[Triumf-seminars] TRIUMF Nuclear Physics Seminar today at 10:00

[TRIUMF Seminars]

Date/Time: Tue 2017-06-13 at 10:00

Location:  Auditorium          

Speaker:   Mark Spieker (University of Cologne/ Germany)

Title:     A pygmy quadrupole resonance in the stable Sn isotopes

Abstract: An extensive experimental study of the recently predicted pygmy quadrupole resonance (PQR) in the stable even-even Sn isotopes [1] will be presented. In this study, (alpha, alpha' gamma) and (gamma,gamma') experiments were performed on 124Sn [2] as well as life-time measurements in 112,114Sn using the recently established (p,p'; gamma) Doppler-shift attenuation (DSA) coincidence technique [3]. In all experiments, Jpi = 2+ states below an excitation energy of 5 MeV were populated. The E2 strength integrated over the full transition densities could be extracted from the (gamma,gamma') and the (p, p' gamma) DSA experiments, while the (alpha, alpha' gamma) experiment at the chosen kinematics strongly favors the excitation of surface modes because of the strong alpha-particle absorption in the nuclear interior. The excitation of such modes is in accordance with the quadrupole-type oscillation of the neutron skin predicted by a microscopic approach based on self-consistent density functional theory and the quasiparticle-phonon model (QPM).
The newly determined gamma-decay branching ratios hint at a non-statistical character of the E2 strength, as it has also been recently pointed out for the case of the pygmy dipole resonance (PDR). This allows us to distinguish between PQR-type and multiphonon excitations and, consequently, supports the recent first experimental indications of a PQR in 124Sn [2, 4].

Supported by the Deutsche Forschungsgemeinschaft (ZI 510/7-1).
[1] N. Tsoneva and H. Lenske, Phys. Lett. B 695, 174 (2011).
[2] M. Spieker, N. Tsoneva, A. Zilges et al., Phys. Lett. B 752, 102 (2016).
[3] A. Hennig, A. Zilges et al., Nucl. Instr. and Meth. A 794, 171 (2015).
[4] L. Pellegri, A. Bracco, N. Tsoneva et al., Phys. Rev. C 92, 014330 (2015).



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