Cross-section for D(p,p)D elastic scattering from 1.8 to 3.2 MeV at the laboratory angles of 155° and 165°

The D(p,p)D cross-sections for elastic scattering of proton on deuterium over incident proton energy range from 1.8 to 3.2 MeV at both laboratory angles of 155° and 165° were measured. A thin solid state target Ni/TiD_x/Ta/Al used for cross-section measurement was fabricated by firstly depositing layers of Ta, Ti and Ni film on the Al foil substrate of about 7 μm in turn using magnetron sputtering and then deuterating under the deuterium atmosphere. The areal density of metal element in each layer of film was measured with RBS analysis by using a 4.0 MeV ⁴He ion beam, while the areal density of the deuterium absorbed in the Ti film was measured with ERD analysis by using a 6.0 MeV ¹⁶O ion beam. The results show that the cross-sections of p-D scattering under this experimental circumstance were much enhanced over the Rutherford cross-section value. It was found that the enhancement increases linearly as the energy of the incident beam increases. The total uncertainty in the measurements was less than 7.5%.     

Effects of ion irradiation on the structural transformation of sol-gel derived TEOS/MTES thin films

Ion beam processing of organic/inorganic thin films has been shown to be an effective means in converting polymeric films into their final ceramic-like state. In this study, hybrid sol-gel derived thin films based on TEOS (tetraethylorthosilicate) Si(OC₂H₅)₄ and MTES (methyltriethoxysilane) CH₃Si(OC₂H₅)₃ were prepared and deposited on Si substrates by spin coating. After the films were allowed to air dry, they were heat treated at 300 °C for 10 min. Ion irradiation was performed at room temperature using 125 keV H⁺ and 250 keV N²⁺ ions with fluences ranging from 1 × 10¹⁴ to 5 × 10¹⁶ ions/cm². FT-IR and Raman spectroscopies were used to quantify the chemical structural transformations which occurred including the evolution of the organic components, the cross-linking of silica clusters, and the clustering of carbon.     

Synthesis and characterization of low-temperature precursors of thorium-uranium (IV) phosphate-diphosphate solid solutions

Several compositions of new precursor of thorium-uranium (IV) phosphate-diphosphate solid solutions (Th_4−xU_x(PO₄)₄P₂O₇, called β-TUPD) were synthesized in closed PTFE containers either in autoclave (160 °C) or on sand bath (90-160 °C). All the samples appeared to be single phase. From XRD data and TEM observations, the diffraction lines matched well with that of pure thorium phosphate-hydrogenphosphate hydrate (TPHPH), Th₂(PO₄)₂(HPO₄) · H₂O, which confirmed the preparation of a complete solid solution between pure thorium and uranium (IV) compounds. TGA/DTA experiments showed that samples of thorium-uranium (IV) phosphate-hydrogenphosphate hydrate (TUPHPH) prepared at 150-160 °C were monohydrated leading to the proposed formula Th_2−x/2U_x/2(PO₄)₂(HPO₄) · H₂O. The variation of the XRD diagrams versus the heating temperature showed that TUPHPH remained crystallized and single phase from room temperature to 200 °C. After heating between 200 °C and 800 °C, the presence of diphosphate groups in the solid was evidenced. In this range of temperature, the solid was transformed into the low-temperature monoclinic form of thorium-uranium (IV) phosphate-diphosphate (α-TUPD). This latter compound finally turned into well-crystallized, homogeneous and single-phase β-TUPD (orthorhombic form) above 930-950 °C for x values lower than 2.80. For higher x values, a mixture of β-TUPD, α-Th_1−zU_zP₂O₇ and U_2−wTh_wO(PO₄)₂ was obtained. By this new chemical route of preparation of β-TUPD solid solutions, the homogeneity of the samples is significantly improved, especially considering the distribution of thorium and uranium.     

Stopping of 0.3-1.2 MeV/u protons and alpha particles in Si

The stopping cross sections ε(E) of silicon for protons and alpha particles have been measured over the velocity range 0.3-1.2 MeV/u from a Si//SiO₂//Si (SIMOX) target using the Rutherford backscattering spectrometry (RBS) with special emphasis put on experimental aspects. A detection geometry coupling simultaneously two solid-state Si detectors placed at 165° and 150° relative to each side of the incident beam direction was used to measure the energies of the scattered ions and determine their energy losses within the stopping medium. In this way, the basic energy parameter, E_x, at the Si/SiO₂ interface for a given incident energy E₀ is the same for ions backscattered in the two directions off both the Si and O target elements, and systematic uncertainties in the ε(E) data mainly originating from the target thickness are significantly minimized. A powerful computer code has been elaborated for extracting the relevant ε(E) experimental data and the associated overall uncertainty that amounts to less than 3%. The measured ε(E) data sets were found to be in fair agreement with Paul’s compilation and with values calculated by the SRIM 06 computer code. In the case of ⁴He⁺ ions, experimental data for the γ effective charge parameter have been deduced by scaling the measured stopping cross sections to those of protons crossing the same target with the same velocity, and compared to the predictions of the SRIM 06 computer code. It is found that the γ-parameter values generated by the latter code slightly deviate from experiment over the velocity region around the stopping cross section maximum where strong charge exchanges usually occur.     

Photoluminescence induced by Si implantation into Si3N4 matrix

Up to the present, photoluminescence (PL) was obtained from near stoichiometric or amorphous Si nitride films (SiN_x) after annealing at high temperatures. As a consequence, the existence of PL bands has been reported in the 400–900 nm range. In the present contribution, we report the first PL results obtained by Si implantation into a stoichiometric 380 nm Si₃N₄ film. The Si excess is obtained by a 170 keV Si implantation at different temperatures with a fluence of Φ = 10¹⁷ Si/cm². Further, we have annealed the samples in a temperature range between 350 and 900 °C in order to form the Si precipitates. PL measurements were done using an Ar laser as an excitation source, and a broad PL band basically centered at 910 nm was obtained. We show that the best annealing condition is obtained at T_a = 475 °C for the samples implanted at 200 °C, with a PL yield 20% higher than the obtained at room temperature implantation. Finally, we have varied the implantation fluence and, consequently, the Si nanocrystals size. However, no variation was observed nor in the position neither in the intensity of the PL band. We concluded that the PL emission is due to radiative states at the matrix and the Si nanocrystals interface, as previously suggested in the literature.     

Xenon-ion-induced and thermal mixing of Co/Si bilayers and their interplay

Studies on ion-irradiated transition-metal/silicon bilayers demonstrate that interface mixing and silicide phase formation depend sensitively on the ion and film parameters, including the structure of the metal/Si interface. Thin Co layers e-gun evaporated to a thickness of 50 nm on Si(1 0 0) wafers were bombarded at room temperature with 400-keV Xe⁺ ions at fluences of up to 3 × 10¹⁶ cm⁻². We used either crystalline or pre-amorphized Si wafers the latter ones prepared by 1.0-keV Ar-ion implantation. The as-deposited or Xe-ion-irradiated samples were then isochronally annealed at temperatures up to 700 °C. Changes of the bilayer structures induced by ion irradiation and/or annealing were investigated with RBS, XRD and HRTEM. The mixing rate for the Co/c-Si couples, Δσ²/Φ = 3.0(4) nm⁴, is higher than the value expected for ballistic mixing and about half the value typical for spike mixing. Mixing of pre-amorphized Si is much weaker relative to crystalline Si wafers, contrary to previous results obtained for Fe/Si bilayers. Annealing of irradiated samples produces very similar interdiffusion and phase formation patterns above 400 °C as in the non-irradiated Co/Si bilayers: the phase evolution follows the sequence Co₂Si → CoSi → CoSi₂.     

The ternary system: silicon-uranium-vanadium

Phase equilibria in the system Si-U-V were established at 1100 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed, U₂V₃Si₄ and (U_1−xV_x)₅Si₃, for which the crystal structures were elucidated by X-ray powder data refinement and found to be isotypic with the monoclinic U₂Mo₃Si₄-type (space group P2₁/c; a = 0.6821(3), b = 0.6820(4), c = 0.6735(3) nm, β = 109.77(1)°) and the tetragonal W₅Si₃-type (space group I4/mcm, a = 1.06825(2), c = 0.52764(2) nm), respectively. (U_1−xV_x)₅Si₃ appears at 1100 °C without any significant homogeneity region at x ∼ 0.2 resulting in a formula U₄VSi₃ which corresponds to a fully ordered atom arrangement. DTA experiments clearly show decomposition of this phase above 1206 °C revealing a two-phase region U₃Si₂ + V₃Si. At 1100 °C U₄VSi₃ is in equilibrium with V₃Si, V₅Si₃, U₃Si₂ and U(V). At 800 °C U₄VSi₃ forms one vertex of the tie-triangle to U₃Si and V₃Si. Due to the rather high thermodynamic stability of V₃Si and the corresponding tie-lines V₃Si + liquid at 1100 °C and V₃Si + U(V) below 925 °C, no compatibility exists between U₃Si or U₃Si₂ and vanadium metal.     

Applicability of a catalytic reduction method using a palladium–copper catalyst and hydrazine for the denitration of a highly concentrated nitrate salt solution

Denitration of a highly concentrated sodium nitrate (NaNO₃) aqueous solution via a catalytic reduction method using a palladium–copper catalyst supported on carbon powder (Pd–Cu/C) and hydrazine (N₂H₄) was investigated. It was demonstrated that nitrate ion (NO₃ ^?) in a 5 mol L^?1 NaNO₃ solution was completely reduced through an intermediate nitrite ion (NO₂ ^?) to nitrogen compounds such as nitrogen, nitrous oxide, and ammonia. By comparing the reaction rates of NO₃ ^? and NO₂ ^? obtained using catalysts with various Pd–Cu compositions and different reductants (hydrogen (H₂) or N₂H₄), it was determined that the catalyst with a molar ratio of Pd:Cu = 1:0.66 provides the maximum reaction rates for NO₃ ^? and NO₂ ^? using N₂H₄, and that not only the reactions of NO₃ ^? and NO₂ ^? but also that of N₂H₄ were affected by the Pd–Cu composition.     

Experimental studies on measurements of mass attenuation coefficients of boric acid at different concentration

Measurements have been made to determine variation of the mass attenuation coefficients of H₃BO₃ according to percentage increasing concentration of H₃BO₃ by using an extremely narrow-collimated-beam transmission method in the energy range 15.746–40.930 keV with an X-ray transmission method. The characteristic K_α and K_β X-rays of the different elements (Zr, Mo, Ag, In, Sb, Ba and Pr) passed through boric acid was detected with a high-resolution Si(Li) detector. Results are presented and discussed in this paper.     

Monte Carlo calculation of the core of the heavy water zero power reactor (HWZPR) using MCNP4c

The MCNP4c code, based on the probabilistic approach, was used to simulate 3D configuration of the core of the heavy water zero power reactor (HWZPR). In present work, first, all of the constituents of the core such as fuel pellets, fuel element, moderator (D₂O) and annular graphite reflector were modeled using MCNP4c code. Then calculations of axial and radial neutron fluxes were performed in three energy groups such as thermal (0-0.625 eV), epithermal (0.625-550 eV), and fast (0.550-20 MeV). The cadmium ratio was calculated as well and the neutron flux parameters such as extrapolated height (H_e), extrapolated radius (R_e) and physical center of the core (z₀) were computed using cadmium ratio. Comparison of the neutron flux parameters with the experimental data showed that the MCNP4c model of the HWZPR was validated.     

Synthesis and characterization of lithium silicate powders

Lithium-based ceramics, such as Li₂O, LiAlO₂, Li₄SiO₄, Li₂SiO₃, Li₂TiO₃and Li₂ZrO₃, have long been recognized as promising tritium breeding-materials for D-T fusion reactor blankets. Among these candidate materials, lithium orthosilicate (Li₄SiO₄) and lithium metasilicate (Li₂SiO₃) are recommended by many ITER research teams as the first selection for the solid tritium breeder. Li₄SiO₄ has even been selected as the breeder material for the helium-cooled solid breeder test blanket module (HCSB TBM) in China and EU. In present study, the processes of solid-state reaction between amorphous silica and Li₂CO₃ powders was studied by thermogravimetry analysis-differential scanning calorimetry (TGA/DSC); the lithium silicate powders were synthesized at 700, 800 and 900 ° C with Li:Si molar ratios of 0.5, 1, 2 and 4, respectively, using solid-state reaction method. The as-prepared lithium silicates were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results show that the phase composition and morphology of the as-prepared samples change with the different synthesis conditions. At low temperature of 700 °C, all samples contain the amorphous silica, and the major crystalline phase is Li₂SiO₃ with different microstructure for Li/Si ratio of 0.5, 1 and 2. As for Li/Si=4, 98% purity of Li₄SiO₄ can be obtained at 700 °C. At high temperature of 900 °C, the significant sinterization effect will occur in all samples and Li₄SiO₄ will even decompose. The results also show that pure Li₄SiO₄ can be synthesized by calcining at 800 ° C for 4 h, and its’ solid-state reaction synthesis may be divided into two steps:

(1)

515-565 °C: Li₂CO₃+SiO₂→Li₂SiO₃+CO₂;

(2)

565-754 °C: Li₂CO₃+SiO₂→Li₂SiO₃+CO₂ and then Li₂SiO₃+Li₂CO₃→Li₄SiO₄+CO₂.

While Li/Si=2, 99% purity of and pure Li₂SiO₃ can be obtained at 800 and 900 °C, respectively.     

Proton transfer in SrCeO3-based oxide with internal reformation under supply of CH4 and H2O

Mass and charge transfer in a proton-conducting ceramic with internal reformation under the supply of CH₄ + H₂O was experimentally investigated for application to a fuel detritiation system of a fusion reactor. The oxide used in the present experiment was SrCe_0.95Yb_0.05O_3−a, and the electrodes were composed of Ni–SiO₂ paste and Ni wire mesh. The system was described by CH₄ + H₂O∣Ni∣SrCe_0.95Yb_0.05O_3−a∣NiO∣O₂ + H₂O. Plots of the I–V (electric current density versus cell potential) characteristic curve were determined under the conditions of different H₂O/CH₄ concentration ratios and temperatures of 600–800 °C. It was found that the system could work well even without any external CH₄ reformer. Mass-transfer process in/on the porous Ni electrode and in the ceramic electrolyte was experimentally clarified. The distribution of carbon depositions in the porous electrode was also determined with EDX by scanning over entire surface in the scope of SEM. The ratio of CH₄ to H₂ direct decomposition to its steam-reforming reaction was found to be different from location to location in the porous Ni electrode.     

Strain relaxation of epitaxial SiGe layers on Si(1 0 0) improved by hydrogen implantation

We propose a new method to fabricate strain relaxed high quality Si_1−xGe_x layers on Si by hydrogen implantation and thermal annealing. Hydrogen implantation is used to form a narrow defect band slightly below the SiGe/Si interface. During subsequent annealing hydrogen platelets and cavities form, giving rise to strongly enhanced strain relaxation in the SiGe epilayer. As compared to thermally induced strain relaxed Si–Ge epilayers, the hydrogen implanted and annealed samples show a greatly reduced threading dislocation density and a much higher degree of strain relaxation (90%). We assume that the hydrogen induced defect band promotes strain relaxation via preferred nucleation of dislocation loops in the defect band which extend to the interface to form misfit segments. The samples have been investigated by X-ray diffraction, Rutherford backscattering spectrometry and transmission electron microscopy.     

Influence of hydrocarbons on vibrational excitation of H2 molecules

The influence of light hydrocarbons on vibrational excitation of H₂ generated in a special source of excited molecules has been studied. Molecule dissociation on the hot tungsten filament and atom recombination on cooled walls is used for the production of molecular excitation in the source. Specific influence of CH₄, C₂H₄ and C₂H₆ on vibrational distribution of hydrogen molecules from the source is presented here. Production of vibrationally excited H₂ molecules due to the thermal dissociation on the hot filament is observed when C₂H₄ (ethene) and C₂H₆ (ethane) are introduced alone in the source. These molecules appear to be produced by direct process on the hot filament in the case of ethene while in the case of ethane H₂(v) is produced by the similar process as for H₂. Production of H₂(v) is not observed when only CH₄ is introduced into the source. In this case vibrational relaxation of H₂(v) is observed when CH₄ is introduced into the source in addition to H₂. Studied processes are relevant for the modelling of edge plasma in tokamaks.     

Stopping power of polymeric foils for swift heavy ions

The stopping power of polypropylene PP(C₃H₆) and Polyethylene naphthalate PEN (C₇H₅O₂) polymeric foils has been measured, using transmission technique, for Si, Cl and Ti ions covering the energy range 1.0–4.5 MeV/u. These measured stopping power values have been compared with the corresponding values generated from the widely used semi-empirical formulations and standard data tables. The applicability of these formulations and data tables, in the light of the experimental values, is highlighted.     

Effective atomic numbers of some composite mixtures including borax

Effective atomic numbers for (PbO and Na₂B₄O₇10H₂O) and (UO₂(NO₃)₂, and Na₂B₄O₇10H₂O) mixtures against changing contents of PbO, Na₂B₄O₇10H₂O, and UO₂(NO₃)₂ were measured in the X-ray energy range from 25.0 to 58.0 keV. The gamma rays emitted by a ²⁴¹Am annular source have been sent on the absorbers which emits their characteristic X-rays to be used in transmission arrangement. The X-rays were counted by a Si(Li) detector with a resolution of 146 eV at 5.90 keV. The changing compositions of the compounds were assigned to be 0, 0.167, 0.333, 0.500, 0.666, 0.833 and total masses of the mixtures were adjusted to be identical. Also, the total effective atomic numbers of each mixture were estimated by using the mixture rule. The measured values were compared with estimated values for the mixtures.     

Mass attenuation coefficients,effective atomic numbers and electron densities of undoped and differently doped GaAs and InP crystals

The total mass attenuation coefficients (μ/ρ), for GaAs, GaAs (semi-insulating; S-I) GaAs:Si (N⁺), GaAs:Zn, InP:Fe, InP:Fe–As, InP:S and InP:Zn crystals were measured at 22.1, 25.0, 59.5 and 88.0 keV photon energies. The samples were irradiated with ¹⁰⁹Cd and ²⁴¹Am radioactive point sources using transmission arrangement. The X- and γ-rays were counted by a Si (Li) detector with resolution of 160 eV at 5.9 keV. Total atomic and electronic cross-sections (σ_t and σ_e), effective atomic numbers (Z_eff) and electron densities (N_el) were determined using the obtained μ/ρ values for the investigated crystals.     

Differential cross-sections for nuclear reactions on Al and Si induced by deuterons at low energy (1-2 MeV)

Recent progress in thin film techniques has made possible the fabrication of stable and pollution-free reference standards. Thin Si₃N₄ film (thickness 70 nm) and thin Al foil (150 nm) were selected to measure the differential cross-sections of nuclear reactions induced by deuterons, from 1 to 2 MeV. The absence of oxygen and carbon in the standard, as well as the stoichiometry, were checked prior to measurement by RBS. The differential cross-sections of the ²⁷Al(d,p₀p₁)²⁸Al, ²⁷Al(d,p₂p₃)²⁸Al, ²⁷Al(d,p₅p₆)²⁸Al, ²⁷Al(d,p₉)²⁸Al, ²⁷Al(d,p₁₀)²⁸Al, ²⁷Al(d,p₁₁)²⁸Al, ²⁷Al(d,p₁₂)²⁸Al, ²⁷Al(d,α₀)²⁵Mg and ²⁷Al(d,α₂)²⁵Mg reactions for aluminium and ²⁸Si(d,p₀)²⁹Si- ²⁹Si(d,p₁)³⁰Si, ²⁸Si(d,p₁)²⁹Si- ²⁹Si(d,p₂)³⁰Si, ²⁸Si(d,p₂)²⁹Si, ²⁸Si(d,p₃)²⁹Si, ²⁸Si(d,p₉p₁₀)²⁹Si reactions for silicon were determined for a detector angle of 150°.     

12C(α,α)12C resonant elastic scattering at 5.7 MeV as a tool for carbon quantification in silicon-based heterostructures

The incorporation of carbon into substitutional sites in Si or Si_1−xGe_x attracts increasing interest due to the enhanced possibilities in strain and band gap engineering of group IV heterostructures. Precise and accurate measurement of carbon concentration is, however, quite difficult to achieve. We focused our attention on the study of the alpha resonant elastic scattering in the 5.7 MeV energy region. We measured the scattering cross-section in the range 5.4–6.0 MeV at a laboratory scattering angle of 170°. The results indicate that the cross-section value is enhanced with respect to the Rutherford one of an almost constant factor (×130) in an energy interval about 100 keV wide. This allows a more accurate measurement of carbon concentration than with the normally used 4.265 MeV resonance. The experimental procedure to deal with non-Rutherford scattering of Si has been also determined. The resonant scattering at 5.72 MeV has been used, in combination with Rutherford Backscattering Spectrometry (RBS) at 3.0 MeV, to determine the carbon content of three Si_1−x−yGe_xC_y samples. This has also been used, in channelling geometry, to determine the substitutional carbon fraction of the samples.