Most people, when asked what they thought the most expensive metal in the world was, would be inclined to say gold, silver, or even platinum. Although we consider these metals ‘precious’, and indeed they are close to the top of the list, they are by no means the most expensive and can all be trumped by one metal – Californium.
Californium is a rare earth metal and does not occur naturally on the planet. It is a radioactive metallic chemical element with the symbol Cf and atomic number 98. Not only is a gram of Californium worth US$27 million, it is second only to antimatter when it comes to the most expensive materials in the world.
The element was first made in the 1950s at the University of California Radiation Laboratory in Berkeley, hence the name Californium which it takes from its origins. It is a silver/white actinide metal with a melting point of 900 ± 30 °C. It is also exceedingly radioactive and just one microgram of Californium releases up to 170 million neutron particles every minute.
Uses of Californium include the detection of gold and platinum. At US$56 per gram for gold and US$60 per gram for platinum these 2 metals are still high on the list of the world’s most expensive elements, but far from the cost of Californium. It can also be used in a device called a neutron moisture gauge to detect oil/water bearing layers within wells.
More uses are expected to be discovered for Californium as at the moment only a few of its compounds are known.