How does beta decay change the identity of an atom?

Beta decay changes the identity of an atom by altering the number of protons in its nucleus, which defines the atomic number and thus the chemical element itself. This process occurs through the weak force, causing a transformation between neutrons and protons.1234

There are three primary processes of beta decay:

• Negative beta decay (${\beta }^{-}$): A neutron in the nucleus becomes a proton, emitting an electron and an antineutrino. This increases the atomic number by one while the mass number remains the same.51
• Positron emission (${\beta }^{+}$): A proton in the nucleus decays into a neutron, emitting a positron and a neutrino. This decreases the atomic number by one.1
• Electron capture: An orbiting electron is captured by the nucleus and combines with a proton to form a neutron, emitting a neutrino. This also decreases the atomic number by one.1

In all these cases, the atom is transmuted into a different element because the number of protons—the fundamental identifier of an element—has changed.1