In this model is assumed that protons from the source do not mutually interact, and that they move to target without influence of outside forces. Proton is scattered with atom, and neighbor atoms do not take part in that. Also, it is supposed that material is homogeneous and that there are no changes of its density in process of energy absorption. During protons passage through materials, following processes happen: loss of energy in inelastic and elastic scattering with atoms, and loss of energy in nonelastic nuclear interactions. If protons trajectory is divided into huge number of steps, on each step, protons passage can be simulated according to the Condensed-Random-Walk model. Step length is determinate by conditions of angular distribution and fluctuation of energy loss. Physical picture of these processes is described by ICRU49 tables and Ziegler's analytical methods from his TRIM program functions for stopping power, Moliere's angular distribution, Vavilov's distribution with Sulek's correction per all electron orbits, Young-Chadwick's cross sections (GNASH) or Sobolevsky Multi Stage Dinamical Model (SHIELHIT) - MSDM Generator for nonelastic nuclear interactions.
Simulation model of protons passage is based on two groups of data. The first group contains data for average energy loss, cross sections for nonelastic nuclear interactions and atomic data for exitational potentials. The second group of data serves for inverse angular distribution calculation and for fluctuation distribution of energy loss and also for probabilities of nonelastic nuclear interactions on proton step calculations. Both groups of data are prepared by program SRNADAT, for each material in function of energy and angle. Model is as closer to physical picture of protons passage as data-base of prepared data is denser. Therefore, energy scale above 10 MeV is linear, and below that energy scale is logarithmic. Distributions are inverted with great number (100 - 1000) of values for preselected probabilities to avoid interpolation in simulation.