Monte carlo transport codes for use in the space radiation environment.

PHITS (Particle and Heavy-Ion Transport code System) [1] is a general purpose particle and heavy-ion MC transport code which can transport neutrons from thermal energies up to 200 GeV. The 3-dimensional Monte-Carlo radiation transport code was developed with collaboration of several institutes including JAEA, RIST, KEK and Chalmers University of Technology. The same method as in the MCNP4C code [2] is employed for neutrons with energies between 1 meV and 20 MeV based on the Evaluated Nuclear Data such as the ENDF-B/VI [3], JENDL-3.3 [4,5]; and for p and n up to 3 GeV for the JENDL-HE [6,7] file.Above 20 MeV, the Bertini model with free p-p and n-n cross sections parameterized according to Niita et al. [8] is used up to 3 GeV, while the simulation model JAM (Jet AA Microscopic Transport Model) developed by Nara et al. [6] is used above 3 GeV for nucleons, above 2.5 GeV for pions, and for all energies for all other baryons. JAM is a hadronic cascade model, which explicitly treats all established hadronic states including resonances with explicit spin and isospin as well as their anti-particles. For protons and other hadrons, JAM is used above 1 MeV, but for charged particles below 1 MeV only the ionization process is considered until the particles are stopped. PHITS also uses Evaluated Nuclear Data for photon and electron transport below 1 GeV in the same manner as in the MCNP4C code based on the Ion Transport System (ITS) code, version 3.0 [9]. The energy range of electrons and photons is restricted to the energy region 1 keV 1 GeV at the present, but the extension of the maximum energy of these particles is in progress. PHITS can also transport nuclei in any solid, gas or liquid material. Below 10 MeV/n, only the ionization process for the nucleus transport is taken into account, but above 10 MeV/n the nucleus-nucleus collisions up to 100 GeV/n is described by the simulation model JQMD (JAERI Quantum Molecular Dynamics) developed by Niita et al. [10]. In the QMD model, the nucleus is described as a self-binding system of nucleons, which are interacting with each other through the effective interactions in the framework of molecular dynamics. One can estimate the yields of emitted light particles, fragments and excited residual nuclei resulting from the heavy ion collision. The QMD simulation, as well as the JAM simulation, describes the dynamical stage of the reactions. At the end of the dynamical stage, excited nuclei are created and must be forced to decay in a statistical way to get the final observed state. In PHITS the GEM model [11] (Generalized Evaporation Model) is default employed for light particle evaporation and fission process of the excited residual nucleus.