It was on February 28th, 1928 that CV Raman announced his discovery of New radiation-subsequently named the Raman Effect- that won him the Noble prize.
In nuclear physics, nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei). The fission process often produces free neutrons and releases a very large amount of energy.
Thus, The Nuclear Fission is caused by the impact of Neutrons.