Does pulsing in spallation neutron sources affect radiation damage?

Modern neutron sources, such as the planned European Spallation Source (ESS), will operate in a pulsed mode with very short pulses at relatively high frequencies. Presently, the judgement of radiation damage resulting under such conditions depends on the available experimental experience with radiation damage caused by comparable continuous irradiation and on modelling for extending this experience to pulsed irradiation. In the present contribution, this combination of available experimental and theoretical experience is used to judge possible pulsing effects on radiation damage and related macroscopic phenomena in metallic materials. Significant pulsing effects require: (1) a proper relationship of the lifetimes of mobile defects to the time scales of pulsing, and (2) sufficiently large pulsing-induced fluctuations of defect fluxes to relevant sinks. It is shown that the first condition, quantified by a `relative dynamic biasʹ, is fulfilled under ESS conditions. Application of the second condition, quantified by an `absolute dynamic biasʹ, to pulsing sensitive processes such as cavity nucleation and creep by climb controlled dislocation glide shows, however, that the damage yield of one pulse in ESS and similar facilities is much too small to allow any significant pulsing effect.