Measurement of PuO₂ film thickness by electron probe microanalysis (EPMA) calibration curve method

Journal Article · 28 December 2019 · Journal of Nuclear Materials

DOI: https://doi.org/10.1016/j.jnucmat.2019.151968 · OSTI ID:1597211

Stanford, J. A. ^[1]; Teslich, N. ^[1]; Donald, S. ^[1]; Saw, C. K. ^[1]; Gollott, R. ^[1]; Dinh, L. N. ^[1]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Plutonium (Pu) surfaces are highly reactive toward oxygen containing species and, therefore, invariably covered with oxides (e.g. PuO₂) during transport and handling. The actual thickness of the surface oxide may dictate if a plutonium part is suitable for a certain application. As a result, a cost-effective, quick, non-destructive, yet reliable means to measure the oxide layer thickness formed on Pu samples is desirable. In this study, the cross-sections of a series of room temperature grown oxides on Pu samples were trenched by focus ion beam (FIB) then observed by scanning electron microscopy (SEM) to measure the surface oxide thicknesses, which were then combined with the corresponding oxygen k-ratios provided by electron probe microanalysis (EPMA) to form calibration curves. Oxide thickness measurements for the calibration curves were made on samples within the typical SEM observable range for PuO₂ (35–400 nm). The portion of the calibration curve in the thinner oxide region (<35 nm) were approximated via Pouchou and Pichoir’s Φ(ρz) theory. Two specimens with micrometer-thick PuO₂ standards (one formed at room temperature and the other at higher temperature with a higher level of crystallinity) were made for the k-ratios in this study, allowing EPMA users to choose the standard that best suits their needs. If the surface corrosion is known to be PuO₂ (from the environment in which the Pu sample is stored) or if the stoichiometry of the surface oxide is confirmed by a preliminary/compliment technique, these calibration curves allow EPMA users to quickly and efficiently determine PuO₂ thicknesses from the measured oxygen k-ratios of their samples. The methodology presented in this study can also be used as a template for creating calibration curves for oxides grown on other actinides.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1597211
• Alternate ID(s): OSTI ID: 1581010
• Report Number(s): LLNL-JRNL-791483; 990598; TRN: US2103785
• Journal Information: Journal of Nuclear Materials, Vol. 530, Issue C; ISSN 0022-3115
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English