Why do nuclei emit the alpha, beta, and gamma radiation?
As we have said before, when the number of nucleons in the nucleus increases, it reaches some point at which Coulomb’s repelling force (between the protons) predominates the attracting nuclear force. Such nucleus is unstable and sooner or later it decays. An unstable nucleus emits an alpha or beta particle and so it transforms into a nucleus of some other element. A and Z are the symbols for the mass number and the atomic number (here of the nucleus before it decays) respectively. The nucleus of helium (which is the alpha particle) consists of two protons and two neutrons. So, if decaying atom emits the alpha particle, the mass number of the daughter atom equals A-4, and the atomic number equals Z-2.
