Nuclear Resonance Fluorescence Excitations around 2 MeV in U-235 and Pu-239

A search for nuclear resonance fluorescence excitations in U and Pu within the energy range of 1.0- to 2.5-MeV was performed using a 4-MeV, continuous, bremsstrahlung source at the High Voltage Research Laboratory at the Massachusetts Institute of Technology. Measurements utilizing high purity Ge detectors at back angles identified 9 photopeaks in U-235 and 13 photopeaks in Pu-239 in this energy range, most likely dipole excitations. These resonances provide unique signatures that allow the materials to be non-intrusively detected in a variety of environments including fuel cells, waste drums, vehicles and containers. The presence and properties of these states may prove useful in understanding the nuclear structure of even - odd nuclei.