Electron-stimulated desorption of potassium and cesium atoms from oxidized molybdenum surfaces

The electron-stimulated desorption (ESD) yields and energy distributions for potassium (K) and cesium (Cs) atoms have been measured from K and Cs layers adsorbed at 300 K on oxidized molybdenum surfaces with various degrees of oxidation. The measurements were carried out using a time-of-flight method and surface ionization detector. The ESD appearance threshold for K and Cs atoms is independent of the molybdenum oxidation state and is close to the oxygen 2s level ionization energy of 25 eV. Additional thresholds for both K and Cs atoms are observed at about 40 and 70 eV in ESD from layers adsorbed on an oxygen monolayer-covered molybdenum surface; they are associated with resonance processes involving Mo 4p and 4s excitations. The ESD energy distributions for K and Cs atoms consist of single peaks. The most probable kinetic energy of atoms decreases in going from cesium to potassium and with increasing adsorbed metal concentration; it lies in the energy range around 0.35 eV. The K and Cs atom ESD energy distributions from adlayers on an oxygen monolayer-covered molybdenum surface are extended toward very low kinetic energies. The data can be interpreted by means of the Auger stimulated desorption model, in which neutralization of adsorbed alkali-metal ions occurs after filling of holes created by incident electrons in the O 2s, Mo 4s or Mo 4p levels.     

Spectroscopic properties of ZnWO4 single crystal doped with Fe and Li impurities

The influence of Fe and Li co-doping on optical properties of ZnWO₄ crystals have been investigated by optical spectroscopy and electron paramagnetic resonance (EPR). The iron ions were added to the ZnWO₄ composition in the form of Fe⁰, FeO or Fe₂O₃. EPR has been used for determination of the Fe³⁺ concentration. The luminescence and excitation spectra obtained at different temperatures are presented. Under excitation 325 nm, two bands were observed: blue-green emission peaked at 490 nm and red peaked at 650 nm. The blue- green emission is related to Fe³⁺ and their shape depends on the doping method. The red emission is not related to the Fe³⁺.     

The effects of ionizing radiation on the cellulose of woodfree paper

There is presently a concern because the US Postal Service now has 8 electron beam accelerators to treat mail in locations along the east coast and that a sufficient dosage to destroy Anthrax is also strong enough to darken and weaken the paper in the postal envelopes. In addition to direct photolytic scission of the cellulose chain, irradiation darkens paper, swells pulp fibres, increases hygroscopicity, and renders the cellulose more soluble in alkaline solution and more susceptible to acid hydrolysis. This report will focus on the effect of electron beam irradiation on degradation of cellulose of fine papers. Three reference papers were selected, sorted into postal envelopes and exposed to electron beam irradiation. The results have shown that irradiation at the dosage used to treat mail by the US Postal Service depolymerizes and oxidizes the cellulose. Depolymerization is responsible for a decrease of paper strength while oxidation induces darkening of the paper. Irradiating at high electron beam energy is less damaging than using lower energy. Moreover, linear relationships have been found between the number of chain scission (CSN) in cellulose and the irradiation dosage as well as between CSN and Zero-Span Breaking Length. These relationships make the strength loss predictable.     

Studies on Single-electron Oxidation of N-Alkyl-p-Phenylenediamines and Benzidines in Aqueous Acetonitrile by Cyclovoltammetry and ESR Spectroscopy

It is demonstrated by cyclovoltammetry and ESR spectroscopy that N,N,N,'N,'-tetramethyl; tetraethgl, tetra-n-propyl, tetra-n-butyl-p-phenylenediamine and tetraethyl, tetra-n-propyl-p-benzidine undergo deprotonat ion and two consecutive single electron transfer step CE reaction at electrode in aqueous acetonitrile with the corresponding radical cations as the intermediate. The bivalent cations produced at the electrode react not only with hydroxyl anion in the medium to give quinone but also with the N-alkyl-p-phenylene-diamines or benzidines to produce the corresponding radical cations.     

LOW POWER MEASUREMENTS ON THE NEW RF OUTPUT SYSTEM OF A 170 GHZ, 2 MW COAXIAL CAVITY GYROTRON

The design of the quasi optical (q. o.) RF output system for the first industrial prototype of the European 170 GHz, 2 MW, CW coaxial cavity gyrotron for electron cyclotron heating and current drive in ITER has been verified at a low power level. Results of measurements with a high quality TE_34,19-mode generator are in good agreement with the design calculations. This strengthens the confidence both to the employed design codes and to the manufacturing quality of the launcher and mirrors.     

Differential algebraic method for computing the high order aberrations of practical electron lenses

Differential algebraic method is of an effective technique in computer numerical analysis. It implements exactly differentiation up to arbitrary high order based on the nonstandard analysis. Some complicated nonlinear dynamics problems including high order aberrations of electron optics systems can be solved by mapping properties of differential algebraic quantities. However, the existing electron optical differential algebraic method can only be applied to those problems where the electric and/or magnetic fields are expressed in analytic forms. In this paper, the principle of differential algebraic method is applied to practical electron lenses whose electric/magnetic fields are in the forms of discrete arrays, for example, the files computed by FEM or FDM method. Thus the developed new differential algebraic method is applicable to engineering design. The programs were written for computing the high order aberrations of practical electron lenses. An example is given to show that the numerical results have good accuracy compared with the results computed by using the electric fields expressed in analytical form; the accuracy is limited only by the accuracy of the numerical computation of the fields and the arithmetic errors, and it is enough for engineering design.     

Ultrastructural Evaluation of 585-nm Pulsed-Dye Laser-Treated Glottal Dysplasia

OBJECTIVE/HYPOTHESIS: To describe the ultrastructural changes occurring within pulsed-dye laser (PDL)-treated glottal tissues. STUDY DESIGN: Prospective. METHODS: Nine patients presenting with glottal dysplasia requiring biopsy to rule out microinvasive carcinoma were enrolled in this prospective study. At least two samples were obtained in each case: one from a PDL-treated area and another from a non-PDL-treated area (obtained from a nonphonatory region as an internal control). In some cases, a third sample was obtained from the junction between PDL- and non-PDL-treated areas. All samples were examined with light microscopy (H and E stain) and transmission electron microscopy. Observations were made of morphological changes within the epithelium, epithelial/ superficial lamina propria (SLP) junction, and the lamina propria of tissues treated with the PDL. Eight of nine patients were followed for a period of 9-25 months (mean, 18 months) with two recurrences that were retreated with awake-PDL and followed for an additional 8.3 and 9.5 months without recurrence. Vocal fold appearance returned to normal within 3-4 weeks posttreatment. RESULTS: Intraepithelial desmosome junctions were preferentially destroyed, and regional blood vessels were coagulated. The PDL consistently caused a separation of epithelial cells away from the basement membrane. CONCLUSIONS: The PDL allowed for both a surgical and a nonsurgical multimodality method for treatment of precancerous lesions with minimal effects on the SLP.     

Oxidation and contact resistance of Sn-Ag coated superconducting strands for the Large Hadron Collider (LHC)

The oxides formed on the Sn-Ag coated Large Hadron Collider (LHC) superconducting cables during a 200 °C heat treatment in air are described and the oxide composition is compared with the interstrand contact resistance (R_C). The analysis of more than 250 interstrand contact areas shows that the higher the average Cu content with respect to the Sn content in the oxide, the higher is R_C. During the 200 °C heat treatment, Sn in the coating is transformed into a Cu₃Sn layer, on which an oxide grows that consists essentially of a thin outermost layer of CuO on top of Cu₂O, similar to the oxide structure formed on bare Cu. The underlying Cu₃Sn layer acts as an O diffusion barrier that prevents O diffusion into the Cu bulk during the subsequent cable heat treatment under high pressure. On contact zones where the Cu₃Sn layer is not formed during the 200 °C heat treatment mainly Sn oxide grows and R_C is comparatively low.     

Transfer ionization in isocharge sequence ion and Ne collisions

The dependence of the ratio R1 for transfer ionization to single capture for Cq+, Nq+, Oq+, Neq+ ions on Ne target upon the electronic structure of the projectile is studied. For Aq+-Ne collisions the ratio R1 decreases as the atomic number Z of the projectile increases for q=4,5,6,7 sequences which provides strong evidence for the increase of the binding energy of the target valence electron after single electron capture. The increase in binding energy depends both upon the atomic number of the projectile and the target atom.     

Ar辅助确定Al等离子体电子温度

用Ar气作保护气时 ,Nd :YAG脉冲激光烧蚀Al靶 ,将诱发Ar气电离 ,并产生丰富的Ar离子谱线辐射。文章根据Ar离子谱线辐射信息 ,分析了ArⅡ 385 0 5 7,ArⅡ 386 85 3,ArⅡ 4 0 4 2 91 ,ArⅡ 4 0 7 2 0 1nm等 4条谱线的时间分辨行为 ,计算了Al等离子体的电子温度。结果发现 :Al等离子体的电子温度约 1 5 0 0 0～2 2 0 0 0K ,随延迟时间的增加 ,电子温度单调衰减