Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S14: Nuclear Structure IILive
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Sponsoring Units: DNP Chair: Belen Monteagudo-Godoy, FRIB |
Monday, April 19, 2021 1:30PM - 1:42PM Live |
S14.00001: $\beta$-decay studies of $A=107$ fission products with the Modular Total Absorption Spectrometer (MTAS) Peng Shuai Determination of the feeding intensities in $\beta$-decay of fission products is of high importance to address the reactor antineutrino anomaly and model the reactor decay heat. $\beta$-decay measurements with high-resolution but low-efficiency detectors may suffer from the Pandemonium effect, which leads to the misinterpretation of the feeding to high excited levels as the feeding to low-lying levels. Modular Total Absorption Spectrometer (MTAS), which has almost $99\%$ gamma detection efficiency, is an ideal spectrometer to determine the true $\beta$ feeding intensities free from Pandemonium effect. MTAS has been utilized to measure the beta decay pattern of several fission products that are high-priority contributors to reactor decay heat and antineutrino spectrum. In this talk, we will present some preliminary results of $A=107$ decays measured at CARIBU (ANL) in March, 2020. The $\beta$-branching of $^{107}$Mo, which is absent in current nuclear dataset, is determined experimentally. We found the $\gamma$ energy of $^{107}$Tc deposit in MTAS is increasing to about $\sim 2.2$ MeV, while the number calculated using current nuclear data is only $\sim 0.8$ MeV. This suggests a large shift of the antineutrino spectrum of $^{107}$Tc towards lower energy. [Preview Abstract] |
Monday, April 19, 2021 1:42PM - 1:54PM Live |
S14.00002: Gamma-ray spectroscopy of the $\beta$-decay of $\ce{^{141}}$Ba into $\ce{^{141}}$La for antineutrino spectrum calculations Javier Rufino, Jr, M. Alcorta, P. Bertone, M. Carpenter, J. Clark, C. Hoffman, R. Janssens, F. Kondev, T. Lauritsen, C. Lister, E. McCutchan, R. Pardo, A. Rogers, G. Savard, D. Seweryniak, R. Vondrasek, S. Zhu The antineutrino spectrum from a reactor is composed of spectra from nearly 800 fission fragments. Despite this large number of isotopes, antineutrino summation calculations have demonstrated that fluctuations in the spectrum shape can be attributed to just a few nuclei, those strongly produced in fission and with specific decay properties – the so-called fine structure. This work aims to provide improved nuclear data on strongly produced isotopes, in order to better quantify the fine structure and determine its impact on new reactor antineutrino experiments. The experiment was performed at Argonne National Laboratory where a beam of $^{141}$Cs was produced at the CARIBU facility and implanted into the center of Gammasphere. We studied the $\beta$ decay of the daughter, $^{141}$Ba and precisely determined the $\gamma$-ray energies and intensities. A significant revision to the level scheme of $^{141}$La over the literature was obtained. The new level scheme as well as the impact on antineutrino spectrum calculations will be presented. [Preview Abstract] |
Monday, April 19, 2021 1:54PM - 2:06PM Live |
S14.00003: Nucleon localization function in rotating nuclei Tong Li, Mengzhi Chen, Chunli Zhang, Witold Nazarewicz, Markus Kortelainen The electron localization function was originally introduced in atomic physics to visualize atomic shell structures and molecular bonds. In nuclear physics, a nucleon localization function (NLF) has been used to characterize cluster structures in light nuclei, fragment formation in fission and pasta phases in neutron stars. In this work we use a generalized NLF, which involves both time-even and time-odd local densities, to study the nuclear response to rotation. Illustrative calculations for the superdeformed yrast band of $^{152}$Dy were carried out by using the cranked Skyrme-Hartree-Fock method. The self-consistent results are compared to the cranked harmonic oscillator. We find that the nodal pattern of the NLF results from a constructive interference between kinetic-energy and particle densities. The pattern along the major axis of the nucleus comes from single-particle orbits with large aligned angular momentum; the variation along the minor axis is associated with deformation-aligned levels. The NLF allows a simple interpretation of shell structure evolution in rotating nuclei in terms of the angular-momentum alignment of individual nucleons. We expect that the NLF will become a useful tool in studies of various nuclear collective modes and time-dependent processes. [Preview Abstract] |
Monday, April 19, 2021 2:06PM - 2:18PM Live |
S14.00004: Landscape of pear-shaped even-even nuclei Sylvester Agbemava, Yunchen Cao, Anatoli Afanasjev, Witold Nazarewicz, Erik Olsen Reflection asymmetric shapes play an important role in nuclear stability, spectroscopy, decays and fission. For this study, global analysis of ground-state octupole deformations for even-even nuclei with $Z\leq 110$ and $N\leq 210$ has been performed using nuclear density functional theory (DFT) with several non-relativistic and covariant energy density functionals. In this way, we can identify the best candidates for reflection-asymmetric shapes. The calculations are performed in the frameworks of axial reflection-asymmetric Hartree-Fock Bogoliubov theory and relativistic Hartree-Bogoliubov theory. We consider five Skyrme and four covariant energy density functionals. This allows us to better understand systematic trend of octupole instability throughout the nuclear landscape. Several regions of ground-state octupole deformation were predicted. In addition to the “traditional” regions of neutron-deficient actinide nuclei around $^{224}$Ra and neutron-rich lanthanides around $^{146}$Ba, we identified vast regions of reflection-asymmetric shapes in very neutron-rich nuclei around. $^{200}$Gd and $^{288}$Pu. Our analysis suggests promising candidates with stable ground-state octupole deformation, primarily in the neutron-deficient actinide region, that can be reached experimentally [Preview Abstract] |
Monday, April 19, 2021 2:18PM - 2:30PM Live |
S14.00005: WalletCraft: A New Database of Ground State and Long-lived Isomeric Properties E.A. McCutchan, S. Zhu, A.B. Hayes, B. Shu, A. Mattera, A.A. Sonzogni The Nuclear Wallet Cards booklet is a long-standing product of the National Nuclear Data Center that provides data on the ground state and long-lived isomers in all experimentally observed nuclei. Data have traditionally been made available in a printed handbook, an ASCII file, and through a searchable web-based application. The Wallet Cards database has recently undergone a complete modernization resulting in a new database called WalletCraft. WalletCraft is an expansible object-oriented database including not only recommended values, but also incorporating all source measurements. Details of WalletCraft will be presented, along with opportunities for expansion of the database. [Preview Abstract] |
Monday, April 19, 2021 2:30PM - 2:42PM Live |
S14.00006: Modernization and Expansion of the Evaluated Nuclear Structure Data File Database Adam Hayes, Elizabeth McCutchan, Shinjae Yoo, Andrea Mattera, Sean McCorkle, Benjamin Shu, Alejandro Sonzogni, Carlos Soto, Shaofei Zhu, Filip Kondev, Caleb Mattoon The Evaluated Nuclear Structure Data File (ENSDF) database is the comprehensive nuclear structure and decay database, containing all published experimental nuclear structure and decay data for the 3300 observed nuclides, along with carefully evaluated recommended values and uncertainties. ENSDF is the leading source of nuclear structure and decay data worldwide for both basic and applied sciences, exceeding 3.2M lookups per year via the NNDC website. A complete modernization of the ENSDF database is underway, creating an expansible object-oriented database and API from the restrictive 80-column ASCII format in use since its inception. The upgrade will allow for the addition of a wide variety of content, such as continuous spectra, and provide access to modern computational and search tools. Machine learning techniques are being developed in parallel to automate the insertion of new results into the companion database for pre-evaluated published results (XUNDL), reducing the time between ENSDF evaluations and improving database currency. The modernized database will be amenable to the addition of arbitrary types of open data. [Preview Abstract] |
Monday, April 19, 2021 2:42PM - 2:54PM Live |
S14.00007: Intrinsic Electric Quadrupole Moment of the $K^\pi=8^-$ Isomeric State in $^{178}$Hf Shaofei Zhu The lifetime of the 9$^-$ state in the rotational band based on the 4.0 s, $K^\pi =8^-$, isomeric state ($^{178}$Hf$^{m_{1}}$) from the decay of the 31-yr isomer ($^{178}$Hf$^{m_{2}}$) was determined to be 99(2) ps by means of the fast-timing technique using two LaBr$_3$(Ce) scintillators. The $\delta(E2/M1)$ mixing ratios of the $\Delta I =1$ $\gamma$ rays depopulating levels in this band were deduced from $\gamma$-$\gamma$ angular correlations by using a $^{178}$Hf$^{m_{2}}$ radioactive source located at the center of the Gammasphere HPGe detector array. The new results, together with previous spectroscopic information, provide a different way to extract the intrinsic quadrupole moment of $Q_0=6.45(14)~eb$ for the $^{178}$Hf$^{m_{1}}$ band. A possible explanation for the reduction of the $^{178}$Hf$^{m_1}$ nuclear charge radius is presented. [Preview Abstract] |
Monday, April 19, 2021 2:54PM - 3:06PM Live |
S14.00008: Rotational bands beyond the Elliott model Ryan Zbikowski, Calvin W. Johnson, Anna E. McCoy, Mark A. Caprio, Patrick J. Fasano Rotational bands are commonplace in the spectra of atomic nuclei. Inspired by early descriptions of these bands by quadrupole deformations of a liquid drop, Elliott constructed discrete nucleon representations of $\mathrm{SU}(3)$ from fermionic creation and annihilation operators. Ever since, Elliott's model has been foundational to descriptions of rotation in nuclei. Later work, however, suggested the symplectic extension $\mathrm{Sp}(3,R)$ provides a more unified picture. We decompose no-core shell-model nuclear wave functions into symmetry-defined subspaces for several beryllium isotopes, as well as $^{20}$Ne, using the quadratic Casimirs of both Elliott's $\mathrm{SU}(3)$ and $\mathrm{Sp}(3,R)$. The band structure, delineated by strong $B(E2)$ values, has a more consistent description in $\mathrm{Sp}(3,R)$ rather than $\mathrm{SU}(3)$. In particular, we confirm previous work finding in some nuclides strongly connected upper and lower bands with the same underlying symplectic structure. [Preview Abstract] |
Monday, April 19, 2021 3:06PM - 3:18PM Live |
S14.00009: Nuclear Structure of 214Po from 226Ra decay Sophia Balderrama, Elizabeth McCutchan, Shaofei Zhu, Jing Li, Dirk Weisshaar Nuclei in the neutron-rich region around $^{208}$Pb offer a perfect testing ground for realistic shell model interactions, yet experimental data become increasing sparse moving east from the closed shell. The decay of $^{226}$Ra offers a simple way to study several neutron-rich A=214 nuclei which are populated in $\beta$ decays along the decay chain. In particular, we use GRETINA at NSCL, MSU to perform $\gamma$ - $\gamma$ angular correlation and polarization measurements to make spin/parity assignments. The methods of analysis and revised level scheme will be presented. [Preview Abstract] |
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