Californium

"Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made at the University of California, Berkeley in 1950 by bombarding curium with alpha particles (helium-4 ions). It is an actinide element, the sixthtransuranium element to be synthesized, and has the second-highest atomic mass of all the elements that have been produced in amounts large enough to see with the unaided eye (after einsteinium). The element was named after California and the University of California. It is the heaviest element to occur naturally on Earth; heavier elements can only be produced by synthesis."

"Two crystalline forms exist for californium under normal pressure: one above 900 °C and one below 900 °C. A third form exists at high pressure. Californium slowly tarnishes in air at room temperature. Compounds of californium are dominated by a chemical form of the element, designated californium(III), that can participate in three chemical bonds. The most stable of californium's twenty known isotopes is californium-251, which has a half-life of 898 years. This short half-life means the element is not found in significant quantities in the Earth's crust.^[a] Californium-252, with a half-life of about 2.64 years, is the most common isotope used and is produced at the Oak Ridge National Laboratory in the United States and the Research Institute of Atomic Reactors in Russia."