Nuclear waste storage materials are inevitable in nuclear industry for preventing the release of radioactive waste products. Glassy carbon has been considered being beneficial to be used in the dry cask needed for nuclear waste storage. Thus, we studied the migration of ruthenium implanted in glassy carbon upon annealing. Our investigations show that ruthenium implantation caused defects in the glassy carbon structure, with more defects observed in the room temperature as-implanted samples compared to those implanted at 200 degrees C. Annealing the as-implanted samples from 500 to 800 degrees C showed no significant change in the ruthenium depth profiles, indicating the non-diffusivity of ruthenium in glassy carbon at these temperatures. However, annealing at higher temperatures (from 900 and 1300 degrees C) resulted in an increase in the maximum depth profile peaks, accompanied by a shift towards the surface, and a decrease in the full-width at half-maximum. These changes indicate the aggregation of ruthenium atoms in the near-surface region. Additionally, more ruthenium aggregation was observed in room temperature implanted samples compared to those implanted at 200 degrees C. This difference is attributed to the higher concentration of defects in room temperature implanted samples, which promotes ruthenium aggregation. Moreover, the migration and aggregation of ruthenium in the near-surface region contributed to an increase in the surface roughness of the glassy carbon.

We present characterization of the glassy carbon and vanadium implanted glassy carbon. Glassy carbon (GC) substrates were implanted with 15 keV Vanadium ions to a fluence ranging from 1 x 1012 to 1 x 1015 V+/cm at room temperature. Raman spectroscopy was used to monitor the structural changes in the samples as a result of the implantation. The Raman spectrum of the pristine glassy carbon sample shows the characteristic D and G peaks at 1350 cm-1 and 1588 cm-1. Raman spectra of samples implanted at 1 x 1012, 5 x 1012 and 1 x 1013 V+/ cm respectively show that the glassy carbon structure remains unchanged when compared to that of the pristine glassy carbon. This indicates that the low fluence implantation of vanadium does not result in the radiation damage of the glassy carbon structure. High fluence implantation at 1 x 1014 and 1 x 1015 V+/cm resulted in a slight change of the Raman spectrum of glassy carbon. The D and G peaks merged slightly into each other and became wider suggesting that the samples became damaged after implanting at these high fluence.

The effect of implantation temperature on the migration behaviour of xenon (Xe) implanted into glassy carbon and the effect of annealing on radiation damage retained by ion implantation were investigated. Glassy carbon substrates were implanted with 320 keV Xe+ to a fluence of 2 x 10(16) cm(-2). The implantation process was performed at room temperature (RT) and 100 degrees C Some of the as-implanted samples were isochronally annealed in vacuum at temperatures ranging from 300 degrees C to 700 degrees C in steps of 100 degrees C for 10 h. The as-implanted and annealed samples were characterized using Rutherford backscattering spectrometry (RBS) and Raman spectroscopy. The RT implanted depth profiles indicated that the migration of Xe towards the surface of glassy carbon was accompanied by a loss of Xe ions. The samples implanted at 100 degrees C indicated no diffusion or loss of Xe after annealing at 300 degrees C. However, annealing at temperatures ranging from 400 degrees C to 700 degrees C resulted in a slight shift in the Xe profile tail-end towards the bulk of glassy carbon. The diffusion coefficients (D) in the temperature range of 300 degrees C-700 degrees C for the RT and 100 degrees C implanted samples, activation energies (E-a), and pre-exponential factors (D-o), were extracted. The values of D ranged from (9.72 +/- 0.48) x 10(-21) to (1.87 +/- 0.09) x 10(-20) m(2)/s with an activation energy of (6.25 +/- 0.31) x 10(-5) eV for RT implanted samples, and the samples implanted at 100 degrees C, D ranged from (3.85 +/- 0.19) x 10(-21) to (6.96 +/- 0.34) x 10(-20) m(2)/s with activation energy of (4.10 +/- 0.02) x 10(-5) eV. The Raman analysis revealed that implantation at the RT amorphised the glassy carbon structure while the samples implanted at 100 degrees C showed mild damage compared to RT implantation. Annealing of the RT-implanted sample resulted in some recovery of the damaged region as a function of increasing annealing temperature.

Thin film diffusion barriers are inevitable in nuclear reactors for preventing the release of radioactive waste products. The combination of chemical stable silicon carbide (SiC) and silicon oxide (SiO2) layers has been considered being beneficial, thus, we studied the migration and stability of strontium implanted SiC upon annealing, owing an additional SiO2 surface layer. Our investigations show that annealing at 1100 and 1200 degrees C retained the Sr atoms in comparison to pure SiC and induced strong strontium segregation at the SiO2/SiC interface and SiO2 surface. However, this enhanced the sublimation of the SiO2 layer, while pure SiO2 layers (i.e., without impurities) showed no sublimation after annealing under the same conditions. On the other hand, higher temperatures at 1300 and 1400 degrees C, resulted also in significant sublimation of the pure SiO2 layer.

The effects of helium (He) bubbles and annealing on the structural evolution and the migration of silver (Ag) implanted into polycrystalline silicon carbide were investigated. Ag ions of 360 keV were implanted into polycrystalline SiC to a fluence of 2 × 10 16 cm−2 at 350 °C (Ag-SiC). Some of the implanted samples were then implanted with He ions of 17 keV to a fluence of 1 × 1017 cm−2 also at 350 °C (Ag + He-SiC). The Ag-SiC and Ag + He-SiC samples were then annealed at 1100 °C for 5 h. The as-implanted and annealed samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Implantation of Ag resulted in the accumulation of defects in SiC without amorphization. Co-implantation of He resulted in the formation of elongated and tiny He bubbles accompanied by the formation of blisters and holes on the surface. Annealing at 1100 °C resulted in some recovery of the SiC crystal structure, indicating that some defects were annealed out in both Ag-SiC and Ag + He-SiC. This was accompanied by the appearance of more holes on the annealed Ag + He-SiC surface and bigger cavities in the co-implanted SiC layer. Some limited migration of implanted Ag accompanied by the formation of Ag precipitates was observed in the as-implanted Ag + He-SiC sample. No migration of Ag was observed in the annealed Ag-SiC samples while migration of Ag towards the surface accompanied by loss was observed in the annealed Ag + He-SiC sample. The migration of Ag in the annealed Ag + He-SiC was also accompanied by the formation of big Ag precipitates trapped in the cavities. Hence, He bubbles assisted the migration of Ag while cavities trapped the Ag in the Ag + He-SiC samples.

Glassy carbon samples were implanted with ruthenium ions to a fluence of 1 x 1016 cm-2 at room temperature (at 150 keV). The implanted samples were annealed isochronally in vacuum from 1000 to 1300 degrees C for 5 h. The resulting microstructural changes were investigated using X-ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM). The diffusion behaviour of ruthenium in glassy carbon was investigated using secondary-ion mass spectrometry (SIMS). Raman results showed that the implantation of ruthenium into glassy carbon caused amorphization and increase the tensile stress in the implanted region. XRD showed that the amount of tensile stress in virgin glassy carbon increased from 0.016 GPa to 0.19 GPa after ion implantation which is in qualitative agreement with the Raman results. Annealing of the samples exhibited more recrystal-lization and changed the tensile stress to compressive stress. SIMS results showed that annealing of the as -implanted samples at 1000 degrees C caused aggregation of the ruthenium atoms, while annealing at higher temper-atures led to some segregation of ruthenium atoms at a depth of 155 nm below the glassy carbon surface. The aggregation of ruthenium atoms after annealing (as observed by SIMS) played a role in the surface roughness as observed by AFM.

The presence of radiation-induced defects and the high temperature of implantation are breeding grounds for helium (He) to accumulate and form He-induced defects (bubbles, blisters, craters, and cavities) in silicon carbide (SiC). In this work, the influence of He-induced defects on the migration of strontium (Sr) implanted into SiC was investigated. Sr-ions of 360 keV were implanted into polycrystalline SiC to a fluence of 2 × 1016 Sr-ions/cm2 at 600°C (Sr-SiC). Some of the Sr-SiC samples were then co-implanted with He-ions of 21.5 keV to a fluence of 1 × 1017 He-ions/cm2 at 350°C (Sr + He-SiC). The Sr-SiC and Sr + He-SiC samples were annealed for 5 h at 1,000°C. The as-implanted and annealed samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Rutherford backscattered spectrometry (RBS). Implantation of Sr retained some defects in SiC, while co-implantation of He resulted in the formation of He-bubbles, blisters, and craters (exfoliated blisters). Blisters close to the critical height and size were the first to exfoliate after annealing. He-bubbles grew larger after annealing owing to the capture of more vacancies. In the co-implanted samples, Sr was located in three regions: the crystalline region (near the surface), the bubble region (where the projected range of Sr was located), and the damage region toward the bulk. Annealing the Sr + He-SiC caused the migration of Sr towards the bulk, while no migration was observed in the Sr-SiC samples. The migration was governed by “vacancy migration driven by strain fileds.”

In order to ascertain the suitability of glassy carbon as a material for encapsulation of nuclear waste, glassy carbon was implanted with Xe and the structural changes and surface modification were investigated before and after annealing. This was performed using Raman spectroscopy analysis, high-resolution transmission electron microscopy (HRTEM) measurements, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The Raman spectrum of the implanted sample showed that ion bombardment amorphised the glassy carbon structure. The HRTEM analysis of the virgin glassy carbon exhibited some features which are similar to those of fullerenes. One of the features is the appearance of closed onion-like nanoparticles and several graphitic fringes of varying sizes and orientations embedded in the glassy carbon structure. The presence of the onion-like features, as well as the graphitic fringes within the glassy carbon structure, suggest that glassy carbon is a disordered form of carbon. The HRTEM analysis of the as-implanted sample also shows some dark spots within the implanted region which are likely xenon bubbles. The SEM and AFM analysis showed that the grain size becomes larger and more prominent with increasing annealing temperature, leading to an increase in the surface roughness of glassy carbon.

Scanning electron microscopy (SEM), Raman spectroscopy and Rutherford backscattering spectrometry (RBS) were used to study the influence of swift heavy ion (SHI) irradiation and annealing on the microstructure of polycrystalline SiC implanted with silver (Ag). Polycrystalline SiC specimens were first implanted with 360 keV Ag + ions at room temperature (RT) to a fluence of 2 x 1016cmxfffd; 2. Thereafter, some of the implanted samples were irradiated with Xe ions of 167 MeV (SHI) at room temperature to a fluence of 3.4 x 1014 cmxfffd; 2 and 8.4 x 1014 cm-2. Both the as-implanted and implanted then irradiated samples were annealed in vacuum at temperatures ranging from 1100 to 1400 degrees C in steps of 100 degrees C for 5 h. Raman and SEM results showed that implantation of silver (Ag) resulted in complete amorphization of the near surface region of the SiC substrates. However, SHI irradiation of the as-implanted SiC resulted in partial recrystallization of the initially amorphized layer. The asimplanted samples exhibited more crystallinity after annealing at 1100 degrees C as compared to SHI irradiated samples annealed at same conditions. This poor recrystallization of the SHI irradiated SiC samples was due to the amount of impurities (i.e. concentration of Ag atoms) retained after annealing at 1100 degrees C. Raman and SEM results showed that annealing of the as-implanted samples at 1100 degrees C resulted in larger average crystal size compared to the SHI irradiated samples annealed in the same conditions. The intensity of the longitudinal optical (LO) phonon in Raman spectra increases with the increasing the average crystal sizes of SiC.

The use of glassy carbon (GC) as a future nuclear waste storage material depends on its capability to retain all radioactive fission products found in spent nuclear fuels. Selenium (79Se) is found in trace amounts in uranium ores, spent, and reprocessed nuclear fuel. This work investigates the effects of implantation temperature and annealing on the structural evolution and migration of Se implanted GC. To achieve these objectives, 150 keV Se+ was implanted into GC samples separately at room temperature (RT) and 200 degrees C to a fluence of 1 x 1016 cm-2. Some of the as-implanted samples were annealed at 1000, 1100 and 1200 degrees C for 5h and characterised by transmission electron microscopy (TEM), Raman spectroscopy, and secondary ion mass spectrometry (SIMS). Both TEM and Raman spectroscopy showed that implantation caused defects in the GC structures, with more defects in the RT as-implanted sample. Annealing caused the healing of both sample types but retained some radiation damage. No migration of Se atoms was observed in the RT and 200 degrees C as-implanted samples. However, a different migration behaviour was seen after annealing the RT and 200 degrees C samples up to 1200 degrees C, attributed to the trapping and de-trapping of Se atoms in different amounts of defect induced by implantation.

Isothermal annealing studies of selenium-implanted silicon carbide (SiC) were conducted at temperatures >1200 degrees C. Implantation were performed using Se ions of 200 keV to a fluence of 1 x 1016 cm- 2at room temperature, 350 degrees C and 600 degrees C. After implantations, samples were then subjected to an isothermal annealing process at 1300 degrees C, 1350 degrees C and 1400 degrees C for 10 h cycles up to 80 h. The radiation damage in SiC and its morphological change were characterized using Raman spectroscopy and scanning electron microscopy (SEM), respectively. The migration of implanted Se was monitored by Rutherford backscattering spectrometry (RBS). Implantation at RT amorphized SiC while implantation at 350 and 600 degrees C retained crystallinity with defects. Isothermal annealing led to significant recrystallization during the first annealing cycle in all annealing temperatures. The broadening of the Se RBS profile was observed in the RT implanted samples only during the first and second annealing cycles at all annealing temperatures. The diffusion coefficients at 1300 degrees C, 1350 degrees C and 1400 degrees C were estimated to be 1.4 x 10-20 m2s- 1, 2 x 10-20 m2s- 1 and 2.5 x 10-20 m2s- 1, respectively, which yielded to an activation and pre-exponential factor of 2 x 10-22 J and 1.7 x 10-16 m2s- 1 respectively. No measurable diffusion of the Se implanted into SiC was observed in the isothermally annealed hot implanted samples (at implantation temperature of 350 degrees C and 600 degrees C) confirming the radiation enhanced migration of Se in the RT implanted samples.

Polycrystalline SiC wafers were implanted with 360 keV strontium (Sr) ions at room temperature (RT)to a fluence of 2 × 10 16 cm −2 . Some of the implanted samples were irradiated with xenon (Xe) ions of 167 MeV to a fluence of 3.4 × 10 14 cm −2 and 8.4 × 10 14 cm −2 at RT. The as-implanted and implanted then irradiated samples were vacuum annealed (isochronally) at temperatures ranging from 1,100 to 1,400°C in steps of 100°C for 5 h. Annealing induced modification of the microstructure of the implanted and swift heavy ions (SHIs) irradiated SiC was studied by Raman spectroscopy, scanning electron microscopy (SEM) and backscattering spectrometry (RBS). Sr ions bombardment caused formation of an amorphous layer in SiC, while irradiation by Xe ions led to partial recrystallization of the amorphized layer. After annealing at 1,100°C, the samples with low Sr retained ratio showed full recrystallization, while the samples with high Sr retained ratio showed poor recrystallization. This suggests that the presence of Sr within the implanted region inhibited the recrystallization of SiC. Annealing of the as-implanted samples at temperatures from 1,100°C and 1,200°Cresulted in larger average crystal size compared to the SHIsirradiated samples annealed in the same temperature range. The difference in the average crystal sizes between the as-implanted and SHIs irradiated samples was due to the differences in the nucleation rate per amorphous area in the two samples. Ramanspectroscopy results showedthat the intensity of the LO mode of SiC increases with increasing crystal size. However, several factors such as pores and defects in SiC play a role in the decrease of the LO mode intensity of SiC (even if the average crystal size is large).

Crag lizards are restricted to montane areas where biota are strongly exposed to the effects of climate change. We investigated the factors shaping the distribution of Drakensberg crag lizards (Pseudocordylus melanotus melanotus; Cordylidae) by quantifying their elevational ranges, availability of shelter and prey as well as the thermal environment at three elevations. We recorded expected body temperatures using copper models of the lizards at each elevation in the field and in the laboratory, estimating the duration for which lizards must shelter from high temperatures. This correlated strongly with field observations of lizard activity during winter, spring and summer. Our models predicted that at lower elevations, lizards would shelter for longer periods each day, resulting in a marked reduction in time available for essential activities such as feeding and breeding, possibly explaining why these animals do not occur at lower elevations. The distribution and survival of these animals therefore appear to be impacted by the degree to which daytime temperatures limit their activity. Modelling future climate change scenarios at the high elevation site indicates that crag lizards would be resilient against small to moderate warming reflected by RCP4.5 climate change predictions, but populations are unlikely to persist under conditions predicted in the RCP8.5 scenario. This study is important as, unlike broader-scope studies that cannot quantify climate change impacts on individual species, we combine detailed field data with laboratory measurements and modelling of a single species to assess the ecological constraints to which crag lizards are exposed.

The 2015–2017 summer rainfall seasons in both South and southern Africa saw drought and heat stress severely impacting the livestock production sector, as well as agriculture more broadly. Although the region has a longstanding operational forecasting system; tailored forecasting, including that designed for the livestock sector, has declined in presence and operational use in recent years. The potential use of such information to enable the livestock sector to better cope with difficult seasons such as those of 2015–17 is clear. A range of promising initiatives attempt to move South Africa (and the broader southern Africa region) in the direction of improved tailored forecasting, integrated, in part, into the operational system. A number of gaps in application remain, however, and the paper concludes with a discussion as to how the field might move forward, particularly in the light of possible increased frequency of drought and heat stress in the future.

The structural changes, migration behaviour of indium (In) implanted into glassy carbon (GC) and the effect of annealing on radiation damage introduced by ion implantation have been investigated. The GC substrates were implanted with 360 keV indium ions to a fluence of 2.0 x 10(16) ions/cm(2) at room temperature (RT) and 350 degrees C. The RT implanted samples were isochronally annealed in vacuum between 200 and 1000 degrees C for 1 h. The 350 degrees C implanted GC substrates were irradiated 167 MeV with Xe26+ ions at room temperature to a maximum fluence of 5.0 x 10(14) ions/cm(2). The implanted GC structure was damaged and had an almost amorphized structure. Annealing of the RT implanted samples resulted in some recrystallization which increased with temperature and the diffusion behaviour of implanted In. Fickian diffusion of implanted In started after annealing at 300 degrees C, however, structural changes in the GC were observed after annealing at 200 degrees C. Annealing at 400 and 600 degrees C resulted in the diffusion of In toward the surface of GC accompanied by a loss of In. The SHI irradiation of the 350 degrees C implanted samples at increasing fluence, did not result in a detectable migration of implanted In. (c) 2017 Elsevier Ltd. All rights reserved.

The effects of helium (He) in the migration behaviour of silver (Ag) implanted into polycrystalline siclicon carbide (SiC) was investigated. Polycrystalline SiC wafers were first implanted with Ag ions of 360 keV to a fluence of 2 x 10(16) cm(-2) at room temperature (RT) followed by He ions of 17 keV to a fluence of 1 x 10(17) cm(-2) also at RT (Ag &He-SiC), all under vacuum. The Ag&He-SiC samples were then annealed at 1100 degrees C for 5 h under vacuum. The Ag&He-SiC and annealed samples were characterized by transmission electron microscopy (TEM), Raman spectroscopy and elastic recoil detection analysis (ERDA). The results of this study were compared with published results of Ag-only implanted SiC, which was then annealed at 1100 degrees C for 5 h. Nanosized He bubbles in the amorphized SiC around the projected range of the implants were observed in the Ag&He-SiC samples. Annealing the Ag&He-SiC at 1100 degrees C caused appearance of cavity network mostly parallel to the surface but sometimes branching into the bulk and the surface. No migration of implanted Ag was observed in Ag-only implanted SiC while Ag migrated towards the surface and the bulk in Ag&He-SiC samples after annealing at 1100 degrees C. We therefore conclude that helium bubbles have a role in the migration of Ag implanted in SiC.

This study reviews the migration behaviour of selenium in polycrystalline SiC, which acts as the main diffusion barrier in the coated fuel particles for Very High Temperature Reactors. Se ions of 200 keV were implanted into polycrystalline SiC wafers to a fluence of 1 x 1016 cmi 2 at three temperatures, which were room temperature, 350 degrees C and 600 degrees C. The implanted samples were annealed at temperatures ranging from 1000 to 1500 degrees C in steps of 100 degrees C for 10 h. The migration of implanted Se was monitored by Rutherford backscattering spectrometry (RBS) while structural and morphological changes were monitored by Raman spectroscopy and scanning electron microscopy (SEM). Implantation of Se at room temperature amorphized the near surface region of the SiC substrates, while in samples implanted above the critical amorphization temperature the crystal structure was retained with some radiation damage. Annealing at 1000 degrees C resulted in the recrystallization of the amorphized SiC layer. In the case of room temperature implantation, the broadening of the implanted Se profile in RBS spectra was observed to occur after annealing at 1300 degrees C and became significant with an increase in annealing temperature. This broadening was accompanied by a peak shift towards the surface and loss of implanted Se. No broadening was observed in samples implanted above the critical amorphization temperature, but the peak shift towards the surface began after annealing at 1300 degrees C in samples implanted at 350 degrees C and 600 degrees C.

The graphitic phases detected in chemical vapour deposited (CVD) ZrC layers were characterized by glancing angle X-ray diffraction. The layers were deposited at different temperatures ranging from 1250 to 1450°C in steps of 50°C. The precursors used were ZrCl 4 and CH 4 in the presence of hydrogen and argon. A total of seven graphitic phases were detected, five of which have been reported in the literature. However, two new hexagonal graphitic phases, P-6m2 (187) and P-62c (190), were also detected. It is proposed that the appearance of these two (new) phases was due to the influence of impurities in the growth region on the growth kinetics. A comprehensive phase identification process was followed to index all observed diffraction lines, followed by Rietveld analysis, to report on phase composition and crystalline properties. A distinct increase in overall graphite phase composition is observed at the higher CVD temperatures, which confirms the impact from graphitization.

The effect of Sr and Ag co-implantation and recovery annealing on the structural, mechanical and electrical properties of glassy carbon is reported. Glassy carbon was co-implanted with 200 keV Sr and Ag ions to a fluence of 1 x 10(16) ions/cm(2) at room temperature. Combination of Raman spectroscopy and high resolution transmission electron microscopy (HRTEM) showed that the co-implantation of Sr and Ag resulted in amorphisation of the glassy carbon substrate. Raman spectra and HRTEM micrographs obtained after annealing indicated recovery of the glassy carbon structure, however, the recovered structure appears to be graphite-like. Instrumented indentation experiments on the ion-irradiated glassy carbon substrates revealed the formation of a surface layer with considerably enhanced mechanical performance. When annealing the ion implanted samples, these effects were only partially reversible. The effect of the irradiation-induced amorphisation and graphitisation of glassy carbon on its conductivity was also studied. The sample became less conductive after Sr and Ag co-implantation, whereby annealing resulted in an increase in conductivity.

Some diffusing systems segregation towards the surface also occurs. Such a system can be described by adding a force-induced velocity term to the Fick diffusion equation. The profile of an implanted material is usually Gaussian or at least very near a Gaussian function. In this paper this Fick partial differential equation in a force field was solved for an initially Gaussian profile. The simulated profiles exhibit the expected behavior. 200 keV implanted strontium into glassy carbon and isochronically annealed in vacuum from 300 degrees C to 900 degrees C for 1 h. The Sr profiles were determined by RBS (Rutherford backscattering spectrometry). They showed both diffusion and segregation between 400 degrees C to 900 degrees C. These profiles were fitted to the abovementioned solution to extract the diffusion coefficient and segregation drift velocity at each annealing temperature. In the temperature range 400 degrees C to 800 degrees C the diffusion coefficient had an activation energy for diffusion of 0.20 eV and 1.2 nm2/s for the pre-exponential factor D0. The segregation velocity, which is directly proportional to the segregating force, increased with increasing temperature. At annealing temperature of 400 degrees C the average drift velocity towards the surface was 39 pm/s and at 900 degrees C it was an order of maginitude higher at 0.34 nm/s.