Year-end Sale % OFF 
Abstract
AbstractA detailed understanding of the response of mineral phases to the radiation fields experienced in a geological disposal facility (GDF) is currently poorly constrained. Prolongued ion irradiation has the potential to affect both the physical integrity and oxidation state of materials and therefore may alter a structure's ability to react with radionuclides. Radiohalos (spheres of radiation damage in minerals surrounding radioactive (α-emitting) inclusions) provide useful analogues for studying long term α-particle damage accumulation. In this study, silicate minerals adjacent to Th- and U-rich monazite and zircon were probed for redox changes and long/short range disorder using microfocus X-ray absorption spectroscopy (XAS) and high resolution X-ray diffraction (XRD) at Beamline I18, Diamond Light Source. Fe3+ → Fe2+ reduction has been demonstrated in an amphibole sample containing structural OH– groups – a trend not observed in anhydrous phases such as garnet. Coincident with the findings of Pattrick et al. (2013), the radiolytic breakdown of OH– groups is postulated to liberate Fe3+ reducing electrons. Across all samples, high point defect densities and minor lattice aberrations are apparent adjacent to the radioactive inclusion, demonstrated by micro-XRD.
Highlights
WITH the majority of the global stockpiles of radioactive waste destined for long-term (>100,000 years) isolation in a deep geological disposal facility (GDF), a critical understanding of the mechanisms and consequences of radiation damage across mineral phases is essential for building a safety case
Four radiation damaged silicate samples have been analysed by synchrotron microfocus X-ray diffraction (XRD) and Fe K-edge XANES
Diffuse scattering is a common characteristic of low-level point defect accumulation and represents imperfections in lattice periodicity (Chailley et al, 1994), with individual domains of variable defect densities existing over sub-micron scale volumes
Summary
WITH the majority of the global stockpiles of radioactive waste destined for long-term (>100,000 years) isolation in a deep geological disposal facility (GDF), a critical understanding of the mechanisms and consequences of radiation damage across mineral phases is essential for building a safety case. Damage (r = ∼30‒50 μm) form in minerals that surround α-particle emitting inclusions [e.g. Th-rich monazite (CePO4), U-rich zircon (ZrSiO4)], resulting from the high-energy α-particles (4He2+ ions) penetrating into the neighbouring crystal and causing hundreds of atomic displacements at the end of their projected range. An α-particle will lose most of its energy via ionization of the structure through which it penetrates, eventually resulting in a concentration of Frenkel (interstitial) defect accumulation following sufficient energy loss. Ionization effects (such as electron holes and consequent charge imbalances) are likely to anneal or recombine through time, whilst the more enduring structural defects can remain for millions of years (Nasdala et al, 2001, 2006). Termed ‘radiohalos’, silicate minerals commonly exhibit marked discolouration across an irradiated area as a result of the accumulation of these point defects and ionization effects
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
