Study of the pygmy dipole resonance in 94Mo using the coincidence technique

Abstract

Abstract The ( α , α ′ γ ) reaction at E α = 136 MeV 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 J π = 1 − states in 94Mo a γ-decay branch into the J π = 2 1 + 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 ( E 1 ) ↑ strength distribution and α-scattering cross sections.