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 JE: Mini-Symposium Astromers: Nuclear Isomers in Astrophysics I |
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Chair: Kelly Chipps, ORNL Room: Park & Scollay |
Wednesday, October 13, 2021 9:30AM - 10:06AM |
JE.00001: Astromers: Astrophysical Isomers Invited Speaker: G. Wendell Misch Astrophysical nucleosynthesis simulations require accurate nuclear data input, especially the reaction cross sections and decay rates that connect isotopes in a nucleosynthesis network. In most calculations, the inputs typically come from either ground state properties or a thermal equilibrium population of excited states; however, nuclear isomers (metastable excited states) cause some isotopes to behave differently. Some isomers retain their metastibility in astrophysical nucleosynthesis sites, making them astrophysical isomers, or "astromers". When this occurs, such an astromer can undergo transmutation (reaction or decay) at a rate very different from the ground state, and its relative population may be driven far from thermal equilibrium. As a consequence, neither the ground-state nor thermal-equilibrium nuclear properties apply, and the isotope may need to be included in a nucleosynthesis simulation as multiple species: a ground state, and one or more astromers. This issue has been recognized for over forty years, but it has been carefully studied in only a small handful of isotopes. We are at last entering an era of broad research on the topic of astromers, including identifying which are important, new ways to study them in simulations, and what properties are essential to measure experimentally. |
Wednesday, October 13, 2021 10:06AM - 10:18AM |
JE.00002: Study of 34mCl beam production at the National Superconducting Cyclotron Laboratory Olalekan A Shehu, Benjamin Crider, Calem R Hoffman, Tom Ginter The 34Cl(p,γ)35Ar reaction is an important step in the study of the creation of heavy nuclei during the rapid proton capture nucleosynthesis (r-p process) in supernova. Study of this reaction is important for reducing uncertainties in supernova model. Such studies are largely dependent on being able to maximize the 34Cl isomer beam content. One of such experiment was carried out at the National Superconducting Cyclotron Laboratory (NSCL) β-decay experimental station to determine the optimum isomeric ratio in the production of 34Cl. Ions from the Coupled Cyclotron Facility (CCF) at NSCL was implanted on a 3 mm thick CeBr3 implantation detector and subsequent decay was detected using 16 Segmented Germanium Array (SeGA) detectors. The 34Cl was identified using the Time-of-Flight (TOF) and energy loss (△E) information between a scintillator and a silicon PIN detector. To probe and maximize the isomeric beam content of 34Cl, 6 different beam settings were utilized where 2 of the beam settings altered its beam angle before entering the A1900 fragment separator. Three gamma rays (1177, 2127, 3304 keV) corresponding to the decay of 34Cl were detected in the SeGA detectors and this further resulted into the calculation of the absolute rate for each energy. The overall number of 34Cl counts delivered was also calculated to finalize the isomeric beam content for each beam setting. |
Wednesday, October 13, 2021 10:18AM - 10:30AM |
JE.00003: Constraining astrophysical reaction rates on ground-states and astromers at ReA: simultaneous measurement of the 38g,mK(d,p) reactions Steven D Pain, Kelly A Chipps, Raymond L Kozub, Alain Lapierre, Chandana S Sumithrarachchi, Antonio C Villari The combination of ReA@FRIB will provide unique opportunities for simultaneous studies of reactions on nuclides where reactions on ground states and astromers play a role. The ReA facility can provide high-quality mixed beams of ground and isomeric states, the ratio of which can be manipulated by adjusting the fragment separator settings and hold-up times in the stopping and reacceleration process, without impact on beam optics. This control can be used to disentangle reaction cross sections measured on the two beam components with minimal systematic impacts on the experimental response. This technique has been demonstrated with a study of the 38g,mK(d,p) reactions, using ReA@NSCL, to constrain the astrophysical 38g,mK(p,g) reaction rates via mirror symmetry. These reaction rates are bottlenecks impacting the final abundances around the endpoint of nucleosynthesis in ONe novae, including isotopic abundances of Ca and Ar. Details of the technique and experiment will be presented, along with an outlook toward such measurement opportunities at FRIB. |
Wednesday, October 13, 2021 10:30AM - 10:42AM |
JE.00004: Contributions of the $^{24}$Al Isomer to rp-process Nucleosynthesis Nathan A Gerken, Sergio J Almaraz-Calderon, Benjamin W Asher, Eilen Lopez-Saveedra, Lagy T Baby, Kirby W Kemper, Ashton B Morelock, Jesus F Perello, Alexander S Volya, Ingo L Wiedenhoever The $^{24}$Al(p,$\gamma$)$^{25}$Si reaction, is a key step in rp-process nucleosynthesis taking nuclear material out of the Ne-Na region into heavier elements. The rate of this reaction is also important in the identification of isotopic silicon abundances in presolar grains. The existence of low-lying isomers in nuclei could impact rate calculations in astrophysical scenarios. The $^{24}$Na$^{m}$(d,p)$^{25}$Na reaction was studied at the John D. Fox Accelerator Laboratory at Florida State University using a radioactive beam of $^{24}$Na with 90$\%$ of its content in its 1$^{+}$ isomeric state (E$_{ex}$ = 0.472 MeV, t$_{1/2}$ = 20.18 ms). This reaction selectively populated $\ell$ = 0 transfers, allowing the study of low-spin states in $^{25}$Na. Mirror symmetry arguments were then used to extract experimental information of unbound states in $^{25}$Si populated by proton captures on the 1+ isomeric state in $^{24}$Al. In this talk, results of the experiment and astrophysical implications will be presented. |
Wednesday, October 13, 2021 10:42AM - 10:54AM |
JE.00005: Neutron transfer reactions on the ground and isomeric states of a 130Sn beam Kate L Jones, Anissa Bey, Sean P Burcher, James M Allmond, Alfredo Galindo-Uribarri, David C Radford, Sunghoon Ahn, Andrew Ayres, Dan W Bardayan, Jolie A Cizewski, Ronald Garcia, Meridith Howard, Raymond L Kozub, Junjien Liang, Brett Manning, Milan Matos, Caroline Nesaraja, Patrick D O'Malley, Elizabeth Padilla-Rodal, Steven D Pain, Stephen Pittman, Andrew Ratkiewicz, Kyle Schmitt, Michael S Smith, Daniel W Stracener, Robert L Varner The structure of nuclei around 132Sn is of particular interest due to the vicinity of the Z = 50 and N = 82 shell closures and the r-process path. Four states in 131Sn with a strong single-particle-like component have previously been studied via the (d,p) reaction, with limited excitation energy resolution. The 130Sn(9Be,8Be)131Sn and 130Sn(13C,12C)131Sn single-neutron transfer reactions were performed in inverse kinematics at the former Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory using particle-γ coincidence spectroscopy. The uncertainties in the energies of the single-particle-like states have been greatly reduced by using the energies of γ rays. The previous tentative Jπ values have been confirmed. Decays from high-spin states in 131Sn have been observed following transfer on the isomeric component of the 130Sn beam. This is the first measurement of transfer on an isomer in the 132Sn region. The improved energies and confirmed spin-parities of the p-wave states important to the r-process lead to direct-semidirect cross-sections for neutron capture on the ground state of 130Sn at 30 keV that are in agreement with previous analyses. A similar assessment of the impact of neutron-transfer on the isomer would require significant nuclear structure and reaction theory input. |
Wednesday, October 13, 2021 10:54AM - 11:06AM Not Participating |
JE.00006: Investigating the structure of the 0+2 isomeric state of 12Be. Francesc Yasid Ayyad Limonge, Benjamin P Kay The 12Be nucleus is at a crossroad of the nuclear landscape where different phenomena such as neutron halo and disappearance of conventional magic numbers meet. This intriguing isotope has a low-lying isomeric 0+ state of 2.24 MeV with a lifetime of 331 ns (near the neutron separationenergy) which is a potential halo candidate. In this talk, we will present the experimental campaign to elucidate the nature of this isomeric state via elastic and inelastic scattering reactions. The development of the isomeric beam and the experiments will be conducted at ATLAS (ANL) withthe Active Target Time Projection Chamber (AT-TPC). |
Wednesday, October 13, 2021 11:06AM - 11:18AM |
JE.00007: Single-particle structure of 12Be isomeric 0+ state and its possible contribution to 13Be low-lying states Jie Chen, Benjamin P Kay, Daniel Bazin, Calem R Hoffman The Be isotopic chain has been essential for understanding the breakdown of N=8. The disappearance of N = 8 magic number is, among other things, evidenced by the presence of a low-lying isomeric state 0+ at 2.24 MeV in 12Be. A recent one-neutron transfer reaction applied an isomer-tagging and obtained the s-wave component ~39% for the 0+2 state while only ~19% for the g.s. In order to directly measure the spectroscopic factor of the 02+ state in 12Be, a new measurement of 11Be(d,p)12Be reaction has been proposed using ISOLDE Solenoid Spectrometer (ISS) at CERN, taking advantage of its excellent resolution to isolate the 02+ and 2+ doublet. To determine the evolution of the s1/2, p1/2 and d5/2 single-particle energies, and to investigate the contribution of the core excitation component, an experiment was proposed to study the structure of the low-lying states of 13Be using a (d,p) reaction on a 12Be beam containing both its ground and isomeric states. The measurement will be carried out at the RCNP, using the active target time projection chamber (AT-TPC) from NSCL, Michigan State University. |
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