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Electron impact single and double ionization cross-sections for krypton and xenon have been calculated in the binary encounter approximation (BEA). The accurate expression for σ E (cross-section for energy transfer E) including exchange and interference as given by Vriens and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. The theoretical cross-sections for single and double ionization of krypton are in fair agreement with the experimental data. Experimental results of double ionization of xenon indicate some contribution from indirect ionization mechanisms. On the basis of the present work, it is concluded that there is a small contribution to double ionization and a relatively large contribution to single ionization from a vacancy in the 4d shell.

Polycrystalline samples of samarium barium tungstate [ Sm2(Ba0.5W0.5)2O7 : (SBW)] pyrochlore structure type oxides have been prepared by a solid-state reaction technique. X-ray diffraction (XRD) patterns of this compound at room temperature suggest the formation of a single phase compound with orthorhombic structure. Studies of the dielectric constant and dielectric loss of compound as a function of frequency (4 kHz–1 MHz) at room temperature, and as a function of temperature (23–350°C) at 20 and 50 kHz frequencies suggest that the compound does not have dielectric anomaly. The variation of dc resistivity suggests the semiconductor characteristics of the material. The value of activation energy (E a ~ 0.43 at 20 kHz and E a ~ 0.29 at 50 kHz) of the above mentioned compound has been calculated from the slope of the ln σac versus 1/T graph in the high temperature region (> 240°C). The low value of activation energy supports the superionic nature of the compounds in the high temperature region.

Electron impact single ionization cross sections of copper have been calculated in the binary encounter approximation using accurate expression for ¡ as given by Vriens and HartreeFock momentum distribution for the target electron. The BEA calculation based on the usual procedure does not show satisfactory agreement with experiment in this case but a striking modification is found to be successful in explaining the experimental observations. The discrepancy is linked with the ionization of the ¿ ½¼ electrons and probably effective single ionization does not take place from ¿ shell of copper leading to smaller values of experimental cross sections.