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 LG: Nuclear Structure : A = 70-100 |
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Chair: Jun Chen, MSU Room: Copley & Kenmore |
Wednesday, October 13, 2021 2:00PM - 2:12PM |
LG.00001: Identification of a new isomeric state in 76Zn following the β decay of 76Cu Aaron Chester, Alex Brown, Michael P Carpenter, James J Carroll, Christopher J Chiara, Patrick Copp, Benjamin P Crider, Jason T Harke, Daniel Hoff, Kay Kolos, Sean N Liddick, Brenden Longfellow, Mejdi J Mogannam, Timilehin H Ogunbeku, Andrea L Richard, Olalekan A Shehu, Ronald Unz, Yongchi Xiao Shell evolution far from stability can be explored by measuring the properties of isomeric states, which provide a sensitive probe of the microscopic structure of the nucleus. Beta decay is an attractive method for isomer identification because daughter nuclei can be populated in an excited state which subsequently decays to the ground state through one or more isomeric transitions. A β-decay experiment was recently performed at the National Superconducting Cyclotron Laboratory (NSCL) to identify and study isomeric states in the vicinity of the doubly magic nucleus 78Ni. Radioactive ions produced by beam fragmentation at the NSCL's Coupled Cyclotron Facility were implanted into a CeBr3 scintillator detector coupled to a position-sensitive photomultiplier tube (PSPMT). Ancillary arrays of HPGe clover and LaBr3 detectors were positioned around the implantation detector to measure β-delayed γ rays. The entire suite of detectors was instrumented with the NSCL Digital Data Acquisition System (DDAS). Dynode traces recorded by DDAS were analyzed to selectively identify isomeric transitions. The previously observed 2634-keV level in 76Zn, populated following the β decay of 76Cu, was identified as isomeric with a half-life of 25.4(4) ns. A combination of timing and γ-ray spectroscopy was used to confirm this assignment. Shell-model calculations were performed which indicate that this state may be a high-spin negative-parity state formed by the occupation of the neutron 0g9/2 orbital. The experimental results and theoretical interpretation will be presented. |
Wednesday, October 13, 2021 2:12PM - 2:24PM |
LG.00002: Mass of self-conjugate nucleus 80Zr reveals a deformed double shell closure at N=Z=40 Alec S Hamaker, Erich Leistenschneider, Rahul Jain, Georg Bollen, Samuel Andrea Giuliani, Kasey R Lund, Witold Nazarewicz, Leo Neufcourt, Catherine R Nicoloff, Daniel J Puentes, Ryan J Ringle, Chandana S Sumithrarachchi, Isaac T Yandow The neutron-deficient region around 80Zr is an area of great interest for nuclear structure due to the rapid change in nuclear shape with proton and neutron numbers. For the self-conjugate 80Zr nucleus, spherical and deformed structures are expected to coexist at low energies, and their competition strongly depends on the size of the calculated N=Z=40 gap. In addition to shape-coexistence effects, 80Zr offers a venue to study the Wigner energy reflecting an additional binding in self-conjugate nuclei and their neighbors. Mass differences can be used to probe the strength of these effects; however, mass data in the region is sparse. In this talk, I will present results from the first Penning trap mass measurement of 80Zr using the Low Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory. Our measurement reveals a significant enhancement in the binding energy of 80Zr. Through binding-energy indicators, we attribute this enhancement to the deformed double shell closure at N=Z=40 and an increase in the Wigner energy of this exotic system. A statistical Bayesian model mixing analysis employing eleven global nuclear mass models demonstrates difficulties with reproducing the observed mass anomaly using current theory. |
Wednesday, October 13, 2021 2:24PM - 2:36PM |
LG.00003: Nuclear Excitation via Electron Capture with TITAN Jon B Ringuette, Kyle G Leach, Ania Kwiatkowski, Iris Dillmann, Zachary Hockenbery, Thomas Brunner, Corrina Andreoiu Nuclear Excitation via Electron Capture (NEEC) is the inverse process of internal electron conversion, where a free electron is captured into an atomic vacancy simultaneously exciting the nucleus to a higher-energy state. This process occurs naturally in hot astrophysical environments, and can excite nuclei in these isomeric states to shorter-lived states that would decay at a much faster rate than under terrestrial conditions, thus affecting reaction flows or survival rate of nuclei. Since NEEC is a resonant process, experimental access in the lab to study these cases requires strong atomic charge-state control over the sample, as well as careful selection and preparation of nuclear states that may be compatible with efficient electron recombination. Using an open-geometry electron beam ion trap (EBIT) in the TITAN experiment at the TRIUMF facility we are able to perform these studies with a high level of control and sensitivity. In this talk I will discuss the experimental concept, cases that we plan on studying in the near future, simulation results, as well as current and ongoing upgrades being made to the TITAN system. |
Wednesday, October 13, 2021 2:36PM - 2:48PM |
LG.00004: Nuclear excitation by electron capture in excited ions Simone Gargiulo, Ivan Madan, Fabrizio Carbone Since its recent observation in the 93Mo isomer depletion, nuclear excitation by electron capture (NEEC) is the object of a live debate: the large measured excitation probability Pexc differs by nine orders of magnitude from the state-of-the-art theoretical predictions. A new study slightly increased this theoretical limit, accounting for the momentum distribution of the target electrons. Authors showed that the depletion probability increases by several orders of magnitude in case of the L-shell. However, these L-channels do not contribute significantly to the Pexc. So far, the evaluation of the NEEC cross section has been carried out widely using the assumption that the ion is in its electronic ground state prior to the capture (GSA), prohibiting the capture in the innermost-shells as soon as the atomic orbitals fill up. For 73Ge this means that NEEC into K-shell cannot occur: the energy released through a K-capture exceeds the nuclear transition energy. By lifting this restriction and considering NEEC in excited ions, we show for 73Ge that many more capture channels emerge. These excited electronic configurations make K-capture now possible, through new channels with resonance strengths larger than any other channel obtained under GSA. |
Wednesday, October 13, 2021 2:48PM - 3:00PM |
LG.00005: Beta decay properties in the doubly magic 78Ni region Krzysztof Piotr P Rykaczewski, Robert Grzywacz, Nathan Brewer, Bertis C Rasco, Daniel W Stracener, James Allmond 78Ni is the only doubly magic nucleus known to exhibit both decay modes, the β-delayed gamma and β-delayed neutron emission. These properties of 78Ni and of nuclei around it, recently studied by BRIKEN collaboration, determine the content of the seed region for the further evolution of the r-process nucleosynthesis. |
Wednesday, October 13, 2021 3:00PM - 3:12PM |
LG.00006: First measurement of β-decay strength to neutron-unbound states in the decay of Cu isotopes with N≥50 Maninder Singh, Rin Yokoyama, Robert Grzywacz, Thomas T King, Shunji Nishimura, Jeremy Bundgaard, Pierre Brionnet, Nathan Brewer, Ian C Cox, Aleksandra Fijalkowska, Luis M Fraile, Shintaro Go, Andrea Gottardo, Marek Karny, Andrew M Keeler, Agnieszka Korgul, Miguel Madurga, Krzysztof Miernik, Shree K Neupane, Megumi NIIKURA, Shimizu Noritaka, Marek Pfützner, Monika Piersa, Mustafa M Rajabali, Charlie C Rasco, Krzysztof Rykaczewski, Michal Silkowski, michal Stepaniuk, Jose L Tain, Alvaro Tolosa-Delgado, Zhengyu Xu, Marzena Wolinska-Cichocka Cu isotopes with N ≥ 50 lying on the r-process pathway offer a laboratory to study the nature of nuclear forces in nuclei with a large neutron-to-proton (N/Z) ratio and also engage in β-delayed neutron emission. Most of the β-decay strength from the decay of these nuclei is expected due to Gamow-Teller transitions above the neutron separation energy of the daughter nucleus. An experiment for measuring the strength distribution in the 78Ni region (27≤Z≤33) was performed at the RIBF facility at RIKEN Nishina Center, JAPAN using a YSO-based implantation detector [1] and VANDLE [2] array for Time-of-Flight-based spectroscopy of the β-delayed neutrons. For γ-ray detection, two HPGe clovers and 10 LaBr3 detectors were used. This contribution presents the first results on the β-decay feeding to neutron-unbound states in the decay of 79,80,81Cu. For 79Cu decay, we identified neutrons in the energy range ~ 0.3-2.3 MeV, emitted from neutron-unbound states in 79Zn. We also identified neutrons in coincidence with the 2+→0+ transition of 730 keV to the ground state in 78Zn, needed to ascertain the excitation energy for strength distribution. For 80,81Cu (N = 51,52), we report on the first measurement of the β-delayed neutron spectra. These measurements will highlight the impact of the N=50 shell-closure on β-decay. |
Wednesday, October 13, 2021 3:12PM - 3:24PM |
LG.00007: Abstract Withdrawn
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Wednesday, October 13, 2021 3:24PM - 3:36PM |
LG.00008: Constraining the ground-state spin of 71Kr by β-delayed proton emission Sanjanee W Waniganeththi, Daniel E Hoff, Andrew M Rogers, Peter C Bender, Kristyn H Brandenburg, Katherine L Childers, Jason A Clark, Alexander C Dombos, Emery Doucet, Shilun Jin, Rebecca Lewis, Sean N Liddick, Christopher J Lister, Zachary P Meisel, Chris Morse, Hendrik Schatz, Konrad Schmidt, Douglas B Soltesz, Shiv K Subedi Nuclei in the vicinity of the N=Z line are a sensitive probe of isospin symmetry. In particular, the character of low-lying and ground states of the T=1/2 mirror pair, 71Kr and 71Br, has been under debate for several decades where 71Br has a first-excited state energy of only 10 keV. β-delayed protons emitted from 71Kr were measured via an implantation-decay experiment at NSCL using the Beta counting station coupled to SeGA. We report results on the first experimental observation of β-decay feeding the 407-keV level in 71Br and delayed-proton feeding to the 944-keV state of 70Se. Several methods for determining the β-delayed proton branching were investigated, highlighting an often-neglected source of systematic error. The intensity of γ-ray transitions was used to build the low lying β-decay scheme of 71Kr, allowing for a better understanding of the symmetry between 71Kr and 71Br. This material is based upon work supported by the U.S. DOE, Office of Science, Office of Nuclear Physics under Award No. DE- FG02-94ER40848, DE-FG02-88ER40387 and DE-AC02-06CH11357; the NNSA through the Nuclear Science and Security Consortium under Award No. DE-NA0003180, DE-NA0003221, DE-NA0002132 and DE- NA0000979; and the NSF under Contract No. PHY-1102511. |
Wednesday, October 13, 2021 3:36PM - 3:48PM |
LG.00009: Study of beta-delayed multi-neutron emission of the neutron-rich Ga isotopes Rin N Yokoyama, Robert Grzywacz, Bertis C Rasco, Nathan Brewer, Krzysztof Rykaczewski, Jose L Tain, Iris Dillmann, Shunji Nishimura, Deuksoon Ahn, Alfredo Estrade, Alejandro Algora, James M Allmond, Jorge Agramunt, Hidetada Baba, Sunghan Bae, Carlo Bruno, Roger Caballero-Folch, Francisco Calvino, Patrick Coleman-Smith, Guillem Cortes, Tom Davinson, C\'{e}sar Domingo-Pardo, Naoki Fukuda, Shintaro Go, Christopher J. Griffin, Jeongsu Ha, Oscar Hall, Laura Harkness-Brennan, Joseph Heideman, Tadaaki Isobe, David Kahl, Marek Karny, Toshihiko Kawano, Le Hong Khiem, Thomas T King, Gabor Kiss, Agnieszka Korgul, Shigeru Kubono, Marc Labiche, Ian Lazarus, Jenny H. C. Lee, Johnson Liang, Jiajian Liu, Giuseppe Lorusso, Miguel Madurga, Keishi Matsui, Krzysztof Miernik, Fernando Montes, Ana I. Morales, Paul Morrall, Neerajan Nepal, Robert D. Page, Vi H. Phong, Monika Piersa, Mark Prydderch, Vic F. E. Pucknell, Mustafa M Rajabali, Berta Rubio, Yukiya Saito, Hiroyoshi Sakurai, Yohei Shimizu, John Simpson, Maninder Singh, Daniel W Stracener, Toshiyuki Sumikama, Rebecca A Surman, Hiroshi Suzuki, Hiroyuki Takeda, Ariel Tarife\~{n}o-Saldivia, Stephen L. Thomas, Alvaro Tolosa-Delgado, Marzena Wolinska-Cichocka, Phil Woods, Xin X. Xu
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