Microscopic analysis of quadrupole collective motion in Cr--Fe nuclei: II. Doorway nature of mixed-symmetry states

Abstract

The mixed-symmetry collective modes are investigated in Cr-Fe nuclei, by analyzing the realistic shell-model wavefunctions via the H^n-cooling method. It is clarified that the relatively low-lying mixed-symmetry states behave like doorway states. For these nearly spherical nuclei, the lowest mixed-symmetry state is shown to have $J^P=2^+$. An indication of the mixed-symmetry 3^+ state is obtained. The sequence of the mixed-symmetry 2^+, 1^+ and 3^+ levels and its nucleus-dependence are discussed. Calculated M1 and M3 transitions in the low-energy region suggest that the mixed-symmetry 1^+ and 3^+ components are detectable. We investigate the B(M1) distribution in a wider energy range, without breaking the isospin quantum number. It is confirmed that the mixed-symmetry 1^+ component is well separated from the peak of the spin excitation. The isospin-raising component has a peak, separated well from the isospin-conserving one. The orbital angular-momentum contributes destructively to the spin excitations.