RALPH E. OESPER University of Cincinnati, Cincinnati, Ohio
OTTO HAHNcertainly never envisioned the atom bomb when he and F. St.rassmann'found that neutron irmdiation of uranium and thorium splits these heavy elements into two elements of medium ~veight. The first publications appeared on January G and February 10, 1939, in Naturwissenschaften. This finding formed the beginning of the application of the tremendous energies residing in the atomic nuclear forces. There is no need to point out how much the course of military and political history has been altered because of this study in pure nucleonics. However, this was only one of Hahn's many important achievements. Otto Hahn was born on March 8, 1879, at Frankfurt am Main. He studied chemistry at Marbnrg and Munich; the doctorate was taken a t Marburg in 1901 with a dissertation in organic chemistry. Aft,er serving the required year in the armed forces, he returned to Marburg, where for two years he was assistant to Th. Zincke. The winter of 1904-05 was spent a t University College, London, under Ramsay. Here he was assigned the problem of preparing a pure radium salt, and when (1905) in the course of this work he discovered a new radioactive material, namely radiothorium, he decided to leave the organic field and devote his efforts to studies in the new and exciting field. From the fall of 1905 to the summer of 1906, he worked in the physics department a t Montreal under Rutherford. Here he discovered radioactinium, and together with Rutherford studied the action of e-rays on radiothorium and radioactinium. On the recommendation of Ramsay, Dr. Hahn vas given an appointment (1906) in Emil Fischer's depart,. ment a t the University of Berlin here he discovered another new radioelement, which he named mesothorium. In 1907 he habilitated a t Berlin and in 1910 was advanced from dozent to (associate) professor extraordinary. I n these years he published many papers on radioactivity, for the most part jointly with Lise Meitner, who had come to Berlin from Vienna in 1907. Some of the fields of study were radioactive recoil, &ray spectra, new radioactive materials. Together with Otto von Baeyer, he investigated prays, their ahsorbability, magnetic spectra, etc. New radioactive transformation products mere obtained in his laboratory
through application of radioactive recoil, which had recently been discovered by Hahn. In 1912 Professor Hahn was called to the newly founded Kaiser Wilhelm Institut fiir Chemie a t BerlmDahlem. Here he Ivas soon joined by Lise Meitner, whose physical radioactivity researches supplemented hismore chemical lines of study. During World War I, the energies of the Institut were, of course, directed to war purposes. In 1918 Hahn and Meitner discovered protactinium, the long-lived parent substance of the actinium series. The discovery of uranium '2, the first instance of a nuclear isomerism among radioactive atomic species, was announced by Hahn in 1921. Professor Hahn also investigated the absorption and precipitation of minute quantities of materials. He published stndies of normal and abnormal formation of mixed crystals, and dealt with problems whose solution lvas approached by radioactive methods. He used the "emanation method" for testing surface-rich and surface-poor substances. In 1938 he worked out the "strontium method" for determining the earth's age. After the Joliot-Curie discovery of art,ificial radioactivity (1934), and the use of neutrons for atomic nuclear processes by Fermi (1934), Hahn and Meitner together with F. St,rassmann began their collaboration on the processes that take place when uranium and thorium are irradiated with neutrons. The momentous discovery that eventuated in the atom bomb mas made by Hahn and Strassmann in 1938. Thereupon, and until the end of World War 11,he and his associates prepared and studied the many artificially act,ive species that result from the nuclear fission reactions. None of their work was directed to the possible use, civil or military, of the energy released in these processes. Professor Hahn's achievements have brought numerous distinctions and honors. He was awarded the Nobel Prize for Chemistry for 1944. His lectures as visitingprofessor a t Cornell were published (1937) under the title "Applied Radiochemistry." He is a member of many academies and learned societies. From 1946 he was President of the Kaiser Wilhelm Gesellschaft, and since 1948 he has headed its successor the Max Planck Gesellschaft znr Fordernng der Wissenschaften, which now has its seat a t Gottingen.
