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 CG: Mini-Symposium on Decay Spectroscopy of Exotic Nuclei I |
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Chair: Sean Liddick, National Superconducting Cyclotron Laboratory/Michigan State University Room: King's 3 |
Wednesday, October 8, 2014 7:00PM - 7:30PM |
CG.00001: Recent work of decay spectroscopy at RIBF Invited Speaker: P\"{a}r-Anders S\"{o}derstr\"{o}m $\beta$- and isomer-decay spectroscopy are sensitive probes of nuclear structure, and are often the only techniques capable of providing data for exotic nuclei that are producted with very low rates. Decay properties of exotic nuclei are also essential to model astrophysical events responible for the evolution of the universe such as the rp- and r-process. The EURICA project (EUROBALL RIKEN Cluster Array) has been launched in 2012 with the goal of performing spectroscopy of very exotic nuclei. Since 2012, four experimental campaigns have been successfully completed using fragmentation of $^{124}$Xe beam and in-flight-fission of $^{238}$U beam, approaching for example the key nuclei $^{78}$Ni, $^{110}$Zr, $^{100}$Sn, $^{128}$Pd, and $^{138}$Sn. This contribution highlights the experiments performed, results obtained, and discusses the future perspective of the EURICA project.\\[4pt] In collaboration with Shunji Nishimura, Hidetada Baba, RIKEN Nishina Center; Frank Browne, Brighton University; Pieter Doornenbal, RIKEN Nishina Center; Guillaume Gey, Universite Joseph Fourier Grenoble; Tadaaki Isobe and Giuseppe Lorusso, RIKEN Nishina Center; Daniel Lubos, Technische Universitat Munchen; Kevin Mochner, University of Cologne; Zena Patel and Simon Rice, University of Surrey; Hiroyoshi Sakurai, RIKEN Nishina Center; Laura Sinclair, University of York; Toshiyuki Sumikama, Tohoku University; Jan Taprogge, Universidad Autonoma de Madrid; Zsolt Vajta, MTA Atomki; Hiroshi Watanabe, Beihang University; Jin Wu, Peking University; and Zhengyu Xu, University of Tokyo. [Preview Abstract] |
Wednesday, October 8, 2014 7:30PM - 7:45PM |
CG.00002: Study of structure change in neutron-rich Mg isotopes by spin-polarized radioactive beam Hiroki Nishibata, Tadashi Shimoda, Atsuko Odahara One of the important subjects in recent nuclear physics studies is the nuclear structure change as a variety of neutron number. In particular, island of inversion in the neutron-rich mass region around $^{32}$Mg has been attracting much attention. However, the experimental information, such as spins and parities, which are the key quantities to understand the nuclear structure, has not been known well. The detailed level structures of neutron-rich Mg isotopes have been studied by using highly-spin-polarized Na beam at ISAC in TRIUMF. We have obtained the revised and detailed level schemes of $^{28-30}$Mg. These results indicate structure change in neutron-rich Mg isotopes; normal configurations are dominant in $^{28}$Mg, candidates of two intruder levels with negative parity were identified in $^{29}$Mg, and the some levels of two different shapes and one candidate of $\gamma$ vibrational state were found in $^{30}$Mg. For the next step, we will perform an experiment for $^{31}$Mg. The existence of various nuclear structures is also expected in $^{31}$Mg which locates inside island of inversion. The systematic structure change in Mg isotopes together with the preliminary results of $^{31}$Mg will be discussed. [Preview Abstract] |
Wednesday, October 8, 2014 7:45PM - 8:00PM |
CG.00003: Shape evolution in neutron-rich $A \sim 140$ nuclei beyond the doubly-magic nucleus $^{132}$Sn Atsuko Odahara Study for the shape evolution enables us to disentangle competition between spherical (single-particle like) shape and deformed (collective-like) shape as a function of neutron number. Neutron-rich nuclei in the northeast region of the doubly-magic $^{132}$Sn locates in one of the best mass region where a variety of collective modes, not only prolate deformation but also octupole collectivity, are expected to appear. These neutron-rich $A$$\sim$140 nuclei were produced by using in-flight fission reaction of the 345 MeV/u $^{238}$U$^{86+}$ beam at RIKEN RI Beam Factory. This experiment was performed in the framework of the EURICA (EUroball RIken Cluster Array) project based on the highly-efficient $\beta$- and isomer- decay spectroscopy methods. Around 20 extremely neutron-rich nuclei with $Z$=51-55 have been studied in this work. New isomers with half lives of longer than hundreds ns were found in some nuclei, such as the neutron-rich Cs isotopes. Also, preliminary results for the $\beta$ decay of neutron-rich I and Xe isotopes have been obtained. Systematic change of the shape evolution for these neutron-rich isotopes will be discussed. [Preview Abstract] |
Wednesday, October 8, 2014 8:00PM - 8:15PM |
CG.00004: $\beta$-decay half-lives of neutron-rich nuclei at $A\sim110$ on r-process path Ippei Nishizuka, Toshiyuki Sumikama, Frank Browne, Alison Bruce, Shunji Nishimura, Pieter Doornenbal, Giuseppe Lorusso, Zena Patel, Simon Rice, Laura Sinclair, Par-Anders Soderstrom, Hiroshi Watanabe, Jin Wu, Zhengyu Xu, Ayumi Yagi About half of the elements heavier than iron are thought to be produced by rapid-neutron capture process (r-process). The observed natural abundance in solar system was underestimated by a theoretical model at $A\sim 110$, which uses $\beta$-decay half-lives. In the present study, we measured new $\beta$ half-lives of neutron-rich nuclei on r-process path at RIBF in RIKEN. The nuclei of interest were produced by in-flight fission of uranium beam in beryllium target. The WAS3ABi detector which was 5 stacked double-sided silicon strip detectors ($60 \times 40 \times 1$ mm$^3$), was used for the implantation of ions and the detection of both the implanted ions and the subsequently-emitted $\beta$ rays. It is essential to make a position correlation between the mother nucleus and the $\beta$ rays. In this talk, the analysis of the position correlation will be presented in detail. Preliminary results will be also shown. [Preview Abstract] |
Wednesday, October 8, 2014 8:15PM - 8:30PM |
CG.00005: Structure of neutron-rich Zn isotopes Megumi Niikura A $\beta$-decay spectroscopy experiment in the closest vicinity of $^{78}$Ni was performed at RIBF as a part of the EURICA campaign. The low-lying level structure in odd-mass isotonic chain along the neutron magic number of $N=50$ is determined by the neutron single-particle evolution with decreasing proton number. Some reduction of the neutron single-particle energy gap between $2d_{5/2}$ and $3s_{1/2}$ orbitals was already indicated by the $\beta$-decay studies on $^{83}$Ge$_{32}$. Theoretical models, that have attempted to extend this evolution towards $^{78}$Ni, are not yet in agreement. We have performed the $\beta$-decay measurement of neutron-rich Cu isotopes in order to determine the low-lying level structure in Zn istopes which have only two valence protons above $^{78}$Ni. In this contribution, the newly constructed level schemes of $^{79-81}$Zn will be presented. The shell structure and its evolution based on the comparison with shell-model calculations will also be discussed. [Preview Abstract] |
Wednesday, October 8, 2014 8:30PM - 8:45PM |
CG.00006: $\beta$-$\gamma$ spectroscopy of neutron-rich ${}_{60}$Nd isotopes Mana Tanaka, Eiji Ideguchi, Gary Simpson, Rin Yokoyama, Shunji Nishimura, Pieter Doornenbal, P\"ar-Anders S\"oderstr\"om, Giuseppe Lorusso, Zhengyu Xu, Jin Wu, Toshiyuki Sumikama In the neutron-rich part of nuclear landscape around $Z=60$ and beyond $N=90$, evolution of the quadrupole deformations and more higher-order deformations have been predicted. A systematic study of excited states will allow us to elucidate such shape phenomena. This experimental work has been carried out utilizing neutron-rich $Z\sim60$ RI beams available at RIKEN RIBF and a high-efficient $\gamma$-ray spectrometer, EURICA. Isomer and $\beta$-$\gamma$ spectroscopy were performed using a passive stopper and the WAS3ABi active stopper. In our previous isomer spectroscopy of heavy ${}_{60}$Nd isotopes, $K$ isomers and their decay to the ground state rotational bands were systematically observed, which indicate the development of axial-symmetric prolate deformation with increasing neutron numbers. In order to further understand the deformed structure, analysis of $\beta$-$\gamma$ spectroscopy data is on going. By these analysis, spins and parities of ground states in odd-mass Nd isotopes will be examined and non-yrast levels will be elucidated, which reflect the deformation and configuration. In this presentation, latest results of our data analysis will be shown. [Preview Abstract] |
Wednesday, October 8, 2014 8:45PM - 9:00PM |
CG.00007: Study of shape evolution in very neutron-rich Cs isotopes A. Yagi We have searched for the isomers in neutron-rich Cs isotopes of $^{144-148}$Cs in one of the EURICA campaign experiments at RIBF in RIKEN, in order to investigate the shape evolution in the very neutron-rich Cs isotopes. The isomers were produced using the in-flight fission reaction of the 345 MeV/u $^{238}$U$^{86+}$ beam. The fragment separator system consisting of BigRIPS and Zero Degree Spectrometer (ZDS) was tuned for the neutron-rich Sb, Te, I, Xe and Cs isotopes with $A=$140-150. The isotopes were implanted into a stack of 5 double-sided Si strip detectors (WAS3ABi). The beta ray and gamma ray emitted from the stopped isotopes were detected by WAS3ABi and EURICA, respectively. Event-by-event unambiguous particle identification was achieved by careful analyses using the ion-optics matrices as well as the Delta E information from the ion chambers and the timing information from the plastic scintillators. The isomers in $^{145}$Cs, $^{146}$Cs, $^{147}$Cs, $^{148}$Cs were observed for the first time. Isomers in odd-odd $^{146}$Cs, $^{148}$Cs could be explained to be caused by the low-energy transition. On the other hand, isomers in odd $^{145}$Cs, $^{147}$Cs are supposed to be candidate of $K$ isomer, which indicate that these nuclei have prolate deformation. [Preview Abstract] |
Wednesday, October 8, 2014 9:00PM - 9:15PM |
CG.00008: ABSTRACT WITHDRAWN |
Wednesday, October 8, 2014 9:15PM - 9:30PM |
CG.00009: Shape evolution in neutron-rich Te isotopes beyond the doubly-magic $^{132}$Sn P.S. Lee, C.S. Lee, C.-B. Moon, A. Odahara We investigated the internal structure of very neutron-rich Te nuclei for evaluating the nuclear shell evolution above one of the doubly-magic shell closures; Z $=$ 50 and N $=$ 132, $^{132}$Sn. The very neutron-rich nuclides beyond Z \textgreater 50 and N \textgreater 132 were produced following the stopped beam formed by the fission fragmentation between an $^{238}$U beam with 375A MeV and a $^{9}$Be production target at the BigRIPS with a mono energetic degrader, allowing the selection of specific elemental residues in a position-sensitive, and a stack of double-sided silicon strip detectors (DSSD) as an active stopper. By using unambiguous channel selection based on the detection of subsequent beta decays of the neutron-rich reaction products correlated with the implanted ions, we made subsequent gamma-ray spectroscopic measurements in a daughter of interest with the EURICA array in its stopped-beam configuration. In the present work, we report the excited state in the $^{140}$Te isotope. This observation offers an important information on the shape evolution indicating a phase transition from a single-particle mode to collective modes of the Te isotopes. Besides, the beta decay half-lives of $^{138-140}$Sb were deduced with detecting beta particles and gamma rays from their daughter nuclides. [Preview Abstract] |
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