Article · Wikipedia archive · Last revised Jun 4, 2026

Isotopes of einsteinium

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 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.

Last revised
Jun 4, 2026
Read time
≈ 4 min
Length
844 w
Citations
27
Source
Wikipedia ↗
Isotopes of einsteinium (99Es)
Main isotopes1 Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
252Es synth 471.7 d α 248Bk
ε 252Cf
253Es synth 20.47 d α 249Bk
SF –
254Es synth 275.7 d α 250Bk
β− 254Fm
255Es synth 39.8 d β− 255Fm
α 251Bk
SF –

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 2n 3 		Discovery
year34 		Half-life1
 Decay
mode1
n 4 		Daughter
isotope
 Spin and
parity1
n 5n 6
Excitation energyn 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 s5 		α 237Bk 3/2−#
242Es6 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
243mEsn 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
245mEsn 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
247mEsn 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(+)
250mEsn 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
253Esn 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 αn 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)
256mEsn 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:
  1. mEs – Excited nuclear isomer.
  2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. Modes of decay:
    EC: Electron capture


    IT: Isomeric transition
    SF: Spontaneous fission
  5. ( ) spin value – Indicates spin with weak assignment arguments.
  6. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  7. Order of ground state and isomer is uncertain.
  8. Half-life not measured, not included in discovery database
  9. Most common isotope
  10. Theoretically capable of electron capture to 254Cf
References

References

  1. Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3) 030001. doi:10.1088/1674-1137/abddae.
  2. Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3) 030003. doi:10.1088/1674-1137/abddaf.
  3. FRIB Nuclear Data Group. "Discovery of Nuclides Project, Isotope Database". doi:10.11578/frib/2279152.
  4. FRIB Nuclear Data Group. "Discovery of Nuclides Project, Isomer Database". doi:10.11578/frib/2572219.
  5. Khuyagbaatar, J.; Albers, H. M.; Block, M.; Brand, H.; Cantemir, R. A.; Di Nitto, A.; Düllmann, Ch. E.; Götz, M.; Götz, S.; Heßberger, F. P.; Jäger, E.; Kindler, B.; Kratz, J. V.; Krier, J.; Kurz, N.; Lommel, B.; Lens, L.; Mistry, A.; Schausten, B.; Uusitalo, J.; Yakushev, A. (1 October 2020). "Search for Electron-Capture Delayed Fission in the New Isotope 244Md". Physical Review Letters. 125 (14) 142504. Bibcode:2020PhRvL.125n2504K. doi:10.1103/PhysRevLett.125.142504. PMID 33064498. S2CID 223546973.
  6. Khuyagbaatar, J.; Cantemir, R. A.; Düllmann, Ch. E.; Jäger, E.; Kindler, B.; Krier, J.; Kurz, N.; Lommel, B.; Schausten, B.; Yakushev, A. (2024-03-18). "Decay properties of the neutron-deficient isotope Es 242". Physical Review C. 109 (3) 034311. arXiv:2408.01714. doi:10.1103/PhysRevC.109.034311. ISSN 2469-9985.