This short half-life means the element is not found in significant quantities in the Earth's crust.

[a] 252Cf, with a half-life of about 2.645 years, is the most common isotope used and is produced at Oak Ridge National Laboratory (ORNL) in the United States and Research Institute of Atomic Reactors in Russia.

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.

[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.

[12] The element slowly tarnishes in air at room temperature, with the rate increasing when moisture is added.

[21] The element forms a water-soluble chloride, nitrate, perchlorate, and sulfate and is precipitated as a fluoride, oxalate, or hydroxide.

[11] 249Cf is formed by beta decay of berkelium-249, and most other californium isotopes are made by subjecting berkelium to intense neutron radiation in a nuclear reactor.

[11] Californium was first made at University of California Radiation Laboratory, Berkeley, by physics researchers Stanley Gerald Thompson, Kenneth Street Jr., Albert Ghiorso, and Glenn T. Seaborg, about February 9, 1950.

[37] The High Flux Isotope Reactor (HFIR) at ORNL in Oak Ridge, Tennessee, started producing small batches of californium in the 1960s.

[40] The Atomic Energy Commission sold 252Cf to industrial and academic customers in the early 1970s for $10/microgram,[27] and an average of 150 mg (0.0053 oz) of 252Cf were shipped each year from 1970 to 1990.

[42][43][g] Traces of californium can be found near facilities that use the element in mineral prospecting and in medical treatments.

[47] Californium is not a major radionuclide at United States Department of Energy legacy sites since it was not produced in large quantities.

[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.

[53] Only two sites produce 252Cf: Oak Ridge National Laboratory in the U.S., and the Research Institute of Atomic Reactors in Dimitrovgrad, Russia.

[57] 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.

[17] It has been used in educational applications since 1969 when Georgia Institute of Technology got a loan of 119 μg of 252Cf from the Savannah River Site.

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;[63] and in portable metal detectors.

[67] 251Cf has a very small calculated critical mass of about 5 kg (11 lb),[68] high lethality, and a relatively short period of toxic environmental irradiation.

[73] Californium that bioaccumulates in skeletal tissue releases radiation that disrupts the body's ability to form red blood cells.

[74] 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.