[en] Radiation damage of CaF₂, SrF₂ and BaF₂ crystals after thermal treatments in air at high temperatures (above 700⁰C) has been studied and compared with that of as grown samples. An enhancement of the Vsub(k)-centres' production efficiency was found in the three compounds under (LNT) liquid nitrogen temperature X-irradiation. Interstitial atomic hydrogen (H⁰sub(i)) and OH^--interstitial fluorine complexes were also found in SrF₂ and BaF₂ but not in CaF₂ irradiated at LNT. Room temperature (RT) irradiation produces H⁰sub(i) in CaF₂ and H⁰sub(i), OH^--interstitial complexes and substitutional hydrogen ions (H^-sub(s)) in SrF₂ and BaF₂. A different behaviour of the electron spin resonance signal of the H⁰sub(i) centres created at RT and LNT was observed at increased microwave power. (author)

[en] The thermoluminescence (TL) and the thermally stimulated currents (TSC) induced in Al₂O₃ single crystals by X-irradiation at 80 K were studied. Glow peaks at 100 (I), 220 (II), 255 (III) and 275 (IV) K were observed. TSC peaks corresponding to glow peaks I, III and IV have also been obtained. No current peak at 220 (II) K was detected. Glow peaks I, III and IV exhibit common emission bands at 305, 420 and 705 mm, while a predominant band at 285 nm and a small one peaked at 705 nm appear in the emission spectrum of peak II. Optical absorption and photostimulated TL measurements were also made. From these results the ascription of TL processes to hole traps is discussed. (author)

[en] The crystal structure of Ba₂U₂O₇ has been determined by X-ray and neutron diffraction. The structure is of the weberite-type (Na₂MgAlF₇) with uranium in octahedral co-ordination. A discussion of the thermal stability of Ba₂U₂O₇ and its relationship with the other barium uranate phases, is given. (author)

[en] The standard kinetic equations for modeling homogeneous nucleation contain an inconsistency because the terms representing agglomeration are valid only for random distributions of particles, while the building up and breaking down of clusters upsets this randomness. During the nucleation stage proper, agglomeration has only minimal impact on the presumed random distribution of particles. Thus, for low-density sytems in the nucleation regime, this inconsistency may be corrected by replacing the atomistically-based dissociation rate constants with net dissociation rates. A Monte Carlo simulation of cluster break-up in a face-centered-cubic metal has been used to estimate these net rates to be some 30% of the atomistic dissociation rates. Numerical integration of the governing rate equations with and without corrections for correlation indicates that correlation effects increase steady state cluster concentrations, and the nucleation rate, by about an order of magnitude. (author)

[en] We have calculated the phonon dispersion relations of the A15 compound Nb₃Sb using an angular force model approach, the analysis being restricted to third neighbour interactions only. The force constants have been evaluated by fitting them to the measured values of phonons at the zone centre. Good agreement has been observed between theory and the available experimental results. It has been inferred that the angular forces are not of significant importance between different atoms (Nb-Sb). The physical aspects for the same are discussed. (author)

[en] Hafnia, HfO₂, has been studied to 20 GPa at ambient temperature using synchrotron energy-dispersive X-ray powder diffraction methods. Traces of the initial monoclinic (baddeleyite) phase could still be identified at 20 GPa, but a phase transition begins at 2.6 GPa to HfO₂ II, the lines of which can be indexed on an orthorhombic cell (pbcm, Z = 4). The relative intensities of the (111) and (-111) monoclinic reflections suggests that a further phase change may begin near 10 GPa but work at high temperatures is needed to establish this. The bulk compressibility of hafnia is 1.2 x 10^-4 kbar^-1. A Rietveld analysis of the baddeleyite phase gave results in close agreement with earlier work but showed the sample to be internally strained. (author)

[en] The dynamics of a hydrogen atom confined to a pair of sites and interacting with a heat bath is considered using a stochastic Liouville equation (SLE). A modification of the standard degenerate-pair SLE is introduced to accommodate a non-degeneracy in the site energies, as is believed to occur in NbOsub(x)Hsub(y). Neutron scattering lineshapes are obtained explicitly, based on the modified SLE. A non-degeneracy in in the site energies is shown to result in a coexistence of lineshape structures which may be associated with coherent and incoherent transport mechanisms. It is pointed out how this structure, which is characteristic of non-degenerate systems, may appear as a consequence of strong coupling of the hydrogen motion to phonons, even in impurity systems for which the electronic site states are nominally degenerate. (author)

[en] Using an instantaneous-terminal-voltage (ITV) measurement technique, the variation of the oxide field in an MOS capacitor irradiated by X-rays without bias is examined. It is shown that the oxide field during irradiation depends on the device leakage resistance which can be estimated by the newly reported charge-then-decay method, and the flat-band voltage shift due to irradiation is consistent with the field so found, Interestingly, it is found that the device leakage resistance during irradiation for an MOS(p) capacitor is generally smaller than that for an MOS(n) capacitor. The different radiation sensitivities between an MOS(p) and an MOS(n) capacitor should account primarily for the dopant-dependent oxide resistances found in this work instead of the initial work function differences alone. An equivalent circuit is given to describe the dependence of the oxide field during irradiation on the device resistance, and to explain the observations. (author)

[en] Polycrystalline lithium-ammonium sulphate samples were subjected to X-ray diffraction analysis to determine the lattice parameters of the mixed crystals. The compositions of the samples were determined using X-ray microanalysis. The Li_0.5(NH₄)_0.5SO₄ samples were irradiated with different doses of γ-radiation in order to investigate the effect of this ionizing radiation on the phase transition temperatures T_c1 and T_c2. The temperature dependence of the d.c. resistivity, ρ_d.c., and dielectric constant, ε, of the irradiated samples showed (i) a shift of T _c1 to higher temperatures; (ii) a shift of T_c2 to lower temperatures; and (iii) the appearance of a new anomaly near 128⁰C at moderately high γ-doses. The mechanisms giving rise to this behaviour are discussed. (author)

[en] It is widely assumed that the fission gases and the volatile fission products play little or no role in influencing the chemical state of irradiated UO2sub(2+x). We show this to be incorrect when even a small quantity of these fission products is retained within the fuel grains. Prior to intragranular release most of the gases and volatiles occupy neutral trivacancy sites in the host lattice. However, these complexes can bind oxygen to be converted into fission product atoms residing in cation vacancies or (cation + one anion) vacancy complexes, and this results in reduction of the oxide. Here we analyse this behavior and its effect on the oxygen potential and cation volume self-diffusion coefficient. (author)