V Californium-252 (Cf-252) is a synthetic, highly radioactive transuranic element, specifically isotope number 98, not found naturally and produced in specialized nuclear reactors like the HFIR in the USA. Its most crucial property is its ability to spontaneously fission, emitting a large and consistent flux of neutrons. With a relatively short half-life of 2.65 years, its potency and the need for periodic replacement contribute to its high cost and specialized handling requirements in applications such as cross belt analysers.