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Nd 3+ and Ce 3+ can substitute for about 65% of the Ca in monoclinic zirconolite, using AI as a charge compensator in a Ti site. Further substitution up to 85% of Nd 3+ and Ce 3+ produces an orthorhombic structure, while more than 85% substitution produces additional phases. Substitution of Ce 4+ in the Zr site appeared to be quite limited. Incorporation of U 4+ into the Ca and Zr sites in zirconolite gave results which were similar to those observed by others. Both trivalent and tetravalent Np and Pu can be substituted in the Ca and Zr sites, respectively, under oxygen partial pressures of 0.2−1 × 10 −5 atm, provided appropriate charge compensators are present. The implications of these results for formulating actinide-bearing zirconolite-rich ceramics are discussed briefly.

Channel catfish Ictalurus punctatus fingerlings in 30 net-pens in three ponds were naturally infected with Edwardsiella ictaluri. The fish were then treated by feeding Romet®-medicated feed of two different pellet sizes at two different Romet premix formulations. Fish fed any of the four Romet feeds had significantly (P < 0.05) higher percent survival than the nonmedicated controls. Fish fed small pellets of Romet-medicated feed formulated at 5 kg of Romet-30 premix per tonne of feed had significantly higher survival than fish fed large pellets of Romet-medicated feed formulated at 5 kg of Romet-30 premix per tonne of feed or fish fed large or small pellets at 15 kg of Romet-30 premix per tonne. The reduced level of Romet-30 premix (5 kg/ tonne) allowed fingerlings to be legally fed at 3% body weight; hence, more medicated pellets were available to more fish. Fish fed Romet-medicated feed formulated to be fed at 3% body weight (5 kg Romet-30 premix/tonne) gained significantly (P < 0.05) more weig...

In this paper we describe a technique for the determination of 25 elements in natural zirconolite using energy-dispersive analytical electron microscopy (AEM). The method presented here allows one to quantitatively investigate the chemistry of submicron-scale zones in complex oxide minerals. The effects of electron channeling, thickness variability and variations in detector resolution were minimized by using a controlled set of operating procedures and instrument parameters. To provide a high level of accurayy, kATI-factors were determined from standards for most of the 25 elements of interest, including all of the major elements. Each analytical spectrum is reduced to a set of raw peak counts (and errors) using a digital top-hat filter to suppress background followed by multiple least squares fitting of reference spectra. Counting times of 12–15 min per analysis were required to provide suitable counting statistics. Results are presented for zirconolite samples from the contact metamorphic aureole of the Bergell granodiorite intrusion, Switzerland-Italy. A comparison of 43 AEM analyses with 15 analyses obtained by wavelength-dispersive electron probe microanalysis (EPMA) shows that there is excellent agreement between the two data sets in the amounts of individual elements present, chemical trends and overall stoichiometry. An assessment of the combined data set shows that the major substitution mechanisms in the Bergell samples are coupled substitutions involving the M5,6- and M8-sites of the zirconolite structure: M8Ca2+ + M5,6Ti4+→M8REE3+ + M5,6(Al,Fe)3+ and M8Ca2+ + M5,6Ti4+→M8(Th,U)4+ + M5,6 (Mg,Fe)2+.

Two aphasics with a similar level of phonological production difficulty are compared to distinguish the properties of disruption to two stages in the phonological system for producing single words: activation of stored lexical-phonological representations versus construction of phonemic representations. A set of distinguishing behavioral features for breakdown at each stage is generated on the basis of a model of single word production. Important variables for analyzing output include: (a) the unit of phonological encoding (morpheme versus syllable), (b) the phonemic relationship between targets and responses, (c) the effects of target consonant-vowel (CV) structure, and (d) the level of pseudoword production. On a set of production tests, the expected behavioral pattern for impaired lexical-phonological activation was displayed by LW, while the expected behavioral pattern for impaired phonemic planning was displayed by CM.

The efficacy of Sarafin®- and Romet®-medicated feeds fed at 1% body weight was evaluated under field trial conditions for the treatment of naturally induced Edwardsiella ictaluri infections in channel catfish Ictalurus punctatus. When administered daily for 5 d, Sarafin-medicated feed at a dose of 10 mg Sarafin/kg of fish and Romet-medicated feed at a dose of 50 mg Romet/kg of fish significantly increased survival to 73 and 71%, respectively, compared with 64% in fish fed nonmedicated feed. All dead fish tested from both medicated and nonmedicated treatments were positive for E. ictaluri. Fish fed either Sarafin- or Romet-medicated feed gained significantly (P < 0.05) more weight than did nonmedicated fish. Weight gains of medicated fish were indicative of reduced morbidity in the population. Weight gain differences between fish fed Sarafin and those fed Romet was not significant. A significant decrease in the number of fish deaths occurring in groups fed either Sarafin- or Romet-medicated feed w...

The purpose of this study was to investigate how functors are processed at the lexicalphonological level. Four fluent aphasics with impaired ability to fully activate entries in the phonological lexicon, as revealed by their noun production, were asked to repeat and read aloud individual functors. Similarities between their functor and noun production (e.g., level of performance, production of phonological errors) indicated that functors are stored along with content words in the phonological lexicon, and are stored with a similar abstract structure. We also considered whether the sentence-planning system can facilitate the phonological encoding of functors presented in isolation.

Thin crystals of La2O3, La2/3TiO3, La2TiO5, and La2Ti2O7 have been irradiated in situ using 1 MeV Kr2+ ions in the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), at the Argonne National Laboratory (ANL). We observed that La2O3 remained crystalline to a fluence greater than 3.1 × 1016 ions cm-2 at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (Tc) of 840 K for La2Ti2O7, 865 K for La2/3TiO3, and 1027 K for La2TiO5. The Tc values observed in this study, together with previous data for TiO2, are discussed with reference to the phase diagrams for La2O3-TiO2 systems and the different local environments within the crystal structures. Results suggest an observable inverse correlation between Tc and melting temperature (Tm) in the two systems.

Three field trials were conducted to determine the efficacy of Sarafin® (sarafloxacinHCl) in the treatment of naturally induced infections of Edwardsiella ictaluri in channel catfish Ictalurus punctatus. Administering Sarafin in the feed for 5 d at a dose of 10 or 12.5 mg/kg of fish proved efficacious in treating channel catfish infected with E. ictaluri in all three field trials. Average survival of the nonmedicated group was 43% in trial 1, 11°% in trial 2, and 59% in trial 3. Survival of the corresponding Sarafin-medicated groups averaged 68, 48, and 73%. Antibiotic therapy with Sarafin significantly (P < 0.05) improved survival in all trials. In two trials, fish fed Sarafinmedicated feed gained more weight (P < 0.05) than did fish fed nonmedicated feed. In one trial, feed medicated with Romet® (sulfadimethoxine-ormetoprim) was also tested. Romet was administered in the feed at 100 mg/kg of fish, which is twice the recommended dose. This dose was chosen to match the feeding rate of Sarafin (fe...

Polished specimens of well characterised Synroc (a polyphase titanate ceramic designed to immobilise high-level nuclear waste) containing 10 wt% simulated (PW-4b-D) waste were subjected to MCC-2 type dissolution tests at 150°C in doubly deionised water (surface area to volume ratio0.01 ± 0.0005 mm −1 ) for periods of up to 532 d. Scanning electron microscopy (SEM) of the polished surfaces and transverse sections confirmed that Synroc is highly durable and suffers little corrosion even after 532 d in doubly deionised water at 150°C (corrosion of the least resistant major phase, perovskite, was

The energy resolution of an energy dispersive spectrometer (EDS) equipped with an ultrathin window (UTW) and mounted at a high take-off angle (72 degrees) on a transmission electron microscope has been studied under a variety of operating conditions. The spectrometer resolution is close to that specified by the manufacturer, up to count rates of 400 cps. Above 400 cps the resolution deteriorates rapidly, and the MCA dead time and zero width increase. Above 10 keV, the height of the background is much greater than expected for bremsstrahlung and shows the shape which has previously been attributed to backscattered electron flux into the detector. It is postulated that the deterioration in resolution with count rate is caused by backscattered electrons reaching the detector through the UTW.

The oral reading and repetition of nouns was tested in six fluent aphasics at two different times, with the initial testing occurring at least within the first 6 months post-stroke. Results revealed that oral reading was initially more impaired than repetition, and that the latter resolved much more quickly.

Radiation damage and the effect on physical and chemical properties is an important component in the prediction of the long-term stability of waste form materials. As part of the ongoing goal of increasing the accuracy of long-term predictions of radiation damage, two types of material, based on proposed materials with a waste form application have been irradiated. Results have shown that Y2TiO5 (Y2.67Ti1.33O6.67), and Yb2TiO5 (Yb2.67Ti1.33O6.67), both of which are non-stoichiometric, disordered pyrochlore-based compounds, behave significantly different to the stoichiometric, ordered pyrochlore equivalent. For example the critical temperature, the temperature above which materials remain crystalline during irradiation, is found to decrease from the ordered equivalents, e.g. Y2Ti2O7. ⁡ A second material based on La2TiO5 has been found to behave differently to both La2/3TiO3 and La2Ti2O7, with a change in Tc of ∼ 200 K.

A well-characterized Synroc was subjected to durability tests in de-ionized water at 70 °C and 150 °C, and silicate and bicarbonate solutions at 70 °C, to study the effect of temperature and solution composition on the mechanisms of aqueous alteration. SEM and TEM were used before and after durability experiments to characterize the primary and secondary phases in and on the Synroc samples, and to describe changes in morphology and chemistry. Leachant compositions after durability testing were analyzed using ICP/OES and ICP/MS and have been reported elsewhere.8 After durability testing, titaniferous surface layers were observed primarily on perovskite, the most soluble Synroc phase. Electron microscopy demonstrates that the surface layer formed at 70 °C is an amorphous Ti–O film and is fine grained anatase at 150 °C. Congruent dissolution is the major mechanism of perovskite alteration. However, at 150 °C, selective loss of Ca and Sr may occur locally. A number of additional secondary phases were identified, including Al–oxide/hydroxide, Fe–oxide, REE-bearing Ti–oxides, and several silicate phases. The abundance and composition of the secondary phases are related to solution composition and temperature.

Thin crystals of rutile, brookite, and anatase were irradiated in situ in the intermediate voltage electron microscope (IVEM-Tandem Facility) at Argonne National Laboratory using 1.0 MeV Kr ions at a temperature of 50 K. Determination of the critical amorphization fluence has revealed a large difference in the radiation tolerance. Synthetic rutile remained crystalline up to a fluence of $5\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }\text{ions}\text{ }{\text{cm}}^{\ensuremath{-}2}$ and did not show convincing evidence for the onset of amorphization at this fluence level. Natural brookite and anatase, on the other hand, became amorphous at $8.1\ifmmode\pm\else\textpm\fi{}1.8\ifmmode\times\else\texttimes\fi{}{10}^{14}$ and $2.3\ifmmode\pm\else\textpm\fi{}0.2\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ions}\text{ }{\text{cm}}^{\ensuremath{-}2}$, respectively. These results correlate with the number of shared edges, the degree of octahedral distortion, and the volume properties of polymorphs, and we show that the distortion and the volume are intimately linked through interatomic forces in the octahedral framework. The static and dynamic defect calculations indicate that the radiation tolerance of rutile is related, at least in part, to low energy migration pathways for both O and Ti. In order to gain further insight into the problem, we performed molecular dynamics (MD) simulations of small thermal spikes for each polymorph. These simulations are in qualitative agreement with the experiments, with the thermal spikes showing the same relative recovery behavior between the rutile, the brookite, and the anatase structures. The examination of previous MD simulations of ${\text{TiO}}_{2}$ glasses and experimental work on synthetic ${\text{TiO}}_{2}$ materials produced at low temperature provides a conceptual model for the structure of amorphous ${\text{TiO}}_{2}$ produced by ion irradiation of the crystalline polymorphs.

Thin crystals of rutile, brookite, and anatase were irradiated in-situ with 1.0 MeV Kr using the IVEM-TANDEM facility. Synthetic rutile and cassisterite (SnO2, rutile structure) remained crystalline up to 5 × 1015 ion cm-2 at 50 K. Natural brookite and anatase with low impurity levels became amorphous at 8.1 ± 1.8 × 1014 and 2.3 ± 0.2 × 1014 ions cm-2, respectively, at 50 K. Irradiation at higher temperature revealed Tc = 170 K for brookite and 242 K for anatase. Natural rutile with about 2 wt% impurities became amorphous at 9.4 ± 1.8 × 1014 ions cm-2 at 50 K and has a Tc = 207 K. The available data reveal both a structural effect in the polymorphs with low levels of chemical impurities and a chemical effect in natural rutile specimens containing up to about 1.7 wt% impurities.

Selected area electron diffraction patterns are routinely used to determine the effects of irradiation damage in nuclear materials. Using zone axis orientations, the intensities of Bragg beams change from a dynamical to kinematic-like state due to the presence of amorphous domains in the material. Such changes in beam intensities, together with the increased diffuse scattering from the increasing amorphous fraction, present a major obstacle to the determination of cation or anion disorder in the crystalline fraction.

Synthetic pyrochlore samples Y2Ti2-xSnxO7 (x=0.4, 0.8, 1.2, 1.6), Nd2Zr2O7, Nd2Zr1.2Ti0.8O7, and La1.6Y0.4Hf2O7, were irradiated in-situ using the IVEM-TANDEM microscope facility at the Argonne National Laboratory. The critical temperatures for amorphisation have revealed a dramatic increase in tolerance with increasing Sn content for the Y2Ti2-xSnxO7 series. This change has also found to be linear with increasing Sn content. Nd2Zr1.2Ti0.8O7 and La1.6Y0.4Hf2O7 were both found to amorphise, while Nd2Zr2O7 was found to be stable to high doses (2.5×10^15 ions cm-2). The observed results are presented with respect to previously published results for irradiation stability predictions and structural disorder.

Garnets, A3B2C3O12, are considered to be potential host phases for the immobilization of high-level nuclear waste as they can accommodate a number of elements of interest, including Zr, Ti and Fe. The naturally occurring garnet, kimzeyite, Ca3(Zr,Ti)2(Si,Al,Fe)3O12, can contain ˜30wt% Zr. An understanding of the radiation tolerance of these materials is crucial to their potential use in nuclear waste immobilization. In this study two synthetic analogues of kimzeyite of composition Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12 were monitored in situ during irradiation with 1.0 MeV Kr ions using the intermediate voltage electron microscope-Tandem User Facility (IVEM) at Argonne National Laboratory. The structure of these materials was previously determined by neutron diffraction and 57Fe Mössbauer spectroscopy. Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12 have very similar structural properties with cubic Ia3d symmetry, the only significant difference being the presence of Zr and Hf, respectively, on the 6 coordinated B sites.

Crystallisation of zirconolite (CaZrTi2O7) from a stoichiometric alkoxide precursor was studied by X-ray diffraction, differential thermal analysis and high resolution electron microscopy. The X-ray amorphous oxide formed by drying mixed ethanolic solutions crystallised to a disordered fluorite structure on heating to ~ 700 °C. Zirconolite with a pseudo-trigonal structure formed at ~ 900 °C, and at higher temperatures gradually transformed to fully ordered monoclinic zirconolite. Activation energies for the amorphous to fluorite and fluorite to pseudo-trigonal zirconolite transformations were obtained from the DTA measurements by the Ozawa method, but were not consistent with the rates of transformation observed by X-ray diffraction in isothermal measurements. The pseudo-trigonal zirconolite was found by high-resolution electron microscopy to be highly disordered monoclinic zirconolite.

When an aphasic is unable to name an object, giving the patient the opening sounds of the target name will often trigger the correct response. Eighteen aphasic subjects were tested using a gating paradigm to compare word onset durations necessary to elicit correct names after an initial naming failure with those necessary for recognizing the same words when spoken in isolation with no picture present. Prerecognition errors were also examined. Results suggested that the facilitation of naming found when examiners supply word-onset sound cues may be due in part to a two-stage process consisting of stem-completion followed by matching the picture with the potential name as generated.

Titanate ceramic waste forms were prepared using several combinations of calcination atmosphere (N{sub 2}, N{sub 2} {minus} 3.5% H{sub 2},h{sub 2}) and metallic redox buffers (Ni,Fe,Ti,Al) to examine the dependence of microstructure and durability upon oxygen activity. It was found that the microstructures and phase assemblages were mostly insensitive to the fabrication method, although in detail systematic changes were recognized. The correlation of aqueous durability with oxygen fugacity was not straightforward because of density variations in the hot-pressed ceramics. These fluctuations in density dominated the dissolution characteristics of the waste forms and sometimes obscured the more subtle changes associated with redox potential. It is concluded that although the best durability is achieved at lower fugacities (i.e., Ti metal buffer and H{sub 2} calcination atmosphere), a satisfactory product can be produced using any of the preparative routes examined, provided the material is completely densified.

Comparisons have been made between the segmental speech errors of conduction aphasics and normal speakers, despite the fact that the aphasic data have involved single-word production and the normal data have involved multi-word production. To provide a more appropriate aphasic database, the sentence repetition of a conduction aphasic (CM) is presented. Errors that resulted from an interaction between the phonemes of two words were examined and compared with past reports of such errors in normal speakers. Comparisons between the errors of CM and normal speakers revealed similarities, as well as differences. The similarities support the notion that, as with normal speakers, CM's word-interaction errors reflect disruption at the stage of phonemic string construction. For example, the errors of both CM and normal speakers usually involve the interaction of single segments of words from major lexical categories. However, differences exist in the way that such errors are constrained. For example, CM's ...

The tolerance of titanate nuclear waste ceramics to fluctuations in the concentrations of processing contaminants was monitored using x-ray diffraction, electron microscopy, secondary ion mass spectrometry, and analysis of dissolution liquors. Several waste forms were fabricated, all of which contained idealized Purex waste simulant and, in addition, varying quantities of the common waste stream impurities P{sub 2}O{sub 5}, MgO, Fe{sub 2}O{sub 3}, Na{sub 2}O, and SiO{sub 2}. Incorporation of the oxides individually stabilized new phases including monazite (P{sub 2}O{sub 5}), pseudobrookite (MgO), loveringite (Fe{sub 2}O{sub 3}), freudenbergite (Na{sub 2}O), and pollucite (SiO{sub 2})--only the latter phase deleteriously affected waste form performance by promoting cesium dissolution. However, when the processing contaminants were added simultaneously, a number of synergetic effects, particularly the stabilization of a soluble glassy phase, resulted in elemental losses which were an order of magnitude greater for some matrix and radwaste species. It was found that up to 25 wt% of the idealized Purex waste could be incorporated in the waste without diminution of its properties.

In this paper, we present a novel approach for the segmentation of white matter tracts based on Finsler active contours. This technique provides an optimal measure of connectivity, explicitly segments the connecting fiber bundle, and is equipped with a metric which is able to utilize the directional information of high angular resolution data. We demonstrate the effectiveness of the algorithm for segmenting the cingulum bundle.

We report photoluminescence and time-resolved photoluminescence experiments on ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ quantum dots grown by plasma-assisted molecular beam epitaxy. We show photoluminescence from single quantum dots, giving an unambiguous proof of the quantum dot nature of luminescence. In addition, we show that both the photoluminescence intensity and the carrier recombination time remain constant up to $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, reflecting the strong confinement of the carriers inside the quantum dots. We find monoexponential photoluminescence decay times as short as $340\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$, explained by the lack of the quantum confined Stark effect in our structures.

The radiation damage properties of synthetic pyrochlore-defect fluorite compounds containing lanthanides on the A-site and Ti, Zr, Sn, and Hf on the B-site have been studied extensively using Kr ion irradiation. Using statistical analysis, we show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and defect energies. The best current model is able to predict the critical temperature to within about 80 degrees Kelvin. The model indicates that radiation tolerance is correlated with an increase in the X anion coordinate toward the value characteristic of the defect fluorite topology, a smaller unit cell dimension, and lower defect energies. Our analysis also demonstrates that radiation tolerance is promoted by an increase in the Pauling cation-anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. Of the two possible cation sites in ideal pyrochlore, the B-site cation appears to play the major role in bonding. This result is supported, for a subset of pyrochlore compounds, by ab initio calculations, which reveal a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature.

The structural and optical properties of InGaN quantum dots grown by plasma-assisted molecular beam epitaxy (MBE) have been characterised using atomic force microscopy, high-resolution transmission electron microscopy (TEM), Z-contrast scanning TEM, micro-photoluminescence (PL), temperature dependent PL and time-resolved PL. The uncapped InGaN nano-islands have densities of ∼1.5 × 1011 cm−2, heights of (1.7 ± 1.0) nm and diameters of (10 ± 4) nm. These parameters are not substantially changed during overgrowth of a GaN cap and the resulting quantum dots have a composition of In0.15Ga0.85N. The observation of narrow luminescence peaks in micro-PL measurements proves light emission from discrete energy states and the optical properties indicate strong confinement of carriers in the quantum dots and an unusually weak impact of piezoelectric field effects.

The resistance of Ln2Ti2O7 (Ln=lanthanide) compounds to radiation damage is an important topic in the understanding and development of new materials by which radioactive nuclear waste can safely be immobilised. A model has been developed, from previously published density functional theory and molecular orbital theory simulations of the band structure for Ln2Ti2O7 materials. This model provides a chemical interpretation of radiation stability.

High Angular Resolution Electron Channeling Electron Spectroscopy (HARECES) is an analogue of the corresponding X-ray technique (HARECXS) in which one measures the variation of a spectroscopic signal with illumination angle. To date this methodology has been a rarely employed technique in EELS due to the intricacies of instrumenting the experiment and the weak signals which are obtained. We have implemented a computationally mediated procedure to achieve these measurements on both a JEOL 2010F and FEI Tecnai F20 TEM/STEM instruments and in this work report on preliminary measurements of the angular distribution of Carbon K Shell excitation which permits comparison to previous work by Leapman.

A wasteform must meet several key requirements: (i) aqueous durability as related to a repository environment, the measurement of which must also allow for long-term processes such as radiation damage and annealing; (ii) the compositional flexibility to cope with real waste streams, which are often variable and not well characterised; (iii) the wasteform must be easy to process and the process parameters must be large enough to cope with changes; and, (iv) the waste loading must be high enough to make the wasteform economically viable. In this paper, we discuss the effect of ion irradiation on pyrochlore-rich titanate and defect-fluorite zirconate ceramics designed for plutonium immobilisation. Samples, with Ce as an analogue for Pu, were made via oxide routes and consolidated by cold-pressing and sintering. Ion irradiation damage was carried out with 2 MeV Au2+ ions to a fluence of 5 ions nm−2 in the accelerator facilities within the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory. Irradiated and non-irradiated samples were examined by x-ray diffraction, scanning and transmission electron microscopy, x-ray photoelectron and infra-red spectroscopy, and spectroscopic ellipsometry. Samples underwent accelerated leach testing at pH 1.75 (nitric acid) at 90°C for 28 days. The zirconate samples were more ion-irradiation damage resistant than the titanate samples, showing little change after ion-irradiation whereas the titanate samples formed an amorphous surface layer ∼ 500 nm thick. While all samples had high aqueous durability, the titanate leach rate was ∼ 5 times that of the zirconate. The ion-irradiation increased the leach rate of the titanate without impurities by ∼ 5 times. The difference in the leach rates between irradiated and unirradiated zirconate samples is small. However, the zirconates were less able to incorporate impurities than the titanate ceramics and required higher sintering temperatures, ∼ 1500°C compared to 1350°C for the titanates.

Zirconates and titanates, based on the nominal baseline composition developed for the Plutonium Immobilization Project (PIP), have been prepared with and without process impurities. The titanates form pyrochlore as the major phase and the zirconates form a defectfluorite. Little, if any, of each impurity is accommodated in the defect-fluorite and powellite, kimzeyite, a spinel and a silicate glass appear as extra phases in this ceramic. In the titanates the pyrochlore incorporates more impurities, with the remainder being accomodated in zirconolite and a small amount of silicate glass. At extremly high levels of impurities, traces of magnetoplumbite, perovskite, and loveringite were found. The defect-fluorite zirconate phase is more radiation damage resistant than the titanate pyrochlore, though the secondary phases in the zirconate will reduce the radiation damage resistance of zirconate monoliths. To produce a dense product the oxide-route zirconate required sintering temperatures of about 1550°C, 200°C higher than that required for the titanate. Silicate impurities reduce the sintering temperatures.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Optical emission spectra in the 300-700 nm range were collected from zirconolite and rutile specimens irradiated with a 3 μs pulsed electron beam using a Febetron 706 variable energy pulsed electronbeam generator. The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths ~ 100 nm) bands centred around ~400 nm. Over the range 0.2 MeV to 0.6 MeV, the emission intensity per unit dose versus electron beam energy data from the rutile sample showed a single stage dependence on electron beam energy, whereas the zirconolite data suggested a two stage dependence. Rutile has a threshold of 0.23 ½ 0.02 MeV, which gives an Ed value of 39 ½ 4 eV for oxygen. Zirconolite has a threshold of 0.26 ½ 0.02 MeV, which gives an Ed value of 45 ½4 eV for oxygen. These data are discussed in the context of previously measured and calculated Ed values for other oxides.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Zirconolite is one of the major host phases for actinides in various wasteforms for immobilizing high level radioactive waste (HLW). Over time, zirconolite's crystalline matrix is damaged by {alpha}-particles and energetic recoil nuclei recoil resulting from {alpha}-decay events. The cumulative damage caused by these particles results in amorphization. Data from natural zirconolites suggest that radiation damage anneals over geologic time and is dependant on the thermal history of the material. Proposed HLW containment strategies rely on both a suitable wasteform and geologic isolation. Depending on the waste loading, depth of burial, and the repository-specific geothermal gradient, burial could result in a wasteform being exposed to temperatures of between 100--450 C. Consequently, it is important to assess the effect of temperature on radiation damage in synthetic zirconolite. Zirconolite containing wasteforms are likely to be hot pressed at or below 1,473 K (1,200 C) and/or sintered at or below 1,623 K (1,350 C). Zirconolite fabricated at temperatures below 1,523 K (1,250 C) contains many stacking faults. As there have been various attempts to link radiation resistance to structure, the authors decided it was also pertinent to assess the role of stacking faults in radiation resistance. In this study, they simulate {alpha}-decay damage in two zirconolite samples by irradiating them with 1.5 MeV Kr{sup +} ions using the High Voltage Electron Microscope-Tandem User Facility (HTUF) at Argonne National Laboratory (ANL) and measure the critical dose for amorphization (D{sub c}) at several temperatures between 20 and 773 K. One of the samples has a high degree of crystallographic perfection, the other contains many stacking faults on the unit cell scale. Previous authors proposed a model for estimating the activation energy of self annealing in zirconolite and for predicting the critical dose for amorphization at any temperature. The authors discuss their results and earlier published data in relation to that model.

Eight perovskites of different compositions and pre-existing vacancy contents were irradiated with 1.5 MeV Kr+ ions using the HVEM-Tandem User Facility at Argonne National Laboratory. The critical dose of 1.5 MeV Kr+ ions for amorphisation (Dc) of NaNbO3, SrTiO3 and two natural perovskites varies with composition and may decrease with Na content. The D,c values of 5 members of the solid solution series from SrTiO3 to La0.67TiO3 do not exhibit a simple relationship with vacancy content: In particular, Dc(Sr0 7La0.2TiO3) is extraordinarily high (>170 × 1014 ions cm−2) compared to those of the other (Sr, La)-perovskites in the series, which have Dc values between 2.4 and 11 × 1014 ions cm−2.

Using electron energy-loss filtered transmission electron microscopy (EFTEM), we have observed the formation of silicon-rich zones on the corroded surface of a West Valley (WV6) glass. This layer is approximately 100-200 nm thick and is directly underneath a precipitated smectite clay layer. Under conventional (C)TEM illumination, this layer is invisible; indeed, more commonly used analytical techniques, such as x-ray energy dispersive spectroscopy (EDS), have failed to describe fully the localized changes in the boron and silicon contents across this region. Similar silicon-rich and boron-depleted zones were not found on corroded Savannah River Laboratory (SRL) borosilicate glasses, including SRL-EA and SRL-51, although they possessed similar-looking clay layers. This study demonstrates a new tool for examining the corroded surfaces of materials.

Eight perovskites of different compositions and pre-existing vacancy contents were irradiated with 1.5 MeV Kr+ ions using the HVEM-Tandem User Facility at Argonne National Laboratory. The critical dose of 1.5 MeV Kr+ ions for amorphisation (Dc) of NaNbO3, SrTiO3 and two natural perovskites varies with composition and may decrease with Na content. The Dc values of 5 members of the solid solution series from SrTiO3 to La0.67TiO3 do not exhibit a simple relationship with vacancy content: In particular, Dc(Sr0.7La0.2TiO3) is extraordinarily high (>170 × 1014 ions cm−2) compared to those of the other (Sr, La)-perovskites in the series, which have Dc, values between 2.4 and 11×1014 ions cm−2.

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

Detailed current and flow rate measurements obtained during pulsation mode nano-electrospray of ethylene glycol solutions are presented. High temporal resolution current measurements reveal for the first time that current is observed at the electrode immersed in the electrospray fluid, even when there is no observed spray. This current, believed to be the charging current associated with electrode and meniscus polarization, is dependent upon the voltage applied to the electrospray system. Quantitatively, the total charge transfer that is observed during the non-spray period of the pulsation approximates to that required to obtain electrostatic equilibrium in the conical meniscus, and is relatively independent of the fluid conductivity. A linear relationship exists between this charging current and the observed pulsation frequency. Pulse shape, indicated by the parameters of spray current rise time, fall time, and spray current pulse duration, are observed to be independent of frequency for a given solution. The total charge lost during a single pulsation event is significantly larger than the charge transfer observed during the meniscus replenishment phase of the pulsation. For the solvent tested, the rate at which meniscus charging takes place is linearly dependent upon solution conductivity, and thus appears to scale directly with the electrical relaxation time.

Preliminary analytical and transmission electron microscopy (AEM and TEM) results for a small suite of natural perovskites are reported in this paper and discussed in relation to previous work. We show that perovskite compositions in Synroc and tailored ceramics plot within the known fields of natural perovskite compositions. AEM analyses and electron diffraction work on selected samples indicate that they are predominantly stoichiometric variants of the cubic perovskite structure. Geochemical alteration was observed in one sample of loparite from Bratthagen, Norway. The primary result of this alteration was leaching of Na from the A-site. Although sufficient alpha-decay dose levels for complete amorphization are not realized in this suite of samples, the available data bracket the beginning of the crystalline-amorphous transformation at doses that are ∼ 2-4 times greater than those of zirconolite of similar age. These results may be due to fundamental differences in the damage annealing rates of perovskite and zirconolite.

Zirconolite (CaZrTi2O7), pyrochlore (vIIIA2VIB2IVx6y) and perovskite (CaTiO3) are candidate phases for the immobilisation of rare earth elements (REEs) and actinides (ACTs) in various high level radioactive waste (HLW) forms [1]. The effect of radiation damage on the structure and consequently on the durability of these phases is important to predictive modelling of their behaviour in the repository environment and risk assessment

Synroc is a candidate waste form for the immobilisation of high level radioactive waste (HLW)[1]. It is polyphase titanate ceramic principally comprised of zirconolite, hollandite perovskite and rutile (nominally CaZrTi2O7, (BaxCsy)[(Ti3+, Al)2x+y(Ti4+)8−2x−y]O16), CaTiO3and TiO2respectively). Waste species substitute into the three former phases. In particular, actinides (ACTs) substitute onto the Ca and Zr sites in zirconolite and the Ca site in perovskite. Consequently over time, these phases will suffer alpha-recoil and alpha particle damage while hollandite and rutile will suffer alpha particle damage. The effect of radiation damage on the structure and consequently on the durability of Synroc's constituent phases is important to predictive modelling of Synroc's behaviour in the repository environment and risk assessment.

Synroc-C containing 10wt% simulated PW-4b-D HLW including 0.62 wt% 239Pu was subjected to MCC-1 type leach tests at 70°C in deionised water, silicate and carbonate leachates for 53 d and deionised water for 2472 d. The normalised total (i.e. unfiltered leachate + vessel wall) Pu leach rates in deionised water, silicate and carbonate leachates for periods up to 53 d were found to be of the order of 10-5, 10-4 and 10-4 g m-2 d-1 respectively. After 2472 d, the differential, normalised, Pu leach rate in deionised water dropped to ∼5 × 10-6 (total) and ∼5 × 10-8 (solution - after filtration through a 1000NMW filter) g m-2 d-1. SEM and AEM were used to characterise our starting material and investigate the secondary phases on the surfaces of leached Synroc-C discs. Calculated and measured normalised Pu leach rates are compared and the partitioning of Pu between zirconolite and perovskite is discussed.

Synroc containing 20 wt% simulated high level waste (HLW) was subjected to two sets of leach tests at 150°C where the leachant was and was not replaced during the test (replacement and non-replacement testing). The leachant was a KH-phthalate buffered solution (pH 4.2). Samples were characterised before and after leach testing using SEM, AEM and SIMS. Elemental concentrations in leachates were measured using ICP-MS. In concert with the findings of i) a dissolution study of perovskite in a flowing leachant and ii) a previous Synroc dissolution study (wherein Synroc containing 10 wt% simulated HLW was subjected to periodic replacement, leach testing in deionised water at 150°C), the results of this study show that when the leachant replacement frequency is varied from 7 d to the duration of the test, there is no effect on leach rate or leaching mechanisms.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.