ИСТИНА

The stopping of ions from He to Ar is analyzed in the energy region Е= 0.1–10 MeV/nucleon. The special attention is paid to the processes of ion charge exchange, which lead to the difference between the average ion charge and equilibrium charge [1]. The equilibrium and nonequilibrium charge distributions are calculated by evaluating ion charge-exchange cross sections using the density effect for solid targets. The results of calculations agree with the experimental data in the entire considered energy region. The proposed method for calculating the ion charge-exchange cross sections in solid targets also makes it possible to qualitatively describe the dependence of the average ion charge on the target thickness and calculate the thickness required to establish the equilibrium charge distribution for different energies and charges of the ion nucleus. It is shown that for light ions the equilibrium thickness is sufficiently smaller than the range of ions and the penetration of ions can be described by equilibrium characteristics. For heavier ions with passing through matter, the energy loss of ions must be taken into account in calculations of charge exchange cross sections and average ionic charge, which, in its turn, define the change in ion energy. The approximation of «frozen states» is not valid in this case. The calculation of nonequilibrium charge distributions is necessary because the equilibrium thickness is comparable with the ion ranges. For example, the equilibrium target thickness for Xe54+ ions with energy 6 MeV/nucleon in carbon is about 80% of ion range. The ion range becomes dependent on the initial charge of ion.