# Isotopes of einsteinium

Einsteinium ($_{99}$Es) 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 $^{253}$Es in 1952. There are 18 known radioisotopes from $^{240}$Es to $^{257}$Es, and 4 nuclear isomers. The longest-lived isotope is $^{252}$Es with a half-life of 471.7 days, or around 1.293 years.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity |
| Spin and parity |||
| $^{240}$Es | 99 | 141 | 240.06895(39)# | 6.0(17) s | α (70%) | $^{236}$Bk | 4−# |
| $^{240}$Es | 99 | 141 | 240.06895(39)# | 6.0(17) s | β$^+$ (30%) | $^{240}$Cf | 4−# |
| $^{240}$Es | 99 | 141 | 240.06895(39)# | 6.0(17) s | β$^+$, SF (0.16%) | (various) | 4−# |
| $^{241}$Es | 99 | 142 | 241.06859(25)# | 4.3+2.4 −1.2 s | α | $^{237}$Bk | 3/2−# |
| $^{241}$Es | 99 | 142 | 241.06859(25)# | 4.3+2.4 −1.2 s | β$^+$? | $^{241}$Cf | 3/2−# |
| $^{242}$Es | 99 | 143 | 242.06957(28)# | 16.9(8) s | β$^+$ | $^{242}$Cf | 2+# |
| $^{242}$Es | 99 | 143 | 242.06957(28)# | 16.9(8) s | α (41%) | $^{238}$Bk | 2+# |
| $^{242}$Es | 99 | 143 | 242.06957(28)# | 16.9(8) s | β$^+$, SF (1.5%) | (various) | 2+# |
| $^{243}$Es | 99 | 144 | 243.06951(22)# | 22.1(14) s | α (61%) | $^{239}$Bk | (7/2+) |
| $^{243}$Es | 99 | 144 | 243.06951(22)# | 22.1(14) s | β$^+$ (39%) | $^{243}$Cf | (7/2+) |
| $^{244}$Es | 99 | 145 | 244.07088(20)# | 37(4) s | β$^+$ (95%) | $^{244}$Cf | 6+# |
| $^{244}$Es | 99 | 145 | 244.07088(20)# | 37(4) s | α (5%) | $^{240}$Bk | 6+# |
| $^{244}$Es | 99 | 145 | 244.07088(20)# | 37(4) s | β$^+$, SF (0.011%) | (various) | 6+# |
| $^{245}$Es | 99 | 146 | 245.07119(18)# | 1.11(6) min | β$^+$ (51%) | $^{245}$Cf | (3/2−) |
| $^{245}$Es | 99 | 146 | 245.07119(18)# | 1.11(6) min | α (49%) | $^{241}$Bk | (3/2−) |
| $^{245m}$Es | 30(15)# keV | 30(15)# keV | 30(15)# keV | >50# μs | IT? | $^{245}$Es | 7/2+# |
| $^{245m}$Es | 30(15)# keV | 30(15)# keV | 30(15)# keV | >50# μs | α? | $^{241}$Bk | 7/2+# |
| $^{245m}$Es | 30(15)# keV | 30(15)# keV | 30(15)# keV | >50# μs | β$^+$? | $^{245}$Cf | 7/2+# |
| $^{246}$Es | 99 | 147 | 246.072806(97) | 7.5(5) min | β$^+$ (90.1%) | $^{246}$Cf | 4−# |
| $^{246}$Es | 99 | 147 | 246.072806(97) | 7.5(5) min | α (9.9%) | $^{242}$Bk | 4−# |
| $^{246}$Es | 99 | 147 | 246.072806(97) | 7.5(5) min | β$^+$, SF (.003%) | (various) | 4−# |
| $^{247}$Es | 99 | 148 | 247.073622(21) | 4.55(26) min | β$^+$ (93%) | $^{247}$Cf | (7/2+) |
| $^{247}$Es | 99 | 148 | 247.073622(21) | 4.55(26) min | α (7%) | $^{243}$Bk | (7/2+) |
| $^{247}$Es | 99 | 148 | 247.073622(21) | 4.55(26) min | SF? | (various) | (7/2+) |
| $^{248}$Es | 99 | 149 | 248.075469(56)# | 24(3) min | β$^+$ (99.75%) | $^{248}$Cf | 2−# |
| $^{248}$Es | 99 | 149 | 248.075469(56)# | 24(3) min | α (.25%) | $^{244}$Bk | 2−# |
| $^{248}$Es | 99 | 149 | 248.075469(56)# | 24(3) min | β$^+$, SF (3.5×10$^{−4}$%) | (various) | 2−# |
| $^{249}$Es | 99 | 150 | 249.076409(32)# | 102.2(6) min | β$^+$ (99.43%) | $^{249}$Cf | 7/2+ |
| $^{249}$Es | 99 | 150 | 249.076409(32)# | 102.2(6) min | α (.57%) | $^{245}$Bk | 7/2+ |
| $^{250}$Es | 99 | 151 | 250.07861(11)# | 8.6(1) h | β$^+$ | $^{250}$Cf | 6(+) |
| $^{250}$Es | 99 | 151 | 250.07861(11)# | 8.6(1) h | α? | $^{246}$Bk | 6(+) |
| $^{250m}$Es | 200(150)# keV | 200(150)# keV | 200(150)# keV | 2.22(5) h | β$^+$ | $^{250}$Cf | 1(−) |
| $^{250m}$Es | 200(150)# keV | 200(150)# keV | 200(150)# keV | 2.22(5) h | α? | $^{246}$Bk | 1(−) |
| $^{251}$Es | 99 | 152 | 251.0799914(57) | 33(1) h | EC (99.5%) | $^{251}$Cf | 3/2− |
| $^{251}$Es | 99 | 152 | 251.0799914(57) | 33(1) h | α (.5%) | $^{247}$Bk | 3/2− |
| $^{252}$Es | 99 | 153 | 252.082979(54) | 471.7(19) d | α (78(2)%) | $^{248}$Bk | (4+) |
| $^{252}$Es | 99 | 153 | 252.082979(54) | 471.7(19) d | EC (22(2)%) | $^{252}$Cf | (4+) |
| $^{253}$Es | 99 | 154 | 253.0848212(13) | 20.47(3) d | α | $^{249}$Bk | 7/2+ |
| $^{253}$Es | 99 | 154 | 253.0848212(13) | 20.47(3) d | SF (8.7×10$^{−6}$%) | (various) | 7/2+ |
| $^{254}$Es | 99 | 155 | 254.0880243(32) | 275.7(5) d | α | $^{250}$Bk | 7+ |
| $^{254}$Es | 99 | 155 | 254.0880243(32) | 275.7(5) d | β$^−$ (1.74×10$^{−4}$%) | $^{254}$Fm | 7+ |
| $^{254}$Es | 99 | 155 | 254.0880243(32) | 275.7(5) d | SF (<3×10$^{−6}$%) | (various) | 7+ |
| $^{254m}$Es | 80.4(11) keV | 80.4(11) keV | 80.4(11) keV | 39.3(2) h | β$^−$ (98(2)%) | $^{254}$Fm | 2+ |
| $^{254m}$Es | 80.4(11) keV | 80.4(11) keV | 80.4(11) keV | 39.3(2) h | IT (<3%) | $^{254}$Es | 2+ |
| $^{254m}$Es | 80.4(11) keV | 80.4(11) keV | 80.4(11) keV | 39.3(2) h | α (0.32(1)%) | $^{250}$Bk | 2+ |
| $^{254m}$Es | 80.4(11) keV | 80.4(11) keV | 80.4(11) keV | 39.3(2) h | EC (0.076(7)%) | $^{254}$Cf | 2+ |
| $^{254m}$Es | 80.4(11) keV | 80.4(11) keV | 80.4(11) keV | 39.3(2) h | SF (<0.045%) | (various) | 2+ |
| $^{255}$Es | 99 | 156 | 255.090274(12) | 39.8(12) d | β$^−$ (92.0%) | $^{255}$Fm | (7/2+) |
| $^{255}$Es | 99 | 156 | 255.090274(12) | 39.8(12) d | α (8.0%) | $^{251}$Bk | (7/2+) |
| $^{255}$Es | 99 | 156 | 255.090274(12) | 39.8(12) d | SF (.0041%) | (various) | (7/2+) |
| $^{256}$Es | 99 | 157 | 256.09360(11)# | 7.6 h | β$^−$ | $^{256}$Fm | 7+# |
| $^{256}$Es | 99 | 157 | 256.09360(11)# | 7.6 h | β$^−$, SF (.002%) | (various) | 7+# |
| $^{256m}$Es | 0(100)# keV | 0(100)# keV | 0(100)# keV | 25.4(12) min | β$^−$ | $^{256}$Fm | 0+# |
| $^{257}$Es | 99 | 158 | 257.09598(44)# | 7.7(2) d | β$^−$ | $^{257}$Fm | 7/2+# |
| $^{257}$Es | 99 | 158 | 257.09598(44)# | 7.7(2) d | α? | $^{253}$Bk | 7/2+# |
| This table header & footer: view ||||||||
* ↑ $^m$Es – 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.
* 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* 1 2 3 Order of ground state and isomer is uncertain.
* ↑ Most common isotope
* ↑ Theoretically capable of electron capture to $^{254}$Cf