Anomalously deep penetration of hydrogen and deuterium in assemblies from Nb foils and deuterated polyethylene (CD<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> under the pulse high temperature hydrogen plasma

Studies of the storage and redistribution of hydrogen atoms under pulse high temperature hydrogen plasma that was obtained using a PF-4 Plasma Focus facility in a multilayered structure (sandwich) which consists of two high-purity niobium foils and a deuterium polyethylene film pressed between them have been carried out using the method for elastic recoil detection (ERD). It was established that, with an increase in pulses of the PF-4 facility, the redistribution of implanted hydrogen atoms for large depths occurs in the two Nb foils and deuterated polyethylene. The depths substantially exceed the projective range of paths of hydrogen ions (at their maximum velocity of ∼10⁸ cm/s). A maximum hydrogen concentration of 45 at % is reached in the nearest surface of the second Nb foil to the PF-4 at 20 pulses of hydrogen plasma. An X-ray diffraction analysis showed the presence of a niobium hydride phase in both Nb foils. The redistribution of deuterium atoms from the bound state of deuterated polyethylene into the near-surface layer and the bulk material of the second Nb foil was detected as well. This phenomenon can be attributed to the transfer of implanted hydrogen atoms through the foil assembly and the transfer of deuterium from deuterated polyethylene into the near-surface layer of the second foil under the effect of powerful shock waves that are created by pulse hydrogen plasma and by acceleration in the diffusion of hydrogen and deuterium in the strain field induced by the shock wave.     

Deuterium and hydrogen distribution in a stack of Ta|(CD2) n |Ta foils under the action of high-temperature pulsed nitrogen plasma

Using the method of the elastic recoil detection (ERD) of hydrogen nuclei and a Plasma Focus setup (PF-4), we study the processes of the storage and redistribution of hydrogen and deuterium atoms in a stack of two tantalum foils and a deuterated polyethylene film sandwiched between them under pulsed irradiation with hot nitrogen plasma. It is established that the redistribution of implanted deuterium and hydrogen occurs at greater depths in both tantalum foils after 30 pulses of nitrogen plasma. The maximum concentrations of hydrogen and deuterium, namely 7 and 45 at % are observed on the surface of the second tantalum foil which is more distant from the PF-4 setup. The redistribution of deuterium from deuterated polyethylene onto the surface and volume of both Ta foils is observed. The observed phenomenon can be explained by the breaking of chemical bonds in the deuterated polyethylene and the transfer of freed deuterium into the Ta foils under the action of strong shock waves formed in the structure, as well as the accelerated diffusion of hydrogen and deuterium in the stress field caused by the shock wave.     

Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections have been measured for electron-impact dissociative excitation and ionization of CD₂⁺ leading to formation of CD₂²⁺, CD⁺, C⁺, D₂⁺ and D⁺. The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. The maximum total cross-sections are found to be (1.2±0.1)×10^-17 cm², (6.1±0.7)×10^-17 cm², (6.4±0.7)×10^-17 cm², (26.3±3.8)×10^-19 cm² and (14.9±1.4)×10^-17 cm² for CD₂²⁺, CD⁺, C⁺, D₂⁺ and D⁺ respectively. Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product, which are of significant interest in fusion plasma edge modelling and diagnostics. Conforming to the scheme recently applied in the CD₄⁺ and in the CD₃⁺ articles, the cross-sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic-energy-release distributions are determined for each ionic fragment at selected electron energies.     

Discovery and frequency measurement of short-wavelength far-infrared laser emissions from optically pumped <Superscript>13</Superscript>CD<Subscript>3</Subscript>OH and CHD<Subscript>2</Subscript>OH

A three-laser heterodyne system was used to measure the frequencies of twelve previously observed far-infrared laser emissions from the partially deuterated methanol isotopologues ¹³CD₃OH and CHD₂OH. Two laser emissions, a 53.773 μm line from ¹³CD₃OH and a 74.939 μm line from CHD₂OH, have also been discovered and frequency measured. The CO₂ pump laser offset frequency was measured with respect to its center frequency for twenty-four FIR laser emissions from CH₃OH, ¹³CD₃OH and CHD₂OH. PACS 07.57.Hm; 42.55.Lt; 42.62.Eh     

Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections have been measured for electron-impact dissociativeexcitation and ionization of CD ₂ ⁺ leading toformation of CD ₂ ²⁺ , CD⁺, C⁺,D ₂ ⁺ and D⁺. The animated crossed-beams methodis applied in the energy range from the reaction threshold up to 2.5 keV.The maximum total cross-sections are found to be (1.2±0.1)×10^-17 cm², (6.1±0.7)×10^-17 cm², (6.4±0.7)×10^-17 cm², (26.3±3.8)×10^-19 cm² and (14.9±1.4)×10^-17 cm² forCD ₂ ²⁺ , CD⁺, C⁺,D ₂ ⁺ and D⁺ respectively. Individualcontributions for dissociative excitation and dissociative ionization aredetermined for each singly-charged product, which are of significantinterest in fusion plasma edge modelling and diagnostics. Conforming to thescheme recently applied in the CD ₄ ⁺ and in theCD ₃ ⁺ articles, the cross-sections are presented inclosed analytic forms convenient for implementation in plasma simulationcodes. Kinetic-energy-release distributions are determined for each ionicfragment at selected electron energies.     

EPR and photoluminescence spectra of smooth CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films from T-10 tokamak: The effect of iron impurity

The electron and spin structure of thick smooth hydrocarbon CD _x films (“flakes”) with a high relative deuterium concentration of x ~ 0.5, redeposited from deuterium plasma discharge onto the walls of the vacuum chamber of the T-10 tokamak and containing ~1 at % of 3d-metal impurities due to erosion of the chamber walls, are studied using electron paramagnetic resonance (EPR) and photoluminescence (PL). The resulting spectra are compared for the first time to the EPR and photoluminescence spectra of polymer (soft) a-C:H(D) films (H(D)/C ~ 0.5), which are considered model analogues of smooth CD _x films. A certain similarity of the CD _x films with a-C:H films was found in the electronic structure of the valence band. At the same time, the differences in the EPR and photoluminescence spectra were observed due to the presence of 3d-metal impurities in the CD _x samples, contributing to the conversion of sp ³ → sp ² in the formation of films in the tokamak and upon heating and thermal desorption. An impurity of, presumably, 3d metals was detected for the first time by EPR in the a-C:H films in an amount of approximately 0.2 ppm, related to the evaporation of graphite.     

Lattice dynamics and ferroelectric instability in ordered and disordered PbSc<Subscript>1/2</Subscript>Ta<Subscript>1/2</Subscript>O<Subscript>3</Subscript> and PbSc<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> solid solutions

The dynamic Born charges and the frequency spectra of lattice oscillations in the crystals of ordered and disordered PbSc_1/2Ta_1/2O₃ (PST) and PbSc_1/2Nb_1/2O₃ (PSN) solid solutions have been calculated within the framework of the generalized Gordon-Kim model with allowance for the dipole and quadrupole polarizabilities. The phonon spectra of both compounds contain ferroelectric soft modes. The influence of various interactions on the magnitude of dynamic charges and ferroelectric instability in PSN and PST solid solutions has been studied and it is shown that both these charges and the ferroelectric instability are determined by the competition between long-range dipole-dipole interactions and short-range dipole-charge interactions, the determining role played by the interaction of Nb (Ta) cations and oxygen anions in the Nb-O (Ta-O) bond direction.     

Adsorption and solution of H2 and N2 by Ta and Nb

The condensation and desorption kinetics of H₂ and N₂ on polycrystalline wires of Ta and Nb are examined for solute concentrations between 0.1 and 100 monolayers. Accurate comparisons of adsorbate densities and sticking coefficients on Ta, Nb, Mo and W are obtained by making simultaneous measurements on all four substrates in the same vacuum system. Desorption exhibits second order kinetics for all substrates at all coverages. Desorption activation energies are higher on Ta and Nb than on W and Mo for both gases. Diffusion limited desorption is observed for H₂ at high heating rates. Solution of H₂ occurs at measurable rates (s ? 0.01) in Ta and Nb even at 78 °K while for N₂ no solution is observed for T < 600 °K.     

Absolute cross sections and kinetic energy release distributions for electron-impact ionization and dissociation of CD<Superscript>+</Superscript><Subscript>4</Subscript>

Absolute cross sections for electron-impact dissociative excitation and ionization of CD⁺ ₄ leading to formation of ionic products (CD²⁺ ₄, CD⁺ ₃, CD⁺ ₂, CD⁺, C⁺, D⁺ ₃, D⁺ ₂, and D⁺) have been measured. The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections are found to be (3.8±0.2) ×10^-19 cm²,  cm², (7.1±0.8) ×10^-17 cm², (9.0±0.8) × 10^-17 cm² and (3.7±0.4) ×10^-17 cm² for the heavy carbonaceous ions CD²⁺ ₄, CD⁺ ₃, CD⁺ ₂, CD⁺ and C⁺ respectively. For the light fragments, D⁺ ₃, D⁺ ₂, and D⁺, the cross sections around the maximum are found to be (5.0±0.6) ×10^-19 cm², (1.7± 0.2) ×10^-17 cm² and (10.6±1.0) ×10^-17 cm², respectively. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. The analysis of ionic product velocity distributions allows determination of the kinetic energy release distributions which are seen to extend from 0 to 9 eV for heavy fragments, and up to 14 eV for light ones. The comparison of present energy thresholds and kinetic energy release with available published data gives information about states contributing to the observed processes. Individual contributions for dissociative excitation and dissociative ionization are determined for each detected product. A complete database including cross sections and energies is compiled for use in fusion application.     

Helmholtz transceiver array for improving the |<Emphasis Type="Italic">B</Emphasis><Subscript>1</Subscript>|-field homogeneity at 7-T magnetic resonance imaging

A 16-channel transceiver radiofrequency (RF) array using Helmholtz coils was designed to improve the RF transmission |B ₁ ⁺ |-field homogeneity for human brain magnetic resonance imaging (MRI) at 7 T. A numerical simulation of the proposed Helmholtz transceiver array was performed using the finite-difference time-domain method—the subset of the finite-element method simulation. The simulation results of proposed 16-channel Helmholtz transceiver array were compared with the generally used rectangular transceiver array in term of their |B ₁ ⁺ |-field and specific absorption rate (SAR). The simulation of each single element in 16-channel Helmholtz and rectangular transceiver arrays was compared using water phantom in term of their magnetic flux |B ₁| homogeneity for the full width at half maximum. From the simulation results, the proposed 16-channel Helmholtz transceiver array configuration offers superior |B ₁ ⁺ |-field homogeneity and low SAR at 7 T. These modifications to the coil geometries of the transceiver array coil could be applied to a 7-T MRI, and also extended to increase the homogenous coverage on |B ₁ ⁺ |field with low SAR.     

Mechanoelectric effect in O<Superscript>2−</Superscript> conducting cell: Relations to phase transformations and other lattice changes in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + <Emphasis Type="Italic">x</Emphasis></Subscript>-like oxides

The origin of mechanoelectric voltage arising in an ^2?-conducting solid-state cell O₂,Pt|ZrO₂|Pt, O₂, YBCO due to the pressure applied on the YBCO sample is discussed. It is demonstrated that the mechanoelectric voltage is the sum of the electronic and ionic mechanoelectric contact potentials. The mechanoelectric contact potentials are determined by the work done by the load during an elementary ordering act or another elementary process taking place when the sample absorbs one oxygen atom. Effects related to oxygen atoms being ordered under the load, such as pressure-induced oxygen absorption, enhanced deformation, and change in the order parameter, are discovered.     

Cluster-Type Structure of Amorphous Smooth Hydrocarbon CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Films (<Emphasis Type="Italic">x</Emphasis> ~ 0.5) from T-10 Tokamak

Structure of smooth hydrocarbon CD _x films with a high deuterium ratio x ~ 0.5 redeposited from T-10 tokamak D-plasma discharges (NRC Kurchatov Institute, Moscow) has been studied. For the first time, small and wide angle X-ray scattering technique using synchrotron radiation and neutron diffraction have been employed. A fractal structure of CD _x films is found to consist of mass-fractals with rough border, surface fractals (with rough surface), plane scatterers and linear chains forming a branched and highly cross-linked 3D carbon network. The found fractals, including sp² clusters, are of typical size ~1.60 nm. They include a C₁₃ fragment consisting of three interconnected aromatic rings forming a minimal fractal sp² aggregate 9 × C₁₃. These graphene-like sp² clusters are interconnected and form a 3D lattice which can be alternatively interpreted as a highly defective graphene layer with a large concentration of vacancies. The unsaturated chemical bonds are filled with D, H atoms, linear sp² C=C, C=O, and sp³ structural elements like C-C, C-H(D), C-D_2,3, C-O, O-H, COOH, C _x D(H) _y found earlier from the infrared spectra of CD _x films, which are binding linear elements of a carbon network. The amorphous structure of CD _x films has been confirmed by the results of earlier fractal structure modeling, as well as by researches with X-ray photoelectron spectroscopy which allow finding a definite similarity with the electron structure of their model analogues — polymeric a-C:H and a-C:D films with a disordered carbon network consisting of atoms in sp³ + sp² states.     

Large magnetic entropy change in Nd<Subscript>2/3</Subscript>Sr<Subscript>1/3</Subscript>MnO<Subscript>3</Subscript>

In order to search for new materials for the application of magnetic refrigeration, the polycrystalline perovskite compound Nd_2/3Sr_1/3MnO₃ was prepared by a solid-state method. The dependence of the magnetization on the applied field and temperature was measured near the Curie temperature. In terms of Maxwells equation, the temperature dependence of the absolute value of the isothermal magnetic entropy change |S_M| at various applied fields from 1 T to 5 T was determined. The results showed that a large magnetic entropy change was observed in this compound. The maximum magnetic entropy change |S_M^max|can reach 3.25 J/kgK with an applied field of 1 T at the Curie temperature of 257.5 K, which equals that of Gd. At 5 T applied field, it is 7.57 J/kgK. Such good magnetocaloric properties make this compound a promising candidate for the application of magnetic refrigeration in the room-temperature range. PACS 74.25.Ha; 75.30.-m; 75.30.Sg; 75.50.-y; 75.60.-d     

Acoustic wave propagation in Ni<Subscript>3</Subscript><Emphasis Type="BoldItalic">R</Emphasis> (<Emphasis Type="BoldItalic">R</Emphasis> = Mo,Nb, Ta) compounds

The ultrasonic properties of the hexagonal closed packed structured Ni₃Mo, Ni₃Nb and Ni₃Ta compounds were studied at room temperature for their characterization. For the investigations of ultrasonic properties, the second-order elastic constants using Lennard–Jones potential were computed. The velocities V ₁ and V ₂ have minima and maxima respectively at 45° with the unique axis of the crystal, while V ₃ increases with respect to angle with the unique axis of the crystal. The inconsistent behaviour of angle-dependent velocities is associated with the action of second-order elastic constants. Debye average sound velocities of these compounds increase with the angle and has maximum at 55° with the unique axis at room temperature. Hence, when a sound wave travels at 55° with the unique axis of these materials, the average sound velocity is found to be maximum. The results achieved are discussed and compared with the available experimental and theoretical results.     

Nuclear reactions in the Pd/PdO:D<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and Ti/TiO<Subscript>2</Subscript>:D<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> systems excited by ionizing radiation

The yield of the products of nuclear reactions from deuterated palladium and titanium irradiated by an electron beam and X rays has been studied. Charged particles have been detected by CR-39 track detectors, which are not sensitive to electronic noise, electrons, and X-ray photons. To identify the type of particles and to estimate their energy, three detectors covered by aluminum and copper foils of various thicknesses have been used. It has been established with reliable statistics that 30-keV electrons and X rays initiate the synthesis of deuterons in the Pd/PdO:D _x and Ti/TiO₂:D _x systems with the yield of 3-MeV protons.     

Inclusive measure of |<Emphasis Type="Italic">V</Emphasis><Subscript><Emphasis Type="Italic">ub</Emphasis></Subscript>| with the analytic coupling model

By analyzing B→X _u ℓ ν _ℓ spectra with a model based on soft-gluon resummation and an analytic time-like QCD coupling, we obtain

Dielectric properties of thin ferroelectric Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> films deposited by thermal evaporation

The structure, microstructure, and temperature and field dependences of the dielectric properties of thin (0.5–8.0μm) Sn₂P₂S₆ ferroelectric films deposited onto glass and aluminum foil substrates by thermal vacuum evaporation in a quasi-closed volume are studied. The film-thickness and frequency dependences of the dielectric properties and the unipolarity of the C–V characteristics are explained by the presence of near-surface Schottky-type barrier layers.     

Statistical mechanics of cation ordering in PbSc<Subscript>1/2</Subscript>Ta<Subscript>1/2</Subscript>O<Subscript>3</Subscript> and PbSc<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> solid solutions

A model Hamiltonian for B cation ordering (Sc-Nb(Ta)) in PbSc_1/2Nb_1/2O₃ and PbSc_1/2Ta_1/2O₃ solid solutions is constructed. The parameters of the model Hamiltonian are determined from the ab initio calculation within the ionic crystal model with allowance made for the deformability and the dipole and quadrupole polarizabilities of the ions. The temperatures of the phase transition due to the ordering of the B cations are calculated by the Monte Carlo method in the mean-field and cluster approximations. The phase transition temperatures calculated by the Monte Carlo method (1920 K for PbSc_1/2Ta_1/2O₃ and 1810 K for PbSc_1/2Nb_1/2O₃) are consistent with the experimental data (1770 and 1450 K, respectively). The thermodynamic properties of the cation ordering are investigated using the Monte Carlo method.     

Inelastic neutron scattering in Zr<Subscript>2</Subscript>NiH<Subscript>1.9</Subscript> and Zr<Subscript>2</Subscript>NiH<Subscript>4.6</Subscript>

In this paper we report the results obtained from inelastic neutron scattering measurements on Zr₂NiH_1.9 and Zr₂NiH_4.6 using triple-axis spectrometer at Dhruva reactor, Trombay. The spectrum up to 35 meV represents largely the lattice modes of Zr and Ni atoms. The vibrational frequencies of hydrogen atoms are expected predominantly at higher energies. The phonon spectra from 35–180 meV were recorded using a Be filter as analyser. In order to analyse the observed neutron spectra, we assume a set of Ein-stein modes due to the hydrogen atoms which are delta functions in energy. These delta functions are broadened by the resolution of the instrument. The vibrational frequencies obtained from the fitting of the observed phonon spectra have been assigned to various tetrahedral sites in both the compounds.