Radiation-induced changes in electrical conductivity and structure of BaPbO3 after γ-irradiation

Several barium plumbate (BaPbO₃) solid samples, made from PbO and BaCO₃ powder by chemistry liquid-phase coprecipitation, were investigated before and after γ-irradiation. The solid samples were irradiated by a ⁶⁰Co γ-irradiation source whose dose rate is about 0.7?kGy per hour. The irradiation times were 0, 72, 144, 216, 288 and 360?h. Then, the four-probe method, X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to indicate the changes in electrical conductivity and microstructure of BaPbO₃ after γ-irradiation. The XRD results indicated that the content of PbO was reduced as the irradiation dose was increased and eventually vanished from the surface of samples. However, there was no new obvious substance phase found from the XRD atlas. It seems that the PbO transformed into nearly amorphous Pb₅O₈. The conjecture could be proved by the results of annealing experiment and SEM. The XPS results seem to show that the microstructure of BaPbO₃ was slightly changed.     

Afterglow in bulk AlN single crystals under β-irradiation

Regularities of afterglow at room temperature and of thermoluminescence at further heating up to 673 K have been studied in bulk aluminum nitride single crystals. It has been established that after exposure to β-irradiation luminescence decay at RT may be described by superposition of two exponential components: fast (59 s) and slow (606 s) ones, caused by defects of the anion crystal sublattice O_N- and V_N-centers, respectively. The afterglow spectrum is shown to be characterized by the 3.43 eV band with FWHM=0.61 eV that dominates also in the thermoluminescence under study. From analysis of the TL curves in terms of the general order formalism it has been concluded that variation of the activation energy observed within the 0.46–0.85 eV range with increasing storage of the samples from 5 min to 3 days may be caused by energy distribution of traps on the basis of oxygen-related centers. For the first time the compensation effect has been found, and phenomenologically interpreted for the TL processes of the AlN single crystals. Isokinetic temperature has been estimated within the framework of empiric and non-empiric relations.     

Thermal expansion anisotropy of β-TlInS2 crystals in the course of phase transitions

Basing on the thermal expansion studies performed for β-TlInS₂ crystals in the course of their phase transitions, we have found that the crystals aged for one year are composed from at least two polytypes, which undergo phase transitions at different temperatures. The detailed analysis of anisotropy of the thermal expansion demonstrates that all of the diagonal components of the thermal expansion tensor associated with the eigensystem have almost the same modules but differ by their signs. This leads to appearance of an elliptical conical surface of zero thermal expansion. The orientation of this surface does not depend on the temperature in the temperature interval under study. We have also found that the thermal expansion coefficients along the crystallographic a and b axes are close to zero.     

Formation of optical color and fluorescence centers in polytetrafluoroethylene under γ-irradiation

Fluorescent properties and colors of polytetrafluoroethylene (PTFE) samples were studied as functions of absorbed dose of γ-radiation at a temperature above the melting temperature of the crystallites (327°C) in the dose range 0.2–0.8 MGy. The samples were irradiated at low pressure (10^–6 Torr) in glass ampuls and at atmospheric pressure in a chamber purged with argon. Samples in ampuls acquired an off-white tint and fluoresced weakly. The fluorescence intensity increased slowly as the radiation dose increased from 0.2 to 0.6 MGy and decreased at 0.8 MGy. Samples irradiated in the chamber fluoresced more strongly and acquired colors that changed from gray (0.2 MGy) to dark-brown (0.8 MGy). Color centers were formed only in the sample surface layer. Their appearance was associated with the adsorption of particles of an unknown nature from the environment. The argon-purged samples turned white upon removing their surface layer (50 μm). The intensity and shape of fluorescence bands emitted by these samples remained essentially unaltered, i.e., depended weakly on the absorbed dose in the range 0.2–0.8 MGy.     

Formation of β-iPP in Isotactic Polypropylene/Acrylonitrile–Butadiene–Styrene Blends: Effect of Resin Type,Phase Composition,and Thermal Condition

The formation of β-iPP (β-modification of isotactic polypropylene) in the iPP/ABS (acrylonitrile–butadiene–styrene), iPP/styrene–butadiene (K resin), and iPP/styrene–acrylonitrile (SAN) blends were studied using differential scanning calorimery (DSC), wide angle X-ray diffraction (WAXD), and scanning electron microscopy (SEM). It was found that α-iPP (α-modification of isotactic polypropylene) and β-iPP can simultaneously form in the iPP/ABS blend, whereas only α-iPP exists in the iPP/K resin and iPP/SAN blend samples. The effects of phase composition and thermal conditions on the β-iPP formation in the iPP/ABS blends were also investigated. The results showed that when the ABS content was low, the ABS dispersed phase distributed in the iPP continuous phase, facilitating the growth of β-iPP, and the maximum amount of β-iPP occurred when the composition of iPP/ABS blend approached 80:20 by weight. Furthermore, it was found that the iPP/ABS blend showed an upper critical temperature T _c * at 130°C for the formation of β-iPP. When the crystallization temperature was higher than the T _c *, the β-iPP did not form. Interestingly, the iPP/ABS blend did not demonstrate the lower critical temperature T _c ** previously reported for pure iPP and its blends. Even if the crystallization temperature decreased to 90°C, there was still β-iPP generation, indicating that ABS has a strong ability to induce the β-iPP. However, the annealing experiments results revealed that annealing in the melt state could eliminate the susceptibility to β-crystallization of iPP.     

Hierarchical Distribution of β-Phase in Compression- and Injection-Molded,Polypropylene-Based TPV

The distribution of the β-phase crystals of polypropylene (PP) in different zones of compression and injection moldings molded from PP-based dynamically vulcanized thermoplastic elastomer (TPV) in the presence of a β-nucleating agent (β-NA) was investigated. The influence of shear and cooling conditions and the addition of β-NA on the development of β-phase was examined and discussed based on the one-dimensional heat conduction behaviors with phase change. A hierarchical distribution of β-phase was observed in both compression- and injection-molded TPV/β-NA specimens. For the compression-molded TPV/β-NA specimens, the hierarchical distribution of β-phase induced by β-NA is dominated by the cooling conditions. For the injection-molded TPV/β-NA specimens, the occurrence of β-phase is also mainly induced by the addition of β-NA; the effect of shear on the relative content of β-phase can hardly be observed and the cooling conditions control the hierarchical distribution of β-phase. Both in compression and injection-molded TPV/β-NA specimens, the relative content of β-phase increases from the skin to the core zones, owing to the cooling rate decreasing from the skin to the core zones.     

Phonon density of states in γ-, β-, and α-AgCuS

The ternary superionic conductor AgCuS was studied by means of inelastic neutron scattering at temperatures of 150 to 398 K. The experimental time-of-flight spectra were recalculated into the generalized phonon density of states G(ɛ) in an incoherent approximation. It is shown that G(ɛ) of AgCuS has a nontrivial temperature dependence over the low-energy range. The relation between the temperature dependence of G(ɛ) and the existence of a low-energy mode in AgCuS is discussed. The text was submitted by the authors in English.     

Investigation of thermoluminescence in Li_2B_4O_7 phosphors doped with Cu, Ag and Mg

Li_2B_4O_7 (LBO):Cu,Ag,Mg phosphors have been prepared by the sintering technique. The roles of the Ag and Mg dopants in the phosphors have been studied using the methods of thermoluminescence (TL) glow curves and TL 3D spectra. The results indicated that proper concentrations of Ag and Mg can enhance the TL of LBO:Cu. It was also indicated that the intensity of TL peak at ~130℃ is reduced with the in- creasing Ag concentration, and enhanced with the increasing Mg concentration. From the TL 3D spectra, three emission bands (λ1 = 421 nm, λ2 = 380 nm, λ3 = 350 nm) were observed: the intensity of low energy emission band is reduced and that of the high energy is enhanced with the increasing dopant Ag; on the contrary, the intensity of low energy emission band is enhanced and that of the high energy one is reduced with the increasing dopant Mg.     

Thermal annealing of Stone–Wales defects in fullerenes and nanotubes

Physics of the Solid State - The thermally activated annealing of topological Stone–Wales defects in carbon fullerenes and nanotubes is studied via molecular dynamics. The temperature...     

Microstructure and Phase Composition of Rhenium and Ruthenium-Alloyed Ni–Al–Co System after Thermal Treatment

Russian Physics Journal - The paper presents the transmission electron microscopy investigations of the microstructure and phase composition of the nickel-based superalloy after high temperature...     

Hyperfine interactions of polarized β-emitting12B and12N in Si,Ge, and GaP

Using a nuclear reaction, the polarized short-lived -emitters¹²B and¹²N were implanted into Si, Ge, and GaP crystals. Hyperfine fields were studied via both NMR techniques and an external magnetic holding field H_ext on-off techniques in an H_ext range 0–8 kG and a temperature range 100–1000 K. No significant NMR signal was observed between 2 and 30 MHz for¹²N in Si and Ge despite maintenance of 60% polarization at T100 K and H_ext>4 kG, whereas for¹²B in Si at T>800 K almost full polarization was found at the Larmor frequency.     

Development of β-NMR and β-NQR

The β-NMR (nuclear magnetic resonance) and β-NQR (nuclear quadrupole resonance) technique and its ex-perimental set-up have been developed for the first time in China. The lifetime, magnetic moment and spin polarization of ^12B were determ/ned. The experimental results show the reliability of this newly developed β-NMR and β-NQR set-up.     

Effects of Thermal Treatments on Helium Retention and Thermal Desorption Behaviors in a V-4Ti Aalloy

Vanadium alloys are considered as the promising first wall and structure materials of the future fusion reactors owing to their perfect low neutron-induced radioactivity and good high temperature performance. Helium retention and thermal desorption behaviors are key issues for the applications of vanadium alloys in fusion reactors since helium can be produced by helium discharge cleaning and neutron transmutation. A. van Veen groupt investigated helium trapping and thermal desorption mechanisms in vanadium alloys by using 1 keV helium ion irradiation to the fluence of 10^13～10^14He/cm^2, and the influenee of pre-annealing treatments on helium trapping. Two group of peaks were found at the thermal helium desorption spectrum. They thought one was due to helium-vacancyimpurity clusters and the other was corresponding to helium trapping into pre-existing traps, such as fine-size precipitates.     

Model of grain-boundary self-diffusion in α- and β-phases of titanium and zirconium

A model of the grain-boundary self-diffusion process in metals undergoing phase transitions in the solid state is proposed. The model is based on the ideas and approaches of the theory of nonequilibrium grain boundaries. It is shown that the range of application of basic relations of this theory can be extended, and they can be used to calculate the parameters of grain-boundary self-diffusion in high-temperature and low-temperature phases of metals with phase transition. Based on the constructed model, activation energies of grainboundary self-diffusion in titanium and zirconium are calculated, and their anomalously low values in the low-temperature phase are explained. The calculated activation energies of grain-boundary self-diffusion are in good agreement with experimental data.     

Infrared luminescence, thermoluminescence and defect centres in Er and Yb co-doped ZnAl2O4 phosphor

Er and Yb co-doped ZnAl₂O₄ phosphors were prepared by solution combustion synthesis and the identification of Er and Yb were done by energy-dispersive X-ray analysis (EDX) studies. A luminescence at 1.5 μm, due to the ⁴I_13/2 →⁴I_15/2 transition, has been studied in the NIR region in Er and Yb co-doped ZnAl₂O₄ phosphors upon 980 nm CW pumping. Er-doped ZnAl₂O₄ exhibits two thermally stimulated luminescence (TSL) peaks around 174°C and 483°C, while Yb co-doped ZnAl₂O₄ exhibits TSL peaks around 170°C and 423°C. Electron spin resonance (ESR) studies were carried out to identify defect centres responsible for TSL peaks observed in the phosphors. Room temperature ESR spectrum appears to be a superposition of two distinct centres. These centres are assigned to an O⁻ ion and F⁺ centre. O⁻ ion appears to correlate with the 174°C TSL peak and F⁺ centre appears to relate with the high temperature TSL peak at 483°C in ZnAl₂O₄:Er phosphor.     

Spectrofluorimetric Study and Detection of Ketoconazole in the Presence of β-cyclodextrin

The formation of a complex between ketoconazole and β-cyclodextrin was followed by spectrofluorimety. The inclusion of ketoconazole in β-cyclodextrin cavity enhanced the native fluorescence of the drug. The stoichiometry of the complex was 1:1 β-cyclodextrin to ketoconazole and the stability constant of the complex (log K _f) was determined to be 4.3 ± 0.01 at pH = 7.9 and 3.7 ± 0.04 at pH = 2.6. A sensitive spectrofluorimetric method for the detection of ketoconazole is presented. At optimized experimental conditions, a linear relationship between the fluorescence intensity of the solution and concentration of ketoconazole is observed in the range of 0.01–10 μg ml⁻¹ (5 × 10⁻⁸ M–1.88 × 10⁻⁵ M). The method was applied to the detection of ketoconazole in pharmaceutical products and the results were satisfactory in comparison to the official method (relative error = 2.8% and standard deviation = 0.06 for tablets of ketoconazole). The recovery of ketoconazole from a blood serum sample, determined by the proposed method, was 97.1 ± 2.4%.