In order to properly track what is happening during the different types of radioactive decay, scientists use specific notation to form a decay equation. There are two important numbers in this equation: A - the mass number. This is the number of protons plus the number of neutrons in a nuclide. And Z the atomic number. This is the number of protons in a nuclide.

This image contains two horizontal lines. On the top line there is a large capital A representing the symbol for Mass number, and a description of the Mass number. The text reads 'The number of Protons plus the number of Neutrons in a nuclide'. To the right of this text is an image of a red ball with a white plus sign in it and another image of a yellow ball representing a Proton and a Neutron respectively. On the bottom line there is a large capital Z representing the symbol for Atomic number, and a description of the Atomic number. The text reads 'The number of Protons in a nuclide'. To the right of this text is an image of a red ball with a white plus sign in it representing a Proton.