   #copyright

Californium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


              98            berkelium ← californium → einsteinium
              Dy
             ↑
             Cf
             ↓
             (Uqo)

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                  Name, Symbol, Number californium, Cf, 98
                                                 Chemical series actinides
                                            Group, Period, Block n/a, 7, f
                                      Appearance unknown, probably silvery
                                                    white or metallic gray
                                                   Atomic mass (251) g/mol
                                    Electron configuration [Rn] 5f^10 7s^2
                                Electrons per shell 2, 8, 18, 32, 28, 8, 2
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 15.1 g·cm^−3
                                                     Melting point 1173  K
                                                     (900 ° C, 1652 ° F)
                                                         Atomic properties
                                     Electronegativity 1.3 (Pauling scale)
                                       Ionization energies 1st: 608 kJ/mol
                                                             Miscellaneous
                                             CAS registry number 7440-71-3
                                                         Selected isotopes

   CAPTION: Main article: Isotopes of californium

                                  iso   NA  half-life DM  DE ( MeV)   DP
                                 ^248Cf syn 333.5 d   SF  -         -
                                                      α   6.361     ^244Cm
                                 ^249Cf syn 351 y     SF  -         -
                                                      α   6.295     ^245Cm
                                 ^250Cf syn 13.08 y   α   6.128     ^246Cm
                                                      SF  -         -
                                 ^251Cf syn 898 y     α   6.176     ^247Cm
                                 ^252Cf syn 2.645 y   α   6.217     ^248Cm
                                                      SF  -         -
                                 ^253Cf syn 17.81 d   β^- 0.285     ^253Es
                                                      α   6.124     ^249Cm
                                 ^254Cf syn 60.5 d    SF  -         -
                                                      α   5.926     ^250Cm

                                                                References

   Californium ( IPA: /ˌkalifɔː(r)niəm/) 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).

Notable characteristics

   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.

   Californium has no biological role and only a few californium compounds
   have been made and studied. Included among these are: californium oxide
   (Cf[2]O[3]), californium trichloride (CfCl[3]) and californium
   oxychloride (CfOCl). The only californium ion that is stable in aqueous
   solution is the californium(III) cation.

General uses

   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

   In October, 2006 it was announced that on three occasions
   californium-249 atoms had been bombarded with calcium-48 ions to
   produce ununoctium (element 118), making this the heaviest element ever
   synthesized.

Military use

   ^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.

Nuclear fuel cycle

   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.

History

   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.

Isotopes

   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).

Natural occurrence

   Although californium does not occur naturally on Earth, the element and
   its decay products occur elsewhere in the universe. Their
   electromagnetic emissions are regularly observed in the spectra of
   supernovae.
   Retrieved from " http://en.wikipedia.org/wiki/Californium"
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   with only minor checks and changes (see www.wikipedia.org for details
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