# Isotopes of terbium

Naturally occurring terbium ($_{65}$Tb) is composed of one stable isotope, $^{159}$Tb. Thirty-seven radioisotopes have been characterized, with the most stable being $^{158}$Tb with a half-life of 180 years, $^{157}$Tb with a half-life of 71 years, and $^{160}$Tb with a half-life of 72.3 days. All of the remaining radioactive isotopes have half-lives that are less than 6.907 days, and the majority of these have half-lives that are less than 24 seconds. This element also has 27 meta states, with the most stable being $^{156m1}$Tb (t$_{1/2}$ = 24.4 hours), $^{154m2}$Tb (t$_{1/2}$ = 22.7 hours) and $^{154m1}$Tb (t$_{1/2}$ = 9.4 hours).
The primary decay mode before the most abundant stable isotope, $^{159}$Tb, is electron capture, and the primary mode behind is beta decay. The primary decay products before $^{159}$Tb are element Gd (gadolinium) isotopes, and the primary products after $^{159}$Tb are element Dy (dysprosium) isotopes.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Isotopic abundance |
| Isotopic abundance |||
| $^{135}$Tb | 65 | 70 | 134.96452(43)# | 1.01(28) ms | p | $^{134}$Gd | (7/2−) | |
| $^{139}$Tb | 65 | 74 | 138.94833(32)# | 1.6(2) s | β$^+$ | $^{139}$Gd | 5/2−# | |
| $^{140}$Tb | 65 | 75 | 139.94581(86) | 2.29(15) s | β$^+$ (99.74%) | $^{140}$Gd | (7+) | |
| $^{140}$Tb | 65 | 75 | 139.94581(86) | 2.29(15) s | EC (<3%) | $^{140}$Gd | (7+) | |
| $^{140}$Tb | 65 | 75 | 139.94581(86) | 2.29(15) s | β$^+$, p (0.26%) | $^{139}$Eu | (7+) | |
| $^{141}$Tb | 65 | 76 | 140.94145(11) | 3.5(2) s | β$^+$ | $^{141}$Gd | (5/2−) | |
| $^{141m}$Tb | 0(200)# keV | 0(200)# keV | 0(200)# keV | 7.9(6) s | β$^+$ | $^{141}$Gd | 11/2−# | |
| $^{142}$Tb | 65 | 77 | 141.93928(75) | 597(17) ms | β$^+$ (96.8%) | $^{142}$Gd | 1+ | |
| $^{142}$Tb | 65 | 77 | 141.93928(75) | 597(17) ms | EC (3.2%) | $^{142}$Gd | 1+ | |
| $^{142}$Tb | 65 | 77 | 141.93928(75) | 597(17) ms | β$^+$, p (0.0022%) | $^{141}$Eu | 1+ | |
| $^{142m1}$Tb | 279.7(4) keV | 279.7(4) keV | 279.7(4) keV | 303(17) ms | IT | $^{142}$Tb | 5− | |
| $^{142m2}$Tb | 652.1(6) keV | 652.1(6) keV | 652.1(6) keV | 26(1) μs | IT | $^{142}$Tb | 8+ | |
| $^{143}$Tb | 65 | 78 | 142.935137(55) | 12(1) s | β$^+$ | $^{143}$Gd | (11/2−) | |
| $^{143m}$Tb | 0(100)# keV | 0(100)# keV | 0(100)# keV | 17(4) s | | | 5/2+# | |
| $^{144}$Tb | 65 | 79 | 143.933045(30) | ~1 s | β$^+$ | $^{144}$Gd | 1+ | |
| $^{144m1}$Tb | 396.9(5) keV | 396.9(5) keV | 396.9(5) keV | 4.25(15) s | IT (66%) | $^{144}$Tb | 6− | |
| $^{144m1}$Tb | 396.9(5) keV | 396.9(5) keV | 396.9(5) keV | 4.25(15) s | β$^+$ (34%) | $^{144}$Gd | 6− | |
| $^{144m2}$Tb | 476.2(5) keV | 476.2(5) keV | 476.2(5) keV | 2.8(3) μs | IT | $^{144}$Tb | (8−) | |
| $^{144m3}$Tb | 517.1(5) keV | 517.1(5) keV | 517.1(5) keV | 670(60) ns | IT | $^{144}$Tb | (9+) | |
| $^{144m4}$Tb | 544.5(6) keV | 544.5(6) keV | 544.5(6) keV | <300 ns | IT | $^{144}$Tb | (10+) | |
| $^{145}$Tb | 65 | 80 | 144.92872(12) | 30.9(6) s | β$^+$ | $^{145}$Gd | (11/2−) | |
| $^{145m}$Tb | 860(230) keV | 860(230) keV | 860(230) keV | | | | (3/2+) | |
| $^{146}$Tb | 65 | 81 | 145.927253(48) | 8(4) s | β$^+$ | $^{146}$Gd | 1+ | |
| $^{146m1}$Tb | 150(100)# keV | 150(100)# keV | 150(100)# keV | 24.1(5) s | β$^+$ | $^{146}$Gd | 5− | |
| $^{146m2}$Tb | 930(100)# keV | 930(100)# keV | 930(100)# keV | 1.18(2) ms | IT | $^{146}$Tb | 10+ | |
| $^{147}$Tb | 65 | 82 | 146.9240546(87) | 1.64(3) h | β$^+$ | $^{147}$Gd | (1/2+) | |
| $^{147m}$Tb | 50.6(9) keV | 50.6(9) keV | 50.6(9) keV | 1.87(5) min | β$^+$ | $^{147}$Gd | (11/2−) | |
| $^{148}$Tb | 65 | 83 | 147.924275(13) | 60(1) min | β$^+$ | $^{148}$Gd | 2− | |
| $^{148m1}$Tb | 90.1(3) keV | 90.1(3) keV | 90.1(3) keV | 2.20(5) min | β$^+$ | $^{148}$Gd | (9)+ | |
| $^{148m2}$Tb | 8618.6(10) keV | 8618.6(10) keV | 8618.6(10) keV | 1.310(7) μs | IT | $^{148}$Tb | (27+) | |
| $^{149}$Tb | 65 | 84 | 148.9232538(39) | 4.118(25) h | β$^+$ (83.3%) | $^{149}$Gd | 1/2+ | |
| $^{149}$Tb | 65 | 84 | 148.9232538(39) | 4.118(25) h | α (16.7%) | $^{145}$Eu | 1/2+ | |
| $^{149m}$Tb | 35.78(13) keV | 35.78(13) keV | 35.78(13) keV | 4.16(4) min | β$^+$ (99.98%) | $^{149}$Gd | 11/2− | |
| $^{149m}$Tb | 35.78(13) keV | 35.78(13) keV | 35.78(13) keV | 4.16(4) min | α (0.022%) | $^{145}$Eu | 11/2− | |
| $^{150}$Tb | 65 | 85 | 149.9236648(79) | 3.48(16) h | β$^+$ | $^{150}$Gd | (2)− | |
| $^{150m}$Tb | 461(27) keV | 461(27) keV | 461(27) keV | 5.8(2) min | β$^+$ | $^{150}$Gd | 9+ | |
| $^{151}$Tb | 65 | 86 | 150.9231090(44) | 17.609(1) h | β$^+$ (99.99%) | $^{151}$Gd | 1/2+ | |
| $^{151}$Tb | 65 | 86 | 150.9231090(44) | 17.609(1) h | α (.0095%) | $^{147}$Eu | 1/2+ | |
| $^{151m}$Tb | 99.53(5) keV | 99.53(5) keV | 99.53(5) keV | 25(3) s | IT (93.4%) | $^{151}$Tb | 11/2− | |
| $^{151m}$Tb | 99.53(5) keV | 99.53(5) keV | 99.53(5) keV | 25(3) s | β$^+$ (6.6%) | $^{151}$Gd | 11/2− | |
| $^{152}$Tb | 65 | 87 | 151.924082(43) | 17.8784(95) h | EC (83%) | $^{152}$Gd | 2− | |
| $^{152}$Tb | 65 | 87 | 151.924082(43) | 17.8784(95) h | β$^+$ (17%) | $^{152}$Gd | 2− | |
| $^{152}$Tb | 65 | 87 | 151.924082(43) | 17.8784(95) h | α (<7×10$^{−7}$%) | $^{148}$Eu | 2− | |
| $^{152m1}$Tb | 342.15(16) keV | 342.15(16) keV | 342.15(16) keV | 960(10) ns | IT | $^{152}$Tb | 5− | |
| $^{152m2}$Tb | 501.74(19) keV | 501.74(19) keV | 501.74(19) keV | 4.2(1) min | IT (78.9%) | $^{152}$Tb | 8+ | |
| $^{152m2}$Tb | 501.74(19) keV | 501.74(19) keV | 501.74(19) keV | 4.2(1) min | β$^+$ (21.1%) | $^{152}$Gd | 8+ | |
| $^{153}$Tb | 65 | 88 | 152.9234417(42) | 2.34(1) d | β$^+$ | $^{153}$Gd | 5/2+ | |
| $^{153m}$Tb | 163.175(5) keV | 163.175(5) keV | 163.175(5) keV | 186(4) μs | IT | $^{153}$Tb | 11/2− | |
| $^{154}$Tb | 65 | 89 | 153.924684(49) | 9.994(39) h | β$^+$ | $^{154}$Gd | 3− | |
| $^{154m1}$Tb | 130(50)# keV | 130(50)# keV | 130(50)# keV | 21.5(4) h | β$^+$ | $^{154}$Gd | 0− | |
| $^{154m2}$Tb | 200(150)# keV | 200(150)# keV | 200(150)# keV | 22.7(5) h | β$^+$ | $^{154}$Gd | 7− | |
| $^{154m3}$Tb | 405(150)# keV | 405(150)# keV | 405(150)# keV | 513(42) ns | IT | $^{154}$Tb | | |
| $^{155}$Tb | 65 | 90 | 154.923510(11) | 5.32(6) d | EC | $^{155}$Gd | 3/2+ | |
| $^{156}$Tb | 65 | 91 | 155.9247542(40) | 5.35(10) d | β$^+$ | $^{156}$Gd | 3− | |
| $^{156m1}$Tb | 88.4(2) keV | 88.4(2) keV | 88.4(2) keV | 5.3(2) h | IT | $^{156}$Tb | (0+) | |
| $^{156m2}$Tb | 100(50)# keV | 100(50)# keV | 100(50)# keV | 24.4(10) h | IT | $^{156}$Tb | (7−) | |
| $^{157}$Tb | 65 | 92 | 156.9240319(11) | 71(7) y | EC | $^{157}$Gd | 3/2+ | |
| $^{158}$Tb | 65 | 93 | 157.9254199(14) | 180(11) y | β$^+$ (83.4%) | $^{158}$Gd | 3− | |
| $^{158}$Tb | 65 | 93 | 157.9254199(14) | 180(11) y | β$^−$ (16.6%) | $^{158}$Dy | 3− | |
| $^{158m1}$Tb | 110.3(12) keV | 110.3(12) keV | 110.3(12) keV | 10.70(17) s | IT | $^{158}$Tb | 0− | |
| $^{158m2}$Tb | 388.39(11) keV | 388.39(11) keV | 388.39(11) keV | 0.40(4) ms | IT | $^{158}$Tb | 7− | |
| $^{159}$Tb | 65 | 94 | 158.9253537(12) | Stable | Stable | Stable | 3/2+ | 1.0000 |
| $^{160}$Tb | 65 | 95 | 159.9271746(12) | 72.3(2) d | β$^−$ | $^{160}$Dy | 3− | |
| $^{161}$Tb | 65 | 96 | 160.9275768(13) | 6.948(5) d | β$^−$ | $^{161}$Dy | 3/2+ | |
| $^{162}$Tb | 65 | 97 | 161.9292754(22) | 7.60(15) min | β$^−$ | $^{162}$Dy | (1−) | |
| $^{162m}$Tb | 286(3) keV | 286(3) keV | 286(3) keV | 10# min | | | 4−# | |
| $^{163}$Tb | 65 | 98 | 162.9306536(44) | 19.5(3) min | β$^−$ | $^{163}$Dy | 3/2+ | |
| $^{164}$Tb | 65 | 99 | 163.9333276(20) | 3.0(1) min | β$^−$ | $^{164}$Dy | (5+) | |
| $^{164m}$Tb | 145(12) keV | 145(12) keV | 145(12) keV | 2# min | | | 2+# | |
| $^{165}$Tb | 65 | 100 | 164.9349552(17) | 2.11(10) min | β$^−$ | $^{165}$Dy | (3/2+) | |
| $^{165m}$Tb | 207(5) keV | 207(5) keV | 207(5) keV | 0.81(8) μs | IT | $^{165}$Tb | (7/2−) | |
| $^{166}$Tb | 65 | 101 | 165.9379397(16) | 27.1(15) s | β$^−$ | $^{166}$Dy | (1−) | |
| $^{166m}$Tb | 159.0(15) keV | 159.0(15) keV | 159.0(15) keV | 3.5(4) μs | IT | $^{166}$Tb | 4−# | |
| $^{167}$Tb | 65 | 102 | 166.9400070(21) | 18.9(16) s | β$^−$ | $^{167}$Dy | (3/2+) | |
| $^{167m}$Tb | 200(6) keV | 200(6) keV | 200(6) keV | 1.2(1) μs | IT | $^{167}$Tb | (7/2−) | |
| $^{168}$Tb | 65 | 103 | 167.9433371(45) | 9.4(4) s | β$^−$ | $^{168}$Dy | (4−) | |
| $^{168m}$Tb | 211(1) keV | 211(1) keV | 211(1) keV | 0.71(3) μs | IT | $^{168}$Tb | (6+) | |
| $^{169}$Tb | 65 | 104 | 168.94581(32)# | 5.13(32) s | β$^−$ | $^{169}$Dy | 3/2+# | |
| $^{170}$Tb | 65 | 105 | 169.94986(32)# | 960(78) ms | β$^−$ | $^{170}$Dy | 2−# | |
| $^{171}$Tb | 65 | 106 | 170.95301(43)# | 1.23(10) s | β$^−$ | $^{171}$Dy | 3/2+# | |
| $^{172}$Tb | 65 | 107 | 171.95739(54)# | 760(190) ms | β$^−$ | $^{172}$Dy | 6+# | |
| $^{173}$Tb | 65 | 108 | 172.96081(54)# | 400# ms [>550 ns] | | | 3/2+# | |
| $^{174}$Tb | 65 | 109 | 173.96568(54)# | 240# ms [>550 ns] | | | 2−# | |
| This table header & footer: view |||||||||
* ↑ $^m$Tb – 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 italics symbol as daughter – Daughter product is nearly stable.
* ↑ 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.
* ↑ Discovery of this isotope is disputed.
* 1 2 Fission product