Astatine Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-li ...

(₈₅At) has 39 known

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...

s, all of which are

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

; the range of their mass numbers is from 191 to 229. There are also 24 known

metastable In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball i ...

excited states. The longest-lived isotope is ²¹⁰At, which has a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

of 8.1 hours; the longest-lived isotope existing in naturally occurring

decay chain In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay dire ...

s is ²¹⁹At with a half-life of 56 seconds.

List of isotopes

, - , ¹⁹¹At , style="text-align:right" , 85 , style="text-align:right" , 106 , , 1.7(+11−5) ms , , , (1/2+) , , - , style="text-indent:1em" , ^191mAt , colspan="3" style="text-indent:2em" , , 2.1(+4−3) ms , , , (7/2−) , , - , rowspan=2, ¹⁹²At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 107 , rowspan=2, 192.00314(28) , rowspan=2, 11.5(0.6) ms , α (99.79%) , ¹⁸⁸Bi , rowspan=2, 3+# , rowspan=2, , - , β⁺, SF (0.21%) , (various) , - , rowspan=2 style="text-indent:1em" , ^192mAt , rowspan=2 colspan="3" style="text-indent:2em" , 330(90)# keV , rowspan=2, 88(6) ms , α (99.79%) , ^188mBi , rowspan=2, (9-, 10−) , rowspan=2, , - , β⁺, SF (0.21%) , (various) , - , ¹⁹³At , style="text-align:right" , 85 , style="text-align:right" , 108 , 192.99984(6) , 28(+5−4) ms , α , ¹⁸⁹Bi , (1/2+) , , - , style="text-indent:1em" , ^193m1At , colspan="3" style="text-indent:2em" , 50 keV , 21(5) ms , , , (7/2−) , , - , style="text-indent:1em" , ^193m2At , colspan="3" style="text-indent:2em" , 39 keV , 27(+4−5) ms , , , (13/2+) , , - , rowspan=2, ¹⁹⁴At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 109 , rowspan=2, 193.99873(20) , rowspan=2, 286(7) ms , α , ¹⁹⁰Bi , rowspan=2, (4-, 5-) , rowspan=2, , - , β⁺ (rare) , ¹⁹⁴Po , - , rowspan=2 style="text-indent:1em" , ^194mAt , rowspan=2 colspan="3" style="text-indent:2em" , 480(190) keV , rowspan=2, 323(7) ms , α , ¹⁹⁰Bi , rowspan=2, (9-, 10-) , rowspan=2, , - , IT (rare) , ¹⁹⁴At , - , rowspan=2, ¹⁹⁵At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 110 , rowspan=2, 194.996268(10) , rowspan=2, 328(20) ms , α (75%) , ¹⁹¹Bi , rowspan=2, (1/2+) , rowspan=2, , - , β⁺ (25%) , ¹⁹⁵Po , - , style="text-indent:1em" , ^195mAt , colspan="3" style="text-indent:2em" , 34(7) keV , 147(5) ms , , , (7/2-) , , - , rowspan=2, ¹⁹⁶At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 111 , rowspan=2, 195.99579(6) , rowspan=2, 253(9) ms , α (96%) , ¹⁹²Bi , rowspan=2, (3+) , rowspan=2, , - , β⁺ (4.0%) , ¹⁹⁶Po , - , style="text-indent:1em" , ^196m1At , colspan="3" style="text-indent:2em" , −30(80) keV , 20# ms , , , (10−) , , - , style="text-indent:1em" , ^196m2At , colspan="3" style="text-indent:2em" , 157.9(1) keV , 11 μs , , , (5+) , , - , rowspan=2, ¹⁹⁷At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 112 , rowspan=2, 196.99319(5) , rowspan=2, 0.390(16) s , α (96%) , ¹⁹³Bi , rowspan=2, (9/2−) , rowspan=2, , - , β⁺ (4.0%) , ¹⁹⁷Po , - , style="text-indent:1em" , ^197mAt , colspan="3" style="text-indent:2em" , 52(10) keV , 2.0(2) s , , , (1/2+) , , - , rowspan=2, ¹⁹⁸At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 113 , rowspan=2, 197.99284(5) , rowspan=2, 4.2(3) s , α (94%) , ¹⁹⁴Bi , rowspan=2, (3+) , rowspan=2, , - , β⁺ (6%) , ¹⁹⁸Po , - , style="text-indent:1em" , ^198mAt , colspan="3" style="text-indent:2em" , 330(90)# keV , 1.0(2) s , , , (10−) , , - , rowspan=2, ¹⁹⁹At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 114 , rowspan=2, 198.99053(5) , rowspan=2, 6.92(13) s , α (89%) , ¹⁹⁵Bi , rowspan=2, (9/2−) , rowspan=2, , - , β⁺ (11%) , ¹⁹⁹Po , - , rowspan=2, ²⁰⁰At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 115 , rowspan=2, 199.990351(26) , rowspan=2, 43.2(9) s , α (57%) , ¹⁹⁶Bi , rowspan=2, (3+) , rowspan=2, , - , β⁺ (43%) , ²⁰⁰Po , - , rowspan=3 style="text-indent:1em" , ^200m1At , rowspan=3 colspan="3" style="text-indent:2em" , 112.7(30) keV , rowspan=3, 47(1) s , α (43%) , ¹⁹⁶Bi , rowspan=3, (7+) , rowspan=3, , - , IT , ²⁰⁰At , - , β⁺ , ²⁰⁰Po , - , style="text-indent:1em" , ^200m2At , colspan="3" style="text-indent:2em" , 344(3) keV , 3.5(2) s , , , (10−) , , - , rowspan=2, ²⁰¹At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 116 , rowspan=2, 200.988417(9) , rowspan=2, 85(3) s , α (71%) , ¹⁹⁷Bi , rowspan=2, (9/2−) , rowspan=2, , - , β⁺ (29%) , ²⁰¹Po , - , rowspan=2, ²⁰²At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 117 , rowspan=2, 201.98863(3) , rowspan=2, 184(1) s , β⁺ (88%) , ²⁰²Po , rowspan=2, (2, 3)+ , rowspan=2, , - , α (12%) , ¹⁹⁸Bi , - , style="text-indent:1em" , ^202m1At , colspan="3" style="text-indent:2em" , 190(40) keV , 182(2) s , , , (7+) , , - , style="text-indent:1em" , ^202m2At , colspan="3" style="text-indent:2em" , 580(40) keV , 460(50) ms , , , (10−) , , - , rowspan=2, ²⁰³At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 118 , rowspan=2, 202.986942(13) , rowspan=2, 7.37(13) min , β⁺ (69%) , ²⁰³Po , rowspan=2, 9/2− , rowspan=2, , - , α (31%) , ¹⁹⁹Bi , - , rowspan=2, ²⁰⁴At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 119 , rowspan=2, 203.987251(26) , rowspan=2, 9.2(2) min , β⁺ (96%) , ²⁰⁴Po , rowspan=2, 7+ , rowspan=2, , - , α (3.8%) , ²⁰⁰Bi , - , style="text-indent:1em" , ^204mAt , colspan="3" style="text-indent:2em" , 587.30(20) keV , 108(10) ms , IT , ²⁰⁴At , (10−) , , - , rowspan=2, ²⁰⁵At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 120 , rowspan=2, 204.986074(16) , rowspan=2, 26.2(5) min , β⁺ (90%) , ²⁰⁵Po , rowspan=2, 9/2− , rowspan=2, , - , α (10%) , ²⁰¹Bi , - , style="text-indent:1em" , ^205mAt , colspan="3" style="text-indent:2em" , 2339.65(23) keV , 7.76(14) μs , , , 29/2+ , , - , rowspan=2, ²⁰⁶At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 121 , rowspan=2, 205.986667(22) , rowspan=2, 30.6(13) min , β⁺ (99.11%) , ²⁰⁶Po , rowspan=2, (5)+ , rowspan=2, , - , α (0.9%) , ²⁰²Bi , - , style="text-indent:1em" , ^206mAt , colspan="3" style="text-indent:2em" , 807(3) keV , 410(80) ns , , , (10)− , , - , rowspan=2, ²⁰⁷At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 122 , rowspan=2, 206.985784(23) , rowspan=2, 1.80(4) h , β⁺ (91%) , ²⁰⁷Po , rowspan=2, 9/2− , rowspan=2, , - , α (8.6%) , ²⁰³Bi , - , rowspan=2, ²⁰⁸At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 123 , rowspan=2, 207.986590(28) , rowspan=2, 1.63(3) h , β⁺ (99.5%) , ²⁰⁸Po , rowspan=2, 6+ , rowspan=2, , - , α (0.55%) , ²⁰⁴Bi , - , rowspan=2, ²⁰⁹At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 124 , rowspan=2, 208.986173(8) , rowspan=2, 5.41(5) h , β⁺ (96%) , ²⁰⁹Po , rowspan=2, 9/2− , rowspan=2, , - , α (4.0%) , ²⁰⁵Bi , - , rowspan=2, ²¹⁰At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 125 , rowspan=2, 209.987148(8) , rowspan=2, 8.1(4) h , β⁺ (99.8%) , ²¹⁰Po , rowspan=2, (5)+ , rowspan=2, , - , α (0.18%) , ²⁰⁶Bi , - , style="text-indent:1em" , ^210m1At , colspan="3" style="text-indent:2em" , 2549.6(2) keV , 482(6) μs , , , (15)− , , - , style="text-indent:1em" , ^210m2At , colspan="3" style="text-indent:2em" , 4027.7(2) keV , 5.66(7) μs , , , (19)+ , , - , rowspan=2, ²¹¹At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 126 , rowspan=2, 210.9874963(30) , rowspan=2, 7.214(7) h , EC (58.2%) , ²¹¹Po , rowspan=2, 9/2− , rowspan=2, , - , α (42%) , ²⁰⁷Bi , - , rowspan=3, ²¹²At , rowspan=3 style="text-align:right" , 85 , rowspan=3 style="text-align:right" , 127 , rowspan=3, 211.990745(8) , rowspan=3, 0.314(2) s , α (99.95%) , ²⁰⁸Bi , rowspan=3, (1−) , rowspan=3, , - , β⁺ (0.05%) , ²¹²Po , - , β⁻ (2×10⁻⁶%) , ²¹²Rn , - , rowspan=2 style="text-indent:1em" , ^212m1At , rowspan=2 colspan="3" style="text-indent:2em" , 223(7) keV , rowspan=2, 0.119(3) s , α (99%) , ²⁰⁸Bi , rowspan=2, (9−) , rowspan=2, , - , IT (1%) , ²¹²At , - , style="text-indent:1em" , ^212m2At , colspan="3" style="text-indent:2em" , 4771.6(11) keV , 152(5) μs , , , (25−) , , - , ²¹³At , style="text-align:right" , 85 , style="text-align:right" , 128 , 212.992937(5) , 125(6) ns , α , ''²⁰⁹Bi'' , 9/2− , , - , ²¹⁴At , style="text-align:right" , 85 , style="text-align:right" , 129 , 213.996372(5) , 558(10) ns , α , ²¹⁰Bi , 1− , , - , style="text-indent:1em" , ^214m1At , colspan="3" style="text-indent:2em" , 59(9) keV , 265(30) ns , , , , , - , style="text-indent:1em" , ^214m2At , colspan="3" style="text-indent:2em" , 231(6) keV , 760(15) ns , , , 9− , , - , ²¹⁵At , style="text-align:right" , 85 , style="text-align:right" , 130 , 214.998653(7) , 0.10(2) ms , α , ²¹¹Bi , 9/2− , TraceIntermediate

decay product In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps ( ...

of ²³⁵U , - , rowspan=3, ²¹⁶At , rowspan=3 style="text-align:right" , 85 , rowspan=3 style="text-align:right" , 131 , rowspan=3, 216.002423(4) , rowspan=3, 0.30(3) ms , α (99.99%) , ²¹²Bi , rowspan=3, 1− , rowspan=3, , - , β⁻ (.006%) , ²¹⁶Rn , - , EC (3×10⁻⁷%) , ²¹⁶Po , - , style="text-indent:1em" , ^216mAt , colspan="3" style="text-indent:2em" , 413(5) keV , 100# μs , , , (9−) , , - , rowspan=2, ²¹⁷At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 132 , rowspan=2, 217.004719(5) , rowspan=2, 32.3(4) ms , α (99.98%) , ²¹³Bi , rowspan=2, 9/2− , rowspan=2, TraceIntermediate decay product of ²³⁷Np , - , β⁻ (.012%) , ²¹⁷Rn , - , rowspan=2, ²¹⁸At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 133 , rowspan=2, 218.008694(12) , rowspan=2, 1.5(3) s , α (99.9%) , ²¹⁴Bi , rowspan=2, 1−# , rowspan=2, TraceIntermediate decay product of ²³⁸U , - , β⁻ (0.10%) , ²¹⁸Rn , - , rowspan=2, ²¹⁹At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 134 , rowspan=2, 219.011162(4) , rowspan=2, 56(3) s , α (97%) , ²¹⁵Bi , rowspan=2, (9/2-) , rowspan=2, Trace , - , β⁻ (3.0%) , ²¹⁹Rn , - , rowspan=2, ²²⁰At , rowspan=2 style="text-align:right" , 85 , rowspan=2 style="text-align:right" , 135 , rowspan=2, 220.01541(6) , rowspan=2, 3.71(4) min , β⁻ (92%) , ²²⁰Rn , rowspan=2, 3(−#) , rowspan=2, , - , α (8.0%) , ²¹⁶Bi , - , ²²¹At , style="text-align:right" , 85 , style="text-align:right" , 136 , 221.01805(21)# , 2.3(2) min , β⁻ , ²²¹Rn , 3/2−# , , - , ²²²At , style="text-align:right" , 85 , style="text-align:right" , 137 , 222.02233(32)# , 54(10) s , β⁻ , ²²²Rn , , , - , ²²³At , style="text-align:right" , 85 , style="text-align:right" , 138 , 223.02519(43)# , 50(7) s , β⁻ , ²²³Rn , 3/2−# , , - , ²²⁴At , style="text-align:right" , 85 , style="text-align:right" , 139 , 224.02975(22)# , 2.5(1.5) min , β⁻ , ²²⁴Rn , ,

Alpha decay

Astatine has 23

nuclear isomer A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state, higher energy levels than in the ground state of the same nucleus. "Metastable" describes nuclei whose excited ...

s (nuclei with one or more

nucleon In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number). Until the 1960s, nucleons were ...

s –

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

s or

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

s – in an excited state). A nuclear isomer may also be called a "

meta Meta (from the Greek μετά, '' meta'', meaning "after" or "beyond") is a prefix meaning "more comprehensive" or "transcending". In modern nomenclature, ''meta''- can also serve as a prefix meaning self-referential, as a field of study or ende ...

-state"; this means the system has more

internal energy The internal energy of a thermodynamic system is the total energy contained within it. It is the energy necessary to create or prepare the system in its given internal state, and includes the contributions of potential energy and internal kinet ...

than the "

ground state The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater 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, 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.

Alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...

energy follows the same trend as for other heavy elements. 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. 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. Even though heavier astatine isotopes release less energy, no long-lived astatine isotope exists; this happens due to the increasing role of

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...

. This decay mode is especially important for astatine: as early as 1950, it was postulated that the element has no

beta-stable Beta-decay stable isobars are the set of nuclides which cannot undergo beta decay, that is, the transformation of a neutron to a proton or a proton to a neutron within the nucleus. A subset of these nuclides are also stable with regards to doubl ...

isotopes (i.e. ones that do not undergo beta decay at all), though nuclear mass measurements reveal that ²¹⁵At is in fact beta-stable, as it has the lowest mass of all isobars with ''A'' = 215. A beta decay mode has been found for all other astatine isotopes except for astatine-213, astatine-214, and astatine-216m. Among other isotopes: astatine-210 and the lighter isotopes decay by

positron emission Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron ...

; astatine-216 and the heavier isotopes undergo

; astatine-212 can decay either way; and astatine-211 decays by

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Thi ...

instead. 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 Polonium-210 (210Po, Po-210, historically radium F) is an isotope of polonium. It undergoes alpha decay to stable 206Pb with a half-life of 138.376 days (about months), the longest half-life of all naturally occurring polonium isotopes. First i ...

. 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

nanosecond A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or 10 seconds. The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit ( ...

s. It undergoes

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...

to the extremely long-lived (in practice, stable) isotope

bismuth-209 Bismuth-209 (209Bi) is the isotope of bismuth with the longest known half-life of any radioisotope that undergoes α-decay (alpha decay). It has 83 protons and a magic number of 126 neutrons, and an atomic mass of 208.9803987 amu (atomic mass un ...

References

* * Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Authority control

List of isotopes

Alpha decay

See also

References