Abstract
A new method of solution is proposed for a Boltzmann equation describing the slowing down of charged particles in solids. It seems as if it would be more generally applicable. It can be considered as a multigroup method with the energy groups varying from point to point in a natural way dictated by the local spectrum. The energy moments of the density of moving particles are calculated at each point in the target, and at each point an extremal (in energy) density of particles is constructed. The extremal density allows for particles being stopped, and, hence, removed from the beam.