March 22, 1913.

Hahn’s work at the institute was interrupted by World War I, during which he served as a chemical-weapons specialist in the gas-warfare corps. Occasionally he had to go to Berlin or Döberitz to test the efficiency of gas masks by observing how long it took poison gas to penetrate them. On one of those trips to Berlin in 1917, he arranged his time to do some research with Meitner and the two discovered a new radioactive substance—protactinium, element 91.

After the war, Hahn returned to the institute with Meitner to study the decay processes of protactinium, uranium, and uranium isotopes. He also began to turn his attention to applied radiochemistry. He started a new kind of experiment that resulted in the development of the emanation method to study changes in the surfaces and formation of surfaces in certain precipitates. On April 22, 1922, Hahn’s son, Hanno, was born. In 1928, Hahn became the director of the Kaiser Wilhelm Institute for Chemistry.

Not long after English physicist James Chadwick discovered the neutron in 1932, Italian physicist Enrico Fermi discovered that, by bombarding the elements of the periodic table up to uranium with low-energy neutrons, almost all of them were transformed into radioactive isotopes of the element with the next highest atomic number. When he bombarded the heavy nuclei of uranium (atomic number 92) with neutrons, Fermi concluded that he had produced a transuranium element with an atomic number of 93. In 1934, Hahn and Meitner, along with German chemist Fritz Strassmann, decided to repeat Fermi’s experiments. At first they believed that they had verified Fermi’s results, although the evidence was very complicated and confusing. For the next four years, Hahn and his associates examined the decay patterns and chemical and physical properties of transuranium elements.

In July, 1938, Meitner was forced to flee Nazi Germany, but Hahn and Strassmann continued their research. The neutron bombardment of uranium seemed to produce several radioactive substances whose chemical properties indicated either radium isotopes or barium. Since the prevailing views of physics at the time made barium production from uranium out of the question, radium was the only reasonable conclusion. Yet when it became impossible to separate the radium, Hahn and Strassmann began to realize that, under the action of the neutrons, the uranium had split into two parts of unequal weight, the most accessible of which was barium. The two scientists confirmed their findings using differing procedures, although they could scarcely believe in the transmutation of uranium to barium.

Hahn sent news of his findings to Meitner and she correctly interpreted the phenomenon as a splitting of the uranium nucleus and, with her nephew, Otto Robbert Frisch, named it “fission.” Shortly after the publication of this revolutionary information, Hahn and Strassmann announced the discovery of the second product of uranium fission: the rare gas krypton. When bombarded with slow neutrons, uranium (nuclear charge 92) divided into two fractions, yielding barium (nuclear charge 56) and krypton (nuclear charge 36), with a release of energy.

In the spring of 1945, during World War II, Hahn was arrested by Allied troops and interned in England. There, he learned that he had been awarded the 1944 Nobel Prize in Chemistry for his discovery of the fission of heavy nuclei; at the same time, he was profoundly shaken when he also heard that his discovery had led to the production of atomic bombs that had been detonated over Hiroshima and Nagasaki. He became a firm opponent of nuclear weapons and in 1957 refused to cooperate in the planned West German manufacture of such weapons.

On his return to Germany in 1946, Hahn accepted leadership of the Kaiser Wilhelm Society, which was renamed the Max Planck Society for the Advancement of Science in 1947. From 1948 to 1960, Hahn was the society’s president. Hahn’s son and daughter-in-law were killed in an automobile accident in 1960. His wife never recovered from this shock, and when he died in 1968 at age eighty-nine, she survived him by only two weeks.

Impact

Hahn has been called the cofounder of atomic fission. His was a life of tremendous scientific achievement and historic significance. His careful experimentation and discovery of phenomena previously thought to have been impossible led to the practical conversion of matter into energy and helped usher in the atomic age.

Of his original publications, only one was a full-size scientific text, consisting of his 1933 Baker Lectures at Cornell University and entitled Applied Radiochemistry (1936). However, Hahn was prolific in the recording of his reminiscences about various developments in the evolution of radiochemistry, believing, perhaps, that the personal touch was just as necessary in the communication of scientific information as chemical equations and raw data.

Hahn’s accomplishments were highlighted by the awards that continued to come to him in later life, in addition to his Nobel Prize. In 1966, he shared, with Meitner and Strassmann, the prestigious Enrico Fermi Award, issued by the US Atomic Energy Commission. It was the first time the award went to non-US citizens and thus seems to support the idea that Hahn’s discovery marked the beginning of a new epoch in global scientific history.

Bibliography

Hahn, Otto. Otto Hahn: My Life, the Autobiography of a Scientist. Trans. Ernst Kaiser and Eithne Wilkins. New York: Herder, 1970. Print. A thorough autobiography that presents information on Hahn’s personal life and scientific work.

Hoffman, Klaus. Otto Hahn: Achievement and Responsibility. New York: Springer, 2001. Print. Recounts Hahn’s life and achievements with discussion of the social and scientific responsibilities related to discovering atomic fission.

James, Ioan. Remarkable Physicists: From Galileo to Yukawa. New York: Cambridge UP, 2004. Print. Presents a profile of Hahn as a notable scientist.