The discovery of nuclear fission - generally attributed to the German chemist Otto Hahn, the subject of this biography - is one of the most fascinating episodes in the history of 20th-century science. As a scientific achievement it does not rank very high. In a century that saw the emergence of the theories of relativity and quantum mechanics and the elucidation of the structure of the atom and of the origin of the universe, the experimental discovery of fission merely closed a gap in our knowledge of the make-up of the atomic nucleus. It is a phenomenon that should easily have been foreseen by theoreticians. When Otto Robert Frisch informed Niels Bohr about the concept of fission that he and Lise Meitner had just come upon, Bohr exclaimed: "Oh, what idiots we have all been! Oh, but this is wonderful! This is just as it must be!" But from the point of view of its practical applications and the impact it has had on world affairs, the discovery of fission takes top place. The scientific finding was converted into a huge military and industrial enterprise with staggering speed. The observation by Frisch of the emission of energy at fission, which was immediately followed by the detection of the emission of neutrons in the process, paved the way to the utilisation of a new source of energy for peaceful purposes, as well as to the most destructive weapon that mankind has ever known.
The history of the discovery has been described in a number of books, but it is still controversial and merits a brief summary. In the middle of the 1930s, there was a flurry of research on the production of new radioactive elements. A team in Rome, under Enrico Fermi, managed to convert many ordinary elements into radioactive varieties by bombardment with neutrons. Usually, the radioactive product differs from the target element by, at the most, two places in the periodic table, and the identification of the new species, by physical or chemical methods, presents no difficulties. But the case of uranium was different: the bombardment of uranium with neutrons resulted in the production of a large number of radioactive species, whose identity proved difficult to establish.
The challenge was taken up in Berlin, where Hahn, in collaboration since 1907 with the Austrian physicist Lise Meitner, had established a research centre, making important contributions to the science of radioactivity. Hahn, who had acquired the assistance of a talented chemist, Fritz Strassman, tried to solve the problem by refined chemical processes. He concentrated on one radioactive species, which he found behaved chemically like radium, or, to be more precise, like barium, an element in the middle of the periodic table, far away from the uranium target. Meitner's hypothesis of nuclear isomerisms did not clarify the problem.
When, after the Anschluss of Austria in 1938, Meitner became a German citizen, she was no longer allowed to hold a post in a German institution. In July 1938, she went into exile in Sweden. Hahn kept her informed by letter about the progress of the work. Towards the end of the year, he and Strassman came to the conclusion that the element in question was chemically identical to barium, but they could not understand how this came about.
As it happened, Meitner's nephew, Frisch, who worked in Bohr's institute in Copenhagen, came to Sweden to spend Christmas with his aunt. She showed him the letter from Hahn, which she was at a loss to interpret. But Frisch saw the answer: the nucleus of a very heavy element becomes more and more unstable, and the impact of a neutron is enough to break it into two nearly equal parts, for example, into barium and krypton. A corollary of this event is the release of an amount of energy about 20 times larger than in an ordinary nuclear reaction. Immediately after his return to Copenhagen, Frisch carried out the experiment confirming the large emission of energy. It was he who coined the name fission for the phenomenon.
So much for facts. Now comes the controversy: who deserves the credit for the discovery? Hahn was convinced that he did. In this book, Klaus Hoffmann goes to great lengths to prove that Hahn was the discoverer of fission. I am not convinced. Fission is a purely physical process and Hahn would not have cottoned on to it by himself. Moreover, the important consequence of the discovery, the release of nuclear energy on a practical scale, is the direct outcome of Frisch's work.
Hahn received the 1944 Nobel prize in chemistry. In my opinion, he deserved it, although it should have been shared with Strassman. But there should have been a Nobel prize in physics, awarded to Frisch and Meitner, the true discoverers of fission. There is a precedent for this: Marie Curie received a Nobel prize in physics for the physical aspects of the discovery of radioactivity, and then a Nobel in chemistry for the chemical aspects. In the case of fission, the physics prize was never awarded.
Meitner was very disappointed about missing out on the Nobel, but her contributions to science were recognised in a number of ways, including the naming after her of the element with the atomic number 109 (meitnerium). Frisch never got recognition.
After the use of the atom bomb on Hiroshima and Nagasaki, Hahn felt deep remorse, blaming himself for the tragedy. But there was no cause for him to feel guilty. What he had done was a piece of pure research, and he could not have foreseen its applications. True, he took part in the short-lived German project to make the bomb in the early years of the war. He was forced into this project because of his senior position in German science, but he did the least possible to advance it. In the postwar years, he took an active part in anti-nuclear campaigns, as well as in calling on scientists to be aware of their social responsibilities.
Hoffmann's biography, subtitled "Achievement and Responsibility", was written in German and originally published in 1993 (by the same Springer Verlag) under the German title Otto Hahn : Schuld und Verantwortung , which translates as "guilt and responsibility". No explanation whatsoever is given for this significant change. It is very puzzling: why has a feeling of guilt for the discovery of fission become an achievement for the English-speaking market?
Liberties have also been taken with the text. The translator seems to have taken the view that since Hahn learnt his English in the Edwardian era, this should be reflected in the translation. It is often difficult to understand what the author intended to say. In addition, there are errors of a scientific nature. I have to attribute these to the translator. The author, who has a doctorate in science, is unlikely to have made such bloomers.
Sir Joseph Rotblat, Nobel laureate, was president, Pugwash Conferences on Science and World Affairs, from 1988 to 1997.
Otto Hahn: Achievement and Responsibility
Author - Klaus Hoffmann
ISBN - 0 387 95057 5
Publisher - Springer
Price - £28.00
Pages - 5