Isotopes of astatine

From Wikipedia, the free encyclopedia
  (Redirected from Astatine-217)
Jump to: navigation, search

Astatine (At) has 37 known isotopes, all of which are radioactive; the range of their mass numbers is from 191 to 229. There exist also 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[a]
Mass
number
Mass
excess

[1]
Mass
excess of
daughter[1]
Average
energy of
alpha
decay
Half-life[1]
Probability
of alpha
decay[1]
Alpha
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][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).[3] 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[edit]

nuclide
symbol
Z(p) N(n)  
isotopic mass (u)
 
half-life decay
mode(s)[4][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) millisecond (1/2+)
191mAt 2.1(+4-3) millisecond (7/2-)
193At 85 108 192.99984(6) 28(+5-4) millisecond 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-#
  1. ^ Abbreviations:
    EC: electron capture
    IT: isomeric transition
  2. ^ a b Intermediate decay product of U-235
  3. ^ Intermediate decay product of U-238

Notes[edit]

  • 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[edit]


Notes[edit]

  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 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. Also note that the nuclide's mass excess was not measured, but calculated from theory instead.
  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 very much less stable toward alpha decay than the lighter isotope.

References[edit]

  1. ^ a b c d e f g h i j Audi, G; Wapstra, A H; Thibault, C; Blachot, J; Bersillon, O (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. ^ a b c d Lavrukhina & Pozdnyakov 1966, p. 232.
  3. ^ Rankama, Kalervo (1956). Isotope geology (2nd ed.). Pergamon Press. p. 403. ISBN 978-0-470-70800-2. 
  4. ^ http://www.nucleonica.net/unc.aspx

Bibliography[edit]

  • Lavrukhina, A K; Pozdnyakov, A A (1966). Аналитическая химия технеция, прометия, астатина и франция [Analytical Chemistry of Technetium, Promethium, Astatine, and Francium] (in Russian). Nauka. 


Isotopes of polonium Isotopes of astatine Isotopes of radon
Table of nuclides