Isotopes of astatine
Astatine (At) has 37 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.
There are 32 known isotopes of astatine, with atomic masses (mass numbers) of 191 and 193–223.[1] No stable or even long-lived astatine isotope is known, and no such isotope is expected to exist.[2]
|
Alpha decay characteristics for sample astatine isotopes[lower-alpha 1]
|
||||||
|---|---|---|---|---|---|---|
| Mass number |
Mass excess[3] |
Mass excess of daughter[3] |
Average energy of alpha decay |
Half-life[3] | Probability of alpha decay[3] |
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][clarification needed] 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).[4] A beta decay mode has been found for all astatine isotopes except for astatine-213, astatine-214, astatine-215, 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 decays via either ways; and astatine-211 decays by electron capture instead.[1]
The most stable isotope of astatine is At-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]
Table
| nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life | decay mode(s)[5][n 1] |
daughter isotope(s) |
nuclear spin |
representative isotopic composition (mole fraction) |
range of natural variation (mole fraction) |
|---|---|---|---|---|---|---|---|---|---|
| excitation energy | |||||||||
| 191At | 85 | 106 | 1.7(+11−5) ms | (1/2+) | |||||
| 191mAt | 2.1(+4−3) ms | (7/2−) | |||||||
| 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) | ~40 ms | α | 190Bi | 3+# | ||
| β+ (rare) | 194Po | ||||||||
| 194mAt | 480(190) keV | ~250 ms | α | 190Bi | 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 | 9/2−# | ||||||
| 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 2] | |
| 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− | ||
| β− (.012%) | 217Rn | ||||||||
| 218At | 85 | 133 | 218.008694(12) | 1.5(3) s | α (99.9%) | 214Bi | 1−# | Trace[n 3] | |
| β− (0.10%) | 218Rn | ||||||||
| 219At | 85 | 134 | 219.011162(4) | 56(3) s | α (97%) | 215Bi | 5/2−# | Trace[n 2] | |
| 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 | 3/2−# | ||||
- ↑ Abbreviations:
EC: electron capture
IT: isomeric transition - ↑ 2.0 2.1 Intermediate decay product of 235U
- ↑ Intermediate decay product of 238U
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 masses from IUPAC, which use expanded uncertainties.
See also
 |
Notes
- ↑ 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.
- ↑ 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.
- ↑ "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.
- ↑ 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 very much less stable toward alpha decay than the lighter isotope.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 2.0 2.1 2.2 2.3 Lavrukhina & Pozdnyakov 1966, p. 232.
- ↑ 3.0 3.1 3.2 3.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- Isotope masses from:
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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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Bibliography
- Lua error in package.lua at line 80: module 'strict' not found.
| Isotopes of polonium | Isotopes of astatine | Isotopes of radon |
| 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 |
 |
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 |
 |
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 |
 |
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 |
||
|
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 |
||
