Dielectric properties radiation, effect

In air, PTFE has a damage threshold of 200—700 Gy (2 x 10 — 7 x 10 rad) and retains 50% of initial tensile strength after a dose of 10" Gy (1 Mrad), 40% of initial tensile strength after a dose of 10 Gy (10 lad), and ultimate elongation of 100% or more for doses up to 2—5 kGy (2 X 10 — 5 X 10 rad). During irradiation, resistivity decreases, whereas the dielectric constant and the dissipation factor increase. After irradiation, these properties tend to return to their preexposure values. Dielectric properties at high frequency are less sensitive to radiation than are properties at low frequency. Radiation has veryHtde effect on dielectric strength (86). 

Radiation cross-linking of polyethylene requires considerably less overall energy and less space, and is faster, more efficient, and environmentally more acceptable. Chemically cross-linked PE contains chemicals, which are by-products of the curing system. These often have adverse effects on the dielectric properties and, in some cases, are simply not acceptable. The disadvantage of electron beam cross-linking is a more or less nonuniform dose distribution. This can happen particularly in thicker objects due to intrinsic dose-depth profiles of electron beams. Another problem can be a nonuniformity of rotation of cylindrical objects as they traverse a scanned electron beam. However, the mechanical properties often depend on the mean cross-link density. ... 

Radiation cross-linking of PE requires considerably less overall energy and space, and is faster, more efficient and more environmentally acceptable.93 Chemically cross-linked PE contains chemicals that are byproducts of the curing system. These often have adverse effects on the dielectric properties and, in some cases, are simply not acceptable.94... 

Banford et al. studied the radiation effects on electrical properties of low-density polyethylene (LDPE) at 5 K with the use of a 60Co gamma source and a thermal nuclear reactor [86]. They reported that both the electrical conductivity and the dielectric breakdown strength of LDPE at 5 K were not significantly affected by radiation absorbed doses up to 10s Gy, but an erratic pulse activity under high applied fields was observed in the sample irradiated at 106 Gy. 

The radiation effects on dielectric properties of an epoxy resin (Epilox EG 34 with aromatic amine hardener Nr 105) were studied by Jahn et al. with electron,... 

In this work, we present the effect of 193 nm pulsed UV high intensity radiation on polyimide, a polymer well known for its applications in solid-state technology (thermal stability and dielectric properties). We have used XPS in order to determine the evolution of chemical surface composition versus laser fluence and have obtained some attractive informations about these modifications induced by UV laser radiation. 

Some general conclusion from these studies are (1) Cu/PI TFML structures have excellent thermal and mechanical stability under extremes of temperature, humidity, and radiation (2) the adhesion of polyimide is highly dependent on interface chemistry and surface preparation (3) PI rapidly absorbs and desorbs water, which has an appreciable effect on its dielectric properties and thus the electrical charactersitics of TFML interconnections the electrical design tolerances must accommodate these variations or the package must be hermetically sealed (4) properly baked and sealed TFML packages can maintain MIL-STD internal moisture levels of less than 5000 ppm at 100°C. 

Molecules that have a permanent dipole moment (e.g., water) can rotate in a fast changing electric field of microwave radiation. Additionally, in substances where free ions or ionic species are present the energy is also transferred by the ionic motion in an oscillating microwave field. Owing to both these mechanisms the substance is heated directly and almost evenly. Heating with microwaves is therefore fundamentally different from conventional heating by conduction. The magnitude of this effect depends on dielectric properties of the substance to be heated. 

Measurements of the effect of radiation on the dielectric properties of CVD diamond have been reported using neutron irradiation experiments with fast neutron fluences up to at least lO nm (energy >0.1 MeV) [65]. Differences before and after irradiation were found to be more pronounced at lower frequencies. At 145 GHz specimens that started with values of tan 5 of 2 x 10 maintained these levels (or even showed a decrease in loss). Further experiments to extend radiation fluencies to 10 nm are in progress [68]. 

Newton used a liquid in glass-thermometer to study heat radiation. Rumford and Leslie used a difierential gas thermometer. Herschel reverted to the liquid thermometer, but this was soon replaced by the thermopile (Melloni [3.4]). Some time later (Langley [3.5]) the first bolometers were used. More recently the use of the gas thermometer, in the shape of the Golay [3.6] and Luft cells has been reintroduced and is now widely used in spectrometers. Another type of thermal detector now widely used is that utilizing the pyroelectric effect. In addition to these, several other detection processes have been suggested, including thermal expansion and changed dielectric properties with temperature. 

Ciuprina, E., Zaharescu, T., Ple a, I. Effect of y-radiation on dielectric properties of LDPE-AI2O3 nanocomposites. RadiaL Phys. Chem. 84, 145-150 (2013)... 

In solids, the component of conduction must be added to the dielectric properties. This is especially critical in semi-conductive particles, like carbon based materials. Under microwave radiation, conductive particles loose energy through their displacement. This complicates the estimation of absorption energy, characterized by the equivalent dielectric conductivity, cj, and a loss parameter of a/uteQ. This term increases with increasing temperature. This effect, named thermal runaway, comphcates the control of homogeneous temperature heating. 

If a material could be made extremely thin, for example, to the level of a single layer of molecules, this thin layer would transmit almost all of the infrared radiation, so that its infrared transmission spectrum could be measured. In fact, it is possible to measure a mid-infrared transmission spectrum from a thin soap film. It is usually practically difficult, however, to maintain such a thin film without it being supported by a substrate. For a thin film supported on a substrate, its infrared spectmm is often obtained by utilizing a reflection geometry. Two reflection methods are available for measuring infrared spectra from substrate-supported thin films, depending on the dielectric properties of the substrates used. External-reflection (ER) spectrometry, which is the subject of this chapter, is a technique for extracting useful information from thin films on dielectric (or nonmetallic) substrates, while reflection-absorption (RA) spectrometry, described in Chapter 10, is effective for thin films on metallic substrates [1]. In addition to these two reflection methods, attenuated total-reflection (ATR) spectrometry, described in Chapter 13 and emission spectroscopy, described in Chapter 15 may also be useful in some specific cases. 

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