From Academic Kids
|Name, Symbol, Number||Californium, Cf, 98|
|Period, Block||7, f|
|Appearance||unknown; probably metallic,|
silvery white or gray
|Atomic weight|| amu|
|e-'s per energy level||2,8,18,32,28,8,2|
|State of matter||solid|
|Most stable isotopes|
Californium is a synthetic element in the periodic table that has the symbol Cf and atomic number 98. A radioactive transuranic element, californium has very few uses and was discovered by bombarding curium with alpha particles (helium ions).
Weighable amounts of californium make it possible to determine some of its properties using macroscopic quantities.
Californium-252 (half-life 2.6 years) is a very strong neutron emitter and is thus extremely radioactive and harmful (one microgram spontaneously emits 170 million neutrons per minute). The decay of californium-254 (55-day half-life) may have been detected through telescopes in supernovae remnants. Californium-249 is formed from the beta decay of berkelium-249 and most other californium isotopes are made by subjecting berkelium to intense neutron radiation in a nuclear reactor.
The element does have some specialist applications dealing with its radioactivity but otherwise is largely too difficult to produce to have useful significance as a material. Two of its few uses;
- in neutron moisture gauges which are in turn used to find water and petroleum layers in oil wells and
- as a portable neutron source in gold and silver prospecting via on-the-spot activation analysis.
As of 2004, californium has not been isolated in its metallic form. The only californium ion that is stable in aqueous solution is californium (III). Californium has no biological role and only a few californium compounds have been made and studied. Included among these are: californium oxide (CfO3), californium trichloride (CfCl3) and californium oxychloride (CfOCl).
Californium-251 is famous for having a very small critical mass, creating speculation about possible use in pocket nukes although this urban legend is unfounded since it would be very difficult to make a Californium-251 bomb weighting less than 2kg and the costs of such bomb would be prohibitive.
Californium was first synthesized by University of California, Berkeley researchers Stanely Thompson, Kenneth Street, Jr., Albert Ghiorso and Glenn T. Seaborg in 1950. It was the sixth transuranium element to be discovered and the team announced their discovery on March 17, 1950. It was named after the U.S. state of California and for the University of California, Berkeley (which is nicknamed "Cal").
To produce element 98, the team bombarded a microgram-sized target of curium-242 with 35 MeV alpha particles in the 60-inch Berkeley cyclotron to produced atoms of californium-245 (half-life 44 minutes) and a free neutron.
19 radioisotopes of californium have been characterized, with the most stable being Cf-251 with a half-life of 898 years, Cf-249 with a half-life of 351 years, and Cf-250 with a half-life of 13 years. All of the remaining radioactive isotopes have half-lifes that are less than 2.7 years, and the majority of these have half lifes that are less than 20 minutes. The isotopes of californium range in atomic weight from 237.062 amu (Cf-237) to 256.093 amu (Cf-256).
- Los Alamos National Laboratory - Californium (http://periodic.lanl.gov/elements/98.html)
- It's Elemental - Californium (http://education.jlab.org/itselemental/ele098.html)
- Guide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1