Does pulsing in spallation neutron sources affect radiation damage?

Modern neutron sources, such as the planned European Spallation. Source (ES S), 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 radia tion damage caused by comparable continuous irradiation and on modelling fo r extending this experience to pulsed irradiation. In the present contribut ion, this combination of available experimental and theoretical experience is used to judge possible pulsing effects on radiation damage and related m acroscopic phenomena in metallic materials. Significant pulsing effects req uire: (1) a proper relationship of the lifetimes of mobile defects to the t ime scales of pulsing, and (2) sufficiently large pulsing-induced fluctuati ons of defect fluxes to relevant sinks. It is shown that the first conditio n, quantified by a 'relative dynamic bias', is fulfilled under ESS conditio ns. Application of the second condition, quantified by an 'absolute dynamic bias', 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. (C) 2001 Elsevier Science B.V. All rights reser ved.