Interstitial loop growth in irradiated thin foils

In order to understand the behaviour of materials in an irradiation environment, a knowledge of the interaction between point defects and dislocations is essential. It has been shown previously that using the rate theory continuum method, the loss of defects to the foil surface being accounted for through a smeared-out foil surface sink strength, measurements of interstitial loop growth rate in irradiated thin foils can yield such information. The present work describes a scheme for loop growth in a thin foil, based on the rate theory continuum model, which accounts directly for defect loss to the foil surface. A set of simultaneous time-dependent equations for defect concentrations and loop growth are solved numerically on a finite number of equally-spaced mesh points in the foil. Account is taken of loop overlap onto neighbouring mesh points and of loop intersection with the foil edge. Loop growth measurements in copper have been analysed with this scheme and values deduced for vacancy migration energy and dislocation bias. (orig.)