Which of the following is NOT one of the four most common types of radioactive decay?

Thermal radiation is not classified as one of the four most common types of radioactive decay. The four common types of radioactive decay are alpha decay, beta decay, gamma decay (which includes isomeric transition under its broader category), and neutron decay. Alpha decay involves the emission of helium nuclei, while beta decay involves the conversion of a neutron into a proton with the emission of an electron (or positron). Isomeric transition involves the release of energy in the form of gamma rays as a nucleus shifts from a higher energy state to a lower one.

Thermal radiation, on the other hand, refers to electromagnetic radiation emitted by all matter that has a temperature greater than absolute zero and is not directly related to the process of radioactive decay. It is a form of energy transfer and not a decay process of unstable nuclei.