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 KE: Mini-Symposium Astromers: Nuclear Isomers in Astrophysics II |
Hide Abstracts |
Chair: Sergio Almaraz-Calderon, Florida State University Room: Park & Scollay |
Wednesday, October 13, 2021 11:30AM - 11:42AM |
KE.00001: Measurements of Isomer Energies in Potential “Astromers” Kay Kolos, Guy Savard, G. W. Misch, Matthew R Mumpower, Rodney Orford, Miguel Bencomo, Nicholas D Scielzo, Jason A Clark, Aaron Gallant, Daniel E Hoff, Filip G Kondev, Wei Jia Ong, Dwaipayan Ray, Daniel Santiago-Gonzalez, Kumar S Sharma, Adrian A Valverde, Xinliang L Yan Beta-decay properties like half-lives, decay branching ratios and isomeric states are key inputs for astrophysical nucleosynthesis calculations, and the availability and accuracy of this nuclear data directly impact the quality of different model predictions. Nuclear isomers play a significant role in determining the abundances of the elements in the universe. Refined studies of the influence of the “astromers", the nuclear isomers that are populated in astrophysical environments, have recently demonstrated both that astromers can play a prominent role in nucleosynthesis, and that essential nuclear data is missing [Mis21a, Mis21b]. We proposed a measurement that uses radioactive beams produced at CARIBU to measure the energy difference between the ground state and isomeric states of several key astromers with the Canadian Penning Trap (CPT). Better measurements of the energy of these isomers will improve r-process nucleosynthesis calculations by helping to clarify transition rates, thermalization temperatures, and astromer populations as they freeze out in the rapidly cooling post-r-process environment. |
Wednesday, October 13, 2021 11:42AM - 11:54AM |
KE.00002: Progress at the N=126 factory and its application to identify and characterize long-lived isomers Guy Savard, Maxime Brodeur, Nathan Callahan, Jason A Clark, Daniel P Burdette, Russell Knaack, Biying Liu, Jacob Long, James M Kelly, Patrick D O'Malley, Dwaipayan Ray, Xinliang L Yan, Marc A Yeck The N=126 factory, currently under construction at the ATLAS facility at ANL, will provide access to heavy neutron-rich isotopes of interest to astrophysics and nuclear structure studies. This will allow measurements on isotopes and long-lived isomers in the so-far unexplored region around the N=126 line. The CPT Penning trap mass spectrometer, currently being used at CARIBU to measure masses and identify long-lived isomers, will be moved to the N=126 factory to extend these measurements to heavier nuclei. The N=126 factory and the technique developed to characterize isomers with the CPT spectrometer will be described. Recent results at CARIBU will be presented together with the expected reach of the system when installed at the N=126 factory. |
Wednesday, October 13, 2021 11:54AM - 12:06PM |
KE.00003: Decay properties of low- and high-spin beta-decaying isomers in 146La Nathan Giha, Filip G Kondev, Patrick Copp, Michael P Carpenter, Guy Savard, Kalle Auranen, Jason A Clark, Torben Lauritsen, Walter Reviol, Dariusz Seweryniak, Daniel Santiago-Gonzalez, Sana Stolze, Fredrik Tovesson, Jin Wu, Scott T Marley, Akaa D Ayangeakaa, Daryl J Hartley, Sara A Pozzi The properties of neutron-rich nuclei in the fission-product region are of significant interest to the nuclear-structure and astrophysics fields. These data are also of importance to various applied areas, such as reconstruction of antineutrino spectra for non-proliferation applications and accurate determination of fission product yields. We have studied the beta-decay properties of 146La using the high-purity beams provided by the ANL CARIBU facility and the recently commissioned Gammasphere decay station. For the first time, comprehensive decay schemes for the low- and high-spin isomers in 146La were established and these were found to differ significantly compared to what is presently available in the literature. The spins of the ground and isomeric states were also re-evaluated, and the proposed new values are consistent with the presence of deformed shapes in 146La. Results from these measurements will be presented, together with predictions based on deformed shell model calculations. |
Wednesday, October 13, 2021 12:06PM - 12:18PM |
KE.00004: Level Densities and Gamma-Ray Strengths Inferred from Ground and Isomeric States in 70Cu Andrea L Richard, Sean N Liddick, Artemis Spyrou, Isaac T Yandow, Ryan J Ringle, Aaron Chester, Katherine L Childers, Paul A Deyoung, Jordan Owens-Fryar, Alec S Hamaker, Caley Harris, Rebecca Lewis, Kasey R Lund, Stephanie Lyons, Alicia Palmisano, Daniel J Puentes, Rachel Sandler, Chandana S Sumithrarachchi, Mathis Wiedeking, Yongchi Xiao One of the fundamental assumptions involved in calculations of astrophysical rates and neutron-capture cross sections is the generalized Brink-Axel hypothesis. This states that the gamma-ray strength function (γSF) is independent of how the initial compound nucleus is formed with respect to the initial excitation energy, spin, or parity. Here we test this hypothesis on the basis of the spin-independence of the γSF using 70Cu, which has three β-decaying isomeric states with spins of 6-, 3-, and 1+ for the ground state, 101 keV-state, and 242-keV state, respectively. 70Cu ions were produced at the National Superconducting Cyclotron Laboratory and thermalized in the gas stopper before being transmitted to the Low-Energy Beam Ion Trap Facility (LEBIT), where the isomers were separated based on mass through the LEBIT ion trap. Specific isomers were then delivered from the trap into the Summing NaI (SuN) total absorption spectrometer, where the γSF and nuclear level density (NLD) can be obtained using the β-Oslo method, an indirect technique for constraining neutron-capture cross sections. Preliminary results on the experimental isomer ratios, γSF, and NLD will be presented. |
Wednesday, October 13, 2021 12:18PM - 12:30PM |
KE.00005: Isomer spectroscopy of neutron-rich 180<A<190 nuclei via fragmentation of 198Pt. Kartikeya Sharma, Partha Chowdhury, Andrew M Rogers, Oleg B Tarasov Isomer spectroscopy of deformed neutron-rich nuclei far from stability in the 180<A<190 region were performed at NSCL. Fragmentation products from a newly-developed 198Pt primary beam were implanted in a Si detector stack for particle identification, with decay gamma rays detected in the surrounding GRETINA array. The multi-fold goals of the experiment include nuclear structure (long-predicted K-isomers in neutron-rich Hf nuclei), nuclear astrophysics (decay spectroscopy of nuclei in the r-process pathway relevant for heavy-element nucleosynthesis), isotope discovery (very neutron-rich nuclei), and reaction mechanisms (isomeric yields in fragmentation reactions). Half-life measurements and decay spectroscopy of multi-quasiparticle isomers in neutron-rich Hf, Ta and W nuclei will be presented and discussed. |
Wednesday, October 13, 2021 12:30PM - 12:42PM |
KE.00006: Jade: a radioactive decay network and its application to the treatment of isomers in the r process Trevor M Sprouse, G. W. Misch, Matthew R Mumpower The rapid neutron capture process, or r process, is expected to produce some of the heaviest elements observed to exist in nature. In the immediate aftermath of the r process in astrophysical environments, the nuclei produced are extremely neutron-rich and, therefore, undergo a long period of radioactive decay proceeding through a broad swath of the chart of nuclides, the effect of which can drive a range of observables associated with these events. In this work, we discuss Jade, a radioactive decay network which can include both ground and isomeric nuclear states in modeling the radioactive decay of r process ejecta. |
Wednesday, October 13, 2021 12:42PM - 12:54PM |
KE.00007: Nucleosynthesis Calculations Including the Astromer 85Kr Bradley S Meyer, G. W. Misch, Matthew R Mumpower, Aaron J Couture, Chris Fryer, F. X Timmes The nucleus 85Kr is an astrophysical isomer (an "astromer") since its excited states can be out of equilibrium with its ground state in astrophysical environments. We have computed the nuclear properties of 85Kr as two separate ensembles of states--one tied to the ground state and one tied to the first excited state. We have computed the rate of transitions between these two ensembles, which is the internal equilibration rate for 85Kr, and have also computed transition rates between other species and these two ensembles, such as neutron capture into the ensembles from 84Kr and neutron capture out of each ensemble to 86Kr. With these results, we have included the two ensembles as two separate species (85Krg and 85Krm) in a nuclear reaction network and computed nucleosynthetic yields from a variety of astrophysical settings. We present the results of these calculations, with special attention paid to the role of the 85Kr astromer. |
Wednesday, October 13, 2021 12:54PM - 1:06PM |
KE.00008: A Directed-Graph Branching Treatment of Internal Equilibration Rates and Application to Astromers Sayani Ghosh, Bradley S Meyer The Gupta-Meyer treatment of nuclei with long-lived isomers computes the effective internal equilibration rate by assuming that the higher-lying nuclear levels, through which the ground and isomeric states communicate, are in steady-statel [1]. The effective rate for transition between the ensemble of states associated with the ground state and the ensemble of states associated with the isomeric state then becomes a sum over probabilities of pathways between the ground and isomeric state. These pathways include cycles, and the number of cycles grows dramatically as the temperature increases. Thus, at high temperatures, the number of pathways to sum over becomes large. We have solved for the steady state abundances of the upper-lying levels by means of branchings on a directed graph representing the nuclear levels and the transitions among them. This allows us to factor out the cycles into a factor involving a finite sum, which provides a useful interpretation of the effective transition rates in terms of essential transitions (without cycles) then modified by this factor. The kth best branching algorithm [2] then lets us focus on the most important branchings, which may be relevant for determining the most important transitions for experimental or theoretical study for effective equilibration rates of astromers. |
Wednesday, October 13, 2021 1:06PM - 1:18PM |
KE.00009: Using (p,n) reactions to probe various neutron-induced nucleosynthesis scenarios. Georgios Perdikakis, P. Tsintari, Nikolaos Dimitrakopoulos, Panagiotis Gastis Neutron-induced reactions are key to understand a variety of nucleosynthesis problems. More often than not, however, it is rather hard or even impossible to obtain experimental data on the nuclear reactions of interest that typically involve the reaction of a radioactive nucleus with neutrons. Such reactions are very difficult to measure for short-lived nuclei as neither of the reacting parts can be made into a target. An important effort is being undertaken by the nuclear astrophysics community to find ways to mitigate this experimental limitation using both theory and experiment. While the effort is mostly focused on neutron capture reactions, various astrophysics problems rely critically on the knowledge of reaction rates for (n,p) reactions. In this talk, I will focus on (n,p) reaction rates, and I will present experimental results of our technique that uses (p,n) reactions to constrain (n,p) reactions for nucleosynthesis. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700