Isotopes of actinium

Isotopes of actinium (₈₉Ac)
CD	211Bi
ε	226Ra
α	222Fr
α	223Fr
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Actinium (₈₉Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, thus a standard atomic weight cannot be given. There are 34 known isotopes, from ²⁰³Ac 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
²⁰³Ac^[3]		89	114		56+269 −26 μs	α	¹⁹⁹Fr	(1/2+)
²⁰⁴Ac^[4]		89	115		7.4+2.2 −1.4 ms	α	²⁰⁰Fr
²⁰⁵Ac^[5]		89	116		7.7+2.7 −1.6 ms^[4]	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	α	²¹²Fr	(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⁻ (98.62%)	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]}
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^[6]		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^[7] by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield^[8]
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
²⁴⁸Bk^[9]				> 9 a
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
	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^[10]	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^₡
				1.33 Ma	¹³⁵Cs^₡
	²³⁷Np^ƒ			1.61–6.5 Ma	⁹³Zr	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15–24 Ma		¹²⁹I^₡
²⁴⁴Pu				80 Ma	... nor beyond 15.7 Ma^[11]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma^[11]
₡, 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)

Notable isotopes

Actinium-225

Actinium-225 is a highly radioactive isotope with 136 neutrons. It is an alpha emitter and has a half-life of 9.919 days. As of 2024, it is being researched as a possible alpha source in _targeted alpha therapy.^[12]^[13]^[14] Actinium-225 undergoes a series of three alpha decays – via the short-lived francium-221 and astatine-217 – to ²¹³Bi, which itself is used as an alpha source.^[15] Another benefit is that the decay chain of ²²⁵Ac ends in the nuclide ²⁰⁹Bi,^{[note 1]} which has a considerably shorter biological half-life than lead.^[16]^[17] However, a major factor limiting its usage is the difficulty in producing the short-lived isotope, as it is most commonly isolated from aging parent nuclides (such as ²³³U); it may also be produced in cyclotrons, linear accelerators, or fast breeder reactors.^[18]

Actinium-226

Actinium-226 is an isotope of actinium with a half-life of 29.37 hours. It mainly (83%) undergos beta decay, sometimes (17%) undergo electron capture, and rarely (0.006%) undergo alpha decay.^[1] There are researches on ²²⁶Ac to use it in SPECT.^[19]^[20]

Actinium-227

Actinium-227 is the most stable isotope of actinium, with a half-life of 21.772 years. It mainly (98.62%) undergos beta decay, but sometimes (1.38%) it will undergo alpha decay instead.^[1] ²²⁷Ac is a member of the actinium series. It is found only in traces in uranium ores – one tonne of uranium in ore contains about 0.2 milligrams of ²²⁷Ac.^[21]^[22] ²²⁷Ac is prepared, in milligram amounts, by the neutron irradiation of ²²⁶Ra in a nuclear reactor.^[22]^[23]

{\ce {^{226}_{88}Ra + ^{1}_{0}n -> ^{227}_{88}Ra ->[\beta^-][42.2 \ {\ce {min}}] ^{227}_{89}Ac}}

²²⁷Ac is highly radioactive and was therefore studied for use as an active element of radioisotope thermoelectric generators, for example in spacecraft. The oxide of ²²⁷Ac pressed with beryllium is also an efficient neutron source with the activity exceeding that of the standard americium-beryllium and radium-beryllium pairs.^[24] In all those applications, ²²⁷Ac (a beta source) is merely a progenitor which generates alpha-emitting isotopes upon its decay. Beryllium captures alpha particles and emits neutrons owing to its large cross-section for the (α,n) nuclear reaction:

{\ce {^{9}_{4}Be + ^{4}_{2}He -> ^{12}_{6}C + ^{1}_{0}n + \gamma}}

The ²²⁷AcBe neutron sources can be applied in a neutron probe – a standard device for measuring the quantity of water present in soil, as well as moisture/density for quality control in highway construction.^[25]^[26] Such probes are also used in well logging applications, in neutron radiography, tomography and other radiochemical investigations.^[27]

The medium half-life of ²²⁷Ac makes it a very convenient radioactive isotope in modeling the slow vertical mixing of oceanic waters. The associated processes cannot be studied with the required accuracy by direct measurements of current velocities (of the order 50 meters per year). However, evaluation of the concentration depth-profiles for different isotopes allows estimating the mixing rates. The physics behind this method is as follows: oceanic waters contain homogeneously dispersed ²³⁵U. Its decay product, ²³¹Pa, gradually precipitates to the bottom, so that its concentration first increases with depth and then stays nearly constant. ²³¹Pa decays to ²²⁷Ac; however, the concentration of the latter isotope does not follow the ²³¹Pa depth profile, but instead increases toward the sea bottom. This occurs because of the mixing processes which raise some additional ²²⁷Ac from the sea bottom. Thus analysis of both ²³¹Pa and ²²⁷Ac depth profiles allows researchers to model the mixing behavior.^[28]^[29]

Notes

^ Bismuth-209 decays into thallium-205 with a half-life exceeding 10¹⁹ years, but this half-life is so long that for practical purposes bismuth-209 can be considered stable.

References

^ ^a ^b ^c 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.
^ Wang, J. G.; Gan, Z. G.; Zhang, Z. Y.; et al. (1 March 2024). "α-decay properties of new neutron-deficient isotope 203Ac". Physics Letters B. 850: 138503. doi:10.1016/j.physletb.2024.138503. ISSN 0370-2693.
^ ^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 eight quadrillion years.
^ A. Scheinberg, David; R. McDevitt, Michael (1 October 2011). "Actinium-225 in _targeted Alpha-Particle Therapeutic Applications". Current Radiopharmaceuticals. 4 (4): 306–320. doi:10.2174/1874471011104040306. PMC 5565267. PMID 22202153.
^ Reissig, Falco; Bauer, David; Zarschler, Kristof; Novy, Zbynek; Bendova, Katerina; Ludik, Marie-Charlotte; Kopka, Klaus; Pietzsch, Hans-Jürgen; Petrik, Milos; Mamat, Constantin (20 April 2021). "Towards _targeted Alpha Therapy with Actinium-225: Chelators for Mild Condition Radiolabeling and _targeting PSMA—A Proof of Concept Study". Cancers. 13 (8): 1974. doi:10.3390/cancers13081974. PMC 8073976. PMID 33923965.
^ Bidkar, Anil P.; Zerefa, Luann; Yadav, Surekha; VanBrocklin, Henry F.; Flavell, Robert R. (2024). "Actinium-225 _targeted alpha particle therapy for prostate cancer". Theranostics. 14 (7): 2969–2992. doi:10.7150/thno.96403.
^ Ahenkorah, Stephen; Cassells, Irwin; Deroose, Christophe M.; Cardinaels, Thomas; Burgoyne, Andrew R.; Bormans, Guy; Ooms, Maarten; Cleeren, Frederik (21 April 2021). "Bismuth-213 for _targeted Radionuclide Therapy: From Atom to Bedside". Pharmaceutics. 13 (5): 599. doi:10.3390/pharmaceutics13050599. PMC 8143329.
^ Handbook on the toxicology of metals. Volume 2: Specific metals (Fourth ed.). Amsterdam Boston Heidelberg London: Elsevier, Aademic Press. 2015. p. 655. ISBN 978-0-12-398293-3.
^ Wani, Ab Latif; Ara, Anjum; Usmani, Jawed Ahmad (1 June 2015). "Lead toxicity: a review". Interdisciplinary Toxicology. 8 (2): 55–64. doi:10.1515/intox-2015-0009. PMC 4961898.
^ Dhiman, Deeksha; Vatsa, Rakhee; Sood, Ashwani (September 2022). "Challenges and opportunities in developing Actinium-225 radiopharmaceuticals". Nuclear Medicine Communications. 43 (9): 970–977. doi:10.1097/MNM.0000000000001594. PMID 35950353.
^ Koniar, Helena; Rodríguez-Rodríguez, Cristina; Radchenko, Valery; Yang, Hua; Kunz, Peter; Rahmim, Arman; Uribe, Carlos; Schaffer, Paul (2022-09-12). "SPECT imaging of ²²⁶Ac as a theranostic isotope for ²²⁵Ac radiopharmaceutical development". Physics in Medicine and Biology. 67 (18). doi:10.1088/1361-6560/ac8b5f. ISSN 1361-6560. PMID 35985341.
^ Koniar, Helena; Wharton, Luke; Ingham, Aidan; Rodríguez-Rodríguez, Cristina; Kunz, Peter; Radchenko, Valery; Yang, Hua; Rahmim, Arman; Uribe, Carlos; Schaffer, Paul (2024-07-16). "In vivoquantitative SPECT imaging of actinium-226: feasibility and proof-of-concept". Physics in Medicine and Biology. 69 (15). doi:10.1088/1361-6560/ad5c37. ISSN 1361-6560. PMID 38925140.
^ Hagemann, French (1950). "The Isolation of Actinium". Journal of the American Chemical Society. 72 (2): 768–771. doi:10.1021/ja01158a033.
^ ^a ^b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 946. ISBN 978-0-08-037941-8.
^ Emeleus, H. J. (1987). Advances in inorganic chemistry and radiochemistry. Academic Press. pp. 16–. ISBN 978-0-12-023631-2.
^ Russell, Alan M. and Lee, Kok Loong (2005) Structure-property relations in nonferrous metals. Wiley. ISBN 0-471-64952-X, pp. 470–471
^ Majumdar, D. K. (2004) Irrigation Water Management: Principles and Practice. ISBN 81-203-1729-7 p. 108
^ Chandrasekharan, H. and Gupta, Navindu (2006) Fundamentals of Nuclear Science – Application in Agriculture. ISBN 81-7211-200-9 pp. 202 ff
^ Dixon, W. R.; Bielesch, Alice; Geiger, K. W. (1957). "Neutron Spectrum of an Actinium–Beryllium Source". Can. J. Phys. 35 (6): 699–702. Bibcode:1957CaJPh..35..699D. doi:10.1139/p57-075.
^ Nozaki, Yoshiyuki (1984). "Excess ²²⁷Ac in deep ocean water". Nature. 310 (5977): 486–488. Bibcode:1984Natur.310..486N. doi:10.1038/310486a0. S2CID 4344946.
^ Geibert, W.; Rutgers Van Der Loeff, M. M.; Hanfland, C.; Dauelsberg, H.-J. (2002). "Actinium-227 as a deep-sea tracer: sources, distribution and applications". Earth and Planetary Science Letters. 198 (1–2): 147–165. Bibcode:2002E&PSL.198..147G. doi:10.1016/S0012-821X(02)00512-5.

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
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.

[3] Ac – Excited nuclear isomer.

[4] ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.

[TMS-5] # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).

[6] Modes of decay:

CD: Cluster decay

EC: Electron capture

IT: Isomeric transition

[7] Bold italics symbol as daughter – Daughter product is nearly stable.

[8] ( ) spin value – Indicates spin with weak assignment arguments.

[TNN-9] # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

[13] Has medical uses

[14] Intermediate decay product of ²³⁷Np

[15] Source of element's name

[16] Intermediate decay product of ²³⁵U

[17] Intermediate decay product of ²³²Th

[28] Bismuth-209 decays into thallium-205 with a half-life exceeding 10¹⁹ years, but this half-life is so long that for practical purposes bismuth-209 can be considered stable.

[NUBASE2020-1] 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.

[nostrand332-2] G. D. Considine, ed. (2005). "Chemical Elements". Van Nostrand's Encyclopedia of Chemistry. Wiley-Interscience. p. 332. ISBN 978-0-471-61525-5.

[203Ac-10] Wang, J. G.; Gan, Z. G.; Zhang, Z. Y.; et al. (1 March 2024). "α-decay properties of new neutron-deficient isotope 203Ac". Physics Letters B. 850: 138503. doi:10.1016/j.physletb.2024.138503. ISSN 0370-2693.

[204Ac-11] 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.

[ZhangEtAl2014-12] 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.

[236Ac-Chen-18] 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.

[19] 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.

[20] Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.

[21] 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]."

[22] This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".

[23] 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 eight quadrillion years.

[24] A. Scheinberg, David; R. McDevitt, Michael (1 October 2011). "Actinium-225 in _targeted Alpha-Particle Therapeutic Applications". Current Radiopharmaceuticals. 4 (4): 306–320. doi:10.2174/1874471011104040306. PMC 5565267. PMID 22202153.

[25] Reissig, Falco; Bauer, David; Zarschler, Kristof; Novy, Zbynek; Bendova, Katerina; Ludik, Marie-Charlotte; Kopka, Klaus; Pietzsch, Hans-Jürgen; Petrik, Milos; Mamat, Constantin (20 April 2021). "Towards _targeted Alpha Therapy with Actinium-225: Chelators for Mild Condition Radiolabeling and _targeting PSMA—A Proof of Concept Study". Cancers. 13 (8): 1974. doi:10.3390/cancers13081974. PMC 8073976. PMID 33923965.

[26] Bidkar, Anil P.; Zerefa, Luann; Yadav, Surekha; VanBrocklin, Henry F.; Flavell, Robert R. (2024). "Actinium-225 _targeted alpha particle therapy for prostate cancer". Theranostics. 14 (7): 2969–2992. doi:10.7150/thno.96403.

[27] Ahenkorah, Stephen; Cassells, Irwin; Deroose, Christophe M.; Cardinaels, Thomas; Burgoyne, Andrew R.; Bormans, Guy; Ooms, Maarten; Cleeren, Frederik (21 April 2021). "Bismuth-213 for _targeted Radionuclide Therapy: From Atom to Bedside". Pharmaceutics. 13 (5): 599. doi:10.3390/pharmaceutics13050599. PMC 8143329.

[29] Handbook on the toxicology of metals. Volume 2: Specific metals (Fourth ed.). Amsterdam Boston Heidelberg London: Elsevier, Aademic Press. 2015. p. 655. ISBN 978-0-12-398293-3.

[30] Wani, Ab Latif; Ara, Anjum; Usmani, Jawed Ahmad (1 June 2015). "Lead toxicity: a review". Interdisciplinary Toxicology. 8 (2): 55–64. doi:10.1515/intox-2015-0009. PMC 4961898.

[31] Dhiman, Deeksha; Vatsa, Rakhee; Sood, Ashwani (September 2022). "Challenges and opportunities in developing Actinium-225 radiopharmaceuticals". Nuclear Medicine Communications. 43 (9): 970–977. doi:10.1097/MNM.0000000000001594. PMID 35950353.

[32] Koniar, Helena; Rodríguez-Rodríguez, Cristina; Radchenko, Valery; Yang, Hua; Kunz, Peter; Rahmim, Arman; Uribe, Carlos; Schaffer, Paul (2022-09-12). "SPECT imaging of ²²⁶Ac as a theranostic isotope for ²²⁵Ac radiopharmaceutical development". Physics in Medicine and Biology. 67 (18). doi:10.1088/1361-6560/ac8b5f. ISSN 1361-6560. PMID 35985341.

[33] Koniar, Helena; Wharton, Luke; Ingham, Aidan; Rodríguez-Rodríguez, Cristina; Kunz, Peter; Radchenko, Valery; Yang, Hua; Rahmim, Arman; Uribe, Carlos; Schaffer, Paul (2024-07-16). "In vivoquantitative SPECT imaging of actinium-226: feasibility and proof-of-concept". Physics in Medicine and Biology. 69 (15). doi:10.1088/1361-6560/ad5c37. ISSN 1361-6560. PMID 38925140.

[Hagemann1950-34] Hagemann, French (1950). "The Isolation of Actinium". Journal of the American Chemical Society. 72 (2): 768–771. doi:10.1021/ja01158a033.

[g946-35] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 946. ISBN 978-0-08-037941-8.

[36] Emeleus, H. J. (1987). Advances in inorganic chemistry and radiochemistry. Academic Press. pp. 16–. ISBN 978-0-12-023631-2.

[b1-37] Russell, Alan M. and Lee, Kok Loong (2005) Structure-property relations in nonferrous metals. Wiley. ISBN 0-471-64952-X, pp. 470–471

[38] Majumdar, D. K. (2004) Irrigation Water Management: Principles and Practice. ISBN 81-203-1729-7 p. 108

[39] Chandrasekharan, H. and Gupta, Navindu (2006) Fundamentals of Nuclear Science – Application in Agriculture. ISBN 81-7211-200-9 pp. 202 ff

[40] Dixon, W. R.; Bielesch, Alice; Geiger, K. W. (1957). "Neutron Spectrum of an Actinium–Beryllium Source". Can. J. Phys. 35 (6): 699–702. Bibcode:1957CaJPh..35..699D. doi:10.1139/p57-075.

[41] Nozaki, Yoshiyuki (1984). "Excess ²²⁷Ac in deep ocean water". Nature. 310 (5977): 486–488. Bibcode:1984Natur.310..486N. doi:10.1038/310486a0. S2CID 4344946.

[42] Geibert, W.; Rutgers Van Der Loeff, M. M.; Hanfland, C.; Dauelsberg, H.-J. (2002). "Actinium-227 as a deep-sea tracer: sources, distribution and applications". Earth and Planetary Science Letters. 198 (1–2): 147–165. Bibcode:2002E&PSL.198..147G. doi:10.1016/S0012-821X(02)00512-5.

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