Elastic scattering of 86 MeV9Li and 55 MeV6He on208Pb

The cross sections of elastically scattered⁹Li and⁶He on²⁰⁸Pb were measured. The scattered particles were detected by an annular CR-39 solid state nuclear track detector and the monitoring was done with a triple telescope of silicon detectors. The classical and optical model analyses of the measured elastic cross sections have been carried out. It was shown that the peripheral⁹Li interaction region has a rather high transparency. Strong dynamical polarization of⁹Li ions in the process of scattering is suggested.     

Intercalation of graphene on iridium with samarium atoms

Intercalation of graphene on Ir (111) with Sm atoms is studied by methods of thermal desorption spectroscopy and thermionic emission. It is shown that adsorption of samarium at T = 300 K on graphene to concentrations of N ≤ 6 × 10¹⁴ atoms cm^–2 followed by heating of the substrate leads to practically complete escape of adsorbate underneath the graphene layer. At N > 6 × 10¹⁴ atoms cm^–2 and increasing temperature, a fraction of adsorbate remains on graphene in the form of two-dimensional “gas” and samarium islands and are desorbed in the range of temperatures of 1000–1200 K. Samarium remaining under the graphene is desorbed from the surface in the temperature range 1200–2150 K. Model conceptions for the samarium–graphene–iridium system in a wide temperature range are developed.     

Excited state lifetime during photostimulated desorption of no from a Pt surface

We analyze the rotational energy distribution N(J) for NO molecules desorbed from a Pt (111) surface, taking into account the valence electron excitations, using a simple impulse model. We find a linear dependence between ln N(J) and (E_r)^1/2, where E_r is the rotational energy of the desorbed molecules. The excited state lifetime and the critical residence time in the excited state, evaluated from the given dependences, are close to each other, and in order of magnitude are 10⁻¹⁵ s. We also estimate the frequency and amplitude of the tilting vibrations of the adsorbed molecules in the excited state. Eastern Osetin University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 26–31, July, 1998.     

Desorption of cluster ions from adsorbed methane under cryogenic condition by low-energy ion irradiation

We have investigated ion desorption from adsorbed methane following keV He⁺ ion irradiation. The thickness of the adsorbed layer was precisely controlled. For mono-layered methane, only monomer ions (CH_x⁺) were desorbed by 1 keV He⁺ ion irradiation. On the other hand, a large number of cluster ions (C_nH_x⁺) up to n = 20 were desorbed from multi-layered film. Among cluster ions, molecular ions with CC bonds were found, which indicates that chemical bonds are newly formed by ion irradiation. Based on the results for thickness dependences of the mass spectral patterns, it was elucidated that the monomer ions are desorbed from the top surface layer through single electron excitation. While the cluster ions are formed mainly in the inside of the layers along the nuclear track due to the high-density electronic excitation, which is produced by nuclear collision between incident He⁺ ions and frozen molecules.     

Angular dependent photon-stimulated desorption of ions from a V2O5(010) surface

Using a display-type analyzer, we have measured the angular and energy distribution of O⁺ ions desorbed from a V₂O₅(010) surface by incident photons. The desorbed ions were mass-analyzed using time-of-flight gating techniques. The angular distribution of desorbed ions was found to be strongly peaked in the direction of the surface normal. This strongly directional desorption pattern reflects the local bonding geometry of the topmost oxygen atoms in the surface. The observed photoexcitation spectrum of the ion yiel can be explained with the core level Auger decay model formulated by Knotek and Feibelman.     

A study of the reaction (π+, π+ p) in 12C and 6Li

We have measured the angular and momentum distributions of the scattered pions from the reaction ¹²C(π⁺, π⁺p)¹¹B and ⁶Li(π⁺, π⁺ p)⁵He in a coincidence experiment. We compare our results with the plane and distorted wave impulse approximations.     

Spinpolarisation und Winkelverteilung der Elektronen nach Anregung verschiedener Zustände des Hg-Atoms

At energies above ～ 50 eV, electrons scattered inelastically from mercury atoms show a similarity to elastically scattered electrons in both spin polarization and angular distribution. This similarity vanishes at primary energies below ～ 30 eV for the 6p′³ P ₁-channel (11.0 eV energy loss) and below～ 25 eV for the 6¹ P ₁-channel (6.7 eV energy loss).     

Spectroscopy between 5 and 6 μm with a tunable spin-flip Raman source

We describe the application of a tunable, infrared, spin-flip Raman source to the measurement of the absorption spectra of gases in the spectral region 5–6 μm. Continuous tuning was obtained by using a low finesse Raman crystal cavity to eliminate mode pulling and hopping effects. The effects of atmospheric absorption, and pulse-to-pulse and magnetic field dependent intensity variations were cancelled by using a double beam arrangement. As an illustration of the operation of such a Raman spectrometer we obtain the P and Q branch absorption spectra of nitric oxide at various gas pressures in the spectral region 1890-1835 cm^-1. Studies at low gas pressure and with the tunable source operating close to the threshold for stimulated emission show a resolution of ≈ 0.08 cm^-1, determined by the linewidth of the Raman scattered radiation. This linewidth is shown to be in agreement with a mechanism of stimulated superradiant narrowing of the spontaneously scattered lineshape.     

Low energy alkali ion scattering investigation of Au nanoclusters grown on silicon oxide surfaces

The atomic and electronic structures of Au nanostructures grown by deposition onto various silicon oxide surfaces were probed with low energy alkali ion scattering. Charge state-resolved time-of-flight spectra of scattered 2 keV ³⁹K⁺ ions were collected from Au deposited onto an untreated Si wafer with a native oxide, a thermally grown oxide surface, and atomically-clean Si(111). It is shown that nanoclusters form on both oxides, but not on the clean Si. A quantitative analysis of the ion scattering spectra indicates that the nanoclusters are initially flat, two-dimensional structures that start to develop a second layer at about 0.5 Å of deposited Au and then form three-dimensional islands. The neutral fraction of scattered 2 keV ³⁹K⁺ ions decreases with deposition indicating changes in the quantum state occupancy with cluster size. The shapes of the clusters differ on the native and thermal oxides, leading to shape-dependent neutralization.     

回火金属玻璃小角X射线散射强度的背底校正

提出校正回火金属玻璃（非晶合金）小角ｘ射线散射强度的背底误差的方法：将淬火态非晶合金的小角Ｘ射线散射强度作为在相同的实验条件下得到的回火非晶合金小角Ｘ射线散射强度的背底而予以扣除。并将这样扣除背底和用通常方法扣除背底得到的结果相比较，由前者得到的散射强度遵从Ｐｏｒｏｄ律，并进而得到Ｐｏｒｏｄ常数Ｋ_p＝４．６×１０^-2（ｎｍ^-3），积分不变量Q_s＝１．６３（ｎｍ^-2），比内表面Ｓ_p＝８４ｍ²／ｃｍ³，Ｐｏｒｏｄ半径Ｒ_p＝４．４ｎｍ用通常方法扣除背底后的散射强度不满足Ｐｏｒｏｄ规律。 关键词：     

Superlong pulses of laser oscillation on the 6 1P1-5 1D2 transition of the barium atom

A possibility of CW laser oscillation on atomic transitions between a resonance energy level and a metastable one under conditions when lower laser states are deactivated by electron impacts has been theoretically shown. We determined the plasma parameters so that CW laser action on such transitions of Cu, Au, Ca and Ba atoms may be possible. Superlong laser pulses of 6 μs duration were obtained on the 6 ¹P₁-5 ¹D₂ transition of the barium atom.     

Au-analyte adducts resulting from single massive gold cluster impacts

Utilizing Au₄₀₀⁴⁺ primary ions produces large molecular ion yields, some in excess of unity, with minimal surface damage. A surprising observation is the occurrence of Au-analyte adducts as part of the ejecta desorbed by a single Au-cluster impact. We present data that demonstrate that Au and Au-adducts as secondary ions (e.g., AuCN⁻, AuGly⁻ and AuCsI⁻) are the result of the interaction between a single primary ion, Au₄₀₀⁴⁺ and the target atoms.     

Microwave power absorbed by and scattered from a multilayered zero-index anisotropic metamaterial-semiconductor cylinder

We present here dependencies of scattered and absorbed powers of incident perpendicularly and parallel polarized microwaves by a multilayered cylinder. We consider here the normal (angle ??=90^°) and oblique (angles ??=60^°,30^°,5^°) incidence of microwave on the cylinder. The one consists of a glass core that is coated by the six anisotropic metamaterial and lossy n-Si semiconductor alternative layers. Characteristics of a cylinder with the semiconductor external layer are presented. The dispersion dependency of n-Si losses was taken into account. The metamaterial is a uniaxial anisotropic medium with the electric and magnetic plasma resonances in the frequency range from 1 until 4?GHz. The anisotropic metamaterial can include the constitutive parameters equal to zero. The multilayered cylinder has the external radius equal to 2?mm. The glass core has a radius equal to 0.5?mm. The thickness of all layers is the same. We have compared the scattered and absorbed power dependencies on the microwave polarization, the angle of microwave incidence (the normal and oblique directions of the incidence to the z-axis), and the n-Si specific resistivity. We discovered specific dependencies of scattered and absorbed powers on the parameters.     

The effect of short-range repulsion of electronic shells on the energy spectrum of ions desorbed under the influence of electronic transitions: A relaxation model

A relaxation model is used to investigate the effect of repulsion of electron shells, which is modeled by introducing an initial velocity of the desorbed particles, on the energy distributions of ions desorbed under the action of electronic transitions. The role of reneutralizing processes is considered. Fiz. Tverd. Tela (St. Petersburg) 39, 1679–1682 (September 1997)     

Forward-backward asymmetries in the direct breakup of6Li

The (α+d) breakup of 60 MeV⁶Li scattered from²⁰⁸Pb has been measured inside the grazing angle for c.m. energies of the fragments between 100 keV and 1.5 MeV. The distinctly different anisotropies of the sequential and direct breakup components show that Coulomb dissociation cannot be related in a straightforward manner to the astrophysically relevant⁴He(d, γ)⁶ Li capture reaction.     

Doppler-shift attenuation measurements on Mg by (α, α') and (p,p') reactions

The (α, α') and (p, p') reactions have been used to populate states in ²⁴Mg in order to measure lifetimes of ten states by the Doppler-shift attenuation method. The shifted γ-rays were observed by a planar 5.6 cm³ Ge(Li) detector at 90° to the beam at the target in coincidence with the scattered particles observed in either of two particle detectors located symmetrically with respect to the beam. A computer coupled dual two-parameter arrangement permitted concurrent measurements for all states appreciably populated. The present measured transition probabilities are compared with predictions from a truncated j-j coupling shell-model calculation.     

自由电子激光的能量转换

根据Ｗｅｉｚｓａｃｋｅｒ－Ｗｉｌｌｉａｍｓ近似，把自由电子激光模拟成相对论性电子与赝光子的碰撞，而光子被散射．按照这个物理模型，研究了电子与光子的能量交换，得到了散射光子能量与碰撞前光子能量之间的关系：ε_p=4γ²ε_p⁽⁰⁾散射光子能量的放大是以电子消耗能量为代价的分析。计算了能量交换的规模，并得出自由电子激光中能量转换效率最大为５０％. 关键词：     

Absolute photon yield from silicon surface under electron and ion irradiation

The characteristics of the optical radiation accompanying the bombardment of silicon surface by electrons and medium-energy ions have been studied. The continuous radiation observed in this case is related to interband electronic transitions. The characteristic radiation (which is present in both cases), in the case of ion bombardment, is emitted by silicon atoms sputtered in the excited state and scattered helium ions; in the case of electron bombardment, this radiation is emitted by desorbed excited atoms and residual atmosphere molecules, which cover the silicon surface under study.     

Atom-dimer and dimer-dimer scattering in fermionic mixtures near a narrow Feshbach resonance

We develop a diagrammatic approach for solving few-body problems in heteronuclear fermionic mixtures near a narrow interspecies Feshbach resonance. We calculate s-, p-, and d-wave phaseshifts for the scattering of an atom by a weakly-bound dimer. The fermionic statistics of atoms and the composite nature of the dimer lead to a strong angular momentum dependence of the atom-dimer interaction, which manifests itself in a peculiar interference of the scattered s- and p-waves. This effect strengthens with the mass ratio and is remarkably pronounced in ⁴⁰K-(⁴⁰K-⁶Li) atom-dimer collisions. We calculate the scattering length for two dimers formed near a narrow interspecies resonance. Finally, we discuss the collisional relaxation of the dimers to deeply bound states and evaluate the corresponding rate constant as a function of the detuning and collision energy.     

Influence of the surface structure on the adsorption of hydrogen on platinum,as studied by field emission probe-hole microscopy

The adsorption of hydrogen on platinum was investigated with a field emission microscope, equipped with a probe-hole assembly to enable adsorption studies on individual emitter regions. Adsorption of hydrogen is markedly face-specific. At 95 K and a hydrogen equilibrium pressure smaller than 2 × 10^?9 Torr the work function decreased strongly on the (111) face but increased on the (110) and (210) regions. Three different adsorption states were observed: β-hydrogen which desorbed above 300 K, α-hydrogen which desorbed around 230 K and a very weakly bound γ-state with a maximum heat of adsorption of 6 $\text{kcal}\text{mole}$. The α- and γ-states caused a decrease, the β-state an increase of the work function. The results show that the relative contribution of these three states and their heat of adsorption depend strongly on the crystal face. The β-state appeared to be absent on a smooth (111) plane. Hydrogen bound in the αstate has a relatively high heat of adsorption on the (111) region. A model has been proposed for the nature of the sites on the different surfaces involved in the adsorption of hydrogen.