Nucleus Recoil-Energy in Neutron Capture Reactions

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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

where P denotes the momentum, index n denots the neutron, index T the target nucleus, and index R the recoil.

The general relationship between kinetic energy, EK, and momentum p is given by:

The mass of the neutron is 1 (atomic mass unit). the mass of the target nucleus is A. The new nucleus will therefore have mass A+1. Then

d