Plutonium is one of the most complex elements in the periodic table. Even after several decades of in-depth studies of plutonium compounds and surrogates, there are still questions about how its phase, microstructure and composition influence the physicochemical behavior of this material, which is important for nuclear energy, non-proliferation, homeland security, and nuclear forensics applications. Although several methodologies have been established to accurately obtain physical and chemical information of a bulk plutonium analyte, gaining analogous knowledge from the near surface layers of plutonium is crucial to better understand how these layers evolve when subjected to different conditions. The surface of plutonium has been experimentally studied through diverse techniques (for example, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and secondary ion mass spectroscopy), which have provided valuable information in terms of morphology and composition. However, surface probe microscopy methodologies such as atomic force microscopy (AFM) provide a direct characterization route that enables the acquisition of topographical information while simultaneously mapping almost any probe-sample interaction imaginable, allowing them to be correlated to each other. Here, we report the exploration of the surface of gallium stabilized δ phase plutonium coupons via AFM. Initial results reveal that the plutonium surface is considerably rough and heterogeneous. This is further evidenced via quantitative nanomechanical mapping (QNM), which was done to explore the mechanical properties of the δ phase plutonium surface. QNM images exhibit distinct patterns that are not observed in the topography images. The ability of AFM to achieve nanometer resolution in combination with QNM allows one to collect mechanical information (i.e., elastic modulus, adhesion, deformation, dissipation, etc.) with the same resolution, which denotes a considerable advantage to identify the presence of contaminants, inclusions, surface defects on the surface of plutonium and their effect in its properties in a direct, non-destructive and straight forward manner.
Approved for public release LA-UR-17-29888