Isoscalar (IS) monopole and dipole excitations in 16 O were investigated by the method of shifted basis antisymmetrized molecular dynamics combined with the generator coordinate method. Significant strengths of the IS monopole and dipole transitions were obtained in the low-energy region below the giant resonances. In addition to the compressive mode, which mainly contributes to the high-energy strengths for the IS dipole giant resonance, we obtained a variety of low-energy dipole modes such as the vortical dipole mode in the 1 − 1 state of the vibrating tetrahedral 4α and the 12 C+α cluster structure in the 1 − 2 state. The 1 − 1 state contributes to the significant low-energy strength of the IS dipole transition as 5% of the energy-weighted sum rule, which describes well the experimental data observed by the α inelastic scattering.

We studied dipole excitations in 10 Be based on an extended version of the antisymmetrized molecular dynamics, which can describe 1p-1h excitations and large amplitude cluster modes. Toroidal and compressive dipole operators are found to be good proves to separate the low-energy and highenergy parts of the isoscalar dipole excitations, respectively. Two low-energy 1 − states, the toroidal dominant 1 − 1 state at E ∼ 8 MeV and the E1 dominant 1 − 2 state at E ∼ 16 MeV, were obtained. By analysis of transition current densities, the 1 − 1 states is understood as a toroidal dipole mode with exotic toroidal neutron flow caused by rotation of a deformed 6 He cluster, whereas the 1 − 2 state is regarded as a neutron-skin oscillation mode, which are characterized by surface neutron flow with inner isoscalar flow caused by the surface neutron oscillation against the 2α core.

We investigated cluster and toroidal aspects of isoscalar dipole excitations in 12 C based on the shifted basis antisymmetrized molecular dynamics combined with the generator coordinate method, which can describes 1p-1h excitations and 3α dynamics. In the E = 10 − 15 MeV region, we found two low-energy dipole modes separating from the giant dipole resonance. One is the developed 3α-cluster state and the other is the toroidal dipole mode. The cluster state is characterized by the large amplitude cluster motion beyond the 1p-1h model space, whereas the toroidal dipole mode is predominantly described by 1p-1h excitations on the ground state. The low-energy dipole states are remarkably excited by the toroidal dipole operator, which can measure the nuclear vorticity. For compressive dipole transition strengths, a major part is distributed in the 30 − 50 MeV region for the giant dipole resonance, and 5% of the total energy weighted sum exist in the E < 20 MeV region.

The cross sections of the ^{7}Be(n,α)^{4}He reaction for p-wave neutrons were experimentally determined at E_{c.m.}=0.20-0.81  MeV slightly above the big bang nucleosynthesis (BBN) energy window for the first time on the basis of the detailed balance principle by measuring the time-reverse reaction. The obtained cross sections are much larger than the cross sections for s-wave neutrons inferred from the recent measurement at the n_TOF facility in CERN, but significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the ^{7}Be(n,α)^{4}He reaction rate is not large enough to solve the cosmological lithium problem, and this conclusion agrees with the recent result from the direct measurement of the s-wave cross sections using a low-energy neutron beam and the evaluated nuclear data library ENDF/B-VII.1.

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Low-energy dipole excitations in 10 Be were investigated based on the generator coordinate method with α + 6 He and α + α + 2n cluster models. We obtained three 1 − states in E x < 15 MeV, which show different characters in the E1, compressive dipole, and toroidal dipole transition strengths. We found the strong toroidal dipole transition in the 1 − 1 state, remarkable E1 strength in the 1 − 2 state, and the strong E1 and compressive dipole strength in the 1 − 3 state. The 1 − 1 is described by the α + 6 He cluster structure, where as the 1 − 2 and 1 − 3 states are understood by three-body excitations of the α + α + 2n clustering.

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