Energy loss and straggling of low-velocity heavy atoms in matter

Based on the dielectric-function method, we have investigated the energy loss and straggling of heavy atoms with atomic number ${\mathit{Z}}_1$ passing through the degenerate electron gas at low velocities. The size parameter Λ of the electron cloud on the projectile is newly determined according to the statistical variational method by taking into account the static screening effect of conduction electrons. The analytical formulas obtained here have ${\mathit{Z}}_1$ dependences different from those of existing theories in spite of the same velocity dependence. It is found that the screening effect on Λ enlarges the electronic stopping of the media by a constant value regardless of ${\mathit{Z}}_1$. Numerical results show agreement with the trends of the available data.