Bochum 2009 – wissenschaftliches Programm

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HK: Fachverband Hadronen und Kerne

HK 71: Nuclear Structure and Dynamics I

HK 71.2: Gruppenbericht

Donnerstag, 19. März 2009, 17:00–17:30, H-ZO 40

Systematic studies of the Pygmy Dipole Resonance by means of the (α,α ′ γ) reaction* — •Janis Endres¹, Peter Butler², Muhsin N. Harakeh³, Rolf-Dietmar Herzberg², Reiner Krücken⁴, Norbert Pietralla⁵, Lucia Popescu⁶, Deniz Savran⁵, Marcus Scheck², Felix Siebenhühner⁵, Kerstin Sonnabend⁵, Sotirios Harissopulos⁷, Anastasios Lagoyannis⁷, Heinrich Wörtche³, and Andreas Zilges¹ — ¹IKP, Universität zu Köln — ²Department of Physics, Liverpool, England — ³KVI, University of Groningen, The Netherlands — ⁴Physik-Department E12, TU München — ⁵IKP, TU Darmstadt — ⁶SCK-CEN, Mol, Belgium — ⁷I.N.P. NCSR Demokritos, Athen, Greece

In the last years investigations have been made to study the electric Pygmy Dipole Resonance (PDR), mainly in semi-magic nuclei. Therefore (γ,γ′) photon scattering experiments have been performed systematically [1]. In (α,α′ γ) coincidence experiments at E_α=136 MeV a comparable energy resolution and a high selectivity of E1 transitions can be obtained by using the Big-Byte Spectrometer at KVI [2]. We give an overview about systematic studies on the nuclei ¹⁴⁰Ce, ¹³⁸Ba, ¹²⁴Sn and ⁹⁴Mo. In comparison to the (γ,γ′) reaction a structural splitting of the PDR could be observed which is possibly connected to the different isospin natures of the two groups. There is a low energy part which can be found in (α,α′ γ) as well as in (γ,γ′) reactions and a high energy part which can only be observed in (γ,γ′). * Supported by EURONS and the DFG (SFB 634). [1] U. Kneissl et al., J. Phys. G 32 (2006) R1 [2] D. Savran et al., Phys. Rev. Lett. 97 (2006) 172502