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Titanite (CaTiSiO5) a mineral that has shown promise as an actinide-bearing host phase. Natural titanites contain radionuclides which result in radiation damage to the crystal structure and could e...

Recrystallization of zircons under the influence of fluids was studied using examples from Precambrian rocks (microcline granites, metasedimentary, and mafic rocks) of the Kola Peninsula. All zircon crystals showed complex internal textures visible by cathodoluminescence and backscattered electron (BSE) imaging. Detailed mineralogical and geochemical studies with subsequent secondary ion mass spectrometer U–Pb dating of different zircon domains show that secondary texture formation can be interpreted in terms of metasomatic replacement of zircon crystals on the base of crystallogenetic experimental models. Mechanisms of zircon replacement and interpretation of U–Pb ages for secondary zircon domains are dependent on the degree of damage of the zircon structure and the fluid composition. The recrystallization of metamict zircon without additional supply of new zircon substance (Zr, SiO2) goes with the dissolution of amorphous domains and precipitation of new polycrystalline zircon, which preserves the U–Pb ...

Elastic material properties of metamict titanite (sample E2312) during thermally induced stepwise recrystallization are measured using nanoindentation. Changes of the elastic modulus (E) and the hardness (H) are related to increasing long-range order and vanishing amorphous interface areas. Metamict titanite shows H and E values close to titanite glass. H decreases on annealing until ca. 950 K to 9.08 GPa and increases at higher temperatures, while E increases continuously on annealing up to ca. 168.4 GPa at 1220 K. Crystalline titanite from Rauris shows strong anisotropy and H and E values are clearly larger than those of E2312.

Raman spectra of the uranyl titanate mineral davidite-(La), (La,Ce)(Y,U,Fe2+)(Ti,Fe3+)20(O,OH)38, were analyzed and related to the mineral structure. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U–OH bending vibrations, H2O and (OH)− stretching, bending and libration modes. U–O bond lengths in uranyls and O-H ··· O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of davidite-(La) are in harmony with those of the uranyl oxyhydroxides. The mineral davidite-(La) is metamict, as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader.

The Eastern Segment abutting the Transscandinavian Igneous Belt (TIB) mostly consists of rocks with overlapping igneous ages. In the Eastern Segment west of Lake Vattern, granitoids of clear TIB affinity exhibit strong deformational fabrics. This article presents U–Pb zircon ages from 21 samples spanning the border zone between these deformed TIB rocks in the east, and more thoroughly reworked rocks in the west. Magmatic ages fall in the range 1710–1660 million years, irrespective of the degree of deformation, confirming the overlapping crystallization ages between deformed TIB rocks and orthogneisses of the Eastern Segment. A common history is further supported by leucocratic rocks of similar ages. Prolonged orogenic (magmatic) activity is suggested by continued growth of zircon at 1.66–1.60 Ga. Six of the weakly gneissic rocks show zircons with cathodoluminescence-dark patches and embayments, possibly partly replacing metamict parts of older magmatic crystals, with 207Pb/206Pb ages dominantly between 14...

Raman spectra of the uranyl titanate mineral holfertite Ca x U2−x Ti(O8−x OH4x )·3H2O were analyzed and related to the mineral structure. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U–OH bending vibrations, and H2O stretching and bending. The mineral holfertite is metamict, as is evidenced by the order/disorder of the mineral. Unexpectedly, the Raman spectrum of holfertite does not show any metamictization. The intensities of the UO stretching and bending modes show normal intensity and the bands are sharp.

A fluctuation electron microscopy study of amorphous zircons is reported. A natural metamict zircon sample was compared with amorphous samples prepared by irradiating a gem-quality zircon crystal with a 1.0 MeV beam of N2+ ions over a range of fluences up to 1.5 × 1017 ions/cm2. The two types of amorphous material exhibit similar selected-area diffraction patterns. However, the statistics of the scattering from 1 nm wide volumes indicates that they have significantly different normalised intensity variance plots. Modelling of the variance suggests that the natural metamict zircon consists of paracrystalline grains of zircon embedded within an amorphous ZrSiO4 matrix. The ion-irradiated samples are better modelled as segregated paracrystalline grains of ZrO2 composition within an amorphous SiO2-rich matrix. Although both samples have been rendered disordered by radiation damage, there are two important differences. First, the ion-irradiated materials experience significantly higher fluence rates compared w...

Titanite, CaTiSiO5, occurs in nature in crystalline and metamict modification. Its structure consists of corner-linked TiO6 octahedra, SiO4 tetrahedra and sevenfold coordinated Ca. Metamictization occurs when a mineral contains impurities like U and Th and is exposed to radioactive irradiation. Recoil processes due to alpha radiation change over geological time scales the structure to a state with persisting short-range order but violated long-range order. Raman and infrared spectra and X-ray diffraction data of metamict as well as crystalline and titanite glass reveal local structural phenomena. Raman spectra of metamict titanite differ from spectra of well-crystalline titanite, indicating the breakdown of selection rules. Raman scattering reveals that anisotropy is preserved upon metamictization and that the structural state of highly metamict titanite should not be considered as quasi-amorphous. The metamict state partially recovers its disorder via heat treatment. Annealing-induced shrinking of unit c...

Raman spectra of the uranyl titanate mineral betafite were obtained and related to the mineral structure. A comparison is made with the spectra of uranyl oxyhydroxide hydrates. Observed bands are attributed to the (UO2)2+ stretching and bending vibrations, U–OH bending vibrations and H2O and (OH)− stretching, bending and libration modes. U–O bond lengths in uranyls and O−H···O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of betafite are comparable with those of the uranyl oxyhydroxides. The mineral betafite is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and by bands that are significantly broader.

Infrared spectroscopy provides information on structural sites, hydrogen bond lengths, and concentrations of trace amounts of hydrogen in nominally anhydrous minerals. OH defects in olivine are predominately associated with vacant Si and Mg/Fe sites. However, even trace inclusions of hydrous minerals like serpentine and talc have been detected. In pyroxenes OH defects are also most likely associated with cation vacancies. Garnets of the grossular series contain abundant water in the form of (OH)4 "hydrogarnet" defects. Other garnets show a wide variety of additional OH defects that can only scarcely be assigned. MgSiO3 perovskite, a high-pressure phase of the Earth's mantle, contains only minor amounts of OH defects related to Mg vacancies. Well-crystallized zircons contain only trace amounts of OH defects, whereas large amounts of hydrogen (OH and H2O) have been observed in radiation-damaged, metamict zircon. In rutile-type minerals, OH defects compensate for trivalent cations.

Recent applications of infrared and Raman spectroscopy in the study of the metamict (or "amorphized") state, high-temperature recrystallization and radiation-induced OH species in natural zircon (ZrSiO4) and titanite (CaTiSiO5) are reviewed.

Zircons from one orthogneiss, previously dated by conventional U-Pb to 1766±10 Ma, and one sample of migmatite neosome, previously dated to 1734±5 Ma, all from the Eskolabreen Complex of the Ny Friesland Caledonides, Svalbard, have been analysed by the NORDSIM ion microprobe in order to determine the nature of Caledonian overprinting in these zircons, leading to lower intercept ages close to 400 Ma, and the age of migmatization in the neosome sample. Most ion microprobe analyses fall along a discordia with an upper intercept at 1738±15 Ma, interpreted to reflect magmatic crystallization, and a lower intercept at 385±51 Ma, interpreted to reflect Caledonian overprinting. There is a concentration of near-concordant analyses with an average 207Pb/206Pb age of 1733±5 Ma. Discordant ages appear to be caused by Pb loss from the outer parts of zircon crystals, and sometimes from metamict cores, during Caledonian metamorphism. No distinct new zircon rims yielding concordant Caledonian ages were recorded,...

Dehydration of oriented sections of a radiation-damaged titanite crystal, CaTiSiO5, at temperatures up to 1500K was analysed using infrared spectroscopy. The IR spectra of the untreated sample show only a very weak orientational dependence. The absence of sharp absorption peaks at wave number near 3486 cm−1 in metamict titanite shows that the local environmental configurations of OH species in the metamict titanite differ strongly from that of crystalline titanite. The OH spectra of radiation-damaged titanite can be decomposed into two components: the first component shows anisotropic and sharp spectral features while the second component consists of a broad spectral feature like those observed in disordered silica glasses. It is proposed that the first component is related to the crystalline part of the titanite sample while the second is from the defected and disordered part which suffered strong radiation damage. With increasing annealing temperature, a decrease in the broad absorption between...

Specimens of dry cortical bovine bone and bone equivalent ceramic of Ca/P ratio 1.95 were prepared and subjected to two fast neutron fluences of 1.15 × 106 and 1.13 × 108 n/cm2. Radiation damage was assessed by following their surface morphologies (SEM) and their selected area electron diffraction (SAED) patterns of both specimens using the scanning and diffraction electron microscope techniques. The results indicated that fast neutron irradiation induced phase changes from crystalline to quasi-amorphous state. The amorphism observed in the morphological habit proved the metamictization process as complemented by SAED amorphous hallow especially with the higher fluence.

Synthetic single-crystals of zircon [(100) growth surfaces] were implanted at 77K with 540 keV Pb ions with fluences of 3.3 × 1011 to 5 × 1015 ions/cm2 —a dose range that completely spans the crystalline-to-amorphous transition as determined by Rutherford backscattering/ion-channeling measurements. A chemically unzoned, natural crystal [polished (100) section] was similarly implanted. Both the natural and synthetic crystals, as examined by mechanical-properties microprobe (MPM) methods, exhibited an overall radiation-induced softening (70% reduction) and decrease in modulus (42%) through the crystalline-to-amorphous transition. This transition occurs over a narrow range of dose, i.e. 1 × 1013 to 1 × 1014 Pb ions/cm2. Moreover, below the transition, a pronounced radiation-induced hardening occurs in the near-surface region of the synthetic crystals. This radiation hardening may be due to the accumulation of interstitials. In contrast, the natural zircon showed no hardening; however, its initially ...

The effect of fast neutron bombardment (2 Mev 252Cf source) with fluence of 1.07 × 1010 n/cm2 on the linear thermal expansion of Li-β-alumina ceramics was studied. Two ceramic groups in which the contents of oxides of Li, Na, K as well as B increased at the expense of alumina were prepared. Induced defects in terms of X-ray diffraction analysis were discussed to assess the use and applicability of these ceramics in neutron dosimetry. The thermal expansion data indicated that both groups exhibited reduction in the mean thermal expansion coefficient values upon irradiation. This is parallel with the shift in the lattice planes of the group with higher alumina and amorphism in the other one. Annealing of the neutron induced defects at 1000°C denoted that partial recovery in higher aluminous group is detected. Approximately complete recovery in the other group revealed a higher state of metamictization.

Twenty species of metamict (and allegedly metamict) minerals have been investigated using electron microprobe analysis, high-temperature X-ray analysis, differential thermal analysis, and thermogravimetry. The results are combined with relevant data from the literature as an aid for the identification of metamict minerals.

For a natural single crystal of zircon, ZrSiO4, from Sri Lanka, exhibiting zonation in U and Th contents, the hardness and elastic modulus have been determined as a function of α-decay dose using a mechanical properties microprobe (MPM). The zones vary in thickness from one to hundreds of micrometers, and have uranium and thorium concentrations such that the α-decay dose varies between 2 × 1015 and 1 × 1016 α-decay events/mg (0.15 to 0.65 dpa, displacement per atom). The transition from the crystalline to the aperiodic metamict state occurs over this dose range. For a traverse of 75 indent pairs across layers sampling a large portion of the crystalline-to-metamict transition (3.7 × 1015 to 9.7 × 1015 α-decay events/mg) both the hardness and elastic modulus decrease linearly with increasing α-decay dose. The radiation-induced softening follows a behavior similar to other radiation-induced changes, that is with the expansion of the unit cell parameters there is a decrease in density, birefringence,...

The effects of in-situ electron and ion bombardment in quartz are compared. Both types of irradiation readily induce the metamict transformation and, furthermore, do so in linear proportion over the entire range of their combination. The results suggest that the creation of oxygen vacancies is responsible for the metamict transformation in both cases.

Specimens of synthetic monazite, CePO4, were rendered metamict by bombardment with 3 MeV Argon ions at fluences of 4 ions nm−2 or greater. Differential scanning calorimetry (DSC) was applied to the annealing of these specimens over a temperature range 550–720 K. The stored energy is shown to be 7.3±0.3 cal g1, independent of the fiuence from 4 to 10 ion nm−2. The activation energy of annealing of the damage is 2.7 ±0.3 eV and the temperature dependent rate constant is The application of DSC to the study of annealing of radiation damage in materials is discussed briefly. The saturation value of the stored energy with fiuence of 3 MeV Argon ions is compared to the approach to a saturation level observed in some glasses used to store radioactive wastes.

The bombardment using argon ions of energy 3 MeV of several α-quartz isomorphous crystal structures has been carried out. Non-crystalline metamict forms have been obtained in all cases, using relatively low fluence. The metamict damage cross-sections D M obtained are: 3·l±0·3nm2 (GeO2), 2·7 ± 0·3nm2 (FePO4), 1·9 ± 0·4 nm2 (A1PO4), l·0±0·3nm2 (SiO2) and 0·7±0·3nm2 (GaPO4), and these values decrease with increasing melting points. Recrystallization is observed to occur at relatively low temperatures of less than 0·5 T m. These results are in contrast to earlier studies using fast-neutron irradiation, in which non-crystalline forms were obtained only for SiO2. This is probably due to annealing of the neutron damage for materials of lower melting point during the lengthy irradiation at the temperature of the atomic pile.

Metamict damage cross-sections for pollucite, CaAl12O19 and spinel, irradiated with 3 MeV Ar+ ions, are found to be 0.8±0.4, ∼ 10−2 and ∼ 5 × 10−4 nm2 respectively. The results for CaAl12O19 are discussed and compared to neutron-irradiated BeO. Crystal structures with close packing of oxygen ions (CaAl12O19, spinel) have very small damage cross-sections.

Zirconium silicate powder is converted into a range of metamict conditions, and finally to a non-crystalline condition by Argon or Krypton ion bombardment of energies of 1 to 3.5 MeV. The non-crystalline condition is induced by approximately 2 × 1015 ions per cm2. Further irradiation causes the non-crystalline particles to bloat into extended disc shapes. The glassy metamict state creeps under heavy ion irradiation. Under comparable conditions, silicates such as a-quartz bloat into a similar range of glassy shapes, whereas nitrides such as Si3N4 do not. The metamict state is essentially a glass-type random atomic structural arrangement. This formation of extended glassy shapes under ionic bombardment is an alternative method of formation of some of the glassy constituents of chondrules, tektites and lunar agglutinates by cosmic irradiation. The reported sintering under fast neutron irradiation may be explained by the joining of neighboring particles under glassy irradiation creep.

Lithium niobate plates intended for application as sensors for acoustical monitoring of reactors were subjected to thermal-neutron irradiation near room temperature. By 8 x 10$sup 19$n/cm$sup 2$, a crystal had become highly disordered, as shown by the back-reflection Laue picture, by loss of piezoelectric response, and by loss of optical birefringence. This transformation appears to be a metamictization. Changes in optical absorption, tritium loss, postirradiation lithium migration, surface crazing, and effects of postirradiation storage at room temperature and of heating to 140$sup 0$C are also observed. (auth)

Studies of radiation damage in crystalline insulators usually originate from problems connected with heavy ion impact during ion bombardment, from neutron irradiation with and without fission in nuclear reactors, or from α-decay with the resulting damage due to recoil daughter atoms of the decaying nuclei of actinide compounds. The materials involved cover a broad range of compounds, e.g. from BeO to CmO2 for oxides, for which most work has been done. The damage studied ranges from production of isolated Frenkel pairs to complete amorphization of the crystalline compound (metamictization). The available knowledge is discussed. Emphasis is put on simple binary oxides and on ceramic nuclear fuel materials, i.e. oxides, carbides and nitrides of U and Pu. Recent work on irradiated glasses is also briefly discussed since these glasses are considered as promising media for safe storage of radioactive waste for long periods of time.

Powder mixtures are difficult to analyze since they give complex X-ray diffraction patterns where the patterns of the components are superimposed one over the other with very little indication of which diffraction lines belong to which compound. Heavy ion bombardment causes different damage effects to different inorganic crystal structures and this can be used to differentiate complex diffraction patterns. While some compounds retain their crystallinity under heavy ion bombardment, others become non-crystalline depending on their metamict damage cross-sections. The changes in the X-ray diffraction patterns after bombardment can distinguish the separate patterns unambiguously. In most cases, only the intensities of the diffraction peaks change with irradiation, peak widths and peak positions not altering perceptibly. In some cases, the diffraction peaks do change in width and position, though these can also be used in the analysis. Argon(3 MeV)ionsbombardamonolayerofpowderofsize ∼ 5 μm at a fluenc...

The effect of thermal neutron irradiation due to the B10(n, α)Li7 reaction on the elastic wave velocities and the elastic moduli of tourmaline crystals has been studied. Oriented tourmaline samples have been irradiated with thermal neutrons to 7.6 × 1018n/cm2 and the elastic wave velocities determined by ultrasonic measurements. The elastic wave velocities are not affected by thermal neutron irradiation below 8 × 10l7n/cm2, effects starting to appear at approximately 1 × l018n/cm2 with more important decreases of the elastic wave velocities and of the bulk moduli at fluences of 2.9 × 10l8n/cm2 and 4 × 10l8n/cm2. The decrease of the bulk moduli of the irradiated tourmalines is compared with that of metamict zircons. X-ray diffraction of the irradiated specimens indicates that tourmaline remains crystalline up to a thermal neutron fluence of 7.6 × 1018n/cm2.

Two varieties of allanite have been found in the Kallmorberg iron mine. Some optical data and the d-spacings of the specimens are given. Both allanites are completely unaltered and no metamictization has occurred, in spite of their Precambrian age. The content of radioactive elements is low. The rare-earth elements in the skarn rock containing the low-2V allanite have been determined.

The crystalline→noncrystalline (metamict) transformation in α-quartz under electron irradiation has been studied by transmission electron microscopy (TEM), ultra-high resolution structure imaging (SI) and convergent beam electron diffraction (CBD). The transformation is radiolytic and proceeds in two stages: heterogeneous nucleation of discrete disordered inclusions and slower homogeneous loss of long-range order in the surrounding matrix. Irradiations of dry lunar quartz and of heated synthetic quartz suggest that the heterogeneous component is associated with incorporated water impurity. Analysis of the homogeneous component by CBD and SI suggests a transformation model in which progressive disorder evolves from stochastic relaxations of radio-lytically-damaged [SiO4] coordination units.

Recent geological work in South Australia has resulted in the discovery of a wide range of radioactive minerals, some of which are of economic value. Nearly all known groups of radioactive mineral have been found. Those, including both thorium and uranium rich varieties, are restricted to the Pre-Cambrian provinces and mostly to the Archaean. The minerals are discussed on the basis of both field mode of occurrence and chemical composition. Special mention is made of several minerals which are very rare and which, it is believed, are recorded herein for the first time in Australia. Extensive petrological and related mineragraphic investigation, coupled with field geological work during the past few years, has led to the discovery of an important genetic relationship between soda metasomatism and uranium-titanium metallization in South Australia. The reality of the so-called metamict state and of the mineral davidite is discussed and alternative suggestions are made. The inability of the mineralogi...

X-ray analysis of metamict zircon from a granitic pegmatite NE of Stockholm showed the presence of zircon, baddeleyite and possibly α-christobalite, indicating the decay of zircon into oxides. The heated sample consisted mostly of zircon and cubic zirconia. Another zirconoid from the Ilmen mountains also contained baddeleyite. A summary about the X-ray interferences of zirconoids and a short sketh of the process of metamictization is given.

Mineralogical studies of zircon sand from Kerala beach revealed that about 97% of the grains were unaltered, but they appeared to have a lower degree of crystallinity. About 2% of the grains were found to be partly metamicted. Huttonite (ThSiO4) was found as one of the impurities responsible for the radio activity of the sample.Calcination improved the crystallinity and colour of zircon grains, making them more suitable for use as opacifiers in porcelain glazes. The behaviour of raw and calcined zircon in various types of glazes have been explained.

A literature survey regarding zircon has been carried out covering the period upto 1970. The material is organized into several chapters dealing with occurrence and beneficiation, crystal structure and morphology, the binary system ZrO2-SiO2, synthesis and dissociation of zircon with and without added impurities, thermal properties, metamictization, uses for refractory, glass, enamel, glaze, pigment, porcelain, paint, foundry and other purposes, and ternary systems in which the binary system ZrO2-SiO2 is a part.

Non metamict Ce, La-allanite has been found in quartzo-feldspathic hornfelses at Paritu. Optical properties and an electron microprobe analysis are given.