low-energy dipole excitation modes in ¹⁰Be

 In the past a few decades, research on neutron excess nuclei has been progressing, and a variety of  novel phenomena which can not be seen in N = Z nuclei are found. One of them is low energy dipole (LED) excitation that appears in the energy region lower than the giant dipole resonance. It has not been yet clarified what type of excitation modes contributes to the LED.

 As a candidate for the excitation mode of LEDs, the so-called “pigmy mode”, the excess neutron mode oscillating in opposite phases with respect to the core has been proposed. However, in recent years, a new-type of excitation mode, “toroidal dipole (TD) mode”, which has hydrodynamic vortical character has been attracting an interest. In addition, it is expected that cluster excitation mode contributes isoscalar LED excitations.

 We investigated the LED excitation mode in terms of cluster structure in ¹⁰Be with ⁶He + α and 2α + nn GCM. As a result, we obtain some LED strengths. We reveal TD mode occurred by rotation of deformed ⁶He cluster. Also, cluster excitation contributes isoscalar dipole excitation. In addition, we discuss contribution of cluster excitation to toroidal excitation mode.