Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session DD: Nuclear Structure II |
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Chair: Michael Carpenter, Argonne National Laboratory Room: Salon 4 |
Thursday, October 26, 2017 10:30AM - 10:42AM |
DD.00001: Charge radii of neutron-deficient Ca isotopes A. J. Miller, K. Minamisono, A. Klose, N. Everett, C. Kalman, R. C. Powel, J. Watkins, D. Garand, C. Sumithrarachchi, J. Kr{\"a}mer, B. Maa$\ss$, W. N{\"o}rtersh{\"a}user, D. M. Rossi, C. Kujawa, S. Pineda, J. Lantis, Y. Liu, P. F. Mantica, M. R. Pearson Nucleon shell closures are generally associated with a local minimum in mean-square charge radii, $\left |
Thursday, October 26, 2017 10:42AM - 10:54AM |
DD.00002: Analysis of the $^{48}$Ca neutron skin using a nonlocal dispersive-optical-model self-energy Mack Atkinson, Hossein Mahzoon, Willem Dickhoff, Robert Charity A nonlocal dispersive-optical-model (DOM) analysis of the $^{40}$Ca and $^{48}$Ca nuclei has been implemented. The real and imaginary potentials are constrained by fitting to elastic-scattering data, total and reaction cross sections, energy level information, particle number, and the charge densities of $^{40}$Ca and $^{48}$Ca, respectively. The nonlocality of these potentials permits a proper dispersive self-energy which accurately describes both positive and negative energy observables. $^{48}$Ca is of particular interest because it is doubly magic and has a neutron skin due to the excess of neutrons. The DOM neutron skin radius is found to be $r_{skin} = 0.245$, which is larger than most previous calculations. The neutron skin is closely related to the symmetry energy which is a crucial part of the nuclear equation of state. The combined analysis of $^{40}$Ca and $^{48}$Ca energy densities provides a description of the density dependence of the symmetry energy which is compared with the $^{48}$Ca neutron skin. Results for $^{208}$Pb will also become available in the near future. [Preview Abstract] |
Thursday, October 26, 2017 10:54AM - 11:06AM |
DD.00003: Identifying the T=5 states in $^{48}$Ca Sriteja Upadhyayula, Sunghoon Ahn, Maria Anastasiou, Shadi Bedoor, Justin Browne, Jeffrey Blackmon, Catherine Deibel, Ashley Hood, Joshua Hooker, Curtis Hunt, Yevgen Koshchiy, Jon Lighthall, Wei Jia Ong, Nabin Rijal, Grigory Rogachev, Daniel Santiago-gonzalez, Ingo NSCL, Michigan State University Particle-hole excitations near closed shells carry information on single-particle energies and on two-body interactions. The particle-hole excitations near the doubly magic nuclei are of special interest. Information on the charge-changing particle-hole excitations (T=5 negative parity states) in $^{48}$Ca is not available. We performed an experiment to establish the level scheme of the low-lying negative parity T=5 states in $^{48}$Ca. Excitation functions for the $^{1}$H($^{47}$K,p)$^{47}$K(g.s.) and $^{1}$H($^{47}$K,p)$^{47}$K(3/2$^+$) reactions in the c.m. energy range from 1 MeV to 4.5 MeV were measured. The T=5 states are expected to show up in the p+$^{47}$K excitation function as narrow resonances. This experiment was performed at NSCL using the ReA3 beam of $^{47}$K at energy of 4.6 MeV/u. ANASEN, set in active target mode, was used for this experiment. Experimental results from this experiment will be presented. [Preview Abstract] |
Thursday, October 26, 2017 11:06AM - 11:18AM |
DD.00004: Selection Rules for $^{\mathrm{48}}$Cr Arun Kingan, Michael Quinonez, XiaoFei Yu, Larry Zamick In the single j shell $^{\mathrm{48}}$Cr is the first even-even nucleus for which there are T$=$0 (isoscalar) J$=$1$^{\mathrm{+}}$ states and T$=$1 J$=$0$^{\mathrm{+}}$ states. These states are studied here. This nucleus, in the f$_{\mathrm{7/2}}$ model space, is mid-shell for both neutrons and protons and this leads to many selection rules. Even though seniority is a good quantum~number for identical particles in this shell this~is in~general not true for a system of both~neutrons and protons. Thus,~in $^{\mathrm{48}}$Cr neither the seniority of the neutrons, the protons or the total are good quantum numbers. However S$=$(-1)\textasciicircum ((v$_{\mathrm{p}}+$v$_{\mathrm{n}})$/2) is a good quantum number. Non-zero B(M1) require that S does not change, but for nonzero B(E2)'s~S must change sign. A scissors mode like excitation~involving both spin and orbit is identified. [Preview Abstract] |
Thursday, October 26, 2017 11:18AM - 11:30AM |
DD.00005: Enhanced $\alpha$-Transfer population of the $2^{+}_{ms}$ mixed-symmetry state in $^{52}$Ti Fuad A. Ali, Dennis Muecher, Vinzenz Bildstein, Beau Greaves, Ali. I. Kilic, Jason D. Holt, Christian Berner, R. Gernhaeuser, K. Nowak, S. Hellgartner, R. Lutter, S. Reichert The residual nucleon-nucleon interaction plays a crucial role in nuclear structure physics. In spherical even-even nuclei the quadrupole interaction leads to so called proton-neutron mixed symmetry states, which are sensitive to the underlying subshell structure. We present new data using the MINIBALL germanium array. States in $^{52}$Ti were populated via the $\alpha$-transfer reaction $^{48}$Ca($^{12}$C,$^{8}$Be)$^{52}$Ti using a $^{48}$Ca beam from the Maier-Leibnitz-Laboratory in Munich. In the frame work of IBM-2, Alonso $et$ $al.$ have shown that the population of the 2$^{+}_{ms}$ state is strictly forbidden for the alpha transfer from a doubly magic nucleus. In contrast, we measured a large relative cross section into the 2$^{+}_{2}$ mixed-symmetry state in $^{52}$Ti relative to the $2^+_1$ state of 31.1(20)$\%$. This value exceeds earlier measurements in the $^{140}$Ba nucleus, representing the case of a particular strong population of the 2$^{+}_{ms}$ state. This points towards effects of core polarizations of $^{48}$Ca in the low-lying structure of $^{52}$Ti. We have performed ab-initio shell model calculations to understand the origin of the discovered discrepancies. [Preview Abstract] |
Thursday, October 26, 2017 11:30AM - 11:42AM |
DD.00006: Ground state electromagnetic moments of $^{53}$Fe Kei Minamisono, A. J. Miller, B. A. Brown, D. M. Rossi, B. Maass, W. Noertershaeuser, D. Garand, C. Sumithrarachchi, P. .F. Mantica, R. Beerwerth, S. Fritzsche, A. Klose, Y. Liu, P. Mueller, M. R. Pearson Nuclear structure studies around the $^{56}$Ni nucleus with $N$ = $Z$ = 28 are critical since $^{56}$Ni is considered to be a soft core. In this region of interest, the nuclear magnetic-dipole moment and the electric-quadrupole moment of $^{53}$Fe were determined for the first time. A novel scheme of projectile-fragmentation reactions followed by in-flight separation and gas stopping was used in the present study for laser spectroscopy. Details of the experiment and a comparison with shell model calculations will be presented. [Preview Abstract] |
Thursday, October 26, 2017 11:42AM - 11:54AM |
DD.00007: Total Absorption Spectroscopy Study of the Beta Decay of $^{60}$Mn to Constrain the Neutron Capture Rate of $^{60}$Fe Debra Richman, Artemis Spyrou, Alex Dombos, Aaron Couture Interest in $^{60}$Fe, a long lived radioisotope synthesized in massive stars, has recently peaked. The signature of its decay allows us to probe astrophysical processes, events such as the early formation of the solar system and nucleosynthesis. To understand these observations a complete understanding of the creation, destruction and nuclear properties of $^{60}$Fe in the astrophysical environment are required. Using the beta decay of $^{60}$Mn in conjunction with total absorption spectroscopy (TAS), made possible by the high efficiency gamma ray calorimeter SuN (Summing NaI detector) at the National Superconducting Cyclotron Laboratory (NSCL), to study the distribution of beta-decay intensity over the daughter-nucleus $^{60}$Fe, provides information about the structure of the daughter and improves the predictive power of astrophysical models. In addition to the ongoing TAS analysis, The Beta-Oslo method will be used to extract the nuclear level density and gamma-strength function of $^{60}$Fe providing much needed constraints on the neutron capture reaction rate responsible for the creation of this nucleus. [Preview Abstract] |
Thursday, October 26, 2017 11:54AM - 12:06PM |
DD.00008: Coulomb Excitation of the 64Ni Nucleus and Application of Inverse Kinematics Beau Greaves, Dennis Muecher, Fuad A. Ali, Tom Drake, Vinzenz Bildstein, Christian Berner, Roman Gernhaeuser, K. Nowak, S. Hellgartner, R. Lutter, S. Reichert In this contribution, we present new data on the semi-magic 64Ni nucleus, close to the N$=$40 harmonic oscillator shell gap. Recent studies suggest a complicated existence of shape coexistence in 68Ni, likely caused by type-II shell evolutions. The region studied here thus might define the "shore" of the region of more deformed nuclei in the Island of Inversion below 68Ni. At the Maier-Leibnitz-Laboratory (MLL) in Munich, a beam of 64Ni was excited using Coulomb excitation. The high-granularity MINIBALL HPGe array and a segmented silicon strip detector were used to identify gamma decays in 64Ni. Doppler-shifted attenuation method (DSAM) analysis was applied to the experimental data acquired to resolve the low-lying excited states and acquire a lifetime measurement based on Geant4 simulations of the first excited 2$+$ state, clarifying the previously conflicting results. Furthermore, we show DSAM data following transfer reactions in inverse kinematics. This new method has the potential to provide insight into tests of ab-initio shell model calculations in the sd-pf shell and for the study of nuclear reaction rates. [Preview Abstract] |
Thursday, October 26, 2017 12:06PM - 12:18PM |
DD.00009: Gamma-Gamma Angular Correlation Measurements With GRIFFIN Andrew MacLean The assignment of spins and parities to excited nuclear states plays an important role in determining nuclear structure. There is a directional asymmetry in the emitted radiation from a $\gamma-\gamma$ cascade that depends on the sequence of spin values for the nuclear states, the multipolarities, and the mixing ratios of the emitted $\gamma$-rays. These $\gamma$-ray angular correlations are used for the assignment of spins and parities to the nuclear states, and thus provide a powerful means to elucidate the structure of nuclei away from stability. The first in-beam test of gamma-gamma angular correlation measurements with the GRIFFIN spectrometer at TRIUMF-ISAC were performed with a radioactive beam of $^{66}$Ga. In the daughter nucleus $^{66}$Zn, mixing ratios were measured for various cascades, and are in excellent agreement with literature. The sensitivity to a pronounced 0$^+$-2$^+$-0$^+$ angular correlation was also measured. The ability to assign spins for a 0$^+$-2$^+$-0$^+$ cascade is important for the case of $^{62}$Ga superallowed Fermi $\beta$-decay where a recent measurement was made to clarify two conflicting measurements for the spin assignment of the 2.34 MeV excited state in the daughter. [Preview Abstract] |
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