| |||||||||||||||||||||||||||||||||||||||||||||||||||||
Standard atomic weight Ar°(Ta) | |||||||||||||||||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Natural
tantalum (73Ta) consists of two stable
isotopes: 181Ta (99.988%) and 180m
Ta
(0.012%).
There are also 35 known artificial radioisotopes, 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 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 181Ta, 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.
[4] 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.
Nuclide [n 1] |
Z | N |
Isotopic mass (
Da) [n 2] [n 3] |
Half-life [n 4] |
Decay mode [n 5] |
Daughter isotope [n 6] [n 7] |
Spin and parity [n 8] [n 4] |
Natural abundance (mole fraction) | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Excitation energy [n 4] | Normal proportion | Range of variation | |||||||||||||||||
155 Ta |
73 | 82 | 154.97459(54)# | 2.9+1.5 −1.1 ms [5] |
p | 154Hf | (11/2−) | ||||||||||||
155m Ta |
~323 keV | 12+4 −3 μs [6] |
p | 154Hf | 11/2−? | ||||||||||||||
156 Ta [7] |
73 | 83 | 155.97230(43)# | 106(4) ms | p (71%) | 155Hf | (2−) | ||||||||||||
β+ (29%) | 156Hf | ||||||||||||||||||
156m Ta |
102(7) keV | 0.36(4) s | p | 155Hf | 9+ | ||||||||||||||
157 Ta |
73 | 84 | 156.96819(22) | 10.1(4) ms | α (91%) | 153Lu | 1/2+ | ||||||||||||
β+ (9%) | 157Hf | ||||||||||||||||||
157m1 Ta |
22(5) keV | 4.3(1) ms | 11/2− | ||||||||||||||||
157m2 Ta |
1593(9) keV | 1.7(1) ms | α | 153Lu | (25/2−) | ||||||||||||||
158 Ta |
73 | 85 | 157.96670(22)# | 49(8) ms | α (96%) | 154Lu | (2−) | ||||||||||||
β+ (4%) | 158Hf | ||||||||||||||||||
158m Ta |
141(9) keV | 36.0(8) ms | α (93%) | 154Lu | (9+) | ||||||||||||||
IT | 158Ta | ||||||||||||||||||
β+ | 158Hf | ||||||||||||||||||
159 Ta |
73 | 86 | 158.963018(22) | 1.04(9) s | β+ (66%) | 159Hf | (1/2+) | ||||||||||||
α (34%) | 155Lu | ||||||||||||||||||
159m Ta |
64(5) keV | 514(9) ms | α (56%) | 155Lu | (11/2−) | ||||||||||||||
β+ (44%) | 159Hf | ||||||||||||||||||
160 Ta |
73 | 87 | 159.96149(10) | 1.70(20) s | α | 156Lu | (2#)− | ||||||||||||
β+ | 160Hf | ||||||||||||||||||
160m Ta |
310(90)# keV | 1.55(4) s | β+ (66%) | 160Hf | (9)+ | ||||||||||||||
α (34%) | 156Lu | ||||||||||||||||||
161 Ta |
73 | 88 | 160.95842(6)# | 3# s | β+ (95%) | 161Hf | 1/2+# | ||||||||||||
α (5%) | 157Lu | ||||||||||||||||||
161m Ta |
50(50)# keV | 2.89(12) s | 11/2−# | ||||||||||||||||
162 Ta |
73 | 89 | 161.95729(6) | 3.57(12) s | β+ (99.92%) | 162Hf | 3+# | ||||||||||||
α (.073%) | 158Lu | ||||||||||||||||||
163 Ta |
73 | 90 | 162.95433(4) | 10.6(18) s | β+ (99.8%) | 163Hf | 1/2+# | ||||||||||||
α (.2%) | 159Lu | ||||||||||||||||||
164 Ta |
73 | 91 | 163.95353(3) | 14.2(3) s | β+ | 164Hf | (3+) | ||||||||||||
165 Ta |
73 | 92 | 164.950773(19) | 31.0(15) s | β+ | 165Hf | 5/2−# | ||||||||||||
165m Ta |
60(30) keV | 9/2−# | |||||||||||||||||
166 Ta |
73 | 93 | 165.95051(3) | 34.4(5) s | β+ | 166Hf | (2)+ | ||||||||||||
167 Ta |
73 | 94 | 166.94809(3) | 1.33(7) min | β+ | 167Hf | (3/2+) | ||||||||||||
168 Ta |
73 | 95 | 167.94805(3) | 2.0(1) min | β+ | 168Hf | (2−,3+) | ||||||||||||
169 Ta |
73 | 96 | 168.94601(3) | 4.9(4) min | β+ | 169Hf | (5/2+) | ||||||||||||
170 Ta |
73 | 97 | 169.94618(3) | 6.76(6) min | β+ | 170Hf | (3)(+#) | ||||||||||||
171 Ta |
73 | 98 | 170.94448(3) | 23.3(3) min | β+ | 171Hf | (5/2−) | ||||||||||||
172 Ta |
73 | 99 | 171.94490(3) | 36.8(3) min | β+ | 172Hf | (3+) | ||||||||||||
173 Ta |
73 | 100 | 172.94375(3) | 3.14(13) h | β+ | 173Hf | 5/2− | ||||||||||||
174 Ta |
73 | 101 | 173.94445(3) | 1.14(8) h | β+ | 174Hf | 3+ | ||||||||||||
175 Ta |
73 | 102 | 174.94374(3) | 10.5(2) h | β+ | 175Hf | 7/2+ | ||||||||||||
176 Ta |
73 | 103 | 175.94486(3) | 8.09(5) h | β+ | 176Hf | (1)− | ||||||||||||
176m1 Ta |
103.0(10) keV | 1.1(1) ms | IT | 176Ta | (+) | ||||||||||||||
176m2 Ta |
1372.6(11)+X keV | 3.8(4) µs | (14−) | ||||||||||||||||
176m3 Ta |
2820(50) keV | 0.97(7) ms | (20−) | ||||||||||||||||
177 Ta |
73 | 104 | 176.944472(4) | 56.56(6) h | β+ | 177Hf | 7/2+ | ||||||||||||
177m1 Ta |
73.36(15) keV | 410(7) ns | 9/2− | ||||||||||||||||
177m2 Ta |
186.15(6) keV | 3.62(10) µs | 5/2− | ||||||||||||||||
177m3 Ta |
1355.01(19) keV | 5.31(25) µs | 21/2− | ||||||||||||||||
177m4 Ta |
4656.3(5) keV | 133(4) µs | 49/2− | ||||||||||||||||
178 Ta |
73 | 105 | 177.945778(16) | 9.31(3) min | β+ | 178Hf | 1+ | ||||||||||||
178m1 Ta |
100(50)# keV | 2.36(8) h | β+ | 178Hf | (7)− | ||||||||||||||
178m2 Ta |
1570(50)# keV | 59(3) ms | (15−) | ||||||||||||||||
178m3 Ta |
3000(50)# keV | 290(12) ms | (21−) | ||||||||||||||||
179 Ta |
73 | 106 | 178.9459295(23) | 1.82(3) y | EC | 179Hf | 7/2+ | ||||||||||||
179m1 Ta |
30.7(1) keV | 1.42(8) µs | (9/2)− | ||||||||||||||||
179m2 Ta |
520.23(18) keV | 335(45) ns | (1/2)+ | ||||||||||||||||
179m3 Ta |
1252.61(23) keV | 322(16) ns | (21/2−) | ||||||||||||||||
179m4 Ta |
1317.3(4) keV | 9.0(2) ms | IT | 179Ta | (25/2+) | ||||||||||||||
179m5 Ta |
1327.9(4) keV | 1.6(4) µs | (23/2−) | ||||||||||||||||
179m6 Ta |
2639.3(5) keV | 54.1(17) ms | (37/2+) | ||||||||||||||||
180 Ta |
73 | 107 | 179.9474648(24) | 8.152(6) h | EC (86%) | 180Hf | 1+ | ||||||||||||
β− (14%) | 180W | ||||||||||||||||||
180m1 Ta |
77.1(8) keV | Observationally stable [n 9] [n 10] | 9− | 1.2(2)×10−4 | |||||||||||||||
180m2 Ta |
1452.40(18) keV | 31.2(14) µs | 15− | ||||||||||||||||
180m3 Ta |
3679.0(11) keV | 2.0(5) µs | (22−) | ||||||||||||||||
180m4 Ta |
4171.0+X keV | 17(5) µs | (23, 24, 25) | ||||||||||||||||
181 Ta |
73 | 108 | 180.9479958(20) | Observationally stable [n 11] | 7/2+ | 0.99988(2) | |||||||||||||
181m1 Ta |
6.238(20) keV | 6.05(12) µs | 9/2− | ||||||||||||||||
181m2 Ta |
615.21(3) keV | 18(1) µs | 1/2+ | ||||||||||||||||
181m3 Ta |
1485(3) keV | 25(2) µs | 21/2− | ||||||||||||||||
181m4 Ta |
2230(3) keV | 210(20) µs | 29/2− | ||||||||||||||||
182 Ta |
73 | 109 | 181.9501518(19) | 114.43(3) d | β− | 182W | 3− | ||||||||||||
182m1 Ta |
16.263(3) keV | 283(3) ms | IT | 182Ta | 5+ | ||||||||||||||
182m2 Ta |
519.572(18) keV | 15.84(10) min | 10− | ||||||||||||||||
183 Ta |
73 | 110 | 182.9513726(19) | 5.1(1) d | β− | 183W | 7/2+ | ||||||||||||
183m Ta |
73.174(12) keV | 107(11) ns | 9/2− | ||||||||||||||||
184 Ta |
73 | 111 | 183.954008(28) | 8.7(1) h | β− | 184W | (5−) | ||||||||||||
185 Ta |
73 | 112 | 184.955559(15) | 49.4(15) min | β− | 185W | (7/2+)# | ||||||||||||
185m Ta |
1308(29) keV | >1 ms | (21/2−) | ||||||||||||||||
186 Ta |
73 | 113 | 185.95855(6) | 10.5(3) min | β− | 186W | (2−,3−) | ||||||||||||
186m Ta |
1.54(5) min | ||||||||||||||||||
187 Ta |
73 | 114 | 186.96053(21)# | 2# min [>300 ns] |
β− | 187W | 7/2+# | ||||||||||||
188 Ta |
73 | 115 | 187.96370(21)# | 20# s [>300 ns] |
β− | 188W | |||||||||||||
189 Ta |
73 | 116 | 188.96583(32)# | 3# s [>300 ns] |
7/2+# | ||||||||||||||
190 Ta |
73 | 117 | 189.96923(43)# | 0.3# s | |||||||||||||||
This table header & footer: |
EC: | Electron capture |
IT: |
Isomeric transition
|
p: | Proton emission |
The nuclide 180m
Ta
(m denotes a
metastable state) has sufficient energy to decay in three ways:
isomeric transition to the
ground state of 180
Ta
,
beta decay to
180
W
, and
electron capture to
180
Hf
. However, no radioactivity from any decay mode of this
nuclear isomer has ever been observed. As of 2023, the half-life of 180mTa is calculated from experimental observation to be at least 2.9×1017 (290 quadrillion) years.
[8]
[9]
[10] 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.
[11]
The very unusual nature of 180mTa is that the ground state of this isotope is less stable than the isomer. This phenomenon is exhibited in
bismuth-210m (210mBi) and
americium-242m (242mAm), among other nuclides. 180
Ta
has a half-life of only 8 hours. 180m
Ta
is the only naturally occurring
nuclear isomer (excluding radiogenic and cosmogenic short-living nuclides). It is also the rarest
primordial nuclide in the Universe observed for any element that has any stable isotopes. In an
s-process stellar environment with a thermal energy
kBT = 26 k
eV (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.
[12]
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. [13]
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