Californium is a
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
Cf and
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
98. The element was first synthesized in 1950 at
Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory (LBNL), commonly referred to as the Berkeley Lab, is a United States Department of Energy National Labs, United States national laboratory that is owned by, and conducts scientific research on behalf of, t ...
(then the University of California Radiation Laboratory), by bombarding
curium
Curium is a transuranic, radioactive chemical element with the symbol Cm and atomic number 96. This actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inte ...
with
alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produce ...
s (
helium-4
Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consis ...
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s). It is an
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 first element in the series, actinium. The inform ...
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
Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
(after
einsteinium). The element was named after the university and the
U.S. state of
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
.
Two
crystalline forms exist for californium 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 Few compounds of californium have been made and studied. The only californium ion that is stable in aqueous solutions is the californium(III) cation. The other two oxidation states are IV (strong oxidizing agents) and II (strong reducing agents). ...
are dominated by the +3
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
. The most stable of californium's twenty known
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s is californium-251, with a
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
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
Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research and ...
in the United States and
Research Institute of Atomic Reactors
The Research Institute of Atomic Reactors (; RIAR) is an institute for nuclear reactor research in Dimitrovgrad in Ulyanovsk Oblast, Russia. The institute houses eight nuclear research reactors: SM, Arbus (ACT-1), MIR.M1, RBT-6, RBT-10 / 1, RBT ...
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
Californium (98Cf) is an artificial element, and thus a standard atomic weight 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 rangin ...
to emit
neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
s. For example, californium can be used to help start up
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
s, and it is employed as a source of neutrons when studying materials using
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 o ...
and
neutron spectroscopy Neutron scattering is a spectroscopic method of measuring the 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 ...
. Californium 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 cell
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
s by
bioaccumulating in skeletal tissue.
Characteristics
Physical properties
Californium is a silvery-white
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 first element in the series, actinium. The inform ...
metal with a
melting point
The melting point (or, rarely, liquefaction point) of a substance 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 ...
of and an estimated
boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envir ...
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
Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...
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
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
s with
lanthanide
The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttr ...
metals but little is known about the resulting materials.
The element has two
crystalline forms at
standard atmospheric pressure: a double-
hexagonal close-packed
In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occu ...
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/cm
3 and the β form exists above 600–800 °C with a density of 8.74 g/cm
3. At 48
GPa
Grading in education is the process of applying standardized measurements for varying levels of achievements in a course. Grades can be assigned as letters (usually A through F), as a range (for example, 1 to 6), as a percentage, or as a numbe ...
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
The bulk modulus (K or B) of a substance is a measure of how resistant to compression the substance is. It is defined as the ratio of the infinitesimal pressure increase to the resulting ''relative'' decrease of the volume.
Other moduli describe ...
of a material is a measure of its resistance to uniform pressure. Californium's bulk modulus is , which is similar to trivalent lanthanide metals but smaller than more familiar metals, such as aluminium (70 GPa).
Chemical properties and compounds
Californium exhibits oxidation states of 4, 3, or 2. It typically forms eight or nine bonds to surrounding atoms or ions. Its chemical properties are predicted to be similar to other primarily 3+ valence actinide elements and the element
dysprosium
Dysprosium is the chemical element with the symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it ...
, which is the lanthanide above californium in the periodic table. Compounds in the +4 oxidation state are strong
oxidizing agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ). In ot ...
s and those in the +2 state are strong
reducing agent
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are commonly reducing agents include the Earth meta ...
s.
The element slowly tarnishes in air at room temperature, with the rate increasing when moisture is added. Californium reacts when heated with
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
,
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, or a
chalcogen (oxygen family element); reactions with dry hydrogen and aqueous
mineral acids are rapid.
Californium is only
water-soluble
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solub ...
as the californium(III)
cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
. Attempts to
reduce or oxidize the +3 ion in solution have failed. The element forms a water-soluble
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
,
nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
,
perchlorate
A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...
, and
sulfate and is precipitated as a
fluoride
Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typ ...
,
oxalate, or
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
. Californium is the heaviest actinide to exhibit covalent properties, as is observed in the californium borate.
Isotopes
Twenty
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s of californium are known (
mass number ranging from 237 to 256
); the most stable are
251Cf with
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
898 years,
249Cf with half-life 351 years,
250Cf with half-life 13.08 years, and
252Cf with half-life 2.645 years.
All other isotopes have half-life shorter than a year, and most of these have half-life less than 20 minutes.
249Cf is formed from
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
of berkelium-249, and most other californium isotopes are made by subjecting berkelium to intense neutron radiation in a
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
. Though 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 is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...
) and its tendency to interact with other particles (high
neutron cross section).
Californium-252 is a very strong
neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
emitter, which makes it extremely
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
and harmful.
252Cf, 96.9% of the time,
alpha decay
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...
s to
curium
Curium is a transuranic, radioactive chemical element with the symbol Cm and atomic number 96. This actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inte ...
-248; the other 3.1% of decays are
spontaneous fission
Spontaneous fission (SF) is a form of radioactive decay that is found only in very heavy chemical elements. The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 56 (e.g., iron-56); spontaneous breakdo ...
.
One
microgram (μg) of
252Cf emits 2.3 million neutrons per second, an average of 3.7 neutrons per spontaneous fission.
Most other isotopes of californium, alpha decay to curium (
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
96).
History
Californium was
first made at
University of California
The University of California (UC) is a public land-grant research university system in the U.S. state of California. The system is composed of the campuses at Berkeley, Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Francisco, ...
Radiation Laboratory
The Radiation Laboratory, commonly called the Rad Lab, was a microwave and radar research laboratory located at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts. It was first created in October 1940 and operated until 31 ...
,
Berkeley
Berkeley most often refers to:
*Berkeley, California, a city in the United States
**University of California, Berkeley, a public university in Berkeley, California
* George Berkeley (1685–1753), Anglo-Irish philosopher
Berkeley may also refer ...
, by physics researchers
Stanley Gerald Thompson
Stanley Gerald Thompson (1912–1976) was an American chemist. He discovered together with Glenn T. Seaborg several of the transuranium elements. One of the elements is Californium, which he and several others made. He received Guggenheim Fellow ...
,
Kenneth Street Jr.,
Albert Ghiorso, and
Glenn T. Seaborg
Glenn Theodore Seaborg (; April 19, 1912February 25, 1999) was an American chemist whose involvement in the synthesis, discovery and investigation of ten transuranium elements earned him a share of the 1951 Nobel Prize in Chemistry. His work in ...
, 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-size target of curium-242 () was bombarded with 35 MeV
alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produce ...
s () in the
cyclotron at Berkeley, which produced californium-245 () plus one
free neutron ().
: + → +
To identify and separate out the element,
ion exchange and adsorsion methods were undertaken.
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 the university and the state. 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 #98 in the periodic table,
dysprosium
Dysprosium is the chemical element with the symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it ...
, has a name that 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
hat... searchers a century ago found it difficult to get to California".
Weighable amounts of californium were first produced by the irradiation of plutonium targets at
Materials Testing Reactor at
National Reactor Testing Station
Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Energy Alliance. While the laboratory does other research, historically it has been involved with nu ...
,
eastern Idaho; 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. The isotopes
249Cf to
252Cf 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 Lawrence Radiation Laboratory of the University of California created the first californium compounds—californium trichloride,
californium(III) oxychloride, and californium oxide—by treating californium with steam and hydrochloric acid.
The
High Flux Isotope Reactor
The High Flux Isotope Reactor (HFIR) is a nuclear research reactor at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, United States. Operating at 85 MW, HFIR is one of the highest flux reactor-based sources of neutrons for condense ...
(HFIR) at
Oak Ridge National Laboratory
Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research and ...
(ORNL) in
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 downtown Knoxville. Oak Ridge's population was 31,402 at the 2020 census. It is part of the Knoxville Metropolitan Area. Oak ...
, started producing small batches of californium in the 1960s. By 1995, HFIR nominally produced of californium annually. Plutonium supplied by the United Kingdom to the United States under the
1958 US–UK Mutual Defence Agreement
Events
January
* January 1 – The European Economic Community (EEC) comes into being.
* January 3 – The West Indies Federation is formed.
* January 4
** Edmund Hillary's Commonwealth Trans-Antarctic Expedition completes the third ...
was used for making californium.
The
Atomic Energy Commission sold
252Cf to industrial and academic customers in the early 1970s for $10 per microgram,
and an average of of
252Cf 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
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 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
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United Stat ...
legacy sites since it was not produced in large quantities.
Californium was once believed to be produced in
supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
s, 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
Naturally occurring nickel (28Ni) is composed of five stable isotopes; , , , and , with being the most abundant (68.077% natural abundance). 26 radioisotopes have been characterised with the most stable being with a half-life of 76,000 years, ...
.
The
transuranium elements from
americium
Americium is a synthetic radioactive chemical element with the symbol Am and atomic number 95. It is a transuranic member of the actinide series, in the periodic table located under the lanthanide element europium, and thus by analogy was na ...
to
fermium
Fermium is a synthetic element with the symbol Fm and atomic number 100. It is an actinide and the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic qua ...
, including californium, occurred naturally in the
natural nuclear fission reactor
A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions occur. The conditions under which a natural nuclear reactor could exist had been predicted in 1956 by Japanese American chemist Paul Kuroda. Th ...
at
Oklo
Oklo is a region near the town of Franceville, in the Haut-Ogooué province of the Central African country of Gabon. Several natural nuclear fission reactors were discovered in the uranium mines in the region in 1972.
History
Gabon was a French ...
, but no longer do so.
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...
s of californium, along with those of several other non-primordial elements, were detected in
Przybylski's Star in 2008.
Production
Californium is produced in
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
s and
particle accelerators. Californium-250 is made by bombarding berkelium-249 () with neutrons, forming berkelium-250 () via
neutron capture
Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...
(n,γ) which, in turn, quickly
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
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 is a synthetic radioactive chemical element with the symbol Am and atomic number 95. It is a transuranic member of the actinide series, in the periodic table located under the lanthanide element europium, and thus by analogy was na ...
, 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
The Nuclear Regulatory Commission (NRC) is an independent agency of the United States government tasked with protecting public health and safety related to nuclear energy. Established by the Energy Reorganization Act of 1974, the NRC began operat ...
. Only two sites produce californium-252: the Oak Ridge National Laboratory in the United States, and the
Research Institute of Atomic Reactors
The Research Institute of Atomic Reactors (; RIAR) is an institute for nuclear reactor research in Dimitrovgrad in Ulyanovsk Oblast, Russia. The institute houses eight nuclear research reactors: SM, Arbus (ACT-1), MIR.M1, RBT-6, RBT-10 / 1, RBT ...
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
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it ...
without
nuclear fission
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radio ...
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
Americium is a synthetic radioactive chemical element with the symbol Am and atomic number 95. It is a transuranic member of the actinide series, in the periodic table located under the lanthanide element europium, and thus by analogy was na ...
,
curium
Curium is a transuranic, radioactive chemical element with the symbol Cm and atomic number 96. This actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inte ...
,
berkelium
Berkelium is a transuranic radioactive chemical element with the symbol Bk and atomic number 97. It is a member of the actinide and transuranium element series. It is named after the city of Berkeley, California, the location of the Lawrence Berke ...
, and the californium isotopes 249 to 253 (see diagram).
Applications
Californium-252 has a number of specialized uses as a strong neutron emitter; it produces 139 million neutrons per microgram per minute.
This property makes it useful as a
startup neutron source
Startup neutron source is a neutron source used for stable and reliable initiation of nuclear chain reaction in nuclear reactors, when they are loaded with fresh nuclear fuel, whose neutron flux from spontaneous fission is insufficient for a reliab ...
for some nuclear reactors and as a portable (non-reactor based) neutron source for
neutron activation analysis
Neutron activation analysis (NAA) is the nuclear process used for determining the concentrations of elements in many materials. NAA allows discrete sampling of elements as it disregards the chemical form of a sample, and focuses solely on atomic ...
to detect trace amounts of elements in samples.
Neutrons from californium are used as a treatment of certain
cervical
In anatomy, cervical is an adjective that has two meanings:
# of or pertaining to any neck.
# of or pertaining to the female cervix: i.e., the ''neck'' of the uterus.
*Commonly used medical phrases involving the neck are
**cervical collar
**cervic ...
and
brain cancers
A brain tumor occurs when abnormal cells form within the brain. There are two main types of tumors: malignant tumors and benign (non-cancerous) tumors. These can be further classified as primary tumors, which start within the brain, and secondar ...
where other
radiation therapy
Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radia ...
is ineffective. It has been used in educational applications since 1969 when
Georgia Institute of Technology
The Georgia Institute of Technology, commonly referred to as Georgia Tech or, in the state of Georgia, as Tech or The Institute, is a public research university and institute of technology in Atlanta, Georgia. Established in 1885, it is part of ...
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
Neutron imaging is the process of making an image with neutrons. The resulting image is based on the neutron attenuation properties of the imaged object. The resulting images have much in common with industrial X-ray images, but since the image i ...
of aircraft and weapons components to detect
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
, bad welds, cracks and trapped moisture; and in portable metal detectors.
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 m ...
s 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
In nuclear engineering, a critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fissi ...
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
The Joint Institute for Nuclear Research (JINR, russian: Объединённый институт ядерных исследований, ОИЯИ), in Dubna, Moscow Oblast (110 km north of Moscow), Russia, is an international research cen ...
in
Dubna
Dubna ( rus, Дубна́, p=dʊbˈna) is a town in Moscow Oblast, Russia. It has a status of ''naukograd'' (i.e. town of science), being home to the Joint Institute for Nuclear Research, an international nuclear physics research center and one o ...
,
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
, 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 cm
2 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
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
nuclei.
Precautions
Californium that
bioaccumulates in skeletal tissue releases radiation that disrupts the body's ability to form
red blood cell
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
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
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
emission.
Ionizing radiation
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
emitted by californium on bone and in the liver can cause cancer.
Notes
References
Bibliography
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External links
Californiumat ''
The Periodic Table of Videos'' (University of Nottingham)
NuclearWeaponArchive.org – CaliforniumHazardous Substances Databank – Californium, Radioactive
{{Commons category-inline
Chemical elements
Chemical elements with double hexagonal close-packed structure
Actinides
Synthetic elements
Neutron sources