European Commission Joint Research Centre Institute for Transuranium Elements
Measurement of Radioactivity in the Environment
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- High Resolution Inductively Coupled Mass Spectrometry (HR-ICPMS)
- Ion Chromatography Inductively Coupled Plasma Mass Spectrometry (IC-ICP-MS)
- Glow Discharge Mass Spectrometry (GDMS)
- Capillary Electrophoresis Coupled to Electrospray Mass Spectrometry (CESIMS)
- Capillary Electrophoresis Coupled to Inductivity (CE-ICPMS)
The principle method used at ITU for the characterization of micro radioactive particles containing fissile material is based on secondary ion mass spectrometry (SIMS), even though nuclear track technologies have been developed for their individuation. The main purpose in the analysis of single particles is the determination of their isotopic composition that has been demonstrated successfully for uranium and plutonium particles. From these results, the enrichment of the material produced, the process used for the enrichment as well as the staring material employed (natural or reprocessed uranium) can be identified.
The samples are handled in a clean lab class 100-10, where chemical treatments are performed in order to collect particles from the cotton swipe to the sample holder for further instrumental analysis.
Scanning Electron Microscope-Energy Dispersive X-ray (SEM-EDX) is used after sample preparation to measure the elemental composition of the micrometer-sized particles removed from the cotton swipes. For instance, to search for uranium containing particles the samples are scanned automatically by SEM using the backscattered mode. From these analyses, the number of uranium particles deposited on the planchet, together with their elemental composition and their co-ordinates are obtained.
SEM-EDX offers high elemental sensitivity and can screen large numbers of particles, but the technique does not give uranium or plutonium isotopic information, which can be of critical importance. For this purpose, SIMS that measures secondary ions of U and Pu isotopes by peak switching on an electron multiplier pulse-counting system or with an imaging detection system that produces spatially resolved images for each isotope, is exploited. The particle deposited on the graphite planchet are bombarded with oxygen ions positively charged at an energy of 15 keV, which then provides a SIMS image of the actinides particle present at the surface (fig.1). By reducing the resolution of the primary beam, the secondary ions from individual particles are mass analyzed and detected (fig.2).