A | B | C | D | E | F | G | H | CH | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
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| Standard atomic weight Ar°(U) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay product uranium-234 is also found. Other isotopes such as uranium-233 have been produced in breeder reactors. In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from 214U to 242U (with the exception of 220U). The standard atomic weight of natural uranium is 238.02891(3).
Natural uranium consists of three main isotopes, 238U (99.2739–99.2752% natural abundance), 235U (0.7198–0.7202%), and 234U (0.0050–0.0059%).[5] All three isotopes are radioactive (i.e., they are radioisotopes), and the most abundant and stable is uranium-238, with a half-life of 4.4683×109 years (about the age of the Earth).
Uranium-238 is an alpha emitter, decaying through the 18-member uranium series into lead-206. The decay series of uranium-235 (historically called actino-uranium) has 15 members and ends in lead-207. The constant rates of decay in these series makes comparison of the ratios of parent-to-daughter elements useful in radiometric dating. Uranium-233 is made from thorium-232 by neutron bombardment.
Uranium-235 is important for both nuclear reactors (energy production) and nuclear weapons because it is the only isotope existing in nature to any appreciable extent that is fissile in response to thermal neutrons, i.e., thermal neutron capture has a high probability of inducing fission. A chain reaction can be sustained with a sufficiently large (critical) mass of uranium-235. Uranium-238 is also important because it is fertile: it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope plutonium-239, which also is fissile.
List of isotopes
| Nuclide [n 1] |
Historic name |
Z | N | Isotopic mass (Da)[6] [n 2][n 3] |
Half-life[1] |
Decay mode[1] [n 4] |
Daughter isotope [n 5][n 6] |
Spin and parity[1] [n 7][n 8] |
Natural abundance (mole fraction) | |
|---|---|---|---|---|---|---|---|---|---|---|
| Excitation energy[n 8] | Normal proportion[1] | Range of variation | ||||||||
| 214U[7] | 92 | 122 | 0.52+0.95 −0.21 ms |
α | 210Th | 0+ | ||||
| 215U | 92 | 123 | 215.026720(11) | 1.4(0.9) ms | α | 211Th | 5/2−# | |||
| β+? | 215Pa | |||||||||
| 216U[8] | 92 | 124 | 216.024760(30) | 2.25+0.63 −0.40 ms |
α | 212Th | 0+ | |||
| 216mU | 2206 keV | 0.89+0.24 −0.16 ms |
α | 212Th | 8+ | |||||
| 217U[9] | 92 | 125 | 217.024660(86)# | 19.3+13.3 −5.6 ms |
α | 213Th | (1/2−) | |||
| β+? | 217Pa | |||||||||
| 218U[8] | 92 | 126 | 218.023505(15) | 650+80 −70 μs |
α | 214Th | 0+ | |||
| 218mU | 2117 keV | 390+60 −50 μs |
α | 214Th | 8+ | |||||
| IT? | 218U | |||||||||
| 219U | 92 | 127 | 219.025009(14) | 60(7) μs | α | 215Th | (9/2+) | |||
| β+? | 219Pa | |||||||||
| 221U | 92 | 129 | 221.026323(77) | 0.66(14) μs | α | 217Th | (9/2+) | |||
| β+? | 221Pa | |||||||||
| 222U | 92 | 130 | 222.026058(56) | 4.7(0.7) μs | α | 218Th | 0+ | |||
| β+? | 222Pa | |||||||||
| 223U | 92 | 131 | 223.027961(63) | 65(12) μs | α | 219Th | 7/2+# | |||
| β+? | 223Pa | |||||||||
| 224U | 92 | 132 | 224.027636(16) | 396(17) μs | α | 220Th | 0+ | |||
| β+? | 224Pa | |||||||||
| 225U | 92 | 133 | 225.029385(11) | 62(4) ms | α | 221Th | 5/2+# | |||
| 226U | 92 | 134 | 226.029339(12) | 269(6) ms | α | 222Th | 0+ | |||
| 227U | 92 | 135 | 227.0311811(91) | 1.1(0.1) min | α | 223Th | (3/2+) | |||
| β+? | 227Pa | |||||||||
| 228U | 92 | 136 | 228.031369(14) | 9.1(0.2) min | α (97.5%) | 224Th | 0+ | |||
| EC (2.5%) | 228Pa | |||||||||
| 229U | 92 | 137 | 229.0335060(64) | 57.8(0.5) min | β+ (80%) | 229Pa | (3/2+) | |||
| α (20%) | 225Th | |||||||||
| 230U | 92 | 138 | 230.0339401(48) | 20.23(0.02) d | α | 226Th | 0+ | |||
| SF ? | (various) | |||||||||
| CD (4.8×10−12%) | 208Pb 22Ne | |||||||||
| 231U | 92 | 139 | 231.0362922(29) | 4.2(0.1) d | EC | 231Pa | 5/2+# | |||
| α (.004%) | 227Th | |||||||||
| 232U | 92 | 140 | 232.0371548(19) | 68.9(0.4) y | α | 228Th | 0+ | |||
| CD (8.9×10−10%) | 208Pb 24Ne | |||||||||
| SF (10−12%) | (various) | |||||||||
| CD? | 204Hg 28Mg | |||||||||
| 233U | 92 | 141 | 233.0396343(24) | 1.592(2)×105 y | α | 229Th | 5/2+ | Trace[n 9] | ||
| CD (≤7.2×10−11%) | 209Pb 24Ne | |||||||||
| SF ? | (various) | |||||||||
| CD ? | 205Hg 28Mg | |||||||||
| 234U[n 10][n 11] | Uranium II | 92 | 142 | 234.0409503(12) | 2.455(6)×105 y | α | 230Th | 0+ | [n 12] | 0.000050– 0.000059 |
| SF (1.64×10−9%) | (various) | |||||||||
| CD (1.4×10−11%) | Zdroj:https://en.wikipedia.org?pojem=Isotopes_of_uranium||||||||||