CALIFORNIUM

introduction

Numéro atomique: 98
Groupe: Aucun
Poids atomique: 251
Période: 7
Numero CAS: 7440-71-3

Classification

chalcogènes
Halogène
Gaz rare
lanthanides
actinides
Rare Earth Element
Groupe Platine Métal
Transuranium
Pas d'isotopes stables
Solide
Liquide
Gaz
Solide (prédit)

La description • Usages / Fonction

Californium, the sixth transuranium element to be discovered, was produced by Thompson, Street, Ghioirso, and Seaborg in 1950 by bombarding microgram quantities of curium-242 with 35 MeV helium ions in the Berkeley 60-inch cyclotron. Californium (III) is the only ion stable in aqueous solutions, all attempts to reduce or oxidize californium (III) having failed. The isotope californium-249 results from the beta decay of berkelium-249 while the heavier isotopes are produced by intense neutron irradiation by the reactions. Berkelium-249 is bombarded with a neutron to produce berkelium-250 which subsequently yields californium-250 via beta decay. Additionally, californium-249 can be bombarded with a neutron to yield californium-250. This can be followed by two successive neutron bomabrdments to yield californium-251 and californium-252. The existence of the isotopes californium-249, californium-250, californium-251, and californium-252 makes it feasible to isolate californium in weighable amounts so that its properties can be investigated with macroscopic quantities. Californium-252 is a very strong neutron emitter. One microgram releases 170 million neutrons per minute, which presents biological hazards. Proper safeguards should be used in handling californium. Eighteen isotopes of californium are now recognized. californium-249 and californium-252 have half-lives of 351 years and 900 years, respectively. In 1960 a few tenths of a microgram of californium trichloride, CfCl3, californium oxychloride, CfOCl, and californium oxide, Cf2O3, were first prepared. Reduction of californium to its metallic state has not yet been accomplished. Because californium is a very efficient source of neutrons, many new uses are expected for it. It has already found use in neutron moisture gages and in well-logging (the determination of water and oil-bearing layers). It is also being used as a portable neutron source for discovery of metals such as gold or silver by on-the-spot activation analysis. Californium-252 is now being offered for sale by the Oak Ridge National Laboratory (O.R.N.L.) at a cost of $50/mg and californium-249 at a cost of $160/microgram plus packing charges. It has been suggested that californium may be produced in certain stellar explosions, called supernovae, for the radioactive decay of californium-254 (55-day half-life) agrees with the characteristics of the light curves of such explosions observed through telescopes. This suggestion, however, is questioned. 1

Propriétés physiques

Point de fusion:2*  900 °C = 1173.15 K = 1652 °F
Point d'ébullition:2
sublimation point:2 
Triple point:2 
Point critique:2 
Densité:3  15.1 g/cm3

* - at 1 atm

Configuration de l'électron

Configuration de l'électron:  *[Rn] 7s2 5f10
Bloque: f
Plus haut niveau d'énergie occupés: 7
Électrons de valence: 2

Nombres quantiques:

n = 5
ℓ = 3
m = -1
ms = -½

Bonding

ionisation potentiel   eV 4  kJ/mol  
ionisation potentiel   eV 4  kJ/mol  
ionisation potentiel   eV 4  kJ/mol  
1 6.2817    606.1

Thermochimie

Chaleur spécifique: 
Conductivité thermique: 10 (W/m)/K, 27°C 5
Température de fusion: 
Chaleur de vaporisation: 
État de la matière Enthalpie de formation (ΔHf°)6 Entropy (S°)6 Gibbs Free Energy (ΔGf°)6
(kcal/mol) (kJ/mol) (cal/K) (J/K) (kcal/mol) (kJ/mol)
(g) 61 255.224 50.89 212.92376 53 221.752

isotopes

Nuclide Masse 7 Demi vie 7 Spin nucléaire 7 Énergie de liaison
237Cf 237.06207(54)# 2.1(3) s 5/2+# 1,780.34 MeV
238Cf 238.06141(43)# 21.1(13) ms 0+ 1,788.41 MeV
239Cf 239.06242(23)# 60(30) s [39(+37-12) s] 5/2+# 1,796.48 MeV
240Cf 240.06230(22)# 1.06(15) min 0+ 1,804.55 MeV
241Cf 241.06373(27)# 3.78(70) min 7/2-# 1,812.63 MeV
242Cf 242.06370(4) 3.49(15) min 0+ 1,820.70 MeV
243Cf 243.06543(15)# 10.7(5) min (1/2+) 1,828.77 MeV
244Cf 244.066001(3) 19.4(6) min 0+ 1,836.84 MeV
245Cf 245.068049(3) 45.0(15) min (5/2+) 1,844.91 MeV
246Cf 246.0688053(22) 35.7(5) h 0+ 1,852.98 MeV
247Cf 247.071001(9) 3.11(3) h (7/2+)# 1,851.74 MeV
248Cf 248.072185(6) 333.5(28) d 0+ 1,859.81 MeV
249Cf 249.0748535(24) 351(2) a 9/2- 1,867.88 MeV
250Cf 250.0764061(22) 13.08(9) a 0+ 1,875.95 MeV
251Cf 251.079587(5) 900(40) a 1/2+ 1,884.02 MeV
252Cf 252.081626(5) 2.645(8) a 0+ 1,882.78 MeV
253Cf 253.085133(7) 17.81(8) d (7/2+) 1,890.85 MeV
254Cf 254.087323(13) 60.5(2) d 0+ 1,898.92 MeV
255Cf 255.09105(22)# 85(18) min (7/2+) 1,897.68 MeV
256Cf 256.09344(32)# 12.3(12) min 0+ 1,905.75 MeV
Les valeurs marquées # ne sont pas purement dérivées des données expérimentales, mais au moins en partie des tendances systématiques. Spins avec de faibles arguments d'affectation sont entre parenthèses. 7

Abondance

composés

Information de sécurité


Fiche signalétique - ACI Alloys, Inc.

Pour plus d'informations

Liens externes:

Sources

(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:7.
(2) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:132.
(3) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 4:39-4:96.
(4) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10:178 - 10:180.
(5) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:193, 12:219-220.
(6) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:123-6:137.
(7) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:107-6:122.
(8) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(9) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).