# Isotopes of tantalum

Natural tantalum ($_{73}$Ta) consists of two stable isotopes: $^{181}$Ta (99.988%) and $^{180m}$Ta (0.012%).
There are also 35 known artificial radioisotopes, the longest-lived of which are $^{179}$Ta with a half-life of 1.82 years, $^{182}$Ta with a half-life of 114.43 days, $^{183}$Ta with a half-life of 5.1 days, and $^{177}$Ta with a half-life of 56.56 hours. All other isotopes have half-lives under a day, most under an hour. There are also numerous isomers, the most stable of which (other than $^{180m}$Ta) is $^{178m1}$Ta with a half-life of 2.36 hours. All isotopes and nuclear isomers of tantalum are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
Tantalum has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of $^{181}$Ta, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope $^{182}$ Ta with a half-life of 114.43 days and produce approximately 1.12 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several months. Such a weapon is not known to have ever been built, tested, or used. While the conversion factor from absorbed dose (measured in Grays) to effective dose (measured in Sievert) for gamma rays is 1 while it is 50 for alpha radiation (i.e., a gamma dose of 1 Gray is equivalent to 1 Sievert whereas an alpha dose of 1 Gray is equivalent to 50 Sievert), gamma rays are only attenuated by shielding, not stopped. As such, alpha particles require incorporation to have an effect while gamma rays can have an effect via mere proximity. In military terms, this allows a gamma ray weapon to deny an area to either side as long as the dose is high enough, whereas radioactive contamination by alpha emitters which do not release significant amounts of gamma rays can be counteracted by ensuring the material is not incorporated.

## 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 |
| $^{155}$Ta | 73 | 82 | 154.97425(32)# | 3.2(13) ms | p | $^{154}$Hf | 11/2− | | |
| $^{156}$Ta | 73 | 83 | 155.97209(32)# | 106(4) ms | p (71%) | $^{155}$Hf | (2−) | | |
| $^{156}$Ta | 73 | 83 | 155.97209(32)# | 106(4) ms | β$^+$ (29%) | $^{156}$Hf | (2−) | | |
| $^{156m}$Ta | 94(8) keV | 94(8) keV | 94(8) keV | 360(40) ms | β$^+$ (95.8%) | $^{156}$Hf | (9+) | | |
| $^{156m}$Ta | 94(8) keV | 94(8) keV | 94(8) keV | 360(40) ms | p (4.2%) | $^{155}$Hf | (9+) | | |
| $^{157}$Ta | 73 | 84 | 156.96823(16) | 10.1(4) ms | α (96.6%) | $^{153}$Lu | 1/2+ | | |
| $^{157}$Ta | 73 | 84 | 156.96823(16) | 10.1(4) ms | p (3.4%) | $^{156}$Hf | 1/2+ | | |
| $^{157m1}$Ta | 22(5) keV | 22(5) keV | 22(5) keV | 4.3(1) ms | α | $^{153}$Lu | 11/2− | | |
| $^{157m2}$Ta | 1593(9) keV | 1593(9) keV | 1593(9) keV | 1.7(1) ms | α | $^{153}$Lu | 25/2−# | | |
| $^{158}$Ta | 73 | 85 | 157.96659(22)# | 49(4) ms | α | $^{154}$Lu | (2)− | | |
| $^{158m1}$Ta | 141(11) keV | 141(11) keV | 141(11) keV | 36.0(8) ms | α (95%) | $^{154}$Lu | (9)+ | | |
| $^{158m2}$Ta | 2808(16) keV | 2808(16) keV | 2808(16) keV | 6.1(1) μs | IT (98.6%) | $^{158}$Ta | (19−) | | |
| $^{158m2}$Ta | 2808(16) keV | 2808(16) keV | 2808(16) keV | 6.1(1) μs | α (1.4%) | $^{154}$Lu | (19−) | | |
| $^{159}$Ta | 73 | 86 | 158.963028(21) | 1.04(9) s | β$^+$ (66%) | $^{159}$Hf | 1/2+ | | |
| $^{159}$Ta | 73 | 86 | 158.963028(21) | 1.04(9) s | α (34%) | $^{155}$Lu | 1/2+ | | |
| $^{159m}$Ta | 64(5) keV | 64(5) keV | 64(5) keV | 560(60) ms | α (55%) | $^{155}$Lu | 11/2− | | |
| $^{159m}$Ta | 64(5) keV | 64(5) keV | 64(5) keV | 560(60) ms | β$^+$ (45%) | $^{159}$Hf | 11/2− | | |
| $^{160}$Ta | 73 | 87 | 159.961542(58) | 1.70(20) s | α | $^{156}$Lu | (2)− | | |
| $^{160m}$Ta | 110(250) keV | 110(250) keV | 110(250) keV | 1.55(4) s | α | $^{156}$Lu | (9,10)+ | | |
| $^{161}$Ta | 73 | 88 | 160.958369(26) | 3# s | | | (1/2+) | | |
| $^{161m}$Ta | 61(23) keV | 61(23) keV | 61(23) keV | 3.08(11) s | β$^+$ (93%) | $^{161}$Hf | (11/2−) | | |
| $^{161m}$Ta | 61(23) keV | 61(23) keV | 61(23) keV | 3.08(11) s | α (7%) | $^{157}$Lu | (11/2−) | | |
| $^{162}$Ta | 73 | 89 | 161.957293(68) | 3.57(12) s | β$^+$ (99.93%) | $^{162}$Hf | 3−# | | |
| $^{162}$Ta | 73 | 89 | 161.957293(68) | 3.57(12) s | α (0.074%) | $^{158}$Lu | 3−# | | |
| $^{162m}$Ta | 120(50)# keV | 120(50)# keV | 120(50)# keV | 5# s | | | 7+# | | |
| $^{163}$Ta | 73 | 90 | 162.954337(41) | 10.6(18) s | β$^+$ (99.8%) | $^{163}$Hf | 1/2+ | | |
| $^{163m}$Ta | 138(18)# keV | 138(18)# keV | 138(18)# keV | 10# s | | | 9/2− | | |
| $^{164}$Ta | 73 | 91 | 163.953534(30) | 14.2(3) s | β$^+$ | $^{164}$Hf | (3+) | | |
| $^{165}$Ta | 73 | 92 | 164.950780(15) | 31.0(15) s | β$^+$ | $^{165}$Hf | (1/2+,3/2+) | | |
| $^{165m}$Ta | 24(18) keV | 24(18) keV | 24(18) keV | 30# s | | | (9/2−) | | |
| $^{166}$Ta | 73 | 93 | 165.950512(30) | 34.4(5) s | β$^+$ | $^{166}$Hf | (2)+ | | |
| $^{167}$Ta | 73 | 94 | 166.948093(30) | 1.33(7) min | β$^+$ | $^{167}$Hf | (3/2+) | | |
| $^{168}$Ta | 73 | 95 | 167.948047(30) | 2.0(1) min | β$^+$ | $^{168}$Hf | (3+) | | |
| $^{169}$Ta | 73 | 96 | 168.946011(30) | 4.9(4) min | β$^+$ | $^{169}$Hf | (5/2+) | | |
| $^{170}$Ta | 73 | 97 | 169.946175(30) | 6.76(6) min | β$^+$ | $^{170}$Hf | (3+) | | |
| $^{171}$Ta | 73 | 98 | 170.944476(30) | 23.3(3) min | β$^+$ | $^{171}$Hf | (5/2+) | | |
| $^{172}$Ta | 73 | 99 | 171.944895(30) | 36.8(3) min | β$^+$ | $^{172}$Hf | (3+) | | |
| $^{173}$Ta | 73 | 100 | 172.943750(30) | 3.14(13) h | β$^+$ | $^{173}$Hf | 5/2− | | |
| $^{173m1}$Ta | 173.10(21) keV | 173.10(21) keV | 173.10(21) keV | 205.2(56) ns | IT | $^{173}$Ta | 9/2− | | |
| $^{173m1}$Ta | 1717.2(4) keV | 1717.2(4) keV | 1717.2(4) keV | 132(3) ns | IT | $^{173}$Ta | 21/2− | | |
| $^{174}$Ta | 73 | 101 | 173.944454(30) | 1.14(8) h | β$^+$ | $^{174}$Hf | 3+ | | |
| $^{175}$Ta | 73 | 102 | 174.943737(30) | 10.5(2) h | β$^+$ | $^{175}$Hf | 7/2+ | | |
| $^{175m1}$Ta | 131.41(17) keV | 131.41(17) keV | 131.41(17) keV | 222(8) ns | IT | $^{175}$Ta | 9/2− | | |
| $^{175m2}$Ta | 339.2(13) keV | 339.2(13) keV | 339.2(13) keV | 170(20) ns | IT | $^{175}$Ta | (1/2+) | | |
| $^{175m3}$Ta | 1567.6(3) keV | 1567.6(3) keV | 1567.6(3) keV | 1.95(15) μs | IT | $^{175}$Ta | 21/2− | | |
| $^{176}$Ta | 73 | 103 | 175.944857(33) | 8.09(5) h | β$^+$ | $^{176}$Hf | (1)− | | |
| $^{176m1}$Ta | 103.0(10) keV | 103.0(10) keV | 103.0(10) keV | 1.08(7) ms | IT | $^{176}$Ta | 7+ | | |
| $^{176m2}$Ta | 1474.0(14) keV | 1474.0(14) keV | 1474.0(14) keV | 3.8(4) μs | IT | $^{176}$Ta | 14− | | |
| $^{176m3}$Ta | 2874.0(14) keV | 2874.0(14) keV | 2874.0(14) keV | 0.97(7) ms | IT | $^{176}$Ta | 20− | | |
| $^{177}$Ta | 73 | 104 | 176.9444819(36) | 56.36(13) h | β$^+$ | $^{177}$Hf | 7/2+ | | |
| $^{177m1}$Ta | 73.16(7) keV | 73.16(7) keV | 73.16(7) keV | 410(7) ns | IT | $^{177}$Ta | 9/2− | | |
| $^{177m2}$Ta | 186.16(6) keV | 186.16(6) keV | 186.16(6) keV | 3.62(10) μs | IT | $^{177}$Ta | 5/2− | | |
| $^{177m3}$Ta | 1354.8(3) keV | 1354.8(3) keV | 1354.8(3) keV | 5.30(11) μs | IT | $^{177}$Ta | 21/2− | | |
| $^{177m4}$Ta | 4656.3(8) keV | 4656.3(8) keV | 4656.3(8) keV | 133(4) μs | IT | $^{177}$Ta | 49/2− | | |
| $^{178}$Ta | 73 | 105 | 177.945680(56)# | 2.36(8) h | β$^+$ | $^{178}$Hf | 7− | | |
| $^{178m1}$Ta | 100(50)# keV | 100(50)# keV | 100(50)# keV | 9.31(3) min | β$^+$ | $^{178}$Hf | (1+) | | |
| $^{178m2}$Ta | 1467.82(16) keV | 1467.82(16) keV | 1467.82(16) keV | 59(3) ms | IT | $^{178}$Ta | 15− | | |
| $^{178m3}$Ta | 2901.9(7) keV | 2901.9(7) keV | 2901.9(7) keV | 290(12) ms | IT | $^{178}$Ta | 21− | | |
| $^{179}$Ta | 73 | 106 | 178.9459391(16) | 1.82(3) y | EC | $^{179}$Hf | 7/2+ | | |
| $^{179m1}$Ta | 30.7(1) keV | 30.7(1) keV | 30.7(1) keV | 1.42(8) μs | IT | $^{179}$Ta | 9/2− | | |
| $^{179m2}$Ta | 520.23(18) keV | 520.23(18) keV | 520.23(18) keV | 280(80) ns | IT | $^{179}$Ta | 1/2+ | | |
| $^{179m3}$Ta | 1252.60(23) keV | 1252.60(23) keV | 1252.60(23) keV | 322(16) ns | IT | $^{179}$Ta | 21/2− | | |
| $^{179m4}$Ta | 1317.2(4) keV | 1317.2(4) keV | 1317.2(4) keV | 9.0(2) ms | IT | $^{179}$Ta | 25/2+ | | |
| $^{179m5}$Ta | 1328.0(4) keV | 1328.0(4) keV | 1328.0(4) keV | 1.6(4) μs | IT | $^{179}$Ta | 23/2− | | |
| $^{179m6}$Ta | 2639.3(5) keV | 2639.3(5) keV | 2639.3(5) keV | 54.1(17) ms | IT | $^{179}$Ta | 37/2+ | | |
| $^{180}$Ta | 73 | 107 | 179.9474676(22) | 8.154(6) h | EC (85%) | $^{180}$Hf | 1+ | | |
| $^{180}$Ta | 73 | 107 | 179.9474676(22) | 8.154(6) h | β$^−$ (15%) | $^{180}$W | 1+ | | |
| $^{180m1}$Ta | 75.3(14) keV | 75.3(14) keV | 75.3(14) keV | Observationally stable | Observationally stable | Observationally stable | 9− | 1.201(32)×10$^{−4}$ | |
| $^{180m2}$Ta | 1452.39(22) keV | 1452.39(22) keV | 1452.39(22) keV | 31.2(14) μs | IT | | 15− | | |
| $^{180m3}$Ta | 3678.9(10) keV | 3678.9(10) keV | 3678.9(10) keV | 2.0(5) μs | IT | | (22−) | | |
| $^{180m4}$Ta | 4172.2(16) keV | 4172.2(16) keV | 4172.2(16) keV | 17(5) μs | IT | | (24+) | | |
| $^{181}$Ta | 73 | 108 | 180.9479985(17) | Observationally stable | Observationally stable | Observationally stable | 7/2+ | 0.9998799(32) | |
| $^{181m1}$Ta | 6.237(20) keV | 6.237(20) keV | 6.237(20) keV | 6.05(12) μs | IT | $^{181}$Ta | 9/2− | | |
| $^{181m2}$Ta | 615.19(3) keV | 615.19(3) keV | 615.19(3) keV | 18(1) μs | IT | $^{181}$Ta | 1/2+ | | |
| $^{181m3}$Ta | 1428(14) keV | 1428(14) keV | 1428(14) keV | 140(36) ns | IT | $^{181}$Ta | 19/2+# | | |
| $^{181m4}$Ta | 1483.43(21) keV | 1483.43(21) keV | 1483.43(21) keV | 25.2(18) μs | IT | $^{181}$Ta | 21/2− | | |
| $^{181m5}$Ta | 2227.9(9) keV | 2227.9(9) keV | 2227.9(9) keV | 210(20) μs | IT | $^{181}$Ta | 29/2− | | |
| $^{182}$Ta | 73 | 109 | 181.9501546(17) | 114.74(12) d | β$^−$ | $^{182}$W | 3− | | |
| $^{182m1}$Ta | 16.273(4) keV | 16.273(4) keV | 16.273(4) keV | 283(3) ms | IT | $^{182}$Ta | 5+ | | |
| $^{182m2}$Ta | 519.577(16) keV | 519.577(16) keV | 519.577(16) keV | 15.84(10) min | IT | $^{182}$Ta | 10− | | |
| $^{183}$Ta | 73 | 110 | 182.9513754(17) | 5.1(1) d | β$^−$ | $^{183}$W | 7/2+ | | |
| $^{183m1}$Ta | 73.164(14) keV | 73.164(14) keV | 73.164(14) keV | 106(10) ns | IT | $^{183}$Ta | 9/2− | | |
| $^{183m2}$Ta | 1335(14) keV | 1335(14) keV | 1335(14) keV | 0.9(3) μs | IT | $^{183}$Ta | (19/2+) | | |
| $^{184}$Ta | 73 | 111 | 183.954010(28) | 8.7(1) h | β$^−$ | $^{184}$W | (5−) | | |
| $^{185}$Ta | 73 | 112 | 184.955561(15) | 49.4(15) min | β$^−$ | $^{185}$W | (7/2+) | | |
| $^{185m1}$Ta | 406(1) keV | 406(1) keV | 406(1) keV | 0.9(3) μs | IT | $^{185}$Ta | (3/2+) | | |
| $^{185m2}$Ta | 1273.4(4) keV | 1273.4(4) keV | 1273.4(4) keV | 11.8(14) ms | IT | $^{185}$Ta | 21/2− | | |
| $^{186}$Ta | 73 | 113 | 185.958553(64) | 10.5(3) min | β$^−$ | $^{186}$W | 3# | | |
| $^{186m}$Ta | 336(20) keV | 336(20) keV | 336(20) keV | 1.54(5) min | | | 9+# | | |
| $^{187}$Ta | 73 | 114 | 186.960391(60) | 2.3(60) min | β$^−$ | $^{187}$W | (7/2+) | | |
| $^{187m1}$Ta | 1778(1) keV | 1778(1) keV | 1778(1) keV | 7.3(9) s | IT | $^{187}$Ta | (25/2−) | | |
| $^{187m2}$Ta | 2933(14) keV | 2933(14) keV | 2933(14) keV | 136(24) s | β$^−$ | $^{187m}$W | 41/2+# [≥35/2] | | |
| $^{187m2}$Ta | 2933(14) keV | 2933(14) keV | 2933(14) keV | 136(24) s | IT | $^{187m1}$Ta | 41/2+# [≥35/2] | | |
| $^{188}$Ta | 73 | 115 | 187.96360(22)# | 19.6(20) s | β$^−$ | $^{188}$W | (1−) | | |
| $^{188m1}$Ta | 99(33) keV | 99(33) keV | 99(33) keV | 19.6(20) s | | | (7−) | | |
| $^{188m2}$Ta | 391(33) keV | 391(33) keV | 391(33) keV | 3.6(4) μs | IT | $^{188}$Ta | 10+# | | |
| $^{189}$Ta | 73 | 116 | 188.96569(22)# | 20# s [>300 ns] | β$^−$ | $^{189}$W | 7/2+# | | |
| $^{189m}$Ta | 1650(100)# keV | 1650(100)# keV | 1650(100)# keV | 1.6(2) μs | IT | $^{189}$Ta | 21/2−# | | |
| $^{190}$Ta | 73 | 117 | 189.96917(22)# | 5.3(7) s | β$^−$ | $^{190}$W | (3) | |
| $^{191}$Ta | 73 | 118 | 190.97153(32)# | 460# ms [>300 ns] | | | 7/2+# | |
| $^{192}$Ta | 73 | 119 | 191.97520(43)# | 2.2(7) s | β$^−$ | $^{192}$W | (2) | |
| $^{193}$Ta | 73 | 120 | 192.97766(43)# | 220# ms [>300 ns] | | | 7/2+# | |
| $^{194}$Ta | 73 | 121 | 193.98161(54)# | 2# s [>300 ns] | | | | |
| This table header & footer: view ||||||||||
* ↑ $^m$Ta – 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 Order of ground state and isomer is uncertain.
* ↑ Only known observationally stable nuclear isomer, believed to decay by isomeric transition to $^{180}$Ta, β$^−$ decay to $^{180}$W, or electron capture to $^{180}$Hf with a half-life over 2.9×10$^{17}$ years; also theorized to undergo α decay to $^{176}$Lu
* ↑ One of the few (observationally) stable odd-odd nuclei
* ↑ Believed to undergo α decay to $^{177}$Lu

## Tantalum-180m

The nuclide $^{180m}$ Ta (m denotes a metastable state) is one of a very few nuclear isomers which are more stable than their ground states. Although it is not unique in this regard (this property is shared by bismuth-210m ($^{210m}$Bi) and americium-242m ($^{242m}$Am), among other nuclides), it is exceptional in that it is observationally stable: no decay has ever been observed. In contrast, the ground state nuclide $^{180}$ Ta has a half-life of only 8 hours.
$^{180m}$ Ta has sufficient energy to decay in three ways: isomeric transition to the ground state of $^{180}$ Ta , beta decay to $^{180}$ W , or electron capture to $^{180}$ Hf . However, no radioactivity from any of these theoretically possible decay modes has ever been observed. As of 2023, the half-life of $^{180m}$Ta is calculated from experimental observation to be at least 2.9×10$^{17}$ (290 quadrillion) years. The very slow decay of $^{180m}$ Ta is attributed to its high spin (9 units) and the low spin of lower-lying states. Gamma or beta decay would require many units of angular momentum to be removed in a single step, so that the process would be very slow.
Because of this stability, $^{180m}$ Ta is a primordial nuclide, the only naturally occurring nuclear isomer (excluding short-lived radiogenic and cosmogenic nuclides). It is also the rarest primordial nuclide in the Universe observed for any element which has any stable isotopes. In an s-process stellar environment with a thermal energy k$_B$T = 26 keV (i.e. a temperature of 300 million kelvin), the nuclear isomers are expected to be fully thermalized, meaning that $^{180}$Ta rapidly transitions between spin states and its overall half-life is predicted to be 11 hours.
It is one of only five stable nuclides to have both an odd number of protons and an odd number of neutrons, the other four stable odd-odd nuclides being $^2$H, $^6$Li, $^{10}$B and $^{14}$N.