Abstract
THE cross-section for the scattering of slow neutrons by protons leads to the assumption of a 1S level in the deuteron nucleus, with an energy of about 100,000 volts1. Fermi2 showed that the capture of thermal neutrons by protons can be understood qualitatively as a magnetic dipole transition from a 1S level to the fundamental 3S level of the deuteron. The amount of the capture cross-section would still depend on the sign of the 1S level. For a virtual 1S level, the mean life of neutrons in water (not paraffin) should be = 2·9 × 1024 sec. For a real level = 6·3 × 104 sec. The values for a virtual level are in good agreement with the recently obtained experimental value3 = 2·7 × 104. The evidence obtained by the scattering of thermal neutrons by ortho- and para-hydrogen indicates as well a virtual level4.
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References
Wigner, Phys. Rev., 51, 106 (1937).
Fermi, E., Ric. Sc., 7, 2 (1936).
Frisch, Halban, Koch, NATURE, 170, 895 (1937).
Dunning, Manley, Hoge, and Brickwedde, Phys. Rev., 52, 1076 (1937); Halpern, Esterman, Simson and Stern, Phys. Rev., 52, 142 (1937); Schwinger and Teller, Phys. Rev., 52, 286 (1937).
See Bethe and Bacher, Rev. Modern Physics, 8 (1936). For the number given here the scattering cross-section was assumed to be 18 × 1024 cm.2 for free protons and slow neutrons, and the difference of the magnetic moments of proton and neutron 4.2 nuclear magnetons.
Chadwick, Feather and Bretscher, Proc. Roy. Soc., A, 154, 366 (1937); see also Richardson, R., and Emo, L., Phys. Rev., 53, 234 (1938).
Amaldi, Fermi, Phys. Rev., 50, 899 (1936).
Amaldi, Hafstad and Tuve, Phys. Rev., 51, 896 (1937).
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V. HALBAN, H. Cross-Sections of the Deuteron for the Electric and Magnetic Nuclear Photo-effect. Nature 141, 644–645 (1938). https://doi.org/10.1038/141644a0
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DOI: https://doi.org/10.1038/141644a0
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