Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session PF: Nuclear Structure : A = 50-70 |
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Chair: Christopher Morse, Brookhaven National Laboratory Room: Berkeley & Clarendon |
Thursday, October 14, 2021 9:30AM - 9:42AM |
PF.00001: Exploring the level structure of 59Co and 59Ni at high spin Samuel O Ajayi, Vandana Tripathi, Samuel L Tabor, Elizabeth Rubino, Rebeka Lubna, James Allmond, Lagy T Baby, Caleb Benetti Fusion evaporation reaction induced by a 14C beam of 43 MeV on a thin 48Ti target has been used to populate high spin states in 59Co and 59Ni; populated in the p2n and 3n evaporation channel respectively. Emitted γ rays were detected using the FSU clover array which consists of 6 high purity germanium Clover detectors (with BGO shields for Compton suppression) and several single crystal detectors placed at three different angles. The directional correlation from oriented states (DCO ratio) was measured using ratios of intensities from detectors at 90o and 135o. The polarization asymmetry was also measured, which in addition to the DCO ratios was used to determine the spin and parity of the new energy levels in 59Co. Previously known spins in the 59Co were confirmed and their parity was ascertained. The level scheme of 59Co has been extended to ~ 11 MeV with tentative Jπ = 31/2+. The result was compared with the theoretical shell model calculations within the fp-g9/2d5/2 valence space and was found to agree well. Preliminary results for 59Ni have also been obtained. |
Thursday, October 14, 2021 9:42AM - 9:54AM |
PF.00002: Nuclear resonance fluorescence as a complementary probe of triple shape coexistence in 64Ni Udo Friman-Gayer, Akaa D Ayangeakaa, Sean W Finch, Anne M Forney, Johann Isaak, Xavier James, Robert V Janssens, Samantha R Johnson, Michael D Jones, Filip G Kondev, FNU Krishichayan, David R Little, Bastian Löher, Deniz Savran, Werner Tornow A recent study of 64Ni [1], which combined four complementary experimental techniques, revealed three coexisting shapes, extended shape coexistence first observed in the neutron-rich nickel isotopes to the heaviest stable one, and agreed with Monte-Carlo shell-model (MCSM) calculations. The stability of 64Ni facilitates experiments with nuclear resonance fluorescence and can shed additional light on this nucleus [2]. With the polarized, quasi-monoenergetic photon beam from the HIγS facility [3], 64Ni excited states were populated at energies of 8.7 and 8.95 MeV, and their decays through levels at lower excitation energies were characterized. Specifically, the spins and parities of the observed states were firmly established through γγ-angular correlations. In addition to the excitation energies, and quantum numbers of newly observed levels, information on their decay branching and mixing ratios and lifetimes provide further tests of the MCSM predictions. [1] N. Mărginean et al., Phys. Rev. Lett. 125, 10502 (2020) [2] D. R. Little, PhD Thesis, UNC at Chapel Hill (2020) [3] H. R. Weller et al., Prog. Part. Nucl. Phys. 62, 257 (2009) |
Thursday, October 14, 2021 9:54AM - 10:06AM |
PF.00003: Data-Driven Configuration-Interaction Hamiltonian Extrapolation to 60Ca Aaron Magilligan, B. Alex Brown, Ragnar Stroberg Next generation experiments performed at newly built rare-isotope facilities will provide a greatly expanded view of the neutron rich calcium isotopes. In light of this, we aimed to produce a universal fp-shell interaction tailored to those isotopes which we call UFP-CA. Starting from a state-of-the-art IMSRG interaction, linear combinations of Hamiltonian parameters that define the natural basis of the parameter space are constrained by the latest experimental data for the very neutron-rich calcium, including the recently measured masses of 55-57Ca [1]. We show that this data-driven method for improving the Hamiltonian provides an excellent description of the known binding energies and spectra for the calcium isotopes within the fp model space. This together with comparisons to results from energy-density functional models leads us to conclude that 60Ca is doubly-magic at a similar level to 68Ni. Several predictions are presented for unobserved low-laying excited states in 55-59Ca that should be accessible to future experiments. |
Thursday, October 14, 2021 10:06AM - 10:18AM |
PF.00004: Charge radii of neutron-deficient nickel isotopes Felix Sommer, Kristian König, Dominic M Rossi, Nathan Everett, David Garand, Ruben deGroot, Phillip Imgram, Colton Kalman, Andrew Klose, Jeremy D Lantis, Yuan Liu, Andrew J Miller, Kei Minamisono, Wilfried Nörtershäuser, Skyy V Pineda, Robert Powel, Laura Renth, Elisa Romeo-Romero, Chandana S Sumithrarachchi, Andrea 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 54,55,56Ni using collinear laser spectroscopy technique at BECOLA at NSCL/MSU to investigate how the softness manifests itself in <r2> at and below N = 28. Details of the experiment and results will be discussed. |
Thursday, October 14, 2021 10:18AM - 10:30AM |
PF.00005: Charge radius of neutron deficient 54Ni and symmetry energy constraints using the difference in mirror pair charge radii Skyy V Pineda, Kristian König, Dominic M Rossi, B. Alex Brown, Anthony Incorvati, Jeremy D Lantis, Kei Minamisono, Wilfried Nörtershäuser, Jorge Piekarewicz, Robert Powel, Felix Sommer The charge radius of 54Ni was determined for the first time using collinear laser spectroscopy at the BEam COoling and LAser spectroscopy (BECOLA) facility. Combined with the known charge radius of its mirror partner 54Fe, the slope L of symmetry energy in the nuclear equation of state was determined. The details of the experiment and the mirror-radius analysis will be presented. Also, the obtained L will be compared with that obtained from the neutron star merger GW170817 and PREX-2. |
Thursday, October 14, 2021 10:30AM - 10:42AM |
PF.00006: Abstract Withdrawn
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Thursday, October 14, 2021 10:42AM - 10:54AM |
PF.00007: Structure of 62Co Nirupama Sensharma, Akaa D Ayangeakaa, Robert V Janssens, Matteo Fulghieri, Shaofei Zhu, Michael P Carpenter, Alexandra Gade, Torben Lauritsen, Dariusz Seweryniak, Christopher J Chiara, Partha Chowdhury, Calem R Hoffman, Filip G Kondev, Christopher J Lister, Elizabeth McCutchan An extensive study of the level structure of 62Co has been performed following a complex multinucleon transfer reaction 26Mg( 48Ca, 2α3npγ) 62Co at beam energies of 275, 290 and 320 MeV. The combination of the Gammasphere array, the Fragment Mass Analyzer (FMA) and a focal-plane ionization chamber was used to identify and delineate excited levels in 62Co. As a result, the 62Co level scheme was considerably extended. Based on angular distribution measurements and DCO ratios, various level sequences built upon states of single-particle character were observed. An interpretation of these structures in the framework of the shell model will be presented and the evolution of collectivity in the A ∼ 60 region will be highlighted against the backdrop of the recently observed signatures of collectivity in 62,63Ni [1, 2] and 61Co [3]. |
Thursday, October 14, 2021 10:54AM - 11:06AM |
PF.00008: ENSDF Modernization and JSON Conversion Shu Shu, Jun Chen, Adam Hayes The Evaluated Nuclear Structure Data File (ENSDF) format was originally designed to be stored on 80-column punch cards. The technological limits of the time are reflected in ENSDF’s design choices, which save space at the cost of user-friendliness. Advances in computing technology and storage have since made these conventions far less necessary. In addition, years of nuclear physics research have greatly increased the volume and diversity of nuclear data. Both factors have prompted the National Nuclear Data Center’s (NNDC’s) present work, as an attempt to leverage modern technologies to meet future needs. The ENSDF format is currently being re-designed for use in JavaScript Object Notation (JSON). The present work focuses on a Java library being developed for parsing existing ENSDF datasets and converting them into JSON formats. The library’s design, organization, and uses will be discussed, along with the next steps for its development. |
Thursday, October 14, 2021 11:06AM - 11:18AM |
PF.00009: Neutron Emission from the Isomeric Beta-decays of Co-70 measured by VANDLE at NSCL Kevin Siegl, Andrew M Keeler, Robert Grzywacz, Nathan Brewer, Benjamin P Crider, Aleksandra Fijalkowska, Matthew Hall, Joseph H Hamilton, Sean N Liddick, Miguel Madurga, Patrick D O'Malley, Stan V Paulauskas, Thomas T King, Mustafa M Rajabali, Steven Z Taylor, Enhong Wang, Christopher J Zachary Co-70 beta-decays to Ni-70 by way of two isomers, a (6-) isomer with a half-life of 112ms, and a lower spin isomer listed as (3+) with a half-life of 470ms. As the Q-value for the decay of Co-70 to Ni-70 is 12.6 MeV, and the neutron separation energy of 70Ni is 7.3 MeV, neutron emission is energetically possible. As the two beta-decays of Co-70 have a different structure, it is not certain how both will emit neutrons. Neutron emission may also compete with gamma emission to below the neutron separation energy in the beta-decay child. This neutron emission probability depends on the structure of the beta-decay child (Ni-70) and the properties of the neutron emission product (Ni-69). An array of 42 120cm VANDLE bars were used with a YAP(Yttrium Aluminum Perovskite) inorganic scintillator implant detector to measure both the implanted nuclei from the NSCL fragmentation of the 82Se primary beam and their subsequent beta-decay. Analysis of the Co-70 decays resulted in two distinctly different neutron energy spectra associated with the different half-lives. These spectra were compared with a recently developed model, which combines shell model and statistical model calculations. |
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