High Quality Content by WIKIPEDIA articles! Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles (helium ions) at the University of California, Berkeley. It is the ninth member of the actinide series and was the sixth transuranium element to be synthesized. It is the second-highest atomic mass element to be produced in amounts large enough to see with the unaided eye, after einsteinium. The element was named after California and the University of California.