MIGRATION MECHANISM OF SELF-INTERSTITIAL ATOMS IN MO AFTER LOW-TEMPERATURE IRRADIATION .1. RELAXATION PEAK

The relaxation peak due to [110] self-interstitial atoms (SIAs) in Mo after 20 MeV proton irradiation at 5 K was investigated in single-crys tal specimens with various crystallographic orientations for Frenkel p air concentrations C-FP from 0.1 to 53 ppm using the vibrating reed te chnique at about 500 Hz. The relaxation peak is observed at around 41 K. For the peak height of the 41 K peak, Q(p)(-1), observed in specime ns with the same crystallographic orientation, 1n(Q(p)(-1)/C-FP) shows a linear increase with decreasing 1n(C-FP) over the whole C-FP range, while among different orientations good parallelism is found. The fea tures of the 41 K peak other than Q(p)(-1)/C-FP remain unchanged. Thes e facts suggest that the increase in Q(p)(-1)/C-FP reflects an increas e in the fractional ratio F-1 of SIAs responsible for the 41 K peak (S IA-Is hereafter), where F-1 is found to decrease in proportion to (C-F P)(1/3). All the observed results suggest that SIAs other than SIA-Is are not a result of SIA-Is interacting with each other but are SIAs of a different type (SIA-IIs hereafter). We surmise that both SIA-Is and SIA-IIs are formed during irradiation but that SIA-IIs cannot undergo three-dimensional migration.