Nucleus Recoil-Energy in Neutron Capture Reactions
A nucleus which captures a thermal neutron must, since the momentum is conserved, receive a recoil energy. Immediately after capturing a neutron, the nucleus will emit γ quantas to get rid of the excess energy liberated when the neutron is bound to the nucleus. This also result in a certain amount of recoil energy on the nucleus.
Recoil energy from n-capture
The conservation of momentum demands that
Recoil energy from γ emission