Californium (Cf)

Californium-252 is one of the few practical portable neutron sources: a single microgram emits around 2.3 million neutrons a second by spontaneous fission, which is enough to start a reactor, find gold in ore, or spot water and oil in a borehole. Worldwide production is a few tens of milligrams a year, split between Oak Ridge and Dimitrovgrad, and the price has been quoted around $27 million per gram, making it one of the most expensive substances routinely sold. It is the heaviest element of which weighable quantities have ever been prepared.

Properties

Atomic number

98

Symbol

Cf

Mass number of most stable isotope

[251]

Category

Actinide

Period

7

Block

f-block

Electron configuration

[Rn] 7s² 5f¹⁰

Electrons per shell

2, 8, 18, 32, 28, 8, 2

Melting point

1,173 K — 899.9 °C — 1651.7 °F

Electronegativity

1.3 (Pauling)

Oxidation states

+3

Discovered

1950 by Stanley Thompson, Kenneth Street Jr., Albert Ghiorso and Glenn Seaborg

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁰

Noble gas shorthand

[Rn] 7s² 5f¹⁰

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 28 · P: 8 · Q: 2

What it is used for

• Neutron sources for starting up nuclear reactors
• Portable neutron activation analysis, including gold and silver assay
• Detecting metal fatigue and water in oil wells
• Cancer brachytherapy with neutrons

Hazards

• Powerful neutron emitter; requires substantial shielding well beyond what alpha emitters need
• Bone-seeking if ingested

No stable isotope; the mass given is the mass number of californium-251, the longest-lived at 898 years. Boiling point and density are omitted: no measured values exist.

Neighbours in the table