Helium desorption in 3He implanted tungsten at low fluence and low energy

The behaviour of helium in polycrystalline 3He implanted tungsten at low energy (60 keV) and low fluence (2 × 1013 cm−2) has been studied as a function of post-implantation annealing temperature until 1873 K by means of Nuclear Reaction Analysis. Helium desorption has been observed only from ∼1500 K, suggesting a helium trapping at mono-vacancies. Only ∼75% of the implanted helium has been released after the annealing during 1 h at high temperature (1873 K); besides, the desorption rate decreased from 1673 K. The presence of a second type of helium trapping site is likely to explain this strong helium retention.