The changes in amount and location of layer charge during diagenetic alteration have been investigated for smectites and smectite layers of illite/smectite interstratified minerals (I/S) by X-ray powder diffraction analysis with various expansion behavior tests: 1) ethylene glycol (EG) solvation (XRD); 2) K-saturation and EG solvation; 3) Li-saturation, heating at 250 °C and glycerol or EG solvation (Greene-Kelly test); and 4) alkylammonium saturation. In the course of low-temperature diagenesis but before the onset of illitization, mean layer charge of smectites continuously increases from approximately 0.56 to 0.73 per O20(OH)4 with increasing depth, and tetrahedral charge also increases continuously from approximately 0.21 to 0.38 per O20(OH)4 (beidellitization). The continuous increase in tetrahedral charge without change in peak intensity and shape suggests that the solid-state Al for Si substitution mechanism appears to predominate within beidellitization. After illitization, the content of the beidellitic layers continuously decreases, while the mean layer charge of expandable layers and the content of illite layers in I/S increase. This suggests that the conversion of a beidellitic layer to an illitic layer preferably occurs during early illitization. Thus, before illitization, beidellite-like layers are formed from precursor smectite, and during the early stage of illitization, the high charged beidellitic layers are probably consumed to form illite layers.

The weathering of chlorite, one of the major minerals of the host rock in the uranium ore deposit at Koongarra, Australia, was examined by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), electron microprobe analysis, and transmission electron microscopy (TEM). The conversion sequence of chlorite weathering is: (1) chlorite; (2) chlorite/vermiculite intergrade (showing XRD responses to various treatments intermediate between those of chlorite and vermiculite); (3) interstratified chlorite and vermiculite; (4) vermiculite; and (5) kaolinite. This sequence may be more simply expressed as chlorite ⤒ vermiculite ⤒ kaolinite. The weathering finally changed chlorite into sub-micrometer to micrometer sized Fe minerals and kaolinite. The transformation of chlorite to vermiculite is chemically characterized by an Fe and Mg loss with a slight decrease in the Al/Si ratio. Mg continues to be released throughout the weathering. Fe minerals formed through chlorite weathering are located between chlorite and vermiculite domains (a few μm in size) at first, and then accumulated between grain boundaries, occasionally forming veins. The distribution of Fe minerals is suggestive of preferential pathways of water movement. The time-dependent nature of mineral alteration demonstrated in the present study must be taken into account for the quantitative estimation of radionuclide migration.

Smectite illitization was investigated in felsic volcaniclastic rocks from a drill core near the Kakkonda active geothermal system, Japan, using high-resolution transmission electron microscopy (HRTEM) that provided one-dimensional structure images of mixed-layer illite-smectite (I-S) minerals normal to [M0]. Simulated images of a rectorite-like structure revealed that smectite can be distinguished from illite in mixed-layer I-S by HRTEM if the basal spacing of smectite is larger than that of illite. The larger basal spacing of smectite, 1.3 nm under HRTEM, was obtained by intercalation of dodecylammonium ions into smectitic interlayers. In simulated and observed images normal to [hk0], tetrahedral (T) and octahedral (O) cation planes are imaged as dark lines, an illitic interlayer as a bright line, and a smectitic interlayer as a dark line sandwiched between two bright lines.

The samples are from depths of 435 m (5% I; R0), 635 m (35% I; R0), 656 m (62% I; R1), and 756 m (85% I; R3) where % I is the percentage of illite layers in a sample and R is the Reichweite parameter. Sample 435 consisted mostly of smectite, and illite layers occurred, though small in amount, as M1 units (module of type 1, defined as consisting of two polar T-O-T silicate layers with one central illitic interlayer and two, half smectitic interlayers at the outermost surface; the number corresponds to that of central illitic interlayers). The M1 units were dominant and isolated and consecutive smectite layers (>2) were present in sample 635. Sample 656 consisted mostly of packets of M1 units of 1 to 5 layers containing M2 to M5 units occasionally. Isolated or consecutive smectite layers (>2) were not present in 656. Illite layers occurred almost entirely as M1 units in samples 435, 635 and 656, and the number of M1 units increased with increase in % I. Sample 756 was characterized by the presence of M2 to M10 units accompanied by smectitic interlayers at the external surface and the absence of M1 units and isolated smectite layers. The HRTEM data strongly suggest that illitization in a hydrothermal system occurs by precipitation of M1 units for mixed-layer I-S minerals up to 60% I. This does not require the presence of precursor smectite. Illitization of I-S minerals with >60% I proceeds by precipitation of various types of Mn (n ⩾ 2) units. Illite occurs only as Mn (n ⩾ 1) units throughout illitization.

For a series of mixed-layer illite-smectite (I-S) minerals from a drillhole near the Kakkonda geothermal field, one-dimensional structure analysis by X-ray diffraction (XRD) was performed using Casaturated specimens in both air-dried and ethylene glycol-solvated states. The expandability characteristics of component layers were also examined by means of alkylammonium exchange and Li saturation. The K content in the illite layers was 1.5–1.7/O20(OH)4 in the I-S series from 3 to 85% of I-layer content (% I). The layer charge of the smectite layer varied slightly within the range of 0.3–0.5/O10(OH)2 by alkylammonium exchange experiments and the expandability was independent of the beidellite content within a range of 0–0.5 by the Li-saturation test. The degree of long-range ordering represented by Reichweite (R) parameters varied from R0 to R3 via R1 and R2 with increase in % I. The I-S samples contained <10% vermiculite as the third component and the vermiculite content tended to decrease with progressive illitization.

In contrast to the smectitic R0 samples (<10% I), more illitic R0 (e.g. 35% I) and >R1 I-S samples showed complicated expandability with alkylammonium exchange. The XRD patterns of dodecylammonium-exchanged I-S samples can be interpreted by random interstratification of several types of sub-units such as layer-doublets, layer-triplets and layer-quartets present in the crystallites. This interpretation is consistent with the variation in the occurrence probabilities of layer-multiplets calculated from the junction probabilities and the proportions of layers. Because the interpretation indicates that I-S is a stack of various types of the sub-units, the smectite illitization can be described by a systematic change in the type and proportion of the sub-units constituting crystallites.

We propose a low-contrast pre-coronagraph that can provide additional dark-hole contrast to a main coronagraph.

A nanoparticle catalyst of PtRuAu/C was synthesized by including an Au precursor in the radiolytic process for preparing a PtRu/C catalyst. Their methanol oxidation activity and electrochemical durability were measured by linear sweep voltammetry before and after potential cycling treatment. PtRuAu/C had a significantly higher durability than PtRu/C while maintaining a comparable high activity. The morphology and substructure of the nanoparticles were investigated by energy-dispersive x-ray spectroscopy, x-ray diffraction, and x-ray absorption fine structure spectroscopy. Metallic nanoparticles with diameters of about 2 nm were obtained; they probably had Pt-core/PtRu-shell structures. Transmission electron microscopy observations after potential cycling revealed that 2-nm-diameter nanoparticles containing Au did not coarsen, whereas nanoparticles without Au coarsened significantly to 3.7 nm. Some crystal defaults were observed in the coarsened particles, implying that the coarsening was caused by Ostwald ripening. The Au addition to catalyst particles consisting of PtRu inhibits coarsening and consequently improves the electrochemical durability.

Nanoparticle catalyst of PtRuAu/C for direct methanol fuel cell anodes was synthesized by a radiolytic process. Its methanol oxidation activity and the electrochemical durability were evaluated by using the linear sweep voltammetry and the cyclic voltammety. The Au addition significantly improved the durability in comparison with PtRu/C catalyst without losing its high activity. The atomic structure was characterized with techniques of the transmission electron microscopy, the X-ray diffraction, the X-ray fluorescence spectroscopy and the X-ray absorption fine structure. These results implied that the arrangement of Pt and Ru atoms in the PtRuAu/C has no significant difference from that without Au, possessing a structure of Pt rich core and PtRu alloy shell. We concluded that the improvement in durability could originate from these PtRu nanoparticles decorated with Au, but not from particles with high Au contents.

Boron (B) doped silicon nanowires (SiNWs) were synthesized by laser ablation. Local vibrational modes of B in SiNWs were observed by micro-Raman scattering measurements at room temperature. Broadening due to a coupling between the discrete optical phonon and a continuum of interband hole excitations was also observed in the Si optical phonon peak. This is called Fano broadening. These results prove that B atoms were doped in substitutional sites of crystalline Si core of SiNWs during laser ablation.

Understandings of U transport at the Earth’s surface are quite important especially for the disposal of radioactive waste and the remediation of contaminated ground water. We examined long-term U transport in and around the Koongarra U deposit, Australia, which has been subjected to weathering for the past 2 million years. The formation of saléeite [Mg(UO2)2(PO4)2·10H2O] occurred at the rim of apatite [Ca5(PO4)3(F,OH)], where the ground waters had about 200 - 400 ppb U (∼10-7 mol·l-1) and were undersaturated with respect to saléeite. The laboratory experiments using apatite and U-containing solutions and Rutherford backscattering spectrometry of the apatite surface have suggested that a leached layer of about 100 nm thick is formed on dissolving apatite, saléeite is precipitated only in the leached layer by local saturation, and saléeite precipitated is added to the interface between the leached layer and solution. At lower U concentrations (∼10-8 mol·l-1), U occurred as nanocrystals (20-100 nm in size) of uranyl phosphates such as metatorbernite [Cu(UO2)2(PO4)2·8H2O], scattered between and attached firmly to nanocrystals (2-50 nm in size) of goethite and hematite. A possible mechanism is that U, P, and Mg or Cu adsorbed onto ferrihydrite form nanocrystals of uranyl phosphates during crystallization of goethite and hematite from ferrihydrite. The above two mechanisms significantly lower the U concentration in the ground water that flows into the Koongarra creek, 200 m downstream from the ore deposit, where the U concentration is ∼10-10 mol·l-1. We conclude that the two mechanisms of uranyl-phosphate mineralization control the long-term U transport at Koongarra.

The lichen Trapelia involuta from uraniferous spoil heaps in Cornwall, England, growing directly on the secondary uranium minerals, metazeunerite and metatorbernite, was examined by field-emission scanning electron microscopy and transmission electron microscopy to assess the effect of Trapelia on uranium migration. We observed metazeunerite, sericite and scorodite as well as unidentified Fe-, Pb/As-, Fe/As-, Al/P-, Pb-bearing minerals concentrated in the lichen exciple and medulla. In addition, metazeunerite also occurred in the epithecium. The chemistries, sizes, and occurrences of the above minerals in the lichen suggest that fixation of U as well as Pb, As, Fe, and Al is dependent on lichen physiological processes. We suggest Trapelia accumulates these elements from groundwater and precipitates the above minerals within specific tissues. Our results indicate that some lichens retard uranium migration by accumulating uranium from groundwater and forming uranium-bearing minerals within their tissues.

Adsorption is believed to be a dominant mechanism of uranium distribution between solid and solution, and thus, to play a major role in uranium transport. Because iron oxides and hydroxides are abundant at the Earth's surface and are great adsorbents of uranium, we have examined natural rocks that contain iron minerals along with uranium, and also carried out Fe-U coprecipitation and aging experiments to find how uranium is distributed between Fe minerals. Transmission and scanning electron microscopy reveals that microcrystals (10-50 nm) of metatorbernite (Cu(UO2)2(PO4)28H2O) are scattered within nodules consisting of fine-grained (2-50 nm) goethite and hematite, where the ground water is undersaturated with respect to metatorbernite, for the natural rocks from the Koongarra ore deposit, Australia. The microscopy also reveals that microcrystals (a few nm) of dehydrated schoepite ((UO2)O0.25(OH)1.5) are formed among fine-grained hematite after aging coprecipitated Fe-U in the laboratory, and the solution is undersaturated with respect to schoepite. The beam size of microscopes is found to be important for the chemical analysis of such microcrystals. We detect a strong signal of uranium for a beam size < 40 nm; whereas a weak uranium signal is obtained for a beam size > 150 nm. Our results indicate that such a weak uranium signal should not be taken as a result of homogeneously distributed uranium over goethite and hematite surfaces by, for instance, adsorption. The micrcrystallization observed in both the field and laboratory suggests that fine grained uranyl minerals play a major role in uranium transport and migration.

The migration of radionuclides through rocks is one of the important paths to estimate the impact of radioactive waste disposal on the environment. Because some amount of the radionuclides is sorbed on the minerals of rocks during the migration, Kd model is considered to be used to estimate the radionuclide migration. However, long-term applicability of Kd model is not known.

Rock samples in the secondary ore deposit at Koongarra, Australia, were examined mineralogically to clarify the formation mechanism of saléeite (Mg(UO2)2(PO4)2.10H2O), a major secondary uranium mineral in the secondary ore deposit. Sklodowskite (MgSi2U2O11.7H2O) veinlets, present upstream of the ore deposit, are partially replaced by saléeite. Most grains of apatite (Ca5(P04)3F), an accessory mineral of the host rock, are also replaced by saléeite. Thermodynamic calculations by EQ3NR showed that the present Koongarra ground waters are undersaturated with respect to saléeite and also suggested that saléeite can be precipitated under the condition of higher U or P concentrations. Such conditions can be created at the reaction interfaces of dissolving sklodowskite, which releases U, or dissolving apatite, which releases P. The present study indicates that saléeite is formed by local microscale saturation upstream of the secondary ore deposit, which is different from the formation mechanism of saléeite downstream of the ore deposit, where saléeite microcrystals of 1 – 20 nm in size form by catalysis on iron minerals, the weathering products of the host rock.

A modelling study has been completed to understand the effect of rock alteration on uranium migration at the Koongarra ore deposit, Australia. The model considers the weathering process, the mechanism and rate of chlorite alteration, a major mineral of the host rock, and assumes the presence of reversible sorption sites of chlorite and the presence of reversible and irreversible sorption sites of the weathering products. One- and two-dimensional, calculated uranium concentrations were compared with those observed. Good agreement between the calculated and observed uranium concentration profiles was obtained only when an appropriate fraction of uranium is fixed to the irreversible sorption sites of Fe-minerals produced during weathering of chlorite. On the other hand, the conventional Kd model failed to estimate an adequate uranium concentration profile. The results suggest that the fixation of uranium to Fe-minerals has dominated the migration of uranium in the vicinity of the Koongarra ore deposit.

A rock specimen, collected downstream of the Koongarra uranium ore deposit, Australia, was examined mainly by high resolution transmission electron microscopy in order to understand the uranium fixation mechanism. Uranium was found to exist as saleeite (Mg(UO2)2(PO4)2.10H2O) microcrystals of 1 – 20 nm scattered between iron minerals (mainly goethite and hematite) of 2 – 50 nm. The microtextural relationship between saléeite and the iron minerals revealed that the iron minerals function as catalyst for the formation of saléeite. The intermediate metamict microstructures of the saléeite microcrystals are consistent with the estimated formation age of saléeite, 1 to 3 × 106 years. Uranium has been, thus, fixed as saléeite downstream as well as in the secondary ore deposit. Saléeite in the secondary ore deposit showed completely periodic to fully metamict microstructures, suggesting that saléeite, a major uranium mineral in the secondary ore deposit, probably began to form a few million years ago and continued to form for the next million years.

A series of hydrothermal experiments was performed to determine the effect of layer charge of starting materials on the smectite to illite reaction rate that might be applied to nuclear-waste repository design. The experiments were conducted on K-saturated <2μm fractions of Wyoming smectite (SWy-1) and Tsukinuno smectite (SKu-F, commercially, Kunipia-F) in a closed system at temperatures of 95, 150, 200, 250, 300°C for run durations of up to 477 days with a 1:20 mass ratio of solid to deionized water. The mean layer charge and tetrahedral charge of SKu-F are larger than those of SWy-1. The proportion of smectite layers in illite/smectite interstratified minerals rapidly decreases, and then slowly decreases with increase in reaction time; a plot of In (100/% smectite) vs. time produces two distinct straight lines in all experiments. These lines are suggestive of two first-order kinetic processes with different rates for this reaction; the first process has a greater rate than the second one. An Arrhenius plot of the reaction rates for each process produces a folding and straight lines for the first and second processes, respectively, suggesting that there are at least two parallel processes in the first process, and a dominant process is different between high- and low-temperature reactions. The activation energies of the first and second processes determined from the plots are the same for the two starting materials, meaning that the reaction mechanisms for the two starting materials are the same. However, the rate of the first process is different between the two starting materials, although that of the second process is similar. The difference in the rate of the first process results possibly from the difference in the amount of layer charge between the two starting smectites.

A highly oriented pyroliiic graphite crystal is commonly used as a monochromator for X-ray diffraction and fluorescence analysis (l)-(6). Improvements in the monocliromator performance is desired to increase the range of practical applications.

Secondary uranium minerals from the Koongarra deposit, Northern Territory of Australia, were examined in order to understand the formation and alteration processes of the uranium minerals and their relevance to the migration behavior of uranium, lead, calcium and rare earth elements in the weathered zone. In most of the secondary ore zone, the only stable uranium mineral was saléeite (Mg(UO2)2(PO4)2·10H20), occurring as euhedral platy crystals up to 1 mm in length in veins and at surfaces. Apatite (Ca5(PO4)3F), an accessory mineral of the host rock, has saléeite reaction rims, suggesting formation at the expense of apatite. Ca-uranyl phosphates, such as autunite (Ca(UO2)2(PO4)2·10H2O), were not identified, and Ca-rich uranyl silicates are also absent in the primary ore zone. Pb-bearing uranyl phosphates were found only in the graphite layer cross-cutting the secondary ore zone. In the graphite layer, the local low oxidation condition and high hydrocarbonate content of ground water have affected the formation of uranium minerals and the migration behavior of uranium.

In order to clarify the effect of mineral alteration on nuclide migration, we examined the processes, mechanisms, and kinetics of chlorite weathering, and the uranium concentrations in minerals and rocks at Koongarra, Australia. The observed concentrations of uranium in rocks were compared to those calculated. The sequence of chlorite weathering may be simply expressed as a chlorite → vermiculite → kaolinite conversion. These minerals occur as a function of depth, which corresponds well to uranium concentrations on the meter scale. Iron minerals, closely related to the uranium redistribution, are released during the weathering. The first-order kinetic model of the weathering process suggests that the weathering rate is not constant but time-dependent. The uranium concentrations are qualitatively proportional to the extent of the weathering; the weathered part having higher uranium concentration. Uranium mainly occurs with iron minerals, and sub micron sized saléeite, a uranyl phosphate, is one of the most probable uranyl phases associated with the iron minerals. The uranium fixation mechanisms are probably saléeite microcrystal coprecipitation and sorption to the iron minerals. Our model, which describes uranium concentrations in rocks as a function of time, shows that the transition zone (a vermiculite dominant area) plays an important role in the uranium migration. We have established that weathering of chlorite has affected the redistribution of uranium for more than one million years. The present study demonstrates the significance of mineral alteration when we estimate nuclide migration for geologic time.