Isotopes of actinium

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	†		^155Eu^þ
^244Cm	^241Pu^ƒ	^250Cf	^227Ac^№	10–29		^90Sr	^85Kr	^113mCd^þ
^232U^ƒ		^238Pu^№	^243Cm^ƒ	29–97		^137Cs	^151Sm^þ	^121mSn
^248Bk[3]	^249Cf^ƒ	^242mAm^ƒ		141–351	No fission products have a half-life in the range of 100–210 k years ...
	^241Am^ƒ		^251Cf^ƒ[4]	430–900
		^226Ra^№	^247Bk	1.3 k – 1.6 k
^240Pu	^229Th^№	^246Cm	^243Am^ƒ	4.7 k – 7.4 k
	^245Cm^ƒ	^250Cm		8.3 k – 8.5 k
			^239Pu^ƒ№	24.1 k
		^230Th^№	^231Pa^№	32 k – 76 k
^236Np^ƒ	^233U^ƒ№	^234U^№		150 k – 250 k	‡	^99Tc^₡	^126Sn
^248Cm		^242Pu		327 k – 375 k			^79Se^₡
				1.53 M		^93Zr
	^237Np^№			2.1 M – 6.5 M		^135Cs^₡	^107Pd
^236U^№			^247Cm^ƒ	15 M – 24 M			^129I^₡
^244Pu^№				80 M	... nor beyond 15.7 M years[5]
^232Th^№		^238U^№	^235U^ƒ№	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

Actinium (Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, thus a standard atomic mass cannot be given. There are 31 known isotopes, from ²⁰⁶Ac to ²³⁶Ac, and 2 isomers. Two isotopes are found in nature, ²²⁷Ac and ²²⁸Ac, as intermediate decay products of, respectively, ²³⁵U and ²³²Th. ²²⁸Ac is extremely rare, and almost all natural actinium is ²²⁷Ac.

The most stable isotopes are ²²⁷Ac with a half-life of 21.772 years, ²²⁵Ac with a half-life of 10.0 days, and ²²⁶Ac with a half-life of 29.37 hours. All other isotopes have half-lives under 10 hours, and most under a minute. The shortest-lived known isotope is ²¹⁷Ac with a half-life of 69 ns. Actinium also has two meta states.

Purified ²²⁷Ac comes into equilibrium with its decay products (²²⁷Th and ²²³Fr) after 185 days.^[6]

Table

nuclide symbol	historic name	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)[7][n 1]	daughter isotope(s)[n 2]	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
		excitation energy
^205Ac[8]		89	116		20(+97−9) ms	α	^201Fr
^206Ac		89	117	206.01450(8)	25(7) ms			(3+)
^206m1Ac		80(50) keV			15(6) ms
^206m2Ac		290(110)# keV			41(16) ms			(10−)
^207Ac		89	118	207.01195(6)	31(8) ms [27(+11−6) ms]	α	^203Fr	9/2−#
^208Ac		89	119	208.01155(6)	97(16) ms [95(+24−16) ms]	α (99%)	^204Fr	(3+)
						β^+ (1%)	^208Ra
^208mAc		506(26) keV			28(7) ms [25(+9−5) ms]	α (89%)	^204Fr	(10−)
						IT (10%)	^208Ac
						β^+ (1%)	^208Ra
^209Ac		89	120	209.00949(5)	92(11) ms	α (99%)	^205Fr	(9/2−)
						β^+ (1%)	^209Ra
^210Ac		89	121	210.00944(6)	350(40) ms	α (96%)	^206Fr	7+#
						β^+ (4%)	^210Ra
^211Ac		89	122	211.00773(8)	213(25) ms	α (99.8%)	^207Fr	9/2−#
						β^+ (.2%)	^211Ra
^212Ac		89	123	212.00781(7)	920(50) ms	α (97%)	^208Fr	6+#
						β^+ (3%)	^212Ra
^213Ac		89	124	213.00661(6)	731(17) ms	α	^209Fr	(9/2−)#
						β^+ (rare)	^213Ra
^214Ac		89	125	214.006902(24)	8.2(2) s	α (89%)	^210Fr	(5+)#
						β^+ (11%)	^214Ra
^215Ac		89	126	215.006454(23)	0.17(1) s	α (99.91%)	^211Fr	9/2−
						β^+ (.09%)	^215Ra
^216Ac		89	127	216.008720(29)	0.440(16) ms	α	^212Fr	(1−)
						β^+ (7×10^−5%)	^216Ra
^216mAc		44(7) keV			443(7) µs			(9−)
^217Ac		89	128	217.009347(14)	69(4) ns	α (98%)	^213Fr	9/2−
						β^+ (2%)	^217Ra
^217mAc		2012(20) keV			740(40) ns			(29/2)+
^218Ac		89	129	218.01164(5)	1.08(9) µs	α	^214Fr	(1−)#
^218mAc		584(50)# keV			103(11) ns			(11+)
^219Ac		89	130	219.01242(5)	11.8(15) µs	α	^215Fr	9/2−
						β^+ (10^−6%)	^219Ra
^220Ac		89	131	220.014763(16)	26.36(19) ms	α	^216Fr	(3−)
						β^+ (5×10^−4%)	^220Ra
^221Ac		89	132	221.01559(5)	52(2) ms	α	^217Fr	9/2−#
^222Ac		89	133	222.017844(6)	5.0(5) s	α (99%)	^218Fr	1−
						β^+ (1%)	^222Ra
^222mAc		200(150)# keV			1.05(7) min	α (88.6%)	^218Fr	high
						IT (10%)	^222Ac
						β^+ (1.4%)	^222Ra
^223Ac		89	134	223.019137(8)	2.10(5) min	α (99%)	^219Fr	(5/2−)
						EC (1%)	^223Ra
						CD (3.2×10^−9%)	^209Bi ^14C
^224Ac		89	135	224.021723(4)	2.78(17) h	β^+ (90.9%)	^224Ra	0−
						α (9.1%)	^220Fr
						β^− (1.6%)	^224Th
^225Ac[n 3]		89	136	225.023230(5)	10.0(1) d	α	^221Fr	(3/2−)
						CD (6×10^−10%)	^211Bi ^14C
^226Ac		89	137	226.026098(4)	29.37(12) h	β^− (83%)	^226Th	(1)(−#)
						EC (17%)	^226Ra
						α (.006%)	^222Fr
^227Ac	Actinium[n 4]	89	138	227.0277521(26)	21.772(3) y	β^− (98.61%)	^227Th	3/2−	Trace[n 5]
						α (1.38%)	^223Fr
^228Ac	Mesothorium 2	89	139	228.0310211(27)	6.13(2) h	β^−	^228Th	3+	Trace[n 6]
						α (5.5×10^−6%)	^224Fr
^229Ac		89	140	229.03302(4)	62.7(5) min	β^−	^229Th	(3/2+)
^230Ac		89	141	230.03629(32)	122(3) s	β^−	^230Th	(1+)
^231Ac		89	142	231.03856(11)	7.5(1) min	β^−	^231Th	(1/2+)
^232Ac		89	143	232.04203(11)	119(5) s	β^−	^232Th	(1+)
^233Ac		89	144	233.04455(32)#	145(10) s	β^−	^233Th	(1/2+)
^234Ac		89	145	234.04842(43)#	44(7) s	β^−	^234Th
^235Ac		89	146	235.05123(38)#	40# s	β^−	^235Th	1/2+#
^236Ac		89	147	236.05530(54)#	2# min	β^−	^236Th

1. Abbreviations:
   CD: Cluster decay
   EC: Electron capture
   IT: Isomeric transition
2. Bold italics for nearly-stable isotopes (half-life longer than the age of the universe)
3. Has medical uses
4. Source of element's name
5. Intermediate decay product of ²³⁵U
6. Intermediate decay product of ²³²Th

Notes

• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

See also

• Actinium series

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 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. G. D. Considine, ed. (2005). "Chemical Elements". Van Nostrand's Encyclopedia of Chemistry. Wiley-Interscience. p. 332. ISBN 978-0-471-61525-5.
7. "Universal Nuclide Chart". nucleonica. (registration required (help)).
8. Zhang, Z. Y.; Gan, Z. G.; Ma, L.; Yu, L.; Yang, H. B.; Huang, T. H.; Li, G. S.; Tian, Y. L.; Wang, Y. S.; Xu, X. X.; Huang, M. H.; Luo, C.; Ren, Z. Z.; Zhou, S.G.; Zhou, X. H.; Xu, H. S.; Xiao, G. Q. (January 2014). "α decay of the new neutron-deficient isotope ²⁰⁵Ac". Physical Review C 89 (1): 014308. doi:10.1103/PhysRevC.89.014308.

• Isotope masses from:
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). 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:
  • J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683.
  • M. E. Wieser (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. See editing notes on this article's talk page.
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005.
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.