Californium

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98 berkelium ← californium → einsteinium Dy ↑ Cf ↓ (Uqo) Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	californium, Cf, 98
Element category	actinides
Group, Period, Block	n/a, 7, f
Appearance	silvery
Standard atomic weight	(251)  g·mol−1
Electron configuration	[Rn] 5f10 7s2
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)
Boiling point	1743 K (1470 °C, 2678 °F)
Atomic properties
Oxidation states	2, 3, 4
Electronegativity	1.3 (Pauling scale)
Ionization energies	1st: 608 kJ/mol
Miscellaneous
CAS registry number	7440-71-3
Most-stable isotopes
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 (pronounced /ˌkælɨˈfɔrniəm/) is a metallic chemical element with the symbol Cf and atomic number 98. A radioactive transuranic element, californium is used in starting nuclear reactors, optimizing coal-fired power plants and cement production facilities (via online analyzers), medical treatment of cancer, and oil exploration via down hole well logging. It was first produced by bombarding curium with alpha particles (helium ions).

Contents 1 History 2 Isotopes 3 Occurrence 3.1 Natural occurrence 3.2 Fallout 4 Characteristics 5 Nuclear fuel cycle 6 Applications 6.1 General 6.2 Military 7 References 8 Literature 9 External links

[edit] History

Californium was first synthesized at the University of California, Berkeley by 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.^[1][2][3] They named it after the U.S. state of California and the University of California, Berkeley. Unlike the names for the elements 95 to 97, this name did not reflect the chemical homology of element 98 to its corresponding sixth-period element, dysprosium (No. 66).^[2]

To produce element 98, the team bombarded a microgram-sized target of ²⁴²Cm with 35 MeV alpha particles in the 60-inch (1.52 m) Berkeley cyclotron, which produced atoms of ²⁴⁵Cf (half-life 44 minutes) and a free neutron.

24296Cm + 42He → 24598Cf + 10n

Only 8 grams of ²⁵²Cf have been made in the western world since its discovery by Seaborg in 1950.^{[citation needed]} Plutonium supplied by the United Kingdom to the U.S. under the 1958 US-UK Mutual Defence Agreement was used for californium production.^[4]

[edit] Isotopes

Twenty 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 u (²³⁷Cf) to 256.093 u (²⁵⁶Cf).

²⁵²Cf has a half life of 2.645 years. ²⁵²Cf undergoes α-decay 96.9% of the time while the remaining 3.1% of decays are spontaneous fission. Each spontaneous fission decay emits an average of 3.77 neutrons per fission. ²⁵⁴Cf decays nearly quantitatively by spontaneous fission with a half-life of 60.5 days. Both materials can be used as a neutron source.

[edit] Occurrence

[edit] 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.^[6][7][8][9]

[edit] Fallout

On November 1, 1952, the fallout of the United States hydrogen bomb test Ivy Mike contained plutonium, californium, einsteinium, and other transuranium elements. The isotopes ²⁴⁹Cf, ²⁵²Cf, ²⁵³Cf, and ²⁵⁴Cf were observed for the first time in the debris from the explosion.^[10]

[edit] Characteristics

Weighable amounts of californium make it possible to determine some of its properties using macroscopic quantities.

²⁵²Cf (2.645-year half-life) is a very strong neutron emitter and is thus extremely radioactive and harmful.^{[11][12][13][14][15]} (one microgram spontaneously emits 2,314 million neutrons per second^[16]). 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 (Cf₂O₃), californium trichloride (CfCl₃) and californium oxychloride (CfOCl). The only californium ion that is stable in aqueous solution is the californium(III) cation.

[edit] Nuclear fuel cycle

Californium is produced by neutron capture on berkelium-249. Three californium isotopes with significant halflives are produced, requiring a total of 12 to 14 neutron captures on uranium-238 without nuclear fission or alpha decay. Their neutron cross sections are:

	Capture		Fission		HL
	Th	RI	Th	RI	(a)
250Cf	2000	12000			13.08
251Cf	2900	1600	4800	5500	898
252Cf	20	44	32	1100	2.645

Thus ²⁵⁰Cf and ²⁵¹Cf will be transmuted fairly quickly, with the majority fissioning at mass 251, but with a large fraction surviving to become ²⁵²Cf; the ²⁵²Cf however will not be transmuted or destroyed quickly in a well-thermalized reactor.

²⁵²Cf has a relatively high rate of spontaneous fission. Although still much less likely than alpha decay, this makes californium a significant neutron radiation emitter. MOX fuel containing enough curium would likely contain enough californium after use to preclude manual handling of the spent fuel or its nuclear reprocessing products with a glove box that protects against alpha and beta radiation but not against gamma radiation and especially neutron radiation.

[edit] Applications

[edit] General

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:^[17][18][19]

• 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
• portable metal detectors^[20]
• 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
• ²⁵²Cf is used to detect ground water movement.^[21]

In October 2006 it was announced that three atoms ununoctium (element 118) had been identified at the Joint Institute for Nuclear Research in Dubna as the product of bombardment of californium-249 with calcium-48 ,^[22][23][24] making this the heaviest element ever synthesized.

[edit] Military

²⁵¹Cf is famous for having a very small critical mass of 5 kg,^[25] 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. 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.

[edit] References

[edit] Literature

• Guide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1

[edit] External links

Wikimedia Commons has media related to: Californium

Look up californium in Wiktionary, the free dictionary.

• WebElements.com - Californium
• NuclearWeaponArchive.org - Californium
• It's Elemental - Californium
• Hazardous Substances Databank – Californium, Radioactive

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