# Isotopes of thulium

Naturally occurring thulium ($_{69}$Tm) is composed of one stable isotope, $^{169}$Tm (100% natural abundance). Thirty-nine radioisotopes have been characterized, with the most stable being $^{171}$Tm with a half-life of 1.92 years, $^{170}$Tm with a half-life of 128.6 days, $^{168}$Tm with a half-life of 93.1 days, and $^{167}$Tm with a half-life of 9.25 days. All of the remaining radioactive isotopes have half-lives that are less than 64 hours, and the majority of these have half-lives that are less than 2 minutes. This element also has 26 meta states, with the most stable being $^{164m}$Tm (t$_{1/2}$ 5.1 minutes), $^{160m}$Tm (t$_{1/2}$ 74.5 seconds) and $^{155m}$Tm (t$_{1/2}$ 45 seconds).
The known isotopes of thulium range from $^{144}$Tm to $^{183}$Tm. The primary decay mode before the most abundant stable isotope, $^{169}$Tm, is electron capture, and the primary mode after is beta emission. The primary decay products before $^{169}$Tm are erbium isotopes, and the primary products after are ytterbium isotopes. All isotopes of thulium are either radioactive or, in the case of $^{169}$Tm, observationally stable, meaning that $^{169}$Tm is 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 | Isotopic abundance |
| Isotopic abundance |||
| $^{144}$Tm | 69 | 75 | 143.97621(43)# | 2.3(9) μs | p | $^{143}$Er | (10+) | |
| $^{145}$Tm | 69 | 76 | 144.97039(21)# | 3.17(20) μs | p | $^{144}$Er | (11/2−) | |
| $^{146}$Tm | 69 | 77 | 145.96666(22)# | 155(20) ms | p | $^{145}$Er | (1+) | |
| $^{146m1}$Tm | 304(6) keV | 304(6) keV | 304(6) keV | 73(7) ms | p | $^{145}$Er | (5−) | |
| $^{146m2}$Tm | 437(7) keV | 437(7) keV | 437(7) keV | 200(3) ms | p | $^{145}$Er | (10+) | |
| $^{147}$Tm | 69 | 78 | 146.9613799(73) | 0.58(3) s | β$^+$ (85%) | $^{147}$Er | 11/2− | |
| $^{147}$Tm | 69 | 78 | 146.9613799(73) | 0.58(3) s | p (15%) | $^{146}$Er | 11/2− | |
| $^{147m}$Tm | 62(5) keV | 62(5) keV | 62(5) keV | 360(40) μs | p | $^{146}$Er | 3/2+ | |
| $^{148}$Tm | 69 | 79 | 147.958384(11) | 0.7(2) s | β$^+$ | $^{148}$Er | (10+) | |
| $^{149}$Tm | 69 | 80 | 148.95283(22)# | 0.9(2) s | β$^+$ (99.74%) | $^{149}$Er | 11/2− | |
| $^{149}$Tm | 69 | 80 | 148.95283(22)# | 0.9(2) s | β$^+$, p (0.26%) | $^{148}$Ho | 11/2− | |
| $^{150}$Tm | 69 | 81 | 149.95009(21)# | 3# s | β$^+$ | $^{150}$Er | (1+) | |
| $^{150m1}$Tm | 140(140)# keV | 140(140)# keV | 140(140)# keV | 2.20(6) s | β$^+$ (98.9%) | $^{150}$Er | (6−) | |
| $^{150m1}$Tm | 140(140)# keV | 140(140)# keV | 140(140)# keV | 2.20(6) s | β$^+$, p (1.1%) | $^{149}$Ho | (6−) | |
| $^{150m2}$Tm | 811(140)# keV | 811(140)# keV | 811(140)# keV | 5.2(3) ms | IT | $^{150m1}$Tm | 10+# | |
| $^{151}$Tm | 69 | 82 | 150.945494(21) | 4.17(11) s | β$^+$ | $^{151}$Er | (11/2−) | |
| $^{151m1}$Tm | 93(6) keV | 93(6) keV | 93(6) keV | 6.6(20) s | β$^+$ | $^{151}$Er | (1/2+) | |
| $^{151m2}$Tm | 2655.67(22) keV | 2655.67(22) keV | 2655.67(22) keV | 451(34) ns | IT | $^{151}$Tm | (27/2−) | |
| $^{152}$Tm | 69 | 83 | 151.944476(58) | 8.0(10) s | β$^+$ | $^{152}$Er | (2)− | |
| $^{152m1}$Tm | −100(250) keV | −100(250) keV | −100(250) keV | 5.2(6) s | β$^+$ | $^{152}$Er | (9)+ | |
| $^{152m2}$Tm | 2455(250) keV | 2455(250) keV | 2455(250) keV | 301(7) ns | IT | $^{152}$Tm | (17+) | |
| $^{153}$Tm | 69 | 84 | 152.942058(13) | 1.48(1) s | α (91%) | $^{149}$Ho | (11/2−) | |
| $^{153}$Tm | 69 | 84 | 152.942058(13) | 1.48(1) s | β$^+$ (9%) | $^{153}$Er | (11/2−) | |
| $^{153m}$Tm | 43.2(2) keV | 43.2(2) keV | 43.2(2) keV | 2.5(2) s | α (92%) | $^{149}$Ho | (1/2+) | |
| $^{153m}$Tm | 43.2(2) keV | 43.2(2) keV | 43.2(2) keV | 2.5(2) s | β$^+$ (8%) | $^{153}$Er | (1/2+) | |
| $^{154}$Tm | 69 | 85 | 153.941570(15) | 8.1(3) s | β$^+$ (54%) | $^{154}$Er | (2)− | |
| $^{154}$Tm | 69 | 85 | 153.941570(15) | 8.1(3) s | α (46%) | $^{150}$Ho | (2)− | |
| $^{154m}$Tm | 70(50) keV | 70(50) keV | 70(50) keV | 3.30(7) s | α (58%) | $^{150}$Ho | (9)+ | |
| $^{154m}$Tm | 70(50) keV | 70(50) keV | 70(50) keV | 3.30(7) s | β$^+$ (42%) | $^{154}$Er | (9)+ | |
| $^{155}$Tm | 69 | 86 | 154.939210(11) | 21.6(2) s | β$^+$ (99.17%) | $^{155}$Er | 11/2− | |
| $^{155}$Tm | 69 | 86 | 154.939210(11) | 21.6(2) s | α (0.83%) | $^{151}$Ho | 11/2− | |
| $^{155m}$Tm | 41(6) keV | 41(6) keV | 41(6) keV | 45(4) s | β$^+$ | $^{155}$Er | 1/2+ | |
| $^{156}$Tm | 69 | 87 | 155.938986(15) | 83.8(18) s | β$^+$ (99.94%) | $^{156}$Er | 2− | |
| $^{156}$Tm | 69 | 87 | 155.938986(15) | 83.8(18) s | α (0.064%) | $^{152}$Ho | 2− | |
| $^{156m}$Tm | 400(200)# keV | 400(200)# keV | 400(200)# keV | ~400 ns | IT | $^{156}$Tm | (11−) | |
| $^{157}$Tm | 69 | 88 | 156.936973(30) | 3.63(9) min | β$^+$ | $^{157}$Er | 1/2+ | |
| $^{157}$Tm | 69 | 88 | 156.936973(30) | 3.63(9) min | α (7.5×10$^{−4}$%) | $^{153}$Er | 1/2+ | |
| $^{157m}$Tm | 100(50)# keV | 100(50)# keV | 100(50)# keV | 1.6 s | | | 7/2−# | |
| $^{158}$Tm | 69 | 89 | 157.936980(27) | 3.98(6) min | β$^+$ | $^{158}$Er | 2− | |
| $^{158m}$Tm | 100(50)# keV | 100(50)# keV | 100(50)# keV | ~20 s | | | 5−# | |
| $^{159}$Tm | 69 | 90 | 158.934975(30) | 9.13(16) min | β$^+$ | $^{159}$Er | 5/2+ | |
| $^{160}$Tm | 69 | 91 | 159.935264(35) | 9.4(3) min | β$^+$ | $^{160}$Er | 1− | |
| $^{160m1}$Tm | 67(14) keV | 67(14) keV | 67(14) keV | 74.5(15) s | IT (85%) | $^{160}$Tm | (5+) | |
| $^{160m1}$Tm | 67(14) keV | 67(14) keV | 67(14) keV | 74.5(15) s | β$^+$ (15%) | $^{160}$Er | (5+) | |
| $^{160m2}$Tm | 215(52)# keV | 215(52)# keV | 215(52)# keV | ~200 ns | IT | $^{160}$Tm | (8) | |
| $^{161}$Tm | 69 | 92 | 160.933549(30) | 30.2(8) min | β$^+$ | $^{161}$Er | 7/2+ | |
| $^{161m1}$Tm | 7.51(24) keV | 7.51(24) keV | 7.51(24) keV | 5# min | | | (1/2+) | |
| $^{161m2}$Tm | 78.20(3) keV | 78.20(3) keV | 78.20(3) keV | 110(3) ns | IT | $^{161}$Tm | 7/2− | |
| $^{162}$Tm | 69 | 93 | 161.934001(28) | 21.70(19) min | β$^+$ | $^{162}$Er | 1− | |
| $^{162m}$Tm | 130(40) keV | 130(40) keV | 130(40) keV | 24.3(17) s | IT (81%) | $^{162}$Tm | 5+ | |
| $^{162m}$Tm | 130(40) keV | 130(40) keV | 130(40) keV | 24.3(17) s | β$^+$ (19%) | $^{162}$Er | 5+ | |
| $^{163}$Tm | 69 | 94 | 162.9326583(59) | 1.810(5) h | β$^+$ | $^{163}$Er | 1/2+ | |
| $^{163m}$Tm | 86.92(5) keV | 86.92(5) keV | 86.92(5) keV | 380(30) ns | IT | $^{163}$Tm | (7/2)− | |
| $^{164}$Tm | 69 | 95 | 163.933538(27) | 2.0(1) min | EC (61%) | $^{164}$Er | 1+ | |
| $^{164}$Tm | 69 | 95 | 163.933538(27) | 2.0(1) min | β$^+$ (39%) | $^{164}$Er | 1+ | |
| $^{164m}$Tm | 20(12) keV | 20(12) keV | 20(12) keV | 5.1(1) min | IT (~80%) | $^{164}$Tm | 6− | |
| $^{164m}$Tm | 20(12) keV | 20(12) keV | 20(12) keV | 5.1(1) min | β$^+$ (~20%) | $^{164}$Er | 6− | |
| $^{165}$Tm | 69 | 96 | 164.9324418(18) | 30.06(3) h | β$^+$ | $^{165}$Er | 1/2+ | |
| $^{165m1}$Tm | 80.37(6) keV | 80.37(6) keV | 80.37(6) keV | 80(3) μs | IT | $^{165}$Tm | 7/2+ | |
| $^{165m2}$Tm | 160.47(6) keV | 160.47(6) keV | 160.47(6) keV | 9.0(5) μs | IT | $^{165}$Tm | 7/2− | |
| $^{166}$Tm | 69 | 97 | 165.933562(12) | 7.70(3) h | β$^+$ | $^{166}$Er | 2+ | |
| $^{166m1}$Tm | 122(7) keV | 122(7) keV | 122(7) keV | 348(21) ms | IT | $^{166}$Tm | (6−) | |
| $^{166m2}$Tm | 244(7) keV | 244(7) keV | 244(7) keV | 2(1) μs | IT | $^{166}$Tm | (6−) | |
| $^{167}$Tm | 69 | 98 | 166.9328572(14) | 9.25(2) d | EC | $^{167}$Er | 1/2+ | |
| $^{167m1}$Tm | 179.480(19) keV | 179.480(19) keV | 179.480(19) keV | 1.16(6) μs | IT | $^{167}$Tm | 7/2+ | |
| $^{167m2}$Tm | 292.820(20) keV | 292.820(20) keV | 292.820(20) keV | 0.9(1) μs | IT | $^{167}$Tm | 7/2− | |
| $^{168}$Tm | 69 | 99 | 167.9341785(18) | 93.1(2) d | β$^+$ (99.99%) | $^{168}$Er | 3+ | |
| $^{168}$Tm | 69 | 99 | 167.9341785(18) | 93.1(2) d | β$^−$ (0.010%) | $^{168}$Yb | 3+ | |
| $^{169}$Tm | 69 | 100 | 168.93421896(79) | Observationally Stable | Observationally Stable | Observationally Stable | 1/2+ | 1.0000 |
| $^{169m}$Tm | 316.1463(1) keV | 316.1463(1) keV | 316.1463(1) keV | 659.9(23) ns | IT | $^{169}$Tm | 7/2+ | |
| $^{170}$Tm | 69 | 101 | 169.93580709(79) | 128.6(3) d | β$^−$ (99.87%) | $^{170}$Yb | 1− | |
| $^{170}$Tm | 69 | 101 | 169.93580709(79) | 128.6(3) d | EC (0.131%) | $^{170}$Er | 1− | |
| $^{170m}$Tm | 183.197(4) keV | 183.197(4) keV | 183.197(4) keV | 4.12(13) μs | IT | $^{170}$Tm | 3+ | |
| $^{171}$Tm | 69 | 102 | 170.9364352(10) | 1.92(1) y | β$^−$ | $^{171}$Yb | 1/2+ | |
| $^{171m1}$Tm | 424.9557(15) keV | 424.9557(15) keV | 424.9557(15) keV | 2.60(2) μs | IT | $^{171}$Tm | 7/2− | |
| $^{171m2}$Tm | 1674.43(13) keV | 1674.43(13) keV | 1674.43(13) keV | 1.7(2) μs | IT | $^{171}$Tm | 19/2+ | |
| $^{172}$Tm | 69 | 103 | 171.9384070(59) | 63.6(3) h | β$^−$ | $^{172}$Yb | 2− | |
| $^{172m}$Tm | 476.2(2) keV | 476.2(2) keV | 476.2(2) keV | 132(7) μs | IT | $^{172}$Tm | (6+) | |
| $^{173}$Tm | 69 | 104 | 172.9396066(47) | 8.24(8) h | β$^−$ | $^{173}$Yb | (1/2+) | |
| $^{173m1}$Tm | 317.73(20) keV | 317.73(20) keV | 317.73(20) keV | 10.7(17) μs | IT | $^{173}$Tm | 7/2− | |
| $^{173m2}$Tm | 1905.7(4) keV | 1905.7(4) keV | 1905.7(4) keV | 250(69) ns | IT | $^{173}$Tm | 19/2− | |
| $^{173m3}$Tm | 4047.9(5) keV | 4047.9(5) keV | 4047.9(5) keV | 121(28) ns | IT | $^{173}$Tm | 35/2− | |
| $^{174}$Tm | 69 | 105 | 173.942174(48) | 5.4(1) min | β$^−$ | $^{174}$Yb | 4− | |
| $^{174m1}$Tm | 252.4(7) keV | 252.4(7) keV | 252.4(7) keV | 2.29(1) s | IT (>98.5%) | $^{174}$Tm | 0+ | |
| $^{174m1}$Tm | 252.4(7) keV | 252.4(7) keV | 252.4(7) keV | 2.29(1) s | β$^−$ (<1.5%) | $^{174}$Yb | 0+ | |
| $^{174m2}$Tm | 2091.7(3) keV | 2091.7(3) keV | 2091.7(3) keV | 106(7) μs | IT | $^{174}$Tm | 14− | |
| $^{175}$Tm | 69 | 106 | 174.943842(54) | 15.2(5) min | β$^−$ | $^{175}$Yb | (1/2)+ | |
| $^{175m1}$Tm | 440.0(11) keV | 440.0(11) keV | 440.0(11) keV | 319(35) ns | IT | $^{175}$Tm | 7/2− | |
| $^{175m2}$Tm | 1517.7(12) keV | 1517.7(12) keV | 1517.7(12) keV | 21(14) μs | IT | $^{175}$Tm | 23/2+ | |
| $^{176}$Tm | 69 | 107 | 175.94700(11) | 1.85(3) min | β$^−$ | $^{176}$Yb | (4+) | |
| $^{177}$Tm | 69 | 108 | 176.94893(22)# | 95(7) s | β$^−$ | $^{177}$Yb | 1/2+# | |
| $^{177m}$Tm | 100(100)# keV | 100(100)# keV | 100(100)# keV | 77(11) s | β$^−$ | $^{177}$Yb | 7/2−# | |
| $^{178}$Tm | 69 | 109 | 177.95251(32)# | 10# s [>300 ns] | | | 1−# | |
| $^{179}$Tm | 69 | 110 | 178.95502(43)# | 18# s [>300 ns] | | | 1/2+# | |
| $^{180}$Tm | 69 | 111 | 179.95902(43)# | 3# s [>300 ns] | | | | |
| $^{181}$Tm | 69 | 112 | 180.96195(54)# | 7# s [>300 ns] | | | 1/2+# | |
| $^{182}$Tm | 69 | 113 | 181.96619(54)# | | | | | |
| $^{183}$Tm | 69 | 114 | | | | | | |
| This table header & footer: view |||||||||
* ↑ $^m$Tm – 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.
* 1 2 3 4 5 6 Order of ground state and isomer is uncertain.
* ↑ Believed to undergo α decay to $^{165}$Ho

## Thulium-170

Thulium-170 has a half-life of 128.6 days, decaying by β$^−$ decay about 99.87% of the time and electron capture the remaining 0.13% of the time. Due to its low-energy X-ray emissions, it has been proposed for radiotherapy and as a source in a radiothermal generator.