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The high-pressure structural behaviour of a series of binary thorium compounds Th X ( X = C, N, P, As, Sb, Bi, S, Se, Te) is studied using the all-electron full potential linear muffin-tin orbital (FP-LMTO) method within the generalized gradient approximation (GGA) for the exchange and correlation potential. The calculated equlibrium lattice parameters and bulk moduli, as well as the equations of state agree well with experimental results. New experiments are reported for ThBi and ThN. Calculations are performed for the Th X compounds in the NaCl- and CsCl-type crystal structures, and structural phase transitions from NaCl to CsCl are found in ThP, ThAs, ThSb and ThSe at pressures of 26.1, 22.1, 8.1 and 23.2 GPa, respectively, in excellent agreement with experimental results. ThC, ThN and ThS are found to be stable in the NaCl structure, and ThBi and ThTe in the CsCl structure, for pressures below 50 GPa. The electronic structures of the Th X compounds are studied using the quasiparticle self-consistent GW method ( G: Green function, W: dynamically screened interaction). [ABSTRACT FROM AUTHOR]

Abstract: In this work, multilayered perceptron neural networks (MLPNNs) were presented for the computation of the gamma-ray energy absorption buildup factors (B A ) of seven thermoluminescent dosimetric (TLD) materials [LiF, BeO, Na2B4O7, CaSO4, Li2B4O7, KMgF3, Ca3(PO4)2] in the energy region 0.015–15MeV, and for penetration depths up to 10 mfp (mean-free-path). The MLPNNs have been trained by a Levenberg–Marquardt learning algorithm. The developed model is in 99% agreement with the ANSI/ANS-6.4.3 standard data set. Furthermore, the model is fast and does not require tremendous computational efforts. The estimated B A data for TLD materials have been given with penetration depth and incident photon energy as comparative to the results of the interpolation method using the Geometrical Progression (G-P) fitting formula. [Copyright &y& Elsevier]

Abstract: Using the theory of solvatochromism, the difference in the excited-state (μ e) and ground-state (μ g) dipole moments was determined from Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet, and McRae equations for three 1,2-diazines (pyrrolo-pyridazine derivatives). All of these equations are based on the variation of Stokes shift with solvent's relative permittivity and refractive index. Further, the change in dipole moment value (Δμ) was also calculated using the variation of Stokes shift with the molecular-microscopic empirical solvent polarity parameter. Theoretical μ g values were evaluated by quantum chemical calculations using the DFT method by adopting B3LYP/6-31G* level of theory (Gaussian 03) and using the AM1 method (Chem3D Ultra 8.0). It was observed that, dipole moments of diazines in the excited-state (μ e) were greater than the corresponding ground-state values (μ g), indicating a substantial redistribution of the π-electron densities in a more polar excited-state. Also, with the increase in the polarity of the solvent, the fluorescence emission peak undergoes a red-shift, confirming a π → π* transition. [Copyright &y& Elsevier]

High-pressure powder x-ray diffraction experiments using synchrotron radiation are performed on the yttrium monochalcogenides YS, YSe, and YTe up to a maximum pressure of 23 GPa. The ambient NaCl structure is stable throughout the pressure range covered. The bulk moduli are determined to be 93, 82, and 67 GPa for YS, YSe, and YTe, respectively. First-principles total energy calculations are carried out using the full-potential linear muffin-tin orbital method. The calculated and measured lattice constants and bulk moduli are in good agrement. Under applied pressure, the yttrium monochalcogenides are predicted to undergo a structural transition. Assuming that the high-pressure phase corresponds to the CsCl crystal structure, transition pressures of 53, 36, and 14 GPa are found for YS, YSe, and YTe, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The effective atomic number, Z eff, has been calculated for fatty acids and cysteine. It is shown that Z eff is a useful parameter for low-Z materials at any energy above 1keV. Absorption edges of medium-Z elements may complicate the energy dependence of Z eff below 10keV. The notion of Z eff is perhaps most useful at energies where Compton scattering is dominating, and where Z eff is equal to the mean atomic number, 〈Z〉, over a wide energy range around 1MeV. [Copyright &y& Elsevier]

Abstract: A comprehensive and consistent set of formulas is given for calculating the effective atomic number and electron density for all types of materials and for all photon energies greater than 1keV. The formulas are derived from first principles using photon interaction cross sections of the constituent atoms. The theory is illustrated by calculations and experiments for molecules of medical and biological interest, glasses for radiation shielding, alloys, minerals and liquids. [Copyright &y& Elsevier]

Abstract: The high-pressure, high-temperature structural behaviour of Cd3P2 has been studied using electrical resistance measurements, differential thermal analysis, thermo baric analysis and X-ray diffraction. At room temperature, a phase transformation is observed at 4.0GPa in compression. The experimental zero-pressure bulk modulus of the low-pressure phase is 64.7(7)GPa, which agrees quite well with the calculated value of 66.3GPa using the tight-binding linear muffin-tin orbital method within the local density approximation. Tentatively, the high-pressure phase has an orthorhombic crystal structure with space group Pmmn (#59). The relative volume change at the phase transition is ΔV/V =−5.5%. Amorphization of the sample occurs above 25GPa. A P–T phase diagram of Cd3P2 has been constructed. A metastable phase is observed at ambient conditions after heating the sample to above 600K at about 3GPa. A hexagonal unit cell can describe the crystal structure of the metastable phase. [Copyright &y& Elsevier]

Abstract: Microstructure and crystallization of a Cu50Zr45Al5 metallic glass have been investigated by differential scanning calorimetry, X-ray diffraction and extended X-ray absorption fine structure (EXAFS) using synchrotron radiation. The width of the supercooled region is ΔT x = T x − T g =67K, where T x and T g are the crystallization and the glass transition temperature, respectively; the reduced glass transition temperature is T rg = T g/T l =0.65, where T l is the liquid temperature; and γ = T x/(T g + T l)=0.41. After crystallization of the as-prepared Cu50Zr45Al5 metallic glass, crystalline phases are identified as tetragonal CuZr2 and orthorhombic Cu10Zr7. The local atomic structures deduced from EXAFS reveal that Zr atoms in the as-prepared Cu50Zr45Al5 metallic glass are surrounded by about 5 Cu atoms at a distance of 2.70Å and about 5 Zr atoms at 3.14Å. [Copyright &y& Elsevier]

Abstract: Effects of gamma-ray irradiation on some optical properties of xZnO·2xPbO·(1–3x)B2O3 glasses have been studied in the wavelength range 300–800nm. Decrease in transmittance indicates the formation of color-center defects. Values for the energy-band gap, the width of the energy tail above the mobility gap and the cut-off wavelength have been measured before and after irradiation. Changes in the optical properties are explained in terms of radiation-induced structural defects and the composition of the glass. [Copyright &y& Elsevier]

The structure of ReO3 has been studied over the pressure range from 1.27 to 8.01 GPa by neutron powder time-of-flight diffraction as well as by X-ray diffraction up to 41 GPa using Fluorinert as the pressure-transmitting medium. The cubic Irn3 phase was found to be stable in the pressure range 0.5 to 13.2 GPa and to be highly compressible with a zero-pressure bulk modulus of Bo = 43 (1) GPa. The neutron data were used in least-squares refinements, showing that the ReO6 octahedra remain almost undistorted, while the Re—O—Re bond angle decreases from 166.5 (1) to 146.4 (3)° within the investigated pressure range of 1.27 to 8.01 GPa. The compression mechanism is also described in terms of sphere-packing models of the oxygen anions. [ABSTRACT FROM AUTHOR]

The attenuation of gamma rays in some fatty acids, viz. formic acid (CH2O2), acetic acid (C2H4O2), propionic acid (C3H6O2), butyric acid (C4H8O2), n-hexanoic acid (C6H12O2), n-caprylic acid (C8H16O2), lauric acid (C12H24O2), myristic acid (C14H28O2), palmitic acid (C16H32O2), oleic acid (C18H34O2) and stearic acid (C18H36O2), has been measured at the photon energies 81, 356, 511, 662, 1173 and 1332 keV. Experimental values for the molar extinction coefficient, the effective atomic number and the electron density have been derived and compared with theoretical calculations. There is good agreement between experiment and theory. [Copyright &y& Elsevier]

Novel nanocomposites, consisting of conducting poly(3,4-ethylenedioxythiophene) [PEDOT] and graphene nanoplatelets [GNPs], were successfully synthesized by in-situ chemical-oxidative polymerization of 3,4-ethylenedioxythiophene [EDOT] using ammonium peroxydisulfate as an oxidizing agent. The formation of PEDOT and its incorporation onto the surface of GNPs were confirmed by scanning electron microscopy, Fourier-transform infrared-spectroscopy, and X-ray diffraction. The optical energy band gap, E g opt, was determined by UV–Vis spectroscopy. Dielectric constant and loss as well as AC electrical conductivity, σ AC , were determined in the frequency range from 10 Hz to 8 MHz. The PEDOT-GNP nanocomposites were found to have extremely large dielectric constant, ε ′, significantly high σ AC , and narrow E g opt values. In particular, PEDOT-GNP nanocomposite with 10 wt% GNP has a gigantic dielectric constant of the order of 9 × 105 at 1 kHz and a narrow optical energy band gap of 1.26 eV. The ε ′ values (108 to 105 in the frequency range from 10 Hz to 5 MHz) of PEDOT-10 wt% GNP are the highest among those reported in the literature for carbon based polymer nanocomposites. The massive quantity of micro-capacitors formed in the nanocomposites, prior to the creation of conductive networks, leads to the gigantic dielectric properties. The ε ′ and σ AC values of PEDOT-10 wt% GNP nanocomposite were about 90 and 400 times larger than those of pure PEDOT. Our method should be particularly promising in the development of new materials for high energy storage applications. • PEDOT-GNP nanocomposites are synthesized by in-situ chemical oxidative polymerization. • Dielectric constant, ε ′, band gap, E g opt, and AC conductivity, σ AC , vary with GNP content and frequency. • PEDOT-10 wt% GNP nanocomposite has a gigantic ε ′ of the order of 9 × 105 at 1 kHz and a narrow E g opt of 1.26 eV. • ε ′ and σ AC values of PEDOT-10 wt% GNP nanocomposite are 90 and 400 times larger than those of pure PEDOT. • PEDOT-10 wt% GNP nanocomposite has shown highest ε ′ values for carbon based polymer nanocomposites. [ABSTRACT FROM AUTHOR]

Energy absorption geometric progression (GP) fitting parameters and the corresponding buildup factors have been computed for human organs and tissues, such as adipose tissue, blood (whole), cortical bone, brain (grey/white matter), breast tissue, eye lens, lung tissue, skeletal muscle, ovary, testis, soft tissue, and soft tissue (4-component), for the photon energy range 0.015-15 MeV and for penetration depths up to 40 mfp (mean free path). The chemical composition of human organs and tissues is seen to influence the energy absorption buildup factors. It is also found that the buildup factor of human organs and tissues changes significantly with the change of incident photon energy and effective atomic number, Z(eff). These changes are due to the dominance of different photon interaction processes in different energy regions and different chemical compositions of human organs and tissues. With the proper knowledge of buildup factors of human organs and tissues, energy absorption in the human body can be carefully controlled. The present results will help in estimating safe dose levels for radiotherapy patients and also useful in diagnostics and dosimetry. The tissue-equivalent materials for skeletal muscle, adipose tissue, cortical bone, and lung tissue are also discussed. It is observed that water and MS20 are good tissue equivalent materials for skeletal muscle in the extended energy range.

The effective atomic number, Z(eff), the effective electron density, N(el), and kerma have been calculated for some fatty acids and carbohydrates for photon interaction in the extended energy range from 1 keV to 100 GeV using an accurate database of photon-interaction cross sections and the WinXCom program. The significant variation of Z(eff) and N(el) is due to the variations in the dominance of different interaction processes in different energy regions. The maximum values of Z(eff) and N(el) are found in the low-energy range, where photoelectric absorption is the main interaction process. The minimum values of Z(eff) and N(el) are found at intermediate energies, typically 0.05 MeV < E < 5 MeV, where Compton scattering is dominant. In this case, Z(eff) is equal to the mean atomic number of the bio-molecule. Wherever possible, the calculations are compared with experimental results. A comparison is also made with the single values of the Z(eff) and N(el) provided by the program XMuDat. It is also observed that carbohydrates have a larger kerma than fatty acids in the low-energy region, where photoelectric absorption dominates. In contrast, fatty acids have a larger kerma than carbohydrates in the MeV range, where Compton scattering is the main interaction process.

Spectroscopic and physical properties of Nd3+ doped sodium lead flouro- and chloro-borate glasses of the type 20NaX-30PbO-49.5B2O3-0.5Nd2O3 (X=F and Cl) have been investigated. Optical absorption spectra have been used to determine the Slater Condon (F2, F4, and F6), spin orbit xi4f and Racah parameters (E1, E2, and E3). The oscillator strengths and the intensity parameters Omega2, Omega4 and Omega6 have been determined by the Judd-Ofelt theory, which in turn provide the radiative transition probability (A), total transition probability (A(T)), radiative lifetime (tauR) and branching ratio (beta) for the fluorescent level 4F3/2. The lasing efficiency of the prepared glasses has been characterized by the spectroscopic quality factor (Omega4/Omega6), the value of which is in the range of 0.2-1.5, typical for Nd3+ in different laser hosts. Nephelauxetic effect results in a red shift in the energy levels of Nd3+ for chloroborate glass. The radiative transition probability of the potential lasing transition 4F3/2-->4I11/2 of Nd3+ ions is found to be higher for flouroborate as compared to chloroborate glass.

Amorphouslike diffraction patterns of solid elemental titanium have been detected under high pressure and high temperature using in situ energy-dispersive x-ray diffraction and a multianvil press. The onset pressure and the temperature of formation of amorphous titanium is found to be close to the alpha-beta-omega triple point in the P-T phase diagram. Amorphous Ti has been found to be thermally stable up to 1250 degrees C for at least 3 min at some pressures. By analyzing the conditions for producing amorphous elemental Zr and Ti, we observed a multi-phase-point amorphization phenomenon for preparing single-element bulk amorphous metals. The results reported may open a new way to preparing single-element bulk amorphous metals with a high thermal stability.

Synchrotron-radiation X-ray diffraction studies of ZnO have been performed with special emphasis on the rock-salt-type high-pressure phase. The wurtzite (B4) to rock salt (B1) phase transformation is accompanied by a volume collapse of 18%, which is a very large effect. The lattice constant of the B1 phase at ambient pressure is a(0) = 4.280 (4) A, and the bulk modulus is B(0) = 170 (10) GPa. Comparisons are made with a recently published theoretical equation of state obtained from ab initio perturbed-ion calculations.

The applied equipment, the experimental procedures, and the results obtained in the experimental measurement of x-ray spectra from a microfocus x-ray unit are described. The measured spectra of x rays passing through different absorbers are compared to calculated spectra, based on calculation of the linear absorption coefficient, μ, and the spectrum of the incident radiation. The nice fit between the measured and the calculated spectra testifies to the applicability of the presented method for determination of the linear attenuation coefficient. Such calculations form the basis for a more accurate experimental determination of the contrast reducing build-up factor in industrial radiography.