Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session R3: Invited Session: Quadropole Collectivity and Shape Coexistence around A=100 |
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Sponsoring Units: DNP Chair: Sam Tabor, Florida State University Room: Chatham Ballroom B |
Monday, April 7, 2014 10:45AM - 11:21AM |
R3.00001: Quadrupole Collectivity in Neutron Deficient Sn Isotopes Invited Speaker: Alexandra Gade One of the overarching goals of nuclear physics is the development of a comprehensive model of the atomic nucleus with predictive power across the nuclear chart. Of particular importance for the development of nuclear models is experimental data that consistently track the effect of isospin and changed binding, for example. The chain of Sn isotopes has been a formidable testing ground for nuclear models as some spectroscopic data is available from $N=Z=50$ $^{100}$Sn in the proximity of the proton dripline to $^{134}$Sn, beyond the very neutron-rich doubly magic nucleus $^{132}$Sn. In even-even nuclei, the electromagnetic quadrupole excitation strength is a measure of quadrupole collectivity, sensitive to the presence of shell gaps, nuclear deformation, and nucleon-nucleon correlations, for example. In the Sn isotopes, this transition strength has been reported from $^{104}$Sn to $^{130}$Sn, spanning a chain of 14 even-even Sn isotopes. The trend is asymmetric with respect to midshell and not even the largest-scale shell-model calculations have been able to describe the evolution of transition strength across the isotopic chain without varying effective charges. Implications will be discussed. [Preview Abstract] |
Monday, April 7, 2014 11:21AM - 11:57AM |
R3.00002: Shape Co-existence at N=60: Single Particle Structure of $^{95}$Sr Invited Speaker: Reiner Kr\"ucken The shape coexistence and shape transition at N=60 in the Sr, Zr region is of subject of substantial current experimental and theoretical effort. An important aspect in this context is the evolution of single particle structure for N$<$60 leading up to the shape transition. One-neutron transfer reactions are an ideal tool to study single-particle energies as well as occupation numbers which can be compared to results of modern large scale shell model calculations using a 78Ni core. Here we report on the study of the single-particle structure in $^{95}$Sr via the one-neutron transfer reaction d($^{94}$Sr,p)$^{95}$Sr in inverse kinematics. The experiment was performed at TRIUMF's ISAC facility using the TIGRESS gamma-ray spectrometer in conjunction with the SHARC charge particle detector and a fusion veto detector. The charge state of the singly charged $^{94}$Sr beam extracted from the ISAC UC$_x$ target was increased to 15$^+$ in an ECR source before acceleration to 5.5 AMeV. Gamma-rays as well alight charged particles are detected to extract energies, cross-sections, and proton angular distributions for the low-lying states in $^{95}$Sr. Initial results of this experiment will be discussed in the context of the evolution of single-particle structure in this region. [Preview Abstract] |
Monday, April 7, 2014 11:57AM - 12:33PM |
R3.00003: Inelastic proton scattering of Sn isotopes studied with GRETINA Invited Speaker: Christopher Campbell The chain of semi-magic Sn nuclei, with many stable isotopes, has been a fertile ground for experimental and theoretical studies. Encompassing a major neutron shell from N$=$50 to 82, the properties and structure of these nuclei provided important data for the development of the pairing-plus-quadrupole model. Recent experimental information on B(E2) for 106,108,110,112Sn came as a surprise as it indicated a larger collectivity than the predicted parabolic trend of quadrupole collectivity. These data, instead, show an unexpectedly flat trend even as the number of valence particles is reduced from 12 to 6. To fully understand how collectivity is evolving in these isotopes, 108,110,112Sn have been studied using thick-target, inelastic proton scattering with GRETINA tagging inelastic scattering events by detecting gamma-rays from the prompt decay of states excited in the reaction. We will present the trend of 2$+$ excitation cross-sections, the deduced quadrupole deformation parameters, and observations of other low-lying collective states. Comparison of these (p,p') quadrupole deformation parameters with B(E2) data will provide new insights into the relative importance of proton and neutron contributions to collectivity in these nuclei. [Preview Abstract] |
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