Trap theory of helium partitioning at low doses

Abstract

A time-dependent interstitial clustering model, based on the chemical reaction-rate formalism, has been developed for calculating concentrations of point defects, interstitial clusters, interstitial (free) and trapped helium concentrations during the early stages of irradiation. The various structural defects are assumed to provide saturable and reversible trap sites for helium, and capture and emission by vacancies, interstitials, interstitial clusters, and dislocations are included. When calculations are performed with parameters appropriate for nickel and several helium-dislocation detrapping energies E T D, the model predicts (1) that the helium concentration at vacancy traps increases monotonically with time, while that at interstitial clusters and dislocations attains a maximum and then decreases; (2) that the interstitial cluster number density does not depend on E T Dfor the range of values considered and is therefore insensitive to direct helium-interstitial and helium-dislocation interactions; and (3) that helium partitions primarily to vacancies rather than to interstitial clusters or dislocations, and therefore a majority of helium will be in cavities after long irradiation times.