Bulletin of the American Physical Society
20th Annual Meeting of the APS Northwest Section
Volume 64, Number 9
Thursday–Saturday, May 16–18, 2019; Western Washington University, Bellingham, Washington
Session G2: Nuclear Physics |
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Chair: Adam Fritsch, Gonzaga University Room: Communications Facility 120 |
Saturday, May 18, 2019 1:30PM - 2:00PM |
G2.00001: The Quest to Observe Matter Creation: Searching for Neutrinoless Double-Beta Decay Invited Speaker: Jason Detwiler The Standard Model of particle physics is arguably the most successful theory in human history, but it fails to account for our own existence. It predicts that matter and antimatter would have been created in equal amounts in the Big Bang, but if that were the case we should have experienced a Great Annihilation, and none of us would be here to ponder what just happened. So there must exist processes in which matter and antimatter are generated asymmetrically. However, no such process has yet been observed. Efforts are underway to search for such a matter creation process in the form of neutrinoless double-beta decay, an ultra-rare nuclear process in which two electrons are generated with no accompanying antiparticles. This hypothetical process could occur if the neutrino and the antineutrino are actually one in the same. I will describe the theoretical motivation for the neutrino to have this so-called "Majorana" nature, and it's possible connection to the matter dominance of the universe, to Grand Unification Theories, and to the lightness of the neutrino itself. I will then provide an overview of the broad, international campaign to observe this process, highlighting the excellent chances for discovery in current and next-generation experiments. [Preview Abstract] |
Saturday, May 18, 2019 2:00PM - 2:12PM |
G2.00002: Time reversal violation in radiative beta decay: experimental progress John Behr, Tine Valencic, James McNeil, Melissa Anholm, Alexandre Gorelov, Dan Melconian, Gerald Gwinner, Danny Ashery Once parity was discovered to be maximally violated in nuclear beta decay in the late 1950's, people immediately proposed many observables to see if time reversal symmetry was also broken. It was soon noticed that the presence of matter but no antimatter in the visible universe can't be accounted for with known physics, and extra sources of time-reversal (besides that found in meson-antimeson systems involving strange, bottom, and charm quarks) could provide a mechanism to generate it. A unique observable for our laser-cooled atom trap is to test for a finite correlation between three outgoing momenta. Any scalar triple product of momenta \vec{p_1} \cdot \vec{p_2} \times \vec{p_3}$ flips sign with the sign of time: if its value does not average to zero, that indicates a violation of time-reversal symmetry. Since this scalar trivially vanishes from momentum conservation if there are only three momenta in the final state, to nontrivially test time-reversal symmetry we will measure the correlation $\vec{p_\beta} \cdot \vec{p_\nu} \times \vec{p_\gamma}$ in radiative beta decay. We will show test data from the $\beta^-$ decay of $^{92}$Rb, taken by adding simple $\gamma$ detectors to the present TRIUMF neutral atom trap. [Preview Abstract] |
Saturday, May 18, 2019 2:12PM - 2:24PM |
G2.00003: Spectroscopy of Doubly-magic $^{132}$Sn with GRIFFIN Kenneth Whitmore The region of neutron-rich tin isotopes near mass number 130 is of great interest to nuclear structure. In particular, $^{132}$Sn with 50 protons and 82 neutrons is a doubly magic nucleus which provides an essential benchmark for the shell model far from stability. Understanding the structure of this nucleus provides a foundation for understanding the single-particle nature of excited states in neighboring isotopes. In addition to nuclear structure considerations, isotopes in this region are also relevant to astrophysics, as their decay properties are essential to understanding r-process nucleosynthesis and its role in creating the $A = 130$ abundance peak. The nucleus $^{132}$Sn has been studied following the $\beta^{-}$ decay of $^{132}$In at the ISAC facility at TRIUMF. The high-purity germanium detectors of GRIFFIN were used to detect $\gamma$ rays in combination with $\beta^{-}$ particle detection with SCEPTAR. The experiment was also sensitive to the $\beta$-delayed neutron decay of $^{132}$In through the observation of $\gamma$ rays in $^{131}$Sn and $^{131}$Sb. Results on the decay of $^{132}$In and $\gamma$ spectroscopy of $^{132}$Sn will be discussed. [Preview Abstract] |
Saturday, May 18, 2019 2:24PM - 2:36PM |
G2.00004: Spectroscopic studies of neutron-rich tin isotopes $^{129}$Sn and $^{133}$Sn Fatima H. Garcia, Corina Andreoiu, Kevin Ortner, Kurtis Raymond, Kenneth Whitmore The study of nuclear structure requires understanding of the isotopes in the vicinity of the magic numbers. Acting as the noble gases of the chart of nuclides, the magic numbers confer stability to the nuclei with these numbers of nucleons. The isotopes of tin lie at one of these magic numbers, at $Z=50$, and because of this proton count, tin spans the largest number of total isotopes (40), and the most stable isotopes (10). These radioactive species must be studied at state-of-the-art facilities such as GRIFFIN at TRIUMF. GRIFFIN is a powerful decay spectrometer, used to study species of interest via $\beta$ and $\gamma$ spectroscopy. This mechanism was used in order to studying the tin isotopes $^{129}$Sn and $^{133}$Sn, through the $\beta^{-}$ of their indium parents. With 79 neutrons, $^{129}$Sn lies three neutrons away from the magic number at $N=82$, while $^{133}$Sn is one neutron above the same magic number. Spectroscopic studies of $^{129}$Sn have uncovered twenty new transitions and seven new excited states. A similar analysis of $^{133}$Sn is complicated by a high $\beta n$ branch from the $^{133}$In parent, such that the data is buried in the produced $^{132}$Sn. Results from the study of $^{129}$Sn and $^{133}$Sn and potential implications will be discussed. [Preview Abstract] |
Saturday, May 18, 2019 2:36PM - 2:48PM |
G2.00005: Beta Decay of $^{80,82}$Ga with GRIFFIN and Shape Coexistence in $^{80,82}$Ge Aimee Bell, Corina Andreoiu, Isaiah Djianto, Fatima Garcia, Melanie Gascoine, Kevin Ortner, Kurtis Raymond, Kenneth Whitmore, Jonathan Williams Shape coexistence in atomic nuclei, the existence of structures with different degrees of deformation in a narrow energy range, is an exciting phenomenon present across the chart of nuclides. In our experiment, we searched for evidence of shape coexistence in $^{80}$Ge and $^{82}$Ge by investigating their respective intruder 0$_2$_$^{+}$ states. The experiment was performed at the ISAC-TRIUMF facility where $^{80}$Ge and $^{82}$Ge isotopes were formed from the $\beta$-decay of their parent isotopes, $^{80}$Ga and $^{82}$Ga, respectively. The two Ga beams were produced by the ISOL technique using a 480 MeV proton beam with a 10 $\mu$A current colliding with a UC$_x$ target. A specialized ion source was used to suppress Rb contamination. The $\beta$-decay was measured using the GRIFFIN spectrometer which was equipped with 15 HPGe detectors for $\gamma$-ray detection, a ZDS plastic scintillator for $\beta$-tagging, the PACES array which has 5 Si(Li) detectors for conversion electron spectroscopy and 8 LaBr$_3$ scintillators for fast timing measurements of nuclear levels. Using this array, correlated $\gamma$-$\gamma$, $\gamma$-electron and electron-electron data have been acquired simultaneously, providing a detailed level scheme for $^{80}$Ge. Preliminary results will be presented. [Preview Abstract] |
Saturday, May 18, 2019 2:48PM - 3:00PM |
G2.00006: Commissioning and Initial Operation of the Recoil Mass Spectrometer EMMA at TRIUMF Barry Davids, Nicholas Esker, Matthew Williams The Electromagnetic Mass Analyser (EMMA) is a new vacuum-mode recoil mass spectrometer currently undergoing the final stages of commissioning at the ISAC-II facility of TRIUMF. EMMA employs a symmetric configuration of electrostatic and magnetic deflectors to separate the products of nuclear reactions from the beam, focus them in both energy and angle, and disperse them in a focal plane according to their mass/charge $(m/q)$ ratios. The spectrometer was designed to accommodate the $\gamma$-ray detector array TIGRESS around the target position in order to provide spectroscopic information from electromagnetic transitions. EMMA is intended to be used in the measurement of fusion evaporation, radiative capture, and transfer reactions for the study of nuclear structure and astrophysics. Its complement of focal plane detectors facilitates the identification of recoiling nuclei and subsequent recoil decay spectroscopy. In this talk we shall describe the facility and report on commissioning efforts. [Preview Abstract] |
Saturday, May 18, 2019 3:00PM - 3:12PM |
G2.00007: Geant4 Simulations of Nuclear Isomer Gamma Emission Detection Adam Fritsch, James Brown, Andrew Clusserath, Bryce Makela When an atomic nucleus is excited, it can form a nuclear isomer, a metastable state with a relatively long half-life. By experimentally investigating the energy levels of neutron-rich isomers, nuclear structure models can be better constrained. Using Geant4, Monte Carlo simulations have been performed to determine optimal detector geometry and placement near a target for measurement of nuclear isomer de- excitation via gamma emission. Various beam and target combinations have been simulated. Preliminary results will be presented. [Preview Abstract] |
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