An overview of NRL's NAUTILUS: a combination SIMS-AMS for spatially resolved trace isotope analysis

Abstract

We present a description of the capabilities and performance of the NAval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS) at the U.S. Naval Research Laboratory. The NAUTILUS combines secondary ion mass spectrometry (SIMS) and single-stage accelerator mass spectrometry (SSAMS) into a single unified instrument for spatially resolved trace element and isotope analysis. The NAUTILUS instrument is essentially a fully functional SIMS instrument with an additional molecule-filtering detector, the SSAMS. The combination of these two techniques mitigates the drawbacks of each and enables new measurement paradigms for SIMS-like microanalysis. Highlighted capabilities include molecule-free raster ion imaging for direct spatially resolved analysis of heterogeneous materials with or without perturbed isotopic compositions. The NAUTILUS' sensitivity to trace elements is at least 10× better than commercial SIMS instruments due to near-zero background conditions. We describe the design and construction of the NAUTILUS, and its performance applied to topics in nuclear materials analysis, cosmochemistry, and geochemistry. IntroductionAccelerator mass spectrometry (AMS) is synonymous with ultra-trace isotope analysis, while secondary ion mass spectrometry (SIMS) is the premier spatially resolved, sensitive, surface analysis technique. We have successfully designed and built the NAval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS) at the U.S. Naval Research Laboratory (NRL) 4-9 , which combines the modified hardware from two commercial instruments, an Ametek Cameca ims 4f SIMS 10 and a National Electrostatics Corporation (NEC) single-stage AMS (SSAMS) 11-13 , together with custom control hardware and software. The motivation for this novel combination MS-MS instrument is to utilize the aforementioned advantages of each technique in a manner which simultaneously mitigates each technique's drawbacks. While SIMS maintains excellent sensitivity for materials analysis with down to micrometer spatial and nanometer depth resolution, the sputtering process produces molecular secondary ions. These may interfere at the same mass-tocharge ratio (m/z) with isotopes of interest, especially for high-mass and/or trace analyses. The trade-off between increased mass resolving power (MRP), typically defined as the full width at 10% peak height, and decreased instrumental transmission can make high-mass analyses impractical, especially for trace isotopes (e.g., detection of 236 U in the presence of 235 U 1 H) 14 . AMS excels at removing molecular isobaric interferences, but these instruments typically analyze bulk samples without spatial resolution either due to chemical sample preparation or large sputter source size. While SIMS may analyze positive or negative secondary ions, tandem AMS instruments are limited to injecting negative ions. This dramatically decreases their sensitivity to electropositive elements, since molecular ions such as FeOor UOmust be generated to transport the element of interest, Fe or U,...

U–Pu Mixed Oxide Particle Analysis by NAUTILUS and Implications for Next-Generation Verification Challenges

“…The NAUTILUS is the combination of two commercially available instrument types consisting of a modified CAMECA ims-4f SIMS that is coupled to a ±300 keV National Electrostatics Corporation (NEC) SSAMS. The NAUTILUS was first described by Fahey et al 10 and more completely by Groopman et al 11 Because the front end of the NAUTILUS is identical to a traditional SIMS instrument, the standard sample preparations followed by the IAEA can be used without modification. Therefore, the NAUTILUS can be thought of as a traditional SIMS instrument with a high-end detector (the SSAMS) capable of removing molecular isobars.…”

“…The fragment mode can be used when the molecular form of the analyte dominates (e.g., MOX particles) and/or the contribution of the molecular interference is low (e.g., U-hydride contribution). This mode requires less gas and, therefore, results in less transmission loss due to scattering, effectively resulting in higher precision (see Groopman et al 11 for full details). Fragment mode was used in all of the measurements for this work.…”

“…12 The NAUTILUS control software was written in house using a combination of National Instruments (NI) LabVIEW and Python achieved via Enthought's Python Integration Toolkit for LabVIEW (PITL). A complete overview of the NAUTILUS control software can be found in Groopman et al 11 Briefly, the NAUTILUS control software can analyze the elemental and isotopic composition of individual particles one mass at a time hopping between isotopes of interest. The NAUTILUS control software collects data from a variety of imaging detectors (e.g., MCP and EM) enabling both microscope (SIMS-only) and microprobe (SIMS and SIMS-SSAMS) imaging modes.…”

Spectroscopic and microscopic examination of teeth exposed to green tea at different temperatures

“…The LIBS technique has been a useful tool to discriminate and differentiate elements accurately with high spatial resolution [ 27 ]. Additionally, LIBS is used for the identification of elements in soft tissues [ 28 – 31 ] and mineralized tissues without invasive sampling preparation [ 32 – 36 ]. In the present study, we have quantified the variation of inorganic elements in teeth subjected to hot tea and cold tea (room temperature—RT) in an in vitro model using LIBS.…”

Improved uranium particle analysis by SIMS using O3− primary ions

“…This was not the case for the NRL NAUTILUS, which used an accelerator mass spectrometer to remove interferences and analyze molecular fragments. 9 On non-ideal or real-world environmental samples, it may be infeasible to monitor and correct for these interferences on conventional SIMS instruments. Carbon is a widespread surface contaminant from organic solvents, oils, resins (e.g., poly(methyl methacrylate), PMMA), and is also present in non-ultrapure Si wafers, and in soils.…”