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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 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 the highest atomic mass elements to be produced in amounts large enough to see with the unaided eye. The element was named for California and the University of California.

The element has two crystalline forms under normal pressure, one above 900 °C and one below; a third form exists at high pressure. Californium slowly tarnishes in air at room temperature. It disrupts the body's ability to form red blood cells by bio-accumulating in skeletal tissue. The most stable of californium's twenty isotopes is californium-251, which has a half life of 898 years. Californium-252, whose half life is 2.645 years, is the most common isotope used and is produced at the Oak Ridge National Laboratory in the U.S. state of Tennessee and the Research Institute of Atomic Reactors in Russia.

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

Unlike many other elements heavier than plutonium, enough californium can be collected 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 (it acts like a magnet), between 48 and 66 K it is antiferromagnetic (an intermediate state), and above 160 K it is paramagnetic (external magnetic fields can make it magnetic).[13]

The element has two crystalline forms under normal pressures: a double-hexagonal close-packed form dubbed alpha (α) that exists below 900 °C with a density of 15.10 g/cm3 and a face-centered cubic form designated beta (β) that exists above 900 °C with a density of 8.74 g/cm3.[14] At 48 GPa of pressure the β form changes into an orthorhombic crystal system due to de-localization of the atom's 5f electrons, which frees them to bond.[15][note 1] The resistance to uniform pressure, called the bulk modulus, of californium is 50 ± 5 GPa, which is similar to trivalent lanthanide metals but smaller than more familiar metals, such as aluminium (70 GPa).[15]

Chemical properties and compounds

Californium exhibits valences of 4, 3, or 2, indicating the number of chemical bonds one atom of the element can form.[14] Its chemical properties are predicted to be similar to other 3+ valence actinide elements[16] and the element dysprosium, which is the lanthanide above californium in the periodic table.[17] The element slowly tarnishes in air at room temperature, with the rate increasing with added moisture.[14] Californium reacts when heated with hydrogen, nitrogen, or a chalcogen (oxygen family element); reactions with dry hydrogen and aqueous mineral acids are rapid.[14]

Few californium compounds have been made and studied.[18] The only californium ion that is stable in aqueous solutions is the californium(III) cation.[17] 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.[16] If problems of availability of the element could be overcome, then CfBr2 and CfI2 would likely be stable.[19]

The +3 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.[20] 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]

Further information: [[:Compounds of californium]]

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.[21] All 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.[21] The isotopes of californium range in mass number from 237 to 256.[21]

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.[17] Although californium-251 has the longest half-life, its production yield is only 10% due to its habit of collecting neutrons (high neutron capture) and tendency to interact with other particles (high cross section).[22]

Californium-252 has a half-life of 2.645 years and is a very strong neutron emitter, making it extremely radioactive and harmful.[23][24][25] Californium-252 undergoes alpha decay 96.9% of the time to form curium-248 while the remaining 3.1% of decays are spontaneous fission.[21] One microgram spontaneously emits 2.3 million neutrons per second.[26] Fission neutrons of californium-252 have an energy range of 0 to 13 MeV with a mean value of 2.3 MeV and a most probable value of 1 MeV.[27] Most of the other isotopes of californium decay to isotopes of curium ( Z = 96) via alpha decay.[21]

History

Large pieces of equipment with a man standing nearby.
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.[28] It was the sixth transuranium element to be discovered; the team announced its discovery on March 17, 1950.[29][30][31]

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.[28]

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

Only about 5,000 atoms of californium were produced in this experiment.[32] The discoverers named the new element for California and also the University of California.[33] [note 2]

Weighable quantities of californium were first produced by long-duration irradiation of plutonium targets at the Materials Testing Reactor at the Idaho National Laboratory.[36] The high spontaneous fission rate of californium-252 was observed in these samples. The first experiment with californium in concentrated form occurred in 1958.[28] 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 Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee started producing small batches of californium in the 1960s.[37] By 1995, the HFIR nominally produced 500 milligrams of californium annually.[38] Plutonium supplied by the United Kingdom to the United States under the 1958 US-UK Mutual Defence Agreement was used for californium production.[39]

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;[26] an average of 150 mg of californium-252 were shipped each year from 1970 to 1990.[40] Californium metal was first prepared in 1974 by Haire and Baybarz who reduced californium(III) oxide with lanthanum metal to obtain microgram amounts of sub-micrometer thick films.[41][42][note 3]

Occurrence

Californium is not known to occur naturally on Earth, but very minute amounts might exist due to various nucleosynthesis reactions in uranium ores.[44] Traces of californium can be found near facilities that use the element in mineral prospecting and in medical treatments.[45] The element is fairly insoluble in water, but it adheres well to ordinary soil; concentrations of it in the soil can be 500 times higher than in the water surrounding the soil particles.[44]

Fallout from atmospheric nuclear testing prior to 1980 contributed a small amount of californium to the environment.[44] Californium isotopes with mass numbers 249, 252, 253, and 254 have been observed in the radioactive dust collected from the air after a nuclear explosion.[46] Californium is not a major radionuclide at United States Department of Energy legacy sites since it was not produced in large quantities.[44] [note 4]

Production

See also: Nuclear fuel cycle

Californium is produced in nuclear reactors and particle accelerators.[18] Californium-250 is made by bombarding berkelium-249 with neutrons, forming berkelium-250 which, in turn, quickly beta decays to californium-250 in the following reaction:[51]

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

Bombardment of californium-250 with neutrons produces californium-251 and californium-252.[51]

Prolonged irradiation of americium, curium, and plutonium with neutrons produces milligram amounts of californium-252 and microgram amounts of californium-249.[52] As of 2006, curium isotopes 244 to 248 are irradiated by neutrons in special reactors to produce primarily californium-252 with lesser amounts of isotopes 249 to 255.[53]

Microgram quantities of californium-252 are available for commercial use through the U.S. Nuclear Regulatory Commission.[18] 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 Dimitrovgrad, Russia. As of 2003, the two sites produce 0.25 grams and 0.025 grams of californium-252 per year, respectively.[54]

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.[54] Californium-253 is at the end of a decay chain that starts with uranium-238, includes several isotopes of plutonium, americium, curium, and berkelium and the californium isotopes 249 to 253 (see diagram).

A complex flow diagram showing various isotopes.
Decay chain to produce californium-252

Applications

Large conical structure on a pulley with a man on top and two near the base.
Fifty-ton shipping cask built at Oak Ridge National Laboratory which can transport up to 1 gram of 252Cf.[55]

Californium is the heaviest metal known at this time that has a practical use outside of research laboratories; einsteinium and all other elements above it have sufficiently short half-lifes that they have no use except the production of heavier elements.

Californium-252 has a number of specialized applications as a strong neutron emitter; each microgram of fresh californium produces 139 million neutrons per minute.[26] This property makes californium 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.[56] Neutrons from californium are employed as a treatment of certain cervical and brain cancers where other radiation therapy is ineffective.[14] It has been used in educational applications since 1969 when the Georgia Institute of Technology received a loan of 119 µg of californium-252 from the Savannah River Plant.[57]

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;[58] and in portable metal detectors.[59] 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,[17] and to detect ground water movement.[60] 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%) as important but distant secondary uses.[61]

Californium-251 has a very small critical mass (about 5 kg),[62] high lethality, and a relatively short period of toxic environmental irradiation. The low critical mass of californium led to some exaggerated claims about possible uses for the element. 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"[63]

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 it the heaviest element ever synthesized. The target for this experiment contained about 10 mg of californium-249 deposited on a titanium foil of 32 cm2 area.[64][65][66] Calibration, dosimetry, and fission fragment and half-life studies are other applications of californium.[67]

Precautions

Californium disrupts the body's ability to form red blood cells by bio-accumulating in skeletal tissue.[68] The element plays no natural biological role in any organism due to its intense radioactivity and low concentration in the environment.[45]

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. About 65% of that californium will be deposited in the skeleton, 25% in the liver, and the rest in other organs, or excreted, mainly in urine. Half of the californium deposited in the skeleton and liver are gone in 50 and 20 years, respectively. Californium in the skeleton adheres to bone surfaces before slowly migrating throughout the bone.[44]

The element is most dangerous if taken into the body. In addition, californium-249 and californium-251 can cause tissue damage externally, through gamma ray emission.[44] Ionizing radiation emitted by californium on bone and in the liver can cause cancer. An incidence of two to six fatal cancers are expected to occur for every 100,000 people continuously exposed to soil with an initial average concentration of 1 pCi/g of californium-251 and californium-249, respectively.[44]

Notes

  1. ^ The three lower mass transplutonium elements —americium, curium, and berkelium — require much less pressure to delocalize their 5f electrons.[15]
  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.[34] They added that "the best we can do is to point out [that] ... searchers a century ago found it difficult to get to California."[35]
  3. ^ In 1975, another paper stated that the californium metal prepared the year before was hexagonal Cf2O2S and face-centered cubic CfS.[43] The 1974 work was confirmed in 1976 and work on californium metal continued.[41] Several reference books still say that californium metal has not been prepared.
  4. ^ A 1956 paper reported that electromagnetic emissions possibly caused by the decay of californium-254 were observed in the spectra of some supernovae.[47][48] This conclusion was challenged in 1959[49] and was subsequently regarded as incorrect due to a lack of californium-related decay products.[50]

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.
  11. ^ a b c d e Jakubke 1994, p. 166.
  12. ^ Haire 2006, pp. 1522, 1523.
  13. ^ Haire 2006, p. 1525.
  14. ^ a b c d e f g O'Neil 2006, p. 1713.
  15. ^ a b c Haire 2006, p. 1522.
  16. ^ a b Seaborg 2004.
  17. ^ a b c d CRC 2006, p. 4-8.
  18. ^ a b c Krebs, Robert (2006). The History and Use of our Earth's Chemical Elements: A Reference Guide. Westport, Connecticut: Greenwood Publishing Group. pp. 327–328. ISBN 978-0-313-33438-2.
  19. ^ Greenwood 1997, p. 1272.
  20. ^ Cotton 1999, p. 1163.
  21. ^ a b c d e NNDC 2008.
  22. ^ Haire 2006, p. 1504.
  23. ^ 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.
  24. ^ 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.
  25. ^ Hjalmar, E.; Slätis, H.; 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)
  26. ^ 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)
  27. ^ Dicello, J. F. (1972). "Radiation Quality of Californium-252". Physics in Medicine and Biology. 17 (3): 345. doi:10.1088/0031-9155/17/3/301. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  28. ^ a b c Cunningham 1968, p. 103.
  29. ^ Thompson, S. G. (1950). "Element 98". Physical Review. 78: 298. doi:10.1103/PhysRev.78.298.2. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  30. ^ Thompson, S. G. (1950). "The New Element Californium (Atomic Number 98)" (PDF). Physical Review. 80: 790. doi:10.1103/PhysRev.80.790. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  31. ^ Street, K., Jr.; Thompson, S. G.; Seaborg, G. T. (1950). "Chemical Properties of Californium" (PDF). Journal of the American Chemical Society. 72: 4832. doi:10.1021/ja01166a528.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  32. ^ Seaborg, G. T. (1996). Adloff, J. P. (ed.). One Hundred Years after the Discovery of Radioactivity. Oldenbourg Wissenschaftsverlag. p. 82. ISBN 9783486642520.
  33. ^ Weeks 1968, p. 849.
  34. ^ Heiserman 1992, p. 347.
  35. ^ Weeks 1968, p. 848.
  36. ^ Diamond, H.; Magnusson, L. B.; Mech, J. F. (1954). "Identification of Californium Isotopes 249, 250, 251, and 252 from Pile-Irradiated Plutonium". Physical Review. 94 (4): 1083. doi:10.1103/PhysRev.94.1083. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  37. ^ "The High Flux Isotope Reactor". Oak Ridge National Laboratory. Retrieved 2010-08-22.
  38. ^ Osborne-Lee 1995, p. 11.
  39. ^ "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.
  40. ^ Osborne-Lee 1995, p. 6.
  41. ^ a b Haire 2006, p. 1519.
  42. ^ Haire, R.G.; Baybarz, R.D. (1974). "Crystal structure and melting point of californium metal☆". Journal of Inorganic and Nuclear Chemistry. 36: 1295. doi:10.1016/0022-1902(74)80067-9.
  43. ^ Zachariasen, W. (1975). "On Californium Metal". Inorganic and Nuclear Chemistry. 37 (6): 1441–1442. doi:10.1016/0022-1902(75)80787-1.
  44. ^ a b c d e f g ANL contributors (August 2005). Human Health Fact Sheet: Californium (PDF). Argonne National Laboratory. {{cite book}}: |author= has generic name (help)
  45. ^ a b Emsley 2001, p. 90.
  46. ^ Fields, P. R.; Studier, M. H.; Diamond, H. (1956). "Transplutonium Elements in Thermonuclear Test Debris". Physical Review. 102 (1): 180–182. doi:10.1103/PhysRev.102.180. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  47. ^ Burbidge, G. R.; Hoyle, F.; Burbidge, E. (1956). "Californium-254 and Supernovae" (PDF). Physical Review. 103: 1145. doi:10.1103/PhysRev.103.1145. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  48. ^ Baade, W.; Burbidge, R.; Hoyle, F. (1956). "Supernovae and Californium 254". Publications of the Astronomical Society of the Pacific. 68: 296. Bibcode:1956PASP...68..296B.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  49. ^ Anders, E. (1959). "Californium-254, Iron-59, and Supernovae of Type I". Astrophysical Journal. 129: 327. Bibcode:1959ApJ...129..327A. doi:10.1086/146624.
  50. ^ Ruiz-Lapuente, P. (1996). Thermonuclear supernovae. Springer Science+Business Media. p. 274. ISBN 079234359X. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  51. ^ a b Heiserman 1992, p. 348.
  52. ^ Cunningham 1968, p. 105.
  53. ^ Haire 2006, p. 1503.
  54. ^ a b National Research Council (U.S.). Committee on Radiation Source Use and Replacement (2008). Radiation Source Use and Replacement: Abbreviated Version. Washington, D.C.: National Academies Press. p. 33.
  55. ^ Seaborg, G.T. (1994). Modern alchemy: selected papers of Glenn T. Seaborg. Singapore: World Scientific. p. 245. ISBN 9810214405.
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  57. ^ Osborne-Lee 1995, p. 33.
  58. ^ Osborne-Lee 1995, pp. 26–27.
  59. ^ "Will you be 'mine'? Physics key to detection". Pacific Northwest National Laboratory. 2000-10-25. Archived from the original on 2007-02-18. Retrieved 2007-03-21.
  60. ^ Davis, S. N.; Thompson, Glenn M.; Bentley, Harold W.; Stiles, Gary (2006). "Ground-Water Tracers — A Short Review". Ground Water. 18 (1): 14–23. doi:10.1111/j.1745-6584.1980.tb03366.x.
  61. ^ Osborne-Lee 1995, p. 12.
  62. ^ "Evaluation of nuclear criticality safety data and limits for actinides in transport" (PDF). Institut de Radioprotection et de Sûreté Nucléaire. p. 16. Retrieved 2010-12-20.
  63. ^ Popular Science. 179 (1): 180. July 1961. ISSN 0161-7370. {{cite journal}}: Missing or empty |title= (help)
  64. ^ Oganessian, Yu. Ts. (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}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  65. ^ Sanderson, K. (2006-10-17). "Heaviest element made – again". Nature News. Nature. doi:10.1038/news061016-4.
  66. ^ Schewe, P. (2006-10-17). "Elements 116 and 118 Are Discovered". Physics News Update. American Institute of Physics. Retrieved 2006-10-19. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  67. ^ Osborne-Lee 1995, p. 34.
  68. ^ Cunningham 1968, p. 106.

Bibliography

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Look up californium in Wiktionary, the free dictionary.

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