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

The mixed-symmetry collective modes are investigated in Cr-Fe nuclei, by analyzing the realistic shell-model wave functions via the H{sup 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{sup P}=2{sup +}. An indication of the mixed-symmetry 3{sup +} state is obtained. The sequence of the mixed-symmetry 2{sup +}, 1{sup +}, and 3{sup +} levels and its nucleus dependence are discussed. Calculated M1 and M3 transitions in the low-energy region suggest that the mixed-symmetry 1{sup +} and 3{sup +} 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{sup +} component is well separated from the peak of the spin excitation. The isospin-raising component has a peak, well separated from the isospin-conserving one. The orbital angular-momentum contributes destructively to the spin excitations. {copyright} {ital 1997} {ital The American Physical Society}