Californium is a radioactive chemical element with symbol Cf and atomic number 98. The element was first synthesized in 1950 at the Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory), by bombarding curium with alpha particles (helium-4 ions). It is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all the elements that have been produced in amounts large enough to see with the unaided eye (after einsteinium). The element was named after the university and the state of California.

Two crystalline forms exist for californium under normal pressure: one above and one below 900 °C (1,650 °F). A third form exists at high pressure. Californium slowly tarnishes in air at room temperature. Compounds of californium are dominated by the +3 oxidation state. The most stable of californium's twenty known isotopes is californium-251, which has a half-life of 898 years. This short half-life means the element is not found in significant quantities in the Earth's crust.[a] Californium-252, with a half-life of about 2.645 years, is the most common isotope used and is produced at the Oak Ridge National Laboratory in the United States and the Research Institute of Atomic Reactors in Russia.

Californium is one of the few transuranium elements that have practical applications. Most of these applications exploit the property of certain isotopes of californium to emit neutrons. For example, californium can be used to help start up nuclear reactors, and it is employed as a source of neutrons when studying materials using neutron diffraction and neutron spectroscopy. 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 cells by bioaccumulating in skeletal tissue.

Californium,  98Cf
A very small disc of silvery metal, magnified to show its metallic texture
Pronunciation/ˌkælɪˈfɔːrniəm/ (KAL-ə-FOR-nee-əm)
Mass number251 (most stable isotope)
Californium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)98
Groupgroup n/a
Periodperiod 7
Element category  actinide
Electron configuration[Rn] 5f10 7s2[1]
Electrons per shell
2, 8, 18, 32, 28, 8, 2
Physical properties
Phase at STPsolid
Melting point1173 K ​(900 °C, ​1652 °F)[2]
Boiling point1743 K ​(1470 °C, ​2678 °F) (estimation)[3]
Density (near r.t.)15.1 g/cm3[2]
Atomic properties
Oxidation states+2, +3, +4, +5[4][5]
ElectronegativityPauling scale: 1.3[6]
Ionization energies
  • 1st: 608 kJ/mol[7]
Color lines in a spectral range
Spectral lines of californium
Other properties
Natural occurrencesynthetic
Crystal structuredouble hexagonal close-packed (dhcp)
Double hexagonal close packed crystal structure for californium
Mohs hardness3–4[8]
CAS Number7440-71-3[2]
Namingafter California, where it was discovered
DiscoveryLawrence Berkeley National Laboratory (1950)
Main isotopes of californium[9][10]
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
248Cf syn 333.5 d α (100%) 244Cm
SF (2.9×10−3%)
249Cf syn 351 y α (100%) 245Cm
SF (5.0×10−7%)
250Cf syn 13.08 y α (99.92%) 246Cm
SF (0.08%)
251Cf syn 898 y α 247Cm
252Cf syn 2.645 y α (96.91%) 248Cm
SF (3.09%)
253Cf syn 17.81 d β (99.69%) 253Es
α (0.31%) 249Cm
254Cf syn 60.5 d SF (99.69%)
α (0.31%) 250Cm


Physical properties

Californium is a silvery white actinide metal[12] with a melting point of 900 ± 30 °C (1,650 ± 50 °F) and an estimated boiling point of 1,745 K (1,470 °C; 2,680 °F).[13] The pure metal is malleable and is easily cut with a razor blade. Californium metal starts to vaporize above 300 °C (570 °F) when exposed to a vacuum.[14] Below 51 K (−222 °C; −368 °F) 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 (−113 °C; −172 °F) it is paramagnetic (external magnetic fields can make it magnetic).[15] It forms alloys with lanthanide metals but little is known about them.[14]

The element has two crystalline forms under 1 standard atmosphere of pressure: a double-hexagonal close-packed form dubbed alpha (α) and a face-centered cubic form designated beta (β).[b] The α form exists below 600–800 °C with a density of 15.10 g/cm3 and the β form exists above 600–800 °C with a density of 8.74 g/cm3.[17] At 48 GPa of pressure the β form changes into an orthorhombic crystal system due to delocalization of the atom's 5f electrons, which frees them to bond.[18][c]

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).[18]

Chemical properties and compounds

Representative californium compounds[12][d]
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) bromide CfBr3 yellowish green
+3 californium(III) iodide CfI3 lemon yellow
+3 californium(III) borate Cf[B6O8(OH)5] pale green
+4 californium(IV) oxide CfO2 black brown
+4 californium(IV) fluoride CfF4 green

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[20] and the element dysprosium, which is the lanthanide above californium in the periodic table.[21] The element slowly tarnishes in air at room temperature, with the rate increasing when moisture is added.[17] Californium reacts when heated with hydrogen, nitrogen, or a chalcogen (oxygen family element); reactions with dry hydrogen and aqueous mineral acids are rapid.[17]

Californium is only water-soluble as the californium(III) cation. Attempts to reduce or oxidize the +3 ion in solution have failed.[21] The element forms a water-soluble chloride, nitrate, perchlorate, and sulfate and is precipitated as a fluoride, oxalate, or hydroxide.[20] Californium is the heaviest actinide to exhibit covalent properties, as is observed in the californium borate.[22]


Twenty radioisotopes of californium have been characterized, the most stable being californium-251 with a half-life 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.[10] All the remaining isotopes have half-lives shorter than a year, and the majority of these have half-lives shorter than 20 minutes.[10] The isotopes of californium range in mass number from 237 to 256.[10]

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.[21] 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).[23]

Californium-252 is a very strong neutron emitter, which makes it extremely radioactive and harmful.[24][25][26] Californium-252 undergoes alpha decay 96.9% of the time to form curium-248 while the remaining 3.1% of decays are spontaneous fission.[10] One microgram (µg) of californium-252 emits 2.3 million neutrons per second, an average of 3.7 neutrons per spontaneous fission.[27] Most of the other isotopes of californium decay to isotopes of curium (atomic number 96) via alpha decay.[10]


Berkeley 60-inch cyclotron
The 60-inch-diameter (1.52 m) cyclotron used to first synthesize californium

Californium was first synthesized at the University of California Radiation Laboratory in Berkeley, by the physics researchers Stanley G. Thompson, Kenneth Street, Jr., Albert Ghiorso, and Glenn T. Seaborg on or about February 9, 1950.[28] It was the sixth transuranium element to be discovered; the team announced its discovery on March 17, 1950.[29][30][31]

To produce californium, a microgram-sized target of curium-242 (242
) was bombarded with 35 MeV-alpha particles (4
) in the 60-inch-diameter (1.52 m) cyclotron at Berkeley, which produced californium-245 (245
) plus one free neutron (

+ 4
+ 1


Only about 5,000 atoms of californium were produced in this experiment,[32] and these atoms had a half-life of 44 minutes.[28]

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.[33][e] 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.[35] They added that "the best we can do is to point out [that] ... searchers a century ago found it difficult to get to California."[34]

Weighable quantities of californium were first produced by the irradiation of plutonium targets at the Materials Testing Reactor at the National Reactor Testing Station in eastern Idaho; and these findings were reported in 1954.[36] The high spontaneous fission rate of californium-252 was observed in these samples. The first experiment with californium in concentrated form occurred in 1958.[28] The isotopes californium-249 to californium-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.[12] 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.[37]

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.[38] By 1995, the HFIR nominally produced 500 milligrams (0.018 oz) of californium annually.[39] Plutonium supplied by the United Kingdom to the United States under the 1958 US-UK Mutual Defence Agreement was used for californium production.[40]

The Atomic Energy Commission sold californium-252 to industrial and academic customers in the early 1970s for $10 per microgram[27] and an average of 150 mg (0.0053 oz) of californium-252 were shipped each year from 1970 to 1990.[41][f] 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.[42][43][g]


Traces of californium can be found near facilities that use the element in mineral prospecting and in medical treatments.[45] 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.[46]

Fallout from atmospheric nuclear testing prior to 1980 contributed a small amount of californium to the environment.[46] 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.[47] Californium is not a major radionuclide at United States Department of Energy legacy sites since it was not produced in large quantities.[46]

Californium was once believed to be produced in supernovas, as their decay matches the 60-day half-life of 254Cf.[48] However, subsequent studies failed to demonstrate any californium spectra,[49] and supernova light curves are now thought to follow the decay of nickel-56.[50]

The transuranic elements from americium to fermium, including californium, occurred naturally in the natural nuclear fission reactor at Oklo, but no longer do so.[51]


Californium is produced in nuclear reactors and particle accelerators.[52] Californium-250 is made by bombarding berkelium-249 (249
) with neutrons, forming berkelium-250 (250
) via neutron capture (n,γ) which, in turn, quickly beta decays) to californium-250 (250
) in the following reaction:[53]

+ β

Bombardment of californium-250 with neutrons produces californium-251 and californium-252.[53]

Prolonged irradiation of americium, curium, and plutonium with neutrons produces milligram amounts of californium-252 and microgram amounts of californium-249.[54] 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.[55]

Microgram quantities of californium-252 are available for commercial use through the U.S. Nuclear Regulatory Commission.[52] 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.[56]

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.[56] 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).

Cf 252 Produktion
Scheme of the production of californium-252 from uranium-238 by neutron irradiation


Fifty-ton shipping cask built at Oak Ridge National Laboratory which can transport up to 1 gram of 252Cf.[57] Large and heavily shielded transport containers are needed to prevent the release of highly radioactive material in case of normal and hypothetical accidents.[58]

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.[27] This property makes californium useful as a neutron startup source for some nuclear reactors[17] and as a portable (non-reactor based) neutron source for neutron activation analysis to detect trace amounts of elements in samples.[59][h] Neutrons from californium are employed as a treatment of certain cervical and brain cancers where other radiation therapy is ineffective.[17] 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.[61] 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;[17] neutron radiography of aircraft and weapons components to detect corrosion, bad welds, cracks and trapped moisture;[62] and in portable metal detectors.[63] Neutron moisture gauges 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,[21] and to detect ground water movement.[64] 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%).[65] 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.[65]

Californium-251 has a very small calculated critical mass of about 5 kg (11 lb),[66] 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.[i]

In October 2006, researchers announced that three atoms of oganesson (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.[68][69][70] 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.[71]


Californium that bioaccumulates in skeletal tissue releases radiation that disrupts the body's ability to form red blood cells.[72] The element plays no natural biological role in any organism due to its intense radioactivity and low concentration in the environment.[45]

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.[46]

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.[46]


  1. ^ The Earth formed 4.5 billion years ago, and the extent of natural neutron emission within it that could produce californium from more stable elements is extremely limited.
  2. ^ A double hexagonal close-packed (dhcp) unit cell consists of two hexagonal close-packed structures that share a common hexagonal plane, giving dhcp an ABACABAC sequence.[16]
  3. ^ The three lower-mass transplutonium elements—americium, curium, and berkelium—require much less pressure to delocalize their 5f electrons.[18]
  4. ^ Other +3 oxidation states include the sulfide and metallocene.[19] Compounds in the +4 oxidation state are strong oxidizing agents and those in the +2 state are strong reducing agents.[12]
  5. ^ Europium, in the sixth period directly above element 95, was named for the continent it was discovered on, so element 95 was named americium. Element 96 was named curium for Marie Curie and Pierre Curie as an analog to the naming of gadolinium, which was named for the scientist and engineer Johan Gadolin. Terbium was named for the village it was discovered in, so element 97 was named berkelium.[34]
  6. ^ The Nuclear Regulatory Commission replaced the Atomic Energy Commission when the Energy Reorganization Act of 1974 was implemented. The price of californium-252 was increased by the NRC several times and was $60 per microgram by 1999; this price does not include the cost of encapsulation and transportation.[27]
  7. ^ In 1975, another paper stated that the californium metal prepared the year before was the hexagonal compound Cf2O2S and face-centered cubic compound CfS.[44] The 1974 work was confirmed in 1976 and work on californium metal continued.[42]
  8. ^ By 1990, californium-252 had replaced plutonium-beryllium neutron sources due to its smaller size and lower heat and gas generation.[60]
  9. ^ An article entitled "Facts and Fallacies of World War III" in the July 1961 edition of Popular Science magazine read "A californium atomic bomb need be no bigger than a pistol bullet. You could build a hand-held six-shooter to fire bullets that would explode on contact with the force of 10 tons of TNT."[67]


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External links

251 (number)

251 (two hundred [and] fifty-one) is the natural number between 250 and 252. It is also a prime number.


The actinide or actinoid (IUPAC nomenclature) series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.Strictly speaking, both actinium and lawrencium have been labeled as group 3 elements, but both elements are often included in any general discussion of the chemistry of the actinide elements. Actinium is the more often omitted of the two, because its placement as a group 3 element is somewhat more common in texts and for semantic reasons: since "actinide" means "like actinium", it has been argued that actinium cannot logically be an actinide, even though IUPAC acknowledges its inclusion based on common usage.The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, with the exception being either actinium or lawrencium. The series mostly corresponds to the filling of the 5f electron shell, although actinium and thorium lack any f-electrons, and curium and lawrencium have the same number as the preceding element. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. They all have very large atomic and ionic radii and exhibit an unusually large range of physical properties. While actinium and the late actinides (from americium onwards) behave similarly to the lanthanides, the elements thorium, protactinium, and uranium are much more similar to transition metals in their chemistry, with neptunium and plutonium occupying an intermediate position.

All actinides are radioactive and release energy upon radioactive decay; naturally occurring uranium and thorium, and synthetically produced plutonium are the most abundant actinides on Earth. These are used in nuclear reactors and nuclear weapons. Uranium and thorium also have diverse current or historical uses, and americium is used in the ionization chambers of most modern smoke detectors.

Of the actinides, primordial thorium and uranium occur naturally in substantial quantities. The radioactive decay of uranium produces transient amounts of actinium and protactinium, and atoms of neptunium and plutonium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements. Nuclear weapons tests have released at least six actinides heavier than plutonium into the environment; analysis of debris from a 1952 hydrogen bomb explosion showed the presence of americium, curium, berkelium, californium, einsteinium and fermium.In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods).


Berkelium is a transuranic radioactive chemical element with 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 Berkeley National Laboratory (then the University of California Radiation Laboratory) where it was discovered in December 1949. Berkelium was the fifth transuranium element discovered after neptunium, plutonium, curium and americium.

The major isotope of berkelium, 249Bk, is synthesized in minute quantities in dedicated high-flux nuclear reactors, mainly at the Oak Ridge National Laboratory in Tennessee, USA, and at the Research Institute of Atomic Reactors in Dimitrovgrad, Russia. The production of the second-most important isotope 247Bk involves the irradiation of the rare isotope 244Cm with high-energy alpha particles.

Just over one gram of berkelium has been produced in the United States since 1967. There is no practical application of berkelium outside scientific research which is mostly directed at the synthesis of heavier transuranic elements and transactinides. A 22 milligram batch of berkelium-249 was prepared during a 250-day irradiation period and then purified for a further 90 days at Oak Ridge in 2009. This sample was used to synthesize the new element tennessine for the first time in 2009 at the Joint Institute for Nuclear Research, Russia, after it was bombarded with calcium-48 ions for 150 days. This was the culmination of the Russia–US collaboration on the synthesis of the heaviest elements on the periodic table.

Berkelium is a soft, silvery-white, radioactive metal. The berkelium-249 isotope emits low-energy electrons and thus is relatively safe to handle. It decays with a half-life of 330 days to californium-249, which is a strong emitter of ionizing alpha particles. This gradual transformation is an important consideration when studying the properties of elemental berkelium and its chemical compounds, since the formation of californium brings not only chemical contamination, but also free-radical effects and self-heating from the emitted alpha particles.

Californium(III) polyborate

Californium polyborate is a covalent compound with formula Cf[B6O8(OH)5]. In this compound the californium is in a +3 oxidation state.Californium polyborate is unusual in that californium is covalently bound to the borate. Californium was expected to resemble lanthanide elements in being highly ionic. The polyborate anion is polarisable and flexible. The 5f, 6d, 7s, and 7p orbitals of californium are all involved on the bonding. Most valence electrons are in the 5f orbital, and a significant fraction (​2⁄3) in the 6d orbital, and smaller fractions of one electron are in the 7s and 7p orbitals.

Californium (disambiguation)

Californium is a chemical element with symbol Cf and atomic number 98.

Californium may also refer to:

Californium (video game), a 2016 video game

"Californium", a song on the album Brownout by Headset

Californium (video game)

Californium is an exploration game co-developed by Darjeeling and Nova Productions, and released in February 2016 for Microsoft Windows and OS X. Californium was developed as a tribute to science-fiction author Philip K. Dick on the 30th anniversary of his death. The player controls Elvin Green, a struggling writer dealing with family matters, as he discovers the means to manipulate reality, and explores several surreal landscapes.

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). The element forms a water-soluble chloride, nitrate, perchlorate, and sulfate and is precipitated as a fluoride, oxalate or hydroxide. If problems of availability of the element could be overcome, then CfBr2 and CfI2 would likely be stable.The +3 oxidation state is represented by californium(III) oxide (yellow-green, Cf2O3), californium(III) fluoride (bright green, CfF3) and californium(III) iodide (lemon yellow, CfI3). Other +3 oxidation states include the sulfide and metallocene. Californium(IV) oxide (black brown, CfO2), californium(IV) fluoride (green, CfF4) represent the IV oxidation state. The II state is represented by californium(II) bromide (yellow, CfBr2) and californium(II) iodide (dark violet, CfI2).

Californium oxychloride

Californium oxychloride (CfOCl) is a radioactive compound first discovered in measurable quantities in 1960. It is composed of a single californium cation and one oxychloride anion. It was the first californium compound ever isolated.


Curium is a transuranic radioactive chemical element with symbol Cm and atomic number 96. This element of the actinide series was named after Marie and Pierre Curie – both were known for their research on radioactivity. Curium was first intentionally produced and identified in July 1944 by the group of Glenn T. Seaborg at the University of California, Berkeley. The discovery was kept secret and only released to the public in November 1947. Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains about 20 grams of curium.

Curium is a hard, dense, silvery metal with a relatively high melting point and boiling point for an actinide. Whereas it is paramagnetic at ambient conditions, it becomes antiferromagnetic upon cooling, and other magnetic transitions are also observed for many curium compounds. In compounds, curium usually exhibits valence +3 and sometimes +4, and the +3 valence is predominant in solutions. Curium readily oxidizes, and its oxides are a dominant form of this element. It forms strongly fluorescent complexes with various organic compounds, but there is no evidence of its incorporation into bacteria and archaea. When introduced into the human body, curium accumulates in the bones, lungs and liver, where it promotes cancer.

All known isotopes of curium are radioactive and have a small critical mass for a sustained nuclear chain reaction. They predominantly emit α-particles, and the heat released in this process can serve as a heat source in radioisotope thermoelectric generators, but this application is hindered by the scarcity and high cost of curium isotopes. Curium is used in production of heavier actinides and of the 238Pu radionuclide for power sources in artificial pacemakers. It served as the α-source in the alpha particle X-ray spectrometers installed on several space probes, including the Sojourner, Spirit, Opportunity and Curiosity Mars rovers and the Philae lander on comet 67P/Churyumov–Gerasimenko, to analyze the composition and structure of the surface.


Einsteinium is a synthetic element with symbol Es and atomic number 99. A member of the actinide series, it is the seventh transuranic element.

Einsteinium was discovered as a component of the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein. Its most common isotope einsteinium-253 (half-life 20.47 days) is produced artificially from decay of californium-253 in a few dedicated high-power nuclear reactors with a total yield on the order of one milligram per year. The reactor synthesis is followed by a complex process of separating einsteinium-253 from other actinides and products of their decay. Other isotopes are synthesized in various laboratories, but at much smaller amounts, by bombarding heavy actinide elements with light ions. Owing to the small amounts of produced einsteinium and the short half-life of its most easily produced isotope, there are currently almost no practical applications for it outside basic scientific research. In particular, einsteinium was used to synthesize, for the first time, 17 atoms of the new element mendelevium in 1955.

Einsteinium is a soft, silvery, paramagnetic metal. Its chemistry is typical of the late actinides, with a preponderance of the +3 oxidation state; the +2 oxidation state is also accessible, especially in solids. The high radioactivity of einsteinium-253 produces a visible glow and rapidly damages its crystalline metal lattice, with released heat of about 1000 watts per gram. Difficulty in studying its properties is due to einsteinium-253's decay to berkelium-249 and then californium-249 at a rate of about 3% per day. The isotope of einsteinium with the longest half-life, einsteinium-252 (half-life 471.7 days) would be more suitable for investigation of physical properties, but it has proven far more difficult to produce and is available only in minute quantities, and not in bulk. Einsteinium is the element with the highest atomic number which has been observed in macroscopic quantities in its pure form, and this was the common short-lived isotope einsteinium-253.Like all synthetic transuranic elements, isotopes of einsteinium are very radioactive and are considered highly dangerous to health on ingestion.


Fermium is a synthetic element with 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 quantities, although pure fermium metal has not yet been prepared. A total of 19 isotopes are known, with 257Fm being the longest-lived with a half-life of 100.5 days.

It was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Enrico Fermi, one of the pioneers of nuclear physics. Its chemistry is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the small amounts of produced fermium and all of its isotopes having relatively short half-lives, there are currently no uses for it outside basic scientific research.

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 ranging from 237Cf to 256Cf and one nuclear isomer, 249mCf. The longest-lived isotope is 251Cf with a half-life of 900 years.

Kenneth Street Jr.

Kenneth Street Jr. (1920 – 13 March 2006) was an American chemist. He was part of the team that discovered elements 97 and 98 (berkelium and californium) in 1949 and 1950.Street was born in 1920 in Berkeley, California. He obtained his degree in chemistry in 1943 from the University of California, Berkeley. He then served in World War II as a fighter pilot, with his awards including the Air Medal and the Distinguished Flying Cross. After the war, he returned to Berkeley, obtaining his PhD in nuclear chemistry in 1949, with a thesis titled 'Isotopes of americium and curium'.The work on berkelium and californium was carried out at the Lawrence Radiation Laboratory (now part of the Lawrence Berkeley National Laboratory) with Stanley G. Thompson, Glenn T. Seaborg and Albert Ghiorso. Street joined the faculty at Berkeley in 1949, and became Deputy Director of the Lawrence Radiation Laboratory, and later a professor of chemistry. His specialities and interests were in the areas of nuclear chemistry, geochemistry and geothermal energy.Street retired in 1986, and moved to Taylorsville, California in 1997 with his wife Jane (née Armitage). They had married in 1944 and had three children, two sons and a daughter. Street's interests included walking in the mountains, backpacking and sailing. Street died on 13 March 2006, in Paradise, California.

List of radioactive isotopes by half-life

This is a list of radioactive isotopes ordered by half-life from shortest to longest.

Major actinide

Major actinides is a term used in the nuclear power industry that refers to the plutonium and uranium present in used nuclear fuel, as opposed to the minor actinides neptunium, americium, curium, berkelium, and californium.

Minor actinide

The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium (element 93), americium (element 95), curium (element 96), berkelium (element 97), californium (element 98), einsteinium (element 99), and fermium (element 100). The most important isotopes in spent nuclear fuel are neptunium-237, americium-241, americium-243, curium-242 through -248, and californium-249 through -252.

Plutonium and the minor actinides will be responsible for the bulk of the radiotoxicity and heat generation of used nuclear fuel in the medium term (300 to 20,000 years in the future).The plutonium from a power reactor tends to have a greater amount of Pu-241 than the plutonium generated by the lower burnup operations designed to create weapons-grade plutonium. Because the reactor-grade plutonium contains so much Pu-241 the presence of americium-241 makes the plutonium less suitable for making a nuclear weapon. The ingrowth of americium in plutonium is one of the methods for identifying the origin of an unknown sample of plutonium and the time since it was last separated chemically from the americium.

Americium is commonly used in industry as both an alpha particle and as a low photon energy gamma radiation source. For instance it is used in many smoke detectors. Americium can be formed by neutron capture of Pu-239 and Pu-240 forming Pu-241 which then beta decays to Am-241. In general, as the energy of the neutrons increases, the ratio of the fission cross section to the neutron capture cross section changes in favour of fission. Hence if MOX is used in a thermal reactor such as a boiling water reactor (BWR) or pressurized water reactor (PWR) then more americium can be expected in the used fuel than that from a fast neutron reactor.Some of the minor actinides have been found in fallout from bomb tests. See Actinides in the environment for details.


Nobelium is a synthetic chemical element with symbol No and atomic number 102. It is named in honor of Alfred Nobel, the inventor of dynamite and benefactor of science. A radioactive metal, it is the tenth transuranic element and is the penultimate member of the actinide series. Like all elements with atomic number over 100, nobelium can only be produced in particle accelerators by bombarding lighter elements with charged particles. A total of twelve nobelium isotopes are known to exist; the most stable is 259No with a half-life of 58 minutes, but the shorter-lived 255No (half-life 3.1 minutes) is most commonly used in chemistry because it can be produced on a larger scale.

Chemistry experiments have confirmed that nobelium behaves as a heavier homolog to ytterbium in the periodic table. The chemical properties of nobelium are not completely known: they are mostly only known in aqueous solution. Before nobelium's discovery, it was predicted that it would show a stable +2 oxidation state as well as the +3 state characteristic of the other actinides: these predictions were later confirmed, as the +2 state is much more stable than the +3 state in aqueous solution and it is difficult to keep nobelium in the +3 state.

In the 1950s and 1960s, many claims of the discovery of nobelium were made from laboratories in Sweden, the Soviet Union, and the United States. Although the Swedish scientists soon retracted their claims, the priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that International Union of Pure and Applied Chemistry (IUPAC) credited the Soviet team with the discovery, but retained nobelium, the Swedish proposal, as the name of the element due to its long-standing use in the literature.


Tennessine is a synthetic chemical element with symbol Ts and atomic number 117. It is the second-heaviest known element and the penultimate element of the 7th period of the periodic table.

The discovery of tennessine was officially announced in Dubna, Russia, by a Russian–American collaboration in April 2010, which makes it the most recently discovered element as of 2019. One of its daughter isotopes was created directly in 2011, partially confirming the results of the experiment. The experiment itself was repeated successfully by the same collaboration in 2012 and by a joint German–American team in May 2014. In December 2015, the Joint Working Party of the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics, which evaluates claims of discovery of new elements, recognized the element and assigned the priority to the Russian–American team. In June 2016, the IUPAC published a declaration stating that the discoverers had suggested the name tennessine after Tennessee, United States. In November 2016, they officially adopted the name "tennessine".

Tennessine may be located in the "island of stability", a concept that explains why some superheavy elements are more stable compared to an overall trend of decreasing stability for elements beyond bismuth on the periodic table. The synthesized tennessine atoms have lasted tens and hundreds of milliseconds. In the periodic table, tennessine is expected to be a member of group 17, all other members of which are halogens. Some of its properties may significantly differ from those of the halogens due to relativistic effects. As a result, tennessine is expected to be a volatile metal that neither forms anions nor achieves high oxidation states. A few key properties, such as its melting and boiling points and its first ionization energy, are nevertheless expected to follow the periodic trends of the halogens.

Transuranium element

The transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. All of these elements are unstable and decay radioactively into other elements.

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