Radiation damage clusters

A series of calculations on defect centers induced by radiation damage in alpha-quartz is reported. Ab initio SCF-MO calculations were carried out on a 21 atom cluster, Si50i6 % surrounded by 956 point-ions, designed to simulate alpha-quartz. This two-region approach made it possible to represent the long-range electrostatic effects, present in the crystal, in the SCF-MO cluster. 

JennerTJ, Fulford J, O Neill P (2001) Contribution of base lesions to radiation-induced clustered DNA damage implication for models of radiation response. Radiat Res 156 590-593 Jeppesen C, Buchardt O, Flenriksen U, Nielsen PE (1988) Photocleavage of DNA photofootprinting of E. coli RNA polymerase bound to promoter DNA by azido-9-acridinylamines. Nucleic Acids Res 16 5755-5770... 

X-ray crystallography has provided some details of the location, structure, and protein environment of the Mn4Ca2+ cluster. However, because of the low resolution of the crystal structures reported to date, and the possibility of radiation damage at the catalytic centre, the precise position of each metal ion remains a matter of debate. To some extent these problems have been overcome by applying spectroscopic techniques [22],... 

Other types of information which can be obtained using EELS are oxidation state, coordination number, and cluster size of heavier atomic number elements (25). Applicability and feasibility is just starting to be demonstrated. There are many problems associated with trying to obtain useful quantitative information on small volumes of catalyst. The major concern is radiation damage. Others include, contamination, sample preparation, beam reactivity (especially crucial for redox information), cluster migration and redispersion, support reactivity with the catalyst metals, and desorption of some elements under high vacuum. 

Presence of these interstices provides to the fluorite stmcture extremely specific features. In UO2 particularly, it allows for placement of some radioactive decay products, these sites are responsible for existence of hyperstoichiometric UO2+X phase, where the extra oxygen ions fill the empty interstitial sites in the fluorite lattice etc. First case is extremely important in radiation damaged UO2. Second one is cmcial in oxidation of pure UO2 in atmospheric conditions. Diffusion of atmospheric oxygen into the bulk of crystal brings excess oxygens into empty interstices. These become filled more or less randomly only at low x, at higher concentration of extra anions they form different types of clusters, including so-called 2 2 2 Willis dimers Willis), tetra- and pentameric defects clusters of cuboctahedral symmetry Allen and Tempest). Last defects appear due to interaction of extra anions with intrinsic crystal FP defects (anion Frenkel pairs, i.e. anion vacancies and anion interstitials). 

The interaction of lattice defects in fluorite-like solids under conditions when the thermal motion is restricted, leads to self-assembling of the long-living metastable globular clusters. The same effect was observed in hyper-stoichiometric and radiation-damaged UO2+X Yakub, 2008). At elevated... 

Fe or Ni ion irradiation with energies of a few MeV is mostly used for studies of radiation damage of RPV steels. Previous studies have provided information on the effects of Cu, Mn and other elements, carbides, dose rate and tensile stress on hardness, matrix damage evolution and solute cluster formation in model alloys and commercial steels (e.g. Fujii and Fukuya, 2005 Murakami et al., 2009). These data provide clear evidence of the effects of various metallurgical parameters on hardening and microstructural evolution in Fe-based alloys and RPV steels, although these data cannot be directly or quantitatively correlated to data from neutron-irradiated materials. 

In the first part of this chapter, we provide an overview of the radiation damage processes that control the form of the irradiation-induced microstructure under the radiation conditions reactor pressure vessel (RPV) steels experience in service. We demonstrate that the irradiation damage in RPV steels can broadly be classified as matrix damage (for instance voids, interstitial clusters, dislocation loops, complexes trapped at sinks such as... 

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