On June 24, 1940, John Cockcroft, who would be the British scientist with most responsibility for the early English reactors, met up with two French scientists, Hans von Halban and Leo Kowarski, who had just fled Nazi-conquered France. Kowarski in particular would be key to the very early days of the Canadian reactor program, and the wartime work they would do, in England and later Canada, would form the basis of France’s postwar atomic work. French uranium, of Belgian origin, and French heavy water, of Norwegian origin, were also of vital importance in the eyes of the British.

Cockcroft’s filenote of his meeting with the two Frenchmen is of both specific and general interest to me but it is too detailed to use much of it. When I read it, however, I noted the following, almost throwaway, comment by Cockcroft:

It will be seen from the above that all the reactions contemplated are of the slow neutron type (that is, to do with nuclear power rather than nuclear weapons). They would not therefore be explosive in the ordinary sense, but it was suggested that the radiations produced would be such as to render uninhabitable a very large area.

How fascinating! The early nuclear pioneers rarely spelt out the dangerousness of their work with the forces of nuclear fission. Sometimes it can seem, especially when reading their official pronouncements, that the atomic world is supremely benign and manageable. But my reading has convinced me the reality of their thinking was very different. They understood very well that they were messing with cataclysmic forces underlying physical nature. Here we see Cockcroft warning that nuclear accidents could result in the exclusion zones of Chernobyl and Fukushima.


Cockcroft, John. 1940. Record of a meeting with Dr. von Halban and M. Kowarski. AB 1/210, National Archives, Kew, United Kingdom.