Thermal evolution of the vacancy defects distribution in 1 MeV helium implanted sintered UO2

Abstract

Evolution of vacancy defects as a function of temperature was studied by positron annihilation spectroscopy in 1MeV helium implanted sintered UO2 disks. A slow positron beam coupled with a Doppler broadening spectrometer was used to measure the low and high momentum annihilation fractions, S and W respectively, as a function of positron energy E in UO2 disks implanted at the fluence of 1×10163Hecm−2 before and after annealing. The S(E) and W(E) behaviours change with the annealing temperature in the range from 160 to 1300°C indicating that the vacancy defects distribution evolves. The positron trapping rate at vacancy defects decreases with the increasing annealing temperature with two stages around 250°C and 800°C. We will discuss the phenomena that could explain these annealing stages in comparison with other positron annihilation spectroscopy results and with the 3He depth profile evolution as the function of temperature measured by Nuclear Reaction Analysis.