Fragmentation of the dipole strength in the $N=82$ isotones ${}^{140}$Ce, ${}^{142}$Nd, and ${}^{144}$Sm is calculated using the second random-phase approximation (SRPA). In comparison with the result of the random-phase approximation (RPA), the SRPA provides additional damping of the giant dipole resonance and the redistribution of the low-energy dipole strength. Properties of the low-energy dipole states are significantly changed by the coupling to two-particle–two-hole (2p-2h) states, which are also sensitive to the correlation among the 2p-2h states. Comparison with available experimental data shows a reasonable agreement for the low-energy $E1$ strength distribution.

• Received 7 December 2011

DOI:https://doi.org/10.1103/PhysRevC.85.031302