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 U₂₃₅ from the more common U₂₃₈ (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 U₂₃₅ from U₂₃₈, 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). □

FRISCH, OTTO ROBERT

(b. Vienna, Austria, 1 October 1904; d. Cambridge, England, 22 September 1979)

physics.

Frisch grew up in Vienna. His grandfather, Moriz Frisch, a Polish Jew from Galicia, had settled there and started a printing business in 1877. His father, Justinian Frisch, was a doctor of law and held senior positions in a number of firms, mainly in printing and publishing, His mother, Auguste Meitner, was the daughter of a lawyer and at one time a concert pianist. The small family (there were no other children) seems to have been a very happy one, and Frisch always retained a strong sense of family and of community. Much of his scientific work was collaborative.

With his father’s help Frisch developed a strong interest in mathematics but also enjoyed making things, and at Vienna University he elected to read physics, with mathematics as a second subject. After receiving a doctorate (1926) under the supervision of Karl Przibram, he worked for a year in the laboratory of a small instrument firm, then for three years, in Berlin, at the Physikalisch-Technische Reichsanstalt. This brought him into contact with the strong school of physics at the University of Berlin, and in his last year there he was able to work with Peter Pringsheim. In 1930 Frisch moved to the University of Hamburg, as assistant to the great experimentalist Otto Stern; and over the next three years he worked both with Stern, on diffraction experiments with molecular beams, and with the young Emilio Segré.

In 1933 the racial laws of the National Socialist government compelled Stern. Frisch, and a host of other Jewish physicists to leave the country. Frisch then worked for a short time with Patrick Blackett at Birkbeck College, London, Niels Bohr’s Institute for The oretical Physics in Copenhagen in 1934. In Copenhagen, Frisch, working largely with Hans von Halban, began to concentrate on the field of experimental nuclear physics recently opened up by Enrico Fermi. Despite his strong experimental bias, however, it was for the joint authorship of two theoretical papers that Frisch was to become famous.

The first of these contributions was written over the Christmas holidays in late 1938. Earlier that year Frisch’s aunt, Lise Meitner, had fled from Germany and, after spending time in the Netherlands and Denmark, had joined the Nobel Institute in Stockholm. Meitner was a physicist of distinction who had collaborated for aboutthirty years with Otto Hahn. She had been very kind to Frisch while he was in Berlin, and they had since spent Christmas together regularly. During his visit she received a letter from Otto Hahn that reported the apparent splitting of the uranium nucleus under neutron bombardment. Frisch and Meitner then worked out a simple theoretical interpretation of this phenomenon, which they christened “fission,” Back in Copenhagen, Frisch confirmed the fission interpretation by repeatin the experiment and detecting the fission fragments.

Meanwhile, as war threatened to engulf much of Europe, even Denmark was becoming uncomfortably close to the German state for a Jew. In the summer of 1939, Mark Oliphant responded to Frisch’s clearly expressed desire to move to England by inviting him to Birmingham University for a summer vacation, with a view to a more permanent appointment thereafter. Before the vacation was over, however, war had broken out; Frisch was promptly appointed to a temporary teaching assistantship at Birmingham. While there, he completed with Rudolf Peierls two theoretical papers relating to the possibility of a nuclear chain reaction. In the first, a general paper on subatomic phenomena written for the annual report of the Chemical Society, they concluded, as Bohr had earlier, that there was no possibility of an explosive chain reaction in natural uranium. Before writing this, Frisch had tried to verify experimentally the theoretical calim underlying Bohr’s argument: that the observed fissions were due entirely to the isotope uranium 235, which is less than 1 percent of natural uranium. He was unable to separate out the isotope for experiment, but the attempt got him thinking about what would happen if the isotope could be isolated. Also with Peierls, who had been investigating the mathematics of the chain reaction. Frisch worked out an order-ofmagnitude estimate for the critical size of a sphere of pure uranium 235 (about one pound) needed to sustain a chain reaction. Another calculation gave an estimate for the proportion of fission energy that would be released by such a sphere in an explosion before the sphere split too much to sustain the reaction. The results suggested that a pure uranium 235 bomb might be feasible with only a few pounds of that isotope.

These important investigations were written up in April 1940 in the famous Frisch-Peierls memorandum; and though they did not at first dispel skepticism about the possibilities of a bomb (the separation task seemed impracticably enormous), they led directly to the British wartime atomic energy project and indirectly provided a strong stimulus to the American project. Despite the problems caused by his German background. Frisch made valuable contributions to both projects, first at Liverpool, where he worked from August 1940 to late 1943, and then at Los Alamos, New Mexico, where the combination of his practical resourcefulness and his theoretical command made him a useful troubleshooter. Early in 1946, the war over, he returned to England to become head of the nuclear physics division of the new Atomic Energy Research Establishment at Harwell. The following year he accepted the Jacksonian Professorship of Natural Philosophy at Cambridge.

Frisch was not a natural administrator or a great leader. He delegated the administration of Harwell and lived a relatively quiet life at Cambridge, teaching, supervising research (and undertaking a little of his own), and writing a large number of popular articles and books. His great gift, whether in experimental or theoretical physics, had always been to see things clearly, usually through some simple analogy. His experiments were elegant and straightforward, and his theoretical contributions had the same character. Popular exposition thus came naturally to him.

In 1951 Frisch married Ursula Blau, an artist; they had a son and a daughter. As in his own childhood, art (in which his father had been passionately interested) and music (inherited from his mother’s side) dominated family life. He received the O.B.E. in 1946 and was elected a fellow of the Royal Society in 1948. At Cambridge he was a fellow of Trinity College, Frisch died after an accident, just before his seventy-fifth birthday.

BIBLIOGRAPHY

1. Original Works. A full bibliography of writings is in the obituary by Peierls (see below). The two most significant papers are “Disintegration of Uranium by Neutrons: A New Type of Nuclear Reaction,” in Nature, 143 (1939), 239–240, written with Lise Meitner: and “On the Construction of a “Super-Bomb’: Based on a Nuclear Chain Reaction in Uranium,” written with Rudolf Peierls, part I in Margaret M. Gowing, Britain and Atomic Energy, 1939–1945 (London, 1964), 389–393, and part II in Ronald W. Clark, Tizard (Cambridge, Mass, 1965), 215–217. On the discovery of fission, see “The Discovery of Fission,” in Physics Today, 20 (November 1967), 43–52, written with J. A. Wheeler.

Frisch’s papers, cataloged by the Contemporary Scientific Archives Centre in Oxford (catalog no. 87), are in Trinity College Library, Oxford, and comprise an extensive collection of research notebooks, personal diaries and notebooks, correspondence, and memorabilia, including articles written by and about him.

II. Secondary Literature. The two principal accounts of Frisch’s life are his autobiography, What Little I Remember (Cambridge 1979); and Sir Rudolf Peierls, “Otto Robert Frisch,” in Biographical Memoirs of Fellows of the Royal Society, 27 (1981), 282–306. His wartime work is covered in Margaret M. Gowing, Britain and Atomic Energy, 1939–1945 (London, 1964). On the discovery of fission, see Hans G. Graetzer and David L. Anderson. eds., The Discovery of Nuclear Fission; A Documentary History (New York, 1971).

John Hendry

FRISCH, OTTO ROBERT

FRISCH, OTTO ROBERT (1904–1979) physicist, nephew of the physicist Lise *Meitner. Frisch was born in Vienna but was naturalized as a British citizen (1943). After gaining his D.Phil. in physics from the University of Vienna (1926) he worked at the national physics laboratory in Berlin (1927–30) and with the Nobel physics laureate Otto *Stern in Hamburg (1930–33). With the coming of the Nazis, he left Germany in 1933 to work in Patrick Blackett's laboratory in Birkbeck College, London, before joining Niels *Bohr's laboratory in Copenhagen (1934–38). With the threat of war and invasion, Frisch moved to Mark Oliphant's laboratory in Birmingham, England (1939–40) but joined James Chadwick's laboratory in Liverpool as this was more appropriate for his work. With the merging of U.K. and U.S. research on nuclear weapons he moved to Los Alamos (1943–46), returning to England in 1946 as head of the nuclear physics division at the Atomic Energy Establishment in Harwell. In 1947 he was appointed Jacksonian Professor of natural philosophy at Cambridge University and a fellow of Trinity College, working in the Cavendish Laboratory. He retired in 1972. His initial research in Germany concerned the physical properties of nuclear particles, including the discovery of the magnetic moment of protons. In Copenhagen he studied radioactive isotopes and the outcome of collisions between neutrons and nuclei. At the end of 1938 he and Lise Meitner calculated the enormous energy which could potentially be released by what they termed "fission," the process just described by Otto Hahn and Fritz Strassman whereby uranium nuclei are split by colliding neutrons. He rapidly identified the fission products experimentally in Bohr's laboratory. Frisch was early to recognize the practical implications of sustained fission and, in collaboration with Rudolf Peierls, he calculated that neutrons could induce a chain reaction in a small enough quantity of pure uranium 235 to make a bomb feasible. In Los Alamos he worked in considerable personal danger on the chain reactions in pure uranium 235 and plutonium underlying the first fission bombs. In Cambridge he developed devices for tracking particles, one of which was marketed successfully under his chairmanship. He was also deeply interested in science education and he wrote many well received books for general readers. He continued his commercial and literary interests in retirement. He was elected a fellow of the Royal Society in 1948.

[Michael Denman (2^nd ed.)]