Systematics of the pygmy dipole resonance in stable tin isotopes from resonant photon scattering ⁎

The 112,120Sn(γ,γ′) reactions were studied for different endpoint energies of the incident bremsstrahlung spectrum below the neutron separation energies at the superconducting Darmstadt electron linear accelerator S-DALINAC. Dipole transition strength distributions have been extracted for 112Sn; the analysis of 120Sn is still in progress. In the case of 112Sn a concentration of dipole excitations is observed between 5 and . Combining with existing data for 116,124Sn provides a systematics of the pygmy dipole resonance (PDR) in stable Sn nuclei which serves as a benchmark test of recent microscopic calculations aiming at a description of the PDR in exotic neutron-rich Sn isotopes.