Atomic Number: 98
Atomic Mass: 251.0 amu (atomic mass units)
Melting Point: 900 C (1173 K, 1652 F)
Boiling Point: Unknown
Number of Protons: 98
Number of Electrons: 98
Number of Neutrons: 153
Classification: Rare Earth Metal (Man-made)
Crystal Structure: Unknown
Density @ 293 K: Unknown
The man-made radioactive element californium was first produced by Albert Ghiorso, Glenn T. Seaborg, Kenneth Street Jr. and Stanley G. Thompson, a team of American scientists working at the University of California, Berkeley, California, USA in 1950. They used the sixty inch cyclotron based there to bombard curium-242 with helium ions. This produced some atoms of the isotope californium-245 which has a half-life of forty-five minutes. With each atom of californium produced one free neutron was released. The element was named after both the university and state of California.
To date it has proven impossible to reduce any of the compounds made by californium and so produce the solid metal. For this reason not much is known about the bulk properties of the element. It is one of the transuranium elements belonging to the actinide or actinoid series of rare earth elements. From this it has been deduced that it is metallic and probably sliver-white or gray in color. A number of compounds of californium have been produced including californium dioxide, dicalifornium trioxide, californium trichloride and californium trifluoride. The californium (III) ion is the only ion which is stable in aqueous solutions of californium compounds.
A number of isotopes of californium have been produced all of them unstable. The most stable to date is californium-251 with a half-life of 898 years. It decays by alpha decay to form curium-242. Other isotopes have mass numbers ranging from 237 to 256.
The isotope californium-252 is a very strong neutron emitter. One microgram of californium-252 will emit 170 million neutrons a minute. This property has led to it being used in the neutron moisture gauges that are used in well logging to detect oil and water bearing layers within a well. Californium-252 is also used to aid in the search for new sources of gold or silver. In this field it is used as a portable neutron source for on-site activation analysis.
Isotopes of californium have been used in the production of super-heavy elements such as rutherfordium and dubnium.
Telescopic analysis of super-novae has suggested that californium may be formed in such stellar phenomena. The decay curve of the isotope californium-254 agrees with the light curves seen in supernovae. This hypothesis has not been confirmed.