  The energy distributions of secondary electrons produced by energetic carbon
ions (in the energy range used, e.g., in hadron therapy), incident on liquid
water, are discussed. For low-energy ions, a new parameterization of the
singly-differential ionization cross sections is introduced, based on tuning
the position of the Bragg peak. The resulting parameterization allows a fast
calculation of the energy spectra of secondary electrons at different depths
along the ion's trajectory, especially near the Bragg peak. At the same time,
this parameterization provides penetration depths for a broad range of
initial-ion energies within the therapeutically-accepted error. For high-energy
ions, the energy distribution is obtained with a use of the dielectric response
function approach. Different models are compared and discussed.
