Welcome to the 12th instalment of the Element of the Month – a regular feature on the Radleys blog. As usual, we chose our element of the month by using a random number generator to produce a figure between 1 and 118 – the number of elements in the periodic table (so far). This month we’re looking at atomic number 98, californium (Cf). Californium – The Key Facts Californium is a radioactive element, one of the actinide series. There are twenty radioisotopes of californium, with mass numbers from 237 to 256. The most stable is californium-251, with a half-life of 898 years, but the first to be discovered was californium-245, which has a half-life of only 44 minutes. Californium is generated in particle accelerators and nuclear reactors. It’s the second heaviest element to be produced in a large enough amount to be seen by the naked eye. A Few Fascinating Facts about Californium Following our blog on neptunium, the first transuranium element, californium was the sixth to be discovered. It is similarly unstable and radioactive. Glenn T. Seaborg was one of the scientists who first synthesised it, and he was involved in the discovery of other transuranium elements too – leading to a Nobel Prize in Chemistry (1951), and coverage in our Week in Chemistry blog. Californium was first produced, in 1950, by Seaborg, Stanley Thompson, Kenneth Street, Jr., and Albert Ghiorso at the University of California Radiation Laboratory – the university and state giving the element its name. This team created the new element by bombarding curium-242 with alpha particles in a cyclotron particle accelerator. Each reaction generated an atom of californium-245 and a neutron. It wasn’t until 1974 that californium metal was synthesised by R. G. Haire and R. D. Baybarz, by reducing californium oxide. Depending on its temperature, the magnetic properties of californium metal can change – it can be ferromagnetic, ferrimagnetic, antiferromagnetic or paramagnetic! Most recently, californium was vital in the creation of the heaviest element ever – 118 (ununoctium). This time, a particle accelerator was used to bombard californium-249 with an intense beam of calcium-48. It took researchers two months and billions of calcium ions to synthesise just 3 atoms of element 118, which decayed within milliseconds! Unusually for a transuranium element, californium does have various practical applications. Californium-252, with its half-life of approximately 2.6 years, is a strong neutron emitter. It can be used to start up nuclear reactors and to treat cancer. The neutrons can pass through materials, and so californium-252 can be used to detect gold and silver, landmines in war zones, and bombs in luggage. Neutron radiography can uncover corrosion and other issues in aeroplanes. Californium-252’s neutron emission is also used in moisture gauges to reveal water and oil layers in oil wells, to measure moisture content in soil, and to monitor the movement of groundwater. So that’s californium, the man-made radioactive actinide that’s produced from nuclear reactions. It has no biological roles, but surprisingly many applications.