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arXiv · 1811.07739

Fine structure of the pygmy quadrupole resonance in $^{112,114}$Sn isotopes

N. Tsoneva·M. Spieker·H. Lenske·A. Zilges
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Abstract

The electric quadrupole response in $^{112,114}$Sn isotopes is investigated by energy-density functional (EDF) and three-phonon quasiparticle-phonon model (QPM) theory with special emphasis on 2$^+$ excitations located above the first collective quadrupole state and below 5 MeV. Additional quadrupole strength clustering as a sequence of states similar to the recently observed pygmy quadrupole resonance in $^{124}$Sn is found. The spectral distributions and transition densities of these 2$^+$ states show special features being compatible with oscillations of a neutron skin against the isospin-symmetric nuclear core. Furthermore, two new ($p$, $p' γ$) Doppler-shift attenuation (DSA) coincidence experiments were performed at the SONIC@HORUS setup. Quadrupole states with excitation energies up to 4.2 MeV were populated in $^{112,114}$Sn. Lifetimes and branching ratios were measured allowing for the determination of the reduced quadrupole transition strengths to the ground state. A stringent comparison of the new data to EDF+QPM theory in $^{112}$Sn and $^{114}$Sn isotopes hints at the occurrence of a low-energy quadrupole mode of unique character which could be interpreted as pygmy quadrupole resonance.

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N. Tsoneva, M. Spieker, H. Lenske, A. Zilges. 2018-11-19. Fine structure of the pygmy quadrupole resonance in $^{112,114}$Sn isotopes. https://doi.org/10.1016/j.nuclphysa.2019.07.008

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