The STEREO experiment aims at measuring accurately the antineutrino spectrum [1,2] emitted by the ILL research reactor, for a complete study of the Antineutrino Reactor Anomaly . Installed at 10 m from the core, the target volume of the detector  is filled with a Gd-loaded organic liquid scintillator in order to sign the capture of the neutron produced by a neutrino interaction. The compactness of the target makes the detection efficiency of this neutron heavily relying on the description of the de-excitation of Gd isotopes. Therefore, the FIFRELIN [5,6] code has been coupled with the GEANT4 simulation of the STEREO experiment for a significant improvement of the Data/MC agreement . In this work we present the implementation of several new ingredients in the FIFRELIN code: the primary γ ray intensities from the EGAF  database, the physics of angular correlations between the de-exciting γ rays  and the treatment of X rays that follow the decay via conversion electrons. An output of these improved simulations will be made available soon to the community. Applications to a wider range of isotopes, of interest for neutrino and dark matter physics will be discussed.
Keywords neutron-capture, γ-cascade
We acknowledge the financial support of the Cross-Disciplinary Program on Numerical Simulation of CEA, the French Alternative Energies and Atomic Energy Commission.
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