The High‐Temperature Recovery of Neutron‐Irradiated Rhenium

The recovery of rhenium after neutron irradiation at ≈ 390 °K has been studied up to 1130 °K by means of electrical resistivity measurements at 4.2 °K. Two irradiations were performed in the BR2 reactor at Mol: one up to a fluence of 7.6 × 10⁻¹⁸ n cm⁻² (thermal) and 4.3 × 10¹⁷ n cm⁻² (fast, E > 1 MeV) and the other one up to a fluence of 3.2 × 10¹⁹ n cm⁻² (thermal) and 1.8 × 10¹⁸ n cm⁻² (fast, E > 1 MeV). The irradiation induced resistivity is only partially recovered at 1130 °K, where the annealing of defects is supposed to be complete. This effect is attributed to the transmutation of rhenium into osmium and tungsten. The annealing spectrum between 400 and 1130 °K consists of several peaks, the main peak occurring at about 650 °K (0.19 T_m) preceded by a subpeak at about 620 °K. The latter one is more clearly resolved for the lower irradiation dose. This is also the case for the minor peaks occurring at about 490 and 540 °K. Towards higher temperature continuous recovery occurs in the temperature interval 800 to 1000 °K, whereas a small annealing stage has been observed at about 0.32 T_m. The 0.19 T_m stage shows a peak shift towards lower temperatures for higher defect concentration. It is believed that this stage corresponds to stage III of the pure f.c.c. metals.