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 MF: Nuclear Structure : A = 25-50 |
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Chair: Erin Peters, U of Kentucky Room: Berkeley & Clarendon |
Wednesday, October 13, 2021 4:00PM - 4:12PM |
MF.00001: Shell spectroscopy sensitivity via the ground state population of 26O from halo nuclei in proton removal reactions Paul L Gueye, Thomas Baumann, Thomas Redpath, Belen Monteagudo, Alaura Cunningham, Kevin Fossez, Nathan H Frank, Jimmy Rotureau, Anthony N Kuchera The ground state of 26O is unbound to 2n decay by only 18 ± 3 (stat) ± 4 (sys) keV. The signature of this state enables a unique sensitivity to probe the halo structure of 29Ne. The invariant mass technique was used to reconstruct the decay energies of 25O and 26O produced from 27F (105.3 MeV/u) and 29Ne (112.8 MeV/u) beams impinging on a Be target using the MoNA-Sweeper setup at the National Superconducting Cyclotron Laboratory. The measured distributions obtained from the two beams differ substantially, especially in the low energy region where the low lying 18 keV state is present for 27F but absent for the 29Ne for both 25O and 26O decay energies. This behavior is believed to originate from the halo nature of 29Ne which has a ground state with a Jπ = 3/2-. A density matrix renormalization group (DMRG) calculation predicts energy levels of 27O with respect to a 24O core with a Jπ = 3/2- excited state located at 5.653 MeV above its Jπ = 3/2+ (0.637 MeV) ground state. Coupled with the lower probability of 29Ne(-2p1n) compared to 29Ne(-2p) to produce the 26O, the most likely scenario is a population of such predicted 3/2- state of 27O. |
Wednesday, October 13, 2021 4:12PM - 4:24PM |
MF.00002: Investigation of the high spin structure of 29Si using the (α,d) reaction. Caleb B Benetti, Samuel L Tabor, Catur Wibisono, Gordon W McCann, Kevin T Macon, Kenneth G Hanselman, Juan C Esparza, Ingo L Wiedenhoever, Lagy T Baby The investigation of nuclear structure in the mass A = 16-60 region has provided rich experimental data to test microscopic theory. Previously our group has used the tools and techniques of multi-gamma spectroscopy to chart out the high-spin yrast states in this mass region. Yrast states tend to be more unique for comparison with theory, hence our interest is focused on high spin states. To provide complementary data to gamma spectroscopy, we have explored using the (α,d) direct reaction to produce two nucleon excitations. It has been shown1 that (α,d) reactions have a preference for high spin states since the proton and neutron from the deuteron can both occupy the same state of maximal J. Surprisingly no results for 27Al(α,d)29Si have been published above 5 MeV of excitation in 29Si. Results from such a study conducted at FSU with the Super Enge Split-Pole Spectrograph (SE-SPS) will be reported and comparisons with configuration-interaction calculations using the FSU cross-shell interaction2 will be presented. |
Wednesday, October 13, 2021 4:24PM - 4:36PM |
MF.00003: Neutron-unbound excited states in 31Ne Dayah N Chrisman, Anthony N Kuchera, Thomas Baumann, B A Brown, Nathan H Frank, Paul L Gueye, Belen Monteagudo, Jeffrey A Tostevin The Island of Inversion near the N=20 shell gap is home to nuclei with interesting nuclear structure effects due to a shell inversion with respect to spherical shell model expectations. Studies of 31Ne have revealed that it exhibits a halo structure, characterized by a valence neutron orbiting a deformed 30Ne core. This lightly bound nucleus is expected to have neutron-unbound excited states as it has has a very small separation energy of Sn = 170 keV. An experiment was performed at NSCL at MSU to study the low-lying excited states in 31Ne for the first time, utilizing the MoNA-LISA neutron array. A two-proton knockout reaction populated 31Ne states from an 89 MeV/u 33Mg beam. The neutron-unbound states of 31Ne decay immediately into 30Ne and a neutron. The two-body decay energy was reconstructed via the invariant mass method and shows two broad features. Accompanying shell model calculations using the FSU interaction within NuShellX combined with cross-section calculations using eikonal reaction theory were performed that indicate the spectrum is likely caused by several resonant states in 31Ne. |
Wednesday, October 13, 2021 4:36PM - 4:48PM |
MF.00004: Search for microsecond isomers at the dripline of the island of inversio James Christie, Zhengyu Xu, Robert Grzywacz, Miguel Madurga, Jesse N Farr, Donnie Hoskins, Philipp Wagenknecht, Isidora Fletcher, Thomas T King, Shree K Neupane, Aaron Chester, Joseph Heideman, Andrea L Richard, Kevin Siegl, James M Allmond, Rin N Yokoyama
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Wednesday, October 13, 2021 4:48PM - 5:00PM |
MF.00005: Investigation of the reaction mechanism in the neutron emission from unbound excited states in 27F by the MoNA Collaboration Paul L Gueye, Thomas Redpath, Thomas Baumann, Alaura Cunningham, Belen Monteagudo, Jared Bloch The MoNA Collaboration has been conducting experiments over the past two decades at the National Superconducting Cyclotron Laboratory (NSCL) and is poised to expand its scientific program with the upcoming Facility for Rare Isotope Beams (FRIB), both located in East Lansing, MI. The Collaboration primarily focuses on the study of unbound nuclei along the neutron dripline using invariant mass spectroscopy. A recent analysis of data on the production of 25,26O from 27F and 29Ne beams incident on beryllium targets indicates a possible new and rich program to investigate the production mechanism of these neutron rich nuclei. We have extended this work to study the neutron emission from unbound excited states in 27F (27F → 26F + n) populated via 28Ne(-1p) and 29Ne(-2p) proton removal reactions. This presentation will discuss preliminary results from this study. |
Wednesday, October 13, 2021 5:00PM - 5:12PM |
MF.00006: Nuclear charge radii of neutron-deficient scandium isotopes Kristian L Koenig, Robert Powel, Kei Minamisono, Andrew Klose, Stephan Fritzsche, Helena García Escudero, Jeremy D Lantis, Yuan Liu, Witold Nazarewicz, Wilfried Nörtershäuser, Skyy V Pineda, Paul-Gerhard Reinhard, Dominic M Rossi Charge radii of neutron deficient 40,41Sc (Z=21) isotopes have been determined at the BEam COoler and LAser spectroscopy facility at FRIB to investigate the N=20 shell closure. Particularly, the typical kink structure in the charge radius evolution at N=20 is very weak in Ar, K and Ca while it is strongly pronounced at N=28. With one additional proton in the 1f7/2 shell in Sc, additional cross-shell interactions occur and affect the behavior at the shell closure. The results will be presented, which promote a global understanding of the structure around 40Ca, and the weak shell-closure signature at N=20. |
Wednesday, October 13, 2021 5:12PM - 5:24PM |
MF.00007: Ground State Nuclear Magnetic Moments of 40Sc Robert Powel, Andrew Klose, Kristian König, B A Brown, Jeremy D Lantis, Yuan Liu, Kei Minamisono, Wilfried Nörtershäuser, Skyy V Pineda Collinear laser spectroscopy was performed at the BECOLA facility at NSCL/FRIB/MSU on the 3d4s 3D2↔3d4f 3F3 transition in 40Sc ions and the hyperfine spectrum was observed. The ground state nuclear magnetic moments was newly determined for 40Sc from the hyperfine coupling constants extracted from the obtained hyperfine spectrum. The 40Sc magnetic moment is particularly interesting for studies of nuclear structure as an odd-odd nucleus at the proton drip line in the vicinity of doubly magic 40Ca. The experimental detail and comparison with the additive rule of magnetic moment will be discussed. |
Wednesday, October 13, 2021 5:24PM - 5:36PM |
MF.00008: Shell-model calculations for two-neutron transfer near the island of inversion Juliette K Stecenko, Alan H Wuosmaa We have performed shell-model calculations of two-neutron amplitudes (TNA) relevant for the two-neutron transfer reactions 28Mg(t,p)30Mg and 30Mg(t,p)32Mg. The neutron-rich isotopes of Mg are central to the understanding of intruder configurations responsible for the “Island of Inversion” at N=20. Two-neutron transfer is a powerful tool to study these configurations. With new radioactive-beam facilities, new experiments are planned for similar work. In preparation for such new measurements, we have used the sdpf-mu interaction to calculate two-neutron amplitudes for states in 30,32Mg. The calculations were performed using the code “KSHELL” [1] and ran on the High-Performance Computing Facility at the University of Connecticut. We have also used the TNA from these calculations in DWBA calculations to predict the relative cross sections for populating different states in 30,32Mg via the (t,p) reaction. The results of the calculations, and the implications for future studies of two-neutron transfer in the Mg region will be discussed. |
Wednesday, October 13, 2021 5:36PM - 5:48PM |
MF.00009: Beta Decay of Nutron-Rich Nuclei near N=20 Yiyi Zhu, Peter C Bender, Elizabeth Rubino, Vandana Tripathi, Jesus F Perello, Samuel L Tabor, Sean N Liddick, Aaron Chester, Andrea L Richard, Katie Childer, Benjamin P Crider, Timilehin H Ogunbeku, Andrew M Rogers, Daniel E Hoff, Sudipta Saha Neutron-rich isotopes below 40Ca, a region collectively known as the “island of inversion”, is dominated by deformation arising from the diminishing N=20 shell gap. Isotopes in this region of deformation have been particularly important to our understanding of the evolution of magic numbers from stability towards the neutron dripline. Recently, the beta-decay of isotopes along the southern boundary of the island of inversion has been performed using the CCF at the NSCL. A 48Ca beam was fragmented, the secondary beam was centered around 31Ne isotopes were subsequently selected using the A1900 separator and implanted in the BCS, allowing event-by-event particle identification and analysis to be performed. Excited states in the daughter nuclei are identified by emitted γ-rays collected with 16 Clover-style HPGe and 15 LaBr3 detectors surrounding the BCS in a rhombicuboctahedron geometry. The current presentation will highlight the analysis process and as well as the structure of exotic Mg and Na isotopes. |
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