Probing the multi-scale structural properties of Pu(IV) intrinsic colloids by synchrotron SAXS/XAS techniques Predicting the behavior and reactivity of PARTICLE SIZE, MORPHOLOGY AND AGGREGATION radioactive “hot” particles in the geosphere PROPERTIES requires their thorough characterization, The normalized scattering curves provided in Fig. 1 in absolute if possible in their native environment. unit evidence strong differences for both hydrolytic (HC) and Research progress on Pu(IV) colloids is sonolytic (SC) colloids. The HC displays a Q for low wave0 vectors and tends towards Q at higher wave vectors evidencing-4 particularly challenging because of the a sharp interface typical for 3D objects and compact particles. complex chemistry of the element Pu and The SC exhibits a closer Q at low wave vectors ending with-2 the high radioactivity of all of its isotopes. a Q at larger wave vectors which features are typical from-4 2D elongated objects. Best fit for the SC was obtained with Within this framework, researchers from elongated disk particles of 5.7 nm thickness and more than Marcoule Institute for Separation Chemistry 30 nm size. HC was rather explained using a spherical core- (ICSM), CEA/DES/ISEC/DMRC and MARS shell model constituted by a core matching with an ideal PuO2 fluorite-type Fm-3m oxide structure surrounded by a disordered beamline, have combined synchrotron SAXS Pu-O shell solvated with nitrate counter-ions. Whereas HC size (Small Angle X-ray Scattering) and XAS agreed with previous high-resolution transmission electron (X-ray Absorption Spectroscopy) techniques microscopy (HR-TEM) experiments, the bigger size of the SC (7 nm by HR-TEM) was explained by the aggregation of the NPs to decipher the multi-scale structural in the absence of stabilizing or capping agents.[2] properties of Pu(IV) intrinsic colloids FIGURE 1 prepared by hydrolysis or sonolysis. Anthropogenic activities including nuclear weapon rotation, space conquest or industrial accidents have released substantial amounts of actinides into the environment. The element plutonium, which was thought to be highly immobile regarding its very low solubility in aquatic systems and high sorption ability onto minerals, has been proved to possibly move on the scale of kilometers. Both pseudo and intrinsic Pu colloids have been reported as potential vectors for the environmental migration of actinides, thus strengthening the need for their better description and characterization.[1] Pseudo-colloids refer to natural colloids on which Pu has been incorporated or adsorbed, whereas intrinsic ones rely on the ability of Pu to precipitate and form its own colloid. X ray-based scattering and absorption techniques are very useful to probe directly in the native medium, the nanoparticle (NP) properties including their local structure, oxidation state, size and morphology without any specific sample preparation. Two intrinsic Pu(IV) colloidal forms prepared by hydrolysis of Pu(IV) in water (presence of nitrates from the mother Pu solution) or 20 kHz sonication of PuO powder in pure water under Ar/(10 %)CO atmosphere2 were investigated.[2] 34