Ghoulification

Most ghouls were "created" in the Great War of 2077. Ghouls are alive during Fallout 76 (2102 - 2103), Fallout (2161), Fallout 2 (2241), Fallout 3 (2277), Fallout: New Vegas (2281) and Fallout 4 (2287). All ghouls live considerably longer than normal humans, though they are largely sterile, so much so that the birth of Monica, an unaffected human child of two ghoul parents, was described as miraculous. The unnaturally long lifespan of a ghoul is also due to a mutation within the autonomic nervous system of certain individuals following exposure to specific combinations of ionizing radiation with wavelengths below ten picometers. Radiation that has such a short wavelength, is known as gamma radiation and is normally lethal to healthy humans in even moderate doses. The mutation in response to gamma radiation that produces ghouls disrupts the normal process of decay in the neurotransmitters along the spinal cord. 
High levels of radiation are a crucial factor, but radiation poisoning typically results in death, rather than ghoulification. There are two primary ways in which ghouls can develop from a human. Irradiation and gradual transformation result in ghouls who retain their general human shape, but with a high degree of skin deterioration: Exposed muscle, flaking skin, and damaged connective tissue characterized by the absence of nose and ears. Another is surviving a nuclear blast relatively close to ground zero, suffering burns both thermal and radiation-induced, but surviving. The latter transformation is typically faster and substantially more traumatic for the victim and results in a generally much more horrifying appearance, with exposed bone, asymmetric deformations, and extensive unhealed wounds.
The vast majority of ghouls of both types have developed as a result of exposure during the Great War, but ghoulification is also possible after the War. Camp Searchlight is one such example, with an attack that transformed a majority of the NCR troopers stationed there into ghouls. Camp Searchlight also emphasizes the fact that the nature of the transformation may lead to mental problems. The trauma of transformation can cause a mental breakdown in the victim, causing a rapid degeneration of higher thought processes, causing them to become feral.[21] Moreover, particularly severe irradiation can lead to the creation of luminous necrotic post-humans, or glowing ones with a permanently damaged brain: feral glowing ones are almost invariably hostile.