Калифорний: Синтезделген химиялық элемент

the chemical element

Californium is a synthetic chemical element; it has symbol Cf and atomic number 98. It was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory) 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 elements that have been produced in amounts large enough to see with the naked eye (after einsteinium). It was named after the university and the U. S. state of California. Two crystalline forms exist at normal pressure: one above and one below A third form exists at high pressure. Californium slowly tarnishes in air at room temperature. Californium compounds are dominated by the +3 oxidation state. The most stable of californium's twenty known isotopes is californium 251, with a half life of 898 years. This short half life means the element is not found in significant quantities in the Earth's crust. 252Cf, with a half life of about 2.645 years, is the most common isotope used and is produced at Oak Ridge National Laboratory in the United States and Research Institute of Atomic Reactors in Russia. Californium is one of the few transuranium elements with 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 using neutron diffraction and neutron spectroscopy. It can also be used in nuclear synthesis of higher mass elements; oganesson (element 118) was synthesized by bombarding californium 249 atoms with calcium 48 ions. Users 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.

Californium is a silvery white actinide metal with a melting point of and an estimated boiling point of The pure metal is malleable and is easily cut with a razor blade. Californium metal starts to vaporize above when exposed to a vacuum. Below californium metal is either ferromagnetic or ferrimagnetic (it acts like a magnet), between 48 and 66 K it is antiferromagnetic (an intermediate state), and above it is paramagnetic (external magnetic fields can make it magnetic). It forms alloys with lanthanide metals but little is known about the resulting materials. The element has two crystalline forms at standard atmospheric pressure: a double hexagonal close packed form dubbed alpha (α) and a face centered cubic form designated beta (β). The α form exists below 600–800 °C with a density of 15.10 g/cm3 and the β form exists above 600–800 °C with a density of 8.74 g/cm3. At 48 GPa of pressure the β form changes into an orthorhombic crystal system due to delocalization of the atom's 5f electrons, which frees them to bond. The bulk modulus of a material is a measure of its resistance to uniform pressure. Californium's bulk modulus is 50, which is similar to trivalent lanthanide metals but smaller than more familiar metals, such as aluminium (70 GPa).

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. Nuclear fallout from atmospheric nuclear weapons testing prior to 1980 contributed a small amount of californium to the environment. Californium is not a major radionuclide at United States Department of Energy legacy sites since it was not produced in large quantities. However, subsequent studies failed to demonstrate any californium spectra, and supernova light curves are now thought to follow the decay of nickel 56. The transuranic elements americium to fermium, including californium, occurred naturally in the natural nuclear fission reactor at Oklo, but no longer do so. Spectral lines of californium, along with those of several other non primordial elements, were detected in Przybylski's Star in 2008.

Californium 252 has a number of specialized uses as a strong neutron emitter; it produces 139 million neutrons per microgram per minute. Neutrons from californium are used as a treatment of certain cervical and brain cancers where other radiation therapy is ineffective. It has been used in educational applications since 1969 when Georgia Institute of Technology got a loan of 119 μg of 252Cf from the Savannah River Site. It is also used with online elemental coal analyzers and bulk material analyzers in the coal and cement industries. Neutron penetration into materials makes californium useful in detection instruments such as fuel rod scanners; neutron radiography of aircraft and weapons components to detect corrosion, bad welds, cracks and trapped moisture; and in portable metal detectors. Neutron moisture gauges use 252Cf to find water and petroleum layers in oil wells, as a portable neutron source for gold and silver prospecting for on the spot analysis, and to detect ground water movement. The main uses of 252Cf in 1982 were, reactor start up (48.3%), fuel rod scanning (25.3%), and activation analysis (19.4%). By 1994, most 252Cf was used in neutron radiography (77.4%), with fuel rod scanning (12.1%) and reactor start up (6.9%) as important but secondary uses. In 2021, fast neutrons from 252Cf were used for wireless data transmission. 251Cf has a very small calculated critical mass of about , high lethality, and a relatively short period of toxic environmental irradiation. The low critical mass of californium led to some exaggerated claims about possible uses for the element. In October 2006, researchers announced that three atoms of oganesson (element 118) had been identified at Joint Institute for Nuclear Research in Dubna, Russia, from bombarding 249Cf with calcium 48, making it the heaviest element ever made. The target contained about 10 mg of 249Cf deposited on a titanium foil of 32 cm2 area. Californium has also been used to produce other transuranium elements; for example, lawrencium was first synthesized in 1961 by bombarding californium with boron nuclei.

Californium that bioaccumulates in skeletal tissue releases radiation that disrupts the body's ability to form red blood cells. The element plays no natural biological role in any organism due to its intense radioactivity and low concentration in the environment. Californium can enter the body from ingesting contaminated food or drinks or by breathing air with suspended particles of the element. Once in the body, only 0.05% of the californium will reach the bloodstream. About 65% of that californium will be deposited in the skeleton, 25% in the liver, and the rest in other organs, or excreted, mainly in urine. Half of the californium deposited in the skeleton and liver are gone in 50 and 20 years, respectively. Californium in the skeleton adheres to bone surfaces before slowly migrating throughout the bone. The element is most dangerous if taken into the body. In addition, californium 249 and californium 251 can cause tissue damage externally, through gamma ray emission. Ionizing radiation emitted by californium on bone and in the liver can cause cancer.