Isotopes of californium

Californium (₉₈Cf) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was ²⁴⁵Cf in 1950. There are 20 known radioisotopes ranging from ²³⁷Cf to ²⁵⁶Cf and one nuclear isomer, ^249mCf. The longest-lived isotope is ²⁵¹Cf with a half-life of 898 years.

Main isotopes of californium (₉₈Cf)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^248Cf syn 333.5 d α (100%) ^244Cm SF (2.9×10^−3%) – ^249Cf syn 351 y α (100%) ^245Cm SF (5.0×10^−7%) – ^250Cf syn 13.08 y α (99.92%) ^246Cm SF (0.08%) – ^251Cf syn 898 y α ^247Cm ^252Cf syn 2.645 y α (96.91%) ^248Cm SF (3.09%) – ^253Cf syn 17.81 d β^− (99.69%) ^253Es α (0.31%) ^249Cm ^254Cf syn 60.5 d SF (99.69%) – α (0.31%) ^250Cm

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life	Decay mode [n 4]	Daughter isotope	Spin and parity [n 5][n 6]
	Excitation energy
^237Cf	98	139	237.06207(54)#	2.1(3) s	SF	(various)	5/2+#
					β^+	^237Bk
					α	^233Cm
^238Cf	98	140	238.06141(43)#	21.1(13) ms	SF[n 7]	(various)	0+
					β^+ (rare)	^238Bk
					α (rare)	^234Cm
^239Cf	98	141	239.06242(23)#	60(30) s [39(+37−12) s]	α	^235Cm	5/2+#
					β^+ (rare)	^239Bk
^240Cf	98	142	240.06230(22)#	1.06(15) min	α (98%)	^236Cm	0+
					SF (2%)	(various)
					β^+ (rare)	^240Bk
^241Cf	98	143	241.06373(27)#	3.78(70) min	β^+ (75%)	^241Bk	7/2−#
					α (25%)	^237Cm
^242Cf	98	144	242.06370(4)	3.49(15) min	α (80%)	^238Cm	0+
					β^+ (20%)	^242Bk
					SF (.014%)	(various)
^243Cf	98	145	243.06543(15)#	10.7(5) min	β^+ (86%)	^243Bk	(1/2+)
					α (14%)	^239Cm
^244Cf	98	146	244.066001(3)	19.4(6) min	α (99%)	^240Cm	0+
					EC (1%)	^244Bk
^245Cf	98	147	245.068049(3)	45.0(15) min	β^+ (64%)	^245Bk	(5/2+)
					α (36%)	^241Cm
^246Cf	98	148	246.0688053(22)	35.7(5) h	α	^242Cm	0+
					EC (5×10^−4%)	^246Bk
					SF (2×10^−4%)	(various)
^247Cf	98	149	247.071001(9)	3.11(3) h	EC (99.96%)	^247Bk	(7/2+)#
					α (.04%)	^243Cm
^248Cf	98	150	248.072185(6)	333.5(28) d	α (99.99%)	^244Cm	0+
					SF (.0029%)	(various)
^249Cf	98	151	249.0748535(24)	351(2) y	α	^245Cm	9/2−
					SF (5×10^−7%)	(various)
^249mCf	144.98(5) keV			45(5) µs			5/2+
^250Cf	98	152	250.0764061(22)	13.08(9) y	α (99.92%)	^246Cm	0+
					SF (.077%)	(various)
^251Cf[n 8]	98	153	251.079587(5)	900(40) y	α	^247Cm	1/2+
^252Cf[n 9]	98	154	252.081626(5)	2.645(8) y	α (96.9%)	^248Cm	0+
					SF (3.09%)[n 10]	(various)
^253Cf	98	155	253.085133(7)	17.81(8) d	β^− (99.69%)	^253Es	(7/2+)
					α (.31%)	^249Cm
^254Cf	98	156	254.087323(13)	60.5(2) d	SF (99.69%)	(various)	0+
					α (.31%)	^250Cm
					β^−β^− (rare)	^254Fm
^255Cf	98	157	255.09105(22)#	85(18) min	β^− (99.99%)	^255Es	(7/2+)
					SF (.001%)	(various)
					α (10^−5%)	^251Cm
^256Cf	98	158	256.09344(32)#	12.3(12) min	SF (~100%)	(various)	0+
					α (10^−6%)	^252Cm
					β^−β^− (rare)	^256Fm

1. ^mCf – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Modes of decay:

   EC:	Electron capture
   SF:	Spontaneous fission

5. ( ) spin value – Indicates spin with weak assignment arguments.
6. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
7. Lightest nuclide known to undergo spontaneous fission as the main decay mode
8. High neutron cross-section, tends to absorb neutrons
9. Most common isotope
10. High neutron emitter, average 3.7 neutrons per fission

Actinides vs fission products

Actinides and fission products by half-life
Actinides[1] by decay chain				Half-life range (a)	Fission products of ^235U by yield[2]
4n	4n+1	4n+2	4n+3
						4.5–7%	0.04–1.25%	<0.001%
^228Ra^№				4–6 a	†		^155Eu^þ
^244Cm^ƒ	^241Pu^ƒ	^250Cf	^227Ac^№	10–29 a		^90Sr	^85Kr	^113mCd^þ
^232U^ƒ		^238Pu^ƒ	^243Cm^ƒ	29–97 a		^137Cs	^151Sm^þ	^121mSn
^248Bk[3]	^249Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100–210 ka ...
	^241Am^ƒ		^251Cf^ƒ[4]	430–900 a
		^226Ra^№	^247Bk	1.3–1.6 ka
^240Pu	^229Th	^246Cm^ƒ	^243Am^ƒ	4.7–7.4 ka
	^245Cm^ƒ	^250Cm		8.3–8.5 ka
			^239Pu^ƒ	24.1 ka
		^230Th^№	^231Pa^№	32–76 ka
^236Np^ƒ	^233U^ƒ	^234U^№		150–250 ka	‡	^99Tc^₡	^126Sn
^248Cm		^242Pu		327–375 ka			^79Se^₡
				1.53 Ma		^93Zr
	^237Np^ƒ			2.1–6.5 Ma		^135Cs^₡	^107Pd
^236U			^247Cm^ƒ	15–24 Ma			^129I^₡
^244Pu				80 Ma	... nor beyond 15.7 Ma[5]
^232Th^№		^238U^№	^235U^ƒ№	0.7–14.1 Ga
Legend for superscript symbols ₡  has thermal neutron capture cross section in the range of 8–50 barns ƒ  fissile m  metastable isomer №  primarily a naturally occurring radioactive material (NORM) þ  neutron poison (thermal neutron capture cross section greater than 3k barns) †  range 4–97 a: Medium-lived fission product ‡  over 200 ka: Long-lived fission product

Californium-252

Californium-252 (Cf-252, ²⁵²Cf) undergoes spontaneous fission with a branching ratio of 3.09% and is used in small sized neutron sources. Fission neutrons 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.[6]

This isotope produces high neutron emissions and can be used for a number of applications in industries such as nuclear energy, medicine, and petrochemical exploration.

Nuclear reactors

The neutron sources produced from ²⁵²Cf are most notably used in the start-up of nuclear reactors. Once a reactor is filled with nuclear fuel, the stable neutron emissions from the source material initiates the fission chain reaction.

Military and defense

The portable isotopic neutron spectroscopy (PINS) used by United States Armed Forces, the National Guard, Homeland Security, and U.S. Customs and Border Protection, employs the use of ²⁵²Cf sources to detect hazardous contents found inside artillery projectiles, mortar projectiles, rockets, bombs, land mines, and improvised explosive devices (IED).[7][8]

Oil and petroleum

In the oil industry, ²⁵²Cf neutron sources are used to find layers of petroleum and water in a well. Instrumentation is lowered into the well which bombards the formation with high energy neutrons to determine porosity, permeability, and hydrocarbon presence along the length of the borehole.[9]

Medicine

Californium-252 has also been used in the treatment of serious forms of cancer. In patients suffering from certain types of brain and cervical cancer, ²⁵²Cf can be used as a more cost-effective substitute for radium.[10]

References

1. Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
2. Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.
3. Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
   "The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."
4. This is the heaviest nuclide with a half-life of at least four years before the "Sea of Instability".
5. Excluding those "classically stable" nuclides with half-lives significantly in excess of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is nearly eight quadrillion years.
6. Dicello, J. F.; Gross, W.; Kraljevic, U. (1972). "Radiation Quality of Californium-252". Physics in Medicine and Biology. 17 (3): 345. Bibcode:1972PMB....17..345D. doi:10.1088/0031-9155/17/3/301.
7. "Portable Isotopic Neutron Spectroscopy (PINS) for the Military". Frontier Technology Corp. Retrieved 2016-02-24.
8. Martin, R. C.; Knauer, J. B.; Balo, P. A. (2000-11-01). "Production, distribution and applications of californium-252 neutron sources". Applied Radiation and Isotopes: Including Data, Instrumentation and Methods for Use in Agriculture, Industry and Medicine. 53 (4–5): 785–792. doi:10.1016/s0969-8043(00)00214-1. ISSN 0969-8043. PMID 11003521.
9. "Californium-252 & Antimony-Beryllium Sources". Frontier Technology Corp. Retrieved 2016-02-24.
10. Maruyama, Y.; van Nagell, J. R.; Yoneda, J.; Donaldson, E.; Hanson, M.; Martin, A.; Wilson, L. C.; Coffey, C. W.; Feola, J. (1984-10-01). "Five-year cure of cervical cancer treated using californium-252 neutron brachytherapy". American Journal of Clinical Oncology. 7 (5): 487–493. doi:10.1097/00000421-198410000-00018. ISSN 0277-3732. PMID 6391143.

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.