The SRNA-2K5 package is developed for time independent simulation of proton transport by Monte Carlo techniques for numerical experiments in complex geometry, using PENGEOM from PENELOPE with different material compositions, and arbitrary spectrum of proton generated from the 3D source. This package developed for 3D proton dose distribution in proton therapy and dosimetry, and it was based on the theory of multiple scattering. The compound nuclei decay was simulated by our and Russian MSDM models using ICRU 49 and ICRU 63 data. If protons trajectory is divided on great number of steps, protons passage can be simulated according to Berger's Condensed Random Walk model. Conditions of angular distribution and fluctuation of energy loss determinate step length.
Physical picture of these processes is described by stopping power, Moliere's angular distribution , Vavilov's distribution with Sulek's correction per all electron orbits, and Chadwick's cross sections for nonelastic nuclear interactions, obtained by his GNASH code. According to physical picture of protons passage and with probabilities of protons transition from previous to next stage, which is prepared by SRNADAT program, simulation of protons transport in all SRNA codes runs according to usual Monte Carlo scheme:
(i) proton from the spectrum prepared for random choice of energy, position and space angle is emitted from the source;
(ii) proton is loosing average energy on the step;
(iii) on that step, proton experience a great number of collisions, and it changes direction of movement randomly chosen from angular distribution;
(iv) random fluctuation is added to average energy loss; (v) protons step is corrected with data about protons position before and after scattering;
(vi) there is final probability on step for nonelastic nuclear interaction to happen, and for proton to be absorbed. Compound nucleus decays with emission of protons, neutrons, deuterons, tritons, alpha particles or photons. Particular decay particle is sampled from Poisson's distribution with appropriate average values of multiplication factor of each particle. Energy and angle of particle emission and factors of multiplication are determined from the cross section that obtained by the integration of differential cross section for nonelastic nuclear interaction. Energy and angle of secondary neutron are sampled from emission spectrum. Neutron and photon transport are not included in the current model. They are registered in data file and can be used by other code to simulate their transport. Emitted deuteron, triton and alpha particles are absorbed at the place their creation.