CALIFORNIUM (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Californium is a transuranium element, or "beyond uranium" on the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Uranium is element number 92 in the periodic table, so elements with atomic numbers greater than 92 are said to be transuranium elements.

Discovery and naming

Californium was discovered in 1950 by a research team at the University of California at Berkeley. The team, made up of Glenn Seaborg (1912- ), Albert Ghiorso (1915- ), Kenneth Street, Jr., and Stanley G. Thompson (1912- ), named the new element after the state of California.

Californium was first prepared in a particle accelerator, or an "atom smasher." A particle accelerator accelerates subatomic particles or atoms to very high speeds. The particles collide with a target, such as gold, copper, or tin. The target atoms are converted into new elements by the interaction.

SYMBOL
Cf

ATOMIC NUMBER
98

ATOMIC MASS
251.0796

FAMILY
Actinide
Transuranium element

PRONUNCIATION
cal-uh-FOR-nee-um

To make californium, researchers fired alpha particles (helium atoms without electrons) at a target of curium. Some collisions cause a helium atom (atomic number 2) to become part of a curium atom (atomic number 96), forming a new atom with atomic number 98.

Physical and chemical properties

Very little is known about the properties of californium.

Occurrence in nature

Californium does not occur naturally.

Isotopes

All isotopes of californium are radioactive. The most stable isotope is californium-251. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. A radioactive isotope is one that breaks apart and gives off some form of radiation.

The half life of californium-251 is about 800 years. The half life of a radioactive element is the time it takes for half of a sample of the element to break down. For instance, in 800 years, only half of a 100-gram sample of californium-251 would remain. After another 800 years, only half of that amount (25 grams) would remain.

One isotope of californium is of special interest, californium-252. This isotope has the unusual property of giving off neutrons when it breaks apart. Isotopes that behave in this way are very unusual.

Extraction

Californium does not occur naturally.

Uses

When neutrons collide with an atom, they tend to become part of the nucleus, making the atom less stable:

The radioactive copper then gives off radiation or energy and particles that can be measured.

Based on this property, californium-252 has been used to prospect for oil and to test materials without breaking them apart or destroying them. Neutrons from californium-252 can be used to inspect airline baggage. The luggage can be tested quickly and efficiently without having to open it. The isotope can also be used to determine the amount of moisture in soil, information that is very important to road builders and construction companies.

Californium-252 is also used in medicine. When injected into the body, it is deposited in bones. The radiation it gives off can be used to determine the health of the bone. Californium-252 is also used to treat ovarian and cervical cancer.

Today, californium can be made only in milligram amounts. It is available from the U.S. government for $10 per millionth of a gram. All californium-252 made by the government now comes from the High Flux Isotope Radiator at the Oak Ridge National Laboratory in Tennessee.

Compounds

There are no commercially important compounds of californium.

Neutrons from californium-252 can be used to inspect airline baggage.

Health effects

Radioactive materials, such as californium, are hazardous to living cells. As the atoms decay, they throw off energy and particles that damage or kill the cell. The damaged cells rapidly divide, producing masses called tumors. Cancerous cells can crowd out healthy cells, reduce or stop organ function, and break free to spread through the body.

Californium

melting point: 900°C
boiling point: Unknown
density: Unknown
most common ions: Cf²⁺, Cf³⁺

Element 98, named after the state of California, was first synthesized by the research group of Glenn Seaborg in 1950 at the University of California at

Berkeley. A target of microgram amounts of an isotope of curium (²⁴²Cm) was bombarded with accelerated helium ions in a cyclotron, to produce approximately 5,000 atoms of a californium isotope of mass 245 and a half-life of 44 minutes.

Californium, like all the actinide elements heavier than plutonium, exists in a stable trivalent oxidation state in aqueous solutions . It has also been found to exist in the (less stable) tetravalent oxidation state in solution. The ground state electronic configuration for the atom is 5f¹⁰7s². Metallic californium has a face-centered cubic structure near its melting point and a double hexagonal close-packed structure at temperatures below its melting point. Californium has eighteen isotopes, all of which are radioactive. The longest-lived isotope has a mass number of 251 and a half-life of 900 years. The isotope having mass number 252 and a half-life of 2.65 years undergoes radioactive decay , a fraction of which (3%) is via spontaneous nuclear fission ; it releases neutrons in the fission event. Californium-252 has been used as a neutron source in a variety of analytical techniques, in medical diagnostic tests that require activation analysis , and in the production of short-lived nuclides. Californium neutron sources are used to image low density materials (especially hydrogenous materials). The compactness and portability of ²⁵²Cf neutron sources has resulted in their use in such areas as the detection of metals in deep wells, lunar exploration, and nuclear weapons monitoring.

see also Actinium; Berkelium; Einsteinium; Fermium; Lawrencium; Mendelevium; Neptunium; Nobelium; Plutonium; Protactinium; Rutherfordium; Seaborg, Glenn theodore; Thorium; Uranium.

Gregory R. Choppin

Bibliography

Choppin, Gregory R.; Liljenzin, Jan-Olov; and Rydberg, Jan (2001). Radiochemistry and Nuclear Chemistry, 3rd edition. Woburn, MA: Butterworth-Heinemann.

Seaborg, Glenn T., and Loveland, Walter D. (1990). The Elements beyond Uranium. New York: Wiley-Interscience.

californium (symbol Cf) Radioactive metallic element of the actinide series, first made in 1950 by US nuclear chemist Glenn Seaborg (1912–99) and colleagues at the University of California, Berkeley, by alpha-particle bombardment of the curium isotope Cm²⁴². Californium presents biological dangers because one microgram releases 170 million neutrons a minute. Properties: at.no. 98; most stable isotope Cf²⁵¹ (half-life 800 yr). See also transuranic elements

cal·i·for·ni·um / ˌkaləˈfôrnēəm/ • n. the chemical element of atomic number 98, a radioactive metal of the actinide series. (Symbol: Cf)