The trapping and thermal reemission of 100–300‐eV Ar+and Kr+ions at a polycrystalline nickel target have been studied. For Ar+and Kr+the trapping probabilities are, respectively, 0.020 and 0.015 at 100 eV and 0.46 and 0.33 at 300 eV. A continuous temperature increase of the target releases trapped argon discontinuously by thermally activated processes at temperatures corresponding to activation energies of 1.12, 1.31, 1.48, 1.67, 1.83, and 2.13 eV. These energies are compared with activation energies which are determined by others for the removal of defects resulting from radiation damage or cold working of nickel. The lowest three energies are believed to be correlated, respectively, with interstitial migration, vacancy formation, and vacancy migration near the surface. The highest energy may be due to surface recrystallization from dislocations produced by the ion bombardment. The intermediate energies probably correspond to the motion of nickel surface atoms along the ridges of facets formed during the bombardment.