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 B14: Nuclear Structure ILive
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Sponsoring Units: DNP Chair: Robert V.F. Janssens, University of North Carolina at Chapel Hill, Department of Physics & Astronomy |
Saturday, April 17, 2021 10:45AM - 10:57AM Live |
B14.00001: Quantum Monte Carlo calculations of electron scattering for $A \leq 12$ nuclei in the Short-Time-Approximation Lorenzo Andreoli, Saori Pastore, Maria Piarulli, Joseph Carlson, Stefano Gandolfi I will present ab initio calculations for electron scattering off $A \leq 12$ nuclei. Using Quantum Monte Carlo techniques together with the Argonne $v_18$ and Urbana-IX realistic two- and three-body interactions and ensuing accurate nuclear wavefunctions, we evaluate short-time (high-energy) responses in nuclei. Our approach allows us to obtain response densities, in addition to longitudinal and transverse response functions, and consistently includes two-body physics both in the nucleon-nucleon interaction and electromagnetic currents. Relevant for experiments currently being conducted, e.g. at JLAB, our results provide insight into nucleons in back-to-back kinematics, for different combinations of n and p pairs. [Preview Abstract] |
Saturday, April 17, 2021 10:57AM - 11:09AM Live |
B14.00002: Updates on Analysis of Kinematically Complete Measurements of Three-body Photodisintegration of 3He Forrest Friesen, Mohommad Ahmed, Alex Crowell, Arnas Deltuva, Calvin Howell, Collin Malone, Ronald Malone, Werner Tornow, Henryk Witala We report updates on the analysis of our cross-section data for the 3He($\gamma$,pn)p, 3He($\gamma$,pp)n, and 3He($\gamma$,p)np three-body (3B) photodisintegration reactions. The measurements were performed at the High Intensity $\gamma$-ray Source (HIGS) with a 15 MeV linearly polarized photon beam. The beam-target luminosity was determined in-situ using the 3He($\gamma$,p)d reaction. The experimental setup consisted of a collinear set of gas targets flanked by arrays of neutron detectors and collimated silicon strip detectors, allowing for measurements of a variety of kinematic configurations in 3B photodisintegration. The data are compared to ab-initio three-nucleon calculations via GEANT4 simulations of the experiment that include modeling neutron interactions in the liquid scintillator detectors. [Preview Abstract] |
Saturday, April 17, 2021 11:09AM - 11:21AM Live |
B14.00003: Search for novel decay modes using 11Be at NSCL: an update Jason Surbrook, Yassid Ayyad Limonge, Tamas Budner, Marco Cortesi, Moshe Friedman, Cathleen Fry, Brent Glassman, Molly Janasik, Aaron Kruskie, Ruchi Mahajan, Emmanuel Pollacco, Michael Roosa, Jordan Stomps, Lijie Sun, Tyler Wheeler, Christopher Wrede In 2014, the first indirect evidence of $\beta^-$-delayed proton ($\beta^-$p) emission, a novel radioactive decay mode, was observed via the apparent transmutation of a $^{11}$Be source produced by the ISOL technique to $^{10}$Be using accelerator mass spectrometry (AMS). Although the deduced branching ratio was nearly two orders of magnitude greater than expected, the first direct measurement of the $^{11}$Be($\beta^-$p) decay at TRIUMF in 2019 confirmed it. However, attempts to reproduce the AMS measurements in 2020 did not observe the generation of $^{10}$Be and are now inherently at odds with both previous $\beta^-$p measurements. We present the status of an independent search for low-energy protons emitted in the decay of $^{11}$Be using the Gaseous Detector with Germanium Tagging (GADGET) at the NSCL. The second run has generated 15 times more data than the initial run presented at the 2019 APS April Meeting, providing better statistical precision and background characterization. [Preview Abstract] |
Saturday, April 17, 2021 11:21AM - 11:33AM Live |
B14.00004: A Search for the 12Be Isomeric State Xinyi Wang The spectroscopy of the neutron unbound 13Be is key to understanding the unexpected structural changes of neutron-rich nuclei around N$=$8. Invariant mass spectra from current experiments cannot determine the 1/2$^{\mathrm{-}}$ p-wave location. This p-wave resonance is expected to strongly decay to a long-lived 0$_{\mathrm{2}}^{\mathrm{+}}$ state in 12Be with a mean lifetime of 331(12) ns. Its decay scheme has a 20{\%} branch through the 12Be(2$^{\mathrm{+}}$ ) to the ground state (2.1 MeV) and 80{\%} for an E0 transition giving two 511 keV gamma rays from positron annihilation. A new experiment has been performed by the MoNA Collaboration at the NSCL to study the neutron decay of 13Be to this isomeric state in 12Be. This experiment features a sweeperless MoNA-LISA setup, with a new telescope detector for 12Be fragment, 96 modules of the MoNA-LISA detector for neutrons emitted, and the gamma ray detector CAESAR, placed around the telescope instead of the reaction target due to the long lifetime of the expected isomer. A digital data acquisition system (DDAS) was applied to fragment, beam and gamma detectors, and synchronized with MoNA-LISA VME based electronics to get coincidence of all the decay products. An overview of the experiment will be presented and discussed. [Preview Abstract] |
Saturday, April 17, 2021 11:33AM - 11:45AM Live |
B14.00005: Investigations of alpha clustering in $^{\mathrm{12}}$C using a TPC detector and gamma beams Robin Smith, Moshe Gai, Sarah R. Stern, Deran K. Schweitzer, Mohammad W. Ahmed, Martin Freer, Hans O. U. Fynbo The $^{\mathrm{12}}$C nucleus is well-described as an exotic three alpha particle structure. The low-energy portion of its excitation spectrum is accurately predicted using the algebraic cluster model \textbf{(ACM),} describing the rotation and vibration of alpha particles with D$_{\mathrm{3h}}$ point group symmetry. In addition to the already-established mixed parity ground state rotational band, a series of rotational levels built on the Hoyle state are predicted, which have not yet been observed. Additionally, the question of whether the Hoyle state can be described as an alpha particle condensate has reached its 20$^{\mathrm{th}}$ year, still without resolution. The nature of the Hoyle state has been examined by us, using gamma beams at HI$\gamma $S at TUNL in conjunction with an Optical TPC detector (O-TPC). Sequential and apparent ``direct'' decays of the 2$^{\mathrm{+\thinspace }}$excitation of the Hoyle state$^{\mathrm{\thinspace }}$were unambiguously identified in the O-TPC and an upper limit on the direct decay branching ratio for the 2$^{\mathrm{+}}$ state was obtained. A theoretical extrapolation allowed the direct decay branching ratio of the Hoyle state to be calculated using three body penetration factors. The deduced B.R. was found to be significantly lower than expected for an alpha particle condensate. [Preview Abstract] |
Saturday, April 17, 2021 11:45AM - 11:57AM Live |
B14.00006: High-precision mass spectrometry approaching the nuclear driplines: an investigation of Ne isotopes near the N $=$ 20 Island of Inversion Andrew Jacobs, Eleanor Dunling, Tobias Murboeck, Coulter Walls, Jens Dilling, Ania Kwiatkowski Mass spectrometry is a common technique used to probe the limits of nuclear existence. By measuring the binding energies of exotic nuclei, crucial clues pertaining to the evolution of nuclear shells, the emergence of deformation, and the existence of exotic structures can be discovered. However, the production rates and half-lives of the isotopes of interest drop sharply as they become increasingly exotic while background production rates remain high. This leads to the obstruction of the isotopes of interest inhibiting their measurement. To overcome this, the Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-ToF-MS) was installed at TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN) and performed its first on-line commissioning in 2017. Due to its high sensitivity and background suppression, the TITAN MR-ToF-MS has enabled mass spectrometry of previously inaccessible isotopes. Since its installation, the TITAN MR-ToF-MS has undergone several upgrades to improve the key performance factors of sensitivity, background suppression, and mass accuracy. These upgrades have allowed for access to more exotic nuclides resulting in measurement campaigns approaching the proton dripline and tracking the so-called `archipelago' of shell-breaking effects, such as Ne isotopes approaching N $=$ 20. [Preview Abstract] |
Saturday, April 17, 2021 11:57AM - 12:09PM Live |
B14.00007: Rigid triaxial deformation in $^{76}$Ge A.D. Ayangeakaa, R.V.F. Janssens, J.M. Allmond, B.A. Brown The possible existence of stable triaxial ground-state deformation in even-even nuclei has been a subject much interest in nuclear structure research. This interest has been motivated largely by the longstanding issue of whether axially-asymmetric nuclei are characterized by rigid or soft triaxiality in their ground-state configurations. Indeed, while signatures of static triaxial deformation has long been established at high angular momenta, the experimental observation of rigid triaxiality at low-spin has remained a challenge. In this study, experimental evidence for static triaxial ground-state deformation in $^{76}$Ge will be presented from a model-independent perspective. This will be complemented by results of large-scale shell model calculations and multi-configuration mixing calculations carried out within the framework of the triaxial rotor model. [Preview Abstract] |
Saturday, April 17, 2021 12:09PM - 12:21PM Live |
B14.00008: Precise Q value measurements of $^{112,113}$Ag and $^{115}$Cd with the Canadian Penning Trap for evaluation of potential ultra-low Q value $\beta$-decays N. Gamage, R. Sandler, M. Redshaw, J. Clark, R. Dwaipayan, K. Sharma, R. Orford, F. Buchinger, G. Savard, W. Porter Ultra low Q-value (ULQ) $\beta$-decays in which the parent decays to an excited state of the daughter with a Q$<$1 keV, are of interest as potential candidates for neutrino mass determination experiments, and to investigate atomic interference effects in $\beta$-decay. To date, the only known ULQ $\beta$-decay is that of $^{115}$In to the $^{115}$Sn(3/2$^{+}$) state with Q = 155(24) eV. A number of other potential ULQ $\beta$-decays have been identified using atomic mass and nuclear energy level data, but more precise masses are required to determine if the potential decays are energetically allowed and $<$1 keV. Penning traps have performed more precise Q value determinations for some of these candidates, including $^{89}$Sr and $^{139}$Ba with LEBIT at NSCL/FRIB, which ruled them out, and $^{135}$Cs with JYFLTRAP at Jyv\"{a}skyla, which showed that it is a potential candidate. Here we present results of Q value measurements for candidates $^{112,113}$Ag and $^{115}$Cd performed with the Canadian Penning Trap at Argonne National Laboratory. [Preview Abstract] |
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