We study the character of the first excited 1/2 + state of 9 Be, which is observed as a low-lying sharp peak in the cross section of 9 Be(γ,n)2 4 He just above the 8 Be + n threshold. Using the α + α + n three-body model, we describe the ground and excited unbound states of 9 Be above the α + α + n threshold. Applying the complex scaling method to the three-body model, we find no 1/2 + resonant solutions with the scaling angle of θ 15• , while the low-lying peak in the photodisintegration cross section is reproduced in the present calculation. It is found that the 8 Be + n continuum states dominate the low-lying peak in the cross section. Furthermore, using the analytical continuation of the coupling constant of the three-body interaction for the α + α + n system, we discuss the virtual-state character of the 1/2 + state.

In association with the property of the 1/2 + state observed just above the 8 Be(0 + ) + n threshold energy in 9 Be, we investigate the photodisintegration cross section of an s state in a simple schematic two-body model using the complex scaling method. The photodisintegration cross section, continuum level density, scattering phase shifts, and scattering length are discussed in relation with the virtual state. These scattering observables show strong divergences when a virtual state is located near the physical scattering region.

We study many-body resonances in the neuron-rich 8 He and the mirror proton-rich 8 C using the 4 He +N + N + N + N five-body model with the isospin T = 2 system. Resonances are described with the complex energy eigenvalues as the Gamow states using the complex scaling method. In 8 He, we obtain five states in which four states are resonances, and in 8 C all five states are resonances. We discuss the isospin-symmetry breaking dynamically induced by the Coulomb interaction in the energy spectra and decay widths of the resonances in two mirror nuclei. We predict the resonance energies and decay widths for the future experiments. We also investigate the configurations of valence nucleons above 4 He in two nuclei with the j j coupling scheme, and all the states dominantly have the p-shell configurations. From the configuration mixing, 8 He and 8 C give the similar results, which indicates the good symmetry in two nuclei.

We apply the complex scaling method to the calculation of scattering phase shifts and extract the contributions of resonances in a phase shift and a cross section. The decomposition of the phase shift is shown to be useful in understanding the roles of resonant and nonresonant continuum states. As examples, we apply this method to several two-body systems: (i) a schematic model with the Gyarmati potential, which produces many resonances, (ii) the α-α system, which has a Coulomb barrier potential in addition to an attractive nuclear interaction, and (iii) the α-n system, which has no barrier potential. Using different kinds of potentials, we discuss the reliability of this method to investigate the resonance structure in the phase shifts and cross sections.

The photodisintegration of 9 Be in the energy region lower than E γ = 16 MeV is investigated by using the α + α + n three-body model and the complex scaling method. The cross section exhibits two aspects in two different energy regions. In the low-energy region up to E γ = 6 MeV, the cross section is explained by the transition strengths into the excited resonant states of 9 Be, while the dipole transition into the nonresonant continuum states of 8 Be(2 + ) + n dominates the cross section in the energy region of 6 E γ 16 MeV. Furthermore, it is shown that the dipole strength at E γ ∼ 8 MeV is understood to be caused by the single-neutron excitation from the 8 Be(2 + ) ⊗ νp 3/2 configuration in the ground state.

The structures of continuum states for the s 1/2 , p 3/2 and p 1/2 waves of 5 Li and 5 He mirror nuclei are studied in the complex scaled α + N (N = neutron or proton) two-body model. The resonant, continuum and total terms of the continuum level density and the phase shifts are calculated.

In neutron-rich 8He, we study the soft dipole resonance, which is regarded as a dipole oscillation of four valence neutrons against the 4He core, and its effect on the low-energy electric dipole strength with a 4He+n+n+n+n five-body cluster model. This work is an extended study of the letter (Phys. Rev. C106 (2022) L021302). The five-body unbound 1− states of 8He are obtained with the complex energy eigenvalues by using the complex scaling method and the dipole strength is calculated in terms of the complex-scaled Green’s function. Two kinds of the dominant excitation modes are confirmed in the dipole strength below 20 MeV of the excitation energy. The strengths below 10 MeV are exhausted by the 7He+n channel, which sequentially decays to 6He+n+n. Above 10 MeV, the strengths arise from the soft dipole mode of four neutrons (4n) oscillating against the 4He core. We further explore the possibility of the soft dipole resonance for this state by carefully searching for the resonance pole and finally predict the corresponding resonance with the excitation energy of 14 MeV and the decay width of 21 MeV. The soft dipole resonance exhausts about half of the dipole strength in the relative motion between the 4He core and 4n.

Nuclear reaction data are useful in many fields, e.g., nuclear physics, astrophysics, nuclear engineering, and radiation therapy. It is therefore desirable to make such data freely available through a database. One such database is the EXFOR library, which is maintained under international cooperation. For the benefit of nuclear data users worldwide, the experimental nuclear data obtained at the RIKEN Radioisotope Beam Factory (RIBF) are continuously transmitted into the EXFOR library. We are effectively improving the completeness and usability of the data produced at the RIBF. In addition, a new format is being discussed to create convenient access to the databases for experimentalists and users.