But the masses of the nuclei of
hydrogen, deuterium and tritium are in the ratio of 1:2:3 Therefore, the
nuclei of deuterium and tritium must contain,  in addition to a proton,
some neutral matter The amount of neutral matter present in the nuclei
of these isotopes, expressed in units of mass of a proton, is approximately
equal to one and two, respectively This fact indicates that the nuclei of
atoms contain, in addition to protons, neutral matter in multiples of a
basic unit