Ortsaufgelöste Analyse von Aktiniden mittels resonanter ToF-Laser-SNMS

Das vom Bundesministerium für Bildung und Forschung geförderte Forschungsprojekt Secondary Ionisation of Radioactive Isotopes for Ultra trace analysis with Spatial resolution (SIRIUS) zur Migration von Radionukliden aus einem künftigen Endlager fokusstiert sich auf das Migrations- und Auflösungsverhalten von Mikro- und Nanopartikeln. Für Experimente geeignete Partikel bedürfen einer anfänglichen zerstörungsfreien Charakterisierung, um mit Umweltpartikeln anschließend Speziations- und Auslaugungsexperimente durchführen zu können. Hierzu werden einzeln präparierte Partikel benötigt, die bezüglich der elementaren und isotopen Zusammensetzung charakterisiert wurden, da hierdurch die Herkunft betrachteter Partikel bestimmt werden kann. Radiometrische Untersuchungsmethoden wie gamma- und alpha-Spektrometrie bieten hier neben der Rasterelektronenmikroskopie Informationen bezüglich der Isotopenzusammensetzung, können jedoch entweder nur die kurzlebigen Radionuklide mit entsprechend hohen Zerfallsenergien nachweisen oder sind auf die Zusammensetzung bezüglich der Hauptelemente beschränkt. Eine alternative Nachweismethode für eine Bandbreite von sowohl radioaktiven, als auch stabilen Isotopen bietet die nahezu zerstörungsfreie resonante Laser-Sekundärneutralteilchen-Flugzeit-Massenspektrometrie, die eine isotopenselektive Oberflächenanalyse bei einer lateralen Auflösung im Bereich von 100nm bereitstellt. Das Forschungprojekt beschränkt sich dabei auf das geochemische Migrationsverhalten von Uran, Plutonium, Americium und Technetium, wobei sich die vorliegende Arbeit mit dem Ionisationsverhalten von gesputtertem Uran, Plutonium und Americium von Kernbrennstoffpartikeloberflächen befasst. Bestehende und neu entwickelte zwei- und dreistufige Resonanzionisationsschemata sind auf das Unterdrückungsverhalten isobarer Interferenzen und das Ansprechen verschiedener Isotope eines Elements hin untersucht und optimiert worden. Es wurde der Einfluss von Laserstrahlpolarisationen auf das Isotopensignal untersucht und darüber die Gesamtdrehimpulsquantenzahl eines autoionisierenden Zustands von Plutonium bestimmt. Darüber hinaus erfolgte der erstmalige nahezu zerstörungsfreie Nachweis von 238-Pu bei einem Überschuss an 238-U von mindestens fünf Größenordnungen von einer Brennstoffpartikelprobe aus der Chernobyl Exclusion Zone. Zusätzlich ist über ein durch das Institut für Physik der Johannes Gutenberg-Universität Mainz neu entwickeltes zweistufiges Anregungsschema für Americium der Nachweis des Isotops 242m-Am in derselben Probe bei einer abgeschätzten Gesamtmasse von etwa einem Femtogramm gelungen.Bundesministerium für Bildung und Forschung/SIRIUS/BMBF 2020+ 02NUK044A/E

Influence of the hyperfine structure on plutonium in resonant laser-SNMS

Resonance ionization mass spectrometry is an ultra-sensitive and highly element selective tool for spectroscopy, ionization and detection of atoms and thus enables rare isotope determination. In combination with spatially resolved sputtering of neutrals by an initial ion beam, e.g. within a commercial secondary ion mass spectrometer, an isotope and isobar selective analysis technique with resolution on the micrometer scale for particles and surfaces is realized. Detection of minuscule amounts of specific actinides, e.g. of plutonium, in environmental and technical samples by this ultra-trace analysis technique requires detailed knowledge about the atomic physics of the element. Identification and characterization of the specific resonance ionization scheme applied within the particular geometry of the apparatus in use is needed. An analysis of the dependence of the specifications, specifically regarding the influence of the relative laser beam polarizations is presented here as an aspect, that could have a severe impact on isotope ratio precision and overall efficiency in the resulting ion signal

New horizons in microparticle forensics: Actinide imaging and detection of 238 Pu and 242m Am in hot particles

Micrometer-sized pollutant particles are of highest concern in environmental and life sciences, cosmochemistry, and forensics. From their composition, detailed information on origin and potential risks to human health or environment is obtained. We combine secondary ion mass spectrometry with resonant laser ionization to selectively examine elemental and isotopic composition of individual particles at submicrometer spatial resolution. Avoiding any chemical sample preparation, isobaric interferences are suppressed by five orders of magnitude. In contrast to most mass spectrometric techniques, only negligible mass is consumed, leaving the particle intact for further studies. Identification of actinide elements and their isotopes on a Chernobyl hot particle, including 242mAm at ultratrace levels, proved the performance. Beyond that, the technique is applicable to almost all elements and opens up previously unexplored scientific applications

Cesium and Strontium Contamination of Nuclear Plant Stainless Steel : Implications for Decommissioning and Waste Minimization

Stainless steels can become contaminated with radionuclides at nuclear sites. Their disposal as radioactive waste would be costly. If the nature of steel contamination could be understood, effective decontamination strategies could be designed and implemented during nuclear site decommissioning in an effort to release the steels from regulatory control. Here, batch uptake experiments have been used to understand Sr and Cs (fission product radionuclides) uptake onto AISI Type 304 stainless steel under conditions representative of spent nuclear fuel storage (alkaline ponds) and PUREX nuclear fuel reprocessing (HNO3). Solution (ICP-MS) and surface measurements (GD-OES depth profiling, TOF-SIMS, and XPS) and kinetic modeling of Sr and Cs removal from solution were used to characterize their uptake onto the steel and define the chemical composition and structure of the passive layer formed on the steel surfaces. Under passivating conditions (when the steel was exposed to solutions representative of alkaline ponds and 3 and 6 M HNO3), Sr and Cs were maintained at the steel surface by sorption/selective incorporation into the Cr-rich passive film. In 12 M HNO3, corrosion and severe intergranular attack led to Sr diffusion into the passive layer and steel bulk. In HNO3, Sr and Cs accumulation was also commensurate with corrosion product (Fe and Cr) readsorption, and in the 12 M HNO3 system, XPS documented the presence of Sr and Cs chromates.Peer reviewe

Resonant laser-SNMS for spatially resolved and element selective ultra-trace analysis of radionuclides

The newly developed resonant laser-SNMS system at the IRS Hannover combines the high spatial and decent mass resolution of a TOF-SIMS instrument with the element-selective process of resonant laser ionization. This setup was characterized by use of synthetic uranium, plutonium and technetium samples to prepare and demonstrate the performance for measurements on environmental samples. The laser-SNMS system will be applied for the detection, visualization and ultra-trace analysis of radionuclide containing nanoparticles in environmental samples with strongly reduced or even completely omitted chemical preparation. The necessary suppression of isobaric contamination was demonstrated as well as the first detection of uranium containing particles in a completely unaltered soil sample

Analysis of contaminated nuclear plant steel by laser-induced breakdown spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) has the potential to allow direct, standoff measurement of contaminants on nuclear plant. Here, LIBS is evaluated as an analytical tool for measurement of Sr and Cs contamination on type 304 stainless steel surfaces. Samples were reacted in model acidic (PUREX reprocessing) and alkaline (spent fuel ponds) Sr and Cs bearing liquors, with LIBS multi-pulse ablation also explored to measure contaminant penetration. The Sr II (407.77 nm) and Cs I (894.35 nm) emission lines could be separated from the bulk emission spectra, though only Sr could be reliably detected at surface loadings >0.5 mg cm−2. Depth profiling showed decay of the Sr signal with time, but importantly, elemental analysis indicated that material expelled from LIBS craters is redistributed and may interfere in later laser shot analyses