Search

In recent years investigations have been made to study the electric Pygmy Dipole Resonance (PDR) systematically, mainly in semi-magic nuclei. For this purpose the well understood high resolution (γ,γ′) photon scattering method is used. In complementary (α,α′γ) coincidence experiments at Eα = 136 MeV a similar γ-energy resolution and a high selectivity to E1 transitions can be obtained at the Big-Bite Spectrometer (BBS) at KVI, Groningen. In comparison to the (γ,γ′) method a structural splitting of the PDR is observed in the N = 82 nuclei 138Ba and 140Ce and in the Z = 50 nucleus 124Sn. The low energy part is excited in (γ,γ′) as well as in (α,α′γ) while the high energy part is observed in (γ,γ′) only. The experimental results together with theoretical QPM and RQTBA calculations on 124Sn which are able to reproduce the splitting of the PDR qualitatively are presented. The low-lying group of Jπ = 1- states seem to represent the more isoscalar neutron-skin oscillation of the PDR while the energetically higher-lying states seemingly belong to the transitional region between the PDR and the isovector Giant Dipole Resonance (IVGDR). [ABSTRACT FROM AUTHOR]

Taking advantage of the spin, isospin and Jπ selectivity of cross sections and analysing powers of the tensor polarised 12C(dvector ,2He) reaction, the Jπ = 0-,1-2- components of the spin-dipole resonance in 12B have been investigated. The experiment was performed at the Big-Bite Spectrometer of the KVI taking advantage of purely tensor polarised deuteron beams provided by the AGOR cyclotron. The unique energy resolution achieved at KVI allowed determination of analysing powers for well resolved transitions up to 5 MeV excitation energy. The analysing powers of states with known spin and parity provided the means for the first-time for verification of model-independent predictions of analysing powers at extreme forward angles. In the continuum region, the analysing powers allowed identification of the Jπ components of the IVSGDR, including a 0- component located at Ex = 9.3 MeV. [ABSTRACT FROM AUTHOR]