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

β\beta-decay half-lives as an indicator of shape-phase transition in neutron-rich Zr isotopes with particle-vibration coupling effect

[Background] $\beta$-decay half-life is sensitive to the shell structure near the Fermi levels. Nuclear deformation thus impacts the $\beta$-decay properties. [Purpose] A first-order shape-phase transition in neutron-rich Zr isotopes is predicted by some models. We investigate the $\beta$-decay half-lives of neutron-rich nuclei around $^{110}$Zr, where the shape-phase transition is predicted to occur, to see if the $\beta$-decay half-life can be an indicator of the shape changes. [Method] The proton-neutron quasiparticle random-phase approximation (RPA) is adopted to calculate the Gamow-Teller transitions. In addition, we apply the quasiparticle phonon-vibrational coupling (PVC) to consider the phonon couplings. [Results] The spherical and oblate configurations give similar half-lives but shorter ones than the prolate configuration at the RPA level. The PVC effect further reduces the half-lives in general, but the effect is smaller for the deformed configuration than that for the spherical one. As a result, it makes the shape change from the oblate configuration to the spherical configuration visible. Therefore, a sudden shortening of $\beta$-decay half-lives is always found at the nuclear shape changes. [Conclusions] $\beta$-decay half-life is an indicator of the shape-phase transition. The shape mixing and the roles of the triaxial deformation are subject to study in the future.Comment: 7 pages, 4 figure

Theoretical study of Nb \rm{Nb} isotope productions by muon capture reaction on 100Mo {}^{100} \rm{Mo}

The isotope ${}^{99} \rm{Mo}$, the generator of ${}^{99m} \rm{Tc}$ used for diagnostic imaging, is supplied by extracting from fission fragments of highly enriched uranium in reactors. However, a reactor-free production method of ${}^{99} \rm{Mo}$ is searched over the world from the point of view of nuclear proliferation. Recently, ${}^{99} \rm{Mo}$ production through a muon capture reaction was proposed and it was found that about $50 \, \%$ of ${}^{100} \rm{Mo}$ turned into ${}^{99} \rm{Mo}$ through ${}^{100} \rm{Mo} \left( \mu^-, n \right)$ reaction [arXiv:1908.08166]. However, the detailed physical process of the muon capture reaction is not completely understood. We, therefore, study the muon capture reaction of $^{100} \rm{Mo}$ by a theoretical approach. We used the proton-neutron QRPA to calculate the muon capture rate. The muon wave function is calculated with considering the electronic distribution of the atom and the nuclear charge distribution. The particle evaporation process from the daughter nucleus is calculated by a statistical model. From the model calculation, about $38 \, \%$ of ${}^{100} \rm{Mo}$ is converted to ${}^{99} \rm{Mo}$ through the muon capture reaction, which is in a reasonable agreement with the experimental data. It is revealed that negative parity states, especially $1^-$ state, play an important role in ${}^{100} \rm{Mo} \left( \mu^-, n \right) {}^{99} \rm{Nb}$. The feasibility of ${}^{99} \rm{Mo}$ production by the muon capture reaction is also discussed. Isotope production by the muon capture reaction strongly depends on the nuclear structure.Comment: 9 pages, 4 figures, 4 tables, RIKEN-QHP-426, RIKEN-iTHEMS-Report-1

Post-fission properties of uranium isotopes: a hybrid method with Langevin dynamics and the Hauser-Feshbach statistical model

Background: Precise understanding of nuclear fission is crucial for experimental and theoretical nuclear physics, astrophysics, and industrial applications; however, the complete physical mechanics is unresolved due to the complexities. Purpose: In this study, we present a new method to describe the dynamical-fission process and following prompt-neutron emission, where we combine the dynamical fission calculation based on the Langevin method and the Hauser-Feshbach statistical model. Methods: Two methods are connected smoothly within the universal charge distribution and the energy conservation, allowing us to calculate a sequence of fission dynamics and post-fission phase, including prompt neutron emission. Results: Using a certain set of model parameters, we successfully reproduce the experimental primary-fission yields, total kinetic energy, independent-fission yields, and prompt neutron emissions for the neutron induced fission of ${}^{236}$U, a compound nucleus of ${\rm n} + {}^{235}{\rm U}$. We elucidate the physical mechanism of the characteristic features observed in previous experiments, such as shell properties. Additionally, we apply our calculation to two very neutron-rich uranium isotopes, i.e., ${}^{250}$U and ${}^{255}$U, which are not experimentally confirmed but are important for r-process nucleosynthesis. Theoretical results indicate that ${}^{250}$U exhibits an asymmetric multiple-peak fission yield distribution, while the neutron-rich ${}^{255}$U has a single peak due to symmetric fission. Our method predicts post-neutron emission fragments, where ${}^{250}$U shows a stronger neutron emissivity than ${}^{255}$U. Conclusions: Our framework is highly reproducible in the experiments and shows that the number of emitted neutrons after fission differs significantly in neutron-rich uranium fission depending on distributions of fission variables.Comment: 12 pages, 11 figures, submitted to PRC, Comments are welcom

Screening effects on neutrino-nucleus reactions

Tours symposium on nuclear physics VI : Tours 2006, Tours, France 5-8 September 2006 / editors, M. Arnould ... [et al.