Parity Measurements of Nuclear Levels Using a Free-Electron-Laser Generated<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">γ</mml:mi></mml:math>-Ray Beam

Abstract

The quality and intensity of $\ensuremath{\gamma}$ rays at the High Intensity $\ensuremath{\gamma}$-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 $({10}^{7}\ensuremath{\gamma}/\mathrm{s})$ beam of $100%$ linearly polarized, nearly monoenergetic, $\ensuremath{\gamma}$ rays on the semimagic nucleus ${}^{138}\mathrm{Ba}$. Negative parity quantum numbers have been assigned to 18 dipole excitations of ${}^{138}\mathrm{Ba}$ between 5.5 MeV and 6.5 MeV from azimuthal $\ensuremath{\gamma}$-intensity asymmetries.