The 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 experimentally measurable quantities such as (
a
) the binding energy of the deuteron, (
b
) the total cross-section for neutron-proton scattering (Tuve and Hafstad 1936; Amaldi and Fermi 1936
a
), (
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 1936
b
). The interaction is not completely derivable from the above data, since the values of these quantities depend mainly upon
r
2
V
, where
r
is the mean radius and
V
is the depth of the potential hole.
Parton distributions in radiative corrections to the cross section of electron-proton scattering