Electric and Magnetic Dipole States in $^{238}$U

An investigation of dipole states in $^{238}$U is important for the fundamental understanding of its structure. Precise experimental information on the distribution of $M1$ and $E1$ \mbox{transitions} in $^{238}$U has been obtained using the nuclear resonance \mbox{fluorescence} \mbox{technique} at the High-Intensity $\gamma$-ray Source at the \mbox{Triangle} \mbox{Universities} Nuclear Laboratory. Using 100\% linearly-polarized, \mbox{monoenergetic} \mbox{$\gamma$-ray} beams between incident energies of 2.0 - 5.5 MeV, the spin, \mbox{parity}, width, and $\gamma$-strength of the ground-state deexcitations were \mbox{determined}. These measurements will form a unique data set that can be used for comparison with theoretical models of collective excitations in heavy, deformed nuclei. The data can also provide isotope-specific signatures to search for special nuclear materials.