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HK: Fachverband Physik der Hadronen und Kerne

HK 28: Structure and Dynamics of Nuclei VII

HK 28.2: Vortrag

Dienstag, 15. März 2016, 17:00–17:15, S1/01 A04

Pygmy quadrupole resonance as a manifestation of the nuclear skin — •Nadia Tsoneva^1,2 and Horst Lenske² — ¹Frankfurt Institute for Advanced Studies (FIAS), 60438 Frankfurt am Main, Germany — ²Institut fur Theoretische Physik, Universität Gießen, Heinrich-Buff-Ring 16, D-35392 Gieβen, Germany

Recently, a new mode of nuclear excitation called pygmy quadrupole resonance (PQR) was theoretically predicted in the framework of energy-density functional (EDF) theory plus three-phonon quasiparticle-phonon model (QPM) in Sn isotopic chain. It is closely connected with higher order multipole vibrations of nuclear skin induced by the action of the electromagnetic and hadronic external fields. The predictions initiated new experiments using (¹⁷O,¹⁷O′γ), (α,α′γ) and (γ,γ′) reactions which were carried out in ¹²⁴Sn nucleus. The aim was to probe for the first time experimentally, the possibility of existence of PQR. The detailed analysis of the obtained experimental results in comparison with the EDF+QPM theory indicates clearly the presence of a multitude of discrete low-energy 2⁺ excitations of neutron type which can be addressed to PQR mode. The independent measurements of B(E2) values with different probes and the theory allow to identify the dominant isoscalar character of these states. Furthermore, newly determined γ-decay branching ratios exclude a statistical origin of the PQR strength. The latter are important to discriminate between PQR and multiphonon excitations.
The work is supported by the HIC for FAIR within the framework of the LOEWE program.