Which statement best differentiates elastic from inelastic neutron scattering?

• A. Elastic scattering converts kinetic energy to gamma radiation.
• B. Elastic scattering does not involve any energy transfer to the nucleus.
• C. Elastic scattering preserves total kinetic energy; inelastic scattering results in gamma emission and energy loss.
• D. Elastic scattering produces a slower neutron and a recoiling nucleus.

Answer: (C)

This question hinges on how energy is accounted for in neutron-nucleus collisions. In elastic scattering, the nucleus remains in its ground state, so all the energy before the collision stays as kinetic energy after the collision—the total kinetic energy of the neutron and the recoiling nucleus is conserved. The neutron may change speed and direction, but no energy is left behind in internal excitations or emitted photons.

In contrast, inelastic scattering transfers some energy into internal degrees of freedom of the nucleus. The nucleus can become excited, and after the collision it often de-excites by emitting a gamma ray, which takes away part of the energy. That means the neutron ends up with less kinetic energy than it started with, and energy has effectively left the translational motion via the gamma emission.

Among the options, the best statement captures these energy relationships: elastic scattering preserves total kinetic energy, while inelastic scattering involves energy loss due to internal excitation and often gamma emission. The other choices misstate either that energy is entirely transformed into gamma radiation in elastic scattering, that no energy is transferred to the nucleus in elastic events, or that elastic scattering always produces a slower neutron with a recoiling nucleus.