Direct determination of ground-state transition widths of low-lying dipole states in Ce-140 with the self-absorption technique

The technique of self absorption has been applied for the first time to study the decay pattern of low-lying dipole states of Ce-140. In particular, ground-state transition widths Gamma(0) and branching ratios Gamma(0)/Gamma to the ground state have been investigated in the energy domain of the pygmy dipole resonance. Relative self-absorption measurements allow for a model-independent determination of Gamma(0). Without the need to perform a full spectroscopy of all decay channels, also the branching ratio to the ground state can be determined. The experiment on Ce-140 was conducted at the bremsstrahlung facility of the superconducting Darmstadt electron linear accelerator S-DALINAC. In total, the self-absorption and, thus, Gamma(0) were determined for 104 excited states of Ce-140. The obtained results are presented and discussed with respect to simulations of gamma cascades using the DICEBOX code.