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 ED: Mini-Symposium: The Structural Diversity of Nuclei in the Proximity of N=20 and 28 II |
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Chair: Michael D. Jones, University of North Carolina Room: Hilton Kohala 3 |
Thursday, October 25, 2018 7:00PM - 7:15PM |
ED.00001: Large-scale shell-model calculations for deformed states around 40Ca Yutaka Utsuno, Takatoshi Ichikawa, Noritaka Shimizu, Takaharu Otsuka The deformed band in 40Ca is one of the classical examples of shape coexistence studied more than half a century. This band is considered as states associated with 4p-4h excitation across the N=Z=20 shell gap. In the last decades, while a number of similar 4p-4h (or 4ħω) states are observed around 40Ca, including 36,38,40Ar, 42Ca, and 44Ti, by the state-of-the-art γ-ray spectroscopy, successful systematic calculations for these deformed bands are still missing. In this study, we carry out systematic large-scale shell-model calculations for these 4ħω states. The valence shell consists of the full sd shell plus f7/2+p3/2 orbitals, and the model space is truncated to cover the configurations up to 6ħω excitations. The SDPF-M interaction is used for the initial choice of the effective interaction, and it is modified so that one-neutron separation energies of 40,41Ca and α separation energies of 44Ti and 40Ca are reproduced. This is based on a natural requirement that the N=Z=20 gap and correlation energies within the major shells are preserved in theory. It is shown that the resulting 4ħω states are well reproduced. |
Thursday, October 25, 2018 7:15PM - 7:30PM |
ED.00002: Search for the 1/2_2 intruder bandhead in 35P Marco Salathe, ANL1637 Collaboration Particle-hole sd-pf cross-shell intruder configurations have been observed in the low-lying level scheme of N = 20 even-even nuclei near the Island of Inversion centered around 32Mg. However, the expected 1/2_2 intruder bandhead has not yet been identified in the odd-even nucleus 35P. Previous attempts to identify this state suffered from a large background in the region of interest arising from contaminants in the target. |
Thursday, October 25, 2018 7:30PM - 7:45PM |
ED.00003: Shell structure study on 43S via one-neutron knockout reaction Satoru Momiyama South of 48Ca in the nuclear chart, the erosion of the neutron magic number 28 has been observed.
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Thursday, October 25, 2018 7:45PM - 8:00PM |
ED.00004: Nuclear Spectroscopy of 44,46Ca with Fusion Reactions Induced by Reaccelerated Rare-isotope Beams John Ash, Hironori Iwasaki, Tea Mijatovic, Robert Elder, Mara Grinder, Dirk W Weisshaar, Alexandra Gade, Mark Spieker, Brandon Elman, Brenden Longfellow, Daniel Rhodes, Ching-Yen Wu, Jack Henderson Fusion reactions provide powerful tools to study medium- and high- spin states in a variety of nuclei. With the advent of reaccelerator facilities, rare-isotope beams could provide sufficient intensity to take advantage of this reaction mechanism. Detailed investigation is necessary to evaluate the experimental feasibility of this novel approach; therefore, two studies using beams of stable 40Ar and neutron-rich 45K on a lithium target were performed to access nuclei in the region of 40-48Ca using the ReA3 complex at NSCL. One particular nucleus of interest in the present measurement is 46Ca, where high spin states (J > 6) require neutron particle-hole excitations across the N=28 shell gap. Little is known of such band structures in heavier calcium isotopes, whereas deformed bands associated with intruder configurations have been found on excited 0+ states in 40,42Ca. Using particle and gamma coincidence techniques, reaction channels can be selected to search for unknown transitions. New results are presented and discussed in terms of the shell structure and collective properties in this region. |
Thursday, October 25, 2018 8:00PM - 8:15PM |
ED.00005: Charge radii of neutron-deficient 55, 56Ni K. Minamisono, D. M. Rossi, N. Everett, D. Garand, R. P. de Groote, P. Imgram, C. Kalman, A. Klose, J. D. Lantis, Y. Liu, P. F. Mantica, A. J. Miller, W. Nazarewicz, W. Nörtershäuser, R. C. Powel, P. -G. Reinhard, E. Romeo-Romero, F. Sommer, C. Sumithrarachchi, A. Teigelhöfer The 56Ni nucleus is doubly magic with the neutron number N = 28, which occurs due to a shell gap driven by the spin-orbit force, but is considered to be a soft core. The mean-square charge radii <r2> were determined for 55, 56Ni using collinear laser spectroscopy technique at BECOLA at NSCL/MSU to investigate how the softness manifests itself in <r2> at and below N = 28, and to benchmark nuclear theories. Details of the experiment and preliminary results will be presented. |
Thursday, October 25, 2018 8:15PM - 8:30PM |
ED.00006: Charge radii of neutron-deficient 36,37,38Ca Andrew Jacob Miller, Kei Minamisono, Andrew Klose, B. Alex Brown, Robert Charles Powel, Witold Nazarewicz, David M. Garand, Chandana Sumithrarachchi, Jacob Watkins, Bernhard Maaβ, Wilfried Nörtershäuser, Dominic M. Rossi, Cody Kujawa, Skyy Pineda, Jeremy D. Lantis, Yuan Liu, Paul F. Mantica, Matthew R. Pearson, Andrea Teigelhöfer, P. -G. Reinhard The mean-square charge radii, <r2>, of neutron-deficient 36,37,38Ca below the neutron number N = 20 were determined at the BEam COoler and LAser spectroscopy (BECOLA) facility at NSCL/MSU, using the collinear laser spectroscopy technique. The obtained <r2> are in the vicinity of the proton dripline and impose new challenges on state-of-the-art models, as the coupling of pairing correlations to the continuum becomes critical. The overall behavior of the chain of Ca <r2> across N = 20 and 28 will be discussed, together with the newly determined electromagnetic moments of 37Ca. |
Thursday, October 25, 2018 8:30PM - 8:45PM |
ED.00007: Electric dipole response of $^{50,52}$Ca Yasuhiro Togano The low-energy electric dipole excitation-mode, sometimes called as pygmy dipole resonance (PDR), located at $6 \sim 10$~MeV was extensively studied. However, its structure is not yet clear. The recent theoretical work showed that the PDR strengths are enhanced at $^{48-54}$Ca [1], and it is due to the occupation of low angular-momentum orbit by the valence neutrons. To investigate the evolution of PDR in these Ca isotopes experimentally, the relativistic Coulomb excitation of $^{50,52}$Ca was performed.
The experiment was performed at RIKEN RIBF. The incoming $^{50,52}$Ca beams were impinged on Pb and C targets. The outgoing charged-particles and neutrons were measured by SAMURAI spectrometer and neutron detectors, respectively. The neutron detectors were the combination of NEBULA and the NeuLAND demonstrator. The de-excitation gamma-ray from the reaction residue was measured by the CsI(Na) array CATANA and LaBr$_3$ detectors. In this talk, we will report on the dipole response of $^{50,52}$Ca close to the one-neutron separation energy.
[1] T. Inakura et al., Phys. Rev. C 84, 021302(R) (2011). |
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