Isotopes of californium

Actinides and fission products by half-life
Actinides[1] by decay chain Half-life
range (y)
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 155Euþ
244Cmƒ 241Puƒ 250Cf 227Ac 10–29 90Sr 85Kr 113mCdþ
232Uƒ 238Puƒ№ 243Cmƒ 29–97 137Cs 151Smþ 121mSn
248Bk[3] 249Cfƒ 242mAmƒ 141–351

No fission products
have a half-life
in the range of
100–210 k years ...

241Amƒ 251Cfƒ[4] 430–900
226Ra 247Bk 1.3 k  1.6 k
240Puƒ№ 229Th 246Cmƒ 243Amƒ 4.7 k  7.4 k
245Cmƒ 250Cm 8.3 k  8.5 k
239Puƒ№ 24.1 k
230Th 231Pa 32 k  76 k
236Npƒ 233Uƒ№ 234U 150 k  250 k 99Tc 126Sn
248Cm 242Puƒ 327 k  375 k 79Se
1.53 M 93Zr
237Npƒ№ 2.1 M  6.5 M 135Cs 107Pd
236U 247Cmƒ 15 M  24 M 129I
244Pu 80 M

... nor beyond 15.7 M years[5]

232Th 238U 235Uƒ№ 0.7 G  14.1 G

Legend for superscript symbols
  has thermal neutron capture cross section in the range of 8–50 barns
ƒ  fissile
m  metastable isomer
  naturally occurring radioactive material (NORM)
þ  neutron poison (thermal neutron capture cross section greater than 3k barns)
  range 4–97 y: Medium-lived fission product
  over 200,000 y: Long-lived fission product

Californium (Cf) is an artificial element, and thus a standard atomic mass 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 900 years.


Californium-252 (Cf-252) undergoes spontaneous fission 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 Cf-252 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 chain reaction known as fission.

Military & 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 Cf-252 sources to detect hazardous contents found inside artillery projectiles, mortar projectiles, rockets, bombs, land mines, and improvised explosive devices (IED).[7][8]

Oil & Petroleum

In the oil industry, Cf-252 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]


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, Cf-252 can be used as a more cost-effective substitute for radium.[10]


Z(p) N(n)  
isotopic mass (u)
half-life decay
mode(s)[11][n 1]
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 2] (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 3] 98 153 251.079587(5) 900(40) y α 247Cm 1/2+
252Cf[n 4] 98 154 252.081626(5) 2.645(8) y α (96.9%) 248Cm 0+
SF (3.09%)[n 5] (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
ββ (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
ββ (rare) 256Fm
  1. Abbreviations:
    EC: Electron capture
    SF: Spontaneous fission
  2. Lightest nuclide known to undergo spontaneous fission as the main decay mode
  3. High neutron cross-section, tends to absorb neutrons
  4. Most common isotope
  5. High neutron emitter, average 3.7 neutrons per fission



  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 isotopes have half-lives of at least four years (the longest-lived isotope 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. 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 y. No growth of Cf248 was detected, and a lower limit for the β half-life can be set at about 104 y. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 y."
  4. This is the heaviest isotope with a half-life of at least four years before the "Sea of Instability".
  5. Excluding those "classically stable" isotopes 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.
  11. "Universal Nuclide Chart". nucleonica. (registration required (help)).
Isotopes of berkelium Isotopes of californium Isotopes of einsteinium
Table of nuclides
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