Particle Line Shapes in Heavy-Ion Reactions

The kinetic energy of excited heavy ions produced at high velocity in a nuclear reaction can be modified in flight as a result of emission of $\gamma$ rays. It is shown that the resulting broadened ion-energy line shapes can be expressed analytically and have a pattern which depends on the relative $m$-substate populations produced in the reaction. Previously unexplained spectra are interpreted in this manner and the derived $m$-substate populations compared with calculations.