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 LL: Nuclear Structure VI |
Hide Abstracts |
Chair: Makito Oi, Senshu University Room: Queens 6 |
Saturday, October 17, 2009 2:00PM - 2:15PM |
LL.00001: Beta decay of $^{24}$Si and mirror asymmetry of Gamow-Teller transition strength Yuichi Ichikawa, Toshiyuki Kubo, Nori Aoi, Naoki Fukuda, Tohru Motobayashi, Kazunari Yamada, HIroyoshi Sakurai, Takeo Onishi, Daisuke Suzuki, Hironori Iwasaki, Taro Nakao, Hiroshi Suzuki, Masaru Suzuki, Vaishali Naik, Alok Chakrabarti, B. Alex Brown, Shigeru Kubono, Hidetoshi Yamaguchi, Takumi Nakabayashi, Takashi Nakamura, Toshifumi Okumura, H. Jin Ong, Takashi Teranishi We performed the $\beta$ decay spectroscopy on $^{24}$Si in order to study the behavior of a weakly-bound $s$-wave proton. The behavior of a weakly-bound proton in a proton-rich nucleus is one of the interesting topics to explore exotic nuclear structures such as proton halo. Thomas-Ehrman shift of the proton $s_{1/2}$ orbital induces a configuration change in the wave function. The change can be investigated in terms of the mirror asymmetry for Gamow-Teller transition strengths $B$(GT) for a proton-rich nucleus of $^{24}$Si. The experiment was carried out at the RIPS facility. In this presentation, we will report the experimental results. Discussion on the comparison with theoretical calculations which takes into account the Coulomb force and the Thomas-Ehrman shift is also given. [Preview Abstract] |
Saturday, October 17, 2009 2:15PM - 2:30PM |
LL.00002: Approaching the Island of Inversion: $^{34}$P Peter C. Bender, Calem Hoffman, Mathis Wiedeking, J.M. Allmond, L.A. Bernstein, J.T. Burke, D.L. Bleuel, R.M. Clark, P. Fallon, B.L. Goldblum, T.A. Hinners, H.B. Jeppesen, S.L. Lee, I.-Y. Lee, S.R. Lesher, A.O. Macchiavelli, M.A. McMahan, D. Morris, M. Perry, L. Phair, N.D. Scielzo, S.L. Tabor, V. Tripathi, A. Volya Yrast states in $^{34}$P were investigated using the $^{18}$O($^{18}$O,pn) reaction at energies of 20, 24, 25, 30, and 44 MeV at Florida State University and at Lawrence Berkeley National Laboratory. The level scheme was expanded, $\gamma$-ray angular distributions were measured, and lifetimes were inferred with the Doppler-shift attenuation method by detecting decay protons in coincidence with one or more $\gamma$ rays. The results provide a clearer picture of the evolution of structure approaching the ``Island of Inversion'', particularly how the 1 and 2 particle-hole (ph) states fall in energy with increasing neutron number approaching inversion. Shell model calculations made using a small modification of the WBP interaction reproduce the negative-parity, 1-ph states rather well. [Preview Abstract] |
Saturday, October 17, 2009 2:30PM - 2:45PM |
LL.00003: Disappearence of the N=14 Shell M.J. Strongman, T. Baumann, D. Bazin, N. Frank, S. Mosby, W.A. Peters, A. Schiller, A. Spyrou, M. Thoennessen, C.R. Hoffman, S.L. Tabor, J. Brown, P.A. DeYoung, J.E. Finck, W.F. Rogers The decay-energy spectrum of $^{22}$N was measured in a neutron-fragment coincidence experiment at the National Superconducting Cyclotron Laboratory at MSU. An excited state of $^{22}$N, unbound with respect to neutron emission measured by the Modular Neutron Array (MoNA), was observed in a stripping reaction from a secondary 85 MeV/u $^{26}$F beam. The observed decay energy of 650(50)~keV places the state, which is interpreted to be the first 3$^-$ level, at an excitation energy of 1.93(22)~MeV. Together with the previously measured bound states of $^{22}$N, the reduction of the N = 14 shell gap at the neutron dripline is observed. The magnitude of the reduction of the shell gap indicates the disappearance of the gap and even a possible reoccurrence of the inversion of the $\nu1s_{1/2}$ and the $\nu0d_{5/2}$ levels in the neutron-unbound nucleus $^{21}$C. [Preview Abstract] |
Saturday, October 17, 2009 2:45PM - 3:00PM |
LL.00004: The Structure of Neutron-rich $^{28,29}$Mg Studied through $\beta$-decay of Spin-polarized $^{28,29}$Na Beams at TRIUMF K. Tajiri, K. Kura, M. Kazato, M. Suga, A. Takashima, T. Hori, T. Masue, T. Suzuki, T. Fukuchi, A. Odahara, T. Shimoda, Y. Hirayama, N. Imai, H. Miyatake, M. Pearson, C.D.P. Levy, K.P. Jackson The structure of neutron-rich Mg isotopes in the region of Island of Inversion has been attracting much attention because of vanishing of \textit{N}=20 magic number and their large deformation in the ground states. However, most of the spins and parities of the excited states in Mg isotopes with \textit{A}$\geq$29 are left unknown. We have started systematic $\beta$-decay studies at TRIUMF, Canada, where highly spin-polarized radioactive Na beams are available. The experiment to determine the spins and parities of the states in $^{28,29}$Mg by using spin-polarized $^{28,29}$Na beams were performed at Osaka beam line in TRIUMF. The results are as follows: Many $\gamma$-transitions and energy levels were newly found in $^{28,29}$Mg. In $^{28}$Mg, spins and parities of the 4 levels reported previously were reconfirmed and those of the newly found 7.461 MeV level was assigned to be 2$^{+}$. In $^{29}$Mg, spins and parities of 3 energy levels were assigned for the first time. Shell model calculations were performed with NuShell code by using USD, USDA and USDB interactions to compare with the experimental results. In $^{29}$Mg, we also compared with MCSM calculation. The level structure in $^{28}$Mg was well explained by only sd-shell configurations. [Preview Abstract] |
Saturday, October 17, 2009 3:00PM - 3:15PM |
LL.00005: Medium to high spin spectroscopy of A = 30 - 40 neutron-rich nuclei at JAEA Tsuneyasu Morikawa, Eiji Ideguchi, Shinsuke Ota, Masumi Oshima, Mitsuo Koizumi, Yosuke Toh, Atsushi Kimura, Hideo Harada, Kazuyoshi Furutaka, Shoji Nakamura, Fumito Kitatani, Yuichi Hatsukawa, Toshiyuki Shizuma, Masahiko Sugawara, Hiroari Miyatake, Yutaka Watanabe, Yoshikazu Hirayama, Hideshige Kusakari Motivated by the recent progress in the RI-beam physics and the discovery of the island of inversion, a systematic investigation of the medium to high spin excited states in neutron-rich A = 30 $\sim$ 40 region has been underway as a cooperative study at the JAEA tandem accelerator facility. Since the evolution of shell structure is a function of nuclear deformation and rotation as well as the isospin, systematic understanding of the levels in this neutron-rich region is of great interest. Especially, the systematic identification of the high-spin levels involving the {sd} to {fp} cross-shell excitation could be a key to clarify the evolution of N = 20 neutron shell gap. We will present recent results on some neutron rich nuclei in this mass region and disscuss their shell structure. [Preview Abstract] |
Saturday, October 17, 2009 3:15PM - 3:30PM |
LL.00006: Triaxial deformation and shape coexistence in Ni and Cr isotopes studied by Antisymmetirzed Molecular Dynamics + Bogoliubov method Masaaki Kimura In this talk, I will introduce an extended version of Antisymmetrized Molecular Dynamics (AMD) and discuss the triaxial deformation and shape coexistence in Ni and Cr isotopes based on this extended framework. Recently, we have extended AMD to study the various phenomena in neutron-rich nuclei. By using localized Gaussian wave packets as the basis of quasi particle wave function, AMD is extended to include the pairing correlation (AMD+Bogoliubov). The use of Gaussian wave packets makes it easy to perform the parity and angular momentum projection and Generator Coordinate Calculation (GCM). Characteristic behavior of the 2$^{+}$ energies and B(E2) values in Ni and Cr isotopes have been experimentally observed. Theoretically, based on the shell model and beyond mean-field calculations, their behavior has been discussed in relation to a new magic number in neutron-rich nuclei, and possible triaxial deformation in several isotopes has been pointed out. We have applied AMD+Bogoliubov to Ni and Cr isotopes and the behavior of 2+ energies and B(E2) are reproduced well. It is found that most of isotopes have the shape coexistence and some manifest triaxial deformation. By comparing with the axial calculation, the importance of the triaxial deformation to understand the zigzag behavior of 2+ energies and B(E2) will be discussed. [Preview Abstract] |
Saturday, October 17, 2009 3:30PM - 3:45PM |
LL.00007: Band structures in neutron-rich $A \sim 60-80$ nuclei via deep-inelastic reactions with Gammasphere C.J. Chiara, I. Stefanescu, J.R. Stone, W.B. Walters, M.P. Carpenter, R.V.F. Janssens, B.P. Kay, F.G. Kondev, T. Lauritsen, C.J. Lister, E.A. McCutchan, D. Seweryniak, S. Zhu, R. Broda, B. Fornal, W. Krolas, T. Pawlat, J. Wrzesinski, N.J. Stone Several experiments have been performed at Argonne National Laboratory in the past few years using deep-inelastic reactions on thick $^{238}$U targets to produce neutron-rich nuclei in the $A \sim$ 60 to 80 mass region. Beams of 430-MeV $^{64}$Ni, 530-MeV $^{76}$Ge, and 630-MeV $^{82}$Se have been provided by the ATLAS facility at ANL. Gamma rays were detected with the Gammasphere Ge-detector array. Band structures have been newly observed in a number of neutron-rich nuclei [e.g., I. Stefanescu {\it et al.}, Phys. Rev. C {\bf 79}, 064302 (2009)]. In some cases, spin and parity assignments are strengthened by angular-correlation measurements. These observations can provide insights into the single-particle and collective properties of these nuclei. Highlights of this study will be presented. [Preview Abstract] |
Saturday, October 17, 2009 3:45PM - 4:00PM |
LL.00008: Shell-model description of $N=Z$, $A\sim 70$ nuclei Michio Honma, Takaharu Otsuka, Takahiro Mizusaki, Morten Hjorth-Jensen We present the results of shell-model calculations in the model space consisting of four single-particle orbits $1p_{3/2}$, $0f_{5/2}$, $1p_{1/2}$ and $0g_{9/2}$ using a new semi-microscopic effective interaction. The structure of $N=Z$ nuclei around $^{68}$Se is discussed focusing especially on the role of the $g_{9/2}$ orbit. The development of the band structure is interpreted in terms of successive excitations of nucleons into the $g_{9/2}$ orbit. The triaxial/$\gamma$-soft structure in $^{64}$Ge and the prolate/oblate shape-coexistence in $^{68}$Se are predicted, showing a good correspondence with the experimental data. The isomeric states in $^{66}$As and $^{70}$Br are obtained with the structure of an aligned proton-neutron pair in the $g_ {9/2}$ orbit. In spite of the modest model space, the new interaction turns out to describe rather well properties related to the $g_{9/2}$ orbit in various cases including moderately deformed nuclei. [Preview Abstract] |
Saturday, October 17, 2009 4:00PM - 4:15PM |
LL.00009: UMOA calculations for $^{16}$O, $^{40}$Ca, and $^{56}$Ni Ryoji Okamoto, Shinichiro Fujii, Kenji Suzuki One of the most fundamental problems in nuclear theory is to describe nuclear structure from the underlying nuclear interactions. The unitary-model-operator approach (UMOA) is an {\it ab initio} method which can describe the structure of nuclei beyond the $p$ shell using realistic nuclear forces. In the UMOA, the original Hamiltonian is unitarily transformed, and thus three-or-more-body cluster terms are generated even if we employ only the two-body force as the original interaction. In this work, the UMOA is applied to nuclei around $^{16}$O, $^{40}$Ca, and $^{56}$Ni. The ground-state and single-particle energies for hole states of those nuclei including three-body-cluster effects are calculated with realistic nucleon-nucleon interactions. We show that the calculated results are fairly close to the experimental values. The dependence of the results on the two-body interactions and effects of the genuine three-body force are also discussed. [Preview Abstract] |
Saturday, October 17, 2009 4:15PM - 4:30PM |
LL.00010: Nuclear Structure and Decay Data Evaluation: Status and Perspectives F.G. Kondev, E. Browne, C. Ouellet, B. Pritychenko, C. Reich, A. Sonzogni, S. Tandel, J.K. Tuli, J. Cameron, A. Chen, B. Singh, J. Kelley, E. Kwan, C. Baglin, M.S. Basunia, R.B. Firestone, N. Nica, C.D. Nesaraja, M.S. Smith Reliable nuclear structure data represent the fundamental building blocks of nuclear structure physics and astrophysics research, and are also of vital importance in a large number of applications. Members of the Nuclear Structure and Decay Data Working Group of the U.S. Nuclear Data Program, in collaboration with scientists from Japan and other countries within the International Nuclear Structure and Decay Data Network (under the auspices of IAEA), are involved in compilation, evaluation, and dissemination of nuclear structure and decay data for all known nuclei. The network's principal effort is devoted to the timely revision of information in the Evaluated Nuclear Structure Data File (ENSDF) library, which is the only comprehensive nuclear structure and decay data database that is updated continuously. This presentation will briefly review recent achievements of the network, present on-going activities, and reflect on ideas for future projects and challenges in the field of nuclear structure and decay data evaluation. [Preview Abstract] |
Saturday, October 17, 2009 4:30PM - 4:45PM |
LL.00011: Search for High-Spin Isomer in $^{142}$Pr by RI Beam Induced Fusion Reaction at RCNP A. Takashima, M. Suga, K. Kura, K. Tajiri, M. Kazato, Y. Kenmoku, Y. Ito, K. Yamaguchi, K. Kurata, J. Takatsu, A. Odahara, T. Shimoda, S. Go, E. Ideguchi, Y. Gono, S. Nishimura, H. Watanabe, C. Pertache, T. Suzuki, Y. Wakabayashi Systematic studies of high-spin shape isomers in $N$=83 isotones provided interesting information on the properties of pairing interactions. The high-spin isomer in $^{142}$Pr, which is not effectively populated by any combinations of stable beams and targets, was searched for in the fusion reaction induced by RI beam, $^{130}$Te($^{17}$N, 5n)$^{142}$Pr, at RCNP, Osaka Univ. The $^{17}$N beam was produced in the $^{9}$Be ($^{18}$O, $^{17}$N) $^{10}$B reaction at 9.1 MeV/u. Gamma-rays at the secondary target were detected by a RCNP Ge array consisting of 14 HPGe detectors. Contaminant $\gamma$-rays due to $\beta$-decay of $^{17}$N and the natural activities could be eliminated with the coincidence requirement that the $^{17}$N particles were detected in the PPAC. The $^{17}$N beam of $\sim$10$^{5}$ pps has been obtained with energy of $\sim$4.2 MeV/u. In the preliminary analyses, clearly seen were the $\gamma$-rays deexciting the states with spins up to 21/2 in $^{141}$Pr and the reported $\gamma$-rays after the decay of (9+) isomer with $T_{1/2}$=61 ns in $^{142}$Pr. The results of $\gamma\gamma$ coincidence analyses searching for the isomers will be presented. [Preview Abstract] |
Saturday, October 17, 2009 4:45PM - 5:00PM |
LL.00012: Study of Density and Structure of Oxygen Isotopes with the Cluster-Orbital Shell Model Approach Hiroshi Masui, Kiyoshi Kato, Kiyomi Ikeda We study structure of oxygen isotopes through the analysis of the density and the $s$-wave contribution. From experiments, the r.m.s.radius of oxygen isotopes has an abrupt increase at $^{23}$O from the empirical $A^{1/3}$-low. However, as we have shown with the calculation by using our m-scheme cluster-orbital shell model (COSM) approach, such the abrupt increase can hardly be reproduced only by considering the valence nucleon degree of freedom. In our COSM approach, we construct the core-N Hamiltonian using a semi-microscopic approach by taking into account the Pauli principle for the nucleons in the core. As the nucleon-nucleon potential, we use Volkov No.2 potential. The parameters of the potential are adjusted so as to reproduce the $^{16}$O+2$n$ threshold. Using the potential model described above, however, we obtain the over bound nature as the number of valence nucleon increase. Hence, we perform calculations using slightly weaker potential strength for the valence neutrons so as to reproduce the drip-line at $^{24}$O. In this study, we discuss the density distributions of the isotopes and the contributions of partial waves especially the $s$-wave. [Preview Abstract] |
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