I can not simulated C12(n,α)Be9 reaction

I build a 12C target , I want to research the C12(n,α)Be9 reaction. I record the deposit energy in every event, and get the deposit Energy Spectrum, but , I can not find a peak
of 8.299MeV which is the energy of the C12(n,α)Be9 reaction. I use the QGSP_BERT_HP model and I have tried different data library, but I can not make it.
I don not why, what should I do? Can you help me?