Bulletin of the American Physical Society
6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Sunday–Friday, November 26–December 1 2023; Hawaii, the Big Island
Session F10: Nuclear Structure IV |
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Chair: Krzysztof Piotr Rykaczewski, Oak Ridge National Lab Room: Hilton Waikoloa Village Kohala 3 |
Thursday, November 30, 2023 9:00AM - 9:15AM |
F10.00001: Probing the rapid onset of deformation below 68Ni through the beta decay of 67Mn Victoria Vedia, Bruno Olaizola, Rashmi Umashankar, Adam B Garnsworthy, Corina Andreoiu, Gordon C Ball, Soumendu S Bhattacharjee, Samantha Buck, Roger Caballero-Folch, Iris Dillmann, Fatima H. Garcia, Paul E Garrett, Christopher Griffin, Gwen F Grinyer, Greg Hackman, Kushal Kapoor, E Gyabeng Fuakye, Guy Leckenby, Rebeka Sultana Lubna, Matthew S Martin, Connor Natzke, Marco Rocchini, Yukiya Saito, M Satrazani, James Smallcombe, Pietro Spagnoletti, Carl E Svensson, Daniel Yates, Tammy Zidar One of the best-known divergences from the single-particle shell model description is the existence of islands of inversion [1]. The IoI of the region N=40 draws particular attention since the neutron number 40 was postulated as a non-traditional “magic” number and N = 40 represents the boundary between the negative parity pf shell and the positive-parity g shell. In stable nuclei, the neutron g9/2 orbital is close enough to the pf shell to reduce this shell gap resulting in a more stable subshell closure at N = 50. Measurements of B(E2) values and E(2+) in the neutron-rich region show increased collectivity through the N = 40 shell gap, with the clear exception of 68Ni [2,3]. Deformation and shape coexistence have been identified in the area, LNPS calculations predict triple shape coexistence for 67Co (N=40), with three rotational bands [4]. And, recent experiments on 67Fe (N=41) propose a spin-parity of 5/2+ or 1/2− for its ground state [5] which indicates a significant deformation. In addition, shape coexistence is also expected for 67Fe. Despite the high interest in the region, very limited information is available, to this end, an experiment was performed at the TRIUMFISAC facility utilizing the GRIFFIN spectrometer [6], where the β and βn decay of 67Mn populated the 67,66Fe, 67,66Co and 67,66Ni isotopes. This data set contains orders of magnitude more statistics than previous studies allowing us to build for the first time a complete level scheme of 67Fe and 67Ni, and to improve upon the known β- decay level schemes of 67Co, by expanding the number of transitions and levels, as well as by improving the precision of branching ratios and ground-state half-life measurement. In addition, measurements of level lifetimes down to the picosecond range will allow us to investigate the band structure in these nuclei. For the 67Fe isotope, a good level of statistics will make it possible to measure the energy of the identified isomeric state and improve the lifetime measurement. These results can provide further insight into the detailed structure of the states by comparison to simple models and large-scale shell model calculations in order to confirm or refute the shape coexistence picture predicted by LNPS calculations and the shrinking of the N=40 gap just one proton below 68Ni. Preliminary results from will be presented and discussed. |
Thursday, November 30, 2023 9:15AM - 9:30AM |
F10.00002: Onset of band structure in 70Ga Robert A Haring-Kaye, Faith Palombi, Joachim Dōring, Samuel L Tabor, Brittany L Abromeit, Rebeka Sultana Lubna, Pei-Luan Tai, Vandana Tripathi, Alexander S Volya, Justin M VonMoss, Diego Venegas Vargas, Chin Lung Tan, Michael J Heeschen, Khanh Q Le, Brianna L Harbin Excited states in odd-odd 70Ga were studied using the 62Ni(14C,αpn) fusion-evaporation reaction performed at the John D. Fox Superconducting Accelerator Facility at Florida State University with a beam energy of 50 MeV. The depopulating γ decays were measured in coincidence using a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. An investigation of these coincidences resulted in the addition of 16 new transitions in the 70Ga level scheme, including some which belong to the onset of a new positive-parity band structure likely based on the π g9/2 νg9/2 configuration. Spins and parities were assigned based on directional correlation of oriented nuclei ratios and linear polarization measurements. The excitation energies predicted by shell-model calculations using the JUN45 effective interaction compare favorably with the experimental ones for the positive-parity states, but are generally about 400-500 keV too low for the negative-parity states. Total Routhian surface calculations for the lowest positive-parity configuration with signature α = 0 predict significant triaxiality (γ ≈ -20°) with competing non-collective excitations developing at a spin (J = 8) that corresponds to the onset of the positive-parity band observed experimentally. The calculations for the lowest negative-parity states with α = 0 yielded surfaces that were qualitatively similar. |
Thursday, November 30, 2023 9:30AM - 9:45AM |
F10.00003: Structure of medium-mass nuclei studied by Monte Carlo shell model calculations Yusuke Tsunoda, Noritaka Shimizu, Takaharu Otsuka We have studied medium-mass nuclei of various regions by Monte Carlo shell model (MCSM) calculations. Our MCSM calculations for Ni isotopes reproduce well their properties such as levels and transitions. Shape coexistence of nuclei around 68Ni is predicted by the calculations. Neutron-rich nuclei around N=50 are calculated by using extended model space and shape coexistence of 78Ni is predicted. In this talk, we discuss structure and beta-decay property of neutron-rich nuclei around N=50. |
Thursday, November 30, 2023 9:45AM - 10:00AM |
F10.00004: Nuclear dipole response of 56Fe using photon scattering Anthony P Ramirez, Jack A Silano, Ronald C Malone, Anton P Tonchev, Jutta E Escher, Sean W Finch, Udo Friman-Gayer, Werner Tornow, Akaa D Ayangeakaa, Robert V Janssens, Samantha R Johnson, Nirupama Sensharma, Nadia Tsoneva, Alexander Voinov, Steven W Yates We recently performed a nuclear resonance fluorescence experiment in 56Fe with 100% linearly polarized photons for incident beam energies below the neutron separation energy at the High-Intensity Gamma-ray Source (HIγS) facility at Triangle Universities Nuclear Laboratory (TUNL). From the observed dipole states and their decay pattern and transition strengths, we will deduce the gamma-strength function of 56Fe [1]. With the upgrade of the high-efficiency clover detector array and the increased γ-ray flux at HIγS, we also aim to study the low-energy primary γ-ray transitions induced by incident photon beams using coincidence mode. In this talk, we will give an overview of the experiment and present the preliminary results on the dipole strength distribution in 56Fe below the neutron separation energy, as well as the comparison with literature data [2] and theoretical calculations based on the quasi-particle phonon model [3].
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344. [1] A.P. Tonchev et al., Phys. Rev. Lee. 104 072501 (2010).
[2] T. Shizuma, et al., Phys. Rev. C 87, 024301 (2013). [3] N. Tsoneva and H. Lenske, Physics of Atomic Nuclei 79, 885 (2016). |
Thursday, November 30, 2023 10:00AM - 10:15AM |
F10.00005: Excitations of pygmy dipole resonances in selected molybdenum isotopes within microscopic HFB+QRPA calculations Eun Jin In, Emanuel V Chimanski, Jutta E Escher, Sophie Péru, Walid Younes The study of nuclear excitations, particularly collective excitation modes such as the giant resonance (GR) and pygmy resonance (PR), can reveal important characteristics of the underlying nuclear structure. The PR is a fascinating excitation mode that is more prominent in nuclei with an excess of neutrons. This resonance is typically interpreted as a collective motion in which the neutron excess oscillates against a core. It is known to enhance the neutron capture rates, which are crucial for understanding the creation of elements in our universe. However, our knowledge of the low-lying collective excitations remains incomplete despite decades-long efforts to measure and describe collective phenomena. Our inability to include collective effects in reaction calculations affects a range of applications, from nuclear astrophysics to nuclear energy. |
Thursday, November 30, 2023 10:15AM - 10:30AM |
F10.00006: Experimental studies toward better understanding of beta-delayed neutron emission Robert Grzywacz, Zhengyu Xu, Miguel Madurga Beta-delayed neutron emission process is a dominant decay mode for the majority of neutron-rich nuclei. The neutron-emission part of the process is typically modeled using Hauser-Feshbach formalism under the assumption of the compound nucleus stage. This however requires the presence of a mechanism to transition from configurations populated during beta-decay which, in case prevalent allowed Gamow-Teller type transformation, results in a restricted set of configurations. Detailed measurements of neutron emission probabilities to excited nuclear states can be used as a probe to investigate the validity of the compound-nucleus stage. Experiments were performed on a range of nuclei from nitrogen to iodine to probe the nature of neutron emission after beta decay revealing in some cases non-statistical behavior. A simple model was constructed to link this behavior to the details nuclear structure of involved nuclei, |
Thursday, November 30, 2023 10:30AM - 10:45AM |
F10.00007: Direct measurement of beta-delayed neutron emission for Cobalt Isotopes using VANDLE Kevin Siegl, Andrew M Keeler, Maninder Singh, Rin Yokoyama, Robert Grzywacz, Shintaro Go, Nathan T Brewer, Benjamin P Crider, Aleksandra Fijalkowska, Matthew Hall, Joseph H Hamilton, Thomas T King, Sean N Liddick, Miguel Madurga, Patrick O'Malley, Enhong Wang, Christopher J Zachary Cobalt (Z=27) decays to Nickel (Z=28). Z=28 is a proton magic number. Beta-delayed neutron emission requires decay to above the neutron separation energy of the Nickel beta-daughter. In Cobalt decays, this is achieved through "proton core breaking." Where instead of populating the proton f7/2 orbital from the neutron transition to a proton, the excited proton p3/2 is populated instead. The strength above the neutron separation energy is dependent on the proton shellgap above f7/2 and the neutron shellgap above p1/2, as neutron-rich Cobalt isotopes populate the neutron g9/2 orbital. This is compared to observations of Co-70gs,70m,71,72,73,74,75 from experiments at NSCL and RIKEN, both utilizing VANDLE arrays. The distribution of states above the neutron separation energy of the beta-daughter that undergo neutron emission is modeled by a combination of shell model and statistical model calculations. |
Thursday, November 30, 2023 10:45AM - 11:00AM |
F10.00008: Is neutron emission statistical following β decays near 54Ca? Zhengyu Xu, Robert Grzywacz, Andrea Gottardo, Miguel Madurga To date, state-of-the-art theories treat β-delayed neutron emission (β-n) as a two-step process. Following β decay, neutron-unbound states undergo statistical neutron emission according to the compound-nucleus (CN) hypothesis. However, a large discrepancy was recently observed in the β-n branching ratios of 134In between experimental data and model prediction [1], bringing a challenge to the validity of the approach near shell closures where nuclear level density is generally low. In this contribution, we will present an experimental work studying the β-n branching ratios in the vicinity of 54Ca at the ISOLDE Decay Station at CERN. Combining high-resolution γ and neutron TOF spectroscopy, we measured the neutron branching ratios from the states between 5 and 10 MeV in 51,52,53Ca, respectively, following the β decays of 51,52,53K. The results were compared with the Hauser-Feshbach model [2]. Despite the proximity to the shell closures (Z=20, N=32, 34), we found surprisingly good agreement with only a few exceptions, which were attributed to the nuclear structure effect from the nearby doorway states, the states having large spectroscopic overlaps with the β-n daughter, interacting with the states populated in β decay and affecting the neutron-emission branching ratios. The results provide substantially new insight into understanding the β-n process in medium-heavy and heavy nuclei. |
Thursday, November 30, 2023 11:00AM - 11:15AM |
F10.00009: Study of the β-delayed multi-neutron emission process through γ-neutron spectroscopy of Gallium Isotopes. Rin Yokoyama, Robert Grzywacz, Bertis C Rasco, Krzysztof Piotr P Rykaczewski, Iris Dillmann, Jose-Louis Tain, Shunji Nishimura
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