ISOTOPES OF ACTINIUM

'Actinium' ('Ac') has no stable isotopes. A standard atomic mass cannot be given.
An isotope of actinium occurring within the radioactive disintegration chain of thorium was known as:

★ ''mesothorium II'' : Ac
Naturally occurring actinium is composed of 1 radioactive isotope; ²²⁷Ac. 36 radioisotopes have been characterized with the most stable being ²²⁷Ac with a half-life of 21.772 y, ²²⁵Ac with a half-life of 10.0 days, and ²²⁶Ac with a half-life of 29.37 h. All of the remaining radioactive isotopes have half-lifes that are less than 10 hours and the majority of these have half lifes that are less than 1 minute. The shortest-lived isotope of actinium is ²¹⁷Ac which decays through alpha decay and electron capture. It has a half-life of 69 ns. Actinium also has 2 meta states.
Purified ²²⁷Ac comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.773-year half-life.
The isotopes of actinium range in atomic weight from 206 u (²⁰⁶Ac) to 236 u (²³⁶Ac).

Contents

Table

Notes

References

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	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]	9/2-#
208Ac	89	119	208.01155(6)	97(16) ms [95(+24-16) ms]	(3+)
208mAc	506(26) keV			28(7) ms [25(+9-5) ms]	(10-)
209Ac	89	120	209.00949(5)	92(11) ms	(9/2-)
210Ac	89	121	210.00944(6)	350(40) ms	7+#
211Ac	89	122	211.00773(8)	213(25) ms	9/2-#
212Ac	89	123	212.00781(7)	920(50) ms	6+#
213Ac	89	124	213.00661(6)	731(17) ms	(9/2-)#
214Ac	89	125	214.006902(24)	8.2(2) s	(5+)#
215Ac	89	126	215.006454(23)	0.17(1) s	9/2-
216Ac	89	127	216.008720(29)	0.440(16) ms	(1-)
216mAc	44(7) keV			443(7) µs	(9-)
217Ac	89	128	217.009347(14)	69(4) ns	9/2-
217mAc	2012(20) keV			740(40) ns	(29/2)+
218Ac	89	129	218.01164(5)	1.08(9) µs	(1-)#
218mAc	584(50)# keV			103(11) ns	(11+)
219Ac	89	130	219.01242(5)	11.8(15) µs	9/2-
220Ac	89	131	220.014763(16)	26.36(19) ms	(3-)
221Ac	89	132	221.01559(5)	52(2) ms	9/2-#
222Ac	89	133	222.017844(6)	5.0(5) s	1-
222mAc	200(150)# keV			1.05(7) min	high
223Ac	89	134	223.019137(8)	2.10(5) min	(5/2-)
224Ac	89	135	224.021723(4)	2.78(17) h	0-
225Ac	89	136	225.023230(5)	10.0(1) d	(3/2-)
226Ac	89	137	226.026098(4)	29.37(12) h	(1)(-#)
227Ac	89	138	227.0277521(26)	21.772(3) a	3/2-
228Ac	89	139	228.0310211(27)	6.15(2) h	3+
229Ac	89	140	229.03302(4)	62.7(5) min	(3/2+)
230Ac	89	141	230.03629(32)	122(3) s	(1+)
231Ac	89	142	231.03856(11)	7.5(1) min	(1/2+)
232Ac	89	143	232.04203(11)	119(5) s	(1+)
233Ac	89	144	233.04455(32)#	145(10) s	(1/2+)
234Ac	89	145	234.04842(43)#	44(7) s
235Ac	89	146	235.05123(38)#	40# s	1/2+#
236Ac	89	147	236.05530(54)#	2# min

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.

References

★ Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in ''Nuclear Physics'' A729 (2003).

★ Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). ''Pure Appl. Chem.'' Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).

★ Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.

★
★ Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).

★
★ National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).

★
★ David R. Lide (ed.), Norman E. Holden in ''CRC Handbook of Chemistry and Physics, 85th Edition'', online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.