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 transmission electron microscope (TEM). For irradiation at a low temperature (473 K), microvoids were detected by positron annihilation lifetime (PAL) measurement. For irradiation at a high temperature (673 K), with increasing the irradiation dose a few interstitial (I)-type dislocation loops grew and the total number density of the loops decreased. In a varying temperature irradiation between 473 and 673 K, after a shift to the high temperature the absorption of interstitials to I-type dislocation loops was suppressed by microvoids introduced at the low temperature and the loops shrank or disappeared by vacancies released from microvoids. As the cycle of varying temperature irradiation became short, the effect of the suppression of the defect development became small.