Californium

Named for California, and a powerful source of neutrons that can start up reactors and find gold.

At a glance

Symbol: Cf
Atomic number: 98
Mass number of its longest-lived isotope: [251]
Group: none; it sits in the actinide row below the table
Period: 7
Family: actinide
Electron configuration: [Rn] 5f¹⁰ 7s²
Electronegativity: 1.30
Common ions: Cf³⁺
Isotopes: none are stable; ²⁵¹Cf lasts longest, about 900 years; ²⁵²Cf, with a half-life of 2.6 years, is the useful one

On the table

Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.

Electrons and bonding

Radioactive, like every actinide. It gives up electrons to form positive ions.

Properties

State at 25 °C: solid
What it looks like: silvery, radioactive metal
Melting point: 900 °C
Boiling point: not known
Density: not measured

Where it is found

Not found in nature; made in small amounts in high-flux reactors.

Discovery and name

Stanley Thompson, Kenneth Street Jr., Albert Ghiorso and Glenn Seaborg made it in 1950 at Berkeley by bombarding curium with alpha particles, and named it after the state and its university.

What it is used for

Californium-252 splits on its own and releases neutrons, so a few micrograms can start up nuclear reactors, measure water and oil in rock, find gold and silver ores, scan luggage for explosives, and treat some cancers. Californium-249 was the target used to make oganesson.

In compounds

Cf₂O₃californium(III) oxideCfCl₃californium chloride

Handle with care

An intense neutron source; even micrograms need heavy shielding.