Alexandra Gade

• Elman, Brandon; Gade, Alexandra; Weisshaar, Dirk; Barofsky, Daniel; Bazin, Daniel; Bender, Peter C.; Bowry, Michael; Hjorth-Jensen, Morten; Kemper, Kirby W.; Lipschutz, Samuel; Lunderberg, Erich; Sachmpazidi, Ntiana; Terpstra, Nick; Walters, William B.; Westerberg, A.; Williams, Scott J. & Wimmer, Kathrin (2017). Quadrupole collectivity beyond N = 50 in neutron-rich Se and Kr isotopes. Physical Review C.  ISSN 2469-9985.  96:044332(4), s 1- 8 . doi: 10.1103/PhysRevC.96.044332 Show summary

  We report B(E2; 0+ 1 → 2+ n ) strengths for the neutron-rich 88,90Kr and 86Se isotopes from intermediate-energy Coulomb excitation. The electric quadrupole transition strengths to the first 2+ states complete, with considerably improved uncertainties, the evolution of quadrupole collectivity in the Kr and Se isotopes approaching N = 60, for which 90Kr and 86Se had previously been the most uncertain. We also report significant excitation strength to several higher-lying 2+ states in the krypton isotopes. This fragmentation of B(E2) strength in 88,90Kr confirms shell-model calculations in the π(fpg)-ν(sdgh) shell with an only minimally tuned shell-model setup that is based on a nucleon-nucleon interaction derived from effective field theory and effective charges adjusted to 86Kr.

• Bader, Vincent M.; Gade, Alexandra; Weisshaar, Dirk; Brown, Boyd Alexander; Baugher, Travis; Bazin, Daniel; Berryman, Jill S.; Ekström, Jan Andreas; Hjorth-Jensen, Morten; Stroberg, Steven R.; Walters, William B.; Wimmer, Kathrin & Winkler, Ryan (2013). Quadrupole collectivity in neutron-deficient Sn nuclei: 104Sn and the role of proton excitations. Physical Review C. Nuclear Physics.  ISSN 0556-2813.  88(5:051301) . doi: 10.1103/PhysRevC.88.051301 Show summary

  We report on the experimental study of quadrupole collectivity in the neutron-deficient nucleus 104Sn using intermediate-energy Coulomb excitation. The B(E2;01+→21+) value for the excitation of the first 2+ state in 104Sn has been measured to be 0.180(37) e2b2 relative to the well-known B(E2) value of 102Cd. This result disagrees by more than one sigma with a recently published measurement [ G. Guastalla et al. Phys. Rev. Lett. 110 172501 (2013)]. Our result indicates that the most modern many-body calculations remain unable to describe the enhanced collectivity below midshell in Sn approaching N=Z=50. We attribute the enhanced collectivity to proton particle-hole configurations beyond the necessarily limited shell-model spaces and suggest the asymmetry of the B(E2)-value trend around midshell to originate from enhanced proton excitations across Z=50 as N=Z is approached.

• Jensen, Øyvind; Hagen, Gaute; Hjorth-Jensen, Morten; Brown, Boyd Alexander & Gade, Alexandra (2011). Quenching of spectroscopic factors for proton removal in oxygen isotopes. Physical Review Letters.  ISSN 0031-9007.  107 . doi: 10.1103/PhysRevLett.107.032501 Show summary

  We present microscopic coupled-cluster calculations of the spectroscopic factors for proton removal from the closed-shell oxygen isotopes 14,16,22,24,28O with a chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order. We include coupling-to-continuum degrees of freedom by using a Hartree-Fock basis built from a Woods-Saxon single-particle basis. This basis treats bound and continuum states on an equal footing. We find a significant quenching of spectroscopic factors in the neutron-rich oxygen isotopes, pointing to enhanced many-body correlations induced by strong coupling to the scattering continuum above the neutron emission thresholds.

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