Influence of the irradiation temperature on the intracascade ion mixing
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We present a description of the thermal behavior of cascades in Cu and Ag over a large energy range and irradiation temperatures. For this purpose the binary collision approximation, which gives the profile of the energy deposition, is coupled to a simplified version of the heat equation. In the present calculations, the original liquid drop model [M. Alurralde, A. Caro, and M. Victoria, J. Nucl. Mater. 183, 33 (1991)] has been extended to the case where the lattice is at finite temperatures. The resulting evolution of the liquid cascade is analyzed for PKA energies up to 1 MeV, and the results are compared to experimental observations of mixing rates. We obtain a temperature dependence that adds to the traditional Radiation Enhanced Diffusion, RED, in very good qualitative agreement with experiments on materials showing thermal spikes.
I. INTRODUCTION The parameters that are relevant in understanding the microscopic evolution of displacement damage cascades, such as the number of freely migrating defects or the rate of atomic mixing, can be correctly studied using molecular dynamics simulations, MD. Present-day computer capabilities, though, allow MD simulations with energies below approximately 25 keV.1 Some of the most important results of MD simulations are the prediction of the cascade core melting and the conclusion that the dominant contribution to ion mixing, IM, at low irradiation temperatures is intracascade mass transport during the cooling phase.1"3 The dependence of this effect on lattice temperature for 3 keV cascades in Cu has been studied in Ref. 4. In a previous investigation we assumed that this melting picture is correct for Cu, and applied simple thermodynamics to predict the behavior of higher energy cascades.5'6 Previous alternative attempts to solve the cascade evolution using continuum heat equations gave less information because both the energy deposition profile and the thermodynamic factors entering the equation are in fact unknown, forcing considerable simplifications.78 By coupling the binary collision approximation, BCA, to a simplified version of the heat equation, we obtained a* description of the cascade behavior in several materials over large energy and temperature ranges, correctly accounting for the geometric aspects.5'6 This description provided an estimation of subcascade interactions, in an energy range inaccessible to MD with present-day computational performances.
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On leave from the Comision Nacional de Energia Atomica, Libertador 8250, (1429) Buenos Aires, Argentina. J. Mater. Res., Vol. 8, No. 3, Mar 1993 http://journals.cambridge.org
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In the present work we address the problem of the role of lattice temperature on the behavior of cascades within the framework of the liquid drop model. Besides the obvious effect of increasing the lifetime of the heat spike, two additional effects are expected. One is the decrease of the length of the replacement collision sequences, RCS, as a consequence of the distortion induced by thermal fluctuations along
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