Characterization of radiation defects in quasi-homogeneously damaged tungsten by PALS and TEM

Tungsten (W) foils were irradiated with 122 MeV Ne-20 ions at the Heavy-ion Research Facility in Lanzhou, on which an energy degrader for tailoring the depth distribution of implanting ions was used. SRIM calculation showed that a quasi-homogeneous distribution of atomic displacement damage to 0.16 dpa within a depth of 50 mu m was produced in W. The features of radiation damage were characterized with positron annihilation life spectroscopy (PALS) and transmission electron microscopy (TEM) techniques in this study. Results from PALS study indicated that large vacancy clusters characterized by a long positron lifetime component of similar to 510 ps were formed in the irradiated W. These clusters may be the nano-voids (an average diameter of similar to 1 nm) exhibited in TEM imaging. Radiation-induced dislocation loops were also observed. Both perfect and Frank loops were manifested under the high resolution TEM observation. The experimental observation of a/2 < 1 1 0 > faulted loops in irradiated W was somewhat surprising and it may shed light on the origin of dislocation formation and their evolution in irradiated bcc metals.