We have calculated deposited energies of various energetic ions in carbon nanotubes, to study nuclear point mass effects, with the help of a static Monte Carlo (MC) simulation program. As a result of nuclear point mass effects, we show that at the same incident energy, the iondeposited energy maximizes, while its mass has intermediate mass values, such as 11 B, 12 C and 14 N ion masses, under hundreds keV 4 He, 11 B, 12 C, 14 N, 20 Ne, 28 Si and 40 Ar ion irradiations of a thin-walled carbon nanotube. We also show that at the same incident energy, the coordination defect number maximizes, while its mass has an intermediate mass ( 20 Ne) value, under hundreds keV 4 He, 20 Ne and 40 Ar ion irradiations of the thin-walled nanotube. We derive an ion-deposited energy formula to analyze these maximum phenomena, and compare the MC simulation results with the MD (molecular dynamics) ones.