Diamond powder and monocrystals were bombarded with 72 Mev carbon ions. The photographs in reflected and transmitted light revealed a layer with a thickness estimated as 7 plus or minus 2 mu m, where the bombarding ions stopped, as well as a layer with a thickness of about 70 mu m, where, due to accidental channeling, some ions had penetrated further into the specimens. The contribution of interstitial atoms to expansion of the diamond crystal lattice was estimated as 1. 16 plus or minus 0. 30.