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 KD: Nuclear Astrophysics II |
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Chair: Michael Wiescher, Notre Dame Room: Kohala 4 |
Saturday, October 11, 2014 9:00AM - 9:15AM |
KD.00001: Nuclear Physics and the Classical and Recurrent Nova Outburst Sumner Starrfield Classical novae participate in the cycle of Galactic chemical evolution in which grains and metal enriched gas in their ejecta, supplementing those of supernovae, AGB stars, and Wolf-Rayet stars, are a source of heavy elements for the ISM. Once in the diffuse gas, this material is mixed with the existing gases and then incorporated into young stars and planetary systems during star formation. Infrared observations have confirmed the presence of carbon, SiC, hydrocarbons, and oxygen-rich silicate grains in nova ejecta, suggesting that some fraction of the pre-solar grains recently identified in meteoritic material may come from novae. The mean mass returned by a nova outburst to the ISM probably exceeds $\sim 2\times 10^{-4}$ M$_\odot$. Using the observed nova rate of 35$\pm$11 per year in our Galaxy, it follows that novae introduce more than $\sim 7\times 10^{-3}$ M$_\odot$ yr$^{-1}$ of processed matter into the ISM. Novae are predicted to be the major source of $^{15}$N and $^{17}$O in the Galaxy and to contribute to the abundances of other isotopes in this atomic mass range. I will report on the effects of changes in the nuclear reaction rate libraries on the properties of the outburst and, how these changes alter the predictions. [Preview Abstract] |
Saturday, October 11, 2014 9:15AM - 9:30AM |
KD.00002: ABSTRACT WITHDRAWN |
Saturday, October 11, 2014 9:30AM - 9:45AM |
KD.00003: Stellar neutron sources and s-Process in Massive Stars R. Talwar, G.P.A. Berg, L. Bin, M. Couder, R. deBoer, X. Fang, H. Fujita, Y. Fujita, J. Goerres, K. Hatanaka, T. Ito, T. Kadoya, A. Long, K. Miki, D. Patel, A. Tamii, M. Wiescher, T. Yamamoto, M. Yosoi Potential stellar neutron sources for the s-process in massive stars are associated with $\alpha $-capture reactions on light nuclei. The capture-reaction rates provide the reaction flow for the buildup of the neutron sources $^{22}$Ne, and $^{26}$Mg during the helium-burning phase in stars. A critical influence on these reactions is expected to come from low-energy resonances at stellar energies between 300 keV and 1500 keV. It is possible that these resonances are suspected to correspond to pronounced cluster structures near the $\alpha $-threshold. Direct measurements of capture reactions to study these cluster states are handicapped by the Coulomb barrier and limited detector resolutions. Hence, inelastic $\alpha $-scattering on these nuclei has been used as an alternative tool to probe into the level structure. Also $\alpha $-transfer technique has been used to extract $\alpha $-strength information. In reference to this, the experiments performed using the Grand Raiden Spectrometer at RCNP, Osaka will be discussed and preliminary results will be presented. [Preview Abstract] |
Saturday, October 11, 2014 9:45AM - 10:00AM |
KD.00004: Enrichment of r-process elements in dwarf spheroidal galaxies with chemical and dynamical evolution model Yutaka Hirai, Yuhri Ishimaru, Takayuki R. Saitoh, Michiko S. Fujii, Toshitaka Kajino Recent astronomical observations show large dispersion in relative abundance ratio of Eu to Fe ([Eu/Fe]) of metal-poor stars. While these stars provide clues to reveal galaxy formation, their chemical compositions suggest the site(s) of r-process must be in specific objects. Galaxy formation strongly depends on dynamical evolution process. In addition, stellar nucleosynthesis must be considered to decide the origin of r-process elements. It is thus important to calculate dynamical evolution of galaxies as well as chemical evolution to understand galaxy formation and evolution process. In this study, we construct a new chemical and dynamical evolution model based on N-body/Smoothed Particle Hydrodynamics code ASURA, taking into account of feedback of energy and metals from supernovae (SNe) and neutron star mergers (NSM). We execute models corresponding to three dwarf spheroidal galaxies (dSphs); Sextans, Sculptor, and Fornax. We show that our models successfully reproduce observed metallicity distributions and mass-metallicity relation of dSphs. We also calculate enrichment of Eu in a galaxy, assuming r-process site as SNe or NSM. Comparing predicted [Eu/Fe] with observations of dSphs, we discuss the site of r-process through our model of galaxies. [Preview Abstract] |
Saturday, October 11, 2014 10:00AM - 10:15AM |
KD.00005: Origins of light trans-Fe and r-process elements deduced from Galactic chemical evolution Yuhri Ishimaru, Sachie Arao, Shinya Wanajo, Nicolas Prantzos Compact binary mergers are suggested to be the major site of the r-process elements by recent hydrodynamical and nucleosynthesis studies. It has been pointed out, however, that estimated long lifetimes of compact binaries are in conflict with the presence of large scatters in r-process elements of very metal-poor stars (MPS). To resolve this problem, we examine the role of compact binary mergers in the early Galactic chemical evolution on the assumption that our Galactic halo was formed from clusterings of sub-halos. We find that star-to-star scatters of [r/Fe] in MPS can be well explained with this scenario. Observations of MPS also show large enhancement of Sr relative to Ba, suggesting a distinct site of light trans-Fe elements. Recent nucleosynthesis studies show that electron-capture supernovae (ECSNe) can produce heavy elements up to Zr (Wanajo et al. 2011). Using our inhomogeneous chemical evolution model, we discuss that ECSNe can explain observed enhancement of Zn in MPS as well as of Sr, Y, and Zr. [Preview Abstract] |
Saturday, October 11, 2014 10:15AM - 10:30AM |
KD.00006: Neutron Capture Cross Section Calculations with the Statistical Model Mary Beard, Ethan Uberseder, Michael Wiescher Hauser-Feshbach (HF) cross sections are of enormous importance for a wide range of applications, from waste transmutation and nuclear technologies, to medical applications, and nuclear astrophysics. It is a well observed result that different nuclear input models sensitively affect HF cross section calculations. Less well-known however are the effects on calculations originating from model-specific implementation details (such as level density parameter, matching energy, backshift and giant dipole parameters), as well as effects from non-model aspects, such as experimental data truncation and transmission function energy binning. To investigate the effects or these various aspects, Maxwellian-averaged neutron capture cross sections have been calculated for approximately 340 nuclei. The relative effects of these model details will be discussed. [Preview Abstract] |
Saturday, October 11, 2014 10:30AM - 10:45AM |
KD.00007: Direct Neutron Capture Calculations with Covariant Density Functional Theory Inputs Shi-Sheng Zhang, Jin-Peng Peng, Michael S. Smith, Goran Arbanas, Ray L. Kozub Predictions of direct neutron capture are of vital importance for simulations of nucleosynthesis in supernovae, merging neutron stars, and other astrophysical environments. We calculate the direct capture cross sections for E1 transitions using nuclear structure information from a covariant density functional theory as input for the FRESCO coupled-channels reaction code. We find good agreement of our predictions with experimental cross section data on the double closed-shell targets $^{16}$O, $^{48}$Ca, and $^{90}$Zr, and the exotic nucleus $^{36}$S. Extensions of the technique for unstable nuclei and for large-scale calculations will be discussed. [Preview Abstract] |
Saturday, October 11, 2014 10:45AM - 11:00AM |
KD.00008: Beta-Decay Properties of Neutron-Rich pf-shell Nuclei A.L. Cole, B.A. Brown Determining weak interaction rates of pf-shell nuclei is necessary to model late stage supernova evolution. As all rates cannot be measured, we must develop and test model calculations. We present shell model calculations of $\beta $-decay half-lives and Q-values for $^{\mathrm{47-60}}$Ca, $^{\mathrm{46-57}}$Sc and $^{\mathrm{51-62}}$Ti isotopes. These calculations, performed with NuShellX using three different interaction Hamiltonians, are compared to experimental measurements where possible. [Preview Abstract] |
Saturday, October 11, 2014 11:00AM - 11:15AM |
KD.00009: ABSTRACT WITHDRAWN |
Saturday, October 11, 2014 11:15AM - 11:30AM |
KD.00010: New calculations of $\beta$-delayed neutron emission Matthew Mumpower, Toshihiko Kawano, Peter Moller $\beta$-delayed neutron emission probabilities (Pn-values) are important inputs for nuclear astrophysics applications. We present a new model of $\beta$-delayed neutron emission which combines QRPA and statistical decay calculations. This approach uses microscopic nuclear structure information which starts with Gamow-Teller strength distributions in the daughter nucleus, and then follows the statistical decay until the initial available excitation energy is exhausted. Explicitly included at each neutron emission stage is $\gamma$-ray competition. One consequence of this formalism is a prediction of more neutrons on average being emitted after $\beta$-decay for neutron-rich nuclei towards the neutron dripline. The framework presented here also enables us to extend our calculations to beta-delayed fission and pre-scission neutron emission. We discuss implications of larger Pn-values and new $\beta$-delayed fission rates for the astrophysical $r$ process of nucleosynthesis. [Preview Abstract] |
Saturday, October 11, 2014 11:30AM - 11:45AM |
KD.00011: Acceleration-deceleration system and pre-buncher system for high-intensity 12C pulsed beam Yoshihiro Narikiyo, Kenshi Sagara, Kunihiro Fujita, Hiroyuki Yamaguchi, Kennichi Hamamoto, Tadahiko Ban, Nariaki Tao, Leii Kaku In Kyushu University, the measurement of the cross section 12C $+\alpha \to $16O$+\gamma $ has been planned for astrophysical interest. To perform a high efficiency measurement, an inverse kinematics was employed. Since the cross section at near stellar energy (Ec.m. $=$ 0.7MeV) is extremely small, a few pb, it is of importance to increase the beam intensity. In this study, two improvements were performed. The former is an improvement of the tandem accelerator. Since our accelerator was designed for higher voltage(6 --10MV), the transmission efficiency in our experiment (1--2MV) is poor(12.8{\%}). We developed a novel accelerating method called accele-decel mode. Shorting bars were installed on the tube to make a series of acceleration and deceleration sections, which derive a strong focusing effect. Consequently the beam emittance becomes smaller by a factor of two. The latter is an upgrading a beam pulsing instrument. Although the pulsed beam is necessary for background reduction in our experiment, low conversion efficiency of DC to pulsed beam cause a decrease of the intensity to be 28{\%}. To increase the efficiency, we introduced a pre-bunchar system, and attained it to be 63{\%}. These improvements increased the beam intensity by a factor of four, and enable to measure the cross section at Ec.m. $=$ 1.2MeV. [Preview Abstract] |
Saturday, October 11, 2014 11:45AM - 12:00PM |
KD.00012: ABSTRACT WITHDRAWN |
Saturday, October 11, 2014 12:00PM - 12:15PM |
KD.00013: Development of TOF detector with ultra-thin Formvar films for astrophysics experiment Kenichi Hamamoto At Kyushu university tandem laboratory, we are measuring $^{4}$He ($^{12}$C, $^{16}$O) gamma reaction cross section for the energy range of E$_{\mathrm{cm}}=$ 2.4 to 0.7 MeV by detecting $^{16}$O recoils. The produced $^{16}$O ions are transported to a recoil mass separator where they are separated from the unreacted $^{12}$C beam and they are detected by a particle detector placed at focal plane. Since the energy of the produced $^{16}$O ions were very low, the detector should have as small a thickness as possible. It is also of importance to have large effective area to collect all $^{16}$O ions. To satisfy these requirements, a TOF detector employing micro-channel plates was developed. Special attention was paid to develop an ultra-thin and large area formvar film, which acts as an electron emitter and a cathode electrode. The thickness was estimated to be 4 $\mu$g/cm$^{2}$ by measuring the energy loss of $^{16}$O beam, and the effective area was 80mm in diameter. In this symposium, we will report the method and the result of performance test of the developed TOF detector. [Preview Abstract] |
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