Search results for "Diffusion"
showing 10 items of 1615 documents
Computer modeling of metal colloid formation in tracks of swift heavy ions in ionic solids
2001
Abstract We present results of computer modelling of the aggregation of primary radiation defects—F centers—in ionic crystals within tracks of swift heavy ions. We study how F-aggregate properties depend on the initial density of primary Frenkel defects in the track and its radius. The mean number of F centers in aggregates is typically very small, about five defects, which greatly complicates detection of expected metal colloids by ESR.
Theoretical simulations of I-center annealing in KCl crystals
1995
Abstract This paper focus on theory of diffusion-controlled annealing of the most mobile radiation-induced defects—I centers—in KCl crystals. The kinetics of annealing of pairs of close oppositely charged defects—α-I centers (arising as a result of the tunnelling recombination of primary Frenkel defects—F and H centers) and F-I centers (when H center trap electrons) is calculated taking into account defect diffusion and Coulomb/elastic interaction. Special attention is paid to the conditions under which multi-stage annealing arises; theoretical results are compared with the relevant experimental data.
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…
Temperature dependence of the dynamics of ultrafine particles in a polymeric network
1990
Simple model systems with pronounced dynamical features will help to get a deeper insight into the complicated dynamics of large molecular networks. We investigated the bounded diffusion of ultrafine Fe(OH)3 particles (∼30 A in diameter) in the three-dimensional network of the cation exchanger Dowex 50 W which was solvated with a water solution of sucrose (60 wt%). Mossbauer spectra were recorded in the temperature range from 80 K to 305 K. At temperatures above 250 K broad diffusional lines of different widths appear in the spectrum proving the bounded nature of the diffusion. The line widths strongly increase with temperature to values of several hundred mm/s. Around 300 K a large portion…
Analysis of spatial diffusion of ferric ions in PVA-GTA gel dosimeters through magnetic resonance imaging
2017
Abstract This work focused on the analysis of the temporal diffusion of ferric ions through PVA-GTA gel dosimeters. PVA-GTA gel samples, partly exposed with 6 MV X-rays in order to create an initial steep gradient, were mapped using magnetic resonance imaging on a 7T MRI scanner for small animals. Multiple images of the gels were acquired over several hours after irradiation and were analyzed to quantitatively extract the signal profile. The spatial resolution achieved is 200 μm and this makes this technique particularly suitable for the analysis of steep gradients of ferric ion concentration. The results obtained with PVA-GTA gels were compared with those achieved with agarose gels, which …
Electrical properties of Au/CdZnTe/Au detectors grown by the boron oxide encapsulated Vertical Bridgman technique
2016
Abstract In this work we report on the results of electrical characterization of new CdZnTe detectors grown by the Boron oxide encapsulated Vertical Bridgman technique (B-VB), currently produced at IMEM-CNR (Parma, Italy). The detectors, with gold electroless contacts, have different thicknesses (1 and 2.5 mm) and the same electrode layout, characterized by a central anode surrounded by a guard-ring electrode. Investigations on the charge transport mechanisms and the electrical contact properties, through the modeling of the measured current–voltage ( I – V ) curves, were performed. Generally, the detectors are characterized by low leakage currents at high bias voltages even at room tempera…
Basic study of influence of radiation defects on tritium release processes from lithium silicates
1997
The radiolysis of Li2SiO3 and Li4SiO4 was studied using the chemical scavengers method (CSM), thermoluminescence, lyoluminescence, electron spin resonance and spectrometric methods. The influence of the absorbed dose and many another parameters such as: irradiation conditions, sample preparation conditions and concentration of impurities on the accumulation rate of each type RD and RP were studied. Several possibilities for reducing the radiolysis of silicates were discussed. It has been found that tritium localization on the surface and in grains proceed by two different mechanisms. Tritium thermoextraction from the surface proceeds as chemidesorption of tritiated water, but from the bulk …
Oxygen Diffusion Constants D and K of Tumor Tissue (DS-Carcinosarcoma) and Their Temperature Dependence
1978
To understand more thoroughly the tumor O2 supply conditions, knowledge of O2 diffusivity in tumor tissue is required. Since exact measurements of the O2 diffusion constants of tumor tissue have not been carried out to date, previous investigations of tumor O2 supply had to employ estimated values (6 – 8, 10). The results of these studies are in part contradictory.
PFG n.m.r. study of diffusion anisotropy in oriented ZSM-5 type zeolite crystallites
1991
ZSM-5 zeolite crystallites are oriented by introducing them into a system of parallel capillaries. In this way, by applying pulsed-field gradient (PFG) n.m.r., a direct measurement of the orientation dependence of diffusion in ZSM-5 crystals has become possible. Using methane as a diffusant, the ratio D xy /D z between the diffusivities in the xy plane and in the z direction has been found to be of the order of 4.5. This value is in satisfactory agreement with the behavior expected from both MD calculations and a random walk model of molecular propagation in the two-channel network of ZSM-5-type zeolites.
Versatile use of ion beams for diffusion studies by the modified radiotracer technique
2004
Abstract In the modified radiotracer technique ion beams within a broad energy range are employed. They include energetic light particles ensuring radioactive isotope production via nuclear reactions, keV-ion implantation of radiotracers and sputtering by low energy heavy ions for depth profiling. If the involved ion–solid interactions are properly taken into account, the technique provides an effective means for solid-state diffusion studies under demanding conditions. The various aspects related to the modified radiotracer technique are surveyed and discussed. The reliability of the procedure is demonstrated by comparisons with corresponding profiles obtained by secondary ion mass spectro…