Fusion or fission.
That would be radioactive decay.
This kind of reaction is usually called a "single displacement" or :single replacement" reaction.
An element can only change if the number of protons in its nucleus changes. It is possible to make one kind of element into another, but all these processes can be accomplished only by nuclear means. Gold can be changed into another element in a physics lab, but only with the use of a nuclear reactor or an accelerator of some kind. Any element can be changed into another element, but only by nuclear means.
This reaction is a single displacement reaction, also known as a displacement reaction or a replacement reaction. In this type of reaction, one element replaces another in a compound.
Alpha decay is a kind of radioactive decay in which an alpha particle is emitted from an atom. An alpha particle consists of two protons and two neutrons. Therefore, when an atom of an element undergoes alpha decay, it loses two protons, which changes the atom from one element to another. This is because each different element is identified by the number of protons in its atomic nuclei.
The reaction would be a combination reaction. This type of reaction is also sometimes referred to at a synthesis reaction.
This is called a replacement reaction. When one element replaces another in a compound, it is called single replacement or single displacement. An example isZn + 2HCl ---> ZnCl2 + H2 where the zinc replaces the hydrogen in the acid to form zinc chloride.
One type of atom (element or isotope) is converted to another. This is called nuclear reaction.
a chemical change
Every element has its own kind of atom, identifiable from atoms of another element by its number of protons.
This reaction is a chemical change.
The atomic number is the number of protons in the nucleus of an element. It is what determines what kind of an element it is. When you change the number of protons in the nucleus, you change the type of element.