Search for the Pygmy Dipole Resonance in Ni-68 at 600 MeV/nucleon

The γ decay from Coulomb excitation of 68Ni at 600  MeV/nucleon on a Au target was measured using the RISING setup at the fragment separator of GSI. The 68Ni beam was produced by a fragmentation reaction of 86Kr at 900  MeV/nucleon on a 9Be target and selected by the fragment separator. The γ rays produced at the Au target were measured with HPGe detectors at forward angles and with BaF2 scintillators at backward angles. The measured spectra show a peak centered at approximately 11 MeV, whose intensity can be explained in terms of an enhanced strength of the dipole response function (pygmy resonance). Such pygmy structure has been predicted in this unstable neutron-rich nucleus by theory.