In 1919 Rutherford performed the first artificial nuclear reaction. He was able to demonstrate that when α particles are introduced into a closed sample of N₂ gas, an occasional collision led to the formation of an isotope of O and the release of a proton:

      (1)

Since then many thousands of nuclear reactions have been studied, most of them produced by the bombardment of stable forms of matter with a beam of nucleons or light nuclei as projectiles. Particles which have been used for this purpose include protons, neutrons, deuterons (21H) , α particles, and B, C, N, and O nuclei.