Californium (Cf)

Californium is a radioactive chemical element with the symbol Cf and atomic number 98 in the periodic table of elements. It’s a synthetically produced element, hence it cannot be found in Earth’s crust. Being a member of the actinides family of periodic table elements, californium’s molecular structure can be divalent or trivalent. 

Chemical and Physical Properties of Californium

Atomic number98
Atomic weight (mass)251.00 g.mol-1
Group (number)N/A (Actinides)
Physical stateSolid at room temperature
Electronegativity according to Pauling1.3
Density15.1 g.mol-1 at 20°C
Melting point900°C, 1652°F, 1173 K
Boiling pointUnknown
Van der Waals radiusN/A
Ionic radiusN/A
Most characteristic isotope249Cf, 252Cf
Electronic shell[Rn] 5f10 7s2
The energy of the first ionization608 kJ/mol
The energy of the second ionization1145.4
Discovery dateIn 1950 by Stanley G. Thompson, Kenneth Street, Jr., Albert Ghiorso, and Glenn T. Seaborg

With an atomic mass of 251.00 g.mol -1, and electron configuration [Rn] 5f107s2, californium is a man-made, highly radioactive actinide. Together with berkelium and einsteinium, californium is one of the heaviest elements in the periodic table. It’s so malleable and soft that it can be easily cut with a sharp object. This radioactive metal reaches its melting point at 900°C (1652°F, 1173 K), while its boiling point is unknown. Californium has a +3 oxidation state and an electronegativity of 1.3 according to Pauling.

Its atomic radius according to van der Waals is still unknown. In addition, californium shares its properties with the three previous actinides in the periodic table (americium, curium, and berkelium), as well as with the three actinides that are assigned in the periodic table after it (einsteinium, fermium, and mendelevium).       

How Was Californium Discovered?

In 1950, a team of scientific researchers at the Lawrence Berkeley National Laboratory in Berkeley, California, attempted to bombard curium-242 with alpha particles of helium ions in a 60-inch cyclotron. This procedure was followed by chemical separation of the resulting californium-245 and a free neutron from the other elements by a method called chromatography.

In this way, the American chemists Stanley Gerald Thompson (1912 – 1976), Kenneth Street Jr. (1920-2006), Albert Ghiorso (1915-2010), and Glenn Theodore Seaborg (1912 – 1999) succeeded in producing a new element – californium – at the University of California, Berkeley. 

In 1958, Thompson and the research associate at the University of Chicago’s Metallurgical Laboratory, Burris Cunningham, managed to isolate larger quantities of the pure elemental form of californium by neutron irradiation of plutonium-239 which lasted for five years. Their scientific attempt resulted in the production of 1.2 micrograms of californium. 

How Did Californium Get Its Name?

Since this radioactive chemical element was synthesized at the University of Berkeley, California, it was conveniently named in honor of the University in the state of California. Glen T. This pattern of naming new chemical elements after the location of their discovery was not novel by any stretch of the imagination, though.

For instance, terbium was named after the biggest quarry containing this substance, located in the Swedish village of Ytterby; americium was named in parallel to the element above it – europium, and so on.  

However, this naming approach turned out to be impractical when it came to californium. Since the equivalent lanthanide for californium was the chemical element dysprosium, meaning ‘hard to get’ in Greek, the team of researchers went with the name of the location where the new lanthanide was discovered. 

Where Can You Find Californium?

Despite being a man-made chemical element, it is believed that californium also results from supernovae. However, not being available in nature, this radioactive substance is produced in scientific laboratories via nuclear processes. After the discovery of this chemical element which resulted in traceable amounts, weighable quantities of the californium-252 isotope were produced in 1954. Nowadays, the Oak Ridge National Laboratory in Tennessee produces 25mg of this radioactive substance per year on average using a high flux isotope reactor (HFIR). 

Californium in Everyday Life

Being a strong neutron emitter, californium is widely used in:

  • Medicine (in radiotherapy, used for the treatment of cancer patients);
  • In reactor start-up rods;
  • Neutron moisture gauges that detect layers of water and petroleum in the oil wells;
  • Nuclear reactors as a neutron source for triggering the fission reaction; 
  • Californium is also applied as a neutron source in the neutron activation technique used in the detection of gold and silver ores;
  • The oil industry for determining the permeability and porosity of the oil excavation site, as well as for detection of shale beds and hydrocarbons);
  • The construction industry for analysis of coal and cement via prompt-gamma neutron activation analysis [PGNAA];
  • The military for analysis of the content of explosive devices via portable isotopic neutron spectroscopy [PINS]), as well as for detecting unexploded military ordnance, landmines, etc.
  • Customs, security, and border protection for the material scanners and metal detectors used for inspection of the airline baggage;
  • The production of other transuranium elements that are made with the help of californium. For instance, lawrencium is produced by bombarding californium with boron nuclei. 

The Use of Californium in Radiotherapy

This radioactive substance is widely applied in medicine. Its most important use is as a source of radiation in radiotherapy administered to cancer patients. Namely, by emitting gamma rays and neutrons, californium is used as a substitute for radium in radiotherapy. The Cf-245 isotope is used either for the bombardment of cancerous tissues, or it’s implanted close to the tumorous lump for a more direct influence on it. The latter method also spares the surrounding tissue from being damaged in the process of treatment. 

The Use of Californium in Studying Earth and the Moon

By the means of neutron activation analysis (NAA), which uses radioactive elements such as californium, rock specimens brought from the Moon or taken from the earth are analyzed in order to learn about the structure of the Moon and the contaminants of Earth’s soil, respectively. 

How Dangerous Is Californium?

Being extremely radioactive, californium imposes some severe health hazards if it enters the bodily systems since it’s a carcinogen just like all radioactive chemical elements. Due to the fact that even the shortest exposure to low-level quantities of a radioactive element can lead to adverse health effects, exposure to californium can also lead to damage of the cellular mechanism and various types of cancers, miscarriage, stillbirth, dysfunctionality of the immune system, as well as fertility problems. 

Contaminated food and water sources, as well as dust containing californium isotopes, are the main causes of any adverse health effects. In case this radioactive substance builds up in the body, it may lead to the destruction of red blood cells. Since it’s mostly absorbed in the bloodstream, all organs and tissues can be damaged by the toxicity of this substance. 

Environmental Effects of Californium

The strong radioactivity emitted from californium is a big hazard for all living beings and structures. Due to this, it’s considered a highly biohazardous element. 

Isotopes of Californium

There are no naturally occurring californium isotopes since this chemical element was produced in a laboratory. The radioactive isotope californium-252 (252Cf) with a half-life of 2.645 years is most often used as a source for spontaneous fission of the neutrons in nuclear reactors. With a half-life of around 800 years, californium-251 (251Cf) is the most stable isotope. 



[n 1]

ZNIsotopic mass (Da)


[n 2][n 3]




[n 4]




Spin and



[n 5][n 6]

Excitation energy
237Cf98139237.06207(54)#2.1(3) sSF(various)5/2+#
238Cf98140238.06141(43)#21.1(13) msSF[n 7](various)0+
β+ (rare)238Bk
α (rare)234Cm
239Cf98141239.06242(23)#60(30) s


[39(+37−12) s]

β+ (rare)239Bk
240Cf98142240.06230(22)#1.06(15) minα (98%)236Cm0+
SF (2%)(various)
β+ (rare)240Bk
241Cf98143241.06373(27)#3.78(70) minβ+ (75%)241Bk7/2−#
α (25%)237Cm
242Cf98144242.06370(4)3.49(15) minα (80%)238Cm0+
β+ (20%)242Bk
SF (.014%)(various)
243Cf98145243.06543(15)#10.7(5) minβ+ (86%)243Bk(1/2+)
α (14%)239Cm
244Cf98146244.066001(3)19.4(6) minα (99%)240Cm0+
EC (1%)244Bk
245Cf98147245.068049(3)45.0(15) minβ+ (64%)245Bk(5/2+)
α (36%)241Cm
246Cf98148246.0688053(22)35.7(5) hα242Cm0+
EC (5×10−4%)246Bk
SF (2×10−4%)(various)
247Cf98149247.071001(9)3.11(3) hEC (99.96%)247Bk(7/2+)#
α (.04%)243Cm
248Cf98150248.072185(6)333.5(28) dα (99.99%)244Cm0+
SF (.0029%)(various)
249Cf98151249.0748535(24)351(2) yα245Cm9/2−
SF (5×10−7%)(various)
249mCf144.98(5) keV45(5) µs  5/2+
250Cf98152250.0764061(22)13.08(9) yα (99.92%)246Cm0+
SF (.077%)(various)
251Cf[n 8]98153251.079587(5)900(40) yα247Cm1/2+
252Cf[n 9]98154252.081626(5)2.645(8) yα (96.9%)248Cm0+
SF (3.09%)[n 10](various)
253Cf98155253.085133(7)17.81(8) dβ (99.69%)253Es(7/2+)
α (.31%)249Cm
254Cf98156254.087323(13)60.5(2) dSF (99.69%)(various)0+
α (.31%)250Cm
ββ (rare)254Fm
255Cf98157255.09105(22)#85(18) minβ (99.99%)255Es(7/2+)
SF (.001%)(various)
α (10−5%)251Cm
256Cf98158256.09344(32)#12.3(12) minSF (~100%)(various)0+
α (10−6%)252Cm
ββ (rare)256Fm

Source: Wikipedia


List of Californium Compounds

Some of the most tried and tested californium compounds include oxides, oxysulfates,  oxysulfides, oxyhalides, halides, hydrides, pnictides, tellurides, and chalcogenides. Among these compounds, californium(III) polyborate is the only one that radiates green fluorescence with ultraviolet light and is invisible near infrared fluorescence. 

The most significant compounds of californium include:

  • Californium oxide CfO3
  • Californium oxychloride CfOCl
  • Californium trichloride CfCl3
  • Californium(III) oxyfluoride CfOF
  • Californium(III) polyborate Cf[B6O8(OH)5


5 Interesting Facts and Explanations

  1. Californium is the sixth transuranium element that was discovered and produced in a laboratory. 
  2. Chromatography is a method used for the separation of the constituent elements of a solution that may be in a gaseous, liquid, or solid state. 
  3. Radiation causes such severe damage to our genetic structure that it is further transferred onto next generations in the form of various cancerous diseases.  
  4. Supernovae are the largest explosions of stars that support the formation of new stars by producing a powerful shock wave that further distributes chemical elements in the universe and compresses gas clouds. 
  5. Californium oxychloride is the first isolated californium compound.