Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session DD: Mini-Symposium: The Structural Diversity of Nuclei in the Proximity of N=20 and 28 I |
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Chair: Daniel Bazin, Michigan State University Room: Hilton Kohala 3 |
Thursday, October 25, 2018 9:00AM - 9:30AM |
DD.00001: Exotic Isotopes of Magnesium Invited Speaker: Heather L Crawford The structure of nuclei in the vicinity of expected nuclear shell closures away from stability has been, and continues to be, a cornerstone for nuclear structure study. The confirmation of certain ‘magic numbers’ in exotic nuclei provides insight into the evolution of nucleon configurations with isospin, but perhaps even more light is shed into the structure of the atomic nucleus when expected shell closures are found to be weakened, or entirely disappear. The competition between monopole shifts of single particle energies and pairing plus quadrupole correlations leads to competition between spherical and deformed configurations. Around 32Mg the change in effective single particle spacing reduces the N=20 shell gap and the deformed intruder configuration, with neutron pairs promoted from the sd to the fp shell, is energetically favoured. Recent experimental work in the Mg isotopes has suggested a chain of prolate-deformed nuclei along Z=12, extending to N=28 and 40Mg, where there is a similar development of deformation along the isotonic chain below 48Ca, with the removal of protons driving rapid shape oscillations between the N=28 nuclei. I will give an overview of our knowledge in this part of the nuclear landscape, and discuss the latest experimental results in this region between N=20 and N=28, focusing on the Mg isotopes, and the evolution of their structure with spin, isospin and binding energy. |
Thursday, October 25, 2018 9:30AM - 9:45AM |
DD.00002: Study of neutron-rich nuclei via nuclear force and microscopic theory Naofumi Tsunoda, Takaharu Otsuka, Noritaka Shimizu, Kazuo Takayanagi, Morten Hjorth-Jensen, Toshio Suzuki Kuo-Kurenciglowa (KK) method is a successful many body perturbation theory to construct the effective interaction for the shell model calculations, but has only been for the model space composed of single major shell. We will then present the Extended Kuo-Krenciglowa (EKK) method which enables us to obtain the effective interaction for multi major shell. We will further discuss the applications of this effective interaction to the neutron-rich nuclei including the "island of inversion", where excitations beyond N=20 gap is important. Numbers of empirical effective interactions in this area have been proposed. However, not enough experimental information is obtained yet to fix the parameters in those interactions. In this point of view, comparisons to most recent experiments are shown to clarify what features of our microscopic interaction are different from those of empirical one. |
Thursday, October 25, 2018 9:45AM - 10:00AM |
DD.00003: Core-Excitations in the Ground States of the Neutron-Rich Fluorine Isotopes. Michael David Jones, Heather L Crawford, Christopher M Campbell, Roderick M Clark, Paul Fallon, Mario Cromaz, I-Yang Lee, Augusto O Macchiavelli, Marco Salathe, Daniel Bazin, Alexandra Gade, Dirk W Weisshaar, Peter C Bender, Jason D Holt, Jeff Tostevin, Robert V F Janssens The breakdown of classical shell structure and the appearance of new magic numbers in nuclei with extreme N/Z ratios provide a valuable testing ground for shell-model and ab-initio descriptions. A recent experiment designed to study the evolution of core excitations in the ground states of the neutron-rich Fluorine isotopes was performed at the NSCL with GRETINA and the S800.
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Thursday, October 25, 2018 10:00AM - 10:15AM |
DD.00004: In-beam gamma-ray spectroscopy of F and Ne isotopes near the island of inversion Masahiro Yasuda, Yosuke Kondo, Takashi Nakamura It is known that neutron magic number N=20 disappears in the region of Z=10~12. Study of nuclei in this region, called "island of inversion”, is important for understanding the evolution of shell structure in the neutron-rich region. Currently the south boundary of the island of inversion is not known because available experimental data on neutron-rich F and Ne is not sufficient. We performed in-beam gamma-ray spectroscopy of 29F, 28-30Ne at the RIKEN RI Beam Factory. Secondary beams of 29F, 29,30Ne (~230MeV/u), generated by projectile fragmentation of a 48Ca primary beam on a beryllium target, were impinged on 15cm thick liquid-hydrogen target provided by MINOS. The de-excitation gamma rays were detected with the NaI(Tl) scintillator array DALI2. Outgoing particles were identified by the SAMURAI spectrometer. We investigated high-lying excited states based on gamma-gamma coincidence analysis. In case of nucleon-removal reactions of 29,30Ne and 30Na partial cross sections have also been investigated. In this presentation, we discuss the nuclear structure of these nuclei. This work was done with SAMURAI 21 collaboration. |
Thursday, October 25, 2018 10:15AM - 10:30AM |
DD.00005: Neutron Unbound States in the Island of Inversion Dayah Chrisman, Thomas Baumann, Paul A Deyoung, Nathan Frank, Anthony N Kuchera, John McDonaugh, Robbie Seaton-Todd, William vonSeeger, the MoNA Collaboration The area of the nuclear chart where the N=20 shell gap disappears is within an "island of inversion.” These nuclei are short-lived and require radioactive beams in order to study them and their neutron-unbound excited states. An experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL) to study the unique nuclear structure characteristics of various neutron rich nuclides with A/Z ~ 3, aiming to populate neutron-unbound excited states. MoNA-LISA and the Sweeper magnet were used to perform invariant mass spectroscopy. Preliminary experimental results will be discussed. |
Thursday, October 25, 2018 10:30AM - 10:45AM |
DD.00006: Coulomb breakup reaction of 31Ne and its halo structure Takato Tomai, Takashi Nakamura, Yasuhiro Togano, Yosuke Kondo, Nobuyuki Kobayashi, Hiroki Yamada, Masahiro Yasuda, Mayuko Matsumoto, Tetsuro Shimada It is well known that N=20 shell gap disappears in the "island of inversion." The one-neutron halo nucleus 31Ne, located in the island of inversion, has attracted much attention because it is the first example of a deformation-driven halo nucleus. Recent experimental studies on 31Ne revealed that it has low separation energy Sn=0.15(+0.16)(-0.10) MeV, spectroscopic factor C2S=0.32(+0.21)(-0.17), and ground-state spin and parity 3/2-. This results show that 31Ne is significant p-wave halo component. We have carried out the exclusive Coulomb breakup measurement of 31Ne for the first time using the invariant mass method. The new data enables us to determine the neutron separation energy and spectroscopic factor more precisely than the values determined by the inclusive Coulomb breakup measurement. Coulomb breakup measurement using 31Ne beam at 230 MeV/u with a lead target was performed using SAMURAI spectrometer at RIBF, RIKEN. In this presentation, the experimental results will be discussed. |
Thursday, October 25, 2018 10:45AM - 11:00AM |
DD.00007: Reaction and lifetime studies of 32Mg through 2-proton knockout Robert Elder, Hironori Iwasaki, John Ash, Daniel Bazin, Peter C Bender, Thomas Braunroth, Christopher M Campbell, Heather L Crawford, Brandon Elman, Alexandra Gade, Mara Grinder, Nobuyuki Kobayashi, Charles R Loelius, Brenden Longfellow, Eric Lunderberg, Tea Mijatovic, Jorge Pereira, Daniel Rhodes, Dirk W Weisshaar In the Island of Inversion at N = 20, ground states are dominated by intruder configurations with particle-hole excitations across the shell gap instead of normal 0p0h configurations. For example in 32Mg the yrast band appears to be deformed instead of spherical, indicating that intruder configurations are preferred compared to the normal closed-shell configuration. Until recently, 32Mg had been understood in terms of the competition between the 0p0h and 2p2h configurations but this picture predicts a higher energy and lower (t, p) cross section for the isomeric 0+2 state than was observed. To understand the importance of including the 4p4h configuration we performed reaction and lifetime studies of 32Mg by means of 2p knockout from 34Si at the NSCL. Gamma-ray energy and position information measured by GRETINA was used along with various lifetime measurement techniques that cover a range of possible lifetimes. New results are presented and discussed in the context of competition between normal and intruder configurations. |
Thursday, October 25, 2018 11:00AM - 11:15AM |
DD.00008: Structure of neutron-rich 31Mg by β-decay spectroscopy of spin-polarized 31Na Hiroki Nishibata, Shinnosuke Kanaya, Tadashi Shimoda, Atsuko Odahara, Shota Morimoto, Ayumi Yagi, Hiroshi Kanaoka, Matthew Pearson, Phil Levy, Masaaki Kimura, Naofumi Tsunoda, Takaharu Otsuka The structure of neutron-rich nuclei around the N=20 “island of inversion” has been attracting much attention because of the prevalence of intruder nature and persistence of spherical structure. Recent theories predicted possible shape coexistence in Mg isotopes due to subtle competitions between the spherical mean field and the nuclear correlation, which causes deformation. Even after a variety of experimental studies, the experimental information, in particular spin-parity of excited states, is not yet available in these nuclei. Such a situation prevents us from discussing the nuclear structure. |
Thursday, October 25, 2018 11:15AM - 11:30AM |
DD.00009: ABSTRACT WITHDRAWN
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