Though not often discussed explicitly in literature, sample handling and preparation for advanced characterization techniques is a significant challenge for radiological materials. In this contribution, a detailed description is given of method development associated with characterization of highly radioactive and, in some cases, hygroscopic oxides of technetium. Details are given on developed protocols, fixtures, and tooling designed for x-ray and neutron diffraction, x-ray absorption, Raman spectroscopy, magic angle spinning nuclear magnetic resonance, and electron paramagnetic resonance. In some cases, multiple iterations of improved sample holder design are described. Lessons learned in handling Tc compounds for these and similar characterization methods are discussed.

The local chemistry of technetium-99 (99Tc) in oxide glasses is important for understanding the incorporation and long-term release of Tc from nuclear waste glasses, both those for legacy defense wastes and fuel reprocessing wastes. Tc preferably forms Tc(VII), Tc(IV), or Tc(0) in glass, depending on the level of reduction of the melt. Tc(VII) in oxide glasses is normally assumed to be isolated pertechnetate TcO4- anions surrounded by alkali, but can occasionally precipitate as alkali pertechnetate salts such as KTcO4 and NaTcO4 when Tc concentration is high. In these cases, Tc(VII) is 4-coordinated by oxygen. A reinvestigation of the chemistry of alkali-technetium-oxides formed under oxidizing conditions and at temperatures used to prepare nuclear waste glasses showed that higher coordinated alkali Tc(VII) oxide species had been reported, including those with the TcO5- and TcO6- anions. The chemistry of alkali Tc(VII) and other alkali-Tc-oxides is reviewed, along with relevant synthesis conditions.

Additionally, we report attempts to make 5- and 6-coordinate pertechnetate compounds of K, Na, and Li, i.e. TcO5- and TcO6-. It was found that higher coordinated species are very sensitive to water, and easily decompose into their respective pertechnetates. It was difficult to obtain pure compounds, but mixtures of the pertechnetate and other phase(s) were frequently found, as evidenced by x-ray absorption spectroscopy (XAS), neutron diffraction (ND), and Raman spectroscopy. Low temperature electron paramagnetic resonance (EPR) measurements showed the possibility of Tc(IV) and Tc(VI) in Na3TcO5 and Na5TcO6 compounds.

It was hypothesized that the smaller counter cation would result in more stable pertechnetates. To confirm the synthesis method, LiReO4 and Li5ReO6 were prepared, and their Raman spectra match those in the literature. Subsequently, the Tc versions LiTcO4 and Li5TcO6 were synthesized and characterized by ND, Raman spectroscopy, XANES, and EXAFS. The Li5TcO6 was a marginally stable compound that appears to have the same structure as that known for Li5ReO6. Implications of the experimental work on stability of alkali technetate compounds and possible role in the volatilization of Tc are discussed.

In this study wet chemical methods combined with UV-Vis spectroscopy were performed to quantify Fe(II)/Fe(III) ratios and total iron content of quenched alkali alumino-boro-silicate (simulated nuclear waste) glasses, applying a colorimetric method. We report lessons learned from experimental challenges encountered associated with the colorimetric method, where 1,10 phenanthroline method is complexed with dissolved glass powder and the resulting solution measured for absorbance at 520 nm to determine Fe(II). To obtain total iron, the solution was then equilibrated with a mild reducing agent to chance all Fe to Fe(II), and the absorbance measured again at 520 nm. These absorbance values allowed for calculation of the Fe(II)/Fe(III) ratio, and the total iron content in the glasses. Total Fe measured is somewhat higher than as-batched target values for waste glasses, but very accurate for reference BCR-2G glass. All quenched alumino-boro-silicate glasses analyzed showed a Fe(II)/Fe(III) ratio between 0.06 (± 0.01) and 0.04 (± 0.01). These values are consistent with those obtained for similar glass compositions melted under analogous conditions, indicating a composition of ca. 94-96% Fe(III).

The determination of the long-term stability and corrosion of vitrified nuclear waste is an important aspect of research for the U.S. Department of Energy (DOE). It is necessary to understand the rate and mechanisms of Nuclear Waste Glass (NWG) corrosion to determine whether or not the glassy matrix will be able to retain radionuclides for the required repository performance time period. Glass corrosion and the rate of glass corrosions is determined by both chemical and microscopy. Electron Microprobe Analysis (EPMA) is a common and powerful method utilized in the examination of the chemographic difference between corroded and uncorroded NGWs. In this work, two forms of quantitative and semi-quantitative EPMA methods are defined by optimizing the instruments counting statistics against a standard glass and NIST minerals that have compositions similar to the glasses under examination. Data collected on both the planar and cross-sectioned surfaces of an unaltered simulated NWG by Standard based Wavelength Dispersive Spectroscopy (WDS) was found to be comparable to the theoretical composition of the glass. Conventional standardless Energy Dispersive Spectroscopy (EDS) data collected on the same surfaces was not comparable. However, standard-based EDS analysis is shown to be able to discriminate between unaltered and corroded glass surfaces.

A complete understanding of radioactive waste glass interactions with near-field materials is essential for appropriate nuclear waste repository performance assessment. In many geologic repository designs, Fe is present both in the natural environment and in the containers that will hold the waste glasses. In this paper we discuss investigations of the alteration of International Simple Glass (ISG) in the presence of Fe0 foil and hematite (Fe2O3). Based on solid analysis, ISG alteration is more pronounced in the presence of Fe0 than with hematite. Additionally, typical glass corrosion is observed for distances of 5 mm between Fe materials and ISG, but incorporation of Fe in the alteration layer is only observed for systems exhibiting full contact between Fe0 material and ISG. Solution analysis results indicate that diatomaceous earth minimizes corrosion to a larger extent than fumed silica does when present with iron and ISG.

Using scanning near-field lithography (SNP), it is possible to pattern molecules at surfaces with a resolution as good as 9 nm [M. Montague, R. E. Ducker, K. S. L. Chong, R. J. Manning, F. J. M. Rutten, M. C. Davies and G. J. Leggett, Langmuir23 (13), 7328–7337 (2007)]. However, in common with other scanning probe techniques, SNP has previously been considered a serial process, hindering its use in many applications. IBM’s “Millipede” addresses this problem by utilizing an array of local probes operating in parallel. Here, we describe the construction of two instruments (Snomipedes) that integrate near-field optical methods into the parallel probe paradigm and promise the integration of top–down and bottom–up fabrication methods over macroscopic areas. Both are capable of performing near-field lithography with 16 probes in parallel spanning approximately 2 mm. The instruments can work in both ambient and liquid environments, key to many applications in nanobiology. In both, separate control of writing is possible for each probe. We demonstrate the deprotection of self-assembled monolayers of alkylsilanes with photocleavable protecting groups and subsequent growth of nanostructured polymer brushes from these nanopatterned surfaces by atom-transfer radical polymerization.