Quantification of α-particle radiation damage in zircon

Analysis of radiation damage in natural mineral analogs such as zircon is important for the evaluation of the long-term behavior of nuclear waste forms and for geochronology. Here we present results of experiments to determine the partitioning of radiation damage due to the heavy nuclear recoil of uranium and thorium daughters and the α-particles ejected in an α-decay event in zircon. Synthetic polycrystalline zircon ceramics were doped with 10B and irradiated in a slow neutron flux for 1, 10, and 28 days to achieve the reaction 10B + n → 7Li + α (+2.79 MeV), creating an α event without a heavy nuclear recoil. The 7Li atoms produced in the nuclear reaction were directly detected by NMR “spin-counting”, providing a precise measurement of the α-dose applied to each sample. The amount of damage (number fraction and volume fraction) created by each α-event (one α-event being a 7Li + α-particle) has been quantified using radiological nuclear magnetic resonance and X-ray diffraction data. The number of permanently displaced atoms in the amorphous fraction was determined by 29Si NMR to be 252 ± 24 atoms for the 10B(n,α) event when the heavy recoil is absent, which is broadly in agreement with ballistic Monte Carlo calculations. The unit-cell swelling of the crystalline fraction, determined by X-ray diffraction, is small and anisotropic. The anisotropy is similar to that observed in ancient natural samples and implies an initial anisotropic swelling mechanism rather than an anisotropic recovery mechanism occurring over geological timescales. The small unit-cell volume swelling is only ~6% of the expansion frequently attributed to α-particles associated with an actinide α-decay event. The lattice parameters indicate a volume increase as α function of a dose of 0.21 A3/1018 α-events/g, which is significantly less than the increase of 3.55 A3/1018 α-events/g seen in Pu-doped zircon and 2.18 A3/1018 α-events/g seen in natural zircon. It is concluded that the heavy recoil plays a more important role in unit-cell swelling than previously predicted. The likely mechanism for such an effect is the rapid, and thus defect-rich, recrystallization of material initially displaced by the heavy recoil

The effect of magnesium on the local structure and initial dissolution rate of simplified UK Magnox waste glasses

A series of simplified glasses were prepared to mimic the United Kingdom’'s Magnox radioactive waste glasses and determine the separate effect of the presence of Mg on the glass structure and the initial dissolution rate. These glasses had an alkaline earth (Ca/Mg) content of 6.5 mol% and relative ratios of Si, B and Na similar to 25 wt% waste loaded Magnox waste glass simulant. Each simplified glass had similar macroscopic properties, differing only in Ca/Mg ratio. 25Mg magic angle spinning nuclear magnetic resonance (MASNMR) spectra of the simplified Mg endmember (MgEM) glass (with no Ca) and the full-component simulant glass were similar, consistent with the similar Mg local environments in both glasses. 11B MASNMR spectra of the series of simplified glasses showed a systematic increase in the amount of three-coordinated boron ([3]B) with increasing amounts of Mg. A clear change in the charge balancing of four-coordinated boron ([4]B) by Mg compared with Ca is observed. However, 11B NMR measurements of the leached material showed that the additional [3]B was not preferentially leached from the Mg containing samples. Despite the structural changes in the glass induced by Ca/Mg substitution, initial dissolution rates (r0) remained invariant, within error, with Ca/Mg ratio. This indicates that the poorer aqueous durability of Mg-containing Magnox waste glass measured experimentally in long-term leaching experiments, compared with SON68 glass containing Ca, is not caused by a primary structural effect in the glass.R. Guo acknowledges the EPSRC and the University of Cambridge for an International Doctoral Scholarship. A portion of this work was funded by Radioactive Waste Management Limited (C.T. Brigden, S.W. Swanton and I. Farnan). The UK 850 MHz solid-state NMR Facility used in this research was funded by EPSRC and BBSRC (contract reference PR140003), as well as the University of Warwick including via part funding through Birmingham Science City Advanced Materials Projects 1 and 2 supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF). Collaborative assistance from the 850 MHz Facility Manager (Dinu Iuga, University of Warwick) is acknowledged

Structural effects in UO2 thin films irradiated with fission-energy Xe ions

Uranium dioxide thin films have been successfully grown on LSAT (Al10La3O51Sr14Ta7) substrates by reactive magnetron sputtering. Irradiation by 92 MeV 129Xe23+ ions to simulate fission damage that occurs within nuclear fuels caused microstructural and crystallographic changes. Initially flat and continuous thin films were produced by magnetron sputtering with a root mean square roughness of 0.35 nm determined by AFM. After irradiation, this roughness increased to 60–70 nm, with the films developing discrete microstructural features: small grains (∼3 μm), along with larger circular (up to 40 μm) and linear formations with non-uniform composition according to the SEM, AFM and EDX results. The irradiation caused significant restructuring of the UO2 films that was manifested in significant film-substrate mixing, observed through EDX analysis. Diffusion of Al from the substrate into the film in unirradiated samples was also observed

Structural effects in UO2_2 thin films irradiated with U ions

This work presents the results of a detailed structural characterisation of irradiated and unirradiated single crystal thin films of UO$_2$. Thin films of UO$_2$ were produced by reactive magnetron sputtering onto (0 0 1), (1 1 0) and (1 1 1) single crystal yttria-stabilised zirconia (YSZ) substrates. Half of the samples were irradiated with 110 MeV $^{238}$U$^{31+}$ ions to fluences of 5 $\times$ 10$^{10}$, 5 $\times$ 10$^{11}$ and 5 $\times$ 10$^{12}$ ions/cm$^2$ to induce radiation damage, with the remainder kept for reference measurements. It was observed that as-produced UO$_2$ films adopted the crystallographic orientation of their YSZ substrates. The irradiation fluences used in this study however, were not sufficient to cause any permanent change in the crystalline nature of UO$_2$. It has been demonstrated that the effect of epitaxial re-crystallisation of the induced radiation damage can be quantified in terms of kernel average misorientation (KAM) and different crystallographic orientations of UO$_2$ respond differently to ion irradiation.The irradiation experiment was performed at the Grand Accélérateur National d’Ions Lourds (GANIL) Caen, France, and supported by the French Network EMIR. A.J. Popel acknowledges funding from the UK EPSRC (grant EP/ I036400/1) and Radioactive Waste Management Ltd (formerly the Radioactive Waste Management Directorate of the UK Nuclear Decommissioning Authority, contract NPO004411A-EPS02)

Structural effects in UO2 thin films irradiated with U ions

This work presents the results of a detailed structural characterisation of irradiated and unirradiated single crystal thin films of UO2. Thin films of UO2 were produced by reactive magnetron sputtering onto (0 0 1), (1 1 0) and (1 1 1) single crystal yttria-stabilised zirconia (YSZ) substrates. Half of the samples were irradiated with 110 MeV 238U31+ ions to fluences of 5 × 1010, 5 × 1011 and 5 × 1012 ions/cm2 to induce radiation damage, with the remainder kept for reference measurements. It was observed that as-produced UO2 films adopted the crystallographic orientation of their YSZ substrates. The irradiation fluences used in this study however, were not sufficient to cause any permanent change in the crystalline nature of UO2. It has been demonstrated that the effect of epitaxial re-crystallisation of the induced radiation damage can be quantified in terms of kernel average misorientation (KAM) and different crystallographic orientations of UO2 respond differently to ion irradiation

Experimental constraints on Li isotope fractionation during clay formation

Knowledge of the lithium (Li) isotope fractionation factor during clay mineral formation is a key parameter for Earth system models. This study refines our understanding of isotope fractionation during clay formation with essential implications for the interpretation of field data and the global geochemical cycle of Li. We synthesised Mg-rich layer silicates (stevensite and saponite) at temperatures relevant for Earth surface processes. The resultant solids were characterised by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) to confirm the mineralogy and crystallinity of the product. Bulk solid samples were treated with ammonium chloride to remove exchangeable Li in order to distinguish the Li isotopic fractionation between these sites and structural (octahedral) sites. Bulk solids, residual solids and exchangeable solutions were all enriched in Li compared to the initial solution. On average, the exchangeable solutions had Li values 7‰ lower than the initial solution. The average difference between the residual solid and initial solution Li values () for the synthesised layer silicates was −16.6 ± 1.7‰ at 20  C, in agreement with modelling studies, extrapolations from high temperature experimental data and field observations. Three bonding environments were identified from Li-NMR spectra which were present in both bulk and residual solid Li-NMR spectra, implying that some exchangeable Li remains after treatment with ammonium chloride. The Li-NMR peaks were assigned to octahedral, outer-sphere (interlayer and adsorbed) and pseudo-hexagonal (ditrigonal cavity) Li. By combining the Li-NMR data with mass balance constraints we calculated a fractionation factor, based on a Monte Carlo minimum misfit method, for each bonding environment. The calculated values are −21.5 ± 1.1‰, −0.2 ± 1.9‰ and 15.0 ± 12.3‰ for octahedral, outer-sphere and pseudo-hexagonal sites respectively (errors 1). The bulk fractionation factor () is dependent on the chemistry of the initial solution. The higher the Na concentration in the initial solution the lower the bulk Li value. We suggest this is due to Na outcompeting Li for interlayer sites and as interlayer Li has a high Li value relative to octahedral Li, increased Na serves to lower the bulk Li value. Three experiments conducted at higher pH exhibited lower Li values in the residual solid. This could either be a kinetic effect, resulting from the higher reaction rate at high pH, or an equilibrium effect resulting from reduced Li incorporation in the residual solid and/or a change in Li speciation in solution. This study highlights the power of Li-NMR in experimental studies of clay synthesis to target site specific Li isotope fractionation factors which can then be used to provide much needed constraints on field processes

Diffusive processes in aqueous glass dissolution

AbstractHigh level nuclear waste is often immobilised in a borosilicate glass for disposal. However, this glass corrodes in contact with aqueous solutions. To predict radionuclide releases from wasteforms, their dissolution mechanisms must be understood. Understanding glass dissolution mechanisms presents a challenge across numerous other disciplines and many glass dissolution models still remain conflicted. Here we show that diffusion was a significant process during the later stages of dissolution of a simplified waste glass but was not evidenced during the initial stages of dissolution. The absence of measurable isotopic fractionation in solution initially supports models of congruent dissolution. However, the solution becoming isotopically lighter at later times evidences diffusive isotopic fractionation and opposes models that exclude diffusive transport as a significant mechanism. The periodically sampled isotopic methodologies outlined here provide an additional dimension with which to understand glass dissolution mechanisms beyond the usual measurement of solution concentrations and, post-process, nano-scale analysis of the altered glass.</jats:p

Lung cancer diagnosed following an emergency admission: exploring patient and carer perspectives on delay in seeking help

Purpose Compared to others, patients diagnosed with lung cancer following an emergency, unplanned admission to hospital (DFEA) have more advanced disease and poorer prognosis. Little is known about DFEA patients’ beliefs about cancer and its symptoms or about their help-seeking behaviours prior to admission. Methods As part of a larger single-centre, prospective mixed-methods study conducted in one University hospital, we undertook qualitative interviews with patients DFEA and their carers to obtain their understanding of symptoms and experiences of trying to access healthcare services before admission to hospital. Interviews were recorded and transcribed. Framework analysis was employed. Results Thirteen patients and 10 carers plus 3 bereaved carers took part in interviews. Three patient/carer dyads were interviewed together. Participants spoke about their symptoms and why they did not seek help sooner. They described complex and nuanced experiences. Some (n = 12) had what they recalled as the wrong symptoms for lung cancer and attributed them either to a pre-existing condition or to ageing. In other cases (n = 9), patients or carers realised with hindsight that their symptoms were signs of lung cancer, but at the time had made other attributions to account for them. In some cases (n = 3), a sudden onset of symptoms was reported. Some GPs (n = 6) were also reported to have made incorrect attributions about cause. Conclusion Late diagnosis meant that patients DFEA needed palliative support sooner after diagnosis than patients not DFEA. Professionals and lay people interpret health and illness experiences differently

Evaluation of the performance of a lateral flow device for quantitative detection of anti-SARS-CoV-2 IgG

Introduction: The AbC-19™ lateral flow immunoassay (LFIA) performance was evaluated on plasma samples from a SARS-CoV-2 vaccination cohort, WHO international standards for anti-SARS-CoV-2 IgG (human), individuals ≥2 weeks from infection of RT-PCR confirmed SARS-CoV-2 genetic variants, as well as microorganism serology. Methods: Pre-vaccination to three weeks post-booster samples were collected from a cohort of 111 patients (including clinically extremely vulnerable patients) from Northern Ireland. All patients received Oxford-AstraZeneca COVID-19 vaccination for the first and second dose, and Pfizer-BioNTech for the third (first booster). WHO international standards, 15 samples from 2 variants of concern (Delta and Omicron) and cross-reactivity with plasma samples from other microorganism infections were also assessed on AbC-19™. Results: All 80 (100%) participants sampled post-booster had high positive IgG responses, compared to 38/95 (40%) participants at 6 months post-first vaccination. WHO standard results correlated with information from corresponding biological data sheets, and antibodies to all genetic variants were detected by LFIA. No cross-reactivity was found with exception of one (of five) Dengue virus samples. Conclusion: These findings suggest BNT162b2 booster vaccination enhanced humoral immunity to SARS-CoV-2 from pre-booster levels, and that this antibody response was detectable by the LFIA. In combination with cross-reactivity, standards and genetic variant results would suggest LFIA may be a cost-effective measure to assess SARS-CoV-2 antibody status