Isotopes
| Isotope | Half-life | Probability of spontaneous fission in % |
Emission energy, MeV (yield in %) | Specific activity of | ||
|---|---|---|---|---|---|---|
| α | γ | α, β-particles, Bq/kg | fission, Bq/kg | |||
| 241Am | 432.2(7) years | 4.3(18)×10−10 | 5.485 (84.8) 5.442 (13.1) 5.388 (1.66) |
0.059 (35.9) 0.026 (2.27) |
1.27×1014 | 546.1 |
| 243Am | 7.37(4)×103 years | 3.7(2)×10−9 | 5.275 (87.1) 5.233 (11.2) 5.181 (1.36) |
0.074 (67.2) 0.043 (5.9) |
7.39×1012 | 273.3 |
| 242Cm | 162.8(2) days | 6.2(3)×10−6 | 6.069 (25.92) 6.112 (74.08) |
0.044 (0.04) 0.102 (4×10−3) |
1.23×1017 | 7.6×109 |
| 244Cm | 18.10(2) years | 1.37(3)×10−4 | 5.762 (23.6) 5.804 (76.4) |
0.043 (0.02) 0.100 (1.5×10−3) |
2.96×1015 | 4.1×109 |
| 245Cm | 8.5(1)×103 years | 6.1(9)×10−7 | 5.529 (0.58) 5.488 (0.83) 5.361 (93.2) |
0.175 (9.88) 0.133 (2.83) |
6.35×1012 | 3.9×104 |
| 246Cm | 4.76(4)×103 years | 0.02615(7) | 5.343 (17.8) 5.386 (82.2) |
0.045 (19) | 1.13×1013 | 2.95×109 |
| 247Cm | 1.56(5)×107 years | — | 5.267 (13.8) 5.212 (5.7) 5.147 (1.2) |
0.402 (72) 0.278 (3.4) |
3.43×109 | — |
| 248Cm | 3.48(6)×105 years | 8.39(16) | 5.034 (16.52) 5.078 (75) |
— | 1.40×1011 | 1.29×1010 |
| 249Bk | 330(4) days | 4.7(2)×10−8 | 5.406 (1×10−3) 5.378 (2.6×10−4) |
0.32 (5.8×10−5) | 5.88×1016 | 2.76×107 |
| 249Cf | 351(2) years | 5.0(4)×10−7 | 6.193 (2.46) 6.139 (1.33) 5.946 (3.33) |
0.388 (66) 0.333 (14.6) |
1.51×1014 | 7.57×105 |
| 250Cf | 13.08(9) years | 0.077(3) | 5.988 (14.99) 6.030 (84.6) |
0.043 | 4.04×1015 | 3.11×1012 |
| 251Cf | 900(40) years | ? | 6.078 (2.6) 5.567 (0.9) 5.569 (0.9) |
0.177 (17.3) 0.227 (6.8) |
5.86×1013 | — |
| 252Cf | 2.645(8) years | 3.092(8) | 6.075 (15.2) 6.118 (81.6) |
0.042 (1.4×10−2) 0.100 (1.3×10−2) |
1.92×1016 | 6.14×1014 |
| 254Cf | 60.5(2) days | ≈100 | 5.834 (0.26) 5.792 (5.3×10−2) |
— | 9.75×1014 | 3.13×1017 |
| 253Es | 20.47(3) days | 8.7(3)×10−6 | 6.540 (0.85) 6.552 (0.71) 6.590 (6.6) |
0.387 (0.05) 0.429 (8×10−3) |
9.33×1017 | 8.12×1010 |
| 254Es | 275.7(5) days | < 3×10−6 | 6.347 (0.75) 6.358 (2.6) 6.415 (1.8) |
0.042 (100) 0.034 (30) |
6.9×1016 | — |
| 255Es | 39.8(12) days | 0.0041(2) | 6.267 (0.78) 6.401 (7) |
— | 4.38×1017(β) 3.81×1016(α) |
1.95×1013 |
| 255Fm | 20.07(7) hours | 2.4(10)×10−5 | 7.022 (93.4) 6.963 (5.04) 6.892 (0.62) |
0.00057 (19.1) 0.081 (1) |
2.27×1019 | 5.44×1012 |
| 256Fm | 157.6(13) min | 91.9(3) | 6.872 (1.2) 6.917 (6.9) |
— | 1.58×1020 | 1.4×1019 |
| 257Fm | 100.5(2) days | 0.210(4) | 6.752 (0.58) 6.695 (3.39) 6.622 (0.6) |
0.241 (11) 0.179 (8.7) |
1.87×1017 | 3.93×1014 |
| 256Md | 77(2) min | — | 7.142 (1.84) 7.206 (5.9) |
— | 3.53×1020 | — |
| 257Md | 5.52(5) hours | — | 7.074 (14) | 0.371 (11.7) 0.325 (2.5) |
8.17×1019 | — |
| 258Md | 51.5(3) days | — | 6.73 | — | 3.64×1017 | — |
| 255No | 3.1(2) min | — | 8.312 (1.16) 8.266 (2.6) 8.121 (27.8) |
0.187 (3.4) | 8.78×1021 | — |
| 259No | 58(5) min | — | 7.455 (9.8) 7.500 (29.3) 7.533 (17.3) |
— | 4.63×1020 | — |
| 256Lr | 27(3) s | < 0.03 | 8.319 (5.4) 8.390 (16) 8.430 (33) |
— | 5.96×1022 | — |
| 257Lr | 646(25) ms | — | 8.796 (18) 8.861 (82) |
— | 1.54×1024 | — |
Thirty-one isotopes of actinium and eight excited isomeric states of some of its nuclides were identified by 2010. Three isotopes, 225Ac, 227Ac and 228Ac, were found in nature and the others were produced in the laboratory; only the three natural isotopes are used in applications. Actinium-225 is a member of radioactive neptunium series; it was first discovered in 1947 as a fission product of uranium-233, it is an α-emitter with a half-life of 10 days. Actinium-225 is less available than actinium-228, but is more promising in radiotracer applications. Actinium-227 (half-life 21.77 years) occurs in all uranium ores, but in small quantities. One gram of uranium (in radioactive equilibrium) contains only 2×10−10 gram of 227Ac. Actinium-228 is a member of radioactive thorium series formed by the decay of 228Ra; it is a β– emitter with a half-life of 6.15 hours. In one tonne of thorium there is 5×10−8 gram of 228Ac. It was discovered by Otto Hahn in 1906.
Twenty nine isotopes of protactinium are known with mass numbers 212–240 as well as three excited isomeric states. Only 231Pa and 234Pa have been found in nature. All the isotopes have short lifetime, except for protactinium-231 (half-life 32,760 years). The most important isotopes are 231Pa and 233Pa, which is an intermediate product in obtaining uranium-233 and is the most affordable among artificial isotopes of protactinium. 233Pa has convenient half-life and energy of γ-radiation, and thus was used in most studies of protactinium chemistry. Protactinium-233 is a β-emitter with a half-life of 26.97 days.
Uranium has the highest number (25) of both natural and synthetic isotopes. They have mass numbers of 217–242, and three of them, 234U, 235U and 238U, are present in appreciable quantities in nature. Among others, the most important is 233U, which is a final product of transformations of 232Th irradiated by slow neutrons. 233U has a very higher fission efficiency by low-energy (thermal) neutrons, compared e.g. with 235U. Most uranium chemistry studies were carried out on uranium-238 owing to its long half-life of 4.4×109 years.
There are 19 isotopes of neptunium with mass numbers from 225 to 244; they are all highly radioactive. The most popular among scientists are long-lived 237Np (t½ = 2.20×106 years) and short-lived 239Np, 238Np (t½ ~ 2 days).
Sixteen isotopes of americium are known with mass numbers from 232 to 248. The most important are 241Am and 243Am, which are alpha-emitters and also emit soft, but intense γ-rays; both of them can be obtained in an isotopically pure form. Chemical properties of americium were first studied with 241Am, but later shifted to 243Am, which is almost 20 times less radioactive. The disadvantage of 243Am is production of the short-lived daughter isotope 239Np, which has to be considered in the data analysis.
Among 19 isotopes of curium, the most accessible are 242Cm and 244Cm; they are α-emitters, but with much shorter lifetime than the americium isotopes. These isotopes emit almost no γ-radiation, but undergo spontaneous fission with the associated emission of neutrons. More long-lived isotopes of curium (245–248Cm, all α-emitters) are formed as a mixture during neutron irradiation of plutonium or americium. Upon short irradiation, this mixture is dominated by curium-246, and then curium-248 begins to accumulate. Both of these isotopes, especially 248Cm, have a longer half-life (3.48×105 years) and are much more convenient for carrying out chemical research than 242Cm and 244Cm, but they also have a rather high rate of spontaneous fission. 247Cm has the longest lifetime among isotopes of curium (1.56×107 years), but is not formed in large quantities because of the strong fission induced by thermal neutrons.
Fourteen isotopes of berkelium were identified with mass numbers 238–252. Only 249Bk is available in large quantities; it has a relatively short half-life of 330 days and emits mostly soft β-particles, which are inconvenient for detection. Its alpha radiation is rather weak (1.45×10−3% with respect to β-radiation), but is sometimes used to detect this isotope. 247Bk is an alpha-emitter with a long half-life of 1,380 years, but it is hard to obtain in appreciable quantities; it is not formed upon neutron irradiation of plutonium because of the β-stability of isotopes of curium isotopes with mass number below 248.
Isotopes of californium with mass numbers 237–256 are formed in nuclear reactors; californium-253 is a β-emitter and the rest are α-emitters. The isotopes with even mass numbers (250Cf, 252Cf and 254Cf) have a high rate of spontaneous fission, especially 254Cf of which 99.7% decays by spontaneous fission. Californium-249 has a relatively long half-life (352 years), weak spontaneous fission and strong γ-emission that facilitates its identification. 249Cf is not formed in large quantities in a nuclear reactor because of the slow β-decay of the parent isotope 249Bk and a large cross section of interaction with neutrons, but it can be accumulated in the isotopically pure form as the β-decay product of (pre-selected) 249Bk. Californium produced by reactor-irradiation of plutonium mostly consists of 250Cf and 252Cf, the latter being predominant for large neutron fluences, and its study is hindered by the strong neutron radiation.
| Parent isotope |
t½ | Daughter isotope |
t½ | Time to establish radioactive equilibrium |
|---|---|---|---|---|
| 243Am | 7370 years | 239Np | 2.35 days | 47.3 days |
| 245Cm | 8265 years | 241Pu | 14 years | 129 years |
| 247Cm | 1.64×107 years | 243Pu | 4.95 hours | 7.2 days |
| 254Es | 270 days | 250Bk | 3.2 hours | 35.2 hours |
| 255Es | 39.8 days | 255Fm | 22 hours | 5 days |
| 257Fm | 79 days | 253Cf | 17.6 days | 49 days |
Among the 16 known isotopes of einsteinium with mass numbers from 241 to 257 the most affordable is 253Es. It is an α-emitter with a half-life of 20.47 days, a relatively weak γ-emission and small spontaneous fission rate as compared with the isotopes of californium. Prolonged neutron irradiation also produces a long-lived isotope 254Es (t½ = 275.5 days).
Nineteen isotopes of fermium are known with mass numbers of 242–260. 254Fm, 255Fm and 256Fm are α-emitters with a short half-life (hours), which can be isolated in significant amounts. 257Fm (t½ = 100 days) can accumulate upon prolonged and strong irradiation. All these isotopes are characterized by high rates of spontaneous fission.
Among the 15 known isotopes of mendelevium (mass numbers from 245 to 260), the most studied is 256Md, which mainly decays through the electron capture (α-radiation is ≈10%) with the half-life of 77 minutes. Another alpha emitter, 258Md, has a half-life of 53 days. Both these isotopes are produced from rare einsteinium (253Es and 255Es respectively), that limits their so their availability.
Long-lived isotopes of nobelium and isotopes of lawrencium (and of heavier elements) have relatively small half-lives. For nobelium 11 isotopes are known with mass numbers 250–260 and 262. Chemical properties of nobelium and lawrencium were studied with 255No (t½ = 3 min) and 256Lr (t½ = 35 s). The longest-lived nobelium isotope 259No has a half-life of 1.5 hours.
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