Irradiation effects formation

Various mechanisms for electret effect formation in anodic oxides have been proposed. Lobushkin and co-workers241,242 assumed that it is caused by electrons captured at deep trap levels in oxides. This point of view was supported by Zudov and Zudova.244,250 Mikho and Koleboshin272 postulated that the surface charge of anodic oxides is caused by dissociation of water molecules at the oxide-electrolyte interface and absorption of OH groups. This mechanism was put forward to explain the restoration of the electret effect by UV irradiation of depolarized samples. Parkhutik and Shershulskii62 assumed that the electret effect is caused by the accumulation of incorporated anions into the growing oxide. They based their conclusions on measurements of the kinetics of Us accumulation in anodic oxides and comparative analyses of the kinetics of chemical composition variation of growing oxides. 

Host irradiated polymers show a continuing change in properties for a long period after irradiation. These post-irradiation effects may be attributed to (1) trapped radicals which react slowly with the polymer molecules and with oxygen which diffuses into the polymer (2) peroxides formed by irradiation in the presence of air or trapped within polymers irradiated in vacuum or an inert atmosphere) and slowly decompose with formation of reactive radicals, usually leading to scission, (3) trapped gases in glassy and crystalline polymers which cause localized stress concentrations. 

For technical applications, knowledge of the irradiation behaviour of the Levextrel-TBP resin is important. A detailed study carried out at the Radiochemistry Institute of the Technical University, Munich(21,22), showed that with gamma irradiation the formation rate of dibutyl phosphoric acid (HDBP) and of "non-removable" acidic radiolysis products ("do-bads") is 2 to 5 times lower with Levextrel-TBP resin than with pure TBP the effect is attributed to the "scavanger" action of the aromatic groups in the matrix material. In summary, a high radiation resistance of the resin has become evident. 

Suzuki, T., Kondo, K., Hamada, E., Ito, Y. (2001) Positron irradiation effects on positronium formation in polycarbonates during a positron annihilation experiments . Acta physica polonica A. 99, 515. 

An effective formation of X" takes place during UV irradiation of latexes, rubber solutions and rubber surfaces or PP films. In the latter polymer, the yield of attachment of compound 191 up to 68% was obtained [253]. 

Meldram A, Boatner LA, White CW, Ewing RC (2000b) Ion irradiation effects in nomnetals Formation of nanocrystals and novel microstractures. Mater Res limovations 3 190-204 Meldram A, White CW, Keppens V, Boatner LA, Ewing RC (2000c) Irradiation-induced amorphization of Cd2Nd207 pyrochlore. Can J Phys (submitted)... 

It has been known that various antioxidants reduce VSCs in raw meats. Nam et al. 40) showed that addition of antioxidants such as tocopherols, gallic acid and sesamol reduced the production of some VSCs in raw pork homogenates and patties. Addition of ascobic acid at 0.1% (wt/wt) or sesamol + a-tocopherol each at 0.01% level to ground beef before irradiation effectively reduced lipid oxidation and VSCs 41). Patterson and Stevenson (25) found that dietary supplementation of a-tocopherol and ascorbic acid to hens reduced the yield of total volatiles. Dietary vitamin E added to turkey diets reduced production of MT, DMS, CS2 DMDS and some hydrocarbons and aldehydes of raw turkey meat 42). However, Lee et al. 43) found antioxidant combinations (sesamol+a-tocopherol and gallate+a-tocopherol) had very little effect on the development of off-odor and the formation of VSCs due to irradiation in raw turkey meat. 

Pichot et al. (2001) conducted a preliminary study of irradiation effects on thorium phosphate-diphosphate. Powdered samples were irradiated with 1.5 Gy dose of gamma-rays. The formation of PO b and POO free radicals were detected using electron spin resonance (ESR) and thermoluminescence (TL) methods. These free radicals do not modify the macroscopic properties of the TPD and disappear when the sample is heated at 400°C. The implantation of 1.6 MeV He with a fluence of 10 ions/cm and 5 meV Au with a fluence 4 x 10 ions/cm causes some surface damage to sintered samples. Amorphization and chemical decomposition of the matrix were observed for the dose of 10 ions/cm and higher when irradiated with Pb (200 keV) and Au " (5 MeV). These effects were evidenced by means of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). 

One form of Ag was oriented relative to the original AgNa lattice and the other was not. The decomposition and silver formation was thought to be primarily due to thermal effects, although evidence was found that the form of silver is different in the case of simple thermal decomposition thus irradiation effects play some role in the electron-beam-induced decomposition. These studies are reviewed more fully by Bowden and Yoffe [100]. 

As can be seen in Figure 9.9b, the temperature dependence of (3 for PVA is similar to that of polyethylene (Matsuo et al. 2002). It can be seen that increases as a function of temperature up to -10°C. The increase in has been proved to be due to the positron irradiation effect on a polymer at low temperature. The secondary electrons that escape from the positron spur could be easily trapped in shallow potentials formed between the polymer chains when the motions of the molecular chains and groups are frozen at low temperature. Due to the positron irradiation time (experimental time), the probability of formation would become larger. As can be seen in this figure, becomes a maximum at around -10°C, and begins to decrease with increasing temperature. (3 attains a minimum at ca. 75°C and increases again beyond ca. 75°C. This is due to an apparent increase in the number of holes detected by positron annihilation, because of the thermal expansion of the holes at... 

The irradiation effects on the mechanical properties are significant. The interstitial atoms and vacancies resulting from irradiation-induced atomic displacements give rise to the formation of dislocation loops of interstitial and vacancy type. These dislocation loops act as obstacles to slip dislocations and lead to an increase in yield stress and decrease in elongation upon fracture as a function of dose, as shown in Fig. 3.1-93. The effect saturates at about 10 nm. ... 

Irradiation effects in organic polymers result from the cleavage of chemical bonds and the subsequent reactions of intermediates generated thereby. These reactions lead to significant alterations in the physical properties of polymeric materials, and this topic has been covered in numerous books and articles [12,38-54]. As far as linear chain polymers are concerned, any changes in physical properties are due mainly to the formation of permanent main-chain scissions and intermolecular crosslinks. A general free-radical-based mechanism related to these processes is presented in Scheme 5.11. 

The effect of irradiation on formation of nucleic acid molecules in organs of normal adult rats is thus similar in magnitude to the effect of roentgen rays on the growing Jensen sarcoma, listed in Table XXXVIII. 

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