towards a comprehensive physical modelling of fission chambers.

International audienceFission chambers are neutron detectors used in different types of nuclear reactors. The outgoing pulse shape and the detector response are important parameters from the design point of view. This article presents an overall organization of a new multi-physic, multiobjective fission chamber simulation code. Diverse aspects of the detector physics are implemented in an object-oriented Monte Carlo code, based on Geant4. This simulation code, called Lion, combines stochastic description of several phenomena: the neutron impact, neutron induced fission, fission product and heavy ion penetration, electron transport as well as particle interaction with matter. In addition, the code can calculate transport of charge carriers (free-electrons and ions), the electric field propagation and the acquisition system response. Thanks to the modular design, Lion allows for future extensions in form of new physics modules or new detector types. The article presents a few novel solutions which were not used in previous fission chamber simulation codes (e.g. new models of the fission fragment penetration or a new scheme for space charge modelling). To validate the code, a series of irradiation experiments will be conducted in Minerve reactor in CEA Cadarache and their outcome will be compared to the simulation results