Figure 1. Inelastic scattering of a neutron. Credit: European Nuclear Society.
An elastic collision is a collision in which there is no change in the kinetic energy of the particles involved, i.e., the total kinetic energy of the particles going into the collision is the same as that of the particles heading away from the collision. In everyday situations, for example when two billiard balls collide, some of the kinetic energy is converted into other forms of energy such as heat and sound, so that collisions are never perfectly elastic.
An inelastic collision, also called inelastic scattering, is a collision between bodies in which there is a loss of kinetic energy. In nuclear physics, an inelastic collision is one in which an incoming particle causes excitation or breaking up of the struck nucleus (see Figure 1).