Electron probe microanalysis (EPMA) and Dynamic secondary ion mass spectrometry (D-SIMS) are complementary techniques. Both measure elemental composition at the nanoscale and are frequently found in academic, industrial, and service laboratories. They differ considerably in terms of construction, elemental detection mechanisms and sensitivity. Interestingly, the commercialization of EPMA and D-SIMS instruments coincided with the civil use of nuclear energy in the 1960s and the need for extensive research on nuclear fuels. CAMECA’s shielded EPMA (the SKAPHIA) and D-SIMS instrument (the ACTINIS) facilitate this research by helping to explain the behavior and performance of nuclear fuels, they also play an important role in optimizing nuclear waste management and valuation.
EPMA analysis using wavelength dispersive spectrometers (WDS) is a non-destructive, repeatable, and commonly available microbeam analysis technique in nuclear research centers. However, EPMA instruments cannot measure isotopes, have detection limits around 300 ppm for analyses on radioactive samples, and cannot measure the fusion gas krypton due to overlaps with the Mα1 U X ray line. D-SIMS is a complementary destructive technique that largely overcomes the limitations of EPMA. Studies performed with an ACTINIS on irradiated materials include the nuclear reactions occurring during in core irradiation which are commonly characterized by isotopic ratio measurements, the physical and chemical behavior of fission products by mapping their location, and the characterization of fission gases to measure their radial distribution.
The ACTINIS D-SIMS and the SKAPHIA EPMA are the only instruments in the EPMA and SIMS markets capable of analyzing radioactive samples in a safe environment. These two instruments are distinct but complementary and crucial in the field of nuclear analysis as illustrated in the below study of fission gas performed on CAMECA Shielded D-SIMS and EPMA at CEA Cadarache, France.
Fission gas study in irradiated fuel using Shielded EPMA and Shielded SIMS
A) Shielded EPMA X-ray elemental mappings of Xenon at three different locations (center of the fuel rod, radial position, edge) revealing Xe located in small bubbles at the edge, while it is well dispersed at the center, except in grain boundaries.
B) Xe radial profiles acquired by shielded EPMA and shielded SIMS. Two different contents of Xe were quantified:
Xe dissolved into the fuel (green line for EPMA and yellow points for SIMS: during sample polishing Xe bubbles were broken leading to Xe evaporation
Total Xe content in the fuel (black line for EPMA and red points for SIMS: deducted from the quantification of Nd (EPMA) and from measurements of matrix signal and bubbles peak (SIMS)
Courtesy of Karine Hanifi and Philippe Bienvenu, CEA Cadarache, France
EPMA and SIMS analysis provide complementary information about Xe characterization in irradiated fuel: SIMS enables to characterize deep Xe bubbles (etching of the sample) whereas EPMA gives accurate information on small bubbles close to the surface.
Focus on instrumentation
Let’s now dive into the similarities and differences between Shielded D-SIMS and EPMA.
In EPMAs, an electron beam rasters a sample surface. The beam interacts with the sample which emits characteristic X-Rays. Like traditional EPMAs, the SKAPHIA can analyze nearly all the elements of the periodic table for major and trace element analysis at the sub-micron scale. Additionally, it can analyze samples emitting beta and gamma radiation for quantitative analysis, X-ray mapping, line profile acquisition and data processing. The column, spectrometers and sample stage are installed in a hot cell made of lead or concrete. The instrument is fully remote-controlled (stage, column, diaphragms...), with electronics and computers outside the hot cell environment. WDS spectrometers and stage are shielded to prevent background caused by gamma radiation while Electron detectors (SE and BSE) are protected through specific orientation and retractable covers. The SKAPHIA can be equipped with an energy dispersive spectroscopy (EDS) detector to quantify major elements and up to four WDS detectors for trace element analysis. The SKAPHIA EDS detector is protected through a retractable valve and can be used as a fast tool for acquiring phase data. However, EDS detectors are limited in terms of light element analysis. In nuclear science, quantifying oxygen concentration variations is crucial to understanding the rod oxidation process. WDS analysis of oxygen provides better sensitivity and spectral resolution than the corresponding EDS technique.
In a D-SIMS instrument, an ion beam sputters the sample surface. Some particles emitted from the sample are ionized and subsequently analyzed with a mass spectrometer. Like non-shielded SIMS, the ACTINIS performs high sensitivity depth profiling and isotope ratio measurements as well as element and isotope mapping at sub-micron lateral resolution with excellent detection limits (ppm to ppb). In the ACTINIS, specific adaptations have been developed to protect the operator and minimize manual operations. Like the SKAPHIA, the instrument is fully remote-controlled (sample introduction, stage, column, diaphragms...), with electronics and computers outside the “hot” cell environment.
Both systems are maintained under high vacuum to decrease the collision of ions on their way to the mass analyzer (SIMS) and electrons on their way to various detectors (EPMA) and reduce residual gas contamination. A flat surface is necessary in both systems to optimize the collection of secondary ions (SIMS) or X-rays (EPMA) so sample preparation plays a key role in the analysis process.
Below is a chart comparing various characteristics of the two techniques.
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Shielded SIMS
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Shielded EPMA
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Elemental Mapping
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✔
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✔
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|
Isotopic Analysis
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✔
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✘
|
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Depth Profiling
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✔
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✘
|
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Destructive technique
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✔
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✘
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Imaging
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✔
Ion imaging
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✔
Electron imaging
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|
Simultaneous elemental acquisiton
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✘
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✔
|
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Detection Limits
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Below ppm to ppb
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Tens of ppm
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Elemental Limitations
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Detection limits vary, but nearly
all elements can be measured
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Light elements
(H, He, Li)
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This blog post discusses two different surface-based analysis techniques specifically tailored for the analysis of radioactive samples.
For more information on EPMAs see
•
https://www.cameca.com/products/epma/skaphia
• EPMA tutorial:
https://www.cameca.com/focus/epma-tuto
For more information on D-SIMS see
•
https://www.cameca.com/products/sims
• D-SIMS tutorial:
https://www.cameca.com/focus/sims-tuto
For a comprehensive article on the complementarity of EPMAs and SIMS instruments in the nuclear industry, see
EMAS 2011 Workshop (iop.org)
Authors: Brooke JABLON, Anne-Sophie ROBBES, Paula PERES