MICROSCOPIC ORIGINS OF EFFECTIVE CHARGES IN THE SHELL-MODEL

We use a large-scale 6h Omega calculation for Li-6 with microscopicall y derived two-body interaction to construct the 0h Omega 0p shell effe ctive Hamiltonian, electric quadrupole, and magnetic dipole operators. While the E2 and M1 6h Omega operators are one-body operators with fr ee nucleon charges, the effective operators are two-body operators wit h substantially different renormalization for the isoscalar and isovec tor matrix elements, especially for the E2 operator. We show that thes e operators can be very well approximated by one-body operators provid ed that effective proton and neutron charges are used. The obtained ef fective charges are compatible with those used in phenomenological she ll-model studies. The two-body part of the effective operators is esti mated.