Study of Low-lying dipole strength in Cr isotopes

Low-lying electric and magnetic dipole strength (E1 and M1 respectively), particularly the Pygmy Dipole Resonance (PDR) and Spin-flip M1 excitations, of atomic nuclei have drawn considerable attention in the last decade. The low-lying dipole strength of 50Cr, 52Cr and 54Cr were studied with the method of nuclear resonance fluorescence up to 9.7 MeV using bremsstrahlung provided by the superconducting Darmstadt electron linear accelerator S-DALINAC. The excited states, parities of 50Cr and 54Cr were measured through polarized photon scattering at the High Intensity gamma ray Source (HIγS), Triangle Universities Nuclear Laboratory (TUNL) in Durham, NC, USA. Microscopic calculations within the quasiparticle-phonon nuclear model have been carried out to interpret the dipole-strength distributions of all Cr isotopes. Experimental results are indicating that the onset of the PDR takes place in 50Cr. On the other hand, the strongly excited 1+ state at 3.63 MeV excitation energy of 50Cr is found to be a scissor mode like state. The interesting results obtained in these works will be discussed.