Conversion of one nuclide into another nuclide is called transmutation. Transmutation occurs naturally when unstable nuclei break down into other, smaller nuclei over time, releasing particles and/or energy during radioactive decay. Radioactive decay is not the only process that leads to transmutation. It is possible to form new nuclides artificially, through bombardment of an existing nuclide with another nuclide or a neutron.The first such successful experiment was performed by British scientist Ernest Rutherford in 1911. Rutherford bombarded nitrogen with alpha particles, particles identical to a helium ion (He2+) consisting of two protons and two neutrons, and obtained oxygen-17 and hydrogen.
The heaviest element found in nature is uranium, which has an atomic number of 92. Elements with a higher atomic number than uranium are transmuted artificially using particle accelerators. An element with a higher atomic number than that of uranium is sometimes called a transuranium element.A significant transuranium element is plutonium, with the atomic number 94. Plutonium can form in nuclear reactions, through a series of reactions. First, uranium-238 undergoes neutron bombardment and forms uranium-239.