What is the key factor that determines the type of radiation emitted during decay?

The stability of the nucleus is the key factor that determines the type of radiation emitted during decay. A nucleus is considered stable when the balance between the number of protons and neutrons leads to a strong nuclear force that holds it together effectively. When a nucleus is unstable—often due to an imbalance of protons and neutrons, excessive energy, or other factors—it will undergo radioactive decay in an attempt to reach a more stable configuration.

During this decay process, the type of radiation emitted—whether alpha particles, beta particles, or gamma rays—depends on the specific mechanisms that the unstable nucleus employs to release energy and achieve stability. For example, alpha decay typically involves the emission of helium nuclei from larger atoms, beta decay involves the transformation of a neutron into a proton (or vice versa) leading to the emission of electrons or positrons, and gamma decay often accompanies other types of decay as the nucleus releases excess energy in the form of gamma radiation.

The other factors listed, such as the structure of the atom or the energy levels of electrons, do not fundamentally govern the decay process. While the overall structure of the atom plays a role in defining how electrons are arranged, it does not directly influence nuclear stability. Similarly, while the number of protons