[en] Specimens of high purity nickel were irradiated with high energy heavy ions and the resultant microstructure examined along the ion path using across-sectioning sample preparation technique. Void nucleation was found to be very sensitive to hydrogen introduced into the samples by electropolishing proir to irradiation. Samples containing hydrogen had void densities of about two orders of magnitude greater than outgassed samples. A series of hydrogen doped samples were irradiated with 14 MeV nickel ions to fluences from 2 x 10¹⁵ ions/cm² to 1.4 x 10¹⁷ ions/cm² (peak damage from 2 to 150 dpa). The increase in the collision cross section as the incident ion slows down causes an increase in displacement rate with depth. The variation in the observed void density, void size and void swelling rates with depth indicating the importance of displacement rate on void simulation studies