Thin film samples of multi-walled carbon nanotubes (MWCNTs) were irradiated with 120 MeV gold ions. Transmission electron microscopy (TEM) images of the pristine and irradiated samples were obtained. TEM pictures show that in the irradiated sample, the CNTs are in general shorter and some have their inner cores filled, unlike in the pristine sample. We also find from these images that average inner and outer tube diameters change as a result of ion irradiation. The films were also characterized using Raman spectrometry. Modifications of the disorder mode (D mode) and the tangential mode (G mode) under different irradiation fluences were studied in detail. As fluence increases, the MWCNTs first show damage, then healing under somewhat higher fluences and again amorphization under still higher fluence of ion irradiation.