Background: Observed systematic deviations of the value of the $B(E1;1_1^{-}\to 0_1^{+})/B(E1;3_1^{-}\to 2_1^{+})$ ratio in spherical nuclei from the prediction of the collective model which take into account only quadrupole and octupole collective modes are considered.

Purpose: Our purpose is to evaluate the effect of the isovector dipole and quadrupole-octupole modes coupling on the $B(E1;1_1^{-}\to 0_1^{+})/B(E1;3_1^{-}\to 2_1^{+})$ ratio.

Methods: The Hamiltonian of the phenomenological collective model is used to calculate mixing of the isovector dipole and quadrupole and octupole modes.

Results: The effect of the admixture of the giant dipole resonance to the low-lying collective quadrupole and octupole modes is estimated. The ratio $B(E1;1_1^{-}\to 0_1^{+})/B(E1;3_1^{-}\to 2_1^{+})$ for different nuclei is calculated.

Conclusion: It is shown that the coupling of the quadrupole and octupole collective modes to giant dipole resonance leads to a decrease of the ratio $B(E1;1_1^{-}\to 0_1^{+})/B(E1;3_1^{-}\to 2_1^{+})$ relative to the value 7/3 predicted by the pure collective quadrupole-octupole model.

Close

PrevNext

View figure in article

• Collective levels
• Electromagnetic transitions
• Nuclear structure & decays
• Nuclear transition rates