Isotopes of actinium

Actinium (Ac) has no stable isotopes, 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.^[1]

Contents 1 Table 1.1 Notes 2 See also 3 References

Table

nuclide symbol	historic name	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)[2][n 1]	daughter isotope(s)[n 2]	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
		excitation energy
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) a	β- (98.61%)	227Th	3/2-	Trace[n 5]
						α (1.38%)	223Fr
228Ac	Mesothorium 2	89	139	228.0310211(27)	6.15(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

	Book: Actinium
Wikipedia books are collections of articles that can be downloaded or ordered in print.

• Actinium series

References

• Isotope masses from:
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (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. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf. 
• 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. http://www.iupac.org/publications/pac/75/6/0683/pdf/. 
  • 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. http://iupac.org/publications/pac/78/11/2051/pdf/. 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". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf. 
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/. 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 978-0849304859. 

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