Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session Y13: Nuclear Structure |
Hide Abstracts |
Sponsoring Units: DNP Chair: Daniel Phillips, Ohio University Room: Roosevelt 5 |
Tuesday, January 31, 2017 1:30PM - 1:42PM |
Y13.00001: Examining the interplay between halo effects and deformation in neutron rich neon isotopes Charles Loelius, Hironori Iwasaki, Daniel Bazin, Robert Elder, Brandon Elman, Alexandra Gade, Mara Grinder, Brenden Longfellow, Eric Lunderberg, Sebastian Heil, Alexander Hufnagel, Michael Mathy, Ina Syndikus, Nobu Kobayashi, Joe Belarge, Peter Bender, Dirk Weisshaar, Marina Petri, Kenneth Whitmore $^{27}$Ne serves as an excellent test case for understanding the interplay between halo effects and deformation. It is known that the neighboring isotopes $^{26}$Ne and $^{28}$Ne demonstrate substantial deformation, which indicate a potential for deformation in $^{27}$Ne. At the same time, the 1/2+ excited state is expected to have a single valence neutron in the s orbital near the neutron separation energy and therefore is expected to exhibit halo effects. Due to the interplay between the halo and deformation effects, the \textit{M1} transition strength, which is expected to be large because of the deformation, could be severely reduced, while the \textit{E1} transition strength is expected to be large. To examine this effect, precise knowledge of transition rates is required. In this work, the model-independent Recoil Distance Method was employed with fast RI beams to constrain the lifetime of the 1/2+ state down to the lowest achievable limits of precision. [Preview Abstract] |
Tuesday, January 31, 2017 1:42PM - 1:54PM |
Y13.00002: Shape coexistence in neutron-rich odd-mass S isotopes Tea Mijatovic, Nobuyuki Kobayashi, Hiro Iwasaki, Charles Loelius, Kenneth Whitmore, Robert Elder, Alexandra Gade, Daniel Bazin, Dirk Weisshaar, Peter Bender, Joe Belarge, Eric Lunderberg, Brandon Elman, Brenden Longfellow, Alfred Dewald, Thoryn Haylett, Michael Mathry, Sebastian Heil Collective motions in atomic nuclei at low excitation energies have been characterized by the ground-state shape as a single basis. This picture can be altered in exotic nuclei with unusual proton-to-neutron ratios if the nuclear shape can change drastically at low spin. Recently, there has been an increasing interest for shape-coexistence phenomena in neutron-rich S isotopes and studies suggested fairly large collectivity in ${}^{40,42,44}$S isotopes. We will discuss the search for isomeric or long-lived states in ${}^{45}$S for which no excited states are known in the literature and the pursuit to fully characterize the band structure of the low-lying states in ${}^{43,45}$S, which provide key information to establish a comprehensive picture of the shape coexistence in this region. Direct model-independent measurements of the ${}^{43,45}$S excited states were realized by applying the Recoil Distance Method with the TRIPLEX Plunger in conjunction with GRETINA to fast rare isotope beams at the NSCL. [Preview Abstract] |
Tuesday, January 31, 2017 1:54PM - 2:06PM |
Y13.00003: Neutron-Proton equilibration in dynamically deformed nuclear systems. Alis Rodriguez Manso, A.B. McIntosh, A. Jedele, S.J Yennello Understanding the nuclear Equation of State (nEoS) is fundamental for describing nuclear reaction dynamics, understanding the origin of the elements and characterizing the structure of neutron stars. The density dependence of the asymmetry energy still represents the largest uncertainty in the nEoS. We demonstrate a new time-sensitive method for studying reaction dynamics that may allow new types of constraints on the asymmetry energy. We study neutron-proton equilibration in dynamically deformed nuclear systems by investigating the correlations between the largest fragments produced in collisions of $^{70}$Zn +$^{70}$Zn, $^{64}$Zn +$^{64}$Zn, $^{64}$Ni +$^{64}$Ni and $^{70}$Zn +$^{64}$Zn at $35$ MeV per nucleon measured at the Cyclotron Institute at Texas A\&M University. The extent of equilibration is investigated using the rotation angle as a clock. The equilibration follows an exponential trend with consistent rate constants across a wide variety of reaction partners and systems, indicating the equilibration follows first order kinetics. The statistical and dynamical components are separated on average; the equilibration curve for the purely dynamical is consistent with the overall equilibration curve, indicating the robustness of the method to statistical contamination. [Preview Abstract] |
Tuesday, January 31, 2017 2:06PM - 2:18PM |
Y13.00004: Selective Population of Unbound Positive Parity States in $^{\mathrm{25}}$F and $^{\mathrm{26}}$F Nathan Frank, Jacob Herman, Ali Rabeh, Matthew Tuttle-Timm Unbound Positive Parity States in $^{\mathrm{25}}$F and $^{\mathrm{26}}$F were populated in the one-proton removal reaction from a radioactive $^{\mathrm{27}}$Ne beam. The experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL), where a 101.3 MeV/u $^{\mathrm{27}}$Ne ion beam impinged on a liquid deuterium target populating states in $^{\mathrm{26}}$F. States above the one- and two- neutron separation energies lead to $^{\mathrm{24}}$F and $^{\mathrm{25}}$F, respectively. The MoNA/LISA setup at NSCL was used to detect the fragments in coincidence with neutrons and the decay energy spectra of $^{\mathrm{25}}$F and $^{\mathrm{26}}$F were reconstructed by invariant mass spectroscopy. Resonance energies of approximately 0.35 MeV~ and 0.5 MeV for $^{\mathrm{25}}$F* and $^{\mathrm{26}}$F*, respectively, were extracted. Based on the calculated spectroscopic strength distribution of negative and positive parity states in $^{\mathrm{26}}$F and the selectivity of one proton-removal reactions both states were assigned positive parity. [Preview Abstract] |
Tuesday, January 31, 2017 2:18PM - 2:30PM |
Y13.00005: Competition between radiative and strong force decay Samuel Tabor For nuclear states unbound to neutron decay, radiative emission is often assumed to not dominate over neutron decay mediated by the far stronger strong interaction, except for very low neutron energies and high angular momentum barriers. Recent experimental investigations of $^{\mathrm{19}}$O and $^{\mathrm{27}}$ Mg populated in heavy-ion fusion-evaporation reactions have revealed predominantly gamma decays from a number of states unbound to neutron decay by up to 2 MeV. In most cases the angular momentum barrier is not sufficient to inhibit neutron decay enough to allow E-M decay with widths of up to an eV or so to win. Other inhibitions to particle decay, including low spectroscopic factors, will be discussed. [Preview Abstract] |
Tuesday, January 31, 2017 2:30PM - 2:42PM |
Y13.00006: Nuclear Structure in $^7$$^8$Ge Anne M. Forney, W.B. Walters, J. Sethi, C.J. Chiara, J. Harker, R.V.F. Janssens, S. Zhu, M. Carpenter, M. Alcorta, G. G\"{u}rdal, C.R. Hoffman, B.P. Kay, F.G. Kondev, T. Lauristen, C.J. Lister, E.A. McCutchan, A.M. Rogers$^4$, D. Seweryniak Owing to the importance of the structure of $^{76}$Ge in interpreting double $\beta$ decay studies, the structures of adjacent nuclei have been of considerable interest. Recently reported features for the structures of $^{72,74,76}$Ge indicate both shape coexistence and triaxiality. New data for the excited states of $^{78}$Ge will be reported arising from Gammasphere studies of multinucleon transfer reactions between a $^{76}$Ge beam and thick heavy targets at the ATLAS facility at Argonne National Laboratory. The previously known yrast band is extended to higher spins, candidate levels for a triaxial sequence have been observed, and the associated staggering determined. The staggering in $^{78}$Ge found in this work is not in agreement with theoretical work\footnote{J.J Sun \it{et al.}, Phys. Lett B \textbf{734}, 308 (2014).}. Candidates for negative-parity states and seniority-four states will be discussed. [Preview Abstract] |
Tuesday, January 31, 2017 2:42PM - 2:54PM |
Y13.00007: Precision Cross Sections Measurement of $^{\mathrm{56}}$Fe(n,n$\gamma )$ at 14.1 MeV using Associated Particle Neutron Elemental Imaging Technique Haoyu Wang, David Koltick Integral production cross sections for 846.8 keV and 1238.3 keV prompt gamma rays from 14.1 MeV neutrons interactions on $^{\mathrm{56}}$Fe and are reported, using Associated Particle Neutron Elemental Imaging technique. The experimental technique involves: (1) The development of a VME standard high speed DAQ system and a MATLAB parallel cluster for offline signal analysis with full control of data flow; (2) The advantage of the \textless 1.5 ns coincidence timing resolution between the neutron production and the gamma ray detection to reject noise; (3) A large 30{\%} solid angle gamma ray coverage by an array of NaI(Tl) detectors. The neutron flux is measured through detecting the associated alpha-particle from the D-T fusion reaction in the neutron generator. Present cross section measurements using other techniques with limited timing resolution and solid angle coverage are in agreement at neutron energies lower than 6 MeV. At higher neutron energies reported results can disagree by more than 20{\%}. This more accurate technique presented can distinguish between the differences in the reported results based on pulse-mode neutron source and neutron time-of-flight techniques, at higher neutron energies. [Preview Abstract] |
Tuesday, January 31, 2017 2:54PM - 3:06PM |
Y13.00008: Extracting Spectroscopic Factors of Argon Isotopes from Transfer Reactions Juan Manfredi, J. Lee, M.B. Tsang, W.G. Lynch, J. Barney, J. Estee, S. Sweany, K.W. Brown, G. Cerizza, C. Anderson, H. Setiawan, C. Loelius, Z. Xu, A.M. Rogers, C. Pruitt, L.G. Sobotka, J.M. Elson, C. Langer, Z. Chajecki, G. Chen, K.L. Jones, K. Smith, Z. Xiao, Z. Li, J.R. Winkelbauer A spectroscopic factor (SF) quantifies the single particle occupancy of a given state in a nucleus. For the argon isotopes, there is a discrepancy of the SF between studies that use transfer reactions and knockout reactions. Understanding the SFs of these isotopes, and in particular how the SF changes across the isotopic chain, is important for understanding how single particle structure changes with neutron number. The transfer reactions $^{34}$Ar(p,d) and $^{46}$Ar(p,d) were measured at the National Superconducting Cyclotron Laboratory (NSCL) using the same beam energy (70 MeV/u) as from the previous knockout measurement. Spectroscopic factors were extracted from measured angular distributions via ADWA calculations. Preliminary findings will be presented. [Preview Abstract] |
Tuesday, January 31, 2017 3:06PM - 3:18PM |
Y13.00009: Thin film deposition using rarefied gas jet Dr. Sahadev Pradhan The rarefied gas jet of aluminium is studied at Mach number \textit{Ma }$=$\textit{ (U\textunderscore j / }$\backslash $\textit{sqrt\textbraceleft kb T\textunderscore j / m\textbraceright )}in the range \textit{.01 \textless Ma \textless 2}, and Knudsen number \textit{Kn }$=$\textit{ (1 / (}$\backslash $\textit{sqrt\textbraceleft 2\textbraceright }$\backslash $\textit{pi d\textasciicircum 2 n\textunderscore d H)} in the range \textit{.01 \textless Kn \textless 15}, using two-dimensional (2D) direct simulation Monte Carlo (DSMC) simulations, to understand the flow phenomena and deposition mechanisms in a physical vapor deposition (PVD) process for the development of the highly oriented pure metallic aluminum thin film with uniform thickness and strong adhesion on the surface of the substrate in the form of ionic plasma, so that the substrate can be protected from corrosion and oxidation and thereby enhance the lifetime and safety, and to introduce the desired surface properties for a given application. Here, $H$is the characteristic dimension, \textit{U\textunderscore j}and \textit{T\textunderscore j}are the jet velocity and temperature, \textit{n\textunderscore d}is the number density of the jet, $m$and $d$ are the molecular mass and diameter, and \textit{kb}is the Boltzmann constant. An important finding is that the capture width (cross-section of the gas jet deposited on the substrate) is symmetric around the centerline of the substrate, and decreases with increased Mach number due to an increase in the momentum of the gas molecules. DSMC simulation results reveals that at low Knudsen number \textit{((Kn }$=$\textit{ 0.01);}shorter mean free paths), the atoms experience more collisions, which direct them toward the substrate. However, the atoms also move with lower momentum at low Mach number$,$which allows scattering collisions to rapidly direct the atoms to the substrate. [Preview Abstract] |
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