Angewandte Chemie International Edition
Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Cover Picture (Angew. Chem. Int. Ed. Engl. 5/1990)
The cover illustration shows, in the middle, a table containing the apparatus used by Otto Hahn, Lise Meitner, and Fritz Strassmann in their search for transuranium elements in uranium samples that had been subjected to neutron irradiation: counting tubes and the associated amplifiers for detecting radioactivity, the counters themselves, and power supplies (left and center); neutron sources (background right) and equipment for chemical isolation of the resulting active species (foreground right); and the historic laboratory notebook. It was with these materials that Otto Hahn and Fritz Strtassmann were occupied when they established the presence of radioactive barium in the radiochemical “indicator experiment” on December 17, 1938, an experiment in which uranium nuclei were split into nuclei corresponding to two elements of intermediate mass. Günter Herrmann discusses these historic experiments from the years 1934--1939 in the article beginning on page 481. The fission product barium would today be identified at a glance from its γ-spectrum (shown at the bottom of the illustration), which reveals characteristic γ-lines for three barium isotopes. One of these is barium-139, half-life 83 min, the isotope with which the indicator experiment was actually performed. In the background is depicted a modern apparatus for radiochemical separation, fully automated and computer controlled. Photographs: A. Zschau, GSI Darmstadt, and Deutsches Museum, Munich.