Bulletin of the American Physical Society
2019 Fall Meeting of the APS Division of Nuclear Physics
Volume 64, Number 12
Monday–Thursday, October 14–17, 2019; Crystal City, Virginia
Session FN: Nuclear Structure I |
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Chair: Lee Sobotka, Washington University in Saint Louis Room: Salon K |
Tuesday, October 15, 2019 10:30AM - 10:42AM |
FN.00001: Studying Low-Lying States of $^{\mathrm{9}}$B with a Super-Enge Split-Pole Spectrograph (SE-SPS) Rachel Malecek We used the single-particle transfer reaction, $^{\mathrm{10}}$B($^{\mathrm{3}}$He, $\alpha )$, to investigate the structure of the light, neutron-deficient nucleus $^{\mathrm{9}}$B. We are interested in $^{\mathrm{9}}$B specifically because years of previous efforts have yet to agree on definitive results for the energy, width, and spin-parity of its first-excited state. Over the years, there have been many attempts to measure the energy and width of this state of $^{\mathrm{9}}$B, which is thought to be the mirror of the first-excited state of $^{\mathrm{9}}$Be. However, because this is a difficult state to populate, the experimental results vary between 0.7 to 1.8 MeV for the energy and 0.3 to 1.5 MeV for the width. We performed the $^{\mathrm{10}}$B($^{\mathrm{3}}$He,$\alpha )$ reaction with the tandem accelerator at Florida State University. A 24-MeV $^{\mathrm{3}}$He beam was incident on an isotopically enriched self-supporting $^{\mathrm{10}}$B target. Alpha particles were momentum-analyzed by the new SE-SPS and detected at the focal plane while protons were detected by Double-Sided Silicon Strip Detectors at backward angles. Data was taken every 5 degrees between 5 degrees and 35 degrees in the laboratory frame. Preliminary results will be presented. [Preview Abstract] |
Tuesday, October 15, 2019 10:42AM - 10:54AM |
FN.00002: Nuclear Charge Radii of $^{\mathrm{10,11}}$B Peter Mueller, Alessandro Lovato, R.B. Wiringa, Bernhard Maass, Thomas Huether, Kristian Koenig, Joerg Kraemer, Jan Krause, Wilfried Noertershaeuser, Robert Roth, Felix Sommer, Rodolfo Sanchez, Krzysztof Pachucki, Mariusz Puchalski We present the first laser spectroscopic determination of the change in the nuclear charge radius in boron isotopes. This is achieved by combining high-accuracy \textit{ab initio} mass-shift calculations and a high-resolution measurement of the isotope shift in the transition frequency from the ground state to the respective excited state in boron atoms. Accuracy is increased by orders of magnitude for the stable isotopes $^{\mathrm{10,11}}$B compared to previous measurements. The results are used to extract the difference in the mean-square charge radius \textless $r_{\mathrm{c}}^{\mathrm{2}}$\textgreater $^{\mathrm{11}} \quad -$ \textless $r_{\mathrm{c}}^{\mathrm{2}}$\textgreater $^{\mathrm{10}} \quad = \quad -$0.49(12) fm$^{\mathrm{2}}$. This value serves as a benchmark for new \textit{ab initio} nuclear structure calculations using the no-core shell model and Green's function Monte Carlo approaches. In addition, this work is the foundation for a laser spectroscopic determination of the charge radius of the proton-rich, short-lived $^{\mathrm{8}}$B in preparation at Argonne's ATLAS facility. [Preview Abstract] |
Tuesday, October 15, 2019 10:54AM - 11:06AM |
FN.00003: Weak Decays of Halo Nuclei in Effective Field Theory Zichao Yang, Wael Elkamhawy, Hans-Werner Hammer, Lucas Platter ~ Halo nuclei display a large separation scales, which can be used to treat halo systems using an effective field theory called Halo EFT. We consider the weak decay of valence neutron in one-neutron halo nuclei within this framework for the first time. We calculate the decay strength and the partial decay rate of selected halo nuclei, especially $^{11}$Be and $^{31}$Ne. We describe thereby the process of beta-delayed proton emission. These systems have been considered previously by Baye and Tursunov, but we use updated experimental input parameters. Furthermore, we discuss the uncertainties resulting from these input parameters but also those arising from the effective field theory approach to this process. We discuss the recoil effect of weak decay and resonance in the final state as well. [Preview Abstract] |
Tuesday, October 15, 2019 11:06AM - 11:18AM |
FN.00004: Probing single-particle $^{\mathrm{11}}$C levels produced via the $^{\mathrm{10}}$C(d,p) reaction Matthew Baines, Dan Bardayan, Patrick O'malley, Sebastian Aguilar, Samuel Henderson, Scott Carmichael, Lauren Callahan, Chevelle Boomershine, Jacob Long, Drew Blankstein, Louis Caves, Tan Ahn, Maxime Brodeur, James Kolata, Gavin Lotay, Paul Stevenson There has been tremendous progress in recent years using no-core shell-model approaches to calculate the low-lying level structures of light nuclei. Important constraints to such calculations come from the spectra of single-particle and single-hole states of nuclei near strongly bound spherical nuclei such as Carbon-12. While Carbon-11 has been studied by neutron removal from Carbon-12 and proton addition to Boron-10, the single-neutron states have never been directly probed. The (d,p) reaction on Carbon-10 was studied at the Notre Dame Nuclear Science Laboratory to probe these single-particle states. The experiment and preliminary data will be presented. [Preview Abstract] |
Tuesday, October 15, 2019 11:18AM - 11:30AM |
FN.00005: Ab initio predictions for $^{12}\mathrm{C}$ Anna McCoy, Petr Navratil Obtaining accurate predictions of nuclear structure starting from the interaction between constituent protons and neutrons is a complex, computationally demanding problem, particularly for resonances and continuum states. The \emph{ab initio} no-core shell model with continuum (NCSMC) explicitly builds in both short-range correlations as well as long-range clustering and collective dynamics necessary for accurately describing resonances and continuum states. We present predictions of, e.g., energies, phase shifts and capture cross sections, relevant for the $p+{^{11}\mathrm{B}}\rightarrow{^{12}\mathrm{C}}$ reaction obtained using the NCSMC with interactions from chiral effective field theory as the only input. [Preview Abstract] |
Tuesday, October 15, 2019 11:30AM - 11:42AM |
FN.00006: Measurement of the $B(E2; 2^+ \rightarrow 1^+)$ of $^8$Li and comparisons to \textit{ab initio} calculations S. L. Henderson, T. Ahn, M. A. Caprio, P. J. Fasano, P. D. O'Malley, A. Simon, S. Aguilar, J. J. Kolata, S. Jin Precise measurements of electromagnetic transition strengths in light nuclei can provide stringent tests of nuclear \textit{ab initio} calculations. In the A=7 isobars, specifically $^7$Li and $^7$Be, the B(E2) transition strengths have been used to benchmark different \textit{ab initio} calculations [S.~L.~Henderson \textit{et al.}, Phys.\ Rev.\ C \textbf{99}, 064320 (2019)]. We will continue testing by extending these measurements into the A=8 region and measure the first excited state in $^8$Li, in order to provide additional constraints to these \textit{ab initio} models. These models can give us insight into the structural changes from $^7$Li to $^8$Li due to the addition of a neutron. We have performed a Coulomb excitation experiment to measure the $B(E2; 2+ \rightarrow 1+)$ transition strength in $^8$Li. The $^8$Li was produced and separated with TwinSol and the Coulomb excitation cross section was measured using particle-gamma coincidences. The preliminary B(E2) value will be presented and compared to \textit{ab initio} calculations for $^8$Li, highlighting the structural evolution in Li isotopes due to higher neutron excess. The results of this experiment will also provide a test of the accuracy of available \textit{ab initio} calculations in this light mass region. [Preview Abstract] |
(Author Not Attending)
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FN.00007: Investigating a possible positive value of $K_\tau$, and implications for the symmetry energy Kevin Howard, Umesh Garg, Sierra Weyhmiller, Hidetoshi Akimune, Kyoko Nosaka, Soumya Bagchi, Takanobu Doi, Yuki Fujikawa, Shintaro Okamoto, Mamoru Fujiwara, Tatsuya Furuno, Kento Inaba, Nobu Kobayashi, Shoken Nakamura, Zaihong Yang, Takahiro Kawabata, Nasser Kalantar-Nayestanaki, Muhsin Harakeh, Masatoshi Itoh, Yohei Matsuda, Shinsuke Ota The isoscalar giant monopole resonances (ISGMR) in isotopic chains with large neutron-excess provide excellent constraints for $K_\tau$, the asymmetry term in the nuclear incompressibility. $K_\tau$ has been extracted from the ISGMR in tin and cadmium to be $-550 \pm 100$ MeV, and is critical input to the symmetry energy of nuclear matter. Recent reports on the ISGMR in $^{40,44,48}$Ca contradict the prior studies, concluding that $K_\tau > +500$ MeV. A simultaneous study of the ISGMR in $^{40,42,44,48}$Ca was thus completed at the Research Center for Nuclear Physics. The spectrograph, Grand Raiden, allowed for measurements of background-free angular distributions for inelastic scattering of $386$ MeV $\alpha$-particles. Multipole decomposition analyses isolated the ISGMR strength, and the energies of the compressional mode were extracted. The results and implications will be discussed. [Preview Abstract] |
Tuesday, October 15, 2019 11:54AM - 12:06PM |
FN.00008: The Puzzle of the $^{\mathrm{13}}$Be Jerome Mathew Kovoor, Marija Vostinar, Katherine Jones, Rituparna Kanungo, Sean Burcher, Matthias Holl, Joshua Hooker, Steven D. Pain, Orry Workman A considerable number of experiments have been performed to study the unbound nucleus $^{\mathrm{13}}$Be, however the energy and the ordering of its low-lying states remain unknown. Clarifying the low-lying structure of $^{\mathrm{13}}$Be will help in understanding the evolution of the N$=$8 shell gap and the nature of the nuclei near, or at, the neutron drip line. Additionally, the continuum structures of $^{\mathrm{13}}$Be are important for understanding the Borromean structure of the halo nucleus $^{\mathrm{14}}$Be. We performed the $^{\mathrm{12}}$Be(d,p)$^{\mathrm{13}}$Be transfer reaction in inverse kinematics at ISAC II, TRIUMF. The $^{\mathrm{12}}$Be beam at 9.5 MeV/u interacted with the IRIS solid D$_{\mathrm{2}}$ target, and recoils and ejectiles were detected in an annular silicon detector array. Preliminary analysis and results will be presented here. [Preview Abstract] |
Tuesday, October 15, 2019 12:06PM - 12:18PM |
FN.00009: Search for the $^{15}$Be ground state Anthony Kuchera, Rida Shahid, Nathan Frank, Hayden Karrick The ground state of the unbound nuclide $^{15}$Be remains an open question. The MoNA collaboration has performed two experiments to study the structure of $^{15}$Be at the NSCL. In a first attempt to populate $^{15}$Be, a two-proton removal reaction from a $^{17}$C beam was used and decays were searched for in the $^{14}$Be+n channel. This led to a non-observation due to a lack of $^{14}$Be fragments detected. A follow-up experiment made the first observation of a $^{15}$Be state through the use of a neutron-pickup reaction with a $^{14}$Be beam impinging on a deuterated plastic target. Because of the observed state’s relatively high decay energy, the existence of a $^{15}$Be state lower in energy decaying sequentially through the first excited state in $^{14}$Be resulting in $^{12}$Be+3n is possible. A first attempt to search for this state in the two-proton removal data set yielded low statistics and the data did not indicate the presence of a lower state. The neutron-pickup data are now being reanalyzed to search for the ground state in $^{15}$Be by simultaneously fitting 2-, 3-, 4-body decay energies. Preliminary results indicate evidence for a state in $^{15}$Be decaying by three neutrons that is lower in energy than the previously measured state. [Preview Abstract] |
Tuesday, October 15, 2019 12:18PM - 12:30PM |
FN.00010: Study of the $^{\mathrm{\mathbf{28}}}$\textbf{Mg(t,}$^{\mathrm{\mathbf{30}}}$\textbf{Mg)p reaction to investigate nuclear shell evolution at the boundary of the N}$=$\textbf{20 Island of Inversion} Tammy Zidar Some nuclei far from the valley of stability have been found to have ground state properties that are different than those naively expected from the nuclear shell model. The term island of inversion is used to refer to regions of the nuclear landscape in which deformed intruder configurations dominate nuclear ground, e.g. centered on neutron-rich $^{\mathrm{32}}$Mg. The ratio of $^{\mathrm{30}}$Mg on the border of this region can be used to determine the amount of mixing that occurs moving into the island of inversion. $^{\mathrm{28}}$Mg was delivered by the high-intensity and energy accelerator at the isotope mass separator on-line (HIE-ISOLDE) facility at CERN. The high-purity beam of \textasciitilde 1.8x10$^{\mathrm{6}}$ pps was impinged on a radioactive tritium target resulting in the desired reaction of $^{\mathrm{28}}$Mg(t, $^{\mathrm{30}}$Mg)p. In terms of the experimental setup to study the reaction, two complimentary systems were used: the silicon detector array T-REX, in order to detect and identify the transfer particles, and the MINIBALL -ray spectrometer [2]. The data from these two detectors were used to determine the ratio of the cross-sections of the excited to the ground 0$^{\mathrm{+\thinspace }}$states. Preliminary results and their interpretations will be presented. 1] K. Wimmer et al., Phys. Rev. Lett. 105, 252501 (2010)$\backslash $pard[2] N. Warr et al., Eur. Phys. J. A 49, 40 (2013) [Preview Abstract] |
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