Californium a nuclear explosion. Californium is not a major radionuclide at United States Department of Energy legacy sites since it was not produced in large quantities. Californium was once believed to be produced in supernovas, as their decay matches the 60-day half-life of Cf. However, subsequent studies failed to demonstrate any californium spectra, and supernova light curves are now thought to follow the decay of nickel-56. The transuranic elements from americium to fermium, including californium, occurred naturally in the natural nuclear fission reactor at Oklo, but no longer do so. Californium is produced in nuclear reactors and particle accelerators. Californium-250 is
Californium of 2.645 years. All the remaining isotopes have half-lives shorter than a year, and the majority of these have half-lives shorter than 20 minutes. The isotopes of californium range in mass number from 237 to 256. Californium-249 is formed from the beta decay of berkelium-249, and most other californium isotopes are made by subjecting berkelium to intense neutron radiation in a nuclear reactor. Although californium-251 has the longest half-life, its production yield is only 10% due to its tendency to collect neutrons (high neutron capture) and its tendency to interact with other particles (high neutron cross-section). Californium-252 is a very