Californium
Encyclopedia
Californium is a radioactive
metallic chemical element
with the symbol Cf and atomic number
98. The element was first made in the laboratory in 1950 by bombarding curium
with alpha particle
s (helium
ion
s) at the University of California, Berkeley
. It is the ninth member of the actinide
series and was the sixth transuranium element
to be synthesized. It is the second-highest atomic mass element to be produced in amounts large enough to see with the unaided eye, after einsteinium
. The element was named after California
and the University of California
.
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 bond
s. The most stable of californium's twenty known isotope
s is californium-251, which has a half-life
of 898 years. This short half-life means the element is not found 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 neutron
s. For example, californium can be used to help start up nuclear reactor
s, 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 cell
s by bioaccumulating
in skeletal tissue.
metal with a melting point
of 900 ± 30 °C and an estimated boiling point
of 1745 °C. The pure metal is malleable and is easily cut with a razor blade. Californium metal starts to vaporize above 300 °C when exposed to a vacuum. Below 51 K
(−220 °C) 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 160 K (−110 °C) it is paramagnetic
(external magnetic fields can make it magnetic). It forms alloy
s with lanthanide
metals but little is known about them.
The element has two crystalline form
s under 1 standard atmosphere of pressure: A double-hexagonal close-packed form dubbed alpha (α) and a face-centered cubic
form designated beta (β). The α form exists below 900 °C with a density of 15.10 g/cm3 and the β form exists above 900 °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 de-localization 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 ± 5 GPa, which is similar to trivalent lanthanide metals but smaller than more familiar metals, such as aluminium (70 GPa).
Californium exhibits valences
of 4, 3, or 2; indicating the number of chemical bond
s one atom of this element can form. Its chemical properties are predicted to be similar to other primarily 3+ valence actinide elements and the element dysprosium
, which is the lanthanide above californium in the periodic table. The element slowly tarnishes in air at room temperature, with the rate increasing when moisture is added. Californium reacts when heated with hydrogen
, nitrogen
, or chalcogen
(oxygen family element); reactions with dry hydrogen and aqueous mineral acid
s are rapid.
Californium is only water soluble
as the californium(III) cation. Attempts to reduce or oxidize
the +3 ion in solution have failed. The element forms a water-soluble chloride
, nitrate
, perchlorate
, and sulfate
and is precipitated as a fluoride
, oxalate
, or hydroxide
.
of 898 years, californium-249 with a half-life of 351 years, californium-250 with a half-life of 13.08 years, and californium-252 with a half-life of 2.645 years. All the remaining isotopes have half-lives shorter than a year, and the majority of these have half-lives shorter than 20 minutes. The isotopes of californium range in mass number
from 237 to 256.
Californium-249 is formed from the beta decay
of berkelium-249, and most other californium isotopes are made by subjecting berkelium to intense neutron radiation in a nuclear reactor
. Although californium-251 has the longest half-life, its production yield is only 10% due to its tendency to collect neutrons (high neutron capture
) and its tendency to interact with other particles (high neutron cross-section
).
Californium-252 is a very strong neutron
emitter, which makes it extremely radioactive and harmful. Californium-252 undergoes alpha decay
(the loss of two proton
s and two neutrons) 96.9% of the time to form curium
-248 while the remaining 3.1% of decays are spontaneous fission
. One microgram
(µg) of californium-252 emits 2.3 million neutrons per second, an average of 3.7 neutrons per spontaneous fission. Most of the other isotopes of californium decay to isotopes of curium (atomic number
96) via alpha decay.
by the physics researchers Stanley G. Thompson
, Kenneth Street, Jr.
, Albert Ghiorso
, and Glenn T. Seaborg
on or about February 9, 1950. It was the sixth transuranium element
to be discovered; the team announced its discovery on March 17, 1950.
To produce californium, a microgram-sized target of curium-242 was bombarded with 35 MeV-alpha particle
s in the 60 inches (1,524 mm) cyclotron
at Berkeley, California
, which produced californium-245 plus one free neutron .
Only about 5,000 atoms of californium were produced in this experiment, and these atoms had a half-life of 44 minutes.
The discoverers named the new element after California and the University of California
. This was a break from the convention used for elements 95 to 97, which drew inspiration from how the elements directly above them in the periodic table were named. However, the element directly above element 98 in the periodic table, dysprosium
, has a name that simply means "hard to get at" so the researchers decided to set aside the informal naming convention. They added that "the best we can do is to point out [that] ... searchers a century ago found it difficult to get to California."
Weighable quantities of californium were first produced by the irradiation of plutonium targets at the Materials Testing Reactor at the Idaho National Laboratory
; and these findings were reported in 1954. The high spontaneous fission rate of californium-252 was observed in these samples. The first experiment with californium in concentrated form occurred in 1958. Californium-249 to −252 were isolated that same year from a sample of plutonium-239
that had been irradiated with neutrons in a nuclear reactor for five years. Two years later, in 1960, Burris Cunningham and James Wallman of the Lawrence Radiation Laboratory of the University of California created the first californium compounds—californium trichloride, californium oxychloride, and californium oxide—by treating californium with steam and hydrochloric acid.
The High Flux Isotope Reactor
(HFIR) at the Oak Ridge National Laboratory
(ORNL) in Oak Ridge, Tennessee
, started producing small batches of californium in the 1960s. By 1995, the HFIR nominally produced 500 milligrams of californium annually. Plutonium supplied by the United Kingdom to the United States under the 1958 US-UK Mutual Defence Agreement
was used for californium production.
The Atomic Energy Commission sold californium-252 to industrial and academic customers in the early 1970s for $10 per microgram and an average of 150 mg of californium-252 were shipped each year from 1970 to 1990. Californium metal was first prepared in 1974 by Haire and Baybarz who reduced californium(III) oxide with lanthanum metal to obtain microgram amounts of sub-micrometer thick films.
Californium is not known to occur naturally on Earth, but very minute amounts might exist due to various nucleosynthesis reactions in uranium ores. 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 number
s 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 reported to have been found in supernova spectra, but this has been subsequently regarded as an incorrect identification.
s and particle accelerator
s. Californium-250 is made by bombarding berkelium-249 with neutrons, forming berkelium-250 via neutron capture
(n,γ) which, in turn, quickly beta decay
s (β−) to californium-250 in the following reaction:
Bombardment of californium-250 with neutrons produces californium-251 and californium-252.
Prolonged irradiation of americium
, curium, and plutonium with neutrons produces milligram amounts of californium-252 and microgram amounts of californium-249. As of 2006, curium isotopes 244 to 248 are irradiated by neutrons in special reactors to produce primarily californium-252 with lesser amounts of isotopes 249 to 255.
Microgram quantities of californium-252 are available for commercial use through the U.S. Nuclear Regulatory Commission
. Only two sites produce californium-252 - the Oak Ridge National Laboratory in the United States, and the Research Institute of Atomic Reactors
in Dimitrovgrad, Russia
. As of 2003, the two sites produce 0.25 grams and 0.025 grams of californium-252 per year, respectively.
Three californium isotopes with significant half-lives are produced, requiring a total of 15 neutron captures by uranium-238
without nuclear fission
or alpha decay occurring during the process. Californium-253 is at the end of a production chain that starts with uranium-238, includes several isotopes of plutonium
, americium
, curium
, berkelium
, and the californium isotopes 249 to 253 (see diagram).
to detect trace amounts of elements in samples. Neutrons from californium are employed 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 the Georgia Institute of Technology
received a loan of 119 µg of californium-252 from the Savannah River Plant. It is also used with online elemental coal analyzer
s and bulk material analyzer
s 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 gauge
s use californium-252 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 major uses of californium-252 in 1982 were, in order of use, reactor start-up (48.3%), fuel rod scanning (25.3%), and activation analysis (19.4%). By 1994 most californium-252 was used in neutron radiography (77.4%), with fuel rod scanning (12.1%) and reactor start-up (6.9%) as important but distant secondary uses.
Californium-251 has a very small critical mass (about 5 kg), 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 ununoctium
(element 118) had been identified at the Joint Institute for Nuclear Research
in Dubna, Russia, as the product of bombardment of californium-249 with calcium
-48, making it the heaviest element ever synthesized. The target for this experiment contained about 10 mg of californium-249 deposited on a titanium foil of 32 cm2 area. Californium has also been used to produce other transuranium elements; for example, element 103 (later named lawrencium
) was first synthesized in 1961 by bombarding californium with boron
nuclei.
s. 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.
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
metallic chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
with the symbol Cf and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
98. The element was first made in the laboratory in 1950 by bombarding curium
Curium
Curium is a synthetic chemical element with the symbol Cm and atomic number 96. This radioactive transuranic element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie. Curium was first intentionally produced and identified in summer 1944 by the group of...
with alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
s (helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s) at the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
. It is the ninth member of the actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...
series and was the sixth transuranium element
Transuranium element
In chemistry, transuranium elements are the chemical elements with atomic numbers greater than 92...
to be synthesized. It is the second-highest atomic mass element to be produced in amounts large enough to see with the unaided eye, after einsteinium
Einsteinium
Einsteinium is a synthetic element with the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide.Einsteinium was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein...
. The element was named after California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and the University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
.
Two crystalline forms
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
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
Compounds of californium
Few compounds of californium have been made and studied. The only californium ion that is stable in aqueous solutions is the californium cation. The other two oxidation states are IV and II . The element forms a water-soluble chloride, nitrate, perchlorate, and sulfate and is precipitated as a...
are dominated by a chemical form of the element, designated californium(III), that can participate in three chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
s. The most stable of californium's twenty known isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s is californium-251, which has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 898 years. This short half-life means the element is not found 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
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...
in the United States and the Research Institute of Atomic Reactors
Research Institute of Atomic Reactors
The Research Institute of Atomic Reactors is an institute for nuclear reactor research in Dimitrovgrad in Ulyanovsk Oblast, Russia. The institute houses eight nuclear research reactors: SM, Arbus , MIR.M1, RBT-6, RBT-10 / 1, RBT-10 / 2, BOR-60 and VK-50.-External links:* *...
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
Isotopes of californium
Californium is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 245Cf in 1950. There are 20 known radioisotopes ranging from 237Cf to 256Cf and one nuclear isomer, 249mCf...
to emit neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s. For example, californium can be used to help start up nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s, and it is employed as a source of neutrons when studying materials with neutron diffraction
Neutron diffraction
Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material: A sample to be examined is placed in a beam of thermal or cold neutrons to obtain a diffraction pattern that provides information of...
and neutron spectroscopy
Neutron spectroscopy
Neutron scattering is a spectroscopic method that uses neutron scattering to measure atomic and magnetic motions of atoms. Inelastic neutron scattering observes the change in the energy of the neutron as it scatters from a sample and can be used to probe a wide variety of different physical...
. Californium can also be used in nuclear synthesis of higher mass elements; ununoctium
Ununoctium
Ununoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is...
(element 118) was synthesized by bombarding californium-249 atoms with calcium-48
Calcium-48
Calcium-48 is a rare isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, the only radioactive decay pathway open to it is the extremely rare process of double beta decay...
ions. Use of californium must take into account radiological concerns and the element's ability to disrupt the formation of red blood cell
Red blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s by bioaccumulating
Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...
in skeletal tissue.
Physical properties
Californium is a silvery white actinideActinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...
metal with a melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
of 900 ± 30 °C and an estimated boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
of 1745 °C. The pure metal is malleable and is easily cut with a razor blade. Californium metal starts to vaporize above 300 °C when exposed to a vacuum. Below 51 K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
(−220 °C) californium metal is either ferromagnetic
Ferromagnetism
Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished...
or ferrimagnetic
Ferrimagnetism
In physics, a ferrimagnetic material is one in which the magnetic moments of the atoms on different sublattices are opposed, as in antiferromagnetism; however, in ferrimagnetic materials, the opposing moments are unequal and a spontaneous magnetization remains...
(it acts like a magnet), between 48 and 66 K it is antiferromagnetic (an intermediate state), and above 160 K (−110 °C) it is paramagnetic
Paramagnetism
Paramagnetism is a form of magnetism whereby the paramagnetic material is only attracted when in the presence of an externally applied magnetic field. In contrast with this, diamagnetic materials are repulsive when placed in a magnetic field...
(external magnetic fields can make it magnetic). It forms alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s with lanthanide
Lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...
metals but little is known about them.
The element has two crystalline form
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
s under 1 standard atmosphere of pressure: A double-hexagonal close-packed form dubbed alpha (α) and a face-centered cubic
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
form designated beta (β). The α form exists below 900 °C with a density of 15.10 g/cm3 and the β form exists above 900 °C with a density of 8.74 g/cm3. At 48 GPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
of pressure the β form changes into an orthorhombic crystal system
Orthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
due to de-localization of the atom's 5f electrons
Electron shell
An electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" , followed by the "2 shell" , then the "3 shell" , and so on further and further from the nucleus. The shell letters K,L,M,.....
, which frees them to bond.
The bulk modulus
Bulk modulus
The bulk modulus of a substance measures the substance's resistance to uniform compression. It is defined as the pressure increase needed to decrease the volume by a factor of 1/e...
of a material is a measure of its resistance to uniform pressure. Californium's bulk modulus is 50 ± 5 GPa, which is similar to trivalent lanthanide metals but smaller than more familiar metals, such as aluminium (70 GPa).
Chemical properties and compounds
| state | compound | formula | color |
|---|---|---|---|
| +2 | californium(II) bromide | CfBr2 | yellow |
| +2 | californium(II) iodide | CfI2 | dark violet |
| +3 | californium(III) oxide | Cf2O3 | yellow-green |
| +3 | californium(III) fluoride | CfF3 | bright green |
| +3 | californium(III) chloride | CfCl3 | emerald green |
| +3 | californium(III) iodide | CfI3 | lemon yellow |
| +4 | californium(IV) oxide | CfO2 | black brown |
| +4 | californium(IV) fluoride | CfF4 | green |
Californium exhibits valences
Valence (chemistry)
In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...
of 4, 3, or 2; indicating the number of chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
s one atom of this element can form. Its chemical properties are predicted to be similar to other primarily 3+ valence actinide elements and the element dysprosium
Dysprosium
Dysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime...
, which is the lanthanide above californium in the periodic table. The element slowly tarnishes in air at room temperature, with the rate increasing when moisture is added. Californium reacts when heated with hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, or chalcogen
Chalcogen
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
(oxygen family element); reactions with dry hydrogen and aqueous mineral acid
Mineral acid
A mineral acid is an acid derived from one or more inorganic compounds. A mineral acid is not organic and all mineral acids release hydrogen ions when dissolved in water.-Characteristics:...
s are rapid.
Californium is only water soluble
Aqueous solution
An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending aq to the relevant formula, such as NaCl. The word aqueous means pertaining to, related to, similar to, or dissolved in water...
as the californium(III) cation. Attempts to reduce or oxidize
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
the +3 ion in solution have failed. The element forms a water-soluble chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
, nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
, perchlorate
Perchlorate
Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a...
, and sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
and is precipitated as a fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
, oxalate
Oxalate
Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...
, or hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
.
Isotopes
Twenty radioisotopes of californium have been characterized, the most stable being californium-251 with a half-lifeHalf-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 898 years, californium-249 with a half-life of 351 years, californium-250 with a half-life of 13.08 years, and californium-252 with a half-life of 2.645 years. All the remaining isotopes have half-lives shorter than a year, and the majority of these have half-lives shorter than 20 minutes. The isotopes of californium range in mass number
Mass number
The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion...
from 237 to 256.
Californium-249 is formed from the beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
of berkelium-249, and most other californium isotopes are made by subjecting berkelium to intense neutron radiation in a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
. Although californium-251 has the longest half-life, its production yield is only 10% due to its tendency to collect neutrons (high neutron capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...
) and its tendency to interact with other particles (high neutron cross-section
Neutron cross-section
In nuclear and particle physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. In conjunction with the neutron flux, it enables the calculation of the reaction rate, for example to derive the thermal power...
).
Californium-252 is a very strong neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
emitter, which makes it extremely radioactive and harmful. Californium-252 undergoes alpha decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
(the loss of two proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s and two neutrons) 96.9% of the time to form curium
Curium
Curium is a synthetic chemical element with the symbol Cm and atomic number 96. This radioactive transuranic element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie. Curium was first intentionally produced and identified in summer 1944 by the group of...
-248 while the remaining 3.1% of decays are spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
. One microgram
Microgram
In the metric system, a microgram is a unit of mass equal to one millionth of a gram , or 1/1000 of a milligram. It is one of the smallest units of mass commonly used...
(µg) of californium-252 emits 2.3 million neutrons per second, an average of 3.7 neutrons per spontaneous fission. Most of the other isotopes of californium decay to isotopes of curium (atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
96) via alpha decay.
History
Californium was first synthesized at the University of California, BerkeleyUniversity of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
by the physics researchers Stanley G. Thompson
Stanley Gerald Thompson
Stanley Gerald Thompson was an American chemist. He discovered together with Glenn T. Seaborg several of the transuranium elements. He received a Guggenheim Fellowship in 1954.-External links:*...
, Kenneth Street, Jr.
Kenneth Street, Jr.
Kenneth Street, Jr. was an American chemist. He was part of the team that discovered elements 97 and 98 in 1949 and 1950....
, Albert Ghiorso
Albert Ghiorso
Albert Ghiorso was an American nuclear scientist and co-discoverer of a record 12 chemical elements on the periodic table. His research career spanned five decades, from the early 1940s to the late 1990s.-Early life:...
, and Glenn T. Seaborg
Glenn T. Seaborg
Glenn Theodore Seaborg was an American scientist who won the 1951 Nobel Prize in Chemistry for "discoveries in the chemistry of the transuranium elements", contributed to the discovery and isolation of ten elements, and developed the actinide concept, which led to the current arrangement of the...
on or about February 9, 1950. It was the sixth transuranium element
Transuranium element
In chemistry, transuranium elements are the chemical elements with atomic numbers greater than 92...
to be discovered; the team announced its discovery on March 17, 1950.
To produce californium, a microgram-sized target of curium-242 was bombarded with 35 MeV-alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
s in the 60 inches (1,524 mm) cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
at Berkeley, California
Berkeley, California
Berkeley is a city on the east shore of the San Francisco Bay in Northern California, United States. Its neighbors to the south are the cities of Oakland and Emeryville. To the north is the city of Albany and the unincorporated community of Kensington...
, which produced californium-245 plus one free neutron .
- + → +
Only about 5,000 atoms of californium were produced in this experiment, and these atoms had a half-life of 44 minutes.
The discoverers named the new element after California and the University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
. This was a break from the convention used for elements 95 to 97, which drew inspiration from how the elements directly above them in the periodic table were named. However, the element directly above element 98 in the periodic table, dysprosium
Dysprosium
Dysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime...
, has a name that simply means "hard to get at" so the researchers decided to set aside the informal naming convention. They added that "the best we can do is to point out [that] ... searchers a century ago found it difficult to get to California."
Weighable quantities of californium were first produced by the irradiation of plutonium targets at the Materials Testing Reactor at the Idaho National Laboratory
Idaho National Laboratory
Idaho National Laboratory is an complex located in the high desert of eastern Idaho, between the town of Arco to the west and the cities of Idaho Falls and Blackfoot to the east. It lies within Butte, Bingham, Bonneville and Jefferson counties...
; and these findings were reported in 1954. The high spontaneous fission rate of californium-252 was observed in these samples. The first experiment with californium in concentrated form occurred in 1958. Californium-249 to −252 were isolated that same year from a sample of plutonium-239
Plutonium-239
Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
that had been irradiated with neutrons in a nuclear reactor for five years. Two years later, in 1960, Burris Cunningham and James Wallman of the Lawrence Radiation Laboratory of the University of California created the first californium compounds—californium trichloride, californium oxychloride, and californium oxide—by treating californium with steam and hydrochloric acid.
The High Flux Isotope Reactor
High Flux Isotope Reactor
The High Flux Isotope Reactor is a nuclear research reactor located at Oak Ridge National Laboratory in Oak Ridge, Tennessee, United States...
(HFIR) at the Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...
(ORNL) in Oak Ridge, Tennessee
Oak Ridge, Tennessee
Oak Ridge is a city in Anderson and Roane counties in the eastern part of the U.S. state of Tennessee, about west of Knoxville. Oak Ridge's population was 27,387 at the 2000 census...
, started producing small batches of californium in the 1960s. By 1995, the HFIR nominally produced 500 milligrams of californium annually. Plutonium supplied by the United Kingdom to the United States under the 1958 US-UK Mutual Defence Agreement
1958 US-UK Mutual Defence Agreement
The 1958 US–UK Mutual Defence Agreement is a bilateral treaty between the United States and the United Kingdom on nuclear weapons cooperation.It was signed after the UK successfully tested its first hydrogen bomb during Operation Grapple. While the U.S...
was used for californium production.
The Atomic Energy Commission sold californium-252 to industrial and academic customers in the early 1970s for $10 per microgram and an average of 150 mg of californium-252 were shipped each year from 1970 to 1990. Californium metal was first prepared in 1974 by Haire and Baybarz who reduced californium(III) oxide with lanthanum metal to obtain microgram amounts of sub-micrometer thick films.
Occurrence
Fallout
Fallout
Fallout or nuclear fallout is the residual radiation hazard from a nuclear explosion.Fallout may also refer to:*Fallout , a 1997 post-apocalyptic computer role-playing game released by Interplay Entertainment...
from atmospheric nuclear testing
Nuclear testing
Nuclear weapons tests are experiments carried out to determine the effectiveness, yield and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have tested them...
prior to 1980 contributed a small amount of californium to the environment. Californium isotopes with mass number
Mass number
The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion...
s 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
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
legacy sites since it was not produced in large quantities.
Californium was once reported to have been found in supernova spectra, but this has been subsequently regarded as an incorrect identification.
Production
Californium is produced in nuclear reactorNuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s and particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
s. Californium-250 is made by bombarding berkelium-249 with neutrons, forming berkelium-250 via neutron capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...
(n,γ) which, in turn, quickly beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
s (β−) to californium-250 in the following reaction:
- (n,γ) → + β−
Bombardment of californium-250 with neutrons produces californium-251 and californium-252.
Prolonged irradiation of americium
Americium
Americium is a synthetic element that has the symbol Am and atomic number 95. This transuranic element of the actinide series is located in the periodic table below the lanthanide element europium, and thus by analogy was named after another continent, America.Americium was first produced in 1944...
, curium, and plutonium with neutrons produces milligram amounts of californium-252 and microgram amounts of californium-249. As of 2006, curium isotopes 244 to 248 are irradiated by neutrons in special reactors to produce primarily californium-252 with lesser amounts of isotopes 249 to 255.
Microgram quantities of californium-252 are available for commercial use through the U.S. Nuclear Regulatory Commission
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...
. Only two sites produce californium-252 - the Oak Ridge National Laboratory in the United States, and the Research Institute of Atomic Reactors
Research Institute of Atomic Reactors
The Research Institute of Atomic Reactors is an institute for nuclear reactor research in Dimitrovgrad in Ulyanovsk Oblast, Russia. The institute houses eight nuclear research reactors: SM, Arbus , MIR.M1, RBT-6, RBT-10 / 1, RBT-10 / 2, BOR-60 and VK-50.-External links:* *...
in Dimitrovgrad, Russia
Dimitrovgrad, Russia
Dimitrovgrad is a city in Ulyanovsk Oblast, Russia, located on the Bolshoy Cheremshan River. Population: -History:It was founded in the beginning of the 18th century as a village for workers of the local distillery, which was closed in 1848. As of 1897, its population was 8,500, and in 1919...
. As of 2003, the two sites produce 0.25 grams and 0.025 grams of californium-252 per year, respectively.
Three californium isotopes with significant half-lives are produced, requiring a total of 15 neutron captures by uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
without nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
or alpha decay occurring during the process. Californium-253 is at the end of a production chain that starts with uranium-238, includes several isotopes of plutonium
Isotopes of plutonium
Plutonium is an artificial element, except for trace quantities of primordial 244Pu, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being 238Pu in 1940....
, americium
Isotopes of americium
Americium is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 241Am in 1944....
, curium
Isotopes of curium
Curium is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope synthesized was 242Cm in 1944....
, berkelium
Isotopes of berkelium
Berkelium is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 243Bk in 1949. There are 20 known radioisotopes, from 235Bk to 254Bk, and 6 nuclear isomers...
, and the californium isotopes 249 to 253 (see diagram).
Applications
Californium-252 has a number of specialized applications as a strong neutron emitter, and each microgram of fresh californium produces 139 million neutrons per minute. This property makes californium useful as a neutron startup source for some nuclear reactors and as a portable (non-reactor based) neutron source for neutron activation analysisNeutron activation analysis
In chemistry, neutron activation analysis is a nuclear process used for determining the concentrations of elements in a vast amount of materials. NAA allows discrete sampling of elements as it disregards the chemical form of a sample, and focuses solely on its nucleus. The method is based on...
to detect trace amounts of elements in samples. Neutrons from californium are employed as a treatment of certain cervical
Cervical cancer
Cervical cancer is malignant neoplasm of the cervix uteri or cervical area. One of the most common symptoms is abnormal vaginal bleeding, but in some cases there may be no obvious symptoms until the cancer is in its advanced stages...
and brain cancers where other radiation therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
is ineffective. It has been used in educational applications since 1969 when the Georgia Institute of Technology
Georgia Institute of Technology
The Georgia Institute of Technology is a public research university in Atlanta, Georgia, in the United States...
received a loan of 119 µg of californium-252 from the Savannah River Plant. It is also used with online elemental coal analyzer
Coal analyzer
Coal analyzers are used by coal producers, coal preparation plants and coal-fired power plants to determine coal quality in real time. Coal quality parameters of greatest interest include ash, moisture, sulfur, and energy value...
s and bulk material analyzer
Bulk material analyzer
The term bulk material analyzer is the generic noun for that device which fits around a conveyor belt and conducts real-time elemental analysis of the material on the belt. Other names often found for such a device include belt analyzer, crossbelt analyzer and elemental analyzer...
s in the coal and cement industries.
Neutron penetration into materials makes californium useful in detection instruments such as fuel rod scanners; neutron radiography
Neutron Radiography
Neutron Radiography is the process by which film is exposed by first passing neutrons through an object to produce a visible image of the materials that make up the object. Primarily used in scientific investigations.- Brief History of Neutron Imaging :...
of aircraft and weapons components to detect corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
, bad welds, cracks and trapped moisture; and in portable metal detectors. Neutron moisture gauge
Neutron moisture gauge
A neutron moisture meter is a moisture meter utilizing neutron scattering. The meters are most frequently used to measure the water content in soil or rock. The technique is non-destructive, and is sensitive to moisture in the bulk of the target material, not just at the surface.Water, due to its...
s use californium-252 to find water and petroleum layers in oil wells, as a portable neutron source
Neutron source
A Neutron source is a device that emits neutrons. There is a wide variety of different sources, ranging from hand-held radioactive sources to neutron research facilities operating research reactors and spallation sources...
for gold and silver prospecting for on-the-spot analysis, and to detect ground water movement. The major uses of californium-252 in 1982 were, in order of use, reactor start-up (48.3%), fuel rod scanning (25.3%), and activation analysis (19.4%). By 1994 most californium-252 was used in neutron radiography (77.4%), with fuel rod scanning (12.1%) and reactor start-up (6.9%) as important but distant secondary uses.
Californium-251 has a very small critical mass (about 5 kg), 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 ununoctium
Ununoctium
Ununoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is...
(element 118) had been identified at the Joint Institute for Nuclear Research
Joint Institute for Nuclear Research
The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow Oblast , Russia, is an international research centre for nuclear sciences, with 5500 staff members, 1200 researchers including 1000 Ph.D.s from eighteen member states The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow...
in Dubna, Russia, as the product of bombardment of californium-249 with calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
-48, making it the heaviest element ever synthesized. The target for this experiment contained about 10 mg of californium-249 deposited on a titanium foil of 32 cm2 area. Californium has also been used to produce other transuranium elements; for example, element 103 (later named lawrencium
Lawrencium
Lawrencium is a radioactive synthetic chemical element with the symbol Lr and atomic number 103. In the periodic table of the elements, it is a period 7 d-block element and the last element of actinide series...
) was first synthesized in 1961 by bombarding californium with boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
nuclei.
Precautions
Californium that bioaccumulates in skeletal tissue releases radiation that disrupts the body's ability to form red blood cellRed blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s. 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
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
emission. Ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
emitted by californium on bone and in the liver can cause cancer.