[en] The momentum distributions of hadrons produced in e⁺e^- collisions at a center of mass energy of 29 GeV have been measured. The data used in this analysis were collected by the High Resolution Spectrometer (HRS) at the Positron Electron Project (PEP) in the Spring of 1982. The HRS is a general purpose particle detector consisting of a 16.2 kgauss solenoidal magnet, 17 layers of tracking chambers and multiple layers of lead-scintillator shower counters. The data consist of 8200 hadronic events, corresponding to an integrated luminosity of 19.6 pbarn^-1 at E/sub cm/ = 29 GeV. Using the barrel shower counters' time-of-flight (TOF) measurements, charged particles in the momentum range 0.5-1.9 GeV/c are separated statistically. Measurements of differential cross sections, scaled cross sections, and charged particle fractions are presented and compared with measurements made by the TASSO and the JADE groups

[en] The momentum distributions of hadrons produced in e+e^- collisions at a center of mass energy of 29 GeV have been measured. The data used in this analysis were collected by the High Resolution Spectrometer (HRS) at the Positron Electron Project (PEP) in the Spring of 1982. The HRS is a general purpose particle detector consisting of a 16.2 kgauss solenoidal magnet, 17 layers of tracking chambers and multiple layers of lead-scintillator shower counters. The data consist of 8,200 hadronic events, corresponding to an integrated luminosity of 19.6 pbarn ^-1 at E/sub cm/ = 29 GeV. Using the barrel shower counters' time-of-flight (TOF) measurements, charged particles in the momentum range 0.5 - 1.9 GeV/c are separated statistically. Measurements of differential cross sections, d sigma /dp, scaled cross sections, S*(dsigma/dXp), and charged particle fractions are presented and compared with measurements made by the TASSO and the JADE groups

[en] The authors report the use of a simple microwave discharge ion source for producing ions from a non-gaseous material, without the complication of a magnetic field. The source is simple in design and easily constructed. Discharges which were initiated in argon produced Na⁺ ions from both sodium iodide and pure sodium. The absolute and relative rates of production of Na⁺ ions were found to vary greatly with the discharge pressure and incident microwave power. Operating conditions ranging from 0.016 to 0.064 mbar (1.6-6.4 Pa) and from 20 to 60 W were tested. The percentage of all the ions which were Na⁺ ions in discharges with sodium iodide was as high as 17% while with pure sodium it was as high as 89%. (author)

[en] Monte Carlo simulation calculations on a supercomputer have been made of the mobility of K⁺ ions drifting in pure He and Kr gases respectively under the action of a uniform electric field. Typical errors of 1% or less are achieved. By making direct comparisons with other theoretical and experimental data, these calculations have helped to verify both the three-temperature theory used to derive the theoretical mobility as well as the validity of various interaction potentials proposed. Results of these comparisons together with an earlier one for the K⁺-Ar system provide evidence that the three-temperature theory is generally applicable for the three different ion-neutral mass ratios studied, but yields a slight overestimation of the mobility around the peak mobility region. It is also found that the recent universal scaling law potential represents fairly well the collision interaction between the alkali ion and rare-gas atoms studied. (author)

[en] Relativistic distorted-wave method was used to calculate the electron impact excitation collision strengths for transitions 2s²¹S₀-2s2p³P₁ of Be-like isoelectronic ions. The target states were described, respectively, by 10-level, 46-level and 133-level MCDF configuration-expansion. The relativistic continuum orbitals were calculated in the potential field of frozen target-ion charge distribution with semi-classical exchange potential. The influence of the target states on this collision process along the isoelectronic sequence was investigated in the above three MCDF configuration-expansion modes. It was found that the configurations in the n=3 and the n=4 complexes have great influence on both the high and the low Z ions but the influence is relatively small for intermediate Z ions. The latter phenomenon was attributed to competition between opposing correlation and relativistic effects on the collision strengths. (orig.)

[en] Using the sol-gel method, polycrystalline double perovskites Sr₂FeMoO₆ with nanometer-scale grain size have been synthesized in the ambience of a controlled stream of different gaseous H₂-Ar mixtures during annealing. X-ray diffraction (XRD) results indicated that with an increasing proportion of H₂, the component of the SrMoO₄ impurity present in the crystallites first decreased, but then increased again with further increase of the H₂ proportion. The XRD results were further supported by independent sample analysis using Raman spectroscopy. Systematic investigation of the transport properties of the samples indicated that the SrMoO₄ impurity at the grain boundary played a key role in determining the measured resistance and magnetoresistance of Sr₂FeMoO₆. This impurity effect was found to be correlated to the variation of the mixture ratio of the ambient H₂-Ar gas stream surrounding the sample during annealing

[en] Measurements are made of the velocity distributions of He⁺, Ne⁺ and Ar⁺ ions drifting in their respective parent gas under the action of a uniform electric field at room temperature (297-300 K). Experimental results for E/N ranging from 60 to 320 Td are compared with both the Wannier equation for the RMS ion velocity and the corresponding Maxwellian distribution. The typical experimental curve is found to possess only a single maximum with its peak displaced towards the low velocity end and an enhanced high velocity tail in comparison with the Maxwellian. (author)

[en] Hitherto unavailable experimental values of the ratio, D_T/K, of the transverse diffusion coefficient to mobility for Na⁺ ions drifting in helium gas are reported. Results were obtained with estimated accuracies of better than 3% at temperatures between 302 and 304 K, and at electric field to neutral gas density ratios, E/N, ranging from 5 to 400 Td. By an independent approach, the three transport parameters are also computed by Monte Carlo simulation using potentials proposed by previous authors. (author)

[en] By conventional pulsed laser deposition followed by in situ annealing in high vacuum, we have successfully fabricated CdS-doped glass (CDG) nanocrystalline thin films on Si substrates. Photoluminescence (PL) spectra of CDG films show an emission band at about 539 nm (2.30 eV), which is attributed to a new CdO composite formed by the interaction of the CdS nanoparticles and SiO₂ in the film. The PL spectrum arising from the CdO band-band transition has a peak intensity which depends only on deposition times and not on the annealing treatment of the film. However, higher annealing temperatures yielded a greater crystalline size of CdO, as is evident from the resulting redshift of the CdO band in the PL spectra. The presence of CdO in the films was further confirmed by both energy dispersive x-ray and x-ray diffraction (XRD) measurements. Its growth in crystalline size with annealing temperature was also confirmed by analysis of the diffraction peak lines in the XRD spectra. Furthermore, XRD measurements also reveal that the crystal direction of the films was greatly determined by the annealing temperature. Finally, transmission electron microscopy pictures reveal the three different nanocrystalline structures of CDG corresponding to the different films produced with different heat treatments

[en] Group II metal oxides (MgO, CaO, SrO, and BaO) were coated on tungsten or tantalum filaments to form thermionic emitters of positive metal ions. The choice between tungsten and tantalum for optimum performance was empirically found to depend on the oxide material. Total ion emission current and ion purity were generally found to increase with temperature. A stable source of high purity (up to 97%) Ba⁺ ions could be obtained from the BaO-coated filament at 1800 degree C after 150 min of heating. At 1600 degree C, the SrO-coated filament could produce a relatively stable ion current and purity of 97% of Sr⁺ ions. Very pure (99.8%) Ca⁺ ions were emitted at 1950 degree C. However more stable ion current though less pure ions (87% of Ca⁺ at 1800 degree C) were obtained at lower temperatures. MgO-coated filaments using tungsten or tantalum wires were found to be unsuitable as a source of Mg⁺ ions. All the filaments of MgO, CaO, SrO, and BaO were found to produce larger ion current and higher ion purity at higher temperatures. In general, the relative isotopic abundances of ions produced by a thermionic source are reproduced by the natural isotopic abundances of the corresponding metal. It implies that the slight differences in the nuclear masses of the isotopes do not introduce any significant effect on their ion production efficiency. Between tantalum and tungsten as a choice for the filament material, tantalum was found to be a better choice for Ba⁺ and Sr⁺ ions, while tungsten was better for Ca⁺. copyright 1995 American Institute of Physics