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 2WH: Physics Opportunities with High-Resolution Spectrometers CAGRA and GRAND RAIDEN |
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Chair: Michael Carpenter, Argonne National Laboratory Room: Kona 2 |
Tuesday, October 7, 2014 2:00PM - 2:30PM |
2WH.00001: An overview of CAGRA and the RCNP facility Invited Speaker: Eiji Ideguchi The construction of a Compton suppressed Germanium clover array (CAGRA) by a U.S.-Japan collaboration is on going. This array will be used initially at the cyclotron facility of RCNP, Osaka University in Japan and further scientific investigations utilizing RI beams at RIBF, RIKEN Nishina Center is also planned. High-precision capabilities of existing devices at RCNP can be combined with ultra-high precision $\gamma$-decay measurements to gain access to observables at an unprecedented level of detail. Three experimental sites are foreseen: at the EN beam line, where beams of rare isotopes are available; the Grand Raiden Spectrometer, where high-precision coincidence experiments utilizing light-ion reactions can be performed; and the muon beam facility at RCNP. A wide variety of important scientific questions will be addressed, such as the detailed nature of Pygmy dipole and Gamow-Teller resonances, the shell-evolution across the chart of nuclei, searches for superdeformed states, as well as astrophysical applications. In the presentation, an overview of CAGRA project and the RCNP facility will be presented and the scientific opportunities using CAGRA at the RCNP facility will be discussed. [Preview Abstract] |
Tuesday, October 7, 2014 2:30PM - 3:00PM |
2WH.00002: Superdeformation in the $A\sim 40$ mass region Invited Speaker: Anatoli Afanasjev There is a renewed interest to the investigation of the superdeformation in light $A=32-46$ nuclei [1,2]. In my talk, I will present the overview of the current theoretical understanding of the superdeformed structures in this mass region. The major focus will be on the results obtained within the cranked Nilsson+Strutinsky method and more microscopic cranked relativistic Hartree+Bogoliubov and cranked relativistic mean field approaches. The role of underlying shell structure, intruder orbitals and some other aspects of the superdeformation in this mass region will be discussed in detail. The comparison with other regions of superdeformation will be presented. A possible role of hyperdeformation in this mass region will also be discussed.\\[4pt] [1] E. Ideguchi, private communication (2014).\\[0pt] [2] E. Ideguchi et al, Phys. Lett. B 686, 18 (2010). [Preview Abstract] |
Tuesday, October 7, 2014 3:00PM - 3:30PM |
2WH.00003: A search for unexpected bound states in $^{15}$B Invited Speaker: Calem R. Hoffman Bound states in $^{15}$B are to be populated through the one proton removal reaction from a $^{16}$C beam produced at the RCNP EN Course through $^{18}$O fragmentation. $\gamma$-decays from these states will be identified by an array of Compton-suppressed HPGe Clover detectors (CAGRA). The goals consist of i) identifying any previously unobserved and unexpected bound states in $^{15}$B and ii) to assign total angular momenta to known excited states for the first time. At present only two bound states have been observed in $^{15}$B, neither with firm spin or parity assignments [1]. The present work to be discussed is aimed at determining whether an excited 3/2$^-$ state, a state with identical spin-parity as the ground state, resides below the neutron separation energy in $^{15}$B. Such an excited $3/2^-$ state is not predicted to appear below the $^{15}$B $S_n$ by shell-model calculations using various $p$-$sd$ interactions. However, a robust systematic, probably related to the $s$-wave trends found in the single-neutron states in this region [2], has been observed for neutron-rich $N$=10 nuclei and it suggests that the state may appear lower in excitation energy than expected. Providing some measure of validation for the $N$=10 prediction is a similar trend noticed in the energy differences between ground ($p$)$^{2}$ neutron states and excited ($sd$)$^2$ neutron states in the $N$=8 neutron-rich isotones [3]. In addition to a search for this unexpected state, additional spectroscopic information on $^{15}$B will better aid in the understanding of the $N$=10 isotones when transitioning from $^{16}$C into sparsely probed $^{14}$Be. Details of the experimental procedures and motivation will be presented and discussed.\\[4pt] [1] Y. Kondo, T. Nakamura, N. Aoi et al., Phys. Rev. C 71, 044611 (2005).\\[0pt] [2] C. R. Hoffman, B. P. Kay, J. P. Schiffer, Phys. Rev. C 89, 061305(R) (2014).\\[0pt] [3] H. Iwasaki, A. Dewald, C. Fransen et al., Phys. Rev. Lett. 102, 202502 (2009) [Preview Abstract] |
Tuesday, October 7, 2014 3:30PM - 4:00PM |
2WH.00004: COFFEE BREAK
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Tuesday, October 7, 2014 4:00PM - 4:30PM |
2WH.00005: Current situation on Pygmy Dipole Resonance and related topics Invited Speaker: Tsunenori Inakura Sizable $E1$ strengths around the neutron threshold energy have been observed in a number of $N>Z$ nuclei, as are called the pygmy dipole resonance (PDR), while the $E1$ excitations are predominantly concentrated in the giant dipole resonance (GDR). Although the PDR has been suggested to be an $E1$ oscillation of the neutron skin against the inner core, its physical content yet remains obscure. A systematic calculation using the random-phase approximation (RPA) [1] shows that the low-energy $E1$ strengths correlate to the neutron skin thickness in some regions of nuclear chart, supporting the skin-core oscillation interpretation, but not in other regions. Simultaneously, it is also shown that the low-energy $E1$ strengths develop when the neutron Fermi level occupy low-angular-momentum orbit in neutron-rich nuclei, implying that the low-energy $E1$ mode is a neutron emission mode. In this talk, we will present a current situation of the interpretation of the PDR. We emphasize systematic calculations and experiments is needed in order to pin down nature of the PDR. It is important to investigate character of the low-energy $E1$ excitations, since they are relevant to reaction rates in nucleosynthesis. Moreover, if the low-energy $E1$ excitation is really connected the neutron skin properties, we can extract from the low-energy $E1$ strengths, the neutron matter properties. Especially, it is expected to clarify density-dependence of the nuclear symmetry energy, $L$, which is key to structure of neutron stars. We also show the some related topics of the low-energy $E1$ mode (PDR) in the talk.\\[4pt] [1] T. Inakura, T. Nakatsukasa, and K. Yabana, Phys. Rev. C 84, 021302 (2011). [Preview Abstract] |
Tuesday, October 7, 2014 4:30PM - 5:00PM |
2WH.00006: The ($^{6}$Li,$^{6}$Li$'$[3.56 MeV]) reaction as a novel probe for studying the inelastic neutrino-nucleus response in astrophysical scenarios Invited Speaker: Shumpei Noji We have proposed to perform a $({}^{6}\mathrm{Li},{}^{6}\mathrm{Li}'[3.56 \, \mathrm{MeV}])$ experiment at $E _{{}^{6}\mathrm{Li}} = 100 \, \mathrm{MeV}/u$ at $0 ^\circ$ with CAGRA and GRAND RAIDEN. In this reaction the ejectile is in the 3.56-MeV excited state which decays directly to the ground state by $\gamma$ emission, allowing the reaction channel to be identified via the detection of the 3.56-MeV $\gamma$ rays with CAGRA. This reaction exclusively excites $\mathrm{GT}_0$ transitions, namely the pure spin- and isospin-flip transitions in the inelastic channel ($\Delta S = 1, \Delta T = 1, \Delta T_ z = 0)$, whose transition strength [$B(\mathrm{GT}_0)$] is directly connected to, e.g., the inelastic neutrino-nucleus scattering (INNS) cross sections. We plan to measure five targets, ${}^{12}\mathrm{C}$, ${}^{24}\mathrm{Mg}$, ${}^{56}\mathrm{Fe}$, ${}^{93}\mathrm{Nb}$, and ${}^{124}\mathrm{Sn}$, with the aim to establish this new technique as well as address various astrophysical topics including nucleosynthesis ($r$- and $\nu$-processes), supernova neutrino detection, supernova evolution and modeling. In addition, many astrophysical models rely on neutral-current and charged-current neutrino interactions with heavy nuclei for which very little data exists, therefore this experiment and the ${}^{6}\mathrm{Li}$ reaction probe are of high scientific importance. The success of this project could lead to future plans that employ the $({}^{6}\mathrm{Li},{}^{6}\mathrm{Li}')$ reaction in inverse kinematics to study GT$_0$ responses of rare isotopes. [Preview Abstract] |
Tuesday, October 7, 2014 5:00PM - 5:30PM |
2WH.00007: New energy degraded beam project at RIBF -- OEDO project Invited Speaker: Susumu Shimoura We propose construction of an energy-degrading system consisting of a RF deflector with two STQ's after a mono-energetic degrader in the SHARAQ beam line in the RIBF of RIKEN. The RF deflector acts as a focusing element for a secondary beam after a mono-energetic degrader, which provide a reasonably small beam size less than 2 cm (FWHM) even for energies less than 10 $A$ MeV. Possible physics programs especially for combination with $\gamma$-ray detectors arrays are discussed. [Preview Abstract] |
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