  Dislocations can climb out of their glide plane by absorbing (or emitting)
point defects (vacancies and self-interstitial atoms (SIAs)). In contrast with
conservative glide motion, climb relies on the point defects' thermal diffusion
and hence operates on much longer timescales, leading to some forms of creep.
Whilst equilibrium point defect concentrations allow dislocations to climb to
relieve non-glide stresses, point defect supersaturations also lead to osmotic
forces, driving dislocation motion even in the absence of external stresses.
Self-interstitial atoms typically have significantly higher formation energies
than vacancies, so their contribution to climb is usually ignored. However,
under irradiation conditions, both types of defect are athermally created in
equal numbers. In this letter, we use simple thermodynamic arguments to show
that the contribution of interstitials cannot be neglected in irradiated
materials, and that the osmotic force they induce on dislocations is many
orders of magnitude larger than that caused by vacancies. This explains why the
prismatic dislocation loops observed by {\it in situ} transmission electron
microscope irradiations are more often of interstitial rather than vacancy
character. Using discrete dislocation dynamics simulations, we investigate the
effect on dislocation-obstacle interactions, and find reductions in the
depinning time of many orders of magnitude. This has important consequences for
the strength of particle-reinforced alloys under irradiation.
