Configuration mixing calculations based on a first-order perturbation theory are carried out to study higher-shell mixing effects on the stretched $1\hslash \omega$ particle-hole excitations. It is shown that the suppression of the transition strengths which has been observed in electron scattering and in hadronic reactions can be obtained theoretically in all the closed shell nuclei, being in qualitative agreement with experiments.

• Received 25 June 1987

DOI:https://doi.org/10.1103/PhysRevC.36.1657