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Natural
tantalum Tantalum is a chemical element; it has Symbol (chemistry), symbol Ta and atomic number 73. It is named after Tantalus, a figure in Greek mythology. Tantalum is a very hard, ductility, ductile, lustre (mineralogy), lustrous, blue-gray transition ...
(73Ta) consists of two stable
isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...
s: 181Ta (99.988%) and 180mTa (0.012%). There are also 35 known artificial
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...
s, the longest-lived of which are 179Ta with a half-life of 1.82 years, 182Ta with a half-life of 114.43 days, 183Ta with a half-life of 5.1 days, and 177Ta 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 180mTa) is 178m1Ta with a half-life of 2.36 hours. All isotopes and
nuclear isomers A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state levels (higher energy levels). "Metastable" describes nuclei whose excited states have half-lives of 10−9 seco ...
of tantalum are either radioactive or
observationally stable Stable nuclides are isotopes of a chemical element whose nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The nuclei of such isotopes are not radioactive and unlike radionuc ...
, 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 weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...
s (
cobalt Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...
is another, better-known salting material). A jacket of 181Ta, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope with a
half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...
of 114.43 days and produce approximately 1.12  MeV of
gamma radiation A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
, 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 Absorbed dose is a dose quantity which represents the specific energy (energy per unit mass) deposited by ionizing radiation in living matter. Absorbed dose is used in the calculation of dose uptake in living tissue in both radiation protecti ...
(measured in Grays) to effective dose (measured in
Sievert The sievert (symbol: SvPlease note there are two non-SI units that use the same Sv abbreviation: the sverdrup and svedberg.) is a derived unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizin ...
) 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 Radioactive contamination, also called radiological pollution, is the deposition of, or presence of Radioactive decay, radioactive substances on surfaces or within solids, liquids, or gases (including the human body), where their presence is uni ...
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

, -id=Tantalum-155 , 155Ta , style="text-align:right" , 73 , style="text-align:right" , 82 , 154.97425(32)# , 3.2(13) ms , p , 154Hf , 11/2− , , , -id=Tantalum-156 , rowspan=2, 156Ta , rowspan=2 style="text-align:right" , 73 , rowspan=2 style="text-align:right" , 83 , rowspan=2, 155.97209(32)# , rowspan=2, 106(4) ms , p (71%) , 155Hf , rowspan=2, (2−) , rowspan=2, , rowspan=2, , - , β+ (29%) , 156Hf , -id=Tantalum-156m , rowspan=2 style="text-indent:1em" , 156mTa , rowspan=2 colspan="3" style="text-indent:2em" , 94(8) keV , rowspan=2, 360(40) ms , β+ (95.8%) , 156Hf , rowspan=2, (9+) , rowspan=2, , rowspan=2, , - , p (4.2%) , 155Hf , -id=Tantalum-157 , rowspan=2, 157Ta , rowspan=2 style="text-align:right" , 73 , rowspan=2 style="text-align:right" , 84 , rowspan=2, 156.96823(16) , rowspan=2, 10.1(4) ms , α (96.6%) , 153Lu , rowspan=2, 1/2+ , rowspan=2, , rowspan=2, , - , p (3.4%) , 156Hf , -id=Tantalum-157m1 , style="text-indent:1em" , 157m1Ta , colspan="3" style="text-indent:2em" , 22(5) keV , 4.3(1) ms , α , 153Lu , 11/2− , , , -id=Tantalum-157m2 , style="text-indent:1em" , 157m2Ta , colspan="3" style="text-indent:2em" , 1593(9) keV , 1.7(1) ms , α , 153Lu , 25/2−# , , , -id=Tantalum-158 , 158Ta , style="text-align:right" , 73 , style="text-align:right" , 85 , 157.96659(22)# , 49(4) ms , α , 154Lu , (2)− , , , -id=Tantalum-158m1 , style="text-indent:1em" , 158m1Ta , colspan="3" style="text-indent:2em" , 141(11) keV , 36.0(8) ms , α (95%) , 154Lu , (9)+ , , , -id=Tantalum-158m2 , rowspan=2 style="text-indent:1em" , 158m2Ta , rowspan=2 colspan="3" style="text-indent:2em" , 2808(16) keV , rowspan=2, 6.1(1) Î¼s , IT (98.6%) , 158Ta , rowspan=2, (19−) , rowspan=2, , rowspan=2, , - , α (1.4%) , 154Lu , -id=Tantalum-159 , rowspan=2, 159Ta , rowspan=2 style="text-align:right" , 73 , rowspan=2 style="text-align:right" , 86 , rowspan=2, 158.963028(21) , rowspan=2, 1.04(9) s , β+ (66%) , 159Hf , rowspan=2, 1/2+ , rowspan=2, , rowspan=2, , - , α (34%) , 155Lu , -id=Tantalum-159m , rowspan=2 style="text-indent:1em" , 159mTa , rowspan=2 colspan="3" style="text-indent:2em" , 64(5) keV , rowspan=2, 560(60) ms , α (55%) , 155Lu , rowspan=2, 11/2− , rowspan=2, , rowspan=2, , - , β+ (45%) , 159Hf , -id=Tantalum-160 , 160Ta , style="text-align:right" , 73 , style="text-align:right" , 87 , 159.961542(58) , 1.70(20) s , α , 156Lu , (2)− , , , -id=Tantalum-160m , style="text-indent:1em" , 160mTaOrder of ground state and isomer is uncertain. , colspan="3" style="text-indent:2em" , 110(250) keV , 1.55(4) s , α , 156Lu , (9,10)+ , , , -id=Tantalum-161 , 161Ta , style="text-align:right" , 73 , style="text-align:right" , 88 , 160.958369(26) , 3# s , , , (1/2+) , , , -id=Tantalum-161m , rowspan=2 style="text-indent:1em" , 161mTa , rowspan=2 colspan="3" style="text-indent:2em" , 61(23) keV , rowspan=2, 3.08(11) s , β+ (93%) , 161Hf , rowspan=2, (11/2−) , rowspan=2, , rowspan=2, , - , α (7%) , 157Lu , -id=Tantalum-162 , rowspan=2, 162Ta , rowspan=2 style="text-align:right" , 73 , rowspan=2 style="text-align:right" , 89 , rowspan=2, 161.957293(68) , rowspan=2, 3.57(12) s , β+ (99.93%) , 162Hf , rowspan=2, 3−# , rowspan=2, , rowspan=2, , - , α (0.074%) , 158Lu , -id=Tantalum-162m , style="text-indent:1em" , 162mTa , colspan="3" style="text-indent:2em" , 120(50)# keV , 5# s , , , 7+# , , , -id=Tantalum-163 , 163Ta , style="text-align:right" , 73 , style="text-align:right" , 90 , 162.954337(41) , 10.6(18) s , β+ (99.8%) , 163Hf , 1/2+ , , , -id=Tantalum-163m , style="text-indent:1em" , 163mTa , colspan="3" style="text-indent:2em" , 138(18)# keV , 10# s , , , 9/2− , , , -id=Tantalum-164 , 164Ta , style="text-align:right" , 73 , style="text-align:right" , 91 , 163.953534(30) , 14.2(3) s , β+ , 164Hf , (3+) , , , -id=Tantalum-165 , 165Ta , style="text-align:right" , 73 , style="text-align:right" , 92 , 164.950780(15) , 31.0(15) s , β+ , 165Hf , (1/2+,3/2+) , , , -id=Tantalum-165m , style="text-indent:1em" , 165mTa , colspan="3" style="text-indent:2em" , 24(18) keV , 30# s , , , (9/2−) , , , -id=Tantalum-166 , 166Ta , style="text-align:right" , 73 , style="text-align:right" , 93 , 165.950512(30) , 34.4(5) s , β+ , 166Hf , (2)+ , , , -id=Tantalum-167 , 167Ta , style="text-align:right" , 73 , style="text-align:right" , 94 , 166.948093(30) , 1.33(7) min , β+ , 167Hf , (3/2+) , , , -id=Tantalum-168 , 168Ta , style="text-align:right" , 73 , style="text-align:right" , 95 , 167.948047(30) , 2.0(1) min , β+ , 168Hf , (3+) , , , -id=Tantalum-169 , 169Ta , style="text-align:right" , 73 , style="text-align:right" , 96 , 168.946011(30) , 4.9(4) min , β+ , 169Hf , (5/2+) , , , -id=Tantalum-170 , 170Ta , style="text-align:right" , 73 , style="text-align:right" , 97 , 169.946175(30) , 6.76(6) min , β+ , 170Hf , (3+) , , , -id=Tantalum-171 , 171Ta , style="text-align:right" , 73 , style="text-align:right" , 98 , 170.944476(30) , 23.3(3) min , β+ , 171Hf , (5/2+) , , , -id=Tantalum-172 , 172Ta , style="text-align:right" , 73 , style="text-align:right" , 99 , 171.944895(30) , 36.8(3) min , β+ , 172Hf , (3+) , , , -id=Tantalum-173 , 173Ta , style="text-align:right" , 73 , style="text-align:right" , 100 , 172.943750(30) , 3.14(13) h , β+ , 173Hf , 5/2− , , , -id=Tantalum-173m1 , style="text-indent:1em" , 173m1Ta , colspan="3" style="text-indent:2em" , 173.10(21) keV , 205.2(56) ns , IT , 173Ta , 9/2− , , , -id=Tantalum-173m2 , style="text-indent:1em" , 173m1Ta , colspan="3" style="text-indent:2em" , 1717.2(4) keV , 132(3) ns , IT , 173Ta , 21/2− , , , -id=Tantalum-174 , 174Ta , style="text-align:right" , 73 , style="text-align:right" , 101 , 173.944454(30) , 1.14(8) h , β+ , ''174Hf'' , 3+ , , , -id=Tantalum-175 , 175Ta , style="text-align:right" , 73 , style="text-align:right" , 102 , 174.943737(30) , 10.5(2) h , β+ , 175Hf , 7/2+ , , , -id=Tantalum-175m1 , style="text-indent:1em" , 175m1Ta , colspan="3" style="text-indent:2em" , 131.41(17) keV , 222(8) ns , IT , 175Ta , 9/2− , , , -id=Tantalum-175m2 , style="text-indent:1em" , 175m2Ta , colspan="3" style="text-indent:2em" , 339.2(13) keV , 170(20) ns , IT , 175Ta , (1/2+) , , , -id=Tantalum-175m3 , style="text-indent:1em" , 175m3Ta , colspan="3" style="text-indent:2em" , 1567.6(3) keV , 1.95(15) Î¼s , IT , 175Ta , 21/2− , , , -id=Tantalum-176 , 176Ta , style="text-align:right" , 73 , style="text-align:right" , 103 , 175.944857(33) , 8.09(5) h , β+ , 176Hf , (1)− , , , -id=Tantalum-176m1 , style="text-indent:1em" , 176m1Ta , colspan="3" style="text-indent:2em" , 103.0(10) keV , 1.08(7) ms , IT , 176Ta , 7+ , , , -id=Tantalum-176m2 , style="text-indent:1em" , 176m2Ta , colspan="3" style="text-indent:2em" , 1474.0(14) keV , 3.8(4) Î¼s , IT , 176Ta , 14− , , , -id=Tantalum-176m3 , style="text-indent:1em" , 176m3Ta , colspan="3" style="text-indent:2em" , 2874.0(14) keV , 0.97(7) ms , IT , 176Ta , 20− , , , -id=Tantalum-177 , 177Ta , style="text-align:right" , 73 , style="text-align:right" , 104 , 176.9444819(36) , 56.36(13) h , β+ , 177Hf , 7/2+ , , , -id=Tantalum-177m1 , style="text-indent:1em" , 177m1Ta , colspan="3" style="text-indent:2em" , 73.16(7) keV , 410(7) ns , IT , 177Ta , 9/2− , , , -id=Tantalum-177m2 , style="text-indent:1em" , 177m2Ta , colspan="3" style="text-indent:2em" , 186.16(6) keV , 3.62(10) Î¼s , IT , 177Ta , 5/2− , , , -id=Tantalum-177m3 , style="text-indent:1em" , 177m3Ta , colspan="3" style="text-indent:2em" , 1354.8(3) keV , 5.30(11) Î¼s , IT , 177Ta , 21/2− , , , -id=Tantalum-177m4 , style="text-indent:1em" , 177m4Ta , colspan="3" style="text-indent:2em" , 4656.3(8) keV , 133(4) Î¼s , IT , 177Ta , 49/2− , , , -id=Tantalum-178 , 178Ta , style="text-align:right" , 73 , style="text-align:right" , 105 , 177.945680(56)# , 2.36(8) h , β+ , 178Hf , 7− , , , -id=Tantalum-178m1 , style="text-indent:1em" , 178m1Ta , colspan="3" style="text-indent:2em" , 100(50)# keV , 9.31(3) min , β+ , 178Hf , (1+) , , , -id=Tantalum-178m2 , style="text-indent:1em" , 178m2Ta , colspan="3" style="text-indent:2em" , 1467.82(16) keV , 59(3) ms , IT , 178Ta , 15− , , , -id=Tantalum-178m3 , style="text-indent:1em" , 178m3Ta , colspan="3" style="text-indent:2em" , 2901.9(7) keV , 290(12) ms , IT , 178Ta , 21− , , , -id=Tantalum-179 , 179Ta , style="text-align:right" , 73 , style="text-align:right" , 106 , 178.9459391(16) , 1.82(3) y , EC , 179Hf , 7/2+ , , , -id=Tantalum-179m1 , style="text-indent:1em" , 179m1Ta , colspan="3" style="text-indent:2em" , 30.7(1) keV , 1.42(8) Î¼s , IT , 179Ta , 9/2− , , , -id=Tantalum-179m2 , style="text-indent:1em" , 179m2Ta , colspan="3" style="text-indent:2em" , 520.23(18) keV , 280(80) ns , IT , 179Ta , 1/2+ , , , -id=Tantalum-179m3 , style="text-indent:1em" , 179m3Ta , colspan="3" style="text-indent:2em" , 1252.60(23) keV , 322(16) ns , IT , 179Ta , 21/2− , , , -id=Tantalum-179m4 , style="text-indent:1em" , 179m4Ta , colspan="3" style="text-indent:2em" , 1317.2(4) keV , 9.0(2) ms , IT , 179Ta , 25/2+ , , , -id=Tantalum-179m5 , style="text-indent:1em" , 179m5Ta , colspan="3" style="text-indent:2em" , 1328.0(4) keV , 1.6(4) Î¼s , IT , 179Ta , 23/2− , , , -id=Tantalum-179m6 , style="text-indent:1em" , 179m6Ta , colspan="3" style="text-indent:2em" , 2639.3(5) keV , 54.1(17) ms , IT , 179Ta , 37/2+ , , , -id=Tantalum-180 , rowspan=2, 180Ta , rowspan=2 style="text-align:right" , 73 , rowspan=2 style="text-align:right" , 107 , rowspan=2, 179.9474676(22) , rowspan=2, 8.154(6) h , EC (85%) , 180Hf , rowspan=2, 1+ , rowspan=2, , rowspan=2, , - , β− (15%) , ''180W'' , -id=Tantalum-180m1 , style="text-indent:1em" , 180m1Ta , colspan="3" style="text-indent:2em" , 75.3(14) keV , colspan=3 align=center, Observationally stableOne of the few (observationally) stable odd-odd nuclei , 9− , 1.201(32)×10−4 , , -id=Tantalum-180m2 , style="text-indent:1em" , 180m2Ta , colspan="3" style="text-indent:2em" , 1452.39(22) keV , 31.2(14) Î¼s , IT , , 15− , , , -id=Tantalum-180m3 , style="text-indent:1em" , 180m3Ta , colspan="3" style="text-indent:2em" , 3678.9(10) keV , 2.0(5) Î¼s , IT , , (22−) , , , -id=Tantalum-180m4 , style="text-indent:1em" , 180m4Ta , colspan="3" style="text-indent:2em" , 4172.2(16) keV , 17(5) Î¼s , IT , , (24+) , , , -id=Tantalum-181 , 181Ta , style="text-align:right" , 73 , style="text-align:right" , 108 , 180.9479985(17) , colspan=3 align=center, Observationally stableBelieved to undergo α decay to 177Lu , 7/2+ , 0.9998799(32) , , -id=Tantalum-181m1 , style="text-indent:1em" , 181m1Ta , colspan="3" style="text-indent:2em" , 6.237(20) keV , 6.05(12) Î¼s , IT , 181Ta , 9/2− , , , -id=Tantalum-181m2 , style="text-indent:1em" , 181m2Ta , colspan="3" style="text-indent:2em" , 615.19(3) keV , 18(1) Î¼s , IT , 181Ta , 1/2+ , , , -id=Tantalum-181m3 , style="text-indent:1em" , 181m3Ta , colspan="3" style="text-indent:2em" , 1428(14) keV , 140(36) ns , IT , 181Ta , 19/2+# , , , -id=Tantalum-181m4 , style="text-indent:1em" , 181m4Ta , colspan="3" style="text-indent:2em" , 1483.43(21) keV , 25.2(18) Î¼s , IT , 181Ta , 21/2− , , , -id=Tantalum-181m5 , style="text-indent:1em" , 181m5Ta , colspan="3" style="text-indent:2em" , 2227.9(9) keV , 210(20) Î¼s , IT , 181Ta , 29/2− , , , -id=Tantalum-182 , 182Ta , style="text-align:right" , 73 , style="text-align:right" , 109 , 181.9501546(17) , 114.74(12) d , β− , 182W , 3− , , , -id=Tantalum-182m1 , style="text-indent:1em" , 182m1Ta , colspan="3" style="text-indent:2em" , 16.273(4) keV , 283(3) ms , IT , 182Ta , 5+ , , , -id=Tantalum-182m2 , style="text-indent:1em" , 182m2Ta , colspan="3" style="text-indent:2em" , 519.577(16) keV , 15.84(10) min , IT , 182Ta , 10− , , , -id=Tantalum-183 , 183Ta , style="text-align:right" , 73 , style="text-align:right" , 110 , 182.9513754(17) , 5.1(1) d , β− , 183W , 7/2+ , , , -id=Tantalum-183m1 , style="text-indent:1em" , 183m1Ta , colspan="3" style="text-indent:2em" , 73.164(14) keV , 106(10) ns , IT , 183Ta , 9/2− , , , -id=Tantalum-183m2 , style="text-indent:1em" , 183m2Ta , colspan="3" style="text-indent:2em" , 1335(14) keV , 0.9(3) Î¼s , IT , 183Ta , (19/2+) , , , -id=Tantalum-184 , 184Ta , style="text-align:right" , 73 , style="text-align:right" , 111 , 183.954010(28) , 8.7(1) h , β− , 184W , (5−) , , , -id=Tantalum-185 , 185Ta , style="text-align:right" , 73 , style="text-align:right" , 112 , 184.955561(15) , 49.4(15) min , β− , 185W , (7/2+) , , , -id=Tantalum-185m1 , style="text-indent:1em" , 185m1Ta , colspan="3" style="text-indent:2em" , 406(1) keV , 0.9(3) Î¼s , IT , 185Ta , (3/2+) , , , -id=Tantalum-185m2 , style="text-indent:1em" , 185m2Ta , colspan="3" style="text-indent:2em" , 1273.4(4) keV , 11.8(14) ms , IT , 185Ta , 21/2− , , , -id=Tantalum-186 , 186Ta , style="text-align:right" , 73 , style="text-align:right" , 113 , 185.958553(64) , 10.5(3) min , β− , 186W , 3# , , , -id=Tantalum-186m , style="text-indent:1em" , 186mTa , colspan="3" style="text-indent:2em" , 336(20) keV , 1.54(5) min , , , 9+# , , , -id=Tantalum-187 , 187Ta , style="text-align:right" , 73 , style="text-align:right" , 114 , 186.960391(60) , 2.3(60) min , β− , 187W , (7/2+) , , , -id=Tantalum-187m1 , style="text-indent:1em" , 187m1Ta , colspan="3" style="text-indent:2em" , 1778(1) keV , 7.3(9) s , IT , 187Ta , (25/2−) , , , -id=Tantalum-187m2 , rowspan=2 style="text-indent:1em" , 187m2Ta , rowspan=2 colspan="3" style="text-indent:2em" , 2933(14) keV , rowspan=2, 136(24) s , β− , 187mW , rowspan=2, 41/2+#
��35/2, rowspan=2, , rowspan=2, , - , IT , 187m1Ta , -id=Tantalum-188 , 188Ta , style="text-align:right" , 73 , style="text-align:right" , 115 , 187.96360(22)# , 19.6(20) s , β− , 188W , (1−) , , , -id=Tantalum-188m1 , style="text-indent:1em" , 188m1Ta , colspan="3" style="text-indent:2em" , 99(33) keV , 19.6(20) s , , , (7−) , , , -id=Tantalum-188m2 , style="text-indent:1em" , 188m2Ta , colspan="3" style="text-indent:2em" , 391(33) keV , 3.6(4) Î¼s , IT , 188Ta , 10+# , , , -id=Tantalum-189 , 189Ta , style="text-align:right" , 73 , style="text-align:right" , 116 , 188.96569(22)# , 20# s
300 ns, β− , 189W , 7/2+# , , , -id=Tantalum-189m , style="text-indent:1em" , 189mTa , colspan="3" style="text-indent:2em" , 1650(100)# keV , 1.6(2) Î¼s , IT , 189Ta , 21/2−# , , , -id=Tantalum-190 , 190Ta , style="text-align:right" , 73 , style="text-align:right" , 117 , 189.96917(22)# , 5.3(7) s , β− , 190W , (3) , , -id=Tantalum-191 , 191Ta , style="text-align:right" , 73 , style="text-align:right" , 118 , 190.97153(32)# , 460# ms
300 ns, , , 7/2+# , , -id=Tantalum-192 , 192Ta , style="text-align:right" , 73 , style="text-align:right" , 119 , 191.97520(43)# , 2.2(7) s , β− , 192W , (2) , , -id=Tantalum-193 , 193Ta , style="text-align:right" , 73 , style="text-align:right" , 120 , 192.97766(43)# , 220# ms
300 ns, , , 7/2+# , , -id=Tantalum-194 , 194Ta , style="text-align:right" , 73 , style="text-align:right" , 121 , 193.98161(54)# , 2# s
300 ns, , , ,


Tantalum-180m

The nuclide (''m'' denotes a
metastable In chemistry and physics, metastability is 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 is onl ...
state) is one of a very few
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 levels (higher energy levels). "Metastable" describes nuclei whose excited states have Half-life, half-lives of ...
s which are more stable than their ground states. Although it is not unique in this regard (this property is shared by bismuth-210m (210mBi) and americium-242m (242mAm), among other nuclides), it is exceptional in that it is
observationally stable Stable nuclides are isotopes of a chemical element whose nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The nuclei of such isotopes are not radioactive and unlike radionuc ...
: no decay has ''ever'' been observed. In contrast, the ground state nuclide has a half-life of only 8 hours. has sufficient energy to decay in three ways:
isomeric transition A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state levels (higher energy levels). "Metastable" describes nuclei whose excited states have half-lives of 10−9 s ...
to 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 ...
of ,
beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...
to , or
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. Th ...
to . However, no radioactivity from any of these theoretically possible decay modes has ever been observed. As of 2023, the half-life of 180mTa is calculated from experimental observation to be at least (290 quadrillion) years. The very slow decay of 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. Similar suppression of gamma or beta decay occurs for 210mBi, a rather short-lived alpha emitter. Because of this stability, is a
primordial nuclide In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the ...
, the only naturally occurring
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 levels (higher energy levels). "Metastable" describes nuclei whose excited states have Half-life, half-lives of ...
(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 The slow neutron-capture process, or ''s''-process, is a series of nuclear reactions, reactions in nuclear astrophysics that occur in stars, particularly asymptotic giant branch stars. The ''s''-process is responsible for the creation (nucleosynt ...
stellar environment with a thermal energy kBT = (i.e. a temperature of 300 million kelvin), the nuclear isomers are expected to be fully thermalized, meaning that 180Ta 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 2H, 6Li, 10B and 14N.


See also

Daughter products other than tantalum * Isotopes of tungsten * Isotopes of hafnium * Isotopes of lutetium


References

* Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Navbox element isotopes Tantalum
Tantalum Tantalum is a chemical element; it has Symbol (chemistry), symbol Ta and atomic number 73. It is named after Tantalus, a figure in Greek mythology. Tantalum is a very hard, ductility, ductile, lustre (mineralogy), lustrous, blue-gray transition ...