On the Displacement of Corresponding Energy Levels of ${\mathrm{C}}^{13}$ and ${\mathrm{N}}^{13}$

It is investigated to what extent the change in boundary conditions at the nuclear surface due to Coulomb wave function distortion in the external region can explain the relative displacement of the first excited states of ${\mathrm{C}}^{13}$ and ${\mathrm{N}}^{13}$. It is found that the calculated displacement is in the right direction and of a sufficiently large magnitude, but rather sensitively dependent on the definition of nuclear radius.