Study of the pygmy dipole resonance in 94Mo using the (α,α′γ) coincidence technique

The (α,α′γ) reaction at Eα=136MeV was used to study the electric dipole response in the open-shell vibrational nucleus 94Mo below the neutron-separation threshold. The coincidence experiment has been performed at the Kernfysisch Versneller Instituut in Groningen, The Netherlands, exploiting the Big-Bite Spectrometer and an array of large volume High-Purity Germanium (HPGe) detectors. Due to the excellent energy resolution and high selectivity to transitions stemming from the pygmy dipole resonance, singles α-scattering cross sections could be determined for individual electric dipole excitations between 4 and 8 MeV. For three of the excited low-lying Jπ=1− states in 94Mo a γ-decay branch into the Jπ=21+ state could be observed.

The experiment extends the systematic studies of the pygmy dipole resonance by real-photon scattering (γ,γ′) experiments and (α,α′γ) experiments. Recently, a (γ,γ′) experiment on 94Mo was performed at the Darmstadt High-Intensity Photon Setup at the S-DALINAC in Darmstadt, Germany, permitting the comparison of B(E1)↑ strength distribution and α-scattering cross sections.