Excitation function (a.k.a. yield curve) 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.^[1] The yield is the measured intensity of a particular transition.^[2]

The excitation function typically resembles a Gaussian bell curve and is mathematically described by a Breit–Wigner function, owing to the resonant nature of the production of the compound nucleus.^[1][2] The energy value at the maximum yield on the excitation curve corresponds to the energy of the resonance.^[2] The energy interval between 25% and 75% of the maximum yield on the excitation curve are equivalent to the resonance width.^[2]

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.^[1]