An apparatus for determining the secondary electron emission properties of nonconductors
The apparatus described allows the measurement of the secondary emission coefficient and the secondary electron energy distribution from nonconducting surfaces. The potential of the nonconducting surface is stabilized by a cathode very close to it. The use of an oscillatory primary beam allows a measurement of the secondary emission coefficient. The application of a sinusoidally modulated voltage sawtooth allows the determination of the emitted electron energy distribution and measures the potential of the emitting surface. The performance of the apparatus is demonstrated by results obtained from an amorphous magnesium oxide coating.
The Ultimate Sensitivity of Sokolov Image Converter Tubes
The gridded Sokolov tube has been the subject of an analytical and experimental study to determine its ultimate sensitivity. The tube is treated as an electron coupled piezoelectric receiver and detailed consideration of the electron coupling leads to a complete expression for the signal to noise ratio at the output terminal, provided the operating frequency and bandwidth are specified. The factors which lead to the sensitivity are shown to depend on secondary emission characteristics of the piezo-surface, the presence or lack of space charge noise suppression, the electron gun characteristics, the electrode spacing, the tube amplifier matching as well as the dielectric and piezoelectric properties of the receiving element. The part that charging and discharging processes play at the surface is discussed as is the effect of mechanical energy storage. Transit time effects do not normally arise from electron interaction in these tubes but depend on geometrical effects and are consequently excluded from the discussion.
Experimental energy barriers to anions transporting through nanofiltration membranes.
Environmentally relevant contaminants fluoride, chloride, nitrate, and nitrite face Arrhenius energy barriers during transport through nanofiltration (NF) membranes. The energy barriers were quantified using crossflow filtration experiments and were in the range of 7-17 kcal·mol(-1), according to ion type and membrane type (Filmtec NF90 and NF270). Fluoride faced a comparatively high energy barrier for both membranes. This can be explained by the strong hydration energy of fluoride rather than other ion properties such as bare ion radius, fully hydrated radius, Stokes radius, diffusion coefficient, or ion charge. The energy barrier for fluoride decreased with pressure, indicating an impact of directional force on energy barriers. The influence of temperature-induced pore radius variability and viscosity on energy barriers was considered. The novel link between energy barriers and ion properties emphasizes the importance of ion hydration and/or partial dehydration mechanisms in determining transport in NF.