Nuclear Refresher- Unit 1 Page 2 Nuclear decay occurs when a nucleus is unstable or radioactive. It becomes unstable when the neutron to proton ratio is too high or too low. In an attempt to become stable, a particle and/or energy are released, frequently resulting in the identity of the element changing. Some examples of decay are alpha (4He or 20), low energy beta (e or), medium energy gamma which is pure energy (written as Y.), dangerous