Single crystals of diamond were irradiated with carbon ions up to integral fluences of about 10(17) C/cm(2). In order to produce homogeneous damage profiles over a depth of 1 mu m the samples were exposed to calculated sequences of irradiation energies and areal doses. The concomitant evolution of radiation damage was monitored by various techniques including optical absorption and reflection spectrometry, Raman scattering and ion backscattering/channelling measurements. The phase transition crystalline to amorphous is completed in the vicinity of 5 x 10(16) C/cm(2). At this irradiation level, the composition of the damaged layer is mainly made up by amorphous diamond with a minor fraction of a graphitic component, as most clearly seen in the Raman spectra.