# Isotopes of erbium

Naturally occurring erbium ($_{68}$Er) is composed of six stable isotopes, with $^{166}$Er being the most abundant (33.503% natural abundance). Thirty-nine radioisotopes have been characterized with between 74 and 112 neutrons, or 142 to 180 nucleons, with the most stable being $^{169}$Er with a half-life of 9.4 days, $^{172}$Er with a half-life of 49.3 hours, $^{160}$Er with a half-life of 28.58 hours, $^{165}$Er with a half-life of 10.36 hours, and $^{171}$Er with a half-life of 7.516 hours. All of the remaining radioactive isotopes have half-lives that are less than 3.5 hours, and the majority of these have half-lives that are less than 4 minutes. This element also has numerous meta states, with the most stable being $^{167m}$Er (t$_{1/2}$ = 2.269 seconds).
The isotopes of erbium range in atomic weight from 141.9723 u ($^{142}$Er) to 179.9644 u ($^{180}$Er). The primary decay mode before the most abundant stable isotope, $^{166}$Er, is electron capture, and the primary mode after is beta decay. The primary decay products before $^{166}$Er are holmium isotopes, and the primary products after are thulium isotopes. All isotopes of erbium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Natural abundance (mole fraction) | Natural abundance (mole fraction) |
| Nuclide | Excitation energy | Excitation energy | Excitation energy | Half-life | Decay mode | Daughter isotope | Spin and parity | Normal proportion | Range of variation |
| $^{143}$Er | 68 | 75 | 142.96655(43)# | 200# ms | | | 9/2−# | | |
| $^{144}$Er | 68 | 76 | 143.96070(21)# | 400# ms [>200 ns] | | | 0+ | | |
| $^{145}$Er | 68 | 77 | 144.95787(22)# | 900(200) ms | β$^+$ | $^{145}$Ho | 1/2+# | | |
| $^{145}$Er | 68 | 77 | 144.95787(22)# | 900(200) ms | β$^+$, p (?%) | $^{144}$Dy | 1/2+# | | |
| $^{145m}$Er | 205(4)# keV | 205(4)# keV | 205(4)# keV | 1.0(3) s | β$^+$ | $^{145}$Ho | (11/2-) | | |
| $^{145m}$Er | 205(4)# keV | 205(4)# keV | 205(4)# keV | 1.0(3) s | β$^+$, p (?%) | $^{144}$Dy | (11/2-) | | |
| $^{146}$Er | 68 | 78 | 145.952418(7) | 1.7(6) s | β$^+$ | $^{146}$Ho | 0+ | | |
| $^{146}$Er | 68 | 78 | 145.952418(7) | 1.7(6) s | β$^+$, p (?%) | $^{145}$Dy | 0+ | | |
| $^{147}$Er | 68 | 79 | 146.94996(4)# | 3.2(12) s | β$^+$ | $^{147}$Ho | (1/2+) | | |
| $^{147}$Er | 68 | 79 | 146.94996(4)# | 3.2(12) s | β$^+$, p (?%) | $^{146}$Dy | (1/2+) | | |
| $^{147m}$Er | 100(50)# keV | 100(50)# keV | 100(50)# keV | 1.6(2) s | β$^+$ | $^{147}$Ho | (11/2−) | | |
| $^{147m}$Er | 100(50)# keV | 100(50)# keV | 100(50)# keV | 1.6(2) s | β$^+$, p (?%) | $^{146}$Dy | (11/2−) | | |
| $^{148}$Er | 68 | 80 | 147.944735(11)# | 4.6(2) s | β$^+$ (99.85%) | $^{148}$Ho | 0+ | | |
| $^{148}$Er | 68 | 80 | 147.944735(11)# | 4.6(2) s | β$^+$, p (0.15%) | $^{147}$Dy | 0+ | | |
| $^{148m}$Er | 2.9132(4) MeV | 2.9132(4) MeV | 2.9132(4) MeV | 13(3) μs | IT | $^{148}$Er | (10+) | | |
| $^{149}$Er | 68 | 81 | 148.94231(3) | 4(2) s | β$^+$ (93%) | $^{149}$Ho | (1/2+) | | |
| $^{149}$Er | 68 | 81 | 148.94231(3) | 4(2) s | β$^+$, p (7%) | $^{148}$Dy | (1/2+) | | |
| $^{149m1}$Er | 741.8(2) keV | 741.8(2) keV | 741.8(2) keV | 8.9(2) s | β$^+$ (96.3%) | $^{149}$Ho | (11/2−) | | |
| $^{149m1}$Er | 741.8(2) keV | 741.8(2) keV | 741.8(2) keV | 8.9(2) s | IT (3.5%) | $^{149}$Er | (11/2−) | | |
| $^{149m1}$Er | 741.8(2) keV | 741.8(2) keV | 741.8(2) keV | 8.9(2) s | β$^+$, p (0.18%) | $^{148}$Dy | (11/2−) | | |
| $^{149m2}$Er | 2.6111(3) MeV | 2.6111(3) MeV | 2.6111(3) MeV | 0.61(8) μs | IT | $^{149}$Er | (19/2+) | | |
| $^{149m3}$Er | 3.302(7) MeV | 3.302(7) MeV | 3.302(7) MeV | 4.8(1) μs | IT | $^{149}$Er | (27/2−) | | |
| $^{150}$Er | 68 | 82 | 149.937916(18) | 18.5(7) s | β$^+$ | $^{150}$Ho | 0+ | | |
| $^{150m}$Er | 2.7965(5) MeV | 2.7965(5) MeV | 2.7965(5) MeV | 2.55(10) μs | IT | $^{150}$Er | 10+ | | |
| $^{151}$Er | 68 | 83 | 150.937449(18) | 23.5(20) s | β$^+$ | $^{151}$Ho | (7/2−) | | |
| $^{151m1}$Er | 2.5860(5) MeV | 2.5860(5) MeV | 2.5860(5) MeV | 580(20) ms | IT (95.3%) | $^{151}$Er | (27/2−) | | |
| $^{151m1}$Er | 2.5860(5) MeV | 2.5860(5) MeV | 2.5860(5) MeV | 580(20) ms | β$^+$ (4.7%) | $^{151}$Ho | (27/2−) | | |
| $^{151m2}$Er | 10.2866(10) MeV | 10.2866(10) MeV | 10.2866(10) MeV | 0.42(5) μs | IT | $^{151}$Er | (65/2-, 61/2+) | | |
| $^{152}$Er | 68 | 84 | 151.935050(9) | 10.3(1) s | α (90%) | $^{148}$Dy | 0+ | | |
| $^{152}$Er | 68 | 84 | 151.935050(9) | 10.3(1) s | β$^+$ (10%) | $^{152}$Ho | 0+ | | |
| $^{153}$Er | 68 | 85 | 152.935086(10) | 37.1(2) s | α (53%) | $^{149}$Dy | 7/2− | | |
| $^{153}$Er | 68 | 85 | 152.935086(10) | 37.1(2) s | β$^+$ (47%) | $^{153}$Ho | 7/2− | | |
| $^{153m1}$Er | 2.7982(10) MeV | 2.7982(10) MeV | 2.7982(10) MeV | 373(9) ns | IT | $^{153}$Er | (27/2-) | | |
| $^{153m2}$Er | 5.2481(10) MeV | 5.2481(10) MeV | 5.2481(10) MeV | 248(32) ns | IT | $^{153}$Er | (41/2-) | | |
| $^{154}$Er | 68 | 86 | 153.932791(5) | 3.73(9) min | β$^+$ (99.53%) | $^{154}$Ho | 0+ | | |
| $^{154}$Er | 68 | 86 | 153.932791(5) | 3.73(9) min | α (0.47%) | $^{150}$Dy | 0+ | | |
| $^{155}$Er | 68 | 87 | 154.933216(7) | 5.3(3) min | β$^+$ (99.978%) | $^{155}$Ho | 7/2− | | |
| $^{155}$Er | 68 | 87 | 154.933216(7) | 5.3(3) min | α (0.022%) | $^{151}$Dy | 7/2− | | |
| $^{156}$Er | 68 | 88 | 155.931066(26) | 19.5(10) min | β$^+$ | $^{156}$Ho | 0+ | | |
| $^{156}$Er | 68 | 88 | 155.931066(26) | 19.5(10) min | α (1.2×10$^{−5}$%) | $^{152}$Dy | 0+ | | |
| $^{157}$Er | 68 | 89 | 156.931923(28) | 18.65(10) min | β$^+$ | $^{157}$Ho | 3/2− | | |
| $^{157m}$Er | 155.4(3) keV | 155.4(3) keV | 155.4(3) keV | 76(6) ms | IT | $^{157}$Er | 9/2+ | | |
| $^{158}$Er | 68 | 90 | 157.929893(27) | 2.29(6) h | EC | $^{158}$Ho | 0+ | | |
| $^{159}$Er | 68 | 91 | 158.930691(4) | 36(1) min | β$^+$ | $^{159}$Ho | 3/2− | | |
| $^{159m1}$Er | 182.602(24) keV | 182.602(24) keV | 182.602(24) keV | 337(14) ns | IT | $^{159}$Er | 9/2+ | | |
| $^{159m2}$Er | 429.05(3) keV | 429.05(3) keV | 429.05(3) keV | 590(60) ns | IT | $^{159}$Er | 11/2− | | |
| $^{160}$Er | 68 | 92 | 159.929077(26) | 28.58(9) h | EC | $^{160}$Ho | 0+ | | |
| $^{161}$Er | 68 | 93 | 160.930004(9) | 3.21(3) h | β$^+$ | $^{161}$Ho | 3/2− | | |
| $^{161m}$Er | 396.44(4) keV | 396.44(4) keV | 396.44(4) keV | 7.5(7) μs | IT | $^{161}$Er | 11/2− | | |
| $^{162}$Er | 68 | 94 | 161.9287873(8) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.00139(5) | |
| $^{162m}$Er | 2.02601(13) MeV | 2.02601(13) MeV | 2.02601(13) MeV | 88(16) ns | IT | $^{162}$Er | 7(-) | | |
| $^{163}$Er | 68 | 95 | 162.930040(5) | 75.0(4) min | β$^+$ | $^{163}$Ho | 5/2− | | |
| $^{163m}$Er | 445.5(6) keV | 445.5(6) keV | 445.5(6) keV | 580(100) ns | IT | $^{163}$Er | (11/2−) | | |
| $^{164}$Er | 68 | 96 | 163.9292077(8) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.01601(3) | |
| $^{165}$Er | 68 | 97 | 164.9307335(10) | 10.36(4) h | EC | $^{165}$Ho | 5/2− | | |
| $^{165m1}$Er | 551.3(6) keV | 551.3(6) keV | 551.3(6) keV | 250(30) ns | IT | $^{165}$Er | 11/2- | | |
| $^{165m2}$Er | 1.8230(6) MeV | 1.8230(6) MeV | 1.8230(6) MeV | 370(40) ns | IT | $^{165}$Er | (19/2) | | |
| $^{166}$Er | 68 | 98 | 165.9303011(4) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.33503(36) | |
| $^{167}$Er | 68 | 99 | 166.9320562(3) | Observationally Stable | Observationally Stable | Observationally Stable | 7/2+ | 0.22869(9) | |
| $^{167m}$Er | 207.801(5) keV | 207.801(5) keV | 207.801(5) keV | 2.269(6) s | IT | $^{167}$Er | 1/2− | | |
| $^{168}$Er | 68 | 100 | 167.93237828(28) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.26978(18) | |
| $^{168m}$Er | 1.0940383(16) MeV | 1.0940383(16) MeV | 1.0940383(16) MeV | 109.0(7) ns | IT | $^{168}$Er | 4- | | |
| $^{169}$Er | 68 | 101 | 168.9345984(3) | 9.392(18) d | β$^−$ | $^{169}$Tm | 1/2− | | |
| $^{169m1}$Er | 92.05(10) keV | 92.05(10) keV | 92.05(10) keV | 285(20) ns | IT | $^{169}$Er | (5/2)- | | |
| $^{169m2}$Er | 243.69(17) keV | 243.69(17) keV | 243.69(17) keV | 200(10) ns | IT | $^{169}$Er | 7/2+ | | |
| $^{170}$Er | 68 | 102 | 169.9354719(15) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.14910(36) | |
| $^{171}$Er | 68 | 103 | 170.93803746(15) | 7.516(2) h | β$^−$ | $^{171}$Tm | 5/2− | | |
| $^{171m}$Er | 198.61(9) keV | 198.61(9) keV | 198.61(9) keV | 210(10) ns | IT | $^{171}$Er | 1/2− | | |
| $^{172}$Er | 68 | 104 | 171.939363(4) | 49.3(5) h | β$^−$ | $^{172}$Tm | 0+ | | |
| $^{172m}$Er | 1.5009(3) MeV | 1.5009(3) MeV | 1.5009(3) MeV | 579(62) ns | IT | $^{172}$Er | (6+) | | |
| $^{173}$Er | 68 | 105 | 172.94240(21)# | 1.434(17) min | β$^−$ | $^{173}$Tm | (7/2−) | | |
| $^{174}$Er | 68 | 106 | 173.94423(32)# | 3.2(2) min | β$^−$ | $^{174}$Tm | 0+ | | |
| $^{174m}$Er | 1.1115(7) MeV | 1.1115(7) MeV | 1.1115(7) MeV | 3.9(3) s | IT | $^{174}$Er | 8- | | |
| $^{175}$Er | 68 | 107 | 174.94777(43)# | 1.2(3) min | β$^−$ | $^{175}$Tm | 9/2+# | | |
| $^{176}$Er | 68 | 108 | 175.94994(43)# | 12# s [>300 ns] | | | 0+ | | |
| $^{177}$Er | 68 | 109 | 176.95399(54)# | 8# s [>300 ns] | | | 1/2−# | | |
| $^{178}$Er | 68 | 110 | 177.95678(64)# | 4# s [>300 ns] | | | 0+ | | |
| $^{179}$Er | 68 | 111 | 178.96127(54)# | 3# s [>550 ns)] | | | 3/2−# | | |
| $^{180}$Er | 68 | 112 | 179.96438(54)# | 2# s [>550 ns] | | | 0+ | | |
| This table header & footer: view ||||||||||
* ↑ $^m$Er – Excited nuclear isomer.
* ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
* ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
* 1 2 3 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Modes of decay: EC:Electron capture IT:Isomeric transition p:Proton emission
* ↑ Bold symbol as daughter – Daughter product is stable.
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* ↑ Order of ground state and isomer is uncertain.
* ↑ Believed to undergo α decay to $^{158}$Dy or β$^+$β$^+$ to $^{162}$Dy with a half-life over 1.40×10$^{14}$ years
* ↑ Believed to undergo α decay to $^{160}$Dy or β$^+$β$^+$ to $^{164}$Dy
* ↑ Believed to undergo α decay to $^{162}$Dy
* ↑ Believed to undergo α decay to $^{163}$Dy
* ↑ Believed to undergo α decay to $^{164}$Dy
* ↑ Believed to undergo α decay to $^{166}$Dy or β$^−$β$^−$ to $^{170}$Yb with a half-life over 4.10×10$^{17}$ years