Isotopes of einsteinium
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Einsteinium (99Es) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be discovered (in nuclear fallout from the Ivy Mike H-bomb test) was 253Es in 1952. There are 18 known radioisotopes, from 240Es to 257Es, and 8 nuclear isomers. The longest-lived isotope is 252Es with a half-life of 471.7 days or 1.291 years; the second longest, 254Es with half-life of 275.7 days is more available.
List of isotopes
| Nuclide [n 1] |
Z | N | Isotopic mass (Da)[2] [n 2][n 3] |
Discovery year[3][4] |
Half-life[1] |
Decay mode[1] [n 4] |
Daughter isotope |
Spin and parity[1] [n 5][n 6] | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Excitation energy[n 6] | |||||||||||||||||||
| 240Es | 99 | 141 | 240.06895(39)# | 2017 | 6.0(17) s | α (70%) | 236Bk | 4−# | |||||||||||
| β+ (30%) | 240Cf | ||||||||||||||||||
| β+, SF (0.16%) | (various) | ||||||||||||||||||
| 241Es | 99 | 142 | 241.06859(25)# | 1996 | 4.3+2.4 −1.2 s[5] |
α | 237Bk | 3/2−# | |||||||||||
| 242Es[6] | 99 | 143 | 242.06957(28)# | 1994 | 16.9(8) s | β+ | 242Cf | 2+# | |||||||||||
| α (41%) | 238Bk | ||||||||||||||||||
| β+, SF (1.5%) | (various) | ||||||||||||||||||
| 243Es | 99 | 144 | 243.06951(22)# | 1973 | 22.1(14) s | α (61%) | 239Bk | (7/2+) | |||||||||||
| β+? (39%) | 243Cf | ||||||||||||||||||
| 243mEs[n 7] | 50(50)# keV | 2025 | >50# μs | IT? | 243Es | 3/2−# | |||||||||||||
| α? | 239Bk | ||||||||||||||||||
| β+? | 243Cf | ||||||||||||||||||
| 244Es | 99 | 145 | 244.07088(20)# | 1973 | 37(4) s | β+ (95%) | 244Cf | 6+# | |||||||||||
| α (5%) | 240Bk | ||||||||||||||||||
| β+, SF (0.011%) | (various) | ||||||||||||||||||
| 245Es | 99 | 146 | 245.07119(18)# | 1967 | 1.11(6) min | β+ (51%) | 245Cf | (3/2−) | |||||||||||
| α (49%) | 241Bk | ||||||||||||||||||
| 245mEs[n 7] | 30(15)# keV | (1967)[n 8] | >50# μs | IT? | 245Es | 7/2+# | |||||||||||||
| α? | 241Bk | ||||||||||||||||||
| β+? | 245Cf | ||||||||||||||||||
| 246Es | 99 | 147 | 246.07281(10) | 1954 | 7.5(5) min | β+ (90.1%) | 246Cf | 4−# | |||||||||||
| α (9.9%) | 242Bk | ||||||||||||||||||
| β+, SF (0.003%) | (various) | ||||||||||||||||||
| 247Es | 99 | 148 | 247.073622(21) | 1967 | 4.55(26) min | β+ (93%) | 247Cf | (7/2+) | |||||||||||
| α (7%) | 243Bk | ||||||||||||||||||
| 247mEs[n 7] | 50(50)# keV | (2001)[n 8] | >20# μs | IT? | 247Es | (3/2−) | |||||||||||||
| α? | 243Bk | ||||||||||||||||||
| β+ | 247Cf | ||||||||||||||||||
| 248Es | 99 | 149 | 248.07547(6)# | 1956 | 24(3) min | β+ (99.75%) | 248Cf | 2−# | |||||||||||
| α (0.25%) | 244Bk | ||||||||||||||||||
| β+, SF (3.5×10−4%) | (various) | ||||||||||||||||||
| 249Es | 99 | 150 | 249.07641(3)# | 1956 | 102.2(6) min | β+ (99.43%) | 249Cf | 7/2+ | |||||||||||
| α (0.57%) | 245Bk | ||||||||||||||||||
| 250Es | 99 | 151 | 250.07861(11)# | 1956 | 8.6(1) h | β+ | 250Cf | 6(+) | |||||||||||
| 250mEs[n 7] | 200(150)# keV | 1970 | 2.22(5) h | β+ | 250Cf | 1(−) | |||||||||||||
| 251Es | 99 | 152 | 251.079991(6) | 1956 | 33(1) h | EC (99.5%) | 251Cf | 3/2− | |||||||||||
| α (0.5%) | 247Bk | ||||||||||||||||||
| 251mEs | 8.4(10) keV | ----[n 8] | >200# μs | IT? | 251Es | (7/2+) | |||||||||||||
| EC? | 251Cf | ||||||||||||||||||
| 252Es | 99 | 153 | 252.08298(5) | 1956 | 471.7(19) d | α (78%) | 248Bk | (4+) | |||||||||||
| EC (22%) | 252Cf | ||||||||||||||||||
| 253Es[n 9] | 99 | 154 | 253.0848212(13) | 1954 | 20.47(3) d | α | 249Bk | 7/2+ | |||||||||||
| SF (8.7×10−6%) | (various) | ||||||||||||||||||
| 253mEs | 106(4) keV | (1993)[n 8] | >10# μs | IT? | 253Es | 3/2−# | |||||||||||||
| 254Es | 99 | 155 | 254.088024(3) | 1954 | 275.7(5) d | α[n 10] | 250Bk | 7+ | |||||||||||
| β− (1.74×10−4%) | 254Fm | ||||||||||||||||||
| SF (<3×10−6%) | (various) | ||||||||||||||||||
| 254mEs | 80.4(11) keV | 1956 | 39.3(2) h | β− (98%) | 254Fm | 2+ | |||||||||||||
| IT (<3%) | 254Es | ||||||||||||||||||
| α (0.32%) | 250Bk | ||||||||||||||||||
| EC (0.076%) | 254Cf | ||||||||||||||||||
| SF (<0.045%) | (various) | ||||||||||||||||||
| 255Es | 99 | 156 | 255.090274(12) | 1954 | 39.8(12) d | β− (92.0%) | 255Fm | (7/2+) | |||||||||||
| α (8.0%) | 251Bk | ||||||||||||||||||
| SF (0.0041%) | (various) | ||||||||||||||||||
| 256Es | 99 | 157 | 256.09360(11)# | 1981 | 7.6 h | β− | 256Fm | 7+# | |||||||||||
| β−, SF (0.002%) | (various) | ||||||||||||||||||
| 256mEs[n 7] | 0(100)# keV | 1989 | 25.4(12) min | β− | 256Fm | 0+# | |||||||||||||
| 257Es | 99 | 158 | 257.09598(44)# | 1987 | 7.7(2) d | β− | 257Fm | 7/2+# | |||||||||||
| This table header & footer: | |||||||||||||||||||
- mEs – Excited nuclear isomer.
- ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
- # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
- Modes of decay:
EC: Electron capture IT: Isomeric transition SF: Spontaneous fission - ( ) spin value – Indicates spin with weak assignment arguments.
- # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
- Order of ground state and isomer is uncertain.
- Half-life not measured, not included in discovery database
- Most common isotope
- Theoretically capable of electron capture to 254Cf