Otto Robert Frisch

Otto Robert Frisch

The Austrian-British physicist Otto Robert Frisch (1904-1979) was recognized for his significant role in the discovery of nuclear fission.

Otto Robert Frisch was born on October 1, 1904, in Vienna, Austria, the son of Justinian and Auguste (Meitner) Frisch. Though his father had a doctorate in law, his mother was an accomplished musician, and the family had intellectual connections, his father was forced by financial circumstances to pursue a career as a printer. Young Frisch thus grew up in a hardworking bourgeois Jewish family of extensive education and high expectations. Educated in a Viennese gymnasium, he learned Latin, Greek, and some arithmetic, but most of his mathematical training was private and personal.

At the age of ten his father introduced him to Cartesian coordinates, and within a couple of days he had worked out for himself the equation of the circle. At the age of 12 his father again tutored him, this time in trigonometry. Upon learning the definition of sine and cosine, he was shown the equation sin² x + cos² x = 1, to which he replied, "Of course—it's obvious," thereby surprising his father and impressing those who heard the anecdote. Later, he was coached in calculus by Olga Neurath, a blind mathematician acquainted with many members of the Vienna circle of mathematicians and philosophers, with whom Frisch also came into contact. One of the most important events of his gymnasium days came when he had the opportunity to hear Albert Einstein speak on his theory of special relativity, scarcely hoping that one day he would meet him on a professional level.

In 1922 he entered the University of Vienna, graduating in 1926 with a Ph.D. in physics. For a few months he worked as a consultant for Siegmund Strauss, an Austrian inventor tinkering with x-ray dosimeters. From Strauss he must have learned a great deal about the construction of technical measuring apparatus, for this was to be a great strength of Frisch's throughout his long career. A few months later, in 1927, he was offered a research job in Berlin at the German National Physical Laboratory (Physikalische Technische Reichsanstalt ), where he worked in the optics division under Carl Müller. Here he was also the colleague of his eminent aunt Lise Meitner, herself a physicist. She and Otto Hahn had collaborated for 20 years on work eventually to lead to the discovery of uranium fission. Frisch enjoyed his three years in Berlin, conducting research, making friends and contacts, even meeting his aunt's personal friend Einstein.

This period ended in 1930 when the German physics professor Otto Stern offered him a position as assistant, which Frisch later humorously described as a "high-class technician." There he conducted experiments upon molecular beams (that is, moving ionized gas molecules), deflecting them with magnets and measuring their deflection. Such controlled experiments necessitated the use of very delicate, very precise technical equipment which Frisch himself designed.

Germany in 1933 began to be dangerous for Jews. Hitler had come to power and racial laws were passed forbidding Jews to engage in certain activities, so Frisch began to look elsewhere for opportunities. He met Niels Bohr that summer at a conference in Copenhagen and became friendly with him. Then in October he visited England on a research grant, working at Birkbeck College in London under Patrick M. S. Blackett. With his grant nearing expiration in 1934, Bohr invited him back to Copenhagen with the compliment: "You must come to Copenhagen to work with us. We like people who can acutally perform thought experiments" Frisch went and remained for five years. There he continued work he had already begun on radioactivity, looking for new radioactive elements produced by alpha-ray bombardment—work requiring the use of more delicate measuring instruments which, again, he constructed. He also became more intimately acquainted with Bohr, whom he came to admire as the most profound thinker of all the modern physicists.

With Hitler's military successes in Austria in 1938 and Czechoslovakia in 1939, Frisch began to worry that he might be forced to return to Austria, now under German control, where he feared being placed in a concentration camp, so once more he put out feelers to England for possible work. Ironically, this most precarious time of his life also saw him play one of his most crucial scientific roles. Over the Christmas vacation of 1939 Frisch visited his aunt, now in Sweden. She and Otto Hahn were still collaborating— now by letter—in work on radioactivity. Having just received a letter from Hahn, she read it to Frisch while they were on an outing in the snow—she on foot, he on skis. Hahn had written to convey the startling information that uranium bombarded by neutrons produced the lighter element barium. Upon finishing the letter they sat down on a tree trunk, Frisch still in his skis, to calculate upon scraps of paper the possibility that uranium could split into barium. Between them, they were able to work out the probability.

Frisch returned to Copenhagen to inform Bohr and sent a short note of the discovery of nuclear fission (his coinage) to the British scientific journal Nature. In the excitement the concept of a chain reaction was totally missed by Frisch, though a Danish colleague, Christian Muller, quickly pointed it out. Frisch initially thought the idea absurd, suggesting that otherwise no uranium ore deposits could exist without exploding—until he recalled that the impurities within those ores acted as controls by blocking the reaction.

Also at this time (late in 1939) Frisch received a letter from Mark Oliphant, head of the Department of Physics at the University of Birmingham, offering him a nominal job as assistant, the real purpose being to get him further from Germany. His work consisted of meeting with Oliphant's beginning students to clarify whatever Oliphant may have confused them on. With little else to do he interested himself in problems related to uranium fission, especially that of separating U ₂₃₅ from the more common U ₂₃₈ (two forms of uranium differing in number of neutrons, and therefore in stability). Collaborating with Rudolph Peierls, he confirmed Bohr's suggestion that a chain reaction was more likely from U 235 (because less stable). But his calculations upon the rapidity of a chain reaction and the amount of uranium needed for a critical mass disputed Bohr's belief that an atomic bomb was not feasible, for rather than tons of uranium being necessary, only one or two pounds were required. And with the perfection of his and Peierls' techniques for separating U ₂₃₅ from U ₂₃₈, he realized that a more elaborate design with more separation tubes might enable one to produce one pound of uranium in a matter of weeks. This was startling. And it was frightening, for it opened the possibility that the Germans might be capable of constructing the bomb.

Later in 1940 Frisch transferred to the Liverpool Institute. From that base of research, for the next three years, he was to visit Oxford and Cambridge. At Liverpool he worked under James Chadwick, who in 1943 headed the British Atomic-Energy Commission to the United States. Frisch followed him there, first being naturalized as a British citizen—a process which took the remarkably short time of one week. In Washington, D.C., he met General Leslie Groves, who sent him to Los Alamos, New Mexico, to conduct secret research on the atomic bomb under Robert Oppenheimer. There he remained until 1945, seeing the Trinity test succeed in July of that year, near Alamogordo, New Mexico—the first atomic explosion.

After the war's end he returned to England, where from 1945 to 1947 he held the post of division leader in the Atomic Energy Research Establishment at Harwell, under Robert Cockburn. In 1947 he was given the Jackson Chair of Physics at Trinity College in Cambridge, where after a life as a travelling "scholar" he finally settled down, conducting research at the Cavendish Laboratory. In 1951 he married a graphic artist, Ulla Blau; they had two children—Monica Eleanor and David Anthony. Frisch remained at Cambridge, actively working until his retirement in 1972, continuing his research in physics through the use of newer techniques, including bubble chambers, lasers, and computers. The last years of his life were happy and fulfilling. He was, he said in 1979 shortly before his death, "a very lucky man." Among his awards and honors, the two bestowed upon him by his adopted home were most appreciated: the Order of the British Empire—Medal of Freedom (1946) and his election to the Royal Society (1948).

Further Reading

The only biography available is Frisch's autobiography, What Little I Remember (1979). This work is very rewarding—it does not pretend to be scholarly, but it conveys the excitement of Frisch's life, his humor, and his love of science and his fellow scientists. Frisch has also written works popularizing ideas of modern atomic physics. They are obsolete now, but still worth reading: Meet the Atoms (1947) and Atomic Physics Today (1961). □