In 1913 Otto married Edith Junghans, by whom he had one son. Otto was a sickly youth, but after the age of fourteen he was quite healthy. At the local high school he was a good but not outstanding student. His interest in chemistry arose from some dabbling in the subject with a classmate and increased when he attended a series of lectures given to an adult audience. His father wished him to become an architect, but Otto prevailed and entered Marburg University in 1897. His autobiographical reminiscences suggest that he spent more time in the beer halls than in studying, and he expresses regret at his inattention to physics and mathematics. But he must have absorbed a respectable amount of chemistry; after receiving his doctorate in 1901 and following a year’s infantry service, he returned to Marburg as assistant to his principal professor, Theodor Zincke.
Hahn arrived at Fischer’s institute in the fall of 1906 and in order to continue these investigations he established a mutually profitable relationship with Knofler and Company, producers of thorium preparations. While in Canada, he had measured a half-life for radiothorium of about two years; but Boltwood who had tested a number of commercially prepared thorium salts, had found them deficient in radiothorium and had tried unsuccessfully to detect its growth argued for a much longer half-life. From Knofler, Hahn obtained samples prepared a number of years earlier and found that their activities decreased at first and then gradually increased. This was proof of his belief in a long-lived radioelement between thorium and radiothorium, which he separated in 1907 and named mesothorium. Because it was chemically inseparable from radium, which was difficult to obtain in Germany, and owing to the rising medical demand for radium, Knofler successfully marketed high-activity mesothorium as “German radium.”
Within a year of his return to his homeland, Hahn was appointed a Privatdozent in Fischer’s institute, thereby joining the teaching faculty of the University of Berlin; he became a professor in 1910. He became friendly with physics professors Rubens, Nernst, and Warburg, and such younger colleagues as Max von Laue, Otto von Baeyer, James Franck, Gustav Hertz, Peter Pringsheim, and Erich Regener. But the most important physicist to enter his life was Lise Meitner, who came from Vienna in 1907 to do theoretical work under Max Planck and wished also to pursue some studies in experimental radioactivity. This led to the proof that several elements, though not to radiate as they decayed, actually were weak beta emitters. Further work on the magnetic deflection of the beta rays added much to the ultimate explanation of their continuous and line spectra. Hahn also pioneered the method of radioactive recoil in 1909, with which he and Meitner found a few more radioelements.
By the early 1920’s almost all of the naturally occurring radioelements were known, and opportunities for basic research in radiochemistry were limited. Hahn turned toward applications of his specialty