The pygmy quadrupole resonance and neutron-skin modes in 124Sn

M. Spieker, N. Tsoneva, V. Derya, J. Endres, D. Savran, M.N. Harakeh, S. Harissopulos, R.-D. Herzberg, A. Lagoyannis, H. Lenske, N. Pietralla, Lucia-Ana Popescu, M. Scheck , F. Schlüter, K. Sonnabendl, V.I. Stoica, H.J. Wörtche , A. Zilges

    Research outputpeer-review


    We present an extensive experimental study of the recently predicted pygmy quadrupole resonance (PQR) in Sn isotopes, where complementary probes were used. In this study, (α, α'γ ) and (γ , γ') experiments were performed on 124Sn. In both reactions, Jπ = 2+ states below an excitation energy of 5MeV were populated. The E2 strength integrated over the full transition densities could be extracted from the (γ , γ') experiment, while the (α, α'γ ) experiment at the chosen kinematics strongly favors the excitation of surface modes because of the strong α-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 γ -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.
    Original languageEnglish
    Pages (from-to)102-107
    Number of pages6
    JournalPhysics Letters B
    StatePublished - 10 Jan 2016

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