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Separation and Analysis of Sr-90 and Zr-90 for Nuclear Forensic Applications

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Separation and Analysis of Sr-90 and Zr-90 for Nuclear Forensic Applications Separation and Analysis of Sr-90 and Zr-90 for Nuclear Forensic Applications Mémoire Ana Paula Zattoni Maitrise en chimie Maître ès sciences (M.Sc.) Québec, Canada © Ana Paula Zattoni, 2015 Résumé Le présent travail porte sur le développement technologique pour déterminer l'âge des sources de radiostrontium à travers du rapport [Zr-90]/[Sr-90], en utilisant les techniques de spectrométrie de masse et scintillation liquide pour quantifier les deux isotopes. Parce que Sr-90 et Zr-90 sont des interférences isobariques en spectrométrie de masse, une séparation radiochimique est nécessaire pour isoler du Zr-90 avant son analyse. Parmi quatre résines commerciales, la résine DGA a fourni la meilleure performance pour isoler le Zr-90 du Sr-90. Des récupérations supérieures à 99% pour le Zr-90 ont été obtenues. La résine DGA était aussi l'approche la plus rapide et la plus efficace pour éliminer les interférences isobariques du Sr-90 et aussi de l’Y-90 potentiellement présents dans des échantillons contenant des niveaux élevés de radioactivité. Des expériences impliquant l’utilisation d’une cellule de collision pour éliminer des interférences isobariques ont fourni des facteurs de décontamination insuffisants pour des applications en criminalistique nucléaire. iii iv Abstract In this work, a technological development to determine the age of radioactive strontium sources through the [Zr-90]/[Sr-90] ratio using mass spectrometry and liquid scintillation to quantify both isotopes is presented. Because Sr-90 and Zr-90 are isobaric interferences in mass spectrometry, a radiochemical separation to isolate Zr-90 has been shown to be mandatory prior to analysis. Four commercial resins (AG50W-X9, Dowex1-X8, Sr and DGA resins) were tested to isolate Zr-90 from Sr-90. Best performance was observed for the DGA resin, including recoveries higher than 99% for Zr-90. DGA has also demonstrated to be the faster approach and the most efficient not only to eliminate isobaric interferences from Sr- 90, but also from Y-90, potentially present in samples containing high levels of radioactivity. Experiments using a collision cell to eliminate isobaric interferences in a triple quadrupole mass spectrometer (ICP-QQQMS) have also been carried out, but results have demonstrated insufficient decontamination factors for nuclear forensic applications. v vi Table of Contents RÉSUMÉ ................................................................................................................ III ABSTRACT ............................................................................................................ V TABLES LIST ........................................................................................................ IX PICTURES LIST .................................................................................................... XI ABBREVIATIONS LIST ....................................................................................... XIII ACKNOWLEDGMENTS ...................................................................................... XIX INTRODUCTION ..................................................................................................... 1 1. RADIOSTRONTIUM .............................................................................................................................................. 5 1.1. Occurrence and radiological properties of strontium-90 ........................................................... 5 1.2. Applications of strontium-90 .................................................................................................................... 8 1.3. Instability of strontium-90 and the origin of its radioactivity .................................................. 9 1.4. Hazardous effects of strontium-90 ..................................................................................................... 10 2. NUCLEAR THREATS OF SR-90 AND RADIOCHRONOMETRY FOR AGE-DATING APPLICATIONS .......... 13 2.1. Nuclear threats and risks involving orphaned sources ............................................................. 13 2.2. Radiochronometry for nuclear forensic applications ................................................................ 15 3. ANALYTICAL TECHNIQUES TO QUANTIFY SR-90 AND ZR-90 .................................................................. 21 3.1. Principles of mass spectrometry .......................................................................................................... 21 3.1.1. Advantages and disadvantages of MS for the analysis of Zr-90 ........................................ 23 3.1.2. Triple quadrupole mass spectrometers to minimize isobaric interferences ............... 24 3.1.3. Separation of Sr-90 from Zr-90 using reaction cells ............................................................... 26 3.2. Analysis of Sr-90 by liquid scintillation ............................................................................................. 27 4. CHROMATOGRAPHIC TECHNIQUES TO SEPARATE SR-90 AND ZR-90 .................................................... 31 4.1. Principles of chromatography............................................................................................................... 31 4.2. Distribution ratio (D) ................................................................................................................................ 33 4.3. Column performance and efficiency of separation ...................................................................... 34 4.4. Measurement of peak asymmetry ....................................................................................................... 36 4.5. Ion exchange chromatography (IEC) ................................................................................................ 37 4.5.1. Ion exchange resins ................................................................................................................................ 39 4.6. Extraction chromatography (EXC) ..................................................................................................... 40 4.6.1. Extraction process in EXC .................................................................................................................... 41 4.7. IEC and EXC for radiochemical separations and potential applications for Sr-90 and Zr-90 43 5. EXPERIMENTAL ................................................................................................................................................ 47 5.1. Chemicals ........................................................................................................................................................ 47 5.2. Digestion of SrTiO3 ..................................................................................................................................... 47 5.3. Separation tests ........................................................................................................................................... 48 5.4. Omnifit® glass column preparation .................................................................................................. 49 5.5. Methodology .................................................................................................................................................. 49 vii 5.6. Mass spectrometry analysis .................................................................................................................... 50 5.6.1. Performance of reaction cells to separate strontium from zirconium ........................... 52 5.7. Analysis of Sr-90 by liquid scintillation ............................................................................................. 54 6. RESULTS AND DISCUSSION .............................................................................................................................. 55 6.1. Digestion of SrTiO3 ..................................................................................................................................... 55 6.2. Separation of Sr and Zr using a cation-exchange resin ............................................................. 57 6.3. Resin shrinkage and issues for Zr recovery ..................................................................................... 61 6.3.1. Effect of method downscaling on separation efficiency ........................................................ 62 6.4. Separation of Sr and Zr using an anion-exchange resin ........................................................... 64 6.5. IEC versus EXC for the separation of Sr and Zr ............................................................................. 66 6.6. Addition of HF in samples ........................................................................................................................ 69 6.7. Summary of the efficiency of all resins tested ................................................................................ 72 6.8. Performance of DGA method for the recovery of trace levels of Zr ...................................... 73 6.9. Determining the age of a radiostrontium source ......................................................................... 74 6.10. Potential of reaction cell to separate strontium from zirconium ...................................... 76 CONCLUSIONS .................................................................................................... 81 REFERENCES ...................................................................................................... 83 ANNEXE 1 ............................................................................................................
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