Effective operator for the transition density

The effective shell-model operator for electric transition densities is evaluated. The influence of the choice of single-particle wavefunctions, residual interaction (G-matrix) and correlations within the valence shell as well as core-polarisation effects, is investigated. The excitation of the lowest 2⁺ in ⁵⁸Ni is considered as an example. The shape of the transition density can be reproduced only after renormalisation of the effective transition density operator to account for core polarisation. The possible importance of screening terms and many-body terms in the expansion for the effective operator are discussed.