Methods for calculating the (n,2n) reaction-induced damage cross section with different approaches of kinematics

The (n,2n) nuclear reaction is important for neutron irradiation damage. However, its production of two indistinguishable secondary neutrons leads the calculation of displacement damage cross section to be complicated and uncertain. The present work investigates the (n,2n) reaction-induced displacement damage cross section by comparing five methods. The five approaches give consistent damage cross sections within 5% relative deviation for incident neutron energy below 20 MeV, the upper limit for nuclear reactor applications. However, the deviation becomes important for higher incident energy. The proposed KLab2 or KCM2 method is recommended in the case of non-negligible deviation between different calculations, while further investigation on the full correlation between two secondary neutrons as well as the distributions of excited recoils is suggested.