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 14C 211Bi 226Ac synth 29.37 h β− 226Th ε 226Ra α 222Fr 227Ac trace 21.772 y β− 227Th 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
		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)	0.440(16) ms	α	212Fr	(1−)
						β+ (7×10−5%)	216Ra
216mAc		44(7) keV			443(7) µs	α	212Fr	(9−)
217Ac		89	128	217.009347(14)	69(4) ns	α	213Fr	9/2−
						β+ (6.9×10−9%)	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 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%
228 Ra№				4–6 a		155 Euþ
244 Cmƒ	241 Puƒ	250 Cf	227 Ac№	10–29 a	90 Sr	85 Kr	113m Cdþ
232 Uƒ		238 Puƒ	243 Cmƒ	29–97 a	137 Cs	151 Smþ	121m Sn
248 Bk [9]	249 Cfƒ	242m Amƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	241 Amƒ		251 Cfƒ [10]	430–900 a
		226 Ra№	247 Bk	1.3–1.6 ka
240 Pu	229 Th	246 Cmƒ	243 Amƒ	4.7–7.4 ka
	245 Cmƒ	250 Cm		8.3–8.5 ka
			239 Puƒ	24.1 ka
		230 Th№	231 Pa№	32–76 ka
236 Npƒ	233 Uƒ	234 U№		150–250 ka	99 Tc₡	126 Sn
248 Cm		242 Pu		327–375 ka		79 Se₡
				1.53 Ma	93 Zr
	237 Npƒ			2.1–6.5 Ma	135 Cs₡	107 Pd
236 U			247 Cmƒ	15–24 Ma		129 I₡
244 Pu				80 Ma	... nor beyond 15.7 Ma [11]
232 Th№		238 U№	235 Uƒ№	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)

See also

• Actinium series
• Actinide

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 . Retrieved 6 February 2024.
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 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]."
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.

• 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.