Isotopes of actinium

Isotopes of actinium (₈₉Ac)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct ^225Ac trace 9.919 d α ^221Fr CD ^211Bi ^226Ac synth 29.37 h β^− ^226Th ε ^226Ra α ^222Fr ^227Ac trace 21.772 y β^− ^227Th α ^223Fr

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
		Excitation energy[n 7]
^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+)
						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)	440(16) μs	α	^212Fr	(1−)
^216m1Ac		38(5) keV			441(7) μs	α	^212Fr	(9−)
^216m2Ac		422#(100#) keV			~300 ns	IT	^216Ac
^217Ac		89	128	217.009347(14)	69(4) ns	α	^213Fr	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		607(86)# keV			103(11) ns	IT	^218Ac	(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 8]		89	136	225.023230(5)	10.0(1) d	α	^221Fr	(3/2−)	Trace[n 9]
						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 10]	89	138	227.0277521(26)	21.772(3) y	β^− (98.62%)	^227Th	3/2−	Trace[n 11]
						α (1.38%)	^223Fr
^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

1. ^mAc – 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:

   CD:	Cluster decay
   EC:	Electron capture
   IT:	Isomeric transition

5. Bold italics symbol as daughter – Daughter product is nearly stable.
6. ( ) spin value – Indicates spin with weak assignment arguments.
7. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
8. Has medical uses
9. Intermediate decay product of ^237Np
10. Source of element's name
11. Intermediate decay product of ^235U
12. 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		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
₡,  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

Main article: 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]

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

^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:

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

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]

See also

• Actinium series
• Actinide

Notes

1. Bismuth-209 decays into thallium-205 with a half-life exceeding 10^19 years, but this half-life is so long that for practical purposes bismuth-209 can be considered stable.

References

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.
2. G. D. Considine, ed. (2005). "Chemical Elements". Van Nostrand's Encyclopedia of Chemistry. Wiley-Interscience. p. 332. ISBN 978-0-471-61525-5.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
9. 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 Bk^248 with a half-life greater than 9 [years]. No growth of Cf^248 was detected, and a lower limit for the β^− half-life can be set at about 10^4 [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."
10. This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
11. 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.
12. 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.
13. 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.
14. 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.
15. 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.
16. 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.
17. 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.
18. 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.
19. 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.
20. 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.
21. Hagemann, French (1950). "The Isolation of Actinium". Journal of the American Chemical Society. 72 (2): 768–771. doi:10.1021/ja01158a033.
22. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 946. ISBN 978-0-08-037941-8.
23. Emeleus, H. J. (1987). Advances in inorganic chemistry and radiochemistry. Academic Press. pp. 16–. ISBN 978-0-12-023631-2.
24. Russell, Alan M. and Lee, Kok Loong (2005) Structure-property relations in nonferrous metals. Wiley. ISBN 0-471-64952-X, pp. 470–471
25. Majumdar, D. K. (2004) Irrigation Water Management: Principles and Practice. ISBN 81-203-1729-7 p. 108
26. Chandrasekharan, H. and Gupta, Navindu (2006) Fundamentals of Nuclear Science – Application in Agriculture. ISBN 81-7211-200-9 pp. 202 ff
27. 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.
28. Nozaki, Yoshiyuki (1984). "Excess ^227Ac in deep ocean water". Nature. 310 (5977): 486–488. Bibcode:1984Natur.310..486N. doi:10.1038/310486a0. S2CID 4344946.
29. 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.