Atom Probe Mass Spectrometry of Uranium Isotopic Reference Materials

Abstract

Atom probe tomography (APT)-based isotopic analyses are becoming increasingly attractive for analysis applications requiring small volumes of material and sub-micrometer length scales, such as isotope geochemistry, nuclear safety, and materials science. However, there is an open question within the atom probe community as to the reliability of atom probe isotopic and elemental analyses. Using our proposed analysis guidelines, in conjunction with an empirical calibration curve and a machine learning-based adaptive peak fitting algorithm, we demonstrate accurate and repeatable uranium isotopic analyses, via atom probe mass spectrometry, on U 3 O 8 isotopic reference materials. By using isotopic reference materials, each measured isotopic abundance value could be directly compared to a known certified reference value to permit a quantitative statement of accuracy. The isotopic abundance measurements for 235 U and 238 U in each individual APT sample were consistently within ±1.5% relative to the known reference values. The accuracy and repeatability are approaching values consistent with measurements limited primarily by Poisson counting statistics, i.e., the number of uranium atoms recorded.

Atom Probe Tomography for Isotopic Analysis: Development of the 34S/32S System in Sulfides

“…Experimental observations have shown the isotopic variants of an ion species, e.g., 32,32 S 2 + , 32,33 S 2 + , 32,34 S 2 + , 32,36 S 2 + , 33,33 S 2 + , 33,34 S 2 + , 33,36 S 2 + , 34,34 S 2 + , 34,36 S 2 + , and 36,36 S 2 + , have nominally the same peak form (Meisenkothen et al, 2020a(Meisenkothen et al, , 2020b(Meisenkothen et al, , 2020c. The local spectrum in the region of the family of peaks can thus be approximated as a linear combination of the individual constituent peaks, and an optimization algorithm can be used to determine the "best fit" shape, shared in common by the peaks, and the relative intensities of the peaks.…”

“…The background spectrum under the family of peaks was assumed to be a constant and was approximated by averaging the ion counts in hundreds of bins immediately to the left of the family of peaks. Adaptive peak fitting has been used successfully to provide repeatable and accurate isotopic analyses with filtered single-hit corrected-TOF spectra collected for a variety of materials on a LEAP-4000XSi instrument (Meisenkothen et al, 2020a(Meisenkothen et al, , 2020b(Meisenkothen et al, , 2020c. All of our analyses performed with the adaptive peak fitting used corrected-TOF spectra exported from the IVAS (v 3.8.8) Cal/Recon Wizard (i.e., timing signal-only-based data, prior to hit finding and ion feedback filtering) with a bin width of 0.01 ns.…”

“…This work is focused on a method to correct the isobaric interferences in the mass spectra of pyrite (FeS 2 ) to obtain accurate 34 S/ 32 S ratios, and to shed new light on the instrumental artifacts of laser-pulsed APT. We build on the work of Gopon et al (2019Gopon et al ( , 2020 and Meisenkothen et al (2020aMeisenkothen et al ( , 2020c which provided methods for isotopic analysis using APT. By analyzing a set of well-characterized S isotope standards as well as simulated APT datasets, we have developed a better understanding of the artifacts inherent in laser-pulsed APT.…”

Study of LEAP® 5000 Deadtime and Precision via Silicon Pre-Sharpened-Microtip™ Standard Specimens

“…Few APT studies have probed the accuracy and precision of the technique in detail (Prosa et al, 2013b;Meisenkothen et al, 2020a), but this study shows that it is possible to achieve very high precision on Si-isotope fractions. Extending the approach shown here to P-doped silicon, ideally analyzed at higher CSR, would allow one to make reliable measurement of the isotopic abundances for that sample from the Si ++ ions (which do not exhibit hydrides) and use that information to decouple any overlaps at 31 Da.…”

Chemical and elemental mapping of spent nuclear fuel sections by soft X-ray spectromicroscopy

“…Atom probe tomography (APT) analysis (Bachhav et al, 2021(Bachhav et al, , 2020Meisenkothen et al, 2020) was performed on this fuel to investigate atomic composition from similar regions of the fuel pellet to the STXM FIB sections. Specimens were analyzed at the Center for Advanced Energy Studies (CAES) for APT analysis using a Cameca LEAP 4000XHR.…”