Parity measurements of nuclear levels using a free-electron-laser generated γ-ray beam -: art. no. 012502

The quality and intensity of gamma rays at the High Intensity gamma-ray Source are shown to make nuclear resonance fluorescence studies possible at a new level of precision and efficiency. First experiments have been carried out using an intense (10(7) gamma/s) beam of 100% linearly polarized, nearly monoenergetic, gamma rays on the semimagic nucleus Ba-138. Negative parity quantum numbers have been assigned to 18 dipole excitations of Ba-138 between 5.5 MeV and 6.5 MeV from azimuthal gamma-intensity asymmetries.