Nuclear Resonance Fluorescence from Uranium above 2 MeV

The detection of special nuclear materials is critical to the nation's efforts to counter serious threat from nuclear terrorist attacks. A research program has been initiated at TUNL to address the need for new nuclear data on the actinides using the High-Intensity Gamma-Ray Source (HI$\gamma$S). The high-intensity nearly monoenergic and 100\% polarized $\gamma$-ray beams from H$\gamma$S were utilized to search for dipole states in $^{235}$U and $^{238}$U above 2 MeV. This information is necessary for developing technologies using Nuclear-Resonance Fluorescence (NRF) to nonintrusively scan cargo for specific nuclei. The existence of strong nuclear dipole transitions in the actinides above 2 MeV is important for nuclear forensics, because interrogation photons using NRF are the most penetrating at these energies. Results from our experiments at E$_{\gamma} >$ 2.0 MeV on uranium will be presented.