This title appears in the Scientific Report : 2014 

Combined chemical and structural investigations of BaxRa1-xSO4 on the atomic level by TEM and APT
Weber, Juliane (Corresponding Author)
Brandt, Felix / Klinkenberg, Martina / Savenko, Aleksei / Breuer, Uwe / Bosbach, Dirk
Nukleare Entsorgung und Reaktorsicherheit; IEK-6
8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, Bonn (Germany), 2014-07-07 - 2014-07-09
Helmholtz Interdisciplinary Doctoral Training in Energy and Climate Research (HITEC)
Safety Research for Nuclear Waste Disposal
Experimental studies related to long-term safety assessments for the deep geological disposal of spent nuclear fuel suggest that Ra and the formation of the BaxRa1-xSO4 solid solution will be relevant in this context. Doerner and Hoskins derived thermodynamic properties for the formation of the BaxRa1-xSO4 solid solution, e.g. the partition coefficient, from kinetically influenced co-precipitation experiments [1]. Their model is based on assumptions about the uptake and distribution of Ra in the BaxRa1-xSO4 solid. We [2] followed a close-to-equilibrium approach and carried out ToF-SIMS analysis of the solid indicating a homogeneous uptake of Ra into the solid in amounts as predicted by thermodynamic calculations [3]. However, for a detailed investigation of the recrystallization process, nano-analytical methods need to be established in order to investigate the homogeneity of the Ra distribution.Transmission electron microscopy (TEM) provides detailed structural information and is a well-established technique for many different materials. There has been a major progress in the resolution of TEM due to aberration correction [4]. For the detailed chemical analysis of a sample, atom probe tomography is a powerful tool with resolution up to the atomic level. Since the development of the laser-assisted Atom Probe Tomography (APT), the analysis of electrically non-conductive samples is possible [5]. The combination of these two methods makes the achievement of both structural and chemical information at the atomic level possible. By using a special sample holder, even the analysis of the same sample with both methods is possible. Here, we present a method development for the combined characterization of BaSO4 (barite) by atom probe tomography (APT) and transmission electron microscopy (TEM). This method will be later applied to the characterization of BaxRa1-xSO4. Preparation is done by focused ion beam (FIB) from particles with a size of 10 40 µm. Electrical non-conductivity and poor thermal conductivity of barite leaves the APT-analysis of this mineral challenging. [1] H.A. Doerner & W.M. Hoskins, Journal of the American Chemical Society,(1925), 47, 662-675.[2] M. Klinkenberg et al., Environmental Science & Technique, (2014) accepted.[3] V. Vinograd et al., Geochimica et Cosmochimica Acta, (2013), 122, 398-417. [4] K. Urban, Science, (1998), 321, 506-510. [5] T. Kelly & D. Larson, Annular Revision of Material Research, (2012), 42, 1-31.