Isotopes of actinium (₈₉Ac)

Main isotopes^[1]			Decay
	abundance	half-life (t_1/2)	mode	product
²²⁵Ac	trace	9.919 d	α	²²¹Fr
²²⁵Ac	trace	9.919 d	¹⁴C	²¹¹Bi
²²⁶Ac	synth	29.37 h	β⁻	²²⁶Th
			ε	²²⁶Ra
			α	²²²Fr
²²⁷Ac	trace	21.772 y	β⁻	²²⁷Th
²²⁷Ac	trace	21.772 y	α	²²³Fr

Actinium (₈₉Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, thus a standard atomic weight cannot be given. There are 33 known isotopes, from ²⁰⁴Ac to ²³⁶Ac, and 7 isomers. Three isotopes are found in nature, ²²⁵Ac, ²²⁷Ac and ²²⁸Ac, as intermediate decay products of, respectively, ²³⁷Np, ²³⁵U, and ²³²Th. ²²⁸Ac and ²²⁵Ac are extremely rare, so 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.

Purified ²²⁷Ac comes into equilibrium with its decay products (²²⁷Th and ²²³Fr) after 185 days.^[2]

List of isotopes

Nuclide ^{[n 1]}	Historic name	Z	N	Isotopic mass (Da) ^{[n 2]}^{[n 3]}	Half-life	Decay mode ^{[n 4]}	Daughter isotope ^{[n 5]}	Spin and parity ^{[n 6]}^{[n 7]}	Isotopic abundance
Nuclide ^{[n 1]}	Historic name	Excitation energy^{[n 7]}			Half-life	Decay mode ^{[n 4]}	Daughter isotope ^{[n 5]}	Spin and parity ^{[n 6]}^{[n 7]}	Isotopic abundance
²⁰⁴Ac^[3]		89	115		7.4+2.2 −1.4 ms	α	²⁰⁰Fr
²⁰⁵Ac^[4]		89	116		7.7+2.7 −1.6 ms^[3]	α	²⁰¹Fr	9/2−?
²⁰⁶Ac		89	117	206.01450(8)	25(7) ms	α	²⁰²Fr	(3+)
^206m1Ac		80(50) keV			15(6) ms	α	²⁰²Fr
^206m2Ac		290(110)# keV			41(16) ms	α	^202mFr	(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+)
²⁰⁸Ac		89	119	208.01155(6)	97(16) ms [95(+24−16) ms]	β⁺ (1%)	²⁰⁸Ra	(3+)
^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−)
²⁰⁹Ac		89	120	209.00949(5)	92(11) ms	β⁺ (1%)	²⁰⁹Ra	(9/2−)
²¹⁰Ac		89	121	210.00944(6)	350(40) ms	α (96%)	²⁰⁶Fr	7+#
²¹⁰Ac		89	121	210.00944(6)	350(40) ms	β⁺ (4%)	²¹⁰Ra	7+#
²¹¹Ac		89	122	211.00773(8)	213(25) ms	α (99.8%)	²⁰⁷Fr	9/2−#
²¹¹Ac		89	122	211.00773(8)	213(25) ms	β⁺ (.2%)	²¹¹Ra	9/2−#
²¹²Ac		89	123	212.00781(7)	920(50) ms	α (97%)	²⁰⁸Fr	6+#
²¹²Ac		89	123	212.00781(7)	920(50) ms	β⁺ (3%)	²¹²Ra	6+#
²¹³Ac		89	124	213.00661(6)	731(17) ms	α	²⁰⁹Fr	(9/2−)#
²¹³Ac		89	124	213.00661(6)	731(17) ms	β⁺ (rare)	²¹³Ra	(9/2−)#
²¹⁴Ac		89	125	214.006902(24)	8.2(2) s	α (89%)	²¹⁰Fr	(5+)#
²¹⁴Ac		89	125	214.006902(24)	8.2(2) s	β⁺ (11%)	²¹⁴Ra	(5+)#
²¹⁵Ac		89	126	215.006454(23)	0.17(1) s	α (99.91%)	²¹¹Fr	9/2−
²¹⁵Ac		89	126	215.006454(23)	0.17(1) s	β⁺ (.09%)	²¹⁵Ra	9/2−
²¹⁶Ac		89	127	216.008720(29)	0.440(16) ms	α	²¹²Fr	(1−)
²¹⁶Ac		89	127	216.008720(29)	0.440(16) ms	β⁺ (7×10⁻⁵%)	²¹⁶Ra	(1−)
^216mAc		44(7) keV			443(7) µs			(9−)
²¹⁷Ac		89	128	217.009347(14)	69(4) ns	α	²¹³Fr	9/2−
²¹⁷Ac		89	128	217.009347(14)	69(4) ns	β⁺ (6.9×10⁻⁹%)	²¹⁷Ra	9/2−
^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−
²¹⁹Ac		89	130	219.01242(5)	11.8(15) µs	β⁺ (10⁻⁶%)	²¹⁹Ra	9/2−
²²⁰Ac		89	131	220.014763(16)	26.36(19) ms	α	²¹⁶Fr	(3−)
²²⁰Ac		89	131	220.014763(16)	26.36(19) ms	β⁺ (5×10⁻⁴%)	²²⁰Ra	(3−)
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−
²²²Ac		89	133	222.017844(6)	5.0(5) s	β⁺ (1%)	²²²Ra	1−
^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 8]}		89	136	225.023230(5)	10.0(1) d	α	²²¹Fr	(3/2−)	Trace^{[n 9]}
²²⁵Ac^{[n 8]}		89	136	225.023230(5)	10.0(1) d	CD (6×10⁻¹⁰%)	²¹¹Bi ¹⁴C	(3/2−)	Trace^{[n 9]}
²²⁶Ac		89	137	226.026098(4)	29.37(12) h	β⁻ (83%)	²²⁶Th	(1)(−#)
						EC (17%)	²²⁶Ra
						α (.006%)	²²²Fr
²²⁷Ac	Actinium^{[n 10]}	89	138	227.0277521(26)	21.772(3) y	β⁻ (98.61%)	²²⁷Th	3/2−	Trace^{[n 11]}
²²⁷Ac	Actinium^{[n 10]}	89	138	227.0277521(26)	21.772(3) y	α (1.38%)	²²³Fr	3/2−	Trace^{[n 11]}
²²⁸Ac	Mesothorium 2	89	139	228.0310211(27)	6.13(2) h	β⁻	²²⁸Th	3+	Trace^{[n 12]}
²²⁸Ac	Mesothorium 2	89	139	228.0310211(27)	6.13(2) h	α (5.5×10⁻⁶%)^{[citation needed]}	²²⁴Fr	3+	Trace^{[n 12]}
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)#	60(4) s	β⁻	²³⁵Th	1/2+#
²³⁶Ac^[5]		89	147	236.05530(54)#	72+345 −33 s	β⁻	²³⁶Th
This table header & footer: view

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

CD: Cluster decay

EC: Electron capture

IT: Isomeric transition
^ Bold italics symbol as daughter – Daughter product is nearly stable.
^ ( ) spin value – Indicates spin with weak assignment arguments.
^ ^a ^b # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
^ Has medical uses
^ Intermediate decay product of ²³⁷Np
^ Source of element's name
^ Intermediate decay product of ²³⁵U
^ Intermediate decay product of ²³²Th

Actinides vs fission products

Actinides and fission products by half-life v t e
Actinides^[6] by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield^[7]
4n	4n + 1	4n + 2	4n + 3	Half-life range (a)	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^[8]	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ^[9]	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^[10]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma^[10]
₡, has thermal neutron capture cross section in the range of 8–50 barns ƒ, fissile №, primarily a naturally occurring radioactive material (NORM) þ, neutron poison (thermal neutron capture cross section greater than 3k barns)

References

^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^ G. D. Considine, ed. (2005). "Chemical Elements". Van Nostrand's Encyclopedia of Chemistry. Wiley-Interscience. p. 332. ISBN 978-0-471-61525-5.
^ ^a ^b Huang, M. H.; Gan, Z. G.; Zhang, Z. Y.; et al. (10 November 2022). "α decay of the new isotope ²⁰⁴Ac". Physics Letters B. 834: 137484. Bibcode:2022PhLB..83437484H. doi:10.1016/j.physletb.2022.137484. ISSN 0370-2693. S2CID 252730841.
^ Zhang, Z. Y.; Gan, Z. G.; Ma, L.; et al. (January 2014). "α decay of the new neutron-deficient isotope ²⁰⁵Ac". Physical Review C. 89 (1): 014308. Bibcode:2014PhRvC..89a4308Z. doi:10.1103/PhysRevC.89.014308.
^ Chen, L.; et al. (2010). "Discovery and investigation of heavy neutron-rich isotopes with time-resolved Schottky spectrometry in the element range from thallium to actinium" (PDF). Physics Letters B. 691 (5): 234–237. Bibcode:2010PhLB..691..234C. doi:10.1016/j.physletb.2010.05.078.
^ 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.
^ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
^ 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]."
^ This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
^ 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.

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.
"News & Notices: Standard Atomic Weights Revised". International Union of Pure and Applied Chemistry. 19 October 2005.
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.

List of isotopes

Actinides vs fission products

See also

References