| |||||||||||||||||||||||||||||||||||||||||||||||||||||
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) 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 (210mBi) and americium-242m (242mAm), 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 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]
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 kBT = 26 keV (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]
Stable nuclides are nuclides that are not radioactive and so do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes.
A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state (higher energy) levels. "Metastable" describes nuclei whose excited states have half-lives 100 to 1000 times longer than the half-lives of the excited nuclear states that decay with a "prompt" half life (ordinarily on the order of 10−12 seconds). The term "metastable" is usually restricted to isomers with half-lives of 10−9 seconds or longer. Some references recommend 5 × 10−9 seconds to distinguish the metastable half life from the normal "prompt" gamma-emission half-life. Occasionally the half-lives are far longer than this and can last minutes, hours, or years. For example, the 180m
73Ta
nuclear isomer survives so long (at least 1015 years) that it has never been observed to decay spontaneously. The half-life of a nuclear isomer can even exceed that of the ground state of the same nuclide, as shown by 180m
73Ta
as well as 186m
75Re
, 192m2
77Ir
, 210m
83Bi
, 212m
84Po
, 242m
95Am
and multiple holmium isomers.
In physics, induced gamma emission (IGE) refers to the process of fluorescent emission of gamma rays from excited nuclei, usually involving a specific nuclear isomer. It is analogous to conventional fluorescence, which is defined as the emission of a photon by an excited electron in an atom or molecule. In the case of IGE, nuclear isomers can store significant amounts of excitation energy for times long enough for them to serve as nuclear fluorescent materials. There are over 800 known nuclear isomers but almost all are too intrinsically radioactive to be considered for applications. As of 2006 there were two proposed nuclear isomers that appeared to be physically capable of IGE fluorescence in safe arrangements: tantalum-180m and hafnium-178m2.
Thorium (90Th) has seven naturally occurring isotopes but none are stable. One isotope, 232Th, is relatively stable, with a half-life of 1.405×1010 years, considerably longer than the age of the Earth, and even slightly longer than the generally accepted age of the universe. This isotope makes up nearly all natural thorium, so thorium was considered to be mononuclidic. However, in 2013, IUPAC reclassified thorium as binuclidic, due to large amounts of 230Th in deep seawater. Thorium has a characteristic terrestrial isotopic composition and thus a standard atomic weight can be given.
Radium (88Ra) has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given. The longest lived, and most common, isotope of radium is 226Ra with a half-life of 1600 years. 226Ra occurs in the decay chain of 238U. Radium has 34 known isotopes from 201Ra to 234Ra.
There are 39 known isotopes of radon (86Rn), from 193Rn to 231Rn; all are radioactive. The most stable isotope is 222Rn with a half-life of 3.823 days, which decays into 218
Po
. Six isotopes of radon, 217, 218, 219, 220, 221, 222Rn, occur in trace quantities in nature as decay products of, respectively, 217At, 218At, 223Ra, 224Ra, 225Ra, and 226Ra. 217Rn and 221Rn are produced in rare branches in the decay chain of trace quantities of 237Np; 222Rn is an intermediate step in the decay chain of 238U; 219Rn is an intermediate step in the decay chain of 235U; and 220Rn occurs in the decay chain of 232Th.
Bismuth (83Bi) has 41 known isotopes, ranging from 184Bi to 224Bi. Bismuth has no stable isotopes, but does have one very long-lived isotope; thus, the standard atomic weight can be given as 208.98040(1). Although bismuth-209 is now known to be radioactive, it has classically been considered to be a stable isotope because it has a half-life of approximately 2.01×1019 years, which is more than a billion times the age of the universe. Besides 209Bi, the most stable bismuth radioisotopes are 210mBi with a half-life of 3.04 million years, 208Bi with a half-life of 368,000 years and 207Bi, with a half-life of 32.9 years, none of which occurs in nature. All other isotopes have half-lives under 1 year, most under a day. Of naturally occurring radioisotopes, the most stable is radiogenic 210Bi with a half-life of 5.012 days. 210mBi is unusual for being a nuclear isomer with a half-life multiple orders of magnitude longer than that of the ground state.
There are two natural isotopes of iridium (77Ir), and 37 radioisotopes, the most stable radioisotope being 192Ir with a half-life of 73.83 days, and many nuclear isomers, the most stable of which is 192m2Ir with a half-life of 241 years. All other isomers have half-lives under a year, most under a day. All isotopes of iridium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
Naturally occurring rhenium (75Re) is 37.4% 185Re, which is stable (although it is predicted to decay), and 62.6% 187Re, which is unstable but has a very long half-life (4.12×1010 years). Among elements with a known stable isotope, only indium and tellurium similarly occur with a stable isotope in lower abundance than the long-lived radioactive isotope.
Naturally occurring xenon (54Xe) consists of seven stable isotopes and two very long-lived isotopes. Double electron capture has been observed in 124Xe and double beta decay in 136Xe, which are among the longest measured half-lives of all nuclides. The isotopes 126Xe and 134Xe are also predicted to undergo double beta decay, but this process has never been observed in these isotopes, so they are considered to be stable. Beyond these stable forms, 32 artificial unstable isotopes and various isomers have been studied, the longest-lived of which is 127Xe with a half-life of 36.345 days. All other isotopes have half-lives less than 12 days, most less than 20 hours. The shortest-lived isotope, 108Xe, has a half-life of 58 μs, and is the heaviest known nuclide with equal numbers of protons and neutrons. Of known isomers, the longest-lived is 131mXe with a half-life of 11.934 days. 129Xe is produced by beta decay of 129I ; 131mXe, 133Xe, 133mXe, and 135Xe are some of the fission products of both 235U and 239Pu, so are used as indicators of nuclear explosions.
There are 39 known isotopes and 17 nuclear isomers of tellurium (52Te), with atomic masses that range from 104 to 142. These are listed in the table below.
Naturally occurring chromium (24Cr) is composed of four stable isotopes; 50Cr, 52Cr, 53Cr, and 54Cr with 52Cr being the most abundant (83.789% natural abundance). 50Cr is suspected of decaying by β+β+ to 50Ti with a half-life of (more than) 1.8×1017 years. Twenty-two radioisotopes, all of which are entirely synthetic, have been characterized, the most stable being 51Cr with a half-life of 27.7 days. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute. This element also has two meta states, 45mCr, the more stable one, and 59mCr, the least stable isotope or isomer.
Americium (95Am) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no known stable isotopes. The first isotope to be synthesized was 241Am in 1944. The artificial element decays by ejecting alpha particles. Americium has an atomic number of 95. Despite 243
Am being an order of magnitude longer lived than 241
Am, the former is harder to obtain than the latter as more of it is present in spent nuclear fuel.
Curium (96Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic weight cannot be given, and it has no stable isotopes. The first isotope synthesized was 242Cm in 1944, which has 146 neutrons.
Mendelevium (101Md) is a synthetic element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 256Md in 1955. There are 17 known radioisotopes, ranging in atomic mass from 244Md to 260Md, and 5 isomers. The longest-lived isotope is 258Md with a half-life of 51.3 days, and the longest-lived isomer is 258mMd with a half-life of 57 minutes.
Dubnium (105Db) is a synthetic element, thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 261Db in 1968. Thirteen radioisotopes are known, ranging from 255Db to 270Db, along with one isomer (257mDb); two more isomers have been reported but are unconfirmed. The longest-lived known isotope is 268Db with a half-life of 16 hours.
Yrast is a technical term in nuclear physics that refers to a state of a nucleus with a minimum of energy for a given angular momentum. Yr is a Swedish adjective sharing the same root as the English whirl. Yrast is the superlative of yr and can be translated whirlingest, although it literally means "dizziest" or "most bewildered". The yrast levels are vital to understanding reactions, such as off-center heavy ion collisions, that result in high-spin states.
Isotopes are distinct nuclear species of the same chemical element. They have the same atomic number and position in the periodic table, but differ in nucleon numbers due to different numbers of neutrons in their nuclei. While all isotopes of a given element have similar chemical properties, they have different atomic masses and physical properties.
In nuclear physics, properties of a nucleus depend on evenness or oddness of its atomic number Z, neutron number N and, consequently, of their sum, the mass number A. Most importantly, oddness of both Z and N tends to lower the nuclear binding energy, making odd nuclei generally less stable. This effect is not only experimentally observed, but is included in the semi-empirical mass formula and explained by some other nuclear models, such as the nuclear shell model. This difference of nuclear binding energy between neighbouring nuclei, especially of odd-A isobars, has important consequences for beta decay.