(b. Warsaw, Russian Poland, 27 May 1887; d. Ann Arbor, Michigan, 18 May 1975)
The son of Herman Fajans, a merchant, and Wanda Wolberg, Kasimir Fajans graduated from high school in Warsaw (1904), and then left Russian Poland to study at the universities of Leipzig (bachelor’s degree, 1907) and Heidelberg (doctorate, 1909). Then came a year of research at Zurich, followed by a second research year (1910–1911) in Ernest Rutherford’s laboratory at the University of Manchester. In 1910 Fajans married Salomea Kaplan, a physician. They had two sons, Edgar and Stefan.
Rutherford and his laboratory attracted some of the best researchers in radioactivity. Since the subject straddled the line between physics and chemistry, generally at least one radiochemist was to be found there. Fajans’ interest in radioactivity had been ignited in 1909 by Philipp Lenard. Who suggested that he report on the subject for his physics colloquium. This was far afield from the physical-organic topic in stereochemical catalysis that Fajans pursued under Georg Bredig for his doctorate. During the year with Richard Willstätter in Zurich, Fajans became interested in the binding forces in carbon compounds. But he also became convinced that he was more interested in physics, particularly radioactivity, than in organic chemistry. The lectures by Albert Einstein which he attended may also have influenced him. Rutherford’s positive response to his request to come to Manchester led to a major redirection in his career.
While in England, Fajans found that the radium decay series branched at radium C, a concept that was not universally accepted at the time. He also collaborated with Henry Moseley in determining the very short half-lives of thorium A (0.14 sec.) and actinium A (0.002 sec.). Most important, however, was the exciting environment created by such colleagues as James Chadwick. Hans Geiger, C. G. Darwin, and others, and the opportunity to learn the status of research into radioactivity’s unsolved problems. One of the reasons Fajans left organic chemistry was its empirical approach, which could not satisfy his strong theoretical leanings. In radioactivity he similarly found the disorder of some thirty radioelements, which were meant to fit into only a dozen boxes of the periodic table of elements, too inharmonious to persist.
Fajans continued his study of radioactivity at the Technische Hochschule in Karlsruhe, where he became an assistant in 1911 and a Privatdozent for physical chemistry in 1913. The key to rationalization of the three known radioactive decay series was the identification of a number of products with short half-lives. Using chemical and especially electrochemical data, Fajans gained some crucial insights which enabled him to announce the group displacement laws in February 1913: alpha-particle emission moves the daughter product two boxes to the left in the periodic table, while beta-particle emission signifies a jump one box to the right.
Fajans was not alone in working on this theory, which, along with the explanation of the phenomenon of radioactivity by Rutherford and Frederick Soddy a decade earlier, became a cornerstone of the science. Other gifted radiochemists, such as Soddy, György Hevesy, and Alexander Russell, also were approaching a solution. Soddy, in fact, published the same theory, admittedly after seeing Fajans’ paper in print, and without having the chemical proof needed to draw the correct conclusions. Despite this apparent plagiarism, and to Fajans’ distress, Soddy received the lion’s share of credit in the English-speaking world, and his term “isotopes,” for the bodies with different radioactive properties but identical chemical characteristics that fit into a single box of the periodic table, easily won out over Fajans’ preferred “pleiades” (named after the star cluster).
Rutherford, in an effort to soothe Fajans’ frustration, assured him that it is not the idea but its proof that is most important. With his student Oswald Göhring, Fajans thereupon searched for and soon found the first isotope of element 91, which the theory predicted. (This was uranium X2, initially called brevium, but changed to protactinium in 1918 when Otto Hahn and Lise Meitner, and, independently, Soddy and John Cranston, found the longestlived isotope.) Another student, Max Lembert, was sent to Harvard to work with the world’s leading expert in atomic-weight determinations, Theodore W. Richards. These two found the weight of inactive lead at the end of the uranium decay series to differ from that of natural lead by far more than experimental error would allow. Richards had built his career on the concept of fixity of elements; the paper he wrote expressed amazement that species of the same element could have different weights. By giving an explanation of the way radioelements fit into “normal” chemistry, Fajans provided the key that solved virtually all radiochemical problems. The consequence was that the science of radiochemistry ceased to exist. Applications such as tracer techniques were later investigated, but few questions of basic science. It took the discovery of artificial radioactivity to resurrect the field in the 1930’s, when it came to be called nuclear chemistry.
Willstätter had moved to Munich and in 1917 invited Fajans there as an associate professor, to inaugurate teaching and research in physical chemistry. Fajans became full professor in 1925, and director of his own new Institute for Physical Chemistry in 1932, built with funds from the Rockefeller Foundation. Investigations begun in Karlsruhe on the identity and quantity of nonweighable amounts of radioelements led to the Fajans-Paneth-Hahn coprecipitation and adsorption rules. These gave quantitative analysis strong new tools, among which Fajans’ adsorption indicators were a vital component. This work in turn drew Fajans’ attention once again to the question of chemical binding, for electrical charges proved to be a dominant factor in the phenomena.
Hitler’s rise to power forced Fajans from Munich in 1935 and, after some months in Cambridge, he accepted a professorship at the University of Michigan (1936–1957). In Ann Arbor some of his students in nuclear chemistry worked closely with James Cork’s cyclotron group, and Fajans himself participated in the discovery of a few new radioisotopes, but his primary interest remained in binding. Although never widely accepted, his quanticule theory, developed from the 1940’s onward to replace the classical concept of valence bonds between neutral atoms, proposed that the electrons of a molecule or crystal are subdivided into groups of definite quantization (quanticules) and that all interactions result from the electric forces acting between nuclei and quanticules.
Fajans was coeditor of the Zeitschrift für Kristallographie (1924–1939) and associate editor of the Journal of Physical and Colloid Chemistry (1948–1949). He was elected to numerous societies and academies of science, among them the academies in Cracow, Leningrad, and Munich, and the Royal Institution of Great Britain. He also received several awards, including the medal of the University of Liège (1948).
I. Original Works, Fajans’ correspondence and miscellaneous papers are preserved in the Michigan Historical Collection, University of Michigan, Ann Arbor. Among his most significant published papers are “Über die komplexe Natur von Radium C,” in Physikalische Zeitschrift, 12 (1911), 369–378; “Radio-active Products of Short Life,” in Philosophical Magazine, 22 (1911), 629–638, written with H. G. J. Moseley; “Über eine Beziehung zwischen der Art einer radioaktiven Umwandlung und dem elektrochemischen Verhalten der betreffenden Radioelemente,” in Physikalische Zeitschrift, 14 (1913), 131–136; “Die Stellung der Radioelemente im periodischen System,” ibid., 136–142; “Über das Uran X2—das neue Element der Uranreihe,” ibid., 877–884, written with O. Göhring; “Das Verhalten der Radio-Elemente bei Fällungsreaktionen,” in Berichte der Deutschen chemischen Gesellschaft, 46 (1913), 3486–3497, written with P. Beer; “Adsorptionsindikatoren für Fällungstitrationen,” in Neuere massanalytische Methoden (Stuttgart, 1956). 313–369; “Quantikel-Theorie der chemischen Bindung,” in Chimia, 13 (1959), 349–366.
Fajans authored a popular text entitled Radioaktivität und die neueste Entwicklung der Lehre von den chemischen Elementen (Braunschweig, 1919). The fourth edition was translated into English as Radioactivity and the Latest Developments in the Study of the Chemical Elements, T. S. Wheeler and W. G. King, trans. (New York, 1923). Other books are Radioelements and Isotopes: Chemical Forces and Optical Properties of Substances (New York, 1931); and Newer Methods of Volumetric Chemical Analysis, W. C. Böttger, ed., Ralph E. Oesper, trans, (New York, 1938), with E. Brennecke, N. H. Furman, H. Stamm, and R. Lang.
Personal reminiscences by Fajans appeared on the occasion of his Pioneer Lecture on Otto Hahn in Journal of Nuclear Medicine, 7 (1966), 402–404; and, in Polish, on the occasion of the centennial of Marie Curie’s birth. in Problemy, 24 (1968), 392–403.
II. Secondary Literature, Jósef Hurwic is currently working on a biography of Fajans. Shorter works are by E. Lange, on the occasion of Fajans’seventieth birthday, in Zeitschrift für Elektrochemie, 61 (1957), 773–774, and, on his eightieth birthday, in Jahrbuch der Bayerischen Akademie der Wissenschaften (1967), 171–173; I. M. Frank in Uspekhi fizicheskikh nauk, 99 (1969), 337. Obituary notices are by Thomas M. Dunn in Nature, 259 (1976). 611; and by J. Hurwic in L’actualité chimique, no. 1 (1976), 28–32. Works dealing specifically with the group displacement laws and atomic weight of lead isotopes are O. U. Anders, “The Place of Isotopes in the Periodic Table; The 50th Anniversary of the Fajans-Soddy Displacement Laws.” in Journal of Chemical Education, 41 (1964), 522–525; L. Badash, “The Suicidal Success of Radiochemistry,” in British Journal for the History of Science, 12 (1979), 245–256; J. B. Conant, “Theodore William Richards and the Periodic Table,” in Science, 168 (1970), 425–428; and Alfred Romer, ed., Radiochemistry and the Discovery of Isotopes (New York. 1970).