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Californium, 98Cf
A very small disc of silvery metal, magnified to show its metallic texture
Californium
Pronunciation/ˌkæləˈfɔːrniəm/ ​(KAL-ə-FOR-nee-əm)
Appearancesilvery
Mass number[251]
Californium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Dy
↑
Cf
↓
—
berkelium ← californium → einsteinium
Atomic number (Z)98
Groupf-block groups (no number)
Periodperiod 7
Block  f-block
Electron configuration[Rn] 5f10 7s2[1]
Electrons per shell2, 8, 18, 32, 28, 8, 2
Physical properties
Phase at STPsolid
Melting point1173 K ​(900 °C, ​1652 °F)[2]
Boiling point1743 K ​(1470 °C, ​2678 °F) (estimation)[3]
Density (near r.t.)15.1 g/cm3[2]
Atomic properties
Oxidation states+2, +3, +4, +5[4][5]
ElectronegativityPauling scale: 1.3[6]
Ionization energies
  • 1st: 608 kJ/mol[7]
Color lines in a spectral range
Spectral lines of californium
Other properties
Natural occurrencesynthetic
Crystal structure ​double hexagonal close-packed (dhcp)
Double hexagonal close packed crystal structure for californium
Mohs hardness3–4[8]
CAS Number7440-71-3[2]
History
Namingafter California, where it was discovered
DiscoveryLawrence Berkeley National Laboratory (1950)
Isotopes of californium
Main isotopes[9][10] Decay
abun­dance half-life (t1/2) mode pro­duct
248Cf synth 333.5 d α100% 244Cm
SF<0.01% –
249Cf synth 351 y α100% 245Cm
SF≪0.01% –
250Cf synth 13.08 y α99.9% 246Cm
SF0.08% –
251Cf synth 898 y α 247Cm
252Cf synth 2.645 y α96.9% 248Cm
SF3.09% –
253Cf synth 17.81 d β−99.7% 253Es
α0.31% 249Cm
254Cf synth 60.5 d SF99.7% –
α0.31% 250Cm
 Category: Californium
| references

Californium (/[invalid input: 'icon']ˌkæl[invalid input: 'ɨ']ˈfɔːrniəm/ KAL-ə-FOR-nee-əm) is a synthetic radioactive metallic chemical element in the actinide series with the symbol Cf and atomic number 98. The element was first produced in 1950 by bombarding curium with alpha particles (helium ions) at the University of California, Berkeley. It was the sixth transuranium element to be synthesized and is one of highest atomic mass elements to be produced in weighable amounts. The element was named for California and the University of California.

Californium is one of the few transuranium elements that have practical applications. Most of these applications exploit the property of certain isotopes of californium to emit neutrons. For example, californium can be used to help start up nuclear reactors, and is employed as a source of neutrons when studying materials with neutron diffraction and neutron spectroscopy. Element 118 was synthesized by bombarding californium-249 atoms with calcium-48 ions.

Characteristics

Physical properties

Weighable amounts of californium make it possible to determine some of its properties. Californium is a silvery white actinide metal[11] with an estimated melting point of 900 ±30°C and an estimated boiling point of 1475 °C.[12] Below 51 K californium metal is either ferromagnetic or ferrimagnetic, between 48 and 66 K it is antiferromagnetic, and above 160 K it is paramagnetic.[13]

The element has two crystalline forms under normal pressures: a double-hexagonal close-packed α form that exists below 900 °C with a density of 15.10 g/cm3 and a face-centered cubic β form with a density of 8.74 g/cm3.[14] At 48 GPa of pressure the β form transitions into an orthorhombic, alpha‐uranium structure.[15] This transition is due to the pressure-induced de-localization of the atom's 5 f electrons, which frees them to bond.[note 1] The resistance to uniform pressure, called the bulk modulus, of californium is 50 ± 5 GPa.[15]

Californium's enthalpy of sublimation—the amount of heat required to transition a substance from a solid to a gas—has been estimated as 163 kJ/mol and 197 kJ/mol.[16] The enthalpy change of solution of the α form is −576.1±3.1 kJ/mol in hydrochloric acid under standard conditions, which fits into a trend for transplutonium metals that started with americium of decreasing enthalpies with increasing atomic numbers.[13] The standard enthalpy of formation (ΔfH0) of Cf3+ (aq), −577±5 kJ/mol, was determined from the enthalpy of solution.[17] The large negative values indicate strong exothermic (energy releasing) reactions.

Chemical properties

Californium exhibits valences of 4, 3, or 2,[14] and its chemical properties are predicted to be similar to other 3+ actinide elements[18] and dysprosium.[19] The element slowly tarnishes in air at room temperature, with the rate increasing with added moisture.[14] Californium reacts when heated in the presence of hydrogen, nitrogen, or a chalcogen and oxidizes when warmed in air; reactions with dry hydrogen hydrides and aqueous mineral acids are rapid.[14] Only californium-249 is suitable for chemical study.[20]

Few californium compounds have been made and studied.[21] The only californium ion that is stable in aqueous solution is the californium(III) cation.[19] The other two oxidation states are IV (strong oxidizing agents) and II (strong reducing agents).[11] The element forms a water-soluble chloride, nitrate, perchlorate, and sulfate and is precipitated as a fluoride, oxalate or hydroxide.[18] If problems of availability of the element could be overcome, then CfBr2 and CfI2 would likely be stable.[22]

The III oxidation state is represented by californium(III) oxide (yellow-green, Cf2O3), californium(III) fluoride (bright green, CfF3) and californium(III) iodide (lemon yellow, CfI3).[11] Other +3 oxidation states include the sulfide and metallocene Cp3Cf.[23] Californium(IV) oxide (black brown, CfO2), californium(IV) fluoride (green, CfF4) represent the IV oxidation state. The II state is represented by californium(II) bromide (yellow, CfBr2) and californium(II) iodide (dark violet, CfI2).[11]

Compounds

Californium(IV) oxide (CfO2) is formed by oxidation at high pressure. It is a black-brown solid that has a cubic crystal structure with a lattice parameter of 531.0 ± 0.2 pm.[24] Californium(III) oxide has a melting point of 1750 °C and exists in two modifications, a body-centered cubic form and a monoclinic form, on either side of about 1400 °C.[24]

Californium(III) bromide (CfBr3) is a green solid with a monoclinic crystal structure.

Californium(III) chloride (CfCl3) is an emerald green compound with a hexagonal structure that can be prepared by combining Cf2O3 with hydrochloric acid at 500 °C.[25] CfCl3 is then used as a feeder stock to form the yellow-orange tri-iodide CfI3, which in turn can be reduced to the lavender-violet di-iodide CfI2.[26]

Californium(III) fluoride (CfF3) is a yellow-green solid with two temperature dependent crystalline structures; at lower temperatures CfF3 has a orthorhombic structure and at higher temperatures it has trigonal structure.[27] Californium(IV) fluoride (CfF4) is a bright green solid with a monoclinic crystal structure.[28]

Californium(II) iodide (CfI2) is a deep purple solid with a stable rhombohedral structure at room temperature and an unstable hexagonal structure.[29] Californium(III) iodide (CfI3) is a lemon-yellow and light green solid that has a rhombohedral structure and sublimes at ~800 °C.[29]

Californium(III) oxyfluoride (CfOCl) is prepared by hydrolysis of californium(III) fluoride (CfF3) at high temperature.[30] Californium(III) oxychloride (CfOCl) is prepared by hydrolysis of the hydrate of californium(III) chloride at 280–320 °C.[31]

Heating the sulfate in air at about 1200 °C and then reducing with hydrogen at 500 °C produces the sesquioxide (Cf2O3).[25] The hydroxide Cf(OH)3 and the trifluoride CfF3 are slightly soluble.[32]

Isotopes

Main article: Isotopes of californium

Twenty radioisotopes of californium have been characterized, the most stable being californium-251 with a half-life of 898 years, californium-249 with a half-life of 351 years, and californium-250 with a half-life of 13.08 years.[33] All of the remaining radioactive isotopes have half-lives that are shorter than 2.7 years, and the majority of these have half-lives shorter than 20 minutes.[33] The isotopes of californium range in mass number from 237 to 256.

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.[19] Although californium-251 has the longest half-life, its production yield is only 10% due to its high neutron capture and fission cross section.[34]

Californium-252 has a half-life of 2.645 years and is a very strong neutron emitter, making it extremely radioactive and harmful.[35][36][37][38][39] Californium-252 undergoes α-decay 96.9% of the time while the remaining 3.1% of decays are spontaneous fission.[33] One microgram spontaneously emits 2.314 million neutrons per second.[40]

History

The 60-inch-diameter (1,500 mm) cyclotron used to first synthesize californium

Californium was first synthesized at the University of California, Berkeley by the physics researchers Stanley G. Thompson, Kenneth Street, Jr., Albert Ghiorso, and Glenn T. Seaborg on or about February 9, 1950.[41] It was the sixth transuranium element to be discovered, and this team announced its discovery on March 17, 1950.[42][43][44]

To produce californium, a microgram-sized target of curium-242 was bombarded with 35 MeV alpha particles in the 60-inch-diameter (1,500 mm) cyclotron at Berkeley, California, which produced nuclei of californium-245 (half-life 44 minutes), plus one free neutron.[41]

242
96Cm
 + 4
2He
 → 245
98Cf
 + 1
0
n

Only about 5,000 atoms of californium were produced in this experiment.[45] The discoverers named the new element for California and also the University of California.[46][note 2] Californium metal was first prepared in 1974 by Haire and Baybarz from the reduction of californium(III) oxide with lanthanum metal.[47][note 3]

Weighable quantities of californium were first produced by long-duration irradiation of plutonium targets at the Materials Testing Reactor at the Idaho National Laboratory.[48] The high spontaneous fission rate of californium-252 was observed in these samples. The first experiment with californium in concentrated form occurred in 1958.[41] Californium-249 to −252 were isolated that same year from a sample of plutonium-239 that had been irradiated with neutrons in a nuclear reactor for five years.[11]

The High Flux Isotope Reactor (HFIR) at the Savannah River Site in South Carolina started producing small batches of californium in the 1960s.[49] The Atomic Energy Commission began selling, leasing, or lending small amounts of californium-252 to industrial and academic customers in the early 1970s for $10 per microgram;[40] an average of 150 mg of californium-252 were shipped each year from 1970 to 1990.[50]

Milligram-quantities of californium can only be made in specialized high-flux reactors; there are only two reactors operating that can efficiently produce it: the High Flux Isotope Reactor in the United States and the Research Institute of Atomic Reactors in Dimitrovgrad, Russia. By 1995, the HFIR nominally produced 502 grams of californium annually.[51] Plutonium supplied by the United Kingdom to the United States under the 1958 US-UK Mutual Defence Agreement was used for californium production.[52]

Occurrence

Californium is not known to occur naturally on the Earth but very minute amounts might exist in some uranium ores.[53] Compounds containing the element are produced in nuclear reactors but pure samples of the metal have not been made in particle accelerators.[21] Its use in mineral prospecting and in medical treatments and research means it can be found near facilities that use californium.[54] The element is fairly insoluble in water, but it adheres well to ordinary soil. Therefore, concentrations of it in the soil can be 500 times higher than in interstitial water.[53]

Fallout from atmospheric nuclear testing prior to 1980 contributed a small amount of californium to the environment.[53] Californium isotopes with mass numbers 249, 252, 253, and 254 were observed for the first time in the radioactive dust collected from the air after an explosion.[55] Californium is not a major radionuclide at United States Department of Energy legacy sites since it was not produced in large quantities.[53]

The element californium and its decay products may occur elsewhere in the universe. Electromagnetic emissions possibly caused by the decay of californium-254 are observed in the spectra of some supernovas.[56][57][19]

Production

See also: Nuclear fuel cycle

Californium-250 is produced by bombarding berkelium-249 with neutrons. This forms berkelium-250 which quickly beta decays to californium-250 in the following reaction:[58]

249
97Bk
(n,y)250
97Bk
 → 250
98Cf
 + β−

Bombardment of californium-250 with neutrons produces californium-251 and 252.[58]

Prolonged irradiation of americium, curium, and plutonium with neutrons produces milligram amounts of californium-252 and microgram amounts of californium-249.[25] As of 2006, curium isotopes 244 to 248 are irradiated by neutrons in special reactors to produce primarily californium-242 with lessor amounts of isotopes 249 to 255.[59]

Millionth gram quantities of californium-252 are available for commercial use through the U.S. Nuclear Regulatory Commission.[21] Only two sites produce californium-252; Oak Ridge National Laboratory near Knoxville, Tennessee, in the United States and the Research Institute of Atomic Reactors in Dmitrovgrad, Russia. As of 2003, the two sites produce 0.25 grams and 0.025 grams of californium-252 per year, respectively.[60]

Three californium isotopes with significant half-lives are produced, requiring a total of 14 neutron captures by uranium-238 without nuclear fission or alpha decay occurring during the process.[60]

Decay chain to produce californium-252

Applications

Energy spectrum of neutrons emitted by californium-252.[61]
Fifty-ton shipping cask built at Oak Ridge National Laboratory which can transport up to 1 gram of 252Cf.[62]

Californium-252 has a number of specialized applications as a strong neutron emitter; each microgram of fresh californium produces 139 million neutrons per minute.[40] This makes it useful as a neutron startup source for some nuclear reactors[14] and as a portable (non-reactor based) neutron source for neutron activation analysis to detect trace amounts of elements in samples.[63] Neutrons from californium are employed as a treatment of certain cervical and brain cancers where other radiation therapy is ineffective.[14] It is also used in educational applications since 1969 when the Georgia Institute of Technology received a loan of 119 mg of californium-252 from the Savannah River Plant.[64]

Neutron penetration into materials makes it useful in detection instruments such as fuel rod scanners;[14] neutron radiography of aircraft and weapons components to detect corrosion, bad welds, cracks and trapped moisture;[65] in airport neutron-activation detectors of explosives, and in portable metal detectors.[66] Neutron moisture gauges use californium-252 to find water and petroleum layers in oil wells, as a portable neutron source for gold and silver prospecting for on-the-spot analysis,[19] and to detect ground water movement.[67] In 1982, most californium-252 was used in reactor start-up (48.3%), fuel rod scanning (25.3%), or activation analysis (19.4%); by 1994 most californium-252 was used in neutron radiography (77.4%), with fuel rod scanning (12.1%) and reactor start-up (6.9%) highly important but distant secondary uses.[68]

Californium-251 has a very small critical mass (about 5 kg),[69] high lethality, and a relatively short period of toxic environmental irradiation. This low critical mass led to some exaggerated claims being made. In an article entitled "Facts and Fallacies of World War III" in the July, 1961 edition of Popular Science magazine, the claim was made that "A californium atomic bomb need be no bigger than a pistol bullet. You could build a hand-held six-shooter to fire bullets that would explode on contact with the force of 10 tons of TNT"[70]

In October 2006, researchers announced that three atoms of ununoctium (element 118) had been identified at the Joint Institute for Nuclear Research in Dubna, Russia, as the product of bombardment of californium-249 with calcium-48, making this the heaviest element ever synthesized.[71][72][73] Calibration and dosimetry, and fission fragment and half-life studies are other applications of californium.[74]

Precautions

Californium disrupts the body's ability to form red blood cells by bio-accumulating in skeletal tissue.[75] The element plays no natural biological role in any organism due to its intense radioactivity and low concentration in the environment.[54]

Californium can enter the body from ingesting contaminated food or drinks or by breathing air with suspended particles of the element. Once in the body, only 0.05% of the californium will reach the bloodstream.[53] About 65% of that californium will be deposited in the skeleton, 25% in the liver, and the rest in other organs, or is excreted, mainly in urine.[53] Half of the californium deposited in the skeleton and liver are gone in 50 and 20 years, respectively.[53] Californium in the skeleton adheres to bone surfaces before slowly migrating throughout the bone.

The element is most dangerous if taken into the body but gamma rays emitted by californium-249 and californium-251 cause external tissue damage.[53] Ionizing radiation emitted by californium on bone and in the liver can cause cancer. Two to six out of 100,000 people are estimated to die of a fatal cancer if they were continuously exposed to soil with an initial average concentration of 1 pCi/g of californium-251 and californium-249, respectively.[53]

Notes

  1. ^ The three lower mass transplutonium elements require much less pressure to de-localize their 5f electrons.(Haire 2006, p. 1522)
  2. ^ This name was a break from the convention that had been used for the elements 95 to 97, which drew their inspiration from how the elements directly above them in the periodic table were named. Europium, in the sixth period directly above element 95, was named for the continent it was discovered on, so element 95 was named americium. Element 96 was named for Marie Curie and Pierre Curie as an analog to the naming of gadolinium, which was named for the scientist and engineer Johan Gadolin. Terbium was named for the city it was discovered in, so element 97 was named berkelium. However, the element directly above element 98 in the periodic table, dysprosium, has a name that simply means "hard to get at" so the researchers decided to set-aside the informal naming convention.(Heiserman 1992, p. 347) They added that "the best we can do is to point out [that] ... searchers a century ago found it difficult to get to California."(Weeks 1968, p. 848)
  3. ^ In 1975, another paper stated that the californium metal prepared the year before was hexagonal Cf2O2S and face-centered cubic CfS. Zachariasen, W. (1975). "On Californium Metal". Inorganic Nuclear Chemistry. 37 (6): 1441–1442. doi:10.1016/0022-1902(75)80787-1. The 1974 work was confirmed in 1976 and work on californium metal continued.(Haire 2006, p. 1519) Several reference books still say that californium metal has not been prepared.

References

  1. ^ CRC 2006, p. 1.14.
  2. ^ a b c CRC 2006, p. 4.56.
  3. ^ Joseph Jacob Katz; Glenn Theodore Seaborg; Lester R. Morss (1986). The Chemistry of the actinide elements. Chapman and Hall. p. 1038. ISBN 9780412273704. Retrieved 11 July 2011.
  4. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1265. ISBN 978-0-08-037941-8.
  5. ^ Kovács, Attila; Dau, Phuong D.; Marçalo, Joaquim; Gibson, John K. (2018). "Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States". Inorg. Chem. 57 (15). American Chemical Society: 9453–9467. doi:10.1021/acs.inorgchem.8b01450. OSTI 1631597. PMID 30040397. S2CID 51717837.
  6. ^ Emsley 1998, p. 50.
  7. ^ CRC 2006, p. 10.204.
  8. ^ CRC 1991, p. 254.
  9. ^ CRC 2006, p. 11.196.
  10. ^ Sonzogni, Alejandro A. (Database Manager), ed. (2008). "Chart of Nuclides". National Nuclear Data Center, Brookhaven National Laboratory. Retrieved 1 March 2010.
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  12. ^ Haire 2006, pp. 1522, 1523.
  13. ^ a b Haire 2006, p. 1525.
  14. ^ a b c d e f g O'Neil 2006, p. 1713.
  15. ^ a b Haire 2006, p. 1522.
  16. ^ Haire 2006, p. 1523.
  17. ^ Fugere, J. (1984). "The Enthalpy of Solution of Californium Metal and the Standard Enthalpy of Formation of Cf3+ (aq)". Journal of the Less Common Metals. 98 (2): 315–321. doi:10.1016/0022-5088 (84) 90305-9. {{cite journal}}: Check |doi= value (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
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  19. ^ a b c d e CRC 2006, p. 4-8.
  20. ^ Emeleus, H. J. (1987). Advances in Inorganic Chemistry. Academic Press. p. 33. ISBN 9780120236312.
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  22. ^ Greenwood 1997, p. 1272.
  23. ^ Cotton 1999, p. 1163.
  24. ^ a b Baybarz, R. D. (1972). "On the Californium Oxide System". Inorganic and Nuclear Chemistry. 34 (2): 557–565. doi:10.1016/0022-1902(72)80435-4. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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  26. ^ Cotton, Simon (2006). Lanthanide and Actinide Chemistry. West Sussex, England: John Wiley & Sons. p. 168. ISBN 047001005. {{cite book}}: Check |isbn= value: length (help)
  27. ^ Stevenson, J. N (1973). "The Trigonal and Orthorhombic Crystal Structures of CfF3 and their Temperature Relationship". Inorganic Nuclear Chemistry. 35 (10): 3481–3486. doi:10.1016/0022-1902(73)80356-2. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  28. ^ Chang, C-T. P. (1990). "Magnetic Susceptibility of Californium Fluorides". Physical Review B. 41 (13): 9045–9048. doi:10.1103/PhysRevB.41.9045. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  29. ^ a b Macintyre, J. E. (1992). Dictionary of inorganic compounds. Chapman and Hall, CRC Press. p. 2826. ISBN 978-0-412-30120-9. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  30. ^ Peterson, J. R. (1968). "Preparation and Crystal Structure of Californium Oxyfluoride, CfOF". Inorganic Nuclear Chemistry. 30 (11): 2955–2958. doi:10.1016/0022-1902(68)80155-1. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  31. ^ Copeland, J. C. (1969). "Crystallography of the Compounds of Californium. II. Crystal Structure and Lattice Parameters of Californium Oxychloride and Californium Sesquioxide". Inorganic Nuclear Chemistry. 31 (3): 733–740. doi:10.1016/0022-1902(69)80020-5. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |unused_data= ignored (help)
  32. ^ Cuningham 1968, p. 105.
  33. ^ a b c NNDC 2008.
  34. ^ Haire 2006, p. 1504.
  35. ^ Hicks, D. A.; Ise, John; Pyle, Robert V. (1955). "Multiplicity of Neutrons from the Spontaneous Fission of Californium-252". Physical Review. 97 (2): 564–565. doi:10.1103/PhysRev.97.564.
  36. ^ Hicks, D. A.; Ise, John; Pyle, Robert V. (1955). "Spontaneous-Fission Neutrons of Californium-252 and Curium-244". Physical Review. 98 (5): 1521–1523. doi:10.1103/PhysRev.98.1521.
  37. ^ Hjalmar, E.; Slätis, H. and Thompson, S.G. (1955). "Energy Spectrum of Neutrons from Spontaneous Fission of Californium-252". Physical Review. 100 (5): 1542–1543. doi:10.1103/PhysRev.100.1542.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  38. ^ United States Patent 7118524: "Dosimetry for californium-252 (252) neutron-emitting brachytherapy sources and encapsulation, storage, and clinical delivery thereof" bei Freepatentsonline.com.
  39. ^ Dillon, M. B.; et al. (2004-03-18). "The NARAC Emergency Response Guide to Initial Airborne Hazard Estimates" (PDF). National Atmospheric Release Advisory Center. UCRL:UCRL-TM-202990. Retrieved 2008-11-14. {{cite web}}: Explicit use of et al. in: |author= (help)
  40. ^ a b c R. C. Martin, J. B. Knauer, P. A. Balo (1999). "Production, Distribution, and Applications of Californium-252 Neutron Sources". Applied Radiation and Isotopes. 53 (4–5): 785. doi:10.1016/S0969-8043(00)00214-1. PMID 11003521.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  41. ^ a b c Cunningham 1968, p. 103.
  42. ^ Thompson, S. G.; et al. (1950). "Element 98". Physical Review. 78: 298. doi:10.1103/PhysRev.78.298.2. {{cite journal}}: Explicit use of et al. in: |author= (help)
  43. ^ Thompson, S. G.; et al. (1950). "The New Element Californium (Atomic Number 98)" (PDF). Physical Review. 80: 790. doi:10.1103/PhysRev.80.790. {{cite journal}}: Explicit use of et al. in: |author= (help)
  44. ^ Street, K., Jr.; Thompson, S. G. and Seaborg, G. T. (1950). "Chemical Properties of Californium". J. Am. Chem. Soc. 72: 4832. doi:10.1021/ja01166a528.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  45. ^ Seaborg, G. T. (1996). Adloff, J. P. (ed.). One Hundred Years after the Discovery of Radioactivity. Oldenbourg Wissenschaftsverlag. p. 82. ISBN 9783486642520.
  46. ^ Weeks 1968, p. 849.
  47. ^ Haire 2006, p. 1519.
  48. ^ Diamond, H.; Magnusson, L. B.; Mech, J. F.; Stevens, C. M.; Friedman, A. M.; Studier, M. H.; Fields, P. R.; Huizenga, J. R. (1954). "Identification of Californium Isotopes 249, 250, 251, and 252 from Pile-Irradiated Plutonium". Phys Rev. 94 (4): 1083. doi:10.1103/PhysRev.94.1083.
  49. ^ "The High Flux Isotope Reactor". Oak Ridge National Laboratory. Retrieved 2010-08-22.
  50. ^ Osborne-Lee 1995, p. 6.
  51. ^ Osborne-Lee 1995, p. 11.
  52. ^ "Plutonium and Aldermaston – an historical account" (PDF). UK Ministry of Defence. 2001-09-04. Archived from the original (PDF) on 2006-12-13. Retrieved 2007-03-15.
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  54. ^ a b Emsley 2001, p. 90.
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  57. ^ Baade, W.; et al. (1956). "Supernovae and Californium 254". Publications of the Astronomical Society of the Pacific. 68: 296. {{cite journal}}: Explicit use of et al. in: |author= (help)
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  71. ^ Oganessian, Yu. Ts.; et al. (2006). "Synthesis of the isotopes of elements 118 and 116 in the californium-249 and 245Cm+48Ca fusion reactions". Physical Review C. 74: 044602–044611. doi:10.1103/PhysRevC.74.044602. {{cite journal}}: Explicit use of et al. in: |author= (help)
  72. ^ Sanderson, K. (2006-10-17). "Heaviest element made – again". nature@news.com. Nature. doi:10.1038/news061016-4.
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  • CRC contributors (2006). David R. Lide (ed.). Handbook of Chemistry and Physics (87th ed.). Boca Raton, Florida: CRC Press, Taylor & Francis Group. ISBN 0-8493-0487-3. {{cite book}}: |author= has generic name (help)
  • Cunningham, B. B. (1968). "Californium". In Clifford A. Hampel (editor) (ed.). The Encyclopedia of the Chemical Elements. New York: Reinhold Book Corporation. LCCN 68-29938. {{cite book}}: |editor= has generic name (help); Cite has empty unknown parameter: |coauthors= (help)CS1 maint: ref duplicates default (link)
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  • Haire, Richard G. (2006). "Californium". In Morss; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Springer. ISBN 1402035551.{{cite book}}: CS1 maint: ref duplicates default (link)
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  • O'Neil, Marydale J.; Heckelman, Patricia E.; Roman, Cherie B., eds. (2006). The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (14th ed.). Whitehouse Station, NJ, USA: Merck Research Laboratories, Merck & Co., Inc. ISBN 0-911910-00-X.
  • Osborne-Lee, I.W. (1995). "Californium-252: A Remarkable Versatile Radioisotope". Oak Ridge Technical Report ORNL/TM-12706. doi:10.2172/205871. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: ref duplicates default (link)
  • Seaborg, Glenn T. (2004). "Californium". In Geller, Elizabeth (ed.). Concise Encyclopedia of Chemistry. New York City: McGraw-Hill. ISBN 0-07-143953-6.{{cite encyclopedia}}: CS1 maint: ref duplicates default (link)
  • Weeks, Mary Elvira (1968). "21: Modern Alchemy". Discovery of the Elements. Easton, PA: Journal of Chemical Education. pp. 848–850. ISBN 0766138720. LCCCN 68-15217. {{cite book}}: Unknown parameter |coauthor= ignored (|author= suggested) (help)CS1 maint: ref duplicates default (link)

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