Insight Into Disorder, Stress and Strain of Radiation Damaged Pyrochlores: A Possible Mechanism for the Appearance of Defect Fluorite.

We have examined the irradiation response of a titanate and zirconate pyrochlore-both of which are well studied in the literature individually-in an attempt to define the appearance of defect fluorite in zirconate pyrochlores. To our knowledge this study is unique in that it attempts to discover the mechanism of formation by a comparison of the different systems exposed to the same conditions and then examined a range of techniques that cover a wide length scale. The conditions of approximately 1 displacement per atom He ions were used to simulate long term waste storage conditions as outlined by previous results from Ewing in a large enough sample volume to allow for neutron diffraction, as not attempted previously.

Synthesis and Structure of Oxygen Deficient Lead-Technetium Pyrochlore, the First Example of a Valence V Technetium Oxide.

The structure of lead-technetium pyrochlore has been refined in space group with = 10.36584(2) Å using a combination of synchrotron X-ray and neutron powder diffraction data and confirmed via Electron Diffraction. The oxide is found to be oxygen deficient with a stoichiometry of PbTcO.

Modelling of reusable target materials for the production of fission produced Mo using MCNP6.2 and CINDER90.

Current fission-based methods of Mo production require single use uranium targets which leads to spent uranium waste. This waste could be reduced if a target is developed that does not require dissolution so that it can be reused for multiple production runs. MCNP6.

Structures and Phase Transitions in Pertechnetates.

The temperature dependence of the structures of four pertechnetates (TcO = Ag, Tl, Rb, Cs) from 90 K to their melting points is described. Synchrotron X-ray diffraction measurements show that RbTcO undergoes a 4/ to 4/ transition near 530 K that is associated with a change in the orientation of the TcO tetrahedra about the scheelite axis. AgTcO also exhibits a tetragonal scheelite type structure, and this is retained between 90 and 750 K, above which it melted.

Development of LEU-based targets for radiopharmaceutical manufacturing: A review.

Mo is an essential medical isotope that comprises of at least 70% of radioactive procedures globally. Currently an essential component of Mo manufacturing is the uranium target from which Mo is produced by fission. As the world moves towards low enriched uranium (LEU) targets due to non-proliferation concerns it is becoming of interest to find methods to increase the efficiency of the LEU targets in order to reduce the ever increasing nuclear waste levels of which a long term solution for disposal or treatment has yet to be satisfactorily found.

The Quantification of Radiation Damage in Orthophosphates Using Confocal μ-Luminescence Spectroscopy of Nd.

In this study, we present a new concept based on the steady-state, laser-induced photoluminescence of Nd, which aims at a direct determination of the amorphous fraction in monazite- and xenotime-type orthophosphates on a micrometer scale. Polycrystalline, cold-pressed, sintered LaPO, and YPO ceramics were exposed to quadruple Au-ion irradiation with ion energies 35 MeV (50% of the respective total fluence), 22 MeV (21%), 14 MeV (16%), and 7 MeV (13%). Total irradiation fluences were varied in the range 1.

Comparing results of X-ray diffraction, µ-Raman spectroscopy and neutron diffraction when identifying chemical phases in seized nuclear material, during a comparative nuclear forensics exercise.

This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear forensic round-robin exercise. In this work powder X-ray diffraction (p-XRD) is regarded as the reference technique. Neutron diffraction produced a superior high-angle diffraction pattern relative to p-XRD.

The Effect of Milling Time on the Microstructural Characteristics and Strengthening Mechanisms of NiMo-SiC Alloys Prepared via Powder Metallurgy.

A new generation of alloys, which rely on a combination of various strengthening mechanisms, has been developed for application in molten salt nuclear reactors. In the current study, a battery of dispersion and precipitation-strengthened (DPS) NiMo-based alloys containing varying amounts of SiC (0.5-2.

Thermal Expansion Behavior in TcO. Toward Breaking the Tc-Tc Bond.

The structure of TcO between 25 and 1000 °C has been determined in situ using X-ray powder diffraction methods and is found to remain monoclinic in space group P2/c. Thermal expansion in TcO is highly anisotropic, with negative thermal expansion of the b axis observed above 700 °C. This is the result of an anomalous expansion along the a axis that is a consequence of weakening of the Tc-Tc bonds.

Intricate disorder in defect fluorite/pyrochlore: a concord of chemistry and crystallography.

Intuitively scientists accept that order can emerge from disorder and a significant amount of effort has been devoted over many years to demonstrate this. In metallic alloys and oxides, disorder at the atomic scale is the result of occupation at equivalent atomic positions by different atoms which leads to the material exhibiting a fully random or modulated scattering pattern. This arrangement has a substantial influence on the material's properties, for example ionic conductivity.

The role of π-bonding on the high temperature structure of the double perovskites Ba2CaUO6 and BaSrCaUO6.

The high temperature structural behaviour of the uranium perovskites Ba2CaUO6 and BaSrCaUO6 has been investigated using a combination of synchrotron X-ray and neutron powder diffraction. Ba2CaUO6 undergoes a complex sequence of structures associated with the progressive loss of cooperative octahedral tilting: P21/n → I2/m → I2/m → I4/m → Fm3[combining macron]m. The observation of the intermediate tetragonal structure, I4/m, in this, contrasts with the previously reported rhombohedral R3[combining macron] intermediate formed by the Ba2SrUO6 oxide.

An unconventional method for measuring the Tc L3-edge of technetium compounds.

Tc L3-edge XANES spectra have been collected on powder samples of SrTcO3 (octahedral Tc(4+)) and NH4TcO4 (tetrahedral Tc(7+)) immobilized in an epoxy resin. Features in the Tc L3-edge XANES spectra are compared with the pre-edge feature of the Tc K-edge as well as other 4d transition metal L3-edges. Evidence of crystal field splitting is obvious in the Tc L3-edge, which is sensitive to the coordination number and oxidation state of the Tc cation.

Novel rattling of K atoms in aluminium-doped defect pyrochlore tungstate.

Rattling dynamics have been identified as fundamental to superconductivity in defect pyrochlore osmates and aluminium vanadium intermetallics, as well as low thermal conductivity in clathrates and filled skutterudites. Combining inelastic neutron scattering (INS) measurements and ab initio molecular dynamics (MD) simulations, we use a new approach to investigate rattling in the Al-doped defect pyrochlore tungstates: AAl0.33W1.

The Effect of a Rapid Heating Rate, Mechanical Vibration and Surfactant Chemistry on the Structure-Property Relationships of Epoxy/Clay Nanocomposites.

The role of processing conditions and intercalant chemistry in montmorillonite clays on the dispersion, morphology and mechanical properties of two epoxy/clay nanocomposite systems was investigated in this paper. This work highlights the importance of employing complementary techniques (X-ray diffraction, small angle X-ray scattering, optical microscopy and transmission electron microscopy) to correlate nanomorphology to macroscale properties. Materials were prepared using an out of autoclave manufacturing process equipped to generate rapid heating rates and mechanical vibration.

Electroacoustic isoelectric point determinations of bauxite refinery residues: different neutralization techniques and minor mineral effects.

Bauxite refinery residue (BRR) is a highly caustic, iron hydroxide-rich byproduct from alumina production. Some chemical treatments of BRR reduce soluble alkalinity and lower residue pH (to values <10) and generate a modified BRR (MBRR). MBRR has excellent acid neutralizing (ANC) and trace-metal adsorption capacities, making it particularly useful in environmental remediation.

Formation and stability of Pb-, Zn- & Cu-PO₄ phases at low temperatures: implications for heavy metal fixation in polar environments.

Low temperatures and frequent soil freeze-thaw in polar environments present challenges for the immobilisation of metals. To address these challenges we investigated the chemical forms of Pb, Zn and Cu in an Antarctic landfill, examined in vitro reaction kinetics of these metals and orthophosphate at 2 and 22 °C for up to 185 days, and subjected the products to freeze-thaw. Reaction products at both temperatures were similar, but the rate of production varied, with Cu-PO(4) phases forming faster, and the Zn- and Pb-PO(4) phases slower at 2 °C.

Structure and cation ordering in spinel-type TcCo2O4. An example of a trivalent technetium oxide.

The structure of TcCo(2)O(4) has been determined using a combination of synchrotron X-ray and neutron powder diffraction methods. It has an inverse spinel structure where the Tc occupies the octahedral sites. Both the refined Tc-O distance and X-ray absorption spectra suggest the Tc is predominantly trivalent.

Structural phase transitions and magnetic order in SrTcO3.

The structure of the perovskite SrTcO(3) has been investigated using both synchrotron X-ray and neutron powder diffraction. At room temperature SrTcO(3) is orthorhombic as a consequence of cooperative tilting of the corner sharing TcO(6) octahedra. The tilts are sequentially removed as the sample is heated with the oxide displaying the sequence of structres Pnma→Imma→I4/mcm→Pm ̅3m.

High temperature magnetic ordering in the 4d perovskite SrTcO3.

We present evidence for possibly the highest magnetic ordering temperature in any compound without 3d transition elements. Neutron powder diffraction measurements, at both time-of-flight and constant wavelength sources, were performed on two independently prepared SrTcO3 powders. SrTcO3 adopts a distorted perovskite structure with G-type antiferromagnetic ordering and has a moment of 1.

Antiferromagnetism in a technetium oxide. Structure of CaTcO3.

The technetium perovskite CaTcO(3) has been synthesized. Combining synchrotron X-ray and neutron diffraction, we found that CaTcO(3) is an antiferromagnetic with a surprisingly high Neel temperature of ∼800 K. The transition to the magnetic state does not involve a structural change, but there is obvious magnetostriction.

Microcrystalline hexagonal tungsten bronze. 1. Basis of ion exchange selectivity for cesium and strontium.

The structural basis of selectivity for cesium and strontium of microcrystalline hexagonal tungsten bronze (HTB) phase Na(x)WO(3+x/2).zH(2)O has been studied using X-ray and neutron diffraction techniques, 1D and 2D (23)Na magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and radiochemical ion exchange investigations. For the HTB system, this study has shown that scattering techniques alone provide an incomplete description of the disorder and rapid exchange of water (with tunnel cations) occurring in this system.