Nuclear Resonance Fluorescence from $^{238}$U

Nuclear resonance fluorescence provides unambiguous isotope identification by observing de-excitations of nuclear levels of $\gamma$-ray transitions characteristic of the isotope of interest as high-energy $\gamma$ rays penetrate protective shielding, acting as an identifier of hidden nuclear materials. Using the mono-energetic $\gamma$-ray source at the HI$\gamma$S facility to investigate the nucleus $^{238}$U through the ($\gamma$, $\gamma$') reaction, we measured the widths of low-spin states observed at incident $\gamma$-ray beam energies in the range of 2.94 to 4.40 MeV.