A change in nuclear charge means that the element has been changed into a different element. Only through such radioactive decays or nuclear reactions can transmutation , the age-old dream of the alchemists, actually occur. The mass number, A, of an a particle is four, so the mass number, A , of the decaying nucleus is reduced by four. He is two, and therefore the atomic number of the nucleus, the number of protons, is reduced by two. This can be written as an equation analogous to a chemical reaction.
Energy is released in the process of a decay.
Careful measurements show that the sum of the masses of the daughter nucleus and the a particle is a bit less than the mass of the parent isotope. Since the mass of an electron is a tiny fraction of an atomic mass unit, the mass of a nucleus that undergoes b decay is changed by only a tiny amount. The mass number is unchanged. The nucleus contains no electrons. Rather, b decay occurs when a neutron is changed into a proton within the nucleus.