under what condition is an atom radioactive
Radioactive decay occurs in unstable atomic nuclei â that is, ones that donât have enough binding energy to hold the nucleus together due to an excess of either protons or neutrons. It comes in three main types â named alpha, beta and gamma for the first three letters of the Greek alphabet.Alpha decay.fter a nucleus undergoes alpha or beta decay, it is often left in an excited state with excess energy. Just as an electron can move to a lower energy state by emitting a photon somewhere in the ultraviolet to infrared range, an atomic nucleus loses energy by emitting a gamma ray.