Structural considerations for elastic magnetic electron-nucleus scattering

To explain the form factors obtained by magnetic electron scattering on ¹⁷O it is clear that core polarization has to be taken into account. We discuss how this can be done by means of the Hartree-Fock theory. We note that projection from an intrinsic state of definite K gives an incorrect answer for weakly deformed systems such as ¹⁷O and we present an alternative procedure for extracting the moments. Using a purely velocity dependent Skyrme interaction (only t₀ and t₁ are non-zero) a Hartree-Fock calculation is carried out for the seventeen-nucleon system. The calculation leads to a suppression of the M3 form factor. It is emphasized that the suppression arises from the fact that not only is the ¹⁶O core deformed, but that spin-up particles have a different deformation than spin-down particles. This arises from the spin dependence of the interaction and from the Pauli principle. A peculiar feature with the interaction that is used is that the M5 form factor gets enhanced. This is attributed to the repulsive velocity dependent term in the interaction. The origin of the velocity dependence is discussed. The effect of the velocity dependence on the magnetic moment operator is also considered.