Microscopic calculation of the optical-model potential for 40Ca

The optical-model potential for 40Ca is derived microscopically from a realistic one-boson-exchange potential and evaluated in momentum space. For the real part of the potential the Brueckner-Hartree-Fock term is considered, while for the imaginary part the lowest order term comes from the 2-particle-1-hole contribution to the self-energy. Attempts are made to approximate the real and imaginary part of this nonlocal potential by appropriate parametrizations for a local potential. As a first step Woods-Saxon potentials are considered for the central parts, while for fitting the spin-orbit splitting derivative Woods-Saxon potentials are used. The resulting parameters are in good agreement with recent determinations from experimental data. The fit of the central parts of the nonlocal potential is improved considerably if the Woods-Saxon ansatz for the local approximation is supplemented by a repulsive term of short range. A similar improvement is also achieved by allowing for an energy-dependent depth of the potential. (orig.)