Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session JH: Mini-symposium on Nuclear Physics in Extreme Astrophysical Conditions II |
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Sponsoring Units: DNP JPS Chair: Carl Brune, Ohio University Room: Ritz-Carlton Hotel Plantation 1 |
Thursday, September 22, 2005 9:00AM - 9:15AM |
JH.00001: $\beta -$decay properties of r-process nuclei in the region around $^{137}$Sb J. Pereira, R. Kessler, F. Attalach, T. Fastermann, H. Geissel, U. Giesen, M. Hannawald, M. Hausmann, M Hellstrom, K.-L. Kratz, H. Mahmud, M.N. Mineva, G. Munzenberg, B. Pfeiffer, P. Santi, H. Schatz, C. Scheidenberger, k Schmidt, R. Schneider, J. Stadlmann, A. Stolz, K. Summerer, E. Wefers, P.J. Woods Studies aimed to explore the $\beta $-decay properties of very neutron rich nuclei are very important, since $\beta $-decays processes are related to the location and height of the r-process peak abundances. To this end, an experiment has been performed at GSI (Darmstad) to determine the T$_{1/2 }$and P$_{n}$ values of nuclei in the region around $^{137}$Sb. Different exotic nuclei, including some important ``waiting points'' around the A=130 region were produced by fission of a 750 MeV/u $^{238}$U beam. The separated fragments were implanted into a stack of four double sided Silicon strip detectors, allowing a correlation between implantation and $\beta $-decays; $\beta $-delayed neutrons were measured with the Mainz 4$\pi $ neutron long counter. Results obtained from this experiment will be presented. [Preview Abstract] |
Thursday, September 22, 2005 9:15AM - 9:30AM |
JH.00002: Shell model study of odd-odd nuclei with N=81 and their role in astrophysics Kengo Ogawa, Hitoshi Nakada, Takehito Hayakawa, Toshiyuki Shizuma, Toshitaka Kajino An odd-odd nucleus $^{138}$La is a key nucleus to understand the nucleosynthesis process in supernova explosions since it is considered to be synthesized by neutrino-induced reactions in SNe. We have investigated the structures of the odd-odd $N=81$ nuclei near $^{138}$La theoretically. The observed $J=1^+$ ground state in $^{140}$Pr suggests us the strongly correlated proton wave function, since a configuration $(0g_{7/2})^8(1d_{5/2})^1_p \times (1d_ {3/2}^{-1})_n$ which is predicted by a simple shell model does not favor the $J=1^+$ ground state. Therefore by taking into account more general configurations and truncation based on the seniority scheme, we have carried out the shell model calculation and succeeded in reproducing the lowlying level structure of $^ {140}$Pr. Other results of the calculation will be presented at the meeting. We will also discuss the astrophysical role of $^{138}$La. [Preview Abstract] |
Thursday, September 22, 2005 9:30AM - 9:45AM |
JH.00003: Birds and the B(GT)s: Gamow-Teller Strengths from (t,3He) Charge Exchange Measurements Meredith Howard, S.D. Reitzner, E.E. Smith, S. Austin, D. Bazin, A.L. Cole, M. Famiano, A. Gade, D. Galaviz Redondo, G.W. Hitt, W. Martinez, M. Matos, H. Schatz, B. Sherrill, C. Simenel, A. Stolz, R.G.T. Zegers, B. Davids, Y. Shimbara, C. Samanta In pre-collapse and post-bounce stars, electrons excite Gamow-Teller (GT) resonances. Our current understanding of supernova explosion dynamics is guided by models that use data and calculations of GT strength (B(GT)) distributions for many nuclei. While measuring B(GT) for all nuclei is an unreasonable chore, limited charge exchange data can 1) reduce uncertainties for important nuclei and 2) vet assumptions/calculations used in different isotopic regions. (T,3He) experiments run at the National Superconducting Cyclotron Laboratory (NSCL) use a 450 MeV secondary triton beam to measure strengths with a resolution of about 150 keV from dispersion matching. Preliminary results from a recent experiment on 24Mg, 63Cu and 94Mo targets are discussed. This work is supported by JINA and the NSF (PHY 0214783, 0110253, 0140255). [Preview Abstract] |
Thursday, September 22, 2005 9:45AM - 10:00AM |
JH.00004: Isospin Asymmetry in Nuclei and Neutron Stars Andrew Steiner The role of isospin asymmetry in neutron stars and nuclei is investigated. We discuss the causes of correlations among the neutron skin thickness in heavy nuclei, the pressure of neutron-rich matter near saturation density, the derivative of the nuclear symmetry energy at the same density and the radii of moderate mass neutron stars. The impact of symmetry energy constraints for the mass and moment of inertia contained within neutron star crusts and the threshold density for the nucleon direct Urca process, all of which are potentially measurable, is explored. We comment on the minimum neutron star radius, assuming that only nucleonic matter exists within the star. We discuss these results in the light of recent mass and radius measurements which have the potential to offer tighter constraints on the theory. [Preview Abstract] |
Thursday, September 22, 2005 10:00AM - 10:15AM |
JH.00005: Nuclear Physics Input to Models of the Supernova Phenomenon Jirina Rikovska Stone, Anthony Mezzacappa The density and temperature dependence of the energy per particle of a system (the Equation of State (EOS)) is a fundamental ingredient of all models of nuclear matter and stars. As nucleons and leptons form the main components of all stars, the best possible description of the strong and weak interactions amongst these particles is essential for a correct understanding of birth, life and death of stars. To date, no model predicts the explosion of a core collapse supernova. The problem may lie with the EOS currently used. We give examples of EOS's, based on different models of nuclear interactions, suitable for models of core-collapse supernovae and examine the sensitivity of calculated radial positions of shock waves, mass fractions in the supernova core, pressure and temperature profiles and some other features to the choice of the equation of state. Two new EOSs, one based on a fully selfconsistent Hartree-Fock model, shedding new light on the phase transition between homogeneous and inhomogeneous nuclear matter and the other, based on the quark model, describing high density homogeneous matter with strange baryons, will be discussed. [Preview Abstract] |
Thursday, September 22, 2005 10:15AM - 10:30AM |
JH.00006: Equations of State for Supernova Simulations James Lattimer New formulations of dense matter equations of state suitable for use in supernova and neutron star simulations are described. These equations of state are based on the compressible liquid droplet model of Lattimer et al. (Nucl. Phys. A432, 646 [1985]) and contain several modifications and improvements to the models of Lattimer \& Swesty (Nucl. Phys. A535, 331 [1991]). Changes include consideration of the nuclear neutron skin, convergence even for arbitrarily low temperatures, electron fractions and densities, and the incorporation of relativistic field-theoretical nucleon interactions in addition to non-relativistic potential nuclear forces. For each nuclear interaction, surface energy parameters are evaluated from Thomas-Fermi semi-infinite calculations, so that surface properties remain consistent with bulk matter properties. Comparisons are made between models with significantly different nucleon-nucleon interaction parametrizations, and with results obtained from conventional ``nuclear statistical equilibrium'' calculations at lower densities. The properties of cold neutron star matter in the crust of neutron stars and implications for the astrophysical r-process are also discussed. [Preview Abstract] |
Thursday, September 22, 2005 10:30AM - 10:45AM |
JH.00007: Fission and the Termination of the Astrophysical r-Process Peter Moller, Karl-Ludwig Kratz, Khalil Farouqi, Bernd Pfeiffer Recent significant progress in modeling the fission process allows us to model the r-process termination more realistically than previously. In the macroscopic-microscopic approach we now calculate fission potential-energy surfaces as functions of millions of different nuclear shapes [1]. In contrast other calculations have only considered around 1000 shapes.. We have used our recently developed approach to calculate barrier heights for more than 1000 nuclei The inner barrier has been studied in a 3-dimensional deformation space, including axial asymmetry; for the outer barrier region it is necessary to use a 5-dimensional deformation space. Once we have established which of the inner or outer barrier peaks defines the fission-barrier height we perform r-process calculations taking into account fission at the termination of the r-process path. First results and conclusions will be presented.\\ [1] P. Moller, D. G. Madland, A. J. Sierk, and A. Iwamoto, Nature {\textbf 409} (2001)785 [Preview Abstract] |
Thursday, September 22, 2005 10:45AM - 11:00AM |
JH.00008: Primordial magnetic field, CMB, and BBN Dai Yamazaki, Kiyotomo Ichiki, Taka Kajino, Grant Mathews The cosmic microwave background (CMB)anisotropies give important information to constrain cosmological parameters including the universal baryon density. Recent CMB observations have been extended to higher multipoles $l>$1000 to exhibit an excess power than the standard model prediction in cosmological theory which best fits the Wilkinson Microwave Anisotropy Probe data at lower multipoles $l<$900. This would make another uncertainty in resolving the discrepancy of baryon density determined from CMB and Big- Bang nucleosynthesis. Thus we consider the effect of the cosmological primordial magnetic field that affects strongly the CMB power spectrum. We calculate the CMB temperature anisotropies generated by the power-law magnetic field at the last scattering surface in order to explain the excess power at higher multipoles, and also try to constraint more accurately the baryon density and upper limit to primordial magnetic field. [Preview Abstract] |
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