Which interaction involves transfer of kinetic energy from a neutron to a nucleus without exciting the nucleus?

• A. Elastic Scatter
• B. Inelastic Scatter
• C. Photoelectric Effect
• D. Pair Production

Answer: (A)

Elastic scattering occurs when a neutron collides with a nucleus and transfers some kinetic energy without exciting the nucleus. In this process, there is no change in the nucleus’s internal energy state—the nucleus remains in its ground state—so no gamma radiation or other internal transitions are produced. The collision simply redistributes energy between the moving neutron and the recoiling nucleus, with total kinetic energy conserved (in the absence of other losses). How much energy the neutron loses depends on the masses involved: if the nucleus is much heavier than the neutron, the neutron slows only a little; if the masses are closer, more energy can be transferred to the nucleus. This is exactly what distinguishes elastic scattering from inelastic scattering, where part of the kinetic energy goes into exciting the nucleus to a higher energy level (and may be followed by gamma emission). The other two options involve interactions with photons rather than neutrons: the photoelectric effect and pair production do not describe transferring neutron kinetic energy to a nucleus without excitation.