Abstract
Radiative neutron capture reaction is generally the main reaction inducing atomic displacements and nuclear heating for low incident neutron energy, even though its contribution to total displacement damage is quite limited in general. The multiple photon emission without identifying the correlations between photons leads the calculated recoil energy to be uncertain. The present work recommends a formula for computing the average recoil energy by assuming the isotropic photon emissions, while the upper limit has been implemented in some codes. The recommended method is identical to the one used in NJOY if the photon distributions are in MF12-MF15, whereas the photon yield is not included in NJOY when photon yields are included in MF6. The presently recommended method for KERMA factor calculation is numerically validated against Tripoli-4 neutron-photon coupling Monte Carlo simulations. Due to the negligible contribution of neutron kick, the correction of the kinematic KERMA factor is quasi-identical to that of photon kick by the yield Y (or Y2 for upper limit). This conclusion is however not applicable for displacement damage calculation if the maximum photon kick is close to the threshold displacement energy. In such a case, detailed consideration of photon emission cascades rather than approximate analytical formulae should be included for accurate calculation of neutron capture reaction-induced damage cross section.
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