Pedro Brogueira 1, Patrícia Gonçalves 2, Ana Keating 2, Dalmiro Maia 3, Mário Pimenta 2, Bernardo Tomé 2 1 IST, Instituto Superior Técnico, 2 LIP, Laboratório de Instrumentação e Física Experimental de Partículas, 3 FCUP,Faculdade de Ciências da Universidade do Porto Geant4 is a detector simulation toolkit providing a general infrastructure for description of geometry and materials; particle transport and interaction with matter; visualisation of geometries, tracks and hits. Its application areas include high energy physics and nuclear experiments, medical, accelerator and space physics studies. 3 cm The Geant4 model for the instrument was used to: Study the interaction of secondary particles induced by the structural frame and electronics circuits. Generate the response functions for the instrument simulator. Study the radiation dose expected by electronics, calorimeters and trackers. Assess the device performance as a radiation monitor and as a scientific instrument. Radiation dose in the tracker planes Energy deposited in the crystal by electrons, protons and alphas as a function of the incident energy Geant4 simulation of a proton crossing the detector with the emission of scintillation photons MarsREC Radiation Environment Module employs Geant4 and includes as parameters: Martian time, detection position, solar longitude, solar cycle modulated cosmic ray and solar particle event spectra, 4-D EMCD atmosphere, geology and MOLA topology. Martian altitude and soil composition as a function of latitude and longitude Illustration of the effect of Martian surface topology in the shape of theMartian atmospheric layers. Martian surface iron content as a function of latitude and longitude 0 8 Martian surface water content as a function of latitude and longitude The framework developed will be capable of: Predicting the high-energy radiation environment at the surface of Mars for different locations and solar longitudes. Tracking all primary and secondary particles (showing the relative importance of the backscattered neutron component of the radiation environment). Calculating the energy spectra and particle species, radiation fluxes at component level, energy depositions and doses Computing SEU rates in specific components. Predicting radiation environment variation with the climate changes along the Martian year. Evaluating Dose Equivalents and Dose depositions at Mars surface Total fluence of particles at Martian surface as a function of solar longitude It will measure fluxes and energy distributions of electrons, protons and ions in relevant energy ranges: MeV per nucleon for protons and ions and MeV for electrons The instrument, based on a scintillating crystal, is capable of performing not only as a radiation switch, but also as a scientific instrument. A new generation of compact, lightweight (< 1kg), general purpose radiation monitors are needed for future Space Missions (e.g. BepiColombo).