In the overall design of an inertial fusion reactor driven by ion beams or lasers the target design plays a central role. The concept of central ignition is used to reduce the input energy of the driver as much as possible. In this respect, the range of the 3.5 MeV alpha particles at 1–20 keV released by the fusion reactions i n D-T is crucial for estimating the driver parameters. Further, for the calculation of the pellet gain and the burn processes, the ranges of alpha particles at temperatures up to 200 keV and at densities up to 1000 g·cm−3 must be accurately known. The 14.1 MeV neutrons produced during the D-T reaction can collide with the deuterium and tritium ions and produce suprathermal knock-on ions which then slow down in the background plasma. This effect must also be calculated, especially for reactor-size pellets for which the pellet ρR is comparable to the neutron mean free path. The stopping power of low atomic fusion products and deuterium and tritium ions in D-T is calculated, using the dielectric function theory for the stopping power of electrons. The theory of the energy deposition of ions in fully ionized, quantum and classical, ideal and non-ideal dense plasmas is reviewed. The GORGON computer code is used for the numerical calculations. The results obtained are compared with the results of other authors and with their theoretical methods.