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 compounds hexagonal structure. Californium(III) iodide (CfI) is a lemon-yellow solid that has a rhombohedral structure and sublimes at ~800 °C. Californium(III) oxyfluoride (CfOF) is prepared by hydrolysis of californium(III) fluoride (CfF) at high temperature. Californium(III) oxychloride (CfOCl) is prepared by hydrolysis of the hydrate of californium(III) chloride at 280–320 °C. Heating the sulfate in air at about 1200 °C and then reducing with hydrogen at 500 °C produces the sesquioxide (CfO). The hydroxide Cf(OH) and the trifluoride CfF are slightly soluble. Californium(III) oxychloride (CfOCl) was the first californium compound to be discovered. Californium(III) polyborate is unusual in that californium is covalently