Irradiation, crystal defects

In a more general application, thermoluminescence is used to study mechanisms of defect annealing in crystals. Electron holes and traps, crystal defects, and color-centers are generated in crystals by isotope or X-ray irradiation at low temperatures. Thermoluminescent emission during the warmup can be interpreted in terms of the microenvironments around the various radiation induced defects and the dynamics of the annealing process (117-118). ... 

Reaction Cavities of Alkanones in Neat Solid Phases. The early report that irradiation of crystalline 7-tridecanone at 10°C does not result in discernible photoreaction [267] has been corroborated subsequently with other solid symmetrical n-alkanones [268]. However, careful scrutiny of the irradiated ketone reveals traces of Norrish II products in ratios which are very close to those found from photoreactions in solution. On this basis, it was concluded that the source of the photoproducts is reactions occurring at crystal defect sites. 

A theoretical analysis of the experimental kinetics for Vk centres in KC1-Tl, as well as for self-trapped holes in a-Al203 and Na-salt of DNA, is presented in [55]. The fitting of theory to the experimental curves is shown in Fig. 4.4. Partial agreement of theory and experiment observed in the particular case of Vk centres was attributed to the violation of the continuous approximation in the diffusion description. This point is discussed in detail below in Section 4.3. Note in conclusion that the fact of the observation of prolonged increase in recombination intensity itself demonstrated slow mobility of defects. In the case of pure irradiated crystals, it is a strong... 

However, there could also be an alternate rationale. Belyaeva et al (Ref 49) suggest that the decompn of crystalline RDX begins at crystal defects already present or temp induced (possibly also induced by pre-irradiation). De-compn leads to deformation of the crystal lattice and more defects. If decompn products cannot diffuse, they crack the crystal which leads to a suddenly increased evolution of gas. This model can explain the memory and preirradiation effects, but is incapable of explaining... 

Figure 26 Normalized longitudinal resistivity p, of a single crystal of (TMTSF)2C104 at 4.2 K versus concentration of irradiation-induced defects (mole %). Initially, linear behavior is observed, corresponding to Matthiessen s rule, followed by an exponential behavior corresponding to Eqs. (11) and (12) (see the text). (From Ref. 112.)...

There are two types of lattice defects that occur in all real crystals and at very high concentration in irradiated crystals. These are known as point defects and line defects. Point defects occur as the result of displacements of atoms from their normal lattice sites. The displaced atoms usually occupy sites that are not in the lattice framework they are then known as interstitials. The empty lattice site left behind by the interstitial is called a vacancy. Avacancy produced by displacement of an anion or cation, along with its interstitial ion, is called a Frenkel pair, or simply a... 

In subsequent experiments, Biersack, et al. (29) used the boron (n,alpha) reaction to show the effect of pre- and post-irradiation damage on boron implantation profiles. By post-irradiating a boron implant in silicon with 200 keV H2, a migration of the boron to the Induced damage sites was observed. In the same paper, diffusion and trapping of lithium ions in niobium were reported. Using the lithium (n,alpha) reaction, they mapped irradiation Induced crystal defects through a depth of several micrometers with respect to several sample treatment conditions. 

Tompkins and Young [216] investigated the photolysis of KN3 by studying optically the defects that accompanied photolysis. In comparison with defects observed in the alkali halides, they identified the defects as F and V centers more recent experiments clearly disprove these assignments [69]. They did, however, observe the colloidal band at 727 nm, formed after heating previously irradiated crystals to 270°C. It was assumed that the centers form by diffusion of potassium along dislocations and are trapped. Finely ground KN3 showed... 

Various indications suggest that high-energy irradiation polymerizations are started at crystal defects. If a crystal is scratched, the polymer chains will start to grow at this point. In addition, the points where polymerizations begin are randomly distributed. Because of the density difference between polymer and monomer, polymerizations in monomer crystals lead to the buildup of stresses which produce further crystal defects. New polymerizations can be started at these new defects sites. Electron microscope pictures show a number of craters caused by polymerizations, which, after a further polymerization time, become surrounded by satellite craters. 

Thermoluminescence measurements observing crystal defects in, e.g., quartz grains being as impurity on the surface of some foods (vegetables) can also be successfully applied (Farkas 2004). Another standardized method is based on the irradiated fat-containing foods using the mass-spectrometric detection 2-alkyl-cyclobutanones after gas chromatographic separation O Fig. 23.17 (Delincee 2002). 

This chapter will discuss the macroscopic and microscopic properties of Generation IV reactor materials, and the advances in characterization of irradiation-induced defects and in mesoscale modeling of irradiation damage. The majority of the examples provided are based on ferritic-martensitic (F-M) steels, even though they might not always be primary candidates for Generation IV reactors, but the reported defects and microstmctural features are typical of other irradiated alloys, and F-M steels are used as an illustrative example. In some cases, comparisons will be made to austenitic steels to illustrate how differences in crystal stmcture and alloy composition can cause large differences in radiation response. 

Examples of defects are cation vacancies (V centres), anion vacancies (E centres) and impurities in crystals. Defects can be generated in various ways, such as irradiation with ultraviolet or ionizing radiation, or by imperfect crystallization. An example is a defect (latent image) generated in photographic emulsion by light irradiation. In addition, finely divided solid... 

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