The charging stability of different silica glasses studied by measuring the secondary electron emission yield

This paper reports that the charging properties of lead silica, Suprasil silica and Infrasil silica are investigated by measuring the secondary electron emission （SEE） yield. At a primary electron beam energy of 25 keV, the intrinsic SEE yields measured at very low injection dose are 0.54, 0.29 and 0.35, respectively for lead silica, Suprasil and Infrasil silica glass. During the first e-beam irradiation at a high injection current density, the SEE yields of lead silica and Suprasil increase continuously and slowly from their initial values to a steady state. At the steady state, the SEE yields of lead silica and Suprasil are 0.94 and 0.93, respectively. In Infrasil, several charging and discharging processes are observed during the experiment. This shows that Infrasil does not reach its steady state. Two hours later, all samples are irradiated again in the same place as the first irradiation at a low current density and low dose. The SEE yields of lead silica, Suprasil and Infrasil are 0.69, 0.76 and 0.55, respectively. Twenty hours later, the values are 0.62, 0.64 and 0.33, respectively, for lead silica, Suprasil and Infrasil. These results show that Infrasil has poor charging stability. Comparatively, the charging stability of lead silica is better, and Suprasil has the best characteristics.

Surface potential uniformity and sensitivity of large-area PTFE electret discs of different thicknesses produced by a modified corona poling rotating system for dosimetry applications

In this study,large-area(6-cm diameter)Teflon polytetrafluoroethylene(PTFE)discs of different thicknesses(0.2-,0.5-and 1-mm)were negatively and positively charged by using the“modified single point-to-plane corona poling rotating system”.The effects of some crucial parameters of the PTFE disc as well as the modified corona poling rotating system on the PTFE surface potential uniformity such as.(a)PTFE disc thickness,(b)PTFE disc polarity and(c)needle-to-PTFE disc distance were successfully reported.Accordingly,closer needle-to-PTFE disc distance,positive charging mode and thinner PTFE disc provided a better PTFE surface potential uniformity.However,the effects of PTFE charge polarity and needle distance on the electrostatic charge potential uniformity were much more remarkable in comparison with the effects of PTFE thickness.Additionally,the surface potential distribution profiles of charged PTFE discs were totally flat and independent of the PTFE thickness at 5-and 13-mm needle distances for the negative and positive charging modes,respectively.At the optimized charging conditions,large-area PTFE electret disc(0.5-mm-thick)with positive uniform surface charge potential especially at the edges up to
1.8 kV with stability up to 77 days studied was produced by applying a new multiple heat treatment protocol to the PTFE disc for radon dosimetry.As also observed in this study,the sensitivity of PTFE electret dosimeters to a defined radon gas concentration increases as the PTFE thickness increases.Meanwhile,0.5-mm-thick PTFE electret disc produced was selected to be used as a high quality electret dosimeter with acceptable and superior parameters for different applications in particular medium-term radiation dosimetry in both low and high dose rate ionizing radiation fields.

Charge distribution into illuminated dye-doped surface stabilized ferroelectric liquid crystal cell

Surface stabilized （anti） ferroelectric liquid crystal cells can be used as an optically addressed media for optical data processing. The structure of the cell has to contain a photo sensible agent, i.e, an absorbing dye-doped orienting layer. The all-optical generation of the diffractive grating can be done due to the switching parameters of the smectic slab within cells with a sensitive layer. This Letter considers a study of the optically induced charge generation into the dye-doped layer, and the explanation of the phenomena of the selective molecular director reorientation, while cell driving what leads to the induction of phase grating.