Hello!
The fission of an atom that has a large atomic number can be induced by bombarding the atom with neutrons.
Nuclear fission occurs when a heavy nucleus divides into two or more lighter nuclei. This reaction is induced by the bombarding of neutrons into the nucleus, making it unstable (like throwing an orange to a perfectly arranged orange pyramid at the supermarket). The unstable nucleus breaks down into lighter elements, releasing more neutrons which contribute to the chain reaction.
Have a nice day!