Isotopes of astatine

Astatine (₈₅At) has 39 known isotopes, all of which are radioactive; the range of their mass numbers is from 191 to 229. There also exist 23 metastable excited states. The longest-lived isotope is ²¹⁰At, which has a half-life of 8.1 hours; the longest-lived isotope existing in naturally occurring decay chains is ²¹⁹At with a half-life of 56 seconds.

Main isotopes of astatine (₈₅At)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^209At syn 5.41 h β^+ ^209Po α ^205Bi ^210At syn 8.1 h β^+ ^210Po α ^206Bi ^211At syn 7.21 h ε ^211Po α ^207Bi

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life	Decay mode [n 4]	Daughter isotope	Spin and parity [n 5][n 6]	Isotopic abundance
	Excitation energy[n 6]
^191At	85	106		1.7(+11−5) ms			(1/2+)
^191mAt				2.1(+4−3) ms			(7/2−)
^192At	85	107	192.00314(28)	11.5(0.6) ms	α (99.79%)	^188Bi	3+#
					β^+, SF (0.21%)	(various)
^192mAt	330(90)# keV			88(6) ms	α (99.79%)	^188mBi	(9-, 10−)
					β^+, SF (0.21%)	(various)
^193At	85	108	192.99984(6)	28(+5−4) ms	α	^189Bi	(1/2+)
^193m1At	50 keV			21(5) ms			(7/2−)
^193m2At	39 keV			27(+4−5) ms			(13/2+)
^194At	85	109	193.99873(20)	286(7) ms	α	^190Bi	(4-, 5-)
					β^+ (rare)	^194Po
^194mAt	480(190) keV			323(7) ms	α	^190Bi	(9-, 10-)
					IT (rare)	^194At
^195At	85	110	194.996268(10)	328(20) ms	α (75%)	^191Bi	(1/2+)
					β^+ (25%)	^195Po
^195mAt	34(7) keV			147(5) ms			(7/2-)
^196At	85	111	195.99579(6)	253(9) ms	α (96%)	^192Bi	(3+)
					β^+ (4.0%)	^196Po
^196m1At	−30(80) keV			20# ms			(10−)
^196m2At	157.9(1) keV			11 µs			(5+)
^197At	85	112	196.99319(5)	0.390(16) s	α (96%)	^193Bi	(9/2−)
					β^+ (4.0%)	^197Po
^197mAt	52(10) keV			2.0(2) s			(1/2+)
^198At	85	113	197.99284(5)	4.2(3) s	α (94%)	^194Bi	(3+)
					β^+ (6%)	^198Po
^198mAt	330(90)# keV			1.0(2) s			(10−)
^199At	85	114	198.99053(5)	6.92(13) s	α (89%)	^195Bi	(9/2−)
					β^+ (11%)	^199Po
^200At	85	115	199.990351(26)	43.2(9) s	α (57%)	^196Bi	(3+)
					β^+ (43%)	^200Po
^200m1At	112.7(30) keV			47(1) s	α (43%)	^196Bi	(7+)
					IT	^200At
					β^+	^200Po
^200m2At	344(3) keV			3.5(2) s			(10−)
^201At	85	116	200.988417(9)	85(3) s	α (71%)	^197Bi	(9/2−)
					β^+ (29%)	^201Po
^202At	85	117	201.98863(3)	184(1) s	β^+ (88%)	^202Po	(2, 3)+
					α (12%)	^198Bi
^202m1At	190(40) keV			182(2) s			(7+)
^202m2At	580(40) keV			460(50) ms			(10−)
^203At	85	118	202.986942(13)	7.37(13) min	β^+ (69%)	^203Po	9/2−
					α (31%)	^199Bi
^204At	85	119	203.987251(26)	9.2(2) min	β^+ (96%)	^204Po	7+
					α (3.8%)	^200Bi
^204mAt	587.30(20) keV			108(10) ms	IT	^204At	(10−)
^205At	85	120	204.986074(16)	26.2(5) min	β^+ (90%)	^205Po	9/2−
					α (10%)	^201Bi
^205mAt	2339.65(23) keV			7.76(14) µs			29/2+
^206At	85	121	205.986667(22)	30.6(13) min	β^+ (99.11%)	^206Po	(5)+
					α (0.9%)	^202Bi
^206mAt	807(3) keV			410(80) ns			(10)−
^207At	85	122	206.985784(23)	1.80(4) h	β^+ (91%)	^207Po	9/2−
					α (8.6%)	^203Bi
^208At	85	123	207.986590(28)	1.63(3) h	β^+ (99.5%)	^208Po	6+
					α (0.55%)	^204Bi
^209At	85	124	208.986173(8)	5.41(5) h	β^+ (96%)	^209Po	9/2−
					α (4.0%)	^205Bi
^210At	85	125	209.987148(8)	8.1(4) h	β^+ (99.8%)	^210Po	(5)+
					α (0.18%)	^206Bi
^210m1At	2549.6(2) keV			482(6) µs			(15)−
^210m2At	4027.7(2) keV			5.66(7) µs			(19)+
^211At	85	126	210.9874963(30)	7.214(7) h	EC (58.2%)	^211Po	9/2−
					α (42%)	^207Bi
^212At	85	127	211.990745(8)	0.314(2) s	α (99.95%)	^208Bi	(1−)
					β^+ (0.05%)	^212Po
					β^− (2×10^−6%)	^212Rn
^212m1At	223(7) keV			0.119(3) s	α (99%)	^208Bi	(9−)
					IT (1%)	^212At
^212m2At	4771.6(11) keV			152(5) µs			(25−)
^213At	85	128	212.992937(5)	125(6) ns	α	^209Bi	9/2−
^214At	85	129	213.996372(5)	558(10) ns	α	^210Bi	1−
^214m1At	59(9) keV			265(30) ns
^214m2At	231(6) keV			760(15) ns			9−
^215At	85	130	214.998653(7)	0.10(2) ms	α	^211Bi	9/2−	Trace[n 7]
^216At	85	131	216.002423(4)	0.30(3) ms	α (99.99%)	^212Bi	1−
					β^− (.006%)	^216Rn
					EC (3×10^−7%)	^216Po
^216mAt	413(5) keV			100# µs			(9−)
^217At	85	132	217.004719(5)	32.3(4) ms	α (99.98%)	^213Bi	9/2−	Trace[n 8]
					β^− (.012%)	^217Rn
^218At	85	133	218.008694(12)	1.5(3) s	α (99.9%)	^214Bi	1−#	Trace[n 9]
					β^− (0.10%)	^218Rn
^219At	85	134	219.011162(4)	56(3) s	α (97%)	^215Bi	(9/2-)	Trace[n 7]
					β^− (3.0%)	^219Rn
^220At	85	135	220.01541(6)	3.71(4) min	β^− (92%)	^220Rn	3(−#)
					α (8.0%)	^216Bi
^221At	85	136	221.01805(21)#	2.3(2) min	β^−	^221Rn	3/2−#
^222At	85	137	222.02233(32)#	54(10) s	β^−	^222Rn
^223At	85	138	223.02519(43)#	50(7) s	β^−	^223Rn	3/2−#
^224At	85	139	224.02975(22)#	2.5(1.5) min	β^−	^224Rn

1. ^mAt – 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
   IT:	Isomeric transition

5. ( ) spin value – Indicates spin with weak assignment arguments.
6. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
7. Intermediate decay product of ²³⁵U
8. Intermediate decay product of ²³⁷Np
9. Intermediate decay product of ²³⁸U

Alpha decay

Alpha decay characteristics for sample astatine isotopes[lower-alpha 1]
Mass number	Mass excess[1]	Mass excess of daughter[1]	Average energy of alpha decay	Half-life[1]	Probability of alpha decay[1]	Alpha decay half-life
207	−13.243 MeV	−19.116 MeV	5.873 MeV	1.80 h	8.6%	20.9 h
208	−12.491 MeV	−18.243 MeV	5.752 MeV	1.63 h	0.55%	12.3 d
209	−12.880 MeV	−18.638 MeV	5.758 MeV	5.41 h	4.1%	5.5 d
210	−11.972 MeV	−17.604 MeV	5.632 MeV	8.1 h	0.175%	193 d
211	−11.647 MeV	−17.630 MeV	5.983 MeV	7.21 h	41.8%	17.2 h
212	−8.621 MeV	−16.436 MeV	7.825 MeV	0.31 s	≈100%	0.31 s
213	−6.579 MeV	−15.834 MeV	9.255 MeV	125 ns	100%	125 ns
214	−3.380 MeV	−12.366 MeV	8.986 MeV	558 ns	100%	558 ns
219	10.397 MeV	4.073 MeV	6.324 MeV	56 s	97%	58 s
220	14.350 MeV	8.298 MeV	6.052 MeV	3.71 min	8%	46.4 min
221[lower-alpha 2]	16.810 MeV	11.244 MeV	5.566 MeV	2.3 min	experimentally alpha stable	∞

Astatine has 23 nuclear isomers (nuclei with one or more nucleons – protons or neutrons – in an excited state). A nuclear isomer may also be called a "meta-state"; this means the system has more internal energy than the "ground state" (the state with the lowest possible internal energy), making the former likely to decay into the latter. There may be more than one isomer for each isotope. The most stable of them is astatine-202m1,[lower-alpha 3] which has a half-life of about 3 minutes; this is longer than those of all ground states except those of isotopes 203–211 and 220. The least stable one is astatine-214m1; its half-life of 265 ns is shorter than those of all ground states except that of astatine-213.[1]

Alpha decay energy follows the same trend as for other heavy elements.[2] Lighter astatine isotopes have quite high energies of alpha decay, which become lower as the nuclei become heavier. However, astatine-211 has a significantly higher energy than the previous isotope; it has a nucleus with 126 neutrons, and 126 is a magic number (corresponding to a filled neutron shell). Despite having a similar half-life time as the previous isotope (8.1 hours for astatine-210 and 7.2 hours for astatine-211), the alpha decay probability is much higher for the latter: 41.8 percent versus just 0.18 percent.[1][lower-alpha 4] The two following isotopes release even more energy, with astatine-213 releasing the highest amount of energy of all astatine isotopes. For this reason, it is the shortest-lived astatine isotope.[2] Even though heavier astatine isotopes release less energy, no long-lived astatine isotope exists; this happens due to the increasing role of beta decay.[2] This decay mode is especially important for astatine: as early as 1950, it was postulated that the element has no beta-stable isotopes (i.e. ones that do not undergo beta decay at all),[3] though nuclear mass measurements reveal that ²¹⁵At is in fact beta-stable, as it has the lowest mass of all isobars with A = 215.[4] A beta decay mode has been found for all other astatine isotopes except for astatine-213, astatine-214, and astatine-216m.[1] Among other isotopes: astatine-210 and the lighter isotopes decay by positron emission; astatine-216 and the heavier isotopes undergo beta decay; astatine-212 can decay either way; and astatine-211 decays by electron capture instead.[1]

The most stable isotope of astatine is astatine-210, which has a half-life of about 8.1 hours. This isotope's primary decay mode is positron emission to the relatively long-lived alpha emitter, polonium-210. In total, only five isotopes of astatine have half-lives exceeding one hour: those between 207 and 211. The least stable ground state isotope is astatine-213, with a half-life of about 125 nanoseconds. It undergoes alpha decay to the extremely long-lived isotope (in practice, a stable one) bismuth-209.[1]

See also

1. In the table, under the words "mass excess", the energy equivalents are given rather than the real mass excesses; "mass excess daughter" stands for the energy equivalent of the mass excess sum of the daughter of the isotope and the alpha particle; "alpha decay half-life" refers to the half-life if decay modes other than alpha are omitted.
2. Since astatine-221 has not been shown to undergo alpha decay, the alpha decay energy is theoretical. The value for mass excess is calculated rather than measured.
3. "m1" means that this state of the isotope is the next possible one above – energy greater than – the ground state. "m2" and similar designations refer to further higher energy states. The number may be dropped if there is only one well-established meta state, such as astatine-216m. Note that other designation techniques exist.
4. This means that if decay modes other than alpha are omitted, then astatine-210 has an alpha half-life of 4,628.6 hours (128.9 days) and astatine-211 has one of 17.2 hours (0.9 days). Therefore, astatine-211 is less stable toward alpha decay than the lighter isotope, and is more likely to undergo alpha decay in the same time period.

References

1. 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
2. Lavrukhina & Pozdnyakov 1966, p. 232.
3. Rankama, Kalervo (1956). Isotope geology (2nd ed.). Pergamon Press. p. 403. ISBN 978-0-470-70800-2.
4. Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.

• Lavrukhina, Avgusta Konstantinovna; Pozdnyakov, Aleksandr Aleksandrovich (1966). Аналитическая химия технеция, прометия, астатина и франция [Analytical Chemistry of Technetium, Promethium, Astatine, and Francium] (in Russian). Nauka.
• 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
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• 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.