Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session CA: Weak Interactions rates for Nuclear Astrophysics |
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Chair: Hidetoshi Akimune, Konan University Room: Kohala 1 |
Wednesday, October 8, 2014 7:00PM - 7:45PM |
CA.00001: Decay properties of exotic nuclei relevant to r-process nucleosynthesis Invited Speaker: Shunji Nishimura Systematic studies of decay parameters, such as beta-decay half-lives, excited states, and beta-delayed neutron emissions, are essential to study on the mechanism of a rapid-neutron capture process (r process), which is responsible for the production of elements heavier than iron. RIBF has started providing very neutron-rich nuclei by means of in-flight fission of high intensity $^{238}$U beam at RIKEN Nishina Center. New project EURICA has been launched with the goal of performing $\beta$$\gamma$ spectroscopy of exotic nuclei. Series of campaign experiments were conducted to survey the decay properties of very neutron-rich nuclei. Highlights of recent results and future perspectives will be presented to discuss the nuclear shell evolution and their impacts to the r-process nucleosynthesis. [Preview Abstract] |
Wednesday, October 8, 2014 7:45PM - 8:30PM |
CA.00002: Beta delayed neutrons for nuclear structure and astrophysics Invited Speaker: Robert Grzywacz Beta-delayed neutron emission ($\beta $xn) is a significant or even dominant decay channel for the majority of very neutron-rich nuclei, especially for those on the r-process path. The recent theoretical models predicts that it may play more significant role then previously expected for astrophysics and this realization instigated a renewed experimental interest in this topic as a part of a larger scope of research on beta-decay strength distribution. Because studies of the decay strength directly probe relevant physics on the microscopic level, energy-resolved measurements of the beta-decay strength distribution is a better test of nuclear models than traditionally used experimental observables like half-lives and neutron branching ratios. A new detector system called the Versatile Array of Neutron Detectors at Low Energy (VANDLE) was constructed to directly address this issue. In its first experimental campaign at the Holifield Radioactive Ion Beam Facility neutron energy spectra in key regions of the nuclear chart were measured: near the shell closures at 78Ni and 132Sn, and for the deformed nuclei near 100Rb. In several cases, unexpectedly intense and concentrated, resonant-like, high-energy neutron structures were observed. These results were interpreted within shell model framework which clearly indicated that these neutron emission is driven by nuclear structure effects and are due to large Gamow-Teller type transition matrix elements. This research was sponsored in part by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Cooperative Agreement No. DE-FG52-08NA28552. [Preview Abstract] |
Wednesday, October 8, 2014 8:30PM - 9:15PM |
CA.00003: Core-collapse supernovae and nucleosynthesis Invited Speaker: Carla Frohlich Core-collapse supernovae are the violent deaths of massive stars. These explosions are responsible for enriching the early galaxy with heavy elements. One of the most important open questions in this context is to understand the conditions in the ejecta and the neutrino-driven winds. In particular, the electron fraction, which is primarily set by neutrino interactions, is crucial in determining the type of nucleosynthesis processes which are possible (r-process, weak r-process, neutrino-p-process, e.g.). In this talk, I will discuss the conditions and the nucleosynthesis in core-collapse supernovae with a focus on the neutrino interactions. [Preview Abstract] |
Wednesday, October 8, 2014 9:15PM - 10:00PM |
CA.00004: The r-process in the neutrino-processed ejecta of neutron star mergers Invited Speaker: Shinya Wanajo Recent studies suggest that binary neutron star (NS-NS) mergers robustly produce heavy r-process nuclei above the atomic mass number A $\sim$ 130 because their ejecta consist of almost pure neutrons (electron fraction of Ye $<$ 0.1). However, the production of a small amount of the lighter r-process nuclei (A $\approx$ 90-120) conflicts with the spectroscopic results of r-process-enhanced Galactic halo stars. We present the result of nucleosynthesis calculations based on the fully general relativistic simulation of a NS-NS merger with approximate neutrino transport. It is found that the bulk of the dynamical ejecta are appreciably shock-heated and neutrino processed, resulting in a wide range of Ye ($\approx$ 0.1-0.4). The mass-averaged abundance distribution of calculated nucleosynthesis yields is in reasonable agreement with the full-mass range (A $\approx$ 90-240) of the solar r-process curve. This implies, if our model is representative of such events, that the dynamical ejecta of NS-NS mergers could be the origin of the Galactic r-process nuclei. Our result also shows that radioactive heating after $\sim$1 day from the merging, which gives rise to r-process-powered transient emission, is dominated by the $\beta$-decays of several species close to stability with precisely measured half-lives. [Preview Abstract] |
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