Energy of Neutrons liberated in the Nuclear Fission of Uranium induced by Thermal Neutrons

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IT has been shown that fast neutrons are liberated in the process of nuclear fission induced in uranium by primary thermal neutrons. Two different methods of detection have been used: in the first method1, the primary and (if any) secondary neutrons are absorbed in a medium in which an endo-energetic reaction can take place, leading to the formation of an easily detectable radioactive nucleus. If the energy threshold is situated above the maximum energy of the primary neutrons, any positive results observed must be ascribed to the secondary neutrons. In the second method2, elastic collisions of fast neutrons with heavier nuclei are observed by means of an ionization chamber filled with a gas at atmospheric pressure and connected to a linear amplifier. In order to study separately the effect due to the primary thermal neutrons, the experiment is performed with, and without, a cadmium shield between the source and the uranium mass.

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  1. 1

    Dodé, M., von Halban, jun., H., Joliot, F., and Kowarski, L., C.R., 208, 995 (1939).

  2. 2

    Szilard, L., and Zinn, W., Phys. Rev., 56, 799 (1939).

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VON HALBAN, H., JOLIOT, F. & KOWARSKI, L. Energy of Neutrons liberated in the Nuclear Fission of Uranium induced by Thermal Neutrons. Nature 143, 939 (1939) doi:10.1038/143939a0

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