Interference Effect Between Neutron Direct and Resonance Capture Reactions For Neutron-Rich Nuclei

Interference effect of neutron capture cross section between the compound and direct processes is investigated. The compound process is calculated by resonance parameters and the direct process by the potential mode. The interference effect is tested for neutron-rich $^{82}$Ge and $^{134}$Sn nuclei relevant to $r$-process and light nucleus $^{13}$C which is neutron poison in the $s$-process and produces long-lived radioactive nucleus $^{14}$C ($T_{1/2}=5700$ y). The interference effects in those nuclei are significant around resonances, and low energy region if $s$-wave neutron direct capture is possible. Maxwellian averaged cross sections at $kT=30$ and $300$ keV are also calculated, and the interference effect changes the Maxwellian averaged capture cross section largely depending on resonance position.Comment: 5 pages, 4 figures, poster presentation given at FUSION17 conference, Hobart, Tasmania, Australia, Feb. 20-24, 201

Towards modeling cluster structure of 8^8Be with chiral interaction

How the nuclear force behaves in cluster states, in particular those consisting of the $\alpha$ clusters, has been investigated so far, but not yet elucidated. Today the chiral effective field theory is established and it would shed new light on the microscopic understanding of the cluster states. We aim to address a possible source of the attraction in the cluster states of $^8\mathrm{Be}$ in view of the pion exchange. Namely, we investigate whether the two-pion-exchange interaction acts as a dominant attraction in the $\alpha+\alpha$ system as predicted by a previous work. We describe theoretically the cluster structure of $^8\mathrm{Be}$ by the Brink model, for which the effective interaction is designed from the realistic nuclear force derived through the chiral effective field theory. The two-body matrix elements of the chiral interaction with the local-Gaussian bases are formulated within the approximation of the spin-isospin saturation forming an $\alpha$ particle. Introducing a global prefactor to the chiral interaction phenomenologically, the ground and low-lying excited states of $^8\mathrm{Be}$, the scattering phase shift of the $\alpha$-$\alpha$ system as well, are satisfactorily depicted. The attraction in the cluster states is found to be stemming from the two-pion-exchange contributions dominantly, along with nonnegligible short-range terms. The present work can be the foundation towards constructing realistic cluster models, by which the cluster states will be revealed microscopically in the next step.Comment: 33 pages, 9 figures, 6 table

Extending the Eikonal Approximation to Low Energy

E-CDCC and DEA, two eikonal-based reaction models are compared to CDCC at low energy (e.g. 20AMeV) to study their behaviour in the regime at which the eikonal approximation is supposed to fail. We confirm that these models lack the Coulomb deflection of the projectile by the target. We show that a hybrid model, built on the CDCC framework at low angular momenta and the eikonal approximation at larger angular momenta gives a perfect agreement with CDCC. An empirical shift in impact parameter can also be used reliably to simulate this missing Coulomb deflection.Comment: Contribution to the proceedings of the Conference on "Advances in Radioactive Isotope Science" (ARIS2014). 6 pages, 4 figure

Implementation of chiral two-nucleon forces to nuclear many-body methods with Gaussian-wave packets

Many-body methods that use Gaussian-wave packets to describe nucleon-spatial distribution have been widely employed for depicting various phenomena in nuclear systems, in particular clustering. So far, however, the chiral effective field theory, a state-of-the-art theory of nuclear force, has not been applied to such methods. In this paper, we give the formalism to calculate the two-body matrix elements of the chiral two-nucleon forces using the Gaussian-wave packets. We also visualize the matrix elements and investigate the contributions of the central and tensor forces. This work is a foothold towards an \textit{ab initio} description of various cluster phenomena in view of nucleons, pions, and many-nucleon forces.Comment: 39 pages, 5 figures, 1 tabl

Analysis of a low-energy correction to the eikonal approximation

Extensions of the eikonal approximation to low energy (20MeV/nucleon typically) are studied. The relation between the dynamical eikonal approximation (DEA) and the continuum-discretized coupled-channels method with the eikonal approximation (E-CDCC) is discussed. When Coulomb interaction is artificially turned off, DEA and E-CDCC are shown to give the same breakup cross section, within 3% error, of $^{15}$C on $^{208}$Pb at 20MeV/nucleon. When the Coulomb interaction is included, the difference is appreciable and none of these models agrees with full CDCC calculations. An empirical correction significantly reduces this difference. In addition, E-CDCC has a convergence problem. By including a quantum-mechanical correction to E-CDCC for lower partial waves between $^{15}$C and $^{208}$Pb, this problem is resolved and the result perfectly reproduces full CDCC calculations at a lower computational cost.Comment: 8 pages, 7 figure