Calculation of 0.1-5 MeV electron and positron absorption

Depth distribution of annihilation centres and energy loss of positrons with initial energy of 0.1 to 5 MeV in different absorbers (C, Al, Pb, Sn, Au, Cu) is considered. The multistep method is used to solve the problem of the radiation transfer through a matter. The algorithm of the segment model is described. A method has been developed to take account of the energy spectrum and angular distribution of the particle source, so that the segment model could be used in solving the problem of nonmonoenergetic and nonmonodirectional particle beam transport. In this case, the main part of the algorithm is reserved, and calculation volume does not grow. Dynamics of electron and positron density redistribution with the absorber depth is considered. Comparison of the depth of the maxima of annihilation centres and absorbed energy distributions in a monoenergetic source shows that positrons annihilate mainly in the nondamaged absorber region; annihilation γ quanta in this case provide the information on the pre-radiation matter structure. For a source with the continuous energy spectrum the main part of information is provided from the near-surface region of a sample, the region depth depending on a type of the source spectrum and the experiment geometry