Turning lead into gold was long a dream of alchemists. They never achieved it, but something akin to this occurs every time a nuclear reaction or nuclear decay takes place (%gamma decay excepted): one element becomes another. For example
An atom of carbon becomes an atom of nitrogen.
Radioactive decays are spontaneous processes, and we can do little to change the likelihood of a particular decay happening (chain reactions and atom bombs excepted), but we can promote certain nuclear reactions. For example we can bombard a nucleus with nucleons, %alpha particles or other small nuclei. Such reactions are called artificial transmutations. In general the target nucleus captures the incoming object and an emission of some sort takes place.
The first such artificial transmutation was carried out by Rutherford in 1919. He bombarded
nuclei with
– particles, producing oxygen. In the reaction protons were emitted.
In fact the label 'artificial transmutations' is a bit misleading, since similar things occur naturally during the post main sequence stages in the lifetimes of stars, producing elements up to iron, and in supernovae, the explosion releasing massive amounts of energy and resulting in the tremendous numbers of particles, which may bombard atoms to produce elements heavier than iron. All of these heavier elements are produced in supernovae.