Each element has one or more isotopes with unstable nuclei, which can undergo radioactive decay. In this process, the nucleus can release particles or electromagnetic radiation. When the radius of the nucleus is greater than the radius of action of the strong force, radioactive decay may occur, and the radius of action of the strong force is only a few femtometers.
The most common radioactive decays are as follows:
Alpha decay: The nucleus releases an alpha particle, a helium nucleus containing two protons and two neutrons. The result of decay is a new element with a lower atomic number.
Beta decay: a phenomenon of weak interaction in which a neutron is transformed into a proton or a proton is transformed into a neutron. The former is accompanied by the release of an electron and an antineutrino, while the latter releases a positron and a neutrino. The released electrons or positrons are called beta particles. Therefore, beta decay can increase or decrease the atomic number of the atom by one.
Gamma decay: The energy level of the nucleus is reduced, and electromagnetic radiation is released, usually after the release of alpha particles or beta particles.
The half-life of isotopes with Z protons and N neutrons
Other relatively rare radioactive decays include: releasing neutrons or protons, releasing nuclei or electron clusters, and generating high-speed electrons instead of beta rays and high-energy photons instead of gamma rays through internal conversion.
Each radioisotope has a characteristic decay period, which is the half-life. Half-life is the time required for half of the sample to decay. This is an exponential decay, that is, a constant decay of 50% of the sample during each half-life. In other words, after two half-lives, only 25% of the starting isotope remains.