Isótopos de astato

Isótopos principales de astato  ( ₈₅ At)

Isótopo Decaer abundancia vida media ( t 1/2 ) modo producto 209 en syn 5.41 horas β + 209 Po α 205 Bi 210 en syn 8,1 horas β + 210 Po α 206 Bi 211 en syn 7.21 horas ε 211 Po α 207 Bi

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La astatina ( ₈₅ At) tiene 39 isótopos conocidos , todos los cuales son radiactivos ; el rango de sus números de masa es de 191 a 229. También hay 24 estados excitados metaestables conocidos . El isótopo de vida más larga es ²¹⁰ At, que tiene una vida media de 8,1 horas; el isótopo de vida más larga que existe en las cadenas de desintegración naturales es ²¹⁹ At con una vida media de 56 segundos.

Lista de isótopos

Nuclido [n 1]	Z	norte	Masa isotópica ( Da ) [n 2] [n 3]	Media vida	Modo de caída [n 4]	Isótopo hija	Spin y paridad [n 5] [n 6]	Abundancia isotópica
	Energía de excitación [n 6]
191 en	85	106		1,7 (+ 11−5) ms			(1/2 +)
191m en				2,1 (+ 4−3) ms			(7 / 2−)
192 en	85	107	192.00314 (28)	11,5 (0,6) ms	α (99,79%)	188 Bi	3 + #
					β + , SF (0,21%)	(varios)
192m en	330 (90) # keV			88 (6) ms	α (99,79%)	188m Bi	(9-, 10−)
					β + , SF (0,21%)	(varios)
193 en	85	108	192.99984 (6)	28 (+ 5−4) ms	α	189 Bi	(1/2 +)
193m1 en	50 keV			21 (5) ms			(7 / 2−)
193m2 en	39 keV			27 (+ 4−5) ms			(13/2 +)
194 en	85	109	193.99873 (20)	286 (7) ms	α	190 Bi	(4, 5)
					β + (raro)	194 Po
194m en	480 (190) keV			323 (7) ms	α	190 Bi	(9-, 10-)
					IT (raro)	194 en
195 en	85	110	194.996268 (10)	328 (20) ms	α (75%)	191 Bi	(1/2 +)
					β + (25%)	195 Po
195m en	34 (7) keV			147 (5) ms			(7 / 2-)
196 en	85	111	195.99579 (6)	253 (9) ms	α (96%)	192 Bi	(3+)
					β + (4,0%)	196 Po
196m1 en	−30 (80) keV			20 # ms			(10−)
196m2 en	157,9 (1) keV			11 μs			(5+)
197 en	85	112	196.99319 (5)	0.390 (16) s	α (96%)	193 Bi	(9 / 2−)
					β + (4,0%)	197 Po
197m en	52 (10) keV			2,0 (2) s			(1/2 +)
198 en	85	113	197.99284 (5)	4,2 (3) s	α (94%)	194 Bi	(3+)
					β + (6%)	198 Po
198m en	330 (90) # keV			1,0 (2) s			(10−)
199 en	85	114	198,99053 (5)	6,92 (13) s	α (89%)	195 Bi	(9 / 2−)
					β + (11%)	199 Po
200 en	85	115	199,990351 (26)	43,2 (9) s	α (57%)	196 Bi	(3+)
					β + (43%)	200 Po
200m1 en	112,7 (30) keV			47 (1) s	α (43%)	196 Bi	(7+)
					ESO	200 en
					β +	200 Po
200m2 en	344 (3) keV			3,5 (2) s			(10−)
201 en	85	116	200,988417 (9)	85 (3) s	α (71%)	197 Bi	(9 / 2−)
					β + (29%)	201 Po
202 en	85	117	201.98863 (3)	184 (1) s	β + (88%)	202 Po	(2, 3) +
					α (12%)	198 Bi
202m1 en	190 (40) keV			182 (2) s			(7+)
202m2 en	580 (40) keV			460 (50) ms			(10−)
203 en	85	118	202.986942 (13)	7.37 (13) min	β + (69%)	203 Po	9 / 2−
					α (31%)	199 Bi
204 en	85	119	203,987251 (26)	9.2 (2) min	β + (96%)	204 Po	7+
					α (3,8%)	200 Bi
204m en	587,30 (20) keV			108 (10) ms	ESO	204 en	(10−)
205 en	85	120	204.986074 (16)	26,2 (5) min	β + (90%)	205 Po	9 / 2−
					α (10%)	201 Bi
205m en	2339,65 (23) keV			7,76 (14) μs			29/2 +
206 en	85	121	205.986667 (22)	30,6 (13) min	β + (99,11%)	206 Po	(5) +
					α (0,9%)	202 Bi
206m en	807 (3) keV			410 (80) ns			(10) -
207 en	85	122	206,985784 (23)	1,80 (4) horas	β + (91%)	207 Po	9 / 2−
					α (8,6%)	203 Bi
208 en	85	123	207,986590 (28)	1,63 (3) horas	β + (99,5%)	208 Po	6+
					α (0,55%)	204 Bi
209 en	85	124	208,986173 (8)	5,41 (5) horas	β + (96%)	209 Po	9 / 2−
					α (4,0%)	205 Bi
210 en	85	125	209,987148 (8)	8,1 (4) horas	β + (99,8%)	210 Po	(5) +
					α (0,18%)	206 Bi
210m1 en	2549,6 (2) keV			482 (6) μs			(15) -
210m2 en	4027,7 (2) keV			5,66 (7) μs			(19) +
211 en	85	126	210.9874963 (30)	7.214 (7) horas	CE (58,2%)	211 Po	9 / 2−
					α (42%)	207 Bi
212 en	85	127	211.990745 (8)	0,314 (2) s	α (99,95%)	208 Bi	(1−)
					β + (0,05%)	212 Po
					β - (2 × 10 −6 %)	212 Rn
212m1 en	223 (7) keV			0,119 (3) s	α (99%)	208 Bi	(9−)
					ES (1%)	212 en
212m2 en	4771,6 (11) keV			152 (5) μs			(25−)
213 en	85	128	212.992937 (5)	125 (6) ns	α	209 Bi	9 / 2−
214 en	85	129	213.996372 (5)	558 (10) ns	α	210 Bi	1−
214m1 en	59 (9) keV			265 (30) ns
214m2 en	231 (6) keV			760 (15) ns			9−
215 en	85	130	214.998653 (7)	0,10 (2) ms	α	211 Bi	9 / 2−	Seguimiento [n 7]
216 en	85	131	216.002423 (4)	0,30 (3) ms	α (99,99%)	212 Bi	1−
					β - (0,006%)	216 Rn
					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[a] v t e
Mass number	Massexcess[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[b]	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,^[c] 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][d] 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 (in practice, stable) isotope 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.