Excitation function

Excitation function is a term used in nuclear physics to describe a graphical plot of the yield of a radionuclide or reaction channel as a function of the bombarding projectile energy or the calculated excitation energy of the compound nucleus. 
The excitation function typically resembles a Gaussian bell curve. Mathematically, it is described as a Breit-Wigner function, owing to the resonant nature of the production of the compound nucleus.
A nuclear reaction should be described by a complete study of the exit channel (1n,2n,3n etc) excitation functions in order to allow a determination of the optimum energy to be used to maximize the yield.