The protons and neutrons combined are responsible for the mass of an atom, which is called the mass number or isotopic number. Types of radioactive decay. Up to about silica, the number of protons in an element equals the number of neutrons. Heavier elements can have several isotopic numbers, meaning different numbers of neutrons, but the same number of protons. The discovery of radioactivity was that the occurrence of some isotopes is unstable, such that a new element is formed spontaneously.
Beta decay describes the emission of an electron, which converts a neutron into a proton.
The atomic number increases by 1, whereas the mass number remains the same. A third form of radioactive decay is when a nucleus catches an electron, resulting in the conversion of a proton to a neutron. These three processes all produce some form of radiation. Marie Curie would ultimately succumb to leukemia brought on by such radiation damage. The half-lives of an element.