Californium (Cf)
actinideSolid
Peso atômico padrão
[251]Configuração eletrônica
[Rn] 7s2 5f10Ponto de fusão
899,85 °CPonto de ebulição
N/DDensidade
1,51e+4 kg/m³Estados de oxidação
+2, +3, +4, +5Eletronegatividade (Pauling)
1,3Energia de ionização (1ª)
6,281878 eVAno da descoberta
1950Raio atômico
N/DDetalhes
Californium is a synthetic actinide and one of the heaviest elements obtainable in microgram to milligram quantities. Its chemistry is dominated by the +3 oxidation state and resembles that of other late actinides and lanthanides, though +2 and +4 chemistry is also known under suitable conditions. The isotope ²⁵²Cf is notable for intense spontaneous fission neutron emission, making the element technologically significant despite its extreme scarcity.
Californium does not occur naturally in the Earth’s crust. It was first synthesized in 1950 by Glenn T. Seaborg and his team at the University of California using the reaction 242Cm (4He, n) 245Cf. The element was named for the state where it was first synthesized.
Californium is the second half of the actinide series where its f electrons are further removed or shielded from the valence electrons that those of the lighter actinides. Thus californium resembles the behavior of the lanthanide elements exhibiting divalent, trivalent, and tetravalent oxidation states in solid-state compounds. In solution, the trivalent state is the most stable however the divalent, tetravalent and a possible pentavalent state have been reported. The existence of Cf(V) is questionable.
Californium metal is fairly reactive. On standing in air or moisture, small pieces or foils of Cf metal quickly form an oxide but not in a violent reaction. Two methods have been successful for preparation of Cf metal: reduction of californium trifluoride with lithium metal at elevated temperature and using thorium or lanthanum metal to reduce californium oxide (R. G. Haire, 1982). The largest amount of metal prepared at one time was about 10 milligrams. The metal was eventually determined to be trivalent with a room-temperature double hexagonal close-packed structure. A face centered cubic structure has also been observed for californium metal at high temperature.
Some alloys and numerous solid-state compounds have been prepared with californium in spite of the fact that only small amounts of the element are available at any one time. Californium compounds include oxides, halides, oxyhalides, pnictides, chacogenides hydrides, tellurides, oxysulfate and oxysulfide to name a few. Some organo-californium coumpounds have also been prepared.
Because californium is a very efficient source of neutrons, many new uses are expected for it. It has already found use in neutron moisture gauges 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. 252Cf is now being offered for sale by the Oak Ridge National Laboratory at a cost of $10/mg. As of May, 1975, more than 63 mg have been produced and sold. It has been suggested that californium may be produced in certain stellar explosions, called supernovae, for the radioactive decay of 254Cf (55-day half-life) agrees with the characteristics of the light curves of such explosions observed through telescopes. This suggestion, however, is questioned.
Further reading: Richard G. Haire (2006) Chapter 11, "The Chemistry of the Actinide and Transactinide Element," Third Edition, L. R. Morss, J. Fuger, and N. M. Edelstein, Eds, Springer Publishers.
This element reviewed and Updated by Dr. David Hobart, 2011
Californium was first produced by Stanley G. Thompson, Glenn T. Seaborg, Kenneth Street, Jr. and Albert Ghiorso working at the University of California, Berkeley, in 1950. They bombarded atoms of curium-242 with helium ions using a device known as a cyclotron. This produced atoms of californium-245, an isotope with a half-life of about 45 minutes, and a free neutron.
Californium, the sixth transuranium element to be discovered, was produced by Thompson, Street, Ghioirso, and Seaborg in 1950 by bombarding microgram quantities of 242Cm with 35 MeV helium ions in the Berkeley 60-inch cyclotronproducing 244Cf. Since the lanthanide homologue of californium (dysprosium) has a stable trivalent state in aqueous solution it was anticipated that californium would exhibit a stable trivalent state as well. This accurate prediction allowed for the successful chromatographic separation of californium from other actinides and for its unequivocal identification.
Metallic californium has been prepared only in very small quantities. It is generally described as a silvery, radioactive actinide metal, but ordinary bulk properties are limited by sample size, self-irradiation, heat generation, and isotope composition.
Californium has no ordinary structural or consumer use. The main practical isotope is ²⁵²Cf, used as a compact neutron source for reactor start-up sources, neutron activation analysis, detector calibration, and some industrial gauges. It has also been used in neutron radiography and in specialized searches for fissile material. Medical use has been limited and specialized, including historical neutron brachytherapy research; it is not a routine medical material. Other isotopes are chiefly research targets or intermediates in actinide studies.
Californium-252, an isotope with a half-life of about 2.6 years, is a very strong neutron source. One microgram (0.000001 grams) of californium-252 produces 170,000,000 neutrons per minute. It is being used as a neutron source to identify gold and silver ores through a technique known as neutron activation. It is also being used in devices known as neutron moisture gauges that are used to find water and oil bearing layers in oil wells.
A few compounds of californium have been produced and studied. They include: californium oxide (CfO3), californium trichloride (CfCl3) and californium oxychloride (CfOCl).
Californium's most stable isotope, californium-251, has a half-life of about 898 years. It decays into curium-247 through alpha decay or decays through spontaneous fission.
Isotopes in Industry
252Cf is a very active source of neutrons (2.3×106 neutrons per second per microgram) with a half-life of 2.65 years. The energy spectrum of the neutrons is very similar to that of a fission reactor and small amounts of 252Cf provide an ideal portable source for low neutron flux applications [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf., [625] I. W. Osborne-Lee, C. W. Alexander. Californium-252 A Remarkably Versatile Radioisotope, ORNL/TM-12706, Oak Ridge National Laboratory, Oak Ridge, TN (1995)., [626] R. C. Martin, J. B. Knauer, P. A. Balo. Appl. Radiat. Isot.53, 785 (2000).. 252Cf is used for PGNAA (prompt gamma neutron activation analysis, a method for detecting many chemical elements in samples simultaneously) in the analysis of coal, cement, minerals, weapon components, and chemical munitions [627] NIST. Prompt Gamma-Ray Activation Analysis, NIST (2015), Jan. 20. http://www.nist.gov/mml/csd/inorganic/pgaa.cfm.. This method provides a quick and non-destructive elemental analysis of a sample. For example, 252Cf, as the neutron source for PGNAA, is used to detect the presence of antitank mines [625] I. W. Osborne-Lee, C. W. Alexander. Californium-252 A Remarkably Versatile Radioisotope, ORNL/TM-12706, Oak Ridge National Laboratory, Oak Ridge, TN (1995)..
Neutron activation analysis (NAA) uses 252Cf as a portable neutron source to bombard a small sample from the area of interest with neutrons and analyze the radioactive emissions from that bombardment to help identify silver or gold ore [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf.. 252Cf has been used in neutron moisture gauges to locate water [628] Los Alamos National Laboratory. Periodic Table of Elements: LANL-Californium, Los Alamos National Laboratory (2014), Feb. 25; http://periodic.lanl.gov/98.shtml.. 252Cf is used in borehole geophysical logging for subsurface PGNAA investigation of waste (Fig. IUPAC.98.1) [629] L. J. Bond, R. V. Harris, K. M. Denslow, T. L. Moran, J. W. Griffin, D. M. Sheen, G. E. Dale, T. Schenkel. Evaluation of Non-Nuclear Techniques for Well Logging: Technology Evaluation, PNNL-19867, Pacific Northwest National Laboratory (2010)..
Formation fluid identification uses 252Cf as a chemical neutron source for elastic/inelastic neutron backscattering and/or neutron activation methods in well-logging to determine water- and oil-bearing layers and other downhole properties of the well bore [629] L. J. Bond, R. V. Harris, K. M. Denslow, T. L. Moran, J. W. Griffin, D. M. Sheen, G. E. Dale, T. Schenkel. Evaluation of Non-Nuclear Techniques for Well Logging: Technology Evaluation, PNNL-19867, Pacific Northwest National Laboratory (2010)..
Isotopes in Medicine
252Cf is sometimes used in boron neutron capture therapy (BNCT) as a source of neutrons that can be delivered close to the region of a tumor [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf., [625] I. W. Osborne-Lee, C. W. Alexander. Californium-252 A Remarkably Versatile Radioisotope, ORNL/TM-12706, Oak Ridge National Laboratory, Oak Ridge, TN (1995)., [626] R. C. Martin, J. B. Knauer, P. A. Balo. Appl. Radiat. Isot.53, 785 (2000).. Brachytherapy can use 252Cf to treat many types of cancer [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf., [625] I. W. Osborne-Lee, C. W. Alexander. Californium-252 A Remarkably Versatile Radioisotope, ORNL/TM-12706, Oak Ridge National Laboratory, Oak Ridge, TN (1995)., [626] R. C. Martin, J. B. Knauer, P. A. Balo. Appl. Radiat. Isot.53, 785 (2000)..
Californium chemistry is best developed for Cf³⁺ in aqueous solution and solid salts. Representative compounds include californium(III) oxide, Cf₂O₃, californium(III) chloride, CfCl₃, and californium(III) fluoride, CfF₃. The +4 state is less stable but occurs in compounds such as californium(IV) oxide, CfO₂, under oxidizing conditions. Divalent californium is known in some solid-state and strongly reducing systems. Complexation with nitrate, chloride, fluoride, carbonate, and organic ligands is important for separation chemistry.
See more information at the Californium compound page.
All californium isotopes are radioactive, and hazards depend strongly on isotope and chemical form. ²⁵²Cf presents a severe neutron and gamma radiation hazard even in tiny amounts, while alpha-emitting isotopes are especially dangerous if inhaled or ingested. Self-heating, radiolysis, and contamination control are practical concerns. Work requires heavy shielding, remote handling, sealed sources or containment, and strict criticality and radiological controls where applicable.
Californium has no significant natural environmental cycle. Trace atoms can be formed in nuclear explosions or possibly in intense neutron-flux environments, but environmental inventories are overwhelmingly anthropogenic and extremely small. In the environment it is expected to behave mainly as a trivalent actinide, binding strongly to minerals, organic matter, and fine particles rather than remaining freely mobile. Its ecological relevance is dominated by radiological toxicity, not nutrient chemistry.
Californium is not a commodity metal. It is produced by prolonged neutron irradiation of curium or heavier actinide targets in high-flux reactors, followed by demanding radiochemical separations. Supply is limited by reactor access, target availability, isotope yields, decay losses, and the difficulty of handling intense radiation. ²⁵²Cf sources are supplied in small calibrated quantities for specialized users; substitution by accelerator neutron sources or other radioisotopic sources is often considered when feasible. Recycling usually means recovery and re-encapsulation of source material rather than conventional materials recycling.
Made by bombarding curium with helium ions.
Californium is not a primordial element, because all of its isotopes are radioactive on timescales short compared with the age of Earth and the Solar System. Very neutron-rich actinides, including californium isotopes, may be produced transiently in explosive r-process events such as neutron-star mergers or rare supernova environments, but they decay away. Any extraterrestrial occurrence would be short-lived or artificial.
- ²⁵²Cf emits neutrons largely through spontaneous fission, not by an external accelerator.
- Only very small californium samples are needed for intense neutron-source applications.
- The element was first identified among products from irradiating curium with alpha particles.
- Californium separations are complicated by its chemical similarity to neighboring trivalent actinides.
- Self-irradiation can damage californium solids and alter measured material properties.
Imagens
Propriedades
Física
- Raio de van der Waals
- 245 pm Comparar Raio de van der Waals de todos os elementos →
- Densidade
- 1,51 × 104 kg/m³ Comparar Densidade de todos os elementos →
- Fase nas CNTP
- Sólido Comparar Fase nas CNTP de todos os elementos →
- Ponto de fusão
- 899,85 °C Comparar Ponto de fusão de todos os elementos →
Química
- Eletronegatividade (Pauling)
- 1,3 Comparar Eletronegatividade (Pauling) de todos os elementos →
- Afinidade eletrônica
- -0,5 eV (valor negativo — prevê-se que o átomo não capte um eletrão adicional)
- Energia de ionização (1ª)
- 6,281878 eV Comparar Energia de ionização (1ª) de todos os elementos →
- Energia de ionização (2ª)
- 12,000041 eV Comparar Energia de ionização (2ª) de todos os elementos →
- Energia de ionização (3ª)
- 22,400077 eV Comparar Energia de ionização (3ª) de todos os elementos →
- Energia de ionização (4ª)
- 37,70013 eV Comparar Energia de ionização (4ª) de todos os elementos →
- Energia de ionização (5ª)
- 51,900179 eV Comparar Energia de ionização (5ª) de todos os elementos →
- Estados de oxidação
- +2, +3, +4, +5 Comparar Estados de oxidação de todos os elementos →
- Elétrons de valência
- 3 Comparar Elétrons de valência de todos os elementos →
- Configuração eletrônica
- [Rn] 7s2 5f10
Termodinâmica
- Calor de sublimação
- 4,042079 eV
- Calor de atomização
- 4,042079 eV
- Entalpia de atomização
- 2,031404 eV
Nuclear
- Prótons
- 98 Comparar Prótons de todos os elementos →
- Nêutrons
- 153 Comparar Nêutrons de todos os elementos →
- Isótopos conhecidos
- 20 Comparar Isótopos conhecidos de todos os elementos →
- Isótopos estáveis
- 0 Comparar Isótopos estáveis de todos os elementos →
- Número de massa (mais estável)
- 251
- Isótopo mais estável
- Cf-251
- Ano da descoberta
- 1950
Abundância
N/D
Estrutura cristalina
N/D
Estrutura eletrônica
- Elétrons por camada
- 2, 8, 18, 32, 28, 8, 2 Comparar Elétrons por camada de todos os elementos →
Identificadores
- Número CAS
- 7440-71-3 Comparar Número CAS de todos os elementos →
- Símbolo de termo
- 5I8
- InChI
- InChI=1S/Cf
- Chave InChI
- HGLDOAKPQXAFKI-UHFFFAOYSA-N
Configuração eletrônica Medido
Cf: 5f¹⁰ 7s²[Rn] 5f¹⁰ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f¹⁰ 7s²Modelo atômico
Os isótopos alteram o número de nêutrons, a massa e a estabilidade — não a configuração eletrônica de um átomo neutro.
Modelo atômico esquemático, sem escala.
Assinatura atômica
Espectro de emissão / absorção
Distribuição isotópica
Sem isótopos estáveis.
| Número de massa | Massa atômica (u) | Abundância natural | Meia-vida |
|---|---|---|---|
| 251 Radioativo | 251,0795886 ± 0,0000048 | N/D | 898 anos |
| 249 Radioativo | 249,0748539 ± 0,0000023 | N/D | 351 anos |
| 248 Radioativo | 248,0721851 ± 0,0000057 | N/D | 333.5 dias |
| 255 Radioativo | 255,09105 ± 0,00022 | N/D | 85 minutos |
| 254 Radioativo | 254,087324 ± 0,000013 | N/D | 60.5 dias |
Fase / Estado
Motivo: 874,9 °C abaixo do ponto de sublimação (899,85 °C)
Esquemático, sem escala
Pontos de transição de fase
Energias de transição
Energia necessária para sublimar 1 mol no ponto de sublimação
Densidade
Em condições padrão
Em condições padrão
Espectros atômicos
Mostrando 10 de 98. Ordenado por carga do íon (ordem crescente).
Dados de linhas disponíveis ?
| Íon | Carga | Total de linhas | Probabilidades de transição | Designações dos níveis |
|---|---|---|---|---|
| Cf I | 0 | 26 | 0 | 0 |
| Cf II | +1 | 10 | 0 | 0 |
Dados de níveis disponíveis ?
| Íon | Carga | Níveis |
|---|---|---|
| Cf I | 0 | 2 |
| Cf II | +1 | 2 |
| Cf III | +2 | 2 |
| Cf IV | +3 | 2 |
| Cf V | +4 | 2 |
| Cf VI | +5 | 2 |
| Cf VII | +6 | 2 |
| Cf VIII | +7 | 2 |
| Cf IX | +8 | 2 |
| Cf X | +9 | 2 |
Dados de estrutura cristalina indisponíveis
Raios iônicos
| Carga | Coordenação | Spin | Raio |
|---|---|---|---|
| +3 | 6 | N/D | 95 pm |
| +3 | 9 | N/D | 112.6 pm |
| +4 | 6 | N/D | 82.1 pm |
| +4 | 8 | N/D | 92 pm |
Compostos
Isótopos (5)
Twenty isotopes ranging in atomic mass from 237 to 256 have been reported for californium however the existence of the isotopes with mass of 237 and 238 has not yet been confirmed. The isotope 249Cf results from the beta decay of 249Bk while the heavier isotopes are produced by intense neutron irradiation by nuclear reactors or in thermonuclear explosions. The existence of the isotopes 249Cf, 250Cf, 251Cf, and 252Cf makes it feasible to isolate californium in weighable amounts so that its physicochemical properties can be investigated with macroscopic quantities. The first well-defined structure of a californium compound was the oxychloride by Cunningham and Wallmann a decade after discovery of the element. Microgram quantities of californium have been produced in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) in Tennessee and in Dimitrovgrad high-flux reactors in Russia. Californium-252 is a very strong neutron emitter. One microgram releases 170 million neutrons per minute, which presents biological hazards. Cf-252 also decays by energetic alpha emission (half-life 2.65 years, 6.1 MeV). Proper safeguards should be used when handling californium isotopes.
| Número de massa | Massa atômica (u) | Abundância natural | Meia-vida | Modo de decaimento | |
|---|---|---|---|---|---|
| 251 Radioativo | 251,0795886 ± 0,0000048 | N/D | 898 anos | α ≈100%SF ? | |
| 249 Radioativo | 249,0748539 ± 0,0000023 | N/D | 351 anos | α =100%SF =5.0e-7±0.4% | |
| 248 Radioativo | 248,0721851 ± 0,0000057 | N/D | 333.5 dias | α ≈100%SF =0.0029±0.3% | |
| 255 Radioativo | 255,09105 ± 0,00022 | N/D | 85 minutos | β- =100%SF ?α ? | |
| 254 Radioativo | 254,087324 ± 0,000013 | N/D | 60.5 dias | SF =99.69±0.2%α =0.31±0.2%2β- ? |
Propriedades ampliadas
Raios covalentes (dados ampliados)
- Raio covalente (Pyykkö)
- 168 pm
- Raio covalente (Pyykkö, ligação dupla)
- 140 pm
Raios de van der Waals
- Alvarez
- 305 pm
- UFF
- 331,3 pm
Escalas de numeração
- Mendeleev
- 32
- Pettifor
- 39
- Glawe
- 42
Escalas de eletronegatividade
- Ghosh
- 0
Polarizabilidade e dispersão
- Polarizabilidade dipolar
- 122 a.u.
- Polarizabilidade dipolar (incerteza)
- 20 a.u.
Transições de fase e alótropos
| Ponto de fusão | 1173,15 K |
Categorias de estados de oxidação
Dados de referência avançados
Detalhes dos raios cristalinos (4)
| Carga | CN | Spin | rcrystal (pm) | Origem |
|---|---|---|---|---|
| 3 | VI | 109 | from r^3 vs V plots, | |
| 4 | VI | 96,1 | from r^3 vs V plots, | |
| 4 | VIII | 106 | ||
| 3 | IX | — | 126,6 |
Modos de decaimento dos isótopos (47)
| Isótopo | Modo | Intensidade |
|---|---|---|
| 237 | A | 70% |
| 237 | SF | 30% |
| 237 | B+ | — |
| 238 | SF | 97,5% |
| 238 | A | 2,5% |
| 239 | A | 65% |
| 239 | B+ | — |
| 240 | A | 98,5% |
| 240 | SF | 1,5% |
| 240 | B+ | — |
Dados adicionais
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
Referências (1)
- [5] Californium https://education.jlab.org/itselemental/ele098.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
Referências (1)
- [5] Californium https://education.jlab.org/itselemental/ele098.html
Referências
(9)
Data deposited in or computed by PubChem
The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.
Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.
The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.
Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/
The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.
The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database
This section provides all form of data related to element Californium.
The element property data was retrieved from publications.