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Strassmann, Friedrich Wilhelm (Fritz)

STRASSMANN, FRIEDRICH WILHELM (FRITZ)

(b. Boppard, Germany, 22 February 1902; d. Mainz, Federal Republic of Germany, 22 April 1980)

nuclear chemistry.

Fritz Strassmann was the ninth and last child of Richard Strassmann, a court clerk, and of Julie Bernsmann. His father was transferred to Cologne in 1906, and a year later to Düsseldorf, where Fritz completed elementary school in three years (1908–1911) instead of the normal four. He went on to the municipal Oberrealschule (now Leibniz-Gymnasium). Shortly before he took his final examination (Abitur), his father died. Because all but one of his brothers and sisters had already left home, however, Strassmann was able to pursue his desire to study chemistry.

The industrial and economic crisis of postwar Germany offered discouraging professional prospects for a chemist, but Strassmann had been captivated by the subject in school, and had already carried out chemical experiments in a corner of his mother’s kitchen. Inflation and the smallness of his mothers pension made it impossible for her to finance a university education, so Strassmann chose to study at the Technische Hochschule in Hanover, where he could live nearby with his brother Arthur. After matriculating in 1920, Fritz commuted about sixteen miles (twenty-five kilometers) daily by train for three years before he obtained a room in the home of a milkman near the Technische Hochschule in return for tutoring the milkman’s son. He supported himself by giving private lessons and helping students prepare for their examinations.

After attending the chemical lectures of Wilhelm Biltz, Wilhelm Geilmann (a distinguished expert in analytical chemistry, whom he later appointed to a professorship at his institute in Mainz), Friedrich Quincke, Gustav Keppeler, and Hermann Braune, Strassmann received his diploma as a chemical engineer in 1924 and obtained his doctorate in physical chemistry under the supervision of Braune in 1929. His dissertation dealt with the solubility of iodine in gaseous carbonic acid. Strassmann had been prompted to take his doctorate in physical chemistry by the great unemployment in Germany; the chemical industry had let it be known that such training would provide the best chance for employment. To improve his chances further, Strassmann became a lecture assistant to Braune. Three months later he accepted Otto Hahn’s offer of a partial scholarship granted by the Notgemeinschaft der Deutschen Wissenschaft to the Kaiser Wilhelm Institute for Chemistry at Berlin. Strassmann was motivated by the possibility of learning radiochemistry, which had been introduced into Germany by Hahn. It was the main field of research at the Berlin institute, of which Hahn had become acting director in 1926 and director in 1929. The breadth of Strassmann’s education and training, including practical applications, his knowledge, and above all his skill at chemical analysis, caused Hahn to offer him the scholarship-and twice to submit an application for renewal to the Notgemeinschaft.

When his scholarship expired in September 1932, Strassmann had to support himself again. But he was allowed to continue his research work on “Hahn’s emanation method” (which Strassmann modified from the point of physical chemistry) in Hahn’s private laboratory, without pay but also without the tuition that research students normally had to pay to the institute. In 1934 Lise Meitner, the head of the physics department of Hahn’s institute, persuaded him to grant Strassmann 50 marks per month from a private fund he had at his disposal for special contingencies. After Hitler’s seizure of power and the economic recovery following it, Strassmann refused the lucrative posts offered to him by the chemical industry because entering a firm would have required him to join the Nazi party or a Nazi organization-a step he consistently resisted until the collapse of the German Reich in 1945. This stand also prevented his Habilitation. As early as the fall of 1933 he withdrew from the German Chemical Society, then the professional organization of German chemists, because it had dropped its Jewish members. During the spring of 1943 he and his wife hid a Jewish woman for two months in their apartment, running-in consequence of the frequent bombings-the risk of disclosure, which would have cost them their lives.

After joining the special working team of Meitner and Hahn, Strassmann was employed as assistant as of January 1935 (at half pay for the first years); but the political situation forced him to remain isolated and dependent on Hahn, which prevented him from developing his own field of research, as the other members of the institute did.

Thus it was the political situation with its social consequences, on the one hand, and the liberal political attitude of Hahn as the head of the institute, on the other (on account of which Meitner, whose parents were Jewish, could remain at the institute after 1933 and Strassmann could stay and be employed there after 1935), that made possible the formation of a highly effective interdisciplinary team of these three scientists: the organic and radiochemist Hahn, the theoretical physicist Meitner, and the analytical and physical chemist Strassmann.

On 20 July 1937, Strassmann married the chemist Maria Heckter, to whom he had once given private lessons in Hannover. They had one son, Martin. Strassmann, a self-taught violinist, and Heckter had also been members of a group of young musicians in Hanover, as was a mutual friend, Irmgard Hartmann, (Maria Heckter died of cancer in 1956. Three years later, Strassmann and Irmgard Hartmann were married.)

His studies on Hahn’s emanation method had already earned Strassmann a reputation outside the institute, and his knowledge and skill at chemical analysis (for which he often was consulted by Hahn and the members of the institute) made him the essential third man to join the Hahn-Meitner team when Meitner persuaded Hahn, in the autumn of 1934,1 to embark on the joint investigation of the alleged “transuranics”, which Enrico Fermi and his collaborators had found by bombarding uranium with slow (so-called thermal) neutrons. In the following years Strassmann was the only one of the three who was able to concentrate exclusively upon their common experimental investigations. It was only after Meitner’s emigration to Sweden in mid July 1938 that this teamwork led to the discovery of the fission of uranium nuclei by chemical analysis of the products of neutron irradiation of uranium (and thorium) carried out by Strassmann. But Meitner had been the initiator of these joint investigations; she was the “theoretical head” of the team-as Strassmann characterized her-who kept in touch by letter after leaving Berlin, and she was the one who (together with her nephew Otto Robert Frisch) gave the first and correct theoretical explanation of fission. Nevertheless, Meitner’s absence apparently enabled Strassmann to pursue the approach, based on an investigation he had carried out with her, that led to the discovery.

When she became acquainted with Fermi’s transuranic elements in the autumn of 1934, Meitner wanted to make use of the experience she had acquired with Hahn in identifying radioactive substances between 1907 and the early 1920’s, because Ida Noddack had advanced general objections against Fermi’s chemical precipitations.2 From the physical point of view and in conformity with the displacement laws of Ernest Rutherford (or, rather, of Frederick Soddy and Kasimir Fajans), according to which the atomic decay of an alpha-emitting radioactive isotope (such as uranium 92) leads to a daughter isotope (such as thorium 90) whose place in the periodic table is two positions below that of the parent (that is, the neutron-bombarded element), while the daughter of a beta-emitting isotope (such as proactinium 91) takes the place of the element next to the place of the parent (thorium 90), it had been obvious that Fermi’s beta-emitting uranium produced by neutron irradiation led to elements beyond uranium. And because the actinides were still unknown, Strassmann’s more specific operations chemically corroborated ekarhenium, ekaosmium, and so on, within the decay products of irradiated uranium, while the measurements of the half-life periods led to the certainty that the three beta-ray emitters discovered by Fermi’s group produce three isomeric series of these transuranics.

The results, which were reproduced and accepted around the world, were published in several papers between 1935 and 1938. At the end of their second paper, Hahn and Meitner wrote; “Finally we would like to thank cordially . . . Dr. F. Strassmann for his exceptionally useful collaboration concerning chemical separation”3. From the third paper on, however, Strassmann’s name appeared as coauthor. Although he had taken an active and increasingly independent role in the experimentation from the beginning of the joint research, he was now acknowledged as an equal collaborator. Being the youngest, his name was mentioned last in all these papers (and in all subsequent papers) but one.

In this sole case,4 Hahn (still the head of the institute) is listed last, indicating that he had not directly taken part in the investigations published in the paper. The paper concerned the results of experiments carried out by Strassmann since mid 1937 by order of Meitner, resuming investigations of the products of neutron-irradiated thorium published in mid 19355. At that time they had assumed two decay series: one should have been induced by fast neutrons and have led after alpha decay to an isotope of radium that as a beta emitter transmuted into beta-emitting actinium and thence again into an isotope of thorium; the second series, induced by slow neutrons, should have begun with a new beta-emitting isotope of thorium produced by neutron capture. The new investigations incorporated the experience acquired with the alleged isomeric series of the transuranics. Chemical separations and measurements of the beta radiation led to the conclusion that fast neutrons had produced isomeric series in the case of thorium. Three such isotopes of radium and of actinium seemed to be proved. To separate these isotopes, Strassmann had used barium and lanthanum as the carriers homologous to radium and actinium.

These isomeric isotopes therefore seemed to be confirmed, particularly when H. Braun, Peter Preiswerk, and Paul H. Scherrer published a brief note alleging that they had detected alpha rays after neutron irradiation of thorium6. However, an assistant of Meitner’s, assigned to demonstrate such rays, did not succeed. Only after the discovery of uranium fission could Hahn and Strassmann show that the alleged isotopes of radium and actinium had indeed been the lower homologues barium and lanthanum, produced by a splitting of the thorium nuclei in which alpha rays did not appear.

The discovery of uranium fission took place in connection with the checking of the results of Irene Joliot-Curie and Pavel Savič (Paul Savitch), who in mid 1937 had reported finding a decay product of neutron-irradiated uranium with a 3.5-hour half-life that apparently had escaped the notice of the Berlin team and did not fit into the previous isomeric series. Joliot-Curie and Savič supposed the substance to be an isotope of thorium. But on Meitner’s request, Strassmann had searched as early as 1935, without success, for such a thorium isotope within the decay products of irradiated uranium. Even though he repeated that examination with new and more precise operations, he still could not find thorium in the filtrates. Meitner communicated this negative result by letter to Joliot-Curie and Savič. Thereupon they proposed that the substance was an actinium isotope-which seemed to Meitner, after the refutation of thorium, theoretically most improbable. Thereupon she lost all interest in further investigations of this substance, which was afterward called curiosum in Berlin.

Joliot-Curie and Savič published a further note in mid October 1938, in which the substance now seemed to be confirmed as actinium. They claimed it was similar to the lanthanum of the potassium lanthanum sulfate they used as carrier, from which it should be separable only by fractional crystallization. Although Hahn did not take the new paper seriously. Strassmann felt sure of the reality of the substance, because the Paris scientists had communicated exact decay curves for the first time. He therefore tried to find a theoretical explanation that would encompass the results of both the Paris and the Berlin team. Based on the pattern of the decay scheme of thorium that Meitner and he had found and published, he put forth the following reflections:

  1. The irradiation of uranium with neutrons leads to an alpha-radiating thorium. That would explain why the earlier measurements, carried out with beta counters, had been negative.
  2. The alpha-radiating thorium has to produce a radium.
  3. If these isotopes of radium were beta emitters, then the radium would decay into an actinium, and the actinium potentially into a thorium.
  4. The Paris scientists had used potassium lanthanum sulfate. In this case at least some radium should be in the precipitate because of the sulfate ions. Therefore a fractionation should have produced the effects described [by Joliot-Curie and Savič].
  5. Barium chloride as carrier should elude [exclude] sulfate ions7.

Strassmann was able to convince Hahn of the applicability of these reflections. Meitner, as well as Niels Bohr and Otto Robert Frisch, did, in fact, reject them when Hahn visited the Bohr Institute at Copenhagen for a lecture on 13 November. But Strassmann’s experiments quickly seemed already to have corroborated the reflections-the paper with the first results was delivered to Die Naturwissenschafien on 8 November. Strassmann supposed that the irradiated uranium, as an alpha emitter, decays into a very short-lived thorium isotope, which could not be proved because of its short half-life but should also be an alpha emitter, so that it produces an isotope of radium, which as a beta emitter decays into an actinium isotope that also is a beta emitter, which therefore leads back to thorium, in three (later four) isomeric series. In Copenhagen, Hahn had asked for a theoretical explanation of the “double” (instead of successive) alpha decay caused by slow neutrons.

Meitner’s objections caused the chemists in Berlin to test the results again and again. Strassmann struggled especially with the difficulty of separating by fractional crystallization the alleged active radium produced by the successive alpha decay from the inactive barium used as carrier. In addition, the degree of the enrichment of the radiation was not the same as what they were familiar with. Hahn therefore diluted some natural radium down to the intensity of the preparations separated by Strassmann from the neutron-irradiated uranium with barium chloride as carrier. But the enrichment in this case remained the same as usual. Therefore the artificial radium ought to display the same chemical behavior as the barium. Gradually Strassmann became persuaded that the alleged radium not only behaves like barium but is barium.

Such a view was entered in Strassmann’s laboratory notebook for the first time on 15 December 1938. In the evening of 16 December, he started the famous indicator experiment, being in agreement with the conclusion that Hahn reported to Meitner in a letter of Monday, 19 December 1938:

Of course, there is something about the “radium isotopes” that is so remarkable that I will tell it only to you. The half-lives of the three isotopes are rather exactly ascertained. They are separable from all the elements except barium. All the reactions are correct, except one . . . : The fractionation does not work. Our radium isotopes behave like barium. We do not get a clear enrichment with barium bromide or chromate etc. . . . On Saturday Strassmann and I fractionated one of our [alleged] “radium” isotopes with Msth I [radium 228] as indicator. The mesothorium was enriched as prescribed, our radium was not. . . . We more and more come to the terrible conclusion: Our radium isotopes do not behave like radium, but like barium. . . .8

The measurements were finished on 19 December: The enrichment of the radium 228 in the barium chloride had the right proportion of 6:1, whereas the enrichment of the alleged radium yielded a proportion of nearly 1:2:1. The latter therefore was radioactive barium, which could have been produced only by bursting of the uranium nuclei (later called “fission” by Frisch).

The paper that communicated these results was finished by Hahn on 22 December 1938 and delivered to Die Naturwissenschaften the same day. It appeared on 6 January 1939. Meitner had learned about it by letter some days earlier. The theoretical explanation, which she and her nephew Frisch found immediately, and which led to the identification of the inert gases krypton and xenon as the other products of the splitting of uranium or thorium nuclei, was made known to Hahn on 24 January. The Berlin chemists at once tried to identify these inert gases within the products of splitting uranium (and thorium). After Christmas vacation Strassmann had confirmed the fission by means of other indicator experiments. Because none of the inert gases could be used as a carrier, he now had to develop a novel experimental arrangement, in which an airstream sucks the radioactive gases into a glass tube filled with wadding (later with activated charcoal), which collects the solid decay products of the beta-radiating inert gases. The evidence of the radioactive inert gases followed from the chemically proved existence of active isotopes of strontium and cesium, which resulted from the gases.

Thereby the fission of heavy nuclei was proved, and simultaneously the previous alleged transuranic elements were rejected. Through Strassmann’s revised analyses they turned out, one after the other, to be isotopes or homologues of the carrier substances-that is, products of splitting atoms of uranium or thorium-except one. This exception was the beta decay product of uranium 239, the latter called neptunium (239), which was discovered by Edwin M. McMillan and Philip Abelson in 1940 and a little later, but independently, by Kurt Starke at the Kaiser Wilhelm Institute.

Strassmann then engaged intensively in the study of the chemical nature of this transuranic element, which was of great general interest especially in regard to the problem of the continuation and/or end of the periodic system. Satisfied that element 93 was not an ekarhenium, he was rather inclined to interpret it as a beginning of the “uranides”, a new series similar to the lanthanides following uranium. The puzzle of the chemical nature of the transuranics, which then was still far from being solved, demonstrates very well the difficulties in proving transuranics. Without the knowledge of the actinides and prior to the discovery of fission, Strassmann’s excellent chemical analyses could hardly have led to other interpretations. But from the beginning of 1939, physicists and chemists throughout the world, including the other members of the Berlin institute, took part in clarifying the products of the splitting and decay of heavy nuclei. None of the members of Hahn’s institute participated in any military investigations or applications, however; on the contrary, Strassmann, Hahn, and the others published nearly all their findings even during the war. Unlike Hahn, Strassmann was not interned after the war, but like him, he affirmed (especially in connection with the rearmament of the Federal Republic of Germany in the 1950’s) his opposition to atomic weapons of every kind, feeling sure that the scientist as an expert is obligated to give publicity to his special knowledge. Moreover, he was a confirmed pacifist.

A second field of Strassmann’s research was the determination of the age of minerals from the half-life of present radioactive elements and the enrichment of the products of their decay chain separated chemically. With Ernst Walling (and Hahn) he developed the rubidium-strontium method for the determination of geological age in 1936 and 1937. He resumed this research in 1942 and 1943 at the request of Josef Mattauch, Meitner’s successor as head of the physics department of the Kaiser Wilhelm Institute and an expert on mass spectrography. The method has since become a cornerstone of geochronology. Age determination was also a field of activity at Strassmann’s university institute in Mainz.

Because of the numerous air attacks on Berlin, the Kaiser Wilhelm Institute of Chemistry was transferred to Tailfingen in southwest Germany in early 1944. At the end of the war Hahn was taken into custody and interned in England with other prominent German atomic scientists. Released early in 1946, he was elected president of the Kaiser Wilhelm Society (in 1949 named the Max Planck Society) and went to Göttingen, where the society had been transferred from Berlin. Mattauch, deputy director since 1943, was elected director in 1946 (at the same time Strassmann was elected scientific member of the society), succeeding Hahn as appointed managing director on 1 August 1947. But he was then suffering from pulmonary tuberculosis and spent four years in sanatoria in the Black Forest and Switzerland. Thereupon Strassmann led the institute and was appointed second director in 1950.

A year before that the institute had been transferred to Mainz. Following a suggestion of Frédéric Joliot’s, then high commissioner for atomic energy in the French-occupied zone of Germany and responsible for the institute, Mattauch had entered into negotiations for taking it over with the newly reestablished university and the local authorities in Mainz in May 1946. Because Strassmann had been appointed professor of inorganic and nuclear chemistry at Mainz University on 1 July 1946, he had to conduct the negotiations with the university, the occupation bureaucracy, and the provincial government. Later he had to supervise the construction work-which swallowed up all of the funds intended for the university’s institutes of physics and chemistry, including Strassmann’s own institute. These latter were put off from year to year with provisional arrangements. Until the Max Planck Institute was finally moved in the autumn of 1949, Strassmann had to shuttle between Tailfingen and Mainz, where he had started lecturing in the summer of 1946.

When Mattauch returned to the institute in the autumn of 1951, he demanded for his physics department the greater part of the budget that Strassmann had wrested from the provincial government in tedious negotiations. Mattauch argued that Strassmann’s chemical department should be diminished radically, because Strassmann had in addition a university institute (which, however, had been postponed in favor of the Max Planck Institute). In accord with its rules, the central administration of the society and its president, Hahn, accepted the demands of Mattauch as the director of the institute. Strassmann therefore resigned his directorship and left the institute in 1953 to concentrate all his efforts upon the university Institute for Nuclear Chemistry.

Strassmann had to begin anew. His “institute” consisted of a few rooms dispersed over the campus. The university’s building funds had been exhausted. But in 1954 Strassmann read in the newspaper that I. G. Farbenindustrie would be dismantled so that Badische Anilin- und Soda-Fabriken (B.A.S.F.), a part of this combine, would become independent and thereby liable to pay corporation income tax to the state of Rheinland-Pfalz. He considered that it would be in B.A.S.F.’s interest to support an institution in that state that would provide outstanding instruction and training of the rising generations of chemists. This argument convinced the chairman of the B.A.S.F. board of directors; and negotiations with the state government reached an agreement to use 5 million marks from the corporate income tax paid by B.A.S.F. (in addition to the university’s funds) to build a large institute for the chemical sciences with a special division for nuclear chemistry. The construction work dragged out from 1955 to 1958. Simultaneously Strassmann was negotiating with the German federal government to obtain funds for a neutron generator, which, however, was not put in operation until 1961. But as early as 1958 he had filed an application with the federal minister of atomic energy (Siegfried Balke, an atomic scientist himself) to grant funds for a research reactor and a special institute for nuclear chemistry. These negotiations dragged through official channels until 1962. The erection of the atomic pile (TRIGA Mark II) and the buildings took a long time. The new Institute for Nuclear Chemistry with reactor was inaugurated on 3 April 1967-too late for Strassmann to use the reactor for his own research, although he postponed his retirement at the request of the minister of education until 1970.

Thus Strassmann devoted all his time and energy after the war to building up three chemical institutes in Mainz, and to training and guiding students. Giving up his personal research, he became a highly successful, beloved teacher. He took these sacrifices as a kind of return for the Berlin years he had spent almost exclusively on research. In contrast with the head of the institute at the time, Strassmann did not insist on attaching his name as co-author to the papers of his pupils and assistants. Consequently, his name was gradually forgotten outside of Mainz, even though he received the Enrico Fermi Award, together with Meitner and Hahn, in 1966. His special qualities as a teacher were recognized in 1969, when the Nuclear Chemistry Section of the Society of German Chemists established an annual Fritz Strassmann award for young nuclear chemists. By the time he retired, his Institute for Inorganic and Nuclear Chemistry had attained a worldwide reputation for developing the new methods of rapid analytical separation required to identify extremely short-lived isotopes and transuranic elements. This was the field in which Strassmann himself had specialized since the mid 1930’s.

NOTES

1. See Lise Meitner, “Wege und Irrwege zur Kernenergie”, in Naturwissenschafiliche Rundschau16 (1963), 167–169; and her letter to Max von Laue of 4 September 1941, quoted in K. E. Boeters and J. Lemmerich, eds., Gedächtnisausstellung zum 100. Geburtstag von Albert Einstein, Otto Hahn, Max von Laue, Lise Meitner in der Staatsbibliothek Preussischer Kulturbesitz. Berlin, vom t. Mätz-12. April 1979 (Bad Honnef, 1979), 116.

2. Ida Noddack, “Über das Element 93”, in Angewandte Chemie, 47 (1934), 653f.; against Enrico Fermi, “Possible Production of Elements of Atomic Number Higher Than 92”, in Nature, 133 (1934), 898f.; and Enrico Fermi, Edoardo Amaldi, Oscar d’Agostino, Franco Rasetti, and Emilio Segrè, “Artificial Radioactivity Produced by Neutron Bombardment”, in Proceedings of the Royal SocietyA146 (1934), 483–500.

3. Lise Meitner and Otto Hahn. “Neue Umwandlungsprozesse bei Bestrahlung des Urans mit Neutronen”, in Die Naturwissenschaften, 24 (1936), 158f.; quote, 159.

4. Lise Meitner, Fritz Strassmann, and Otto Hahn, “Künstliche Umwandlungsprozesse bei Bestrahlung des Thoriums mit Neutronen; Auftreten isomerer Reihen durch Abspaltung von α-Strahlen”, in Zeitschrift für Physik, 109 (1938), 538–552.

5. Otto Hahn and Lise Meitner, “Die künstliche Umwandlung des Thorium durch Neutronen: Bildung der bisher fehlenden radioakriven 4n + l-Reihe”, in Die Naturwissenschaften, 23 (1935), 320f.: and, “with exprimental collaboration of F. Strassmann”. “Künstliche radioaktive Atomarten aus Uran und Thor”, in Angewandte Chemie, 49 (1936), 127f.

6.Nature, 140 (1937), 682.

7. See Strassmann, Kernspaltung. . . . p. 17.

8. Most of the letters by Hahn, Meitner and Strassmann that concern the experimental investigations are included in Krafft. Im Schatten . . . . arranged chronologically. See also, for the correspondence 1938-1939 (with some omissions), Dietrich Hahn, ed., Otto Hahn, Erlebnisse und Erkenntnisse (Düsseldorf and Vienna, 1975).

BIBLIOGRAPHY

I. Original Works. A bibliography of Strassmann’s papers is in Krafft. Im Schatten. . . . They include “Über die LOuml;slichkeit von Jod in gasförmiger Kohlensäure”, in Zeitschrift für physikalische Chemie, A143 (1929), 225–243, his dissertation, with Hermann Braune; “Einige neue Anwendungsmöglichkeiten der ’Emaniermethode’”, in Die Naturwissenschatften, 19 (1931), 502–504; “Untersuchungen über Oberflächengrösse und Gitterveränderungen kristallisierter Salze nach der Emaniermethode von Hahn”, in Zeitschrift für physikalische Chemie, B26 (1934), 353–361; “Untersuchungen über den Zusammenhang zwischen Gitterstruktur und Gasdurchlässigkeit organischer Salze nach der Emaniermethode von Hahn”, ibid., 362–372; seven papers with Otto Hahn and Lise Meitner on the decay chains of uranium and thorium, and alleged transuranics; “Die Abscheidung des reinen Strontium-Isotops 87 aus einem alten Rubidiumhaltigen Lepidolith und die Halbwertszeit des Rubidiums”, in Berichte der Deutschen chemischen Gesellschaft, 718 (1938), 1–9, with Ernst Walling; and many papers with Otto Hahn, including “Über die Entstehung von Radiumisotopen aus Uran beim Bestrahlen mit schnellen und verlangsamten Neutronen”, in Die Naturwissenschaften, 26 (1938), 755f.; “Über den Nachweis und das Verhalten der bei der Bestrahlung des Urans mittels Neutronen entstehenden Erdalkalimetalle”, ibid., 27 (1939), 89–95 (includes the discovery of fission); “Nachweis der Entstehung aktiver Bariumisotope aus Uran und Thorium durch Neutronenbestrahlung; Nachweis weiterer aktiver BruchstÜcke bei der Uranspaltung”, ibid., 89–95; “Zur Frage nach der Existenz der ’Trans-Urane’. I: Die end-gÜltige Streichung von Eka-Platin und Eka-Iridium”, ibid., 451–453; “Weitere Spaltprodukte aus der Bestrahlung des Urans mit Neutronen”, ibid., 529–534; “Über einige BruchstÜcke beim Zerplatzen des Thoriums”, ibid., 544–547, also with Siegfried FlÜgge; “Verwendung der ’Emanierfähigkeit’ von Uranverbindungen zur Gewinnung von Spaltprodukten des Urans”, ibid., 28 (1940), 54–61; “Getrennte Abscheidung der bei der Uranspaltung entstehenden Krypton- und Xenon-Isotope”, ibid., 455–458; “Über einige weitere Produkte der Uranspaltung,” ibid., 543–550: “Über die Isolierung und einige Eigenschaften des Elements 93,” ibid., 30 (1942), 256–260; “Einige weitere Spaltprodukte des Urans,” ibid., 31 (1943), 499–501. Other papers are “Über das Zerplatzen des Urankerns durch langsame Neutronen,” in Abhandlungen der Preussischen Akademie der Wissenschaften, Mathematisch-naturwiss, Klasse (1939), no. 12; and “Einiges über die experimentelle Entwirrung der bei der Spaltung des Urans auftretenden Elemente und Atomarten,” ibid., (1942), no. 3, with Hans Götte.

See also “Barium,” in Handbuch der analytischen Chemie, pt. 3, vol. IIa (Berlin, 1940), 365–402, with Maria Strassmann-Hekter; “Die Auffüllung und Erweiterung des periodischen Systems,” in Die Naturwissenschaften, 29 (1941), 492–496; Friedliche Chemie derAtomkerne (Mainz, 1949); “Über einige Strontium- und Yttriumisotope bei der Uranspaltung,” in Zeitschrift für Naturforschung, 11 (1956), 946-954, with Günter Hermann, his successor at Mainz; and “Abtrennung und Bestimmung kurzlebiger Isotope,” in Zeitschrift für Elektrochemie: Berichte der Bunsengeselischaft für physikatische Chemie, 64 (1960), 1011–1014.

The laboratory notebook Chemie II of Hahn and Strassmann, including the experiments and measurements leading to the discovery of fission, and the original apparatus are located in the Deutsches Museum, Munich.

II. Secondary Literature. There is a full biography, including facsimiles of the most important papers and extensive excerpts from the notebooks and the correspondence, in Fritz Krafft, Im Schatten der Sensation: Leben und Wirken von Fritz Strassmann, dargestellt. . . nach Dokumenten und Aufzeichtnungen (Weinheim, 1981). For brief personal sketches, see Hans-Joachim Born’s obituary in Berichte und Mitteilungen der Max-Planck-Geselschaft, no. 3 (1981), 34–36; Gerhart Friedlander and Günter Herrmann in Physics Today, 34 (April 1981), 84, 86; Günter Hermann, “Ein Forscher, der Geschichte machte,” in Jogu: Universitätszeitung, no. 68 (May 1980), 3; and Fritz Krafft, “Ein Leben im Dienste der Chemie und des akademischen Nachwuchses,” in Jahrbuch der Vereinigung “Freunde der Universitä Mainz,” 25/26 (1976/1977), 226–230. There are two autobiographical sketches by Strassmann, both published privately: Damals: Institutsgcschichten, erzählt von Siegfried Knoke und Fritz Strassmann (Mainz, 1976; 2nd ed., 1980), concerning the years at Hanover, and Kernspaltung: Berlin. Dezember 1938 (Mainz, 1978), essential parts reprinted in Fritz Krafft, Im Schatten. . . .

For literature on the discovery of fission, see Lawrence Badash, “Otto Hahn,” in Dictionary of Scientific Biography, VI , 14–17; and the bibliography of secondary literature in Krafft. Im Schatten. . . . See also Walther Gerlach. “Otto Hahn, Lise Meitner, Fritz Strassmann: Die Spaltung des Atomkerns,” in Kurt Fassmann, ed., Die Grossen der Weltgeschichte, XI (Zurich, 1978), 50–71; Fritz Krafft, “Ein frühes Beispiel interdisziplinärer Team-Arbeit: Zur Entdeckung der Kernspaltung durch Hahn, Meitner und Strassmann,” in Physikalische Blätter, 36 (1980), 85–89, 113–118, and “An der Schwell des Atomzeitalters: Die Vorgeschichte der Entdeckung der Kernspaltung im Dezember 1938,” in Berichte zur Wissenschaften, 11 (1988), 227–251; and William R. Shea, ed.. Otto Hahn and the Rise of Nuclear Physics (Dordrecht, 1983), esp. Spencer R. Weart, “The Discovery of Fission and a Nuclear Physics Paradigm,” 91–133; and Fritz Krafft, “Internal and External Conditions for the Discovery of Nuclear Fission by the Berlin Team,” 135–165. For a repetition of the historical experiments, see Helmut Menke and Gunter Herrmann, “Was waren die ‘Transurane’ der dreissiger Jahre in Wirklichkeit?” in Radiochimica acta, 16 (1971), 119–123.

Fritz Krafft

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