Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session 1WC: Workshop on Frontiers in Nuclear Astrophysics I |
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Chair: Taka Kajino, National Astronomical Observatory Room: Kohala 4 |
Tuesday, October 13, 2009 9:00AM - 9:30AM |
1WC.00001: Enrichment of the heaviest elements Th and Pb in the Galaxy Invited Speaker: The heaviest elements Th and Pb are key to understanding the neutron-capture reactions in the Universe. Abundance measurements of these elements for metal-deficient stars in the past dacade provide useful constraints on both the r- and s-processes, and early chemical enrichment in the Galaxy. Recent observational results on abundance ratios of Th to other stable elements in metal-deficient stars, Pb production of both r- and s-processes, and their enrichment history in the Galaxy are reviewed. [Preview Abstract] |
Tuesday, October 13, 2009 9:30AM - 10:00AM |
1WC.00002: First results from RIBF and the scope Invited Speaker: Astrophysical rapid neutron-capture process (r-process) has been recognized to play an important role for the synthesis of approximately half of the heavy elements above iron. Recently, a new generation of accelerator facility (RIBF) has been completed and started providing opportunities of exploring very neutron-rich nuclei along the r-process path region. In this paper, the first results from RIBF will be presented. Furthermore, overall scope of experimental aspects will be discussed related to the astrophysical nucleosynthesis. [Preview Abstract] |
Tuesday, October 13, 2009 10:00AM - 10:30AM |
1WC.00003: Recent and future rp-process experiments at NSCL Invited Speaker: X-ray bursts are powered by a sequence of proton capture reactions and $\beta^{+}$ decays (rp-process). Although much progress has be obtained, key nuclear physics uncertainties remain. Depending on the astrophysical conditions, the rp- process can extend up to the A$\approx$100 mass region. Along the reaction path, even-even N=Z nuclei beyond $^{56}$Ni represent waiting points where abundances acumulate. The half- lives of those isotopes therefore determine the processing time- scale and the final composition once the burst is exhausted. Recent $\beta$-decay experiments of N=Z isotopes $^{84}$Mo, $^ {96}$Cd, $^{98}$In and $^{100}$Sn will be discussed along with their astrophysical implications. In addition to the half-lives, proton capture reactions constitute important nuclear physics input for our understanding of the rp-processes. The new facility ReA3 will provide opportunities for the study of many of the nuclei involved. Future possible experiments will be discussed. [Preview Abstract] |
Tuesday, October 13, 2009 10:30AM - 11:00AM |
1WC.00004: COFFEE BREAK
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Tuesday, October 13, 2009 11:00AM - 11:30AM |
1WC.00005: Study on astrophysical reactions using low-energy RI beams Invited Speaker: In recent years, low-energy RI beams can be produced in a good intensity and they have been used for studying many astrophysical reactions. One of the facilities producing low-energy RI beams is CRIB (CNS Radio-Isotope Beam separator) [1,2], an RI-beam separator of Center for Nuclear Study, University of Tokyo. Taking CRIB as an example, recent improvements on the RI-beam production and experimental results on astrophysical studies are presented. Several experimental approaches have been taken for the studies on astrophysical reactions.The feature of each method are discussed based on real measurements performed at CRIB. One is the direct method, applied for measurements of reactions such as ($\alpha$,p) [3]. Another is the measurement of proton/alpha resonance scattering using the thick target method in inverse kinematics, by which we can obtain information on the resonances relevant in astrophysical reactions [4,5]. A recent fruitful result was from a measurement of proton resonance scattering using a $^7$Be beam [5]. The energy level structure of $^8$B, revealed by the experiment, is especially of interest as it is related with the $^7$Be(p,$\gamma$) $^8$B reaction, responsible for the production of $^8$B neutrinos in the sun. We successfully determined parameters of resonances in $^8$B below 6.7 MeV, which may affect the $^7$Be(p,$\gamma$)$^8$B reaction rate at the solar temparature. Indirect methods, such as ANC and the Trojan Horse Method, were also used in some of the measurements.\\[4pt] [1] S. Kubono et al., Eur. Phys. J. A{\bf 13} (2002) 217.\\[0pt] [2] Y.~Yanagisawa et al., Nucl. Instrum. Meth. Phys. Res., Sect. A {\bf 539} (2005) 74.\\[0pt] [3] M.~Notani et al., Nucl. Phys. A {\bf 764} (2004) 113c.\\[0pt] [4] T.~Teranishi et al., Phys. Lett. B {\bf 650} (2007) 129.\\[0pt] [5] H. Yamaguchi et al., Phys. Lett. B {\bf 672} (2009) 230. [Preview Abstract] |
Tuesday, October 13, 2009 11:30AM - 12:00PM |
1WC.00006: Penning trap mass measurements of nuclides along the astrophysical $rp$- and $\nu p$- process paths Invited Speaker: X-ray bursters and supernovae are examples of explosive stellar phenomena in which nuclides are quickly produced in great quantities. Observed as x-ray bursts, thermonuclear runaways on the surface of neutron stars accreting material from its binary star companion create elements by a nucleosynthetic procoess which involves a series of rapid proton-capture reactions, termed the $rp$ process. The timescale, nuclides produced, and energy released during the $rp$ process are very sensitive to delays encountered at waiting-point nuclides, nuclides in which their slow $\beta$ decay is more probable than net proton capture. A possible mechanism to bypass the waiting-point nuclides is through the $\nu p$ process, in which $(n,p)$ and $(n,\gamma)$ reactions on the waiting-point nuclides, in addition to the proton-capture reactions, are possible. Supernovae are possible sites for the $\nu p$ process as the proton-rich ejecta can absorb antineutrinos to produce the required free neutrons. It is this $\nu p$ process which may resolve the long-standing discrepancy between the observed and predicted abundances of $^{92}$Mo and $^{94}$Mo. Proton-capture $Q$ values of nuclides along the $rp$- and $\nu p$- process paths are required to accurately model the nucleosynthesis, especially at the waiting-point nuclides. In recent years, Penning traps have become the preferred tool to make precise mass measurements of stable and unstable nuclides. To make the best use of these devices in measuring the masses of radioactive nuclides, systems have been developed to quickly, cleanly, and efficiently transport the short-lived, weakly produced nuclides to the Penning traps. This talk will discuss the $rp$ and $\nu p$ nucleosynthetic processes and will highlight the precise Penning trap mass measurements of nuclides along these process paths. [Preview Abstract] |
Tuesday, October 13, 2009 12:00PM - 12:30PM |
1WC.00007: Photonuclear reactions studied with the time-dependent density-functional theory Invited Speaker: Photonuclear reaction cross sections are known to be of fundamental importance in nuclear structure as well as a variety of applications, such as nucleosynthesis and nuclear power. Especially, it is highly desired to improve reliability of E1 strength distribution in unstable nuclei which are not experimentally reachable. We are performing systematic calculations of nuclear photoabsorption cross sections using the time-dependent density-functional theory. For this purpose, we have developed a new numerical approach to the linear response problems, ``Finite Amplitude Method'' (FAM). In this talk, we present recent results of our microscopic calculations with the FAM applied to the Skyrme functionals and discuss properties of nuclear E1 strength distribution in light- and medium-mass nuclei. [Preview Abstract] |
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