Search results for "impur"
showing 10 items of 349 documents
Aggregation of Frenkel defects under irradiation: a mesoscopic approach
1994
The radiation-induced aggregation of Frenkel defects in solids is studied in terms of a mesoscopic approach. The asymmetry in elastic interactions between mobile interstitials (I-I) and between interstitials and vacancies (I-V) plays a decisive riile in the aggregation of similar defects. The conditions for defect aggregation are studied in detail for NaCl crystals. The critical dose rate for aggregation has been calculated as a function of the temperature as well as the aggregation rate as a function of temperature and dose rate. Furthermore, the r&e of deep traps (like impurities and di-vacancies), reducing the mobility of interstitials, and the r&le of dislocations serving as sinks for i…
Modeling of yttrium, oxygen atoms and vacancies in γ-iron lattice
2011
Abstract Development of the oxide dispersion strengthened (ODS) steels for fission and fusion reactors requires a deep understanding of the mechanism and kinetics of Y 2 O 3 nanoparticle precipitation in the steel matrix. Therefore, it is necessary to perform a large-scale theoretical modeling of the Y 2 O 3 formation. In the current study, a series of first-principles calculations have been performed on different elementary clusters consisting of pair and triple solute atoms and containing: (i) the Y–Fe-vacancy pairs, (ii) the two Y atoms substituted for Fe lattice atoms and (iii) the O impurity atoms dissolved in the steel matrix. The latter is represented by a face-centered cubic γ-Fe si…
The experimental observation of the potential barrier for self-trapped exciton decay into F-H pair in KCl-Na crystals
1995
Abstract The optical absorption induced by the electron pulse irradiation of Na+ doped KCl has been measured. Transient optical absorption band of FA centers was observed at 80 K (LNT). The temperature dependence of FA center formation was studied. It is proposed that the obtained activation energy originates from the potential barrier between the STE perturbed by the cation impurity and the nearest neighbour FA-H pair. The mechanism of the suppression of the defect formation by the monovalent cation impurity in alkali halide crystals is discussed.
ODMR of cd impurity centers in gg irradiated BaF2crystals
1995
Abstract The magnetic circular dichroism of the optical absorption (MCD), optically detected magnetic resonance (ODMR) as well as ESR and luminescence in Cd- doped BaF2 crystals γ-irradiated at RT were investigated. MCD signals centered at 295 nm, 290 nm and 365 nm are observed, together with corresponding radiation induced optical absorption bands in the same wavelength regions. The ODMR detected in all these bands is caused by hyperfine (hf) interaction of unpaired spin with Cd− nucleus. Three types of different Cd− related defects have been separated: 1) Cd+ c, represented by the MCD of derivative type centered at 295 nm and hf constant ACd = 480 mT, 2) Cd++c -center having lowered symme…
Radiation-induced electronic and ionic charge storage and release in sapphire
2002
Radiation-induced thermally stimulated relaxation (TSR) processes in the reduced α-Al 2 O 3 (sapphire) crystal were investigated at 290-650 K by means of the TS current (TSC), ionic depolarisation current (TSDC) and electron emission (TSEE) techniques. After thermal (ionic) polarisation of sapphire wide (∼75 K) and asymmetric ionic dipolar TSDC peak at T max 590 K (disorientation of the anion vacancy-related dipoles) was detected. This peak correlates with the wide TSEE peak at T max 615 K, the radiation-induced electrical degradation (RIED) yield rise above 550 K (T max 745 K) and the chromium emission line broadening ip ruby. Above 450-500 K the anion vacancy hopping (migration) starts. T…
Annealing of color centers in LiBaF 3
2002
Results of the glow rate technique to analyze the activation energy of thermostimulated annealing of X-ray created F -type color centers in LiBaF 3 crystals are presented, showing pure and containing oxygen centers. It is shown that depending on the impurity composition two alternative mechanisms are involved in the annealing of color centers. It is proposed that either the anion vacancy governed migration of F -centers resulting in recombination with complementary defects, or the thermal delocalization of radiation created fluorine ( F i ) interstitials captured by anti-structure defects followed by recombination with all kinds of complementary F -type centers are responsible for the recom…
Iron-related luminescence centers in ZnWO 4 :Fe
2002
A systematic spectroscopic study of single ZnWO4 :Fe crystals with different iron concentrations has been performed under excitation by ultraviolet light, by synchrotron radiation or under photostimulation by near-infrared light. The luminescence of Fe3+-related centres has been studied. It is shown that iron centres of different types efficiently promote the formation of crystal defects at low temperatures. Electrons and holes can be trapped near Fe2+ or Fe3+ ions, which is further revealed in phosphorescence, thermostimulated or photostimulated luminescence. At room temperature the main effect of iron impurity is to reduce the light yield of a ZnWO4 scintillator.
ESD of nonthermal halogen atoms from In-doped (001) KBr
1995
Abstract We have measured the kinetic energy distributions of neutral halogen atoms emitted due to electron-stimulated desorption (ESD) from In-doped (001)KBr single crystals. The concentration of In+ in investigated samples varied between 1017 and 1020 particles/cm3. The measurements were performed at target temperature of 150°C. In all cases the energy spectra consist of two peaks. The distribution of low-energy particles can be described by the thermal (Maxwellian) energy spectrum. Particles contributing to the second peak have nonthermal kinetic energies. The emission of halogen atoms having nonthermal energies decreases with an increase in the concentration of In impurities. At the sam…
Direct synthesis of pure brannerite UTi2O6
2019
International audience; A new method based on the precipitation of uranium(IV) and titanium(IV) hydroxide precursors was developed to prepare pure brannerite UTi2O6 samples. In fact, U(IV) dissolved in HCl (6 mol L−1) was mixed to Ti (IV) alkoxyde before a basification step with an excess of NH4OH to obtain a highly reactive nanometric (U,Ti)(OH)4 powder. The obtained powder was then dried under vacuum, pressed into pellets and finally fired at 1300 °C. This method led to the formation of pure brannerite in contrast to previous reported protocols, which showed the formation of impurities such us UO2 and TiO2. The refined unit cell parameters of UTi2O6 led to a = 9.8113(2) Å, b = 3.7681(1) Å…
EPR hyperfine structure of the Mo‐related defect in CdWO 4
2005
The hyperfine structure (hf) of the electron paramagnetic resonance (EPR) spectrum of Mo-related impurity defects in CdWO4 crystals observed previously (U. Rogulis, Radiat. Meas. 29, 287 (1998) [1]) is reconsidered taking into account interactions with two different groups of neighbouring Cd nuclei. The best fit calculated EPR spectrum to the experimental is obtained considering 2 groups of 3 and 2 equivalent Cd nuclei, respectively. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)