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List of isotopes

Nuclide2	Historicname	Z	N	Isotopic mass (Da)34	Half-life	Decaymode5	Daughterisotope6	Spin andparity78	Isotopicabundance
		Excitation energy9
203Ac10		89	114		56+269−26 μs	α	199Fr	(1/2+)
204Ac11		89	115		7.4+2.2−1.4 ms	α	200Fr
205Ac12		89	116		7.7+2.7−1.6 ms13	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)	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	217.009347(14)	69(4) ns	α	213Fr	9/2−
217mAc		2012(20) keV			740(40) ns			(29/2)+
218Ac		89	129	218.01164(5)	1.08(9) μs	α	214Fr	(1−)#
218mAc		607(86)# keV			103(11) ns	IT	218Ac	(11+)
219Ac		89	130	219.01242(5)	11.8(15) μs	α	215Fr	9/2−
220Ac		89	131	220.014763(16)	26.36(19) ms	α	216Fr	(3−)
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(1)%)	218Fr	1−
						β+ (1(1)%)14	222Ra
222mAc		78(21) keV			1.05(5) min	α (98.6%)	218Fr	5+#
						β+ (1.4%)	222Ra
						IT?	222Ac
223Ac		89	134	223.019137(8)	2.10(5) min	α (99%)	219Fr	(5/2−)
						EC (1%)	223Ra
						CD (3.2×10−9%)	209Bi14C
224Ac		89	135	224.021723(4)	2.78(17) h	β+ (90.9%)	224Ra	0−
						α (9.1%)	220Fr
						β− (1.6%)	224Th
225Ac15		89	136	225.023230(5)	10.0(1) d	α	221Fr	(3/2−)	Trace16
						CD (6×10−10%)	211Bi14C
226Ac		89	137	226.026098(4)	29.37(12) h	β− (83%)	226Th	(1)(−#)
						EC (17%)	226Ra
						α (.006%)	222Fr
227Ac	Actinium17	89	138	227.0277521(26)	21.772(3) y	β− (98.62%)	227Th	3/2−	Trace18
						α (1.38%)	223Fr
228Ac	Mesothorium 2	89	139	228.0310211(27)	6.13(2) h	β−	228Th	3+	Trace19
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+#
236Ac20		89	147	236.05530(54)#	72+345−33 s	β−	236Th
This table header & footer: view

Actinides vs fission products

Actinides and fission products by half-life v t e
Actinides21 by decay chain				Half-life range (a)	Fission products of 235U by yield22
4n	4n + 1	4n + 2	4n + 3		4.5–7%	0.04–1.25%	<0.001%
228Ra№				4–6 a		155Euþ
248Bk23				> 9 a
244Cmƒ	241Puƒ	250Cf	227Ac№	10–29 a	90Sr	85Kr	113mCdþ
232Uƒ		238Puƒ	243Cmƒ	29–97 a	137Cs	151Smþ	121mSn
	249Cfƒ	242mAmƒ		141–351 a	No fission products have a half-lifein the range of 100 a–210 ka ...
	241Amƒ		251Cfƒ24	430–900 a
		226Ra№	247Bk	1.3–1.6 ka
240Pu	229Th	246Cmƒ	243Amƒ	4.7–7.4 ka
	245Cmƒ	250Cm		8.3–8.5 ka
			239Puƒ	24.1 ka
		230Th№	231Pa№	32–76 ka
236Npƒ	233Uƒ	234U№		150–250 ka	99Tc₡	126Sn
248Cm		242Pu		327–375 ka		79Se₡
				1.33 Ma	135Cs₡
	237Npƒ			1.61–6.5 Ma	93Zr	107Pd
236U			247Cmƒ	15–24 Ma		129I₡
244Pu				80 Ma	... nor beyond 15.7 Ma25
232Th№		238U№	235Uƒ№	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.²⁶²⁷²⁸ 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.²⁹ Another benefit is that the decay chain of 225Ac ends in the nuclide 209Bi,³⁰ which has a considerably shorter biological half-life than lead.³¹³² 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.³³

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.³⁴ There are researches on 226Ac to use it in SPECT.³⁵³⁶

Actinium-227

Actinium-227 is the most stable isotope of actinium, with a half-life of 21.772 years. It mainly (98.62%) undergos beta decay, but sometimes (1.38%) it will undergo alpha decay instead.³⁷ 227Ac 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.³⁸³⁹ 227Ac is prepared, in milligram amounts, by the neutron irradiation of 226Ra in a nuclear reactor.⁴⁰⁴¹

Ra 88 226 + n 0 1 ⟶ Ra 88 227 → 42.2   min β − Ac 89 227 {\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.⁴² 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:

Be 4 9 + He 2 4 ⟶ C 6 12 + n 0 1 + γ {\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.⁴³⁴⁴ Such probes are also used in well logging applications, in neutron radiography, tomography and other radiochemical investigations.⁴⁵

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.⁴⁶⁴⁷

See also

• Actinium series
• Actinide

Notes

• 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 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.

References

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2. mAc – Excited nuclear isomer. /wiki/Nuclear_isomer ↩

3. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits. ↩

4. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS). ↩

5. Modes of decay: EC:Electron captureCD:Cluster decayIT:Isomeric transition /wiki/Electron_capture ↩

6. Bold italics symbol as daughter – Daughter product is nearly stable. ↩

7. ( ) spin value – Indicates spin with weak assignment arguments. ↩

8. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN). ↩

9. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN). ↩

10. 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. https://doi.org/10.1016%2Fj.physletb.2024.138503 ↩

11. 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. https://doi.org/10.1016%2Fj.physletb.2022.137484 ↩

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14. This decay mode has been observed, but only an upper limit of branching ratio is experimentally known[1] ↩

15. Has medical uses /wiki/Nuclear_medicine ↩

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17. Source of element's name ↩

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21. 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. /wiki/Polonium ↩

22. Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor. /wiki/Thermal_neutron ↩

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24. This is the heaviest nuclide with a half-life of at least four years before the "sea of instability". /wiki/Sea_of_instability ↩

25. 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. /wiki/Primordial_nuclide ↩

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30. 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. /wiki/Isotopes_of_thallium ↩

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