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  • Article


  • Authors: Nguyen, Van Hung; Nguyen, Bao Trung; Nguyen, Cong Toan; Ha, Dang Khoa (2017)

  • Debye-Waller factors (DWFs) of metallic Cu (fcc crystal) in X-ray absorption fine structure (XAFS) presented in terms of cumulant expansion have been studied using the anharmonic correlated Debye model (ACDM). This ACDM is derived using the many-body perturbation approach and the anharmonic effective potential that includes the first shell near neighbor contributions to the vibration between absorber and backscatterer atoms. Analytical expressions of three first XAFS cumulants of Cu have been derived involving more information of phonon-phonon interactions taken from integration over the first Brillouin zone. Morse potential is assumed to describe the single-pair atomic interaction. Numerical results for Cu using the present ACDM show their good agreement with experiment and with th...

  • Article


  • Authors: Nguyen, Van Hung; Nguyen, Cong Toan; Hoang, Thi Khanh Giang (2010)

  • Analytical expressions for the ratio of the root mean square fluctuation in atomic positions on the equilibrium lattice positions and the nearest neighbor distance and the mean melting cgryes of bcc binary alloys haye been derived. This melting curve provides information on Lindemann's melting temperatures of binary alloys with respect to any proportion of constituent elements and on their euctectic points. Numerical results for some bcc binary alloys are found to be in agreement with experiment.

  • Article


  • Authors: Nguyen, Van Hung; Trinh, Thi Hue; Nguyen, Ba Duc (2015)

  • In this work, Morse potential parameters of bcc crystals have been calculated based on the calculation of volume per atom and atomic number in each elementary cell, as well as the energy of sublimation, the compressibility and the lattice constant. They are used for studying the anharmonic interatomic effective potential, local force constant in XAFS (X-ray Absorption Fine Structure) theory. Numerical results for Fe, W and Mo are found to be in good agreement with experiment and with those of other theories.

  • Article


  • Authors: Nguyen, Van Hung; Ngo, Trong Hai; Tong, Sy Tien; Le, Hai Hung (2009)

  • Anharmonic effective potential, effective local force constant, thermal expansion coefficient, three leading cumulants, and EXAFS (Extended X-ray Absorption Fine Structure) of hep crystals have been studied. Analytical expressions for these quantities have been derived. Numerical calculations have been carried out for Zn and Cd. They show a good agreement with experiment results measured at HASYLAB (DESY, Germany) and unnegligible anharmonic effects in the considered quantities.

  • Article


  • Authors: Bui, Van Loat; Nguyen, Van Quan; Le, Tuan Anh; Tran, The Anh; Nguyen, The Nghia; Nguyen, Van Hung (2009)

  • Radioactive sources which used to study were the standardized radioactive of common monoenergetic radionuclide Cs137 and standardized multigamma Co60, Ba133, Eu152. Determination of the absolute efficiency curve and energy resolution as a function of energy of GEM40P4 HPGe spectrometer are presented in this paper.

  • Article


  • Authors: Nguyen, Van Hung; Nguyen, Thi Thu Hoai; Le, Hai Hung (2004)

  • A new procedure for calculation and evaluation of XAFS cumulants of fee crystals containing impurity atom has been developed based on the quantum statistical theory with correlated Einstein model. Analytical expressions for the effective local force constants, correlated Einstein frequency and temperature, first cumulant or net thermal expansion, second cumulant or Debye Waller factor and third cumulant of fee crystals containing impurity atom have been derived. Morse potential parameters of pure crystals and those with impurity included in the derived expressions have been calculated. Numerical results for Cu. Ni. Ni-Cu are found to be in good agreement with experiment

  • Article


  • Authors: Nguyen, Van Hung; Trinh, Thi Hue; Nguyen, Bao Trung; Nguyen, Cong Toan (2017)

  • Anharmonic correlated Debye model is derived for Debye-Waller factors of bcc (body-centered cubic) crystals presented in terms of cumulant expansion up to the fourth order. The many-body effects are taken into account in the present one-dimensional model based on the anharmonic effective potential that includes interactions of absorber and backscatterer atoms with their first shell near neighbors, where Morse potential is assumed to describe the single-pair atomic interaction. Analytical expressions for dispersion relation, correlated Debye frequency and temperature and four first temperature-dependent XAFS (X-ray absorption fine structure) cumulants of bcc crystals have been derived using the many-body perturbation approach. Numerical results for W are found to be in good agreement...

  • Article


  • Authors: Nguyen, Van Hung; Duong, Anh Tuan; Trinh, Duc Thien; Nguyen, Dang Phu; Danh, Bich Do; Pham, Van Vinh (2012)

  • CdTe quantum dots dispersed in water were prepared successfully by the microwave irradiation method. The influence of the pH value of the solution precursor, irradiation time and microwave power on the structure, size and optical properties of CdTe quantum dots was investigated. The fluorescence of CdTe quantum dots studies were illustrated that the samples which were synthesized at pH value of 7 exhibited the best fluorescence. The absorption, fluorescence spectra and TEM images showed that the microwave power and the irradiation time influenced significantly on the size of CdTe quantum dot as well as their optical properties. The fluorescence spectra were red-shift with the increase of the irradiation time and microwave power.

  • Article


  • Authors: Nguyen, Van Hung; Nguyen, Cong Toan; Nguyen, Bao Trung; Ngo, Hoang Giang (2008)

  • Analytical expressions for the Morse potential parameters of diamond crystals have been derived. They contain the energy of sublimation, the compressibility and the lattice constant. Numerical calculations have been carried out for Si and Sn, and the result reflect fundamental calcultion of the anharmonic correlated effective potential parameters have been used for calculation of the anharmonic correlated effective potentials of these crystals in XAFS theory showing clearly anharmonic effects.

  • Article


  • Authors: Nguyen, Van Hung; Bui, Van Loat (2009)

  • The paper resented the results of assessing internal dose for 131I by the direct method for Vietnamese objects that was issued in the Intercomparison Program of IAEA. The results on experimental measurements, caculating intake (I) or 131I to thyroid by the specializing system for measuring thyroid activity, and committed effective dose E(50) using the specializing code of LUDEP 2.0 were shown that the results carrying out at the Nuclear Research Institute were goof and were in accordance with the those of the authors in other laboratories in the world.