Californium
Californium is a
chemical 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.
252Cf (2.6 year
half-life) 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
254Cf (55-day half-life) may have been detected through
telescopes in
supernovae remnants.
249Cf is formed from the
beta decay of
249Bk 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 widespread useful significance as a material. Some of its uses are:
*neutron startup source for some
nuclear reactors, calibrating instrumentation
*treatment of certain
cervical and
brain cancers where other
radiation therapy is ineffective
*
radiography of aircraft to detect
metal fatigue*airport neutron-activation detectors of explosives
*
neutron moisture gauges used to find
water and
petroleum layers in
oil wells
*portable neutron source in
gold and
silver prospecting for on-the-spot analysis
Californium has no biological role and only a few californium
compounds have been made and studied. Included among these are: californium oxide (Cf
O3), californium trichloride (Cf
Cl3) and californium oxychloride (CfOCl). The only californium ion that is stable in
aqueous solution is californium (III).
251Cf is famous for having a very small
critical mass, high lethality, and short period of toxic environmental irradiation relative to radioactive elements commonly used for radiation explosive weaponry, creating speculation about possible use in
pocket nukes. This
urban legend is unfounded since it would be very difficult to make a
251Cf bomb weighing less than 2 kg, and the costs of such a bomb would be prohibitive. Other weaponry uses, such as showering an area with Californium, are not impossible but are seen as inhumane and are subject to inclement weather conditions and porous terrain considerations. Often cited as a consideration is the cost of producing Californium in quantity, but the cost citations are usually due to extra fees that laboratory materials companies insert for sake of caution and market needs. A government need not consider these as prohibitive.
Pertaining to californium's
nuclear fuel cycle, it is important to make sure that the
curium concentration in MOX
Nuclear fuel is kept low, as
neutron irradation of curium will convert some of it to californium. The californium will then cause the used fuel to be more difficult to handle as the californium is a strong
neutron emitter (through spontaneous fission). Hence the concentration of curium and californium among the
Minor actinides are important.
Californium was
first synthesized by
University of California, Berkeley researchers
Stanley G. 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 system.
To produce element 98, the team bombarded a microgram-sized target of
242Cm with 35 MeV
alpha particles in the 60-inch Berkeley
cyclotron which produced atoms of
245Cf (half-life 44 minutes) and a
free neutron.
Nineteen
radioisotopes of californium have been characterized, the most stable being
251Cf with a
half-life of 898 years,
249Cf with a half-life of 351 years, and
250Cf with a half-life of 13 years. All of the remaining
radioactive isotopes have half-lives that are less than 2.7 years, and the majority of these have half-lives shorter than 20 minutes. The isotopes of californium range in
atomic weight from 237.062
amu (
237Cf) to 256.093 amu (
256Cf).
Although californium does not occur naturally on Earth, Cf and its decay products occur in the universe; their electromagnetic emissions are regularly observed in the spectra of
supernovae.
*
Los Alamos National Laboratory - Californium*
It's Elemental - CaliforniumGuide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
*
WebElements.com - Californium*
NuclearWeaponArchive.org - Californium
