Isotopes of actinium

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Actinides and fission products by half-life
Actinides[1] by decay chain Half-life
range (y)		 Fission products of 235U by yield[2]
4n 4n+1 4n+2 4n+3
4.5–7% 0.04–1.25% <0.001%
228Ra№ 4–6 † 155Euþ
244Cm 241Puƒ 250Cf 227Ac№ 10–29 90Sr 85Kr 113mCdþ
232Uƒ 238Pu№ 243Cmƒ 29–97 137Cs 151Smþ 121mSn
248Bk[3] 249Cfƒ 242mAmƒ 141–351

No fission products
have a half-life
in the range of
100–210 k years ...
241Amƒ 251Cfƒ[4] 430–900
226Ra№ 247Bk 1.3 k – 1.6 k
240Pu 229Th№ 246Cm 243Amƒ 4.7 k – 7.4 k
245Cmƒ 250Cm 8.3 k – 8.5 k
239Puƒ№ 24.1 k
230Th№ 231Pa№ 32 k – 76 k
236Npƒ 233Uƒ№ 234U№ 150 k – 250 k ‡ 99Tc₡ 126Sn
248Cm 242Pu 327 k – 375 k 79Se₡
1.53 M 93Zr
237Np№ 2.1 M – 6.5 M 135Cs₡ 107Pd
236U№ 247Cmƒ 15 M – 24 M 129I₡
244Pu№ 80 M

... nor beyond 15.7 M years[5]
232Th№ 238U№ 235Uƒ№ 0.7 G – 14.1 G

Legend for superscript symbols
₡  has thermal neutron capture cross section in the range of 8–50 barns
ƒ  fissile
m  metastable isomer
№  naturally occurring radioactive material (NORM)
þ  neutron poison (thermal neutron capture cross section greater than 3k barns)
†  range 4–97 y: Medium-lived fission product
‡  over 200,000 y: Long-lived fission product

Actinium (Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, 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.[6]

Table

nuclide
symbol		 historic
name		 Z(p) N(n)  
isotopic mass (u)
 		 half-life decay
mode(s)[7][n 1]		 daughter
isotope(s)[n 2]		 nuclear
spin		 representative
isotopic
composition
(mole fraction)		 range of natural
variation
(mole fraction)
excitation energy
205Ac[8] 89 116 20(+97−9) ms α 201Fr
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) y β− (98.61%) 227Th 3/2− Trace[n 5]
α (1.38%) 223Fr
228Ac Mesothorium 2 89 139 228.0310211(27) 6.13(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

References

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  • Isotopic compositions and standard atomic masses from:
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  • Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
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Isotopes of radium Isotopes of actinium Isotopes of thorium
Table of nuclides
Isotopes of the chemical elements
1
H		 2
He
3
Li		 4
Be		 5
B		 6
C		 7
N		 8
O		 9
F		 10
Ne
11
Na		 12
Mg		 13
Al		 14
Si		 15
P		 16
S		 17
Cl		 18
Ar
19
K		 20
Ca		 21
Sc		 22
Ti		 23
V		 24
Cr		 25
Mn		 26
Fe		 27
Co		 28
Ni		 29
Cu		 30
Zn		 31
Ga		 32
Ge		 33
As		 34
Se		 35
Br		 36
Kr
37
Rb		 38
Sr		 39
Y		 40
Zr		 41
Nb		 42
Mo		 43
Tc		 44
Ru		 45
Rh		 46
Pd		 47
Ag		 48
Cd		 49
In		 50
Sn		 51
Sb		 52
Te		 53
I		 54
Xe
55
Cs		 56
Ba		 1 asterisk 72
Hf		 73
Ta		 74
W		 75
Re		 76
Os		 77
Ir		 78
Pt		 79
Au		 80
Hg		 81
Tl		 82
Pb		 83
Bi		 84
Po		 85
At		 86
Rn
87
Fr		 88
Ra		 2 asterisks 104
Rf		 105
Db		 106
Sg		 107
Bh		 108
Hs		 109
Mt		 110
Ds		 111
Rg		 112
Cn		 113
Uut		 114
Fl		 115
Uup		 116
Lv		 117
Uus		 118
Uuo
1 asterisk 57
La		 58
Ce		 59
Pr		 60
Nd		 61
Pm		 62
Sm		 63
Eu		 64
Gd		 65
Tb		 66
Dy		 67
Ho		 68
Er		 69
Tm		 70
Yb		 71
Lu
2 asterisks 89
Ac		 90
Th		 91
Pa		 92
U		 93
Np		 94
Pu		 95
Am		 96
Cm		 97
Bk		 98
Cf		 99
Es		 100
Fm		 101
Md		 102
No		 103
Lr
  1. ↑ 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 isotopes have half-lives of at least four years (the longest-lived isotope 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.
  2. ↑ Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
    "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 y. No growth of Cf248 was detected, and a lower limit for the β− half-life can be set at about 104 y. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 y."
  4. ↑ This is the heaviest isotope with a half-life of at least four years before the "Sea of Instability".
  5. ↑ Excluding those "classically stable" isotopes with half-lives significantly in excess of 232Th; e.g., while 113mCd has a half-life of only fourteen years, that of 113Cd is nearly eight quadrillion years.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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