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 the elements directly above them in the periodic table were named. However, the element directly above element 98 in the periodic table, dysprosium, has a name that simply means "hard to get at" so the researchers decided to set aside the informal naming convention. They added that "the best we can do is to point out [that] ... searchers a century ago found it difficult to get to California." Weighable quantities of californium were first produced by the irradiation of plutonium targets at the Materials Testing Reactor at the National Reactor Testing Station in eastern Idaho; and these findings were