Collective properties of low-lying octupole excitations in 20882Pb126, 6020Ca40 and 288O20 Original Research Article

The octupole strengths of three nuclei: β-stable nucleus 20882Pb126, neutron skin nucleus 6020Ca40 and neutron drip line nucleus 288O20 are studied by using the self-consistent Hartree–Fock calculation with the random phase approximation. The collective properties of low-lying excitations are analyzed by particle–vibration coupling. The results show that there is the coexistence of the collective excitations and the decoupled strong continuum strength near the threshold in the lowest isoscalar states in 6020Ca40 and 288O20. For these three nuclei, both the low-lying isoscalar states and giant isoscalar resonance carry isovector strength. The ratio B(IV)/B(IS) is checked and it is found that, for 20882Pb126, the ratio is equal to ((N−Z)/A)2 in good accuracy, while for 6020Ca40 and 288O20, the ratios are much larger than ((N−Z)/A)2. The study shows that the enhancement of the ratio is due to the excess neutrons that have small binding energies in 6020Ca40 and 288O20.