Defect structures introduced in iron under varying temperature neutron irradiation

Defect structures in iron under varying temperature neutron irradiation and those under constant-temperature irradiation were examined by a transmissi on electron microscope (TEM). For irradiation at a low temperature (473 K), microvoids were detected by positron annihilation lifetime (PAL) measureme nt. For irradiation at a high temperature (673 K), with increasing the irra diation dose a few interstitial (I)-type dislocation loops grew and the tot al number density of the loops decreased. In a varying temperature irradiat ion between 473 and 673 K, after a shift to the high temperature the absorp tion of interstitials to I-type dislocation loops was suppressed by microvo ids introduced at the low temperature and the loops shrank or disappeared b y vacancies released from microvoids. As the cycle of varying temperature i rradiation became short, the effect of the suppression of the defect develo pment became small. (C) 2000 Elsevier Science B.V. All rights reserved.