HERMES-KFA, High-Energy Radiation Transport by Monte-Carlo

1 - Description of program or function: HERMES-KFA consists of a set of Monte Carlo Codes used to simulate particle radiation and interaction with matter. The main codes are HETC, MORSE, and EGS. They are supported by a common geometry package, common random routines, a command interpreter, and auxiliary codes like NDEM that is used to compute the deexcitation photons from nuclear deexcitation after spallation processes. The codes have been modified so that any particle history falling outside the domain of the physical theory of one program can be submitted to another program in the suite to complete the work. Also response data can be submitted by each program, to be collected and combined by a statistic package included within the command interpreter. 2 - Method of solution: The main programs within HERMES use the Monte Carlo method to simulate the history of particles moving in and interacting with matter. HETC (here HET KFA 2) uses Bertini's intra nuclear cascade model for p, n, and pions to describe nonelastic interactions, followed by EVAP5 for the evaporation of the highly excited residual nucleus. A high energy fission model (from RAL) and a semi-empirical model for elastic scattering of protons and neutrons have been added. MORSE uses neutron and gamma cross-sections to describe the behavior of low energy particles. We included a subset of the EPR cross-section library. EGS covers the electromagnetic part of the particle showers. It uses PWLF-functions for the cross-sections pre-computed by PEGS and has implemented the models of photon and electron interaction with atoms. 3 - Restrictions on the complexity of the problem: Problem restrictions arise from the different physical models used and from the statistical behavior of the problem itself. The prediction of particle fluxes or their induced energy dose in geometric regions, where only few particles will ever enter (for example beyond of a bulk shield) is such statistical problem that will imply restrictions. The measure of a distinct isotope in the vector of residual nuclei is an example, where the models (here EVAP) only give a guideline of the mean residual nuclei vector but not the differential measure