Californium

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 sixth transuranium 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. 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.

Californium is one of the few transuranium elements that have practical applications. Most of these applications exploit the property of certain isotopes of californium to emit neutrons. For example, californium can be used to help start up nuclear reactors, and it is employed as a source of neutrons when studying materials with neutron diffraction and neutron spectroscopy. Californium can also be used in nuclear synthesis of higher mass elements; ununoctium (element 118) was synthesized by bombarding californium-249 atoms with calcium-48 ions. Use of californium must take into account radiological concerns and the element's ability to disrupt the formation of red blood cells by bioaccumulating in skeletal tissue.

Occurrence


Very minute amounts of californium exist on Earth due to neutron capture reactions and beta decay in very highly-concentrated uranium-bearing deposits. Traces of californium can be found near facilities that use the element in mineral prospecting and in medical treatments. The element is fairly insoluble in water, but it adheres well to ordinary soil; and concentrations of it in the soil can be 500 times higher than in the water surrounding the soil particles.

Fallout from atmospheric nuclear testing prior to 1980 contributed a small amount of californium to the environment. Californium isotopes with mass numbers 249, 252, 253, and 254 have been observed in the radioactive dust collected from the air after 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 254Cf. However, subsequent studies failed to demonstrate any californium spectra, and supernova light curves are now thought to follow the decay of nickel-56.

Symbol		Cf
Atomic Number		98
Atomic Weight		251.0796
Oxidation States		+3
Electronegativity, Pauling		1.3
State at RT		Solid, Metal
Melting Point, K
Boiling Point, K

Appearance and Characteristics of Californium

Harmful effects:

Californium is harmful due to its radioactivity.

Characteristics:

• Californium is a synthetic radioactive silvery-white metal of moderate chemical reactivity.
• It is a relatively soft, malleable metal and is easily cut with a razor-blade.
• It slowly tarnishes in air to the oxide at room temperature. 
• Californium-252 is a very strong neutron emitter.

Uses of Californium

• Californium-252 (half-life of 2.645 years) is produced in nuclear reactors and has found a variety of uses.
• It is used as a neutron emitter, providing neutrons for the start-up of nuclear reactors.
• It has also been used as a target material for producing transcalifornium elements. Ununoctium, the heaviest of the elements, was produced when a californium target was bombarded with calcium ions. 
• Californium-252 is used in to treat cervical cancer. It is also used to analyze the sulfur content of petroleum and in neutron moisture gauges to measure the moisture content of soil.