Page 21 - Neutrons for Sciences and Society

the German invasion. Inevitably it was a French team (Frédéric Joliot, Lew Kowarski and Hans von Halban13) which prioritised this substance in the studies and experiments on the possibility of creating a chain reaction. ZOE owes a lot to Lew Kowarski (1907- 1987) who designed it then directed the construction. During the war he had the same responsibility for the first Canadian reactor, which also used heavy water as a moderator. A final advantage was that a heavy water pile required about ten times less uranium than a pile using graphite. At that date France had no metallic uranium and had to use uranium oxide. Thus the CEA was forced to develop a ceramic fuel for the first time in the world. This reactor was built at Fontenay-aux-Roses, in the near suburbs of Paris.
In 1952 the CEA created a new site dedicated to civil research on the Saclay plateau near what later became the university of Orsay. On this site French scientists had access to another heavy water reactor (EL2), more powerful generating a flux of 1012 neutrons/cm2/s. Again this reactor was built under the leadership of Kowarski. The flux was sufficient to perform nuclear physics experiments (measurement of cross-sections), but also diffraction, and spectrometry14 employing inelastic neutron scattering.
It was evident that the fluxes at BEPO and EL2 were still inadequate for a large number of experiments. Before envisaging the building of high flux reactors one idea was introduced
13 It is interesting to note that this French team included a Russian and an Austrian. Science is international. This essential point should not be forgotten, and it has contributed to the strength of American science. The atomic bomb could only be created by the USA because this country knew how to welcome European immigrants (Fermi, Szilárd, Einstein, etc).
14 B. Jacrot, C.R. Acad. Sci., (1955) 240, p745-747.
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Chapter 1 - Pre-history