Inelastic scattering of a fast neutron by a nucleus typically results in?

• A. An emitted gamma and a lower-energy neutron.
• B. Immediate fission of the nucleus.
• C. Absorption without emission.
• D. Elastic recoil only.

Answer: (A)

Inelastic scattering involves the neutron transferring part of its energy to the nucleus, putting the nucleus into an excited state. The excited nucleus then releases that energy by emitting a gamma ray as it returns to a lower energy state. The neutron that scatters emerges with less kinetic energy than it started with. So you end up with a lower-energy neutron plus a gamma photon—this combination is the hallmark of inelastic scattering.

This differs from elastic scattering, where the nucleus only recoils and no gamma is emitted; from neutron capture, where the neutron is absorbed and the nucleus typically changes without a promptly emitted fast neutron; and from fission, where the nucleus splits into smaller fragments.