Secondary Ion Mass Spectrometry (SIMS)

Drei primäre Ionenquellen sind je nach Art der Untersuchung einsetzbar: ¹³³Cs⁺ und (¹⁶O₂) für Tiefenuntersuchungen (Tiefenprofil) sowie ⁶⁹Ga⁺ für Oberflächenuntersuchungen (Ionenabbildung). Die Hauptmerkmale der verschiedenen primären Ionenstrahlen sind:

This technique enables precise determination of chemical composition and isotopic distributions with detection limits in the ppm range. It further allows for both depth profiling and high-resolution lateral imaging at micro- and submicrometer scales.

The SIMS ATOMIKA 4000 was installed in 1995 following a comprehensive selection process involving various vendors. It was specifically designed for the analysis of irradiated materials and integrated into a dedicated shielding system developed in-house. This configuration ensures safe handling and analysis of highly radioactive samples.

The maximum allowable activity in the analysis chamber is 1×10¹⁰ Bq (⁶⁰Co equivalent). A glovebox system connected via a closed sample-transfer-system enables secure sample transfers. Materials such as nuclear fuels (UO₂, MOX) and cladding alloys (Zircaloy-2, M5) can be analyzed in detail.

The instrument combines multiple ion sources, including ¹³³Cs⁺, O₂⁺, and ⁶⁹Ga⁺. While cesium and oxygen ions are primarily used for depth profiling, the gallium source enables high-resolution surface imaging and isotope mapping. The addition of a Gallium ion source is a custom feature of this SIMS enabling extended analytical capabilities.

A quadrupole mass filter installed at a 90° angle to the primary ion beam performs ion selection. An electron source provides charge compensation on insulating samples.

The instrument is characterized by a high degree of flexibility and performance. A typical depth resolution of approximately 20 nm are achieved, depending on sample conditions in particular regarding the surface roughness. Using the Ga⁺ source, lateral resolutions in the submicrometer range (~500 nm) are obtainable.

Detection limits are typically in the low ppm range for many matrix compositions.  For instance, in ZrO₂ the detection limit for ⁷Li is approximately 0.5 ppm whereas that of ¹¹B is around 10 ppm.

While many analyses are qualitative, dedicated calibration approaches developed at PSI enable quantitative measurements.

Globally unique methods have been developed for the quantitative analysis of lithium and boron in oxide layers of irradiated cladding. These are based on specially developed calibration strategies using implanted reference materials.

Additionally, advanced approaches for hydrogen mapping in irradiated materials combine cesium pre-coating with high-resolution gallium-based imaging, providing insights complementary to SEM and EPMA techniques [Mine et al., Surf. Interface Anal. (2014), https://www.dora.lib4ri.ch/psi/item/psi:23017].

Over the past decades, the SIMS ATOMIKA 4000 has been used in a wide range of application areas. A central focus is the analysis of nuclear fuels, including the investigation of burnup distributions as well as the distribution of fission products and minor actinides. Equally important is the study of fission gases such as xenon and krypton, whose distribution in the fuel provides insights into material behavior and operating conditions.

Another key area is the analysis of cladding materials. Here, particular attention is given to oxide layers, so-called CRUD layers, and hydrogen-induced changes, all of which are crucial for material integrity. Diffusion processes, for example of ¹⁸O in materials for solid oxide fuel cells, are also part of the application spectrum.

In its early years of operation, the SIMS ATOMIKA 4000 was a predominantly analog system with a user interface running on Mac OS. After 16 years of operation, the instrument underwent a fundamental modernization in 2011. During this upgrade, all analog electronic components were replaced with a fully digital, computer-controlled system running on Windows.

This conversion represented a significant technological advancement and greatly improved both data acquisition and data analysis capabilities. Since then, the instrument has been developed continuously and adapted to new requirements.

The SIMS ATOMIKA 4000 is used both in academic research [e.g., Portier et al., Spectrochimica Acta Part B 73 (2012), https://www.dora.lib4ri.ch/psi/item/psi:12320] and in industrial projects. It is an integral part of numerous collaborations with national and international partners, including LNM, Swiss Nuclear, and various PSI internal laboratories.

On the industrial side, the instrument has been employed in projects with the Electric Power Research Institute (USA), Studsvik (Sweden), the Korea Atomic Energy Research Institute (South Korea), as well as with Swiss nuclear power plant operators. In addition, it serves as the basis for numerous master’s and doctoral theses and collaborations with other PSI laboratories [e.g., R. Frison et al., Nuclear Instruments and Methods in Physics Research B 273 (2012), https://www.dora.lib4ri.ch/psi/item/psi:23639].

Through the combination of specialized shielding, many years of experience, and continuous methodological development, PSI has been among the world-leading institutions for SIMS analyses of radioactive materials, particularly in the areas of lithium and boron quantification as well as nuclear fuel analysis.

Following the acquisition of the original manufacturer (Atomika) in the early 2000s, the discontinuation of the instrument series, and the termination of technical and software support, the end of the Hotlab SIMS became foreseeable. The instrument will be decommissioned in 2026.