The peculiarities of the low-energy ion scattering by polycrystal targets

In the present work, experimental and computer simulation studies of low-energy (E₀ = 80-500 eV) Cs⁺ ions scattering on Ta, W, Re target surfaces and K⁺ ions scattering on Ti, V, Cr target surfaces have been performed for more accurate definition of mechanism of scattering, with a purpose of evaluation of an opportunity of use of slow ions scattering as a tool of surface layers analysis. The choice of the targets was based on the fact that the ratios of atomic masses of target atoms and ions μ = m₂/m₁ were almost the same for all cases considered and greater than 1 (direct mass ratio) however, the difference of binding energies of target atoms in the cases of Cs⁺ and K⁺ scattering was almost twice as much. It has been noticed that the dependencies of the relative energy retained by scattering ions at the maximum of energy distribution versus the initial energy E_m/E₀ (E₀) have a similar shape in all cases. The relative energy retained by scattering ions increases while the initial energy of incidence ions decreases. The curves are placed above each other relative to the binding energies of target atoms, to show what this says about the influence of binding energy on a process of scattering of low-energy ions. The correlation between value of energy change maintained by an ion for different values of E₀ in the case of scattering by targets with different masses of atoms and its binding energies is experimentally established. The contrary behavior of the E_m/E₀ (E₀) dependencies concerning the target atom binding energy quantity E_b for cases with direct (μ > 1) and inverse (μ < 1) mass ratio of colliding particles is established. The comparison of experimental energy distributions with calculated histograms shows that the binary collision approximation cannot elucidate the abnormally great shift in the maxima of relative energy distributions towards greater energy retained by scattering ions.     

DasK-Röntgenemissionsspektrum des Chlors in freien Molekülen

TheKα andKβ spectra of chlorine in free molecules were studied using a special fluorescence X-ray tube and a high resolving curved crystal spectrograph with photoelectric registration. It was found that the wavelength shifts of ClKα₁ obtained for various gaseous compounds do not show the regularities observed with solid compounds of other 3rd period elements. — TheKβ spectrum consists of discrete lines the most intense of which result from transitions of the lonely pair electrons of the chlorine atoms. The spectra of HCl, Cl₂ and CH₃Cl can be explained using optical and betaspectroscopical data and MO calculations. The general structure of ClKβ of organic compounds seems to be determined by the hybridisation type of the carbon atoms bound to the chlorine atoms. Evidence is found for a contribution of molecular vibrational energy to the energies of the X-ray transitions.     

Inner-shell ionization ofZ=25–32 elements by 5-48 MeV32S ions

TheK-shell ionization cross sections of Mn, Ni, Cu, Zn and Ge under³²S bombardment have been measured in the energy range from 5 to 48 MeV. The cross sections are compared with available theories based on a direct Coulomb ionization mechanism and with the predictions of theK-vacancy sharing process. This last process can reasonably account for the measured cross sections at high bombarding energies. The energy shifts of theK _α- andK _β-lines and theK _α/K _β-intensity ratios have also been measured. This information is used to deduce the defect configuration of the atoms. The mechanisms responsible for the multiple vacancy production are discussed.     

Direct inner shell ionization accompanying nuclear fusion reactions with heavy ions

Probabilities for K-shell ionization prior to fusion (half-trajectory collisions) are determined for ⁵¹V, ⁵⁹Co, ⁶²Ni target atoms and 4.5 MeV/u ⁴⁰Ar projectiles. Also measured are energy shifts of the K_α and K_β X-ray lines of residue atoms resulting from multiple inner shell ionization.     

K-shell X-ray production for fluorine ions on target elements Ti to La

The production of target atomK-shell X-rays has been studied for 2 to 28 MeV fluorine ions incident on thin solid targets of 14 elements with atomic numbers Z₂=22 to 57. Total X-ray production cross sections, energy shifts ofK _α andK _β lines andK _α/K _β intensity ratios were measured with a Si(Li) detector. The results of cross section measurements are compared with theoretical predictions of inner shell ionization. In most cases, satisfactory agreement between measured cross sections and theoretical Coulomb ionization cross sections, corrected for the perturbation of the target atom by the projectile charge and for relativistic effects, was obtained.     

Measurement of the strong-interaction shift and broadening of the ground state of the pp̄ atom

The K_α X-rays from pp̄ atoms formed in H₂ gas at normal temperature and pressure are unambiguously identified by coincidences with L X-rays populating the 2P level. Background due to inner bremsstrahlung is suppressed by selecting events annihilating into neutral final states only. The K_α line is observed with a significance of more than 25 standard deviations at an energy of 8.67 (15) keV. From fits to the K_α line we obtain a strong-interaction shift and width of the 1S level, averaged over the unresolved spin singlet and triplet contributions, of ΔE + iΓ/2 = [−0.70(15) + i0.80(20)] keV.     

Projectile Z dependence of double K-shell ionization in light elements by hydrogen- and helium-ion bombardment

The K² X-rays from Be, B and O atoms by H- and He-ion bombardment were measured. The ratio of σ_2K(He) to σ_2K(H) exhibits the projectile Z⁴₁ dependence. This is the first observation of the Z₁-dependence of σ_2K predicted by the Coulomb excitation.     

Study of the energy release region of a heavy-ion flux in nanomaterials by X-ray spectroscopy of multicharged ions

X-ray spectroscopic data are reported on the state of a silicon aerogel medium (SiO₂) irradiated by a Ni ion flux with an energy of 4.7 MeV/nucleon. Radiation from the electron transitions to the K shell in multicharged Si ions is detected with spatial resolution along the direction of the beam propagation in the medium. Calculations performed for the ionization state and population of the levels excited in the silicon atoms of the target provide the estimate T_e = 70–120 eV for the medium electron temperature in the ion tack region. Two-dimensional hydrodynamic calculations provide the estimate T_e = 60–116 eV for the same conditions and densities of 0.5–2.5 g/cm³ of the excited target medium.     

Production rates for π+ K −, pK −, and pπ− atoms in inclusive processes

The yields of π⁺ K ^?, pK ^?, and pπ^? atoms in the reaction p + Al → atom + X at energies of 24, 70, 450 GeV and emission angles of θ_lab=1°–6° are calculated from inclusive-production cross sections for p, π⁺, π^?, and K ^?. Estimates of these hadronic-atom yields for a Ta target are also given. The inclusive-production cross sections for p, π⁺, π^?, and K ^? are obtained within the Lund model of string fragmentation. The accuracy of the calculations is estimated by comparing single particle yields calculated by the Lund model and experimental yields of particles in proton-nucleus interactions.     

Discovery of a superconducting A-15 phase in the V-Re system

A superconducting A-15 type phase of a very unusual stochiometry has been discovered in the vanadium-rhenium system. The phase is stable only above 1500°C and exists over a very limited homogeneity range near 29 atom percent vanadium. The lattice parameters range from 4.8774 to 4.8802 Å with the corresponding superconducting transition temperatures varying from 8.4 K to 7.6 K. X-ray diffraction shows that both Re and V atoms occupy the A-sites, only Re atoms are in the B-sites and there is no evidence of any superstructure. Specific heat measurements give values of γ = 4.03 mJ/g-atomK², β = 0.0285 mJ/g-atomK⁴ and θ_D = 409 K.     

Bulk magnetization study of a DyNi5 single crystal

Magnetization and susceptibility measurements were performed on a single crystal of DyNi₅ along the three main symmetry axes of the ortho-hexagonal cell. Below its ordering temperature (T_c = 11.6 K), b and c are respectively the easy and hard magnetization axes. The strong anisotropy originates from the crystalline electric field acting on the 4f electrons of the Dy³⁺ ions. A small magnetization is induced on nickel atoms by the applied field and the exchange interactions with the dysprosium atoms. The crystal field parameters, the molecular field coefficients and the susceptibility of nickel atoms are determined from the experimental data.     

On a new combined mechanism of hot electron capture in a semiconductor

A new combined (thermal-collisional) mechanism of recombination is proposed. The associated capture cross section is calculated. The electric field ranges where this mechanism comes into play and begins to dominate over the Lax cascade mechanism are established. The calculations are performed for n-type samples with different concentrations N ₀ of neutral impurity atoms and different degrees of compensation K.     

X-ray emission spectra and electronic structure of VO,VN, VC

The experimental K_β5 and L_α emission spectra for vanadium and K_α spectra for nonmetal are studied for vanadium monoxide, nitride and carbide. Using the spectra unfolding the experimental molecular orbital diagrams have been obtained. By the semiempirical Mulliken-Wolfsberg-Helmholz method with the self-consistency on charges and configurations the calculations of electronic structure of clusters [VO₆]^10?, [VN₆]^15? and [VC₆]^20? have been carried out. The results of calculations are compared with the X-ray data. The effects of chemical bonding and charge densities on metal atoms in VO, VN, VC are discussed.     

Energies of electronic K X-rays of muonic atoms

The shifts of the electronic K X-rays in muonic atoms are calculated and compared with the recent experimental data. The shifts may be caused either by the incomplete screening of the nuclear charge by the muon, or by additional electronic vacancies produced by preceding Auger transitions. The first mechanism explains the experiment well. The good agreement between the measured and calculated shifts for K_α and K_β X-rays means that the electron L shell is not strongly depleted when the muon has reached orbits with n = 6 to 9.     

Magnetic hyperfine fields of (Nd2Fe1-xCox)14B AT x = 0.25 between 100 and 780 K

The ⁵⁷Fe Mössbauer spectra are recorded in Nd₂(Fe_1-xCo_x)₁₄B at x = 0.25 in the temperature range 100 to 780 K. T_c the Curie temperature, B̄_hf, the magnetic hyperfine field average over various Fe nuclei of the unit cell and its temperature coefficient α(B̄_hf) in the vicinity of 300 K are found to be 760(5) K, 34.0(3) T and -0.08(1)% K^-1, respectively. The magnetic moment at Fe atoms is estimated to increase up to 12% as a result of the partial substitution by Co atoms. The dependence of the fields upon temperature is observed to be least at the j₂ and k₂ sites as compared to the other sites of Fe. The results for the variation of B_hf at all of the six sites of Fe with respect to temperature are given. A site preference of Fe atoms for the j₂ sites is observed.     

Crystallographic and magnetic investigations on cobalt gallium sulfides: α-CoGa2S4 and γ-CoGa2S4

Crystals of α- and γ-phase CoGa₂S₄ were grown by vapour-phase chemical-transport and fluxmethod, respectively. The α-phase crystallizes in the space group I4&#x0304;, with Co and Ga atoms almost ordered on special positions. The α-form was found to be antiferromagnetically ordered below T = 7 ± 0.5 K. The γ-phase crystallizes in the space group F4&#x0304;3m, showing cationic sites randomly occupied by metal atoms and vacancies. Its magnetic properties were completely determined by the occurrence of short-range magnetic order.     

Generation of characteristic x rays by a terawatt femtosecond chromium-forsterite laser

Characteristic K _α x rays arising when a metallic target is irradiated by femtosecond infrared pulses that are generated by a terawatt chromium-forsterite laser system (1240 nm, 90 mJ, 80 fs) are studied. The absolute yield (up to 3 × 10⁸ photons/sr pulse) and the coefficient of the transformation of laser radiation to K _α radiation (maximum value ≈0.03%) are measured for an iron target. The dependence of the radiation intensity on the angle of incidence of p polarized laser radiation is analyzed. The mechanisms of the production of fast electrons responsible for generating characteristic x rays are discussed.     

Partial molar adiabatic compressibilities of transfer of some amino acids from water to aqueous lactose solutions at different temperatures

Apparent molar adiabatic compressibilities (K_{?, s}) of glycine, L-alanine, L-valine, and L-leucine have been determined in aqueous and mixed aqueous solutions of lactose (2 to 6 mass%) at T = (293.15, 298.15, 303.15, and 308.15) K. From these data partial molar adiabatic compressibilities at infinite dilution (K_{?, s}⁰) have been evaluated to calculate corresponding transfer function. The transfer partial molar adiabatic compressibilities at infinite dilution (ΔK_{?, s}⁰) are found to be positive. The decrease in the magnitude of transfer partial molar adiabatic compressibilities from glycine to L-leucine indicates the dominance of hydrophobic-hydrophobic interactions between the increasing side chains of amino acids. Also, the contributions of NH₃⁺COO⁻ , and CH₂ groups have been calculated by the linear correlation of K_{?, s}⁰ with number of carbon atoms in the alkyl chain of amino acids.     

X-Ray spectral and theoretical investigations of the electronic structure of phenylcyclosilanes (SiPh2) n (n = 4–6)

The X-ray emission SiKα_{1, 2} and SiKβ₁ spectra of a series of phenylcyclosilanes (SiPh₂) _n (n = 4–6) have been obtained. Using the results of quantum-chemical calculations in the density functional theory approximation, the fine structure of SiKβ₁ spectra has been interpreted. Distributions of densities of electron states of silicon atoms over the valence band have been constructed and the types of chemical bonds providing the Si-Si and Si-Ph interactions have been established. Based on the theory of natural bond orbitals, the chemical bonding in the studied series of phenylcyclosilanes has been analyzed.