The angular distribution of protons projected by fast neutrons

Abstract

[P late 16] 1-I n t r o d u c t i o nThe nature of the interaction between neutron and proton has assumed great importance in modern nuclear theory, since it is now generally assumed that these two particles form the fundamental constituents of all nuclei. Little direct evidence exists, however, as to the nature of this interaction.The stable existence of the deuteron shows that the force between neutron and proton is attractive, and for purposes of calculation a " square hole" potential well has generally been assumed. With this model some success has been obtained* in correlating the magnitudes of a number of experi mentally measurable quantities such as (a) the binding energy of the deuteron, (6) the total cross-section for neutron-proton scattering (Tuve and Hafstad 1936; Amaldi and Fermi 1936a), (c) the cross-section for photo electric disintegration of the deuteron (Chadwick and Goldhaber 1935), and (d) the cross-section for capture of neutrons by protons (Amaldi and Fermi 19366). The interaction is not completely derivable from the above data, since the values of these quantities depend mainly upon r2V, where r is the mean radius and V is the depth of the potential hole.The magnitudes of the binding energies of some of the light nuclei (3H, 3He, 4He) can be explained by assuming that the force between neutron and proton falls off very rapidly when the distance between the two particles increases beyond about 2 x 10"13 cm. (Wigner 1933; Thomas 1935; Feenberg 1935)' but the law of variation of force with distance cannot be obtained from the experimental data. The calculations of these binding energies, however, involve assumptions as to the magnitudes of neutron-neutron and proton-proton forces. * For a full account of th e theoretical interpretation of these results see Bethe and Bacher (1936).[ 265 ]

Applications of the photographic method to problems in nuclear physics. II. The scattering of 8.8 and 13 MeV neutrons by protons

“…The energy of the neutrons from such a source is of the order of 2-5 MeV. The best experi ments, for example those of Dee & Gilbert (1937), indicate th at with neutrons of this energy the scattering is isotropic in the centre of mass co-ordinate system of the colliding particles. To avoid circumlocution we refer to this as isotropic scattering.…”