[en] In order to optimize the neutron shieldings in the NEMO 3 detector we plan to use the MICAP/GEANT code. To study the reliability of this code different experiments have been performed in Bordeaux and Prague using Ge detectors. The germanium detector was placed inside of different types of shieldings (iron, lead, polyethylene) to record the γ-rays emitted in the interactions of the neutrons provided by a ²⁵²Cf source. The high energy resolution of the Ge diode allows identifying the photons coming from inelastic scattering (n,n'γ) and capture reactions (n,γ). In order to understand the neutron behaviour the neutron simulation code MICAP/GEANT which permits the study of the neutron interactions from 10^-5 eV up to 20 MeV was used. By comparing the simulations with the experimental data the processes of thermalization and capture in light (polyethylene) and heavy (iron and lead) materials was tested. Following these tests a new library taking into account the decay schemes of the states excited by the (n,γ) or (n,n'γ) has been developed as well as an interface between this library and the MICAP library. The first results obtained show a good agreement between experiment and simulation