Alpha (α) decay
When an alpha particle is emitted from a nucleus the nucleus loses two protons and two neutrons. This means the atomic mass number decreases by 4 and the atomic number decreases by 2. A new element is formed that is two places lower in the Periodic Table than the original element.
Radon decays into polonium when it emits an alpha particle. Here is the equation for that radioactive decay:
Beta (β+) decay
β+ decay occurs when they have too many protons [proton: A sub-atomic particle with a positive charge and a relative mass of 1 found in the nucleus of the atom.] . In this case, a proton is converted into a neutron and a positive beta particle of β+. This is called a positron and has the same mass as an electron but the opposite charge (positive).
The mass number (A) of a radioisotope undergoing β+ decay remains the same but the atomic number (Z) reduces by one.
Beta (β-) decay
In Beta (β-) decay, a neutron changes into a proton plus an electron. The proton stays in the nucleus and the electron leaves the atom with high energy, and we call it a beta particle.
When a beta particle is emitted from the nucleus the nucleus has one more proton and one less neutron. This means the atomic mass number remains unchanged and the atomic number increases by 1.
Carbon-14 is a radioactive isotope of carbon. (It's a carbon atom with 8 neutrons instead of the usual 6.) Here is the equation for the beta decay of carbon-14 into nitrogen.
After alpha or beta decay, nuclei often rearrange themselves. This process causes the loss of energy in the form of gamma rays. There is no effect on either the atomic mass (A) or atomic (Z) numbers.
--> In Double beta decay, A nucleus emits two electrons and two antineutrinos