Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y11: Nuclear Reactions: Heavy-Ions/Rare Isotope Beams ILive
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Sponsoring Units: DNP Chair: Cody Parker, Texas A&M |
Tuesday, April 20, 2021 1:30PM - 1:42PM Live |
Y11.00001: Effect of neutron-excess on above-barrier fusion cross-sections in $^{12−15}$C + $^{12}$C: Evidence for increasing neutron dynamics Romualdo Desouza, Varinderjit Singh, Sylvie Hudan, Zidu Lin, Charles Horowitz Examination of the average fusion cross-section at energies above the fusion barrier for $^{12,13,14,15}$C + $^{12}$C reveals that the fusion cross-section increases more rapidly than can be simply attributed to the increased size. Comparison with static barrier penetration models suggests that dynamics are the origin of this increased cross-section. Calculations with a time-dependent Hartree-Fock model also fail to describe the observed trend suggesting that for neutron-rich nuclei, neutron dynamics may play a larger role than is presently accounted for. [Preview Abstract] |
Tuesday, April 20, 2021 1:42PM - 1:54PM Live |
Y11.00002: Assessing the impact of valence sd neutrons and protons on fusion Rohit Kumar, Varinderjit Singh, J. Vadas, T.K. Steinbach, B.B. Wiggins, S. Hudan, R.T. deSouza Assessing the impact of valence sd neutrons and protons on fusion Experimental near-barrier fusion cross-sections for $^{17}$F + $^{12}$C are compared to the fusion excitation functions for $^{16,18}$O, $^{19}$F, and $^{20}$Ne ions on a carbon target. Comparison of the reduced fusion cross-section for the different systems accounts for the differing static size of the incident ions and changes in fusion barrier. Remaining trends of the fusion cross-section above the barrier are observed. These trends are interpreted as the interplay of the sd protons and neutrons. The experimental data are also compared to a widely-used analytic model of near-barrier fusion, a time-dependent Hartree-Fock model, and coupled channels calculations. [Preview Abstract] |
Tuesday, April 20, 2021 1:54PM - 2:06PM Live |
Y11.00003: Fusion of neutron-rich nuclei around the N$=$20 and N$=$28 shell closure. Sylvie Hudan, James Johnstone, Varinderjit Singh, Rekam Giri, Romualdo deSouza, Dieter Ackermann, Abdelouahad Chbihi, Quentin Hourdille, Austin Abbott, Catherine Balhoff, Andy Hannaman, Alan McIntosh, Maxwell Sorensen, Zach Tobin, Adi Wakhle, Sherry Yennello Fusion in neutron-rich environments is presently a topic of considerable interest. Experiments for an isotopic chain allow systematic exploration of the dependence of fusion on neutron number. To study fusion away from the closed N$=$20 and N$=$28 shells and explore the role of the unpaired proton, experiments were conducted at NSCL's ReA3 facility for $^{\mathrm{39,45,47}}$K$+^{\mathrm{16}}$O, $^{\mathrm{28}}$Si and $^{\mathrm{36,44}}$Ar$+^{\mathrm{16}}$O, $^{\mathrm{28}}$Si at near-barrier energies. Details of the E-TOF experimental technique utilized will be discussed. Preliminary results yielding the experimental fusion excitation functions and comparison to theoretical models will also be presented. [Preview Abstract] |
Tuesday, April 20, 2021 2:06PM - 2:18PM Live |
Y11.00004: Identification of Multinucleon Transfer Products with Short-Lived Daughter Nuclei A. Hood, J. Gauthier, K. Hagel, A. Jedele, Y.-W. Lui, A. McIntosh, L. McIntosh, Z. Tobin, R. Wada, A. Wakhle, S. Yennello Multinucleon transfer (MNT) reactions may offer a way to produce new neutron-rich isotopes of known and yet-to-be discovered elements in the heavy and super-heavy mass regimes. Despite decades of study, many open questions remain about MNT reactions. For example, the mechanisms of multinucleon transfers in low-energy collisions of very heavy ions are not well understood. Experimental data are imperative to verify and refine theoretical models. We have used an active catcher array, developed at Texas A\&M University [1], to study short-lived MNT products of the reaction $^{208}$Pb + $^{208}$Pb with a pulsed beam. While the beam is on, the products are implanted in scintillators coupled to photomultiplier tubes. When the beam is off, subsequent $\alpha$-decays are detected and 2$\mu$s-long waveforms are recorded using digitizers. To identify specific MNT products, we performed a search of single digitized waveforms for correlated $\alpha$-decays of parent and daughter nuclei, where the daughter has a short half-life (t$_{1/2}$ $<$ 0.4$\mu$s). The preliminary results of this analysis will be discussed. [1] Wuenschel, S., et al., PRC 90, 011601 (2014). [Preview Abstract] |
Tuesday, April 20, 2021 2:18PM - 2:30PM Live |
Y11.00005: Fission in the Neutron-deficient Lead Region Adam Anthony, Daniel Bazin, Kyle Brown, Zbigniew Chajecki, Thomas Ginter, William Lynch, Wolfgang Mittig, Chenyang Niu, Joseph Wieske Rare isotope beam facilities offer the opportunity to study the physics of isotopes far from stability. Following the discovery of an unexpected region of asymmetric beta-delayed fission in the neutron deficient mercury region, there has been a flurry of work to study fission properties of other nuclei in the region. At the National Superconducting Cyclotron Laboratory (NSCL), an experiment was designed to measure the fission properties of nuclei in the transition region from asymmetric to symmetric fission. A radioactive beam centered around Pb$^{197}$ was produced by the coupled cyclotrons at the NSCL. Helium-induced fusion-fission properties were measured as a function of beam energy. The Active-Target Time Projection Chamber (AT-TPC) served as the helium gas target and was used to separate fusion-fission events from the background. This talk focuses on using a TPC to measure the properties of fission events in an inverse-kinematics setting. [Preview Abstract] |
Tuesday, April 20, 2021 2:30PM - 2:42PM Live |
Y11.00006: Halo-EFT analyses of knockout reactions of $^{11}\rm Be$ and $^{15}\rm C$ Chlo\"e Hebborn, Pierre Capel Knockout reactions are often used to probe the structure of nuclei in the neutron-rich sector [1,2]. Thanks to its weak binding, the valence neutron is easily knocked out of the nucleus. Moreover, the detection efficiency is high since in this process only the residual nucleus is measured after the collision. In a previous work, we have shown that knockout of one-neutron halo nuclei, such as 11Be and 15C, are sensitive mostly to the asymptotics of the initial state of the projectile [3]. Accordingly, reliable information about the tail of the bound-state wave function can be inferred from such observables. In this talk, I reanalyze the knockout data of Refs. [1,2] on 11Be and 15C using a Halo-EFT model of the projectile constrained with the ANCs predicted by ab initio calculations [4] and a Halo-EFT analysis of transfer data [5]. Our results are in excellent agreement with the experimental data, confirming the prediction of the ab initio calculations [4] and the analysis of transfer data [5]. [1] T. Aumann et al., Phys. Rev. Lett. 84, 35 (2000) [2] J. A. Tostevin et al., Phys. Rev. C 66, 024607 (2002) [3] C. Hebborn and P. Capel, Phys. Rev. C 100, 054607 (2019) [4] A. Calci et al., Phys. Rev. Lett. 117, 242501 (2016) [5] L. Moschini et al., Phys. Rev. C 100, 100, 044615 (2019) [Preview Abstract] |
Tuesday, April 20, 2021 2:42PM - 2:54PM Live |
Y11.00007: Influence of $Z$ and $N$ on Fusion-Evaporation Cross Sections for Heavy Element Synthesis Charles Folden A number of major experiments in recent years have attempted to discover the currently unknown elements 119 and 120. There are no widely accepted reports of decay chains that can be attributed to these elements even though these experiments have reported very small upper limit fusion-evaporation cross sections. These reactions, which have utilized projectiles heavier than $^{\mathrm{48}}$Ca, have cross sections that are much smaller than those for $^{\mathrm{48}}$Ca reacting with the same target. In the current research, the influence of $Z$ and $N$ in both the projectile and target on fusion-evaporation cross sections has been investigated. Projectiles of $^{\mathrm{44,48}}$Ca, $^{\mathrm{45}}$Sc, $^{\mathrm{50}}$Ti, and $^{\mathrm{54}}$Cr reacted with lanthanide targets, and a large number of \textit{xn} and \textit{pxn} excitations functions have been measured using the MARS spectrometer at Texas A{\&}M University. The data have been analyzed using a simple model which suggests that the properties of the compound nucleus are critical to the successful formation of fusion-evaporation products. This talk will give an overview of the experiments, the theoretical model, and the implications for the formation of new superheavy elements. [Preview Abstract] |
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