[en] Damage microstructures are compared at a dose of 10 dpa in a high-purity Fe-Ni-Cr alloy after irradiation in EBR-II and after nickel ion bombardment at temperatures encompassing the peak swelling. The damage features are qualitatively similar, but there are less cavities in the ion bombarded specimens. Incorporation of helium during the ion bombardments improves but does not eliminate this discrepancy. The peak swelling is 2.5 times greater for the neutron irradiations. The upward shift in peak swelling temperature wth damage rate is 125 K, and helium also raises the upper temperature limit for swelling in the ion bombardments. It is concluded that ion bombardments can match a required level of neutron swelling when the appropriate temperature shift and dose equivalency are applied, but the quantitative microstructural aspects are not reproduced. A suggestion is made for mending this inadequacy