Transmutation or nuclear transmutation is a process that involves a change in the nucleus of an atom. When the number of protons in the nucleus of an atom changes, the identity of that atom changes as it is transmuted into another element or isotope. This transmutation process can be either natural or artificial.
Natural or spontaneous transmutation occurs in unstable, radioactive elements. These elements will be transformed into a stable element over a series of decays or a decay chain. For example, uranium-238 transmutes spontaneously into lead-206 through a series of steps. Nuclear transmutations can occur during the spontaneous radioactive decay of naturally occurring thorium and uranium.
Artificial or induced transmutation occurs when atoms of one element are struck with particles in a linear accelerator, cyclotron, or synchrotron. This collision causes the atom to be changed in some way. All of the elements with atomic numbers greater than 92 - such as plutonium - are man-made elements created through transmutation. Most nuclear reactions involve the artificial transmutation of elements, although they are generally referred to more specifically as "fission", "fusion", or "irradiation" instead of being referred to broadly as transmutation.
Artificial transmutation can be accomplished through the use of particle accelerators that strike elements with alpha particles, deuterons, or small nuclei. With this process, some of the protons from the bombarding particles are lodged in the target nucleus, promoting the transmutation into a different element. In a nuclear reactor, the target nucleus is struck with neutrons, resulting in fission of nuclei.
In early experiments, high-speed alpha particles from 214Bi were used to strike a nucleus. In 1919, Rutherford carried out the first nuclear reaction between these alpha particles and nitrogen. In this reaction, a nitrogen nucleus reacted with a high speed helium nucleus to form two new nuclei and a proton. This demonstrated the possibility of transmuting elements. This lead to Rutherford, a physicist, to get the 1908 Nobel Prize in chemistry, for quite ironically, performing alchemy. Although of course this alchemy was not turning lead into gold as so many centuries of alchemists had hoped.