Note: Establishing α-particle radiation damage experiments using the Dalton Cumbrian Facility’s 5 MV tandem pelletron

Bower, William R.; Smith, Andy; Pattrick, R. A. D.; Pimblott, Simon M.

doi:10.1063/1.4917348

Cited by 2 publications

(4 citation statements)

References 8 publications

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“…XAS analysis may suggest a trend toward radiation induced Fe reduction at doses <9 × 10 15 ions/cm 2 , as observed in similar studies . The trend is subtle, because of the high natural Fe 2+ /Fe 3+ ratios in the chlorite sample, but suggests a proportion of the structural Fe 3+ is reduced by ion irradiation.…”

Section: Discussionsupporting

confidence: 67%

“…Samples were irradiated under vacuum with a focused 5 MeV 4 He 2+ ion beam, using the Dalton Cumbrian Facility’s 5 MV tandem pelletron via an established method. − The beam was focused into a pseudo-Gaussian profile, such that the center of the beam delivered a much higher dose than the perimeter. In this way, a single sample was able to accumulate a range of doses over a circular beam spot (area = 1 cm 2 ) suitable for synchrotron microfocus analysis.…”

Section: Methodsmentioning

confidence: 99%

“…XAS analysis may suggest a trend toward radiation induced Fe reduction at doses <9 × 10 15 ions/cm 2 , as observed in similar studies. 10 The trend is subtle, because of the high natural Fe 2+ /Fe 3+ ratios in the chlorite sample, but suggests a proportion of the structural Fe 3+ is reduced by ion irradiation. Fe reduction in α-irradiated phyllosilicates has been postulated to occur via several methods; primarily (i) the recycling and consequent migration of electrons from surface to depth by the incident α-particles, combined with (ii) the liberation of reducing radical electrons generated by the damage induced dissociation of OH − groups.…”

Section: Acs Earth and Space Chemistrymentioning

confidence: 99%

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Radiation Damage Effects in Chlorite Investigated Using Microfocus Synchrotron Techniques

Bower

Pearce

Smith

et al. 2019

ACS Earth Space Chem.

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A detailed understanding of the mechanisms and effects of radiation damage in phyllosilicate minerals is a necessary component of the evaluation of the safety case for a deep geological disposal facility (GDF) for radioactive waste. Structural and chemical changes induced by α-particle damage will affect the performance of these minerals as reactive barrier materials (both in the near and far-field) over time scales relevant to GDF integrity. In this study, two examples of chlorite group minerals have been irradiated at α-particle doses comparable to those predicted to be experienced by the clay buffer material surrounding high-level radioactive waste canisters. Crystallographic aberrations induced by the focused 4 He 2+ ion beam are revealed via high-resolution, microfocus X-ray diffraction mapping. Interlayer collapse by up to 0.5 Å is prevalent across both macrocrystalline and microcrystalline samples, with the macrocrystalline specimen displaying a breakdown of the phyllosilicate structure into loosely connected, multioriented crystallites displaying variable lattice parameters. The damaged lattice parameters suggest a localized breakdown and collapse of the OH − rich, "brucite-like" interlayer. Microfocus Fe K-edge X-ray absorption spectroscopy illustrates this defect accumulation, manifest as a severe damping of the X-ray absorption edge. Subtle Fe 2+ /Fe 3+ speciation changes are apparent across the damaged structures. A trend toward Fe reduction is evident at depth in the damaged structures at certain doses (8.76 × 10 15 alpha particles/cm 2 ). Interestingly, this reductive trend does not increase with radiation dose; indeed, at the maximum dose (1.26 × 10 16 α particles/ cm 2 ) administered in this study, there is evidence for a slight increase in Fe binding energy, suggesting the development of a depth-dependent redox gradient concurrent with light ion damage. At the doses examined here, these damaged structures are likely highly reactive, as sorption capacity will, to an extent, be largely enhanced by lattice disruption and an increase in available "edge" sites.

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Section: Discussionsupporting

confidence: 67%

Section: Methodsmentioning

confidence: 99%

Section: Acs Earth and Space Chemistrymentioning

confidence: 99%

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Radiation Damage Effects in Chlorite Investigated Using Microfocus Synchrotron Techniques

Bower

Pearce

Smith

et al. 2019

ACS Earth Space Chem.

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“…Samples were irradiated using the University of Manchester's newly commissioned 5 MV NEC 15SDH-4 tandem pelletron ion accelerator, equipped with a toroidal volume ion source (TORVIS) at the Dalton Cumbrian Facility, U.K. (Leay et al 2015). Samples were held in a customized target station (Bower et al 2015) and irradiated under vacuum with a focused 4 He 2+ beam. The energy of the ion beam on the sample was held at 5 MeV across all exposures, in line with a-particle energies along the uranium decay chains (48 MeV) (see NNDC, 2013).…”

Section: Ion Irradiationmentioning

confidence: 99%

Radiation damage in biotite mica by accelerated α-particles: A synchrotron microfocus X-ray diffraction and X-ray absorption spectroscopy studyk

Bower

Pearce

Smith³

et al. 2016

American Mineralogist

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A critical radiation damage assessment of the materials that will be present in a Geological Disposal Facility (GDF) for radioactive waste is a priority for building a safety case. Detailed analysis of the effects of high-energy a-particle damage in phyllosilicates such as mica is a necessity, as these are model structures for both the clay-based backfill material and the highly sorbent components of a crystalline host rock. The a-radiation stability of biotite mica [general formula: K(Mg,Fe) 3 (Al,Si 3 O 10) (F,OH) 2 ] has been investigated using the 5 MV tandem pelletron at the University of Manchester's Dalton Cumbrian Facility (DCF) and both the microfocus spectroscopy (I18) and core X-ray absorption spectroscopy (B18) beamlines at Diamond Light Source (U.K.). Microfocus X-ray diffraction mapping has demonstrated extensive structural aberrations in the mica resulting from controlled exposure to the focused 4 He 2+ ion (a-particle) beam. Delivered doses were comparable to a-particle fluences expected in the highly active, near-field of a GDF. At doses up to 6.77 displacements per atom (dpa) in the region of highest particle fluence, biotite mica displays a heterogeneous structural response to irradiation on a micrometer scale, with sequential dilation and contraction of regions of the structure perpendicular to the sheets, as well as a general overall contraction of the phyllosilicate layer spacing. At the peak of ion fluence, the structure collapses under a high point defect density and amorphous areas are pervasive among altered domains of the original lattice. Such structural alterations are likely to affect the material's capacity to sorb and retain escaped radionuclides over long timescales; increased edge site availability may favor increased sorption while interlayer uptake will likely be reduced due to collapse. Radiation-induced reduction of structural iron at the region of highest structural damage across an a-particle's track has been demonstrated by Fe K-edge X-ray absorption near edge spectroscopy (XANES) and local structural disorder has been confirmed by analysis of both potassium K-edge XANES and Fe K-edge extended X-ray absorption fine structure analysis. An infrared absorption study of deformations in the OHstretching region, along with electron probe microanalysis complements the synchrotron data presented here.

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Note: Establishing α-particle radiation damage experiments using the Dalton Cumbrian Facility’s 5 MV tandem pelletron

Cited by 2 publications

References 8 publications

Radiation Damage Effects in Chlorite Investigated Using Microfocus Synchrotron Techniques

Radiation Damage Effects in Chlorite Investigated Using Microfocus Synchrotron Techniques

Radiation damage in biotite mica by accelerated α-particles: A synchrotron microfocus X-ray diffraction and X-ray absorption spectroscopy studyk

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