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 226Ac synth 29.37 h β− 226Th ε 226Ra α 222Fr 227Ac trace 21.772 y β− 227Th α 223Fr 228Ac trace 6.15 h β− 228Th

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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) [3] [n 2] [n 3]	Half-life [1]	Decay mode [1] [n 4]	Daughter isotope [n 5]	Spin and parity [1] [n 6] [n 7]	Isotopic abundance
		Excitation energy [n 7]
203Ac [4]		89	114		56+269 −26 μs	α	199Fr	(1/2+)
204Ac [5]		89	115		7.4+2.2 −1.4 ms	α	200Fr
205Ac		89	116	205.01514(6)	7.7+2.7 −1.6 ms [5]	α	201Fr	9/2−
206Ac		89	117	206.01448(7)	25(7) ms	α	202Fr	(3+)
206mAc		200(70) keV			41(16) ms	α	202mFr	(10−)
207Ac		89	118	207.01197(6)	31(8) ms	α	203Fr	9/2−#
208Ac		89	119	208.01155(7)	97(15) ms	α	204Fr	(3+)
208mAc		500(60) keV			28(7) ms	α	204Fr	(10−)
						IT  ?	208Ac
209Ac		89	120	209.00950(6)	94(10) ms	α	205Fr	(9/2−)
210Ac		89	121	210.00941(7)	350(40) ms	α	206Fr	7+#
211Ac		89	122	211.00767(6)	213(25) ms	α	207Fr	9/2−
212Ac		89	123	212.007836(23)	895(28) ms	α	208Fr	7+
213Ac		89	124	213.006593(13)	738(16) ms	α	209Fr	9/2−
214Ac		89	125	214.006906(15)	8.2(2) s	α (93%)	210Fr	5+
						β+ (7%)	214Ra
215Ac		89	126	215.006474(13)	171(10) ms	α (99.91%)	211Fr	9/2−
						β+ (0.09%)	215Ra
215m1Ac		1796.0(9) keV			185(30) ns	IT	215Ac	(21/2−)
215m2Ac		2488(50)# keV			335(10) ns	IT	215Ac	(29/2+)
216Ac		89	127	216.008749(10)	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	217.009342(12)	69(4) ns	α	213Fr	9/2−
217mAc		2012(20) keV			740(40) ns			29/2+
218Ac		89	129	218.01165(6)	1.00(4) μs	α	214Fr	(1−)
218mAc		607(86)# keV			103(11) ns	IT	218Ac	(11+)
219Ac		89	130	219.01242(6)	9.4(10) μs	α	215Fr	9/2−
220Ac		89	131	220.014755(7)	26.36(19) ms	α	216Fr	(3−)
221Ac		89	132	221.01560(6)	52(2) ms	α	217Fr	9/2−#
222Ac		89	133	222.017844(5)	5.0(5) s	α	218Fr	1−
						β+ (<2%)	222Ra
222mAc		78(21) keV			1.05(5) min	α (98.6%)	218Fr	5+#
						β+ (1.4%)	222Ra
						IT?	222Ac
223Ac		89	134	223.019136(7)	2.10(5) min	α	219Fr	(5/2−)
						EC  ?	223Ra
						CD (3.2×10−9%) [6]	209Bi 14C
224Ac		89	135	224.021722(4)	2.78(16) h	β+ (90.5%)	224Ra	(0−)
						α (9.5%)	220Fr
						β− ?	224Th
225Ac [n 8]		89	136	225.023229(5)	9.9190(21) d	α	221Fr	3/2−	Trace [n 9]
						CD (5.3×10−10%)	211Bi 14C
226Ac		89	137	226.026097(3)	29.37(12) h	β− (83%)	226Th	(1−)
						EC (17%)	226Ra
						α (0.006%)	222Fr
227Ac	Actinium [n 10]	89	138	227.0277506(21)	21.772(3) y	β− (98.62%)	227Th	3/2−	Trace [n 11]
						α (1.38%)	223Fr
228Ac	Mesothorium 2	89	139	228.0310197(22)	6.15(2) h	β−	228Th	3+	Trace [n 12]
229Ac		89	140	229.032947(13)	62.7(5) min	β−	229Th	3/2+
230Ac		89	141	230.036327(17)	122(3) s	β−	230Th	(1+)
231Ac		89	142	231.038393(14)	7.5(1) min	β−	231Th	1/2+
232Ac		89	143	232.042034(14)	1.98(8) min	β−	232Th	(1+)
233Ac		89	144	233.044346(14)	143(10) s	β−	233Th	(1/2+)
234Ac		89	145	234.048139(15)	45(2) s	β−	234Th
235Ac		89	146	235.050840(15)	62(4) s	β−	235Th	1/2+#
236Ac [7]		89	147	236.05499(4)	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:

   EC:	Electron capture
   CD:	Cluster decay
   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 [8] by decay chain				Half-life range (a)	Fission products of 235U by yield [9]
4n	4n + 1	4n + 2	4n + 3		4.5–7%	0.04–1.25%	<0.001%
228 Ra№				4–6 a		155 Euþ
248 Bk [10]				> 9 a
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
	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 [11]	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₡
				1.33 Ma	135 Cs₡
	237 Npƒ			1.61–6.5 Ma	93 Zr	107 Pd
236 U			247 Cmƒ	15–24 Ma		129 I₡
244 Pu				80 Ma	... nor beyond 15.7 Ma [12]
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)

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. ^{[13] [14] [15]} 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. ^[16] 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. ^{[17] [18]} 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. ^[19]

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. ^{[20] [21]}

Actinium-227

Actinium-227 is the most stable isotope of actinium, with a half-life of 21.772 years. It mainly (98.62%) undergoes beta decay, but sometimes (1.38%) it will undergo alpha decay instead. ^{[1] 227}Ac 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. ^{[22] [23] 227}Ac is prepared, in milligram amounts, by the neutron irradiation of ²²⁶Ra in a nuclear reactor. ^{[23] [24]}

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

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. ^[25] 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. ^{[26] [27]} Such probes are also used in well logging applications, in neutron radiography, tomography and other radiochemical investigations. ^[28]

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. ^{[29] [30]}

See also

• Actinium series
• Actinide

Notes

1. Bismuth-209 decays into thallium-205 with a half-life exceeding 10¹⁹ years, but this half-life is so long that for practical purposes bismuth-209 can be considered stable.

References

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4. 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.
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8. 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.
9. Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
10. 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]."
11. This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
12. 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.
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17. 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.
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21. 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.
22. Hagemann, French (1950). "The Isolation of Actinium". Journal of the American Chemical Society. 72 (2): 768–771. doi:10.1021/ja01158a033.
23. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 946. doi:10.1016/C2009-0-30414-6. ISBN   978-0-08-037941-8.
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25. Russell, Alan M. and Lee, Kok Loong (2005) Structure-property relations in nonferrous metals. Wiley. ISBN   0-471-64952-X, pp. 470–471
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• 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 3.0 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.