Known as father of nuclear chemistry, Otto Emil Hahn was a German chemist who was one of the early pioneers of radioactivity and radiochemistry. Hahn won the Nobel Prize in Chemistry for his historic discovery of nuclear fission. He was nominated for the Nobel Prize in Chemistry 22 times and 16 times for the Nobel Prize in Physics before he finally became a Nobel Laureate in 1944.
Otto Hahn, along with his long-time collaborator in research Prof. Lise Meitner, and his student Fritz Strassmann began to research the bombardment of uranium nuclei, leading to the discovery of what came to be known as nuclear fission.
Among all radioactive elements discovered by Otto Hahn, mesothorium-1 (Radium-228) was a significant one. Mesothorium-1 is 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 his first nomination for the 1914 Nobel Prize in Chemistry. However that year, he didn’t win it, but mesothorium began to be used widely for all cancers.
Otto Emil Hahn was born on 8th March 1879 in Frankfurt am Main, Germany. His father Heinrich Hahn (1845–1922) was a prosperous glazier and entrepreneur and his mother Charlotte Hahn, née Giese (1845–1905) was from a royal family. Otto Hahn was raised in a religious home along with his brothers Karl, Heiner, and Julius. He started to take a keen interest in chemistry at the age of 15, and conducted basic experiments in a laundry room in his house.
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.
Hahn began studying chemistry and mineralogy at the University of Marburg in 1897 after he took his Abitur at the Klinger Oberrealschule in Frankfurt. Physics and philosophy were his subordinate subjects. He spent his third and fourth semesters at the University of Munich, studying under Adolf von Baeyer. In 1901, for a dissertation entitled On Bromine Derivatives of Isoeugenol, a subject in classical organic chemistry, Hahn obtained his doctorate at Marburg.
Hahn returned to Marburg after completing his one year military service to work as an assistant to Professor Theodor Zincke. Later, Zincke helped Hahn get a job at University College, London as an assistant to Ramsay’s laboratory. Hahn, working under Ramsay for a year, discovered the thorium isotope, after which he developed an interest in radiochemistry. Encouraged by Ramsay, he changed his mind on working for the industry, and chose to work on radioactivity.
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.
On 22 March 1913, Otto Hahn married young Edith Junghans (1887–1968) in her native city of Stettin, whom he met while attending a conference in Stettin in 1911. Their only child, Hanno, born in 1922, became a distinguished art historian and architectural researcher at Hertziana in Rome.
Discovery of Radio Thorium and other elements
During his time at Ramsay’s laboratory, Hahn discovered a new substance he called radio thorium (thorium-228), which at that time was believed to be a new radioactive element.
Later when he joined Rutherford at McGill University Hahn discovered thorium C (later identified as polonium-212), radium D (later identified as lead-210), and radio actinium (later identified as thorium-227), and investigated the alpha rays of radio thorium.
Mesothorium I (radium-228)
Hahn discovered mesothorium I, mesothorium II, and ionium (later identified as thorium-230) at the University of Berlin after he returned to Germany in 1906.
Otto Hahn was first nominated for the Nobel Prize in Chemistry by Adolf von Baeyer in 1914 for the discovery of mesothorium I (radium-228).
Otto Hahn, along with the help of Lise Meitner, succeeded in demonstrating the radioactive recoil incident to alpha particle emission and interpreting it correctly and was able to use it. Before Hahn, physicist Harriet Brooks had observed radioactive recoil in 1904, but interpreted it wrongly.
During World War I, Hahn was posted to Berlin where he and Meitner isolated a long-lived activity, which they named “proto-actinium”. The International Union of Pure and Applied Chemistry (IUPAC) named the new element protactinium, and confirmed Hahn and Meitner as discoverers in 1949.
Otto Hahn published an article on his discovery of uranium Z (later known as Pa-234), the first illustration of nuclear isomerism, in February 1921.
For his discoveries of mesothorium I, protactinium and nuclear isomerism Hahn was repeatedly nominated for the Nobel Prize in Chemistry in the 1920s by a number of scientists.
Discovery of Nuclear Fission
Otto Hahn along with Lise Meitner and Fritz Strassmann furthered the research begun by Enrico Fermi and his team in 1934 when they bombarded uranium with neutrons. Until 1938, it was believed that the elements with atomic numbers greater than 92 (known as transuranium elements) arose when uranium atoms were bombarded with neutrons.
Hahn and hist team had thought the radioactive transmutation products resulting from their experiments could be radium isotopes. But, he and Strassmann observed that one of the products they found, seemed to be a radioactive form of the much lighter element barium. Finding a group 2 alkaline earth metal was problematic, because it did not logically fit with the other elements found thus far. Hahn initially suspected it to be radium, produced by splitting off two alpha-particles from the uranium nucleus. At the time, the scientific consensus was that even splitting off two alpha particles via this process was unlikely.
Hahn, who did not inform the physicists in his Institute, described the results exclusively in a letter to Meitner on 19 December:
“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.
As a chemist, Hahn was reluctant to propose a revolutionary discovery in physics. However, 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”.
In a later appreciation (1963), Meitner wrote:
“The discovery of nuclear fission by Otto Hahn and Fritz Strassmann opened up a new era in human history. It seems to me that what makes the science behind this discovery so remarkable is that it was achieved by purely chemical means.”
In their second publication on nuclear fission (Die Naturwissenschaften, 1939), Otto Hahn and Fritz Strassmann used for the first time the term Uranspaltung (uranium fission), and predicted the existence and liberation of additional neutrons during the fission process, which was proved to be a chain reaction by Frédéric Joliot and his team in March 1939.
Scientists all over the world 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.
World War II Internment to England:
During the war, Hahn was suspected of working on the German nuclear weapon project to develop an atomic reactor or an atomic bomb, but his only connection was the discovery of fission. 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.
It was here that he and the other German scientists learned about the atom bombs dropped on Hiroshima and Nagasaki in August 1945.
The historian Lawrence Badash wrote:
“The news completely shattered him, for he felt that his discovery of fission had made construction of the atomic bomb possible, and that he was thus personally responsible for the thousands of deaths in Japan. Long before, he had contemplated suicide, when he first recognized the possible military use of fission; now, with the blame of its realization drawn squarely upon his shoulders, suicide again seemed a way to escape his desolation. Fearing this, Max von Laue remained with him until he passed this personal crisis. Never has social responsibility hit a scientist with such impact.”
In January 1946, Hahn, Heisenberg, and von Laue were brought to the city of Göttingen, which was controlled by the British occupation authorities.
Nobel Prize and other honours:
Otto Hahn had been nominated 22 times for the Nobel Prize in Chemistry from 1914 to 1945, and 16 times for the Nobel Prize in Physics from 1937 to 1947.
On 15 November 1945 the Royal Swedish Academy of Sciences announced that Hahn had been awarded the 1944 Nobel Prize in Chemistry “for his discovery of the fission of heavy atomic nuclei.”
List of honours:
- In 1948, Otto Hahn was elected President of the former Kaiser Wilhelm Society, newly renamed as the Max Planck Society.
- 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.
- In 1966, Hahn, Meitner, and Strassmann were honoured with the prestigious Enrico Fermi Award.
- 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.
Death: Otto Hahn died on 28 July 1968.
Advocate of social responsibility:
Soon after the Second World War, Hahn reacted to the dropping of the atomic bombs on Hiroshima and Nagasaki by campaigning against further development and testing of nuclear weapons.
Hahn initiated and organized the Mainau Declaration of 1955, in which he and a number of international Nobel Prize-winners called attention to the dangers of atomic weapons and warned the nations of the world urgently against the use of “force as a final resort”, and which was issued a week after the similar Russell-Einstein Manifesto. In 1956, Hahn repeated his appeal with the signature of 52 of his Nobel colleagues from all parts of the world.
He was also instrumental in and one of the authors of the Göttingen Manifesto of 13 April 1957, in which, together with 17 leading German atomic scientists, he protested against a proposed nuclear arming of the new West German armed forces (Bundeswehr).
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- Nobel Prize for Chemistry for 1944: Prof. Otto Hahn