Excitation function is a term used in nuclear physics to describe a graphical plot of the yield of a radionuclide as a function of the bombarding projectile energy or the calculated excitation energy of the compound nucleus.

A curve is typically parabolic in shape. Mathematically, it is described as a Breit-Wigner function, resembling a Gaussian bell curve.

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 maximise the yield.