Kinetics of Defect Formation in Alkali Halides at Helium Temperatures
The kinetics of defect formation in alkali halides at low temperature was investigated based on the following sequential steps: production of electrons and holes by ionizing radiation, self-trapping of holes to form VK-centers, recombination of VK-centers and electrons followed by a collision sequence to form F- and H-centers ionization of F-centers to form F+-centers, and capture of electrons by the H-centers to form I-centers. The kinetic equations were solved by computer techniques for steady irradiation and for pulse irradiation. Analytic solutions were found for the steady state approximation, valid after the decay of initial transients. During steady irradiation, once the transients have decayed, the total vacancy concentration (and the concentration of the other centers) increases linearly with irradiation time, in agreement with the available meager experimental data. A specific prediction of the kinetic scheme is the flux (dose rate) dependence of the above growth rate-linear in flux at low flux and gradually approaching flux independence at high flux. When the unstable nature of the close F-H pairs is explicitly taken into account, the response of the system to pulse irradiation simulates the experimental data, at least qualitatively.
KeywordsDefect Formation Perfect Crystal Kinetic Scheme Helium Temperature Alkali Halide
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