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The release of 4He implanted to saturation with an energy of 15 keV in polycrystalline Ni by subsequent 3He implantation with equal energy has been measured between 295 and 1053 K. The fraction of 3He that can be exchanged is shown to decrease with increasing temperature up to 800 K. Above this, however, it increases drastically. The results can be interpreted by assuming He trapping in two subsystems: gas bubbles and He-vacancy complexes. At sufficiently high density of the complexes, He atoms can move along interlinked chains of complexes in "relay-race" type of motion in which each individual He-atom moves only one step and an atom from the complex nearest to the surface is released into the vacuum. Above 900 K all complexes should be thermally dissociated. In this case bubble migration may be the mechanism responsible for He re-emission.

Additional information

Authors: ALIMOV V K, Academy of Sciences, Institute of Physical Chemistry, Moscow (SU);SCHERZER B M U, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Article: Radiation Effects and Defects in Solids, Vol. 114 (1990) pp. 137-144
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